Boron nitride compositions, methods of making, and methods of use

Abstract

Embodiments of the disclosure include a boron nitride (BN) composition, comprising a boron nitride layer overlying a seed crystal, wherein the boron nitride layer comprises boron and nitrogen; and impurity concentrations of each of H and 0 between about 1016 cm-3 and about 1021 cm-3, as quantified by calibrated secondary ion mass spectrometry; and the seed crystal comprising at least one of cubic boron nitride and diamond and is characterized by a maximum dimension of between 40 micrometers and 450 millimeters. Embodiments of the disclosure may also include a polycrystalline cubic boron nitride composition, comprising boron and nitrogen, wherein the polycrystalline cubic boron nitride composition comprises: a zincblende crystal structure; a porosity between 0.1% and 50%; and an impurity concentration of each of H and O between 1016 cm-3 and 1021 cm-3, as quantified by calibrated secondary ion mass spectrometry.

Description

BORON NITRIDE COMPOSITIONS,METHODS OF MAKING, AND METHODS OF USEBACKGROUND OF THE DISCLOSURECROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims the benefit of U.S. Provisional Patent Application No. 63 / 512,206, filed July 6, 2023, and U.S. Provisional Patent Application No. 63 / 512,209, filed July 6, 2023, each of which is incorporated by reference herein.FIELD

[0002] This disclosure relates generally to techniques for processing materials for manufacture of novel boron nitride compositions, including mesh-sized cubic boron nitride crystals, polycrystalline cubic boron nitride, cubic boron nitride single crystals, and related materials. Such boron nitride materials can be used for a variety of applications, including grinding, machining, thermal management, and others.DESCRIPTION OF THE RELATED ART

[0003] Cubic boron nitride (cBN) is the second-hardest bulk material, after diamond. Mesh cBN crystals and polycrystalline cBN compositions are of tremendous commercial importance, particularly for grinding and machining applications. While cBN is not quite as hard as diamond, it has considerably better abrasion resistance with respect to ferrous metals, such as steel, cast iron, and related iron-, nickel-, and cobalt-based alloys and superalloys. In addition, cBN has considerably better high- temperature stability than diamond in air or oxidizing environments. Finally, there is considerable interest in cBN as an ultrawide-bandap semiconductor for power device applications, with the single largest issue to further development being the availability of large-area, high-quality bulk cBN substrates.

[0004] CBN was first synthesized in 1957 by the General Electric Company and introduced commercially in 1969, and commercial cBN mesh products are now widespread. However, the phase diagram for boron nitride, including the stable forms cBN and hexagonal boron nitride (hBN), has remained controversial to the present. While some authors have presented evidence that cBN is the stable form of BN at moderate pressures and temperatures, commercial cBNsynthesis continues to require a pressure greater than about 5 GPa, and reports of reduced-pressure synthesis are sparse. Due in part to the high synthesis pressure requirement, the cost of mesh cBN manufacturing remains quite high.

[0005] In addition, the commercial cBN synthesis process is not as well understood or controlled as that for mesh diamond, and the largest diameter for which commercial mesh cBN crystals are available in commercial quantities is approximately 350 micrometers (40 / 50 mesh). Mesh sizes generally refer to particles that are typically separated by size by passing through sieves or screens, with a diameter in the range from about 40 micrometers to about 750 micrometers.

[0006] Mesh cBN is typically incorporated into vitreous, electroplated, brazed, resin, or metal bond systems, and retention of the cBN crystals in the bond system during grinding or machining operations is often a limiting factor with respect to workpiece removal rate, tool lifetime, and net cost to the user.

[0007] Commercial polycrystalline cBN is often bonded to a substrate, such as Co-cemented WC, and often has one or more additional phases present, such as Co, TiN, SiC, or another ceramic composition. These features enhance performance in many machining operations, but may cause limitations in others, for example, due to stresses arising from a mismatch in thermal expansion coefficient or decomposition at high temperature.

[0008] In addition to the outstanding mechanical and abrasion properties of cBN, cBN has one of the highest thermal conductivities of any material, up to about 850 W / m-K for cBN with the naturally-occurring isotope ratio for boron (21.7%10B and 78.3%nB) and up to about 1600 W / m- K for cBN that has been isotopically enriched in either10B ornB. To date, to the best of the inventors’ knowledge, however, polycrystalline cBN has not been employed as a thermal management material in any application of commercial significance, both because of its high cost and the degradation of the thermal properties implied by the additional phases in commercial polycrystalline cBN. Thermal management applications would be facilitated considerably by the ability to directly fabricate near-net-shape parts, which is not possible with conventional techniques.

[0009] Finally, there is considerable interest in cBN as an ultrawide-bandgap semiconductor for next-generation power electronic devices. Relative to other ultrawide-bandgap materials that arecurrently being investigated, such as diamond, P-GaiOa. and AIN, cBN is advantageous in having among the highest bandgaps (6.4 eV) and the ready ability to be doped both n-type and p-type. However, crystal growth of high-quality, large area substrates is not currently possible.

[0010] Due to at least the issues described above, there is a need for alternative growth processes for mesh cBN, polycrystalline cBN, single-crystal cBN, and other cBN and BN materials that require a lower synthesis pressure, have a lower cost, enable larger and higher-quality cBN single crystals, enable superior retention in bond systems, such as vitreous, resin, or metallic bonds, enable higher-purity and higher-thermal-conductivity BN-containing components, and are compatible with near-net- shape fabrication.BRIEF SUMMARY OF THE DISCLOSURE

[0011] Embodiments of the disclosure generally include methods for processing materials for manufacture of mesh-sized cubic boron nitride crystals, polycrystalline cubic boron nitride, and related materials. Such mesh crystals can be used for a variety of applications including grinding, machining, and others.

[0002] Embodiments of the disclosure include a boron nitride (BN) composition, comprising a boron nitride layer overlying a seed crystal, wherein: the boron nitride layer comprises boron and nitrogen; and impurity concentrations of each of H and O are between about 1016cm'3and about 1022cm'3, as quantified by calibrated secondary ion mass spectrometry; and the seed crystal comprises at least one of cubic boron nitride and diamond and is characterized by a maximum dimension of between 40 micrometers and 450 millimeters. The boron nitride layer may further comprise an impurity concentration of one or more of Li, Na, Mg, F, Cl, Be, S, or Si between about 1015cm'3and about 1022cm'3. The boron nitride layer may comprise: a zincblende crystal structure; and point defects characterized by an infrared spectrum having an absorbance per unit thickness of at least 0.01 cm'1for at least one peak falling in a range between about 3000 cm'1and about 3400 cm'1or between about 2100 cm'1and about 2500 cm'1.

[0003] Embodiments of the disclosure also include a polycrystalline cubic boron nitride composition, comprising boron and nitrogen. The polycrystalline cubic boron nitride composition comprises: a zincblende crystal structure; a maximum dimension between 100 micrometers and 450 millimeters; a minimum dimension between 1 micrometer and 25millimeters; a porosity between 0.1% and 50%; and an impurity concentration of each of H and 0 between 1016cm'3and 1022cm’3, as quantified by calibrated secondary ion mass spectrometry.

[0004] Embodiments of the disclosure also include a method for forming a boron nitride composition, comprising: placing a plurality of seed crystals and a nutrient material inside a sealable container, wherein the plurality of seed crystals comprises at least one of cubic boron nitride and diamond, and have a maximum dimension between about 5 micrometers and about 200 millimeters, and the nutrient material comprises boron. Embodiments of the method further comprise adding a mineralizer composition and ammonia to the sealable container, the mineralizer composition comprising at least one of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, F, Cl, Br, or I; and heating the sealable container to a temperature greater than or equal to 350 degrees Celsius for a period greater than or equal to one hour, wherein the heating of the sealable container causes growth of a boron nitride layer on at least one of the plurality of seed crystals, wherein: a weight ratio between the seed crystals and the nutrient is between about one part per million and about 0.999; the ammonia within the sealable container has a density between 0.42 g / cm3and 0.75 g / cm3; and a molar ratio of the mineralizer composition and the ammonia is between about 0.01% and about 75%.

[0005] Embodiments of the disclosure also include an apparatus for forming a boron nitride (BN) composition. The apparatus includes a sealable container comprising one or more walls that define an internal volume; one or more seed crystals disposed within a first region of the internal volume, wherein the one or more seed crystals comprise a material selected from a group consisting of cubic boron nitride (cBN) or diamond; ammonia (NH3) disposed within the internal volume; a mineralizer disposed within the internal volume, wherein the mineralizer comprises a material selected from a group consisting an alkali element, an alkaline earth element, or a halogen; and a nutrient disposed within a second region of the internal volume, wherein the nutrient comprises boron. In some embodiments, the second region is separated from the first region by a first distance.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] So that the manner in which the above recited features of embodiments of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typicalembodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0007] FIGs. 1 A- ID are simplified diagrams illustrating boron nitride phase diagram boundaries or stability diagrams disclosed by various groups.

[0008] FIGs. 2A-2B are simplified diagrams illustrating side views of growth chambers or sealable containers for synthesis of mesh cubic boron nitride according to embodiments of the present disclosure.

[0009] FIG. 2C is a simplified diagram showing a close-up view of a granule for synthesis of mesh cubic boron nitride according to an embodiment of the present disclosure.

[0010] FIG. 3A is a simplified diagram illustrating a side view of a growth chamber or sealable container for synthesis of polycrystalline boron nitride compositions, according to an embodiment of the present disclosure.

[0011] FIGs. 3B and 3C are simplified diagrams showing close-up views of polycrystalline boron nitride compositions and the microstructure thereof, respectively, according to an embodiment of the present disclosure.

[0012] FIG. 3D is a simplified diagram illustrating a side view of a growth chamber or sealable container for synthesis of single-crystal cubic boron nitride compositions, according to an embodiment of the present disclosure.

[0013] FIG. 4 is a schematic diagram showing a mineralizer vessel and a method of use according to an embodiment of the current disclosure.

[0014] FIG. 5A is a schematic diagram showing an externally-heated pressure vessel apparatus, according to an embodiment of the current disclosure.

[0015] FIG. 5B is a schematic diagram showing an internally-heated pressure vessel apparatus according to an embodiment of the current disclosure.

[0016] FIG. 6 is a schematic diagram showing a dual capsule according to an embodiment of the current disclosure.

[0017] FIG. 7 is a schematic diagram showing the dependence of a decrease in percent fill of ammonia as a function of the initial content of hexagonal boron, according to an embodiment of the current disclosure.

[0018] FIG. 8 is a graph showing the dependence of the pressure of an ammonia-filled vessel as a function of temperature and of the density (percent fill) of the ammonia, along with phase boundaries and process conditions, according to embodiments of the current disclosure.

[0019] FIGs. 9 A and 9B are micro-Raman spectra of pyrolytic boron nitride or cubic boron nitride starting materials, respectively, according to embodiments of the current disclosure.

[0020] FIG. 9C is a scanning electron micrograph of an adherent boron nitride coating grown on a cubic boron nitride seed crystal by an ammonothermal process, from which a small portion has delaminated, according to an embodiments of the current disclosure.

[0021] FIG. 9D is a scanning electron micrograph of a cubic boron nitride crystal with a boron nitride coating grown on it by an ammonothermal process, after fracture, according to an embodiment of the current disclosure.

[0022] FIG. 9E is a micro-Raman spectrum of a boron nitride coating grown on a cubic boron nitride seed crystal by an ammonothermal process, according to embodiments of the current disclosure.

[0023] FIG. 9F is a micro-Raman spectrum of a polycrystalline boron nitride layer grown on a pyrolytic boron nitride plate by an ammonothermal process, according to an embodiment of the current disclosure.

[0024] FIG. 9G is a micro-Raman spectrum of a cubic boron nitride layer grown on a cubic boron nitride mesh crystal by an ammonothermal process, according to an embodiment of the current disclosure.

[0025] FIG. 10 is a schematic diagram of a process for synthesizing cubic boron nitride according to an embodiment of the current disclosure.

[0026] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elementsand features of one implementation may be beneficially incorporated in other implementations without further recitation.DETAILED DESCRIPTION OF THE DISCLOSURE

[0027] Embodiments of the disclosure generally include methods for processing materials for manufacture of mesh-sized cubic boron nitride crystals, polycrystalline boron nitride, cubic boron nitride single crystal layers and free-standing single crystals, and related materials. In some embodiments, such mesh crystals and polycrystalline materials can be used for a variety of applications including components used in grinding, machining, thermal management, and other similar applications. Mesh crystals and polycrystalline materials generally include particles or grains that have a maximum dimension generally in the micrometer to millimeter range. However, in other embodiments, the methods disclosed herein can be used to form polycrystalline cubic boron nitride components that have a maximum dimension, such as a length or diameter, between a hundred micrometers and hundreds of millimeters. The methods provided herein can be used to form polycrystalline cubic boron nitride near-net-shape ceramic parts that are used in the microelectronics industry, for example, as ceramic packages or as thermal management components. However, other applications are also possible. In additional embodiments, cubic boron nitride single crystal layers and free-standing crystals can have a maximum dimension in the hundreds of millimeters range. The methods provided herein can also be used to form single crystal cubic boron nitride containing components that may be used to form power devices, such as diodes or transistors, that are used in the microelectronics industry.

[0028] FIGs. 1A-1D show phase diagrams or stability diagrams for boron nitride that have been described by a number of authors. FIG. 1A is a recently-reported phase diagram by Fukunaga and co-workers [0. Fukunaga, et al., Jpn. I. Appl. Phys. 61, 125502 (2022)] showing a number of phase diagram boundaries proposed in previous work. In each case, the cubic BN phase, having a zincblende crystal structure, is stable on the upper left side of the lines (higher pressure, lower temperature) and the hexagonal BN phase is stable on the lower right side of the lines (higher temperature, lower pressure). The BW1963 line refers to a phase boundary, or equilibrium line, reported by Bundy and Wentorf [F. P. Bundy and R. H. Wentorf Ir, I. Chem. Phys. 38, 1144 (1963)], the CB1975 line to a report by Corrigan and Bundy [F. R. Corrigan and F. P. Bundy, I. Chem. Phys. 63, 3812 (1975)], and the F2000 line to a previous report by Fukunaga [O. Fukunaga,Diamond Relat. Mater. 9, 7 (2000)] . Each of these authors regarded hBN as the stable phase under ambient conditions. However, in the early to mid-1990’s, Solozhenko and co-workers proposed that in fact cBN was the stable phase under ambient conditions and that the phase boundary crossed the zero-pressure axis rather than the zero-temperature axis, as shown in dashed line SI 995 [V. S. Solozhenko, High Press. Res. 13, 199 (1995)]. Similar results were reported by Maki, et al. [J. Maki, et al., Proc. 2ndInt. Conf. New Diamond Science & Technology (Washington, DC, 1990), Materials Research Society, Pittsburgh, PA, USA 1991, p. 1051] (not shown in FIG. 1A). In order to try to resolve the discrepant predictions, several authors performed experiments to inter-convert cBN and hBN at elevated pressures and temperatures, enabling an extrapolation to lower pressures and temperatures. FIG. IB shows the results of such experiments by Fukunaga, et al. [O. Fukunaga, et al., Ipn. J. Appl. Phys. 61, 125502 (2022)]. The pressures were calculated on the basis of a calibration procedure and the new line (FNT2022 in FIG. IB) is seen to agree relatively well with the BW1963 and CB1975 lines. The solid symbols in FIG. IB correspond to the cBN- stable side of the equilibrium line and the open symbols to the hBN-stable side of the equilibrium line. FIG. 1C shows results from related experiments performed by Will and co-workers [G. Will, et al., J. Solid State Chemistry 154, 280 (2000)] where the solid symbols represent fast and complete conversion from cBN to hBN with Mg (•,■) or Ei (♦) catalysts present, the open symbols represent slow and incomplete conversion from cBN to hBN with Mg (o,n) or Ei (0) catalysts present, the solid line represents the calculated equilibrium line, and the dashed line represents the phase boundary as estimated by Will et al. Unlike the results of Fukunaga et al., which predict that hBN is the stable phase at ambient conditions, the results of Will, et al. agree with the predictions by Solozhenko and by Maki that cBN is the stable phase at ambient conditions. Will’s measurements of pressure were based not on calibrations but rather on direct, in situ measurements of lattice constants by x-ray diffraction during the phase conversion and may be regarded as being more reliable. Referring now to FIG. ID, “1” refers to the hBN-cBN equilibrium line as calculated by Turkevich [J. Phys.: Condens. Matter 14, 10963 (2002)], “2” refers to the calculated hBN-cBN equilibrium line with 3 atomic percent oxygen present in the BN; “3” refers to pressure and temperature parameters where cBN is typically crystallized, and “4” refers to the pressure dependence of the LhBN <=> L + BN peritectic temperature. FIG. ID shows that the presence of 3% oxygen in the B-N system significantly reduces the temperature of the phase boundary between hBN and cBN. Therefore, it is important to minimize the oxygen content in reactants in order toform cBN under relatively mild conditions. In the view of the present inventors, the BN phase diagram remains controversial. As noted previously, commercial mesh and polycrystalline cBN synthesis continues to be practiced at pressures above 4-5 GPa.

[0029] The present inventors have discovered conditions under which cBN can be synthesized in supercritical ammonia at temperatures between about 350 degrees Celsius and about 1000 degrees Celsius, at pressures between about 200 MPa and about 2 GPa, in apparatus where the pressure is passively generated (that is, self-generated by the fluid itself) and is therefore less expensive and more scalable than a press-based high-pressure apparatus. The new process is expected to reduce the cost of manufacturing of known cBN components and enable manufacturing of new cBN compositions that have not yet been possible or practical, including near-net- shape ceramic cBN parts and large-diameter single-crystal layers and free-standing single crystals.

[0030] Referring to FIG. 2A, a growth chamber 101 suitable for one or more embodiments of the present disclosure may include or consist of the inner surface of an autoclave or pressure vessel, the inner surface of a liner within an autoclave, the inner surface of a capsule within an autoclave or within an internally-heated high-pressure apparatus, or the like. As used here, an autoclave refers to a thick-walled, externally-heated pressure vessel for processing materials at elevated temperature and pressures. An internally-heated high-pressure apparatus, which is also capable of processing materials at elevated temperature and pressure, may also be considered a pressure vessel, although its construction may be quite different than that of a conventional pressure vessel. The autoclave, pressure vessel, or internally-heated high-pressure apparatus will normally have a cylindrical shape and be vertically oriented. The interior volume 103 is filled with supercritical ammonia during operation, in which a mineralizer is dissolved. Growth chamber 101 may be divided into an upper chamber 105 and a lower chamber 107 by a baffle 109. Baffle 109 may include one or more disks, conical portions, spheroidal portions, or the like, with one or more perforations and annular gaps with respect to growth chamber 101, to allow for restricted fluid motion through the baffle. One or more seed crystals 111 may suspended within lower chamber 107 and / or upper chamber 105 from furniture, which may include one or more of basket 141 and frame 143. One or more chunks, particles, or plates of nutrient 113 is placed within at least one of upper chamber 105 and lower chamber 107. The configuration shown in FIG. 2A, with bothseed crystals 111 and nutrient 113 present in both upper chamber 105 and lower chamber 107, may be suitable for investigations of the phase boundary between cBN and hBN, without regard to whether the solubility in the mineralizer-in-supercritical-ammonia system is normal (solubility increases with increasing temperature) or retrograde (solubility decreases with increasing temperature). In certain embodiments, for example, where there is no intentional temperature gradient or temperature difference between upper chamber 105 and lower chamber 107, baffle 109 may be omitted.

[0031] In certain embodiments, each of growth chamber 101, baffle 109 (if present), basket 141, and frame 143 include or consist of at least one of copper, copper-based alloy, silver, silver-based alloy, gold, palladium, platinum, iridium, ruthenium, rhodium, titanium, titanium-based alloy, iron, iron-based alloy, stainless steel, nickel, nickel-based alloy, zirconium, niobium, molybdenum, tantalum, combinations thereof, and the like. In certain embodiments, basket 141 includes or consists of wire cloth.

[0032] In certain embodiments, seed crystals 111 include or consist of one or more of cBN or diamond. In one embodiment, the seed crystals 111 may include or consist of mesh crystals, for example, having a maximum dimension between about 40 micrometers and about 0.75 millimeter. Seed crystals may include or consist of micron powder, for example, having a maximum diameter between about 1 micrometer and about 40 micrometers, between about 5 micrometers and about 35 micrometers, or between 10 micrometers and about 30 micrometers. Seed crystals 111 may be blocky in shape, with a minimum dimension that is greater than about 50%, or greater than about 70%, of their maximum dimension, or they may have a shard shape, with a minimum dimension between about 1% and about 50%, or between about 10% and about 45%, of their maximum dimension. Seed crystals 111 may be prepared by growth at high pressure and high temperature, may be mined (in the case of diamond), may be prepared by conventional milling processes, or may be grown in supercritical ammonia or by a chemical vapor deposition process.

[0033] In certain embodiments seed crystals 111 include or consist of single-crystal cBN or diamond and have a maximum dimension between about 1 millimeter and about 200 millimeters. In some embodiments, the single-crystal cBN or diamond containing seed crystals 111 are greater in size than mesh crystals and are intended for use in device applications, for example. The singlecrystal cBN or diamond containing seed crystals 111 may be characterized by a surface dislocationdensity below about IO10cm'2, below about 109cm'2, below about 108cm'2, below about 106cm'2, below about 105cm'2, or below about 104cm'2. Diamond single crystals are more readily available than cBN single crystals and may have a larger diameter, for example, at least 3 millimeters, at least 10 millimeters, at least 25 millimeters, at least 50 millimeters, at least 100 millimeters or even as large as 200 millimeters. However, diamond has a higher symmetry than cBN, so without special precautions boundaries may be present between nanodomains that nucleated on different atomic surface planes of diamond. In a preferred embodiment, seed crystals 111 consist of single-crystal diamond with a large-area surface having a crystallographic orientation that is mis-oriented from {001 } in a <110> direction by between 0.5 degree and 10 degrees or between 1 degree and 5 degrees, and is mis-oriented in an orthogonal <110> direction by less than about 1 degree, less than about 0.5 degree, less than about 0.2 degree, less than about 0.1 degree, or less than about 0.05 degree, and that is characterized by a single-domain (2x1) reconstruction. The latter structure has been reported on diamond layers grown by chemical vapor deposition (CVD) on high-temperature-high-pressure-grown diamond (001) single crystals [see, for example, T. Tsuno et al., Appl. Phys. Lett. 64, 572 (1994); S. Kono, et al., Surface Sci. 529, 180 (2003)]. These single-domain (001)-(2xl) surface structures include two-atom-high steps, so that cBN nucleating on such step structures can all consist of a single domain. It may also be possible to form single-domain (001)-(2xl) surfaces by hydrogen plasma treatment of <011>- miscut diamond (001) surfaces, based on reports of surface diffusion generated by high-power- density hydrogen plasmas [R. E. Rawles, et al., Diamond Relat. Mater. 6, 791 (1997)]; in other words, homoepitaxial CVD growth may not be required to achieve the desired double-atomic- layer steps. After ammonothermal growth of cBN-on-diamond layers, as described in more detail below, a free-standing cBN seed crystal may be prepared from the ammonothermal-cBN layer on diamond by methods that are known in the art, such as one or more of wire-sawing, grinding, polishing, chemical-mechanical polishing, etching, or oxidation. In some applications, the formed free-standing cBN seed crystal may then be used in subsequent bulk crystal growth processes.

[0034] The nutrient 113 disposed within the growth chamber 101 includes or consists of boron. In certain embodiments, nutrient 113 includes or consists of elemental boron. In certain embodiments, nutrient 113 consists substantially of boron nitride. In certain embodiments, nutrient 113 consists substantially of pyrolytic boron nitride and has a hexagonal crystal structure. The pyrolytic boron nitride may be crushed, milled, or the like, to form micron- or millimeter-sized particles. In certain embodiments, nutrient 113 includes or consists of micro-pyrolytic boron nitride particles or nano-pyrolytic boron nitride particles. In certain embodiments, nutrient 113 includes or substantially consists of a boron nitride powder that includes particles that have a hexagonal crystal structure. In certain embodiments, at least portions of nutrient 113 have a turbostratic and / or wurtzite crystal structure. In certain embodiments, nutrient 113 includes or consists of crystalline or single-crystalline cubic boron nitride, for example, mesh cubic boron nitride.

[0035] In certain embodiments, seed crystals 111 and nutrient 113 include boron having natural isotopic abundance. In certain embodiments, one or both of seed crystals 111 and nutrient 113 include boron that is isotopically enriched, in either10B ornB, to a level above 90%, above 95%, above 98%, or above 99%. The use of isotopically-enriched boron-containing constituents may be desirable for thermal management applications, for example.

[0036] In certain embodiments, nutrient 113 consists substantially of pyrolytic BN particles, plates, or shapes. In certain embodiments, nutrient 113 consists substantially of an hBN containing powder, such as pure hBN powder. The nutrient 113 may be characterized by a particle size distribution having a D10 value between about 0.1 micrometer and about 10 micrometers, or between about 10 micrometers and about 2 millimeters, and a D90 value between about 1 micrometer and about 25 micrometers, or between about 25 micrometers and about 10 millimeters. The particle-size distribution may be measured by various methods that are known in the art, such as laser diffraction, dynamic light scattering, dynamic image analysis, sieve analysis, optical counting, electroresistance counting, sedimentation, acoustic spectroscopy, laser obscuration time, or the like. Referring to the cumulative particle-size distribution, the quantities D10, D50, and D90 refer to the diameters at which 10% of the volume of particles, 50% of the volume of particles, or 90% of the volume of particles, respectively, have a diameter less or equal to than the specified value. In this terminology, the quantities we are calling D10, D50, and D90 are sometimes called DvlO, Dv50, and Dv90, respectively.

[0037] In certain embodiments, nutrient 113 is unintentionally doped. In other embodiments, nutrient 113 is intentionally doped, for example, so as to enable growth of doped ammonothermal BN layers for single-crystal device applications such as power diodes or power transistors, for example, with concentrations between about IxlO15cm’3and about IxlO21cm’3, between IxlO16cm'3and about IxlO20cm'3, or between IxlO17cm'3and about IxlO19cm'3. For example, nutrient 113 may be doped with Be or Mg, to enable p-type conductivity in ammonothermal cBN layers, or with S or Si, to enable n-type conductivity in ammonothermal cBN layers. In the case that nutrient 113 consists essentially of pyrolytic BN (pBN), which is typically formed by chemical vapor deposition (CVD) from BCh and NH3, doping may be achieved by addition of BeCh (for example, formed in situ by reaction of Ch with Be metal at high temperature), Mg(cp)2 (bis(cyclopentadienyl) magnesium), H2S, or SiCU to the reactant gas stream used to form the pBN.

[0038] In some embodiments, the growth chamber 101 consists substantially of a sealed container that consists of or is disposed within an autoclave or pressure vessel during processing. In certain embodiments, the sealed container consists substantially of a sealed capsule, which may include a liner, or of a liner. As briefly discussed above and further discussed below, in some embodiments, the internal volume of a sealed container will include the one or more seed crystals 111, the one or more chunks, particles, or plates of nutrient 113, ammonia (NH3), and a mineralizer composition, which can include one or more of an alkali element, an alkaline earth element, or a halogen. In some embodiments, the sealed container will also include the furniture, which may include one or more of the basket 141 and the frame 143, and optionally one or more baffles 109, which are placed within at least one of the upper chamber 105 and lower chamber 107 of the sealed capsule or liner. The internal volume of the sealed container can be enclosed by a thin walled sheet of material that comprises copper, copper-based alloy, silver, silver-based alloy, gold, palladium, platinum, iridium, ruthenium, rhodium, titanium, titanium-based alloy, iron, iron-based alloy, stainless steel, nickel, nickel-based alloy, zirconium, niobium, molybdenum, tantalum, combinations thereof, and the like. In some embodiments, the thin walled sheet of material can have a wall thickness between about 0.5 and about 10 millimeters (mm), or between about 1 millimeter and about 5 millimeters. In some embodiments, the walls of the sealed container are formed and welded or bonded together to form a hermetically sealed vessel.

[0039] FIG. 2B illustrates a configuration of the growth chamber 101 that consists substantially of a sealable container 600, in which granules 645 fill up a significant percentage of the interior volume 603 of the sealable container 600. The sealable container 600 may include or consist of a capsule, an autoclave, or a liner within an autoclave. The capsule or liner may include one or more of fill tube or upper inlet 623 and lower inlet 625. Granules 645, an expanded view of which isshown schematically in FIG. 2C, include one or more seed crystals 111 embedded within nutrient 113. Granules 645 may have a diameter or characteristic dimension between about 100 micrometers and about 15 millimeters, between about 250 micrometers and about 10 millimeters, or between about 500 micrometers and about 5 millimeters. Preparation of the granules 645 may be facilitated by utilizing hBN powder as nutrient 113.

[0040] In certain embodiments, the weight ratio of seed crystals 111 to nutrient 113 within granules 645 or within sealable container 600 may be between about one part per million and about 0.5, between about 10 parts per million and about 0.2, or between about 0.01% and about 0.1. In one example, the seed crystals 111 include cBN crystals and the nutrient 113 comprises an hBN containing powder. In certain embodiments, seed crystals 111 are mixed with the particles of the nutrient 113 in a V-blender, a convective dry mixer, a powder mixer, a ball mill, in an attrition mill, jet mill, or the like. In certain embodiments, milling media such as ShN4, SiC, ZrO , or AIN, are present during the mixing operation and may be separated from the mixture when milling has been completed. In certain embodiments, the mixing or milling process is performed under an atmosphere of dry air or dry nitrogen. During the mixing or milling process, mechanical bonding between at least a portion of seed crystals 111 and the particles of the nutrient 113 may occur. In certain embodiments, additional components are mixed with seed crystals 111 and particles of the nutrient 113. The additional components may include one or more of graphite, carbon black, ethylene glycol, propylene glycol, a wax composition, or a vinyl polymer such as polyvinyl alcohol. Granules 645 may be formed from a mixed blend of seed crystals 111 and polycrystalline particles of the nutrient 113 by one or more of granulation, tableting, roller compaction, or the like. Granules 645 may have a porosity between about 1% and about 50%, between about 2% and about 25%, or between about 3% and about 15%.

[0041] FIG. 3A illustrates another configuration of the growth chamber 101 that consists substantially of a sealable container 600 in which BN pre-forms 655 fill up a portion of the interior volume 603. The sealable container 600 may include or consist of a capsule, an autoclave, or a liner within an autoclave. The capsule or liner may include one or more of a fill tube, upper inlet 623 and lower inlet 625. BN pre-forms 655, an expanded view of which is shown schematically in FIG. 3B, and a still-further expanded view is shown in FIG. 3C, include one or more seed crystals 111 (e.g., cBN micron powder particles or diamond micron powder particles) embeddedwithin nutrient 113. BN pre-forms 655 may have a maximum dimension, such as a length or diameter, between about 100 micrometers and about 450 millimeters, between about 250 micrometers and about 100 millimeters, or between about 500 micrometers and about 25 millimeters, and a minimum dimension, such as a thickness, between about 1 micrometer and about 25 millimeters, between about 5 micrometers and about 5 millimeters, or between about 25 micrometers and about 2 millimeters. In certain embodiments, BN pre-forms 655 have a simple geometry, such as a disk or a plate, as shown schematically in the upper half of FIG. 3B, or a more complicated shape, as shown schematically in the lower half of FIG. 3B. For example, BN preforms 655 might have a shape suitable for a ceramic package, for example, a 5-sided box, or other shape suitable for a near-net-shape ceramic part. Formation of BN pre-forms 655 may be facilitated by including hBN powder in nutrient 113. In certain embodiments, elemental boron, for example, a powder or a coating, may be included within nutrient 113 within BN pre-forms 655.

[0042] In certain embodiments, the weight ratio of seed crystals 111 to nutrient 113 within BN pre-forms 655 or within sealable container 600 may be between about 25% and about 99.9%, between about 50% and about 99%, between about 75% and about 98%, or between about 85% and about 97%. In certain embodiments, seed crystals 111 are mixed with the particles of the nutrient 113 in a V-blender, a convective dry mixer, a powder mixer, a ball mill, in an attrition mill, jet mill, or the like. In certain embodiments, milling media such as S i 3 N4, SiC, ZrO2, or AIN, are present during the mixing operation and may be separated from the mixture when milling has been completed. In certain embodiments, the mixing or milling process is performed under an atmosphere of dry air or dry nitrogen. During the mixing or milling process, mechanical bonding between at least a portion of seed crystals 111 and particles of the nutrient 113 may occur. In certain embodiments, additional components are mixed with seed crystals 111 and particles of the nutrient 113. The additional components may include one or more of graphite, carbon black, ethylene glycol, propylene glycol, a wax composition, or a vinyl polymer such as polyvinyl alcohol.

[0043] In certain embodiments, seed crystals 111, nutrient 113, and additional solid components, if present, are mixed and dispersed in a slurry on a supporting structure (e.g., substrate or carrier film). In some embodiments, the slurry includes water. In certain embodiments, the slurry includes a polar, aprotic solvent. In certain embodiments, the slurry is substantially free of waterand includes an aliphatic solvent, such as diethylamine, or an aromatic solvent, such as aniline. Avoidance of water and protic solvents may be helpful in minimizing formation of B2O3 and other oxides on the surfaces of seed crystals 111 and nutrient 113. In certain embodiments, the slurry includes one or more of a binder, lubricants, wetting agents, plasticizers, dispersants, deflocculants, other additives, and the like, as are known in the art. In certain embodiments, the slurry includes one or more of a wax composition and urea.

[0044] Organic binders which may be employed in preparation of BN pre-forms 655 as components of the slurry or dry-mixed powder include but are not limited to vinyl polymers such as but not limited to polyvinyl butyral (PVB), polyvinyl alcohol (PVA), polyvinyl chloride (PVC), polyvinyl acetate (PVAc), polyacrylonitrile, mixtures thereof and copolymers thereof, polyethyleneimine, poly methyl methacrylate (PMMA), vinyl chloride- acetate and mixtures thereof, preferably PVB. Plasticizers which may be employed in manufacture of a polycrystalline cBN material include but are not limited to butylbenzyl phthalate, dicarboxylic / tricarboxylic ester- based plasticizers such as but not limited to phthalate-based plasticizers such as but not limited to bis(2-ethylhexyl) phthalate, diisononyl phthalate, bis(n-butyl)phthalate, butylbenzyl phthalate, diisodecyl phthalate, di-n-octyl phthalate, diisooctyl phthalate, diethyl phthalate, diisobutyl phthalate, di-n-hexyl phthalate and mixtures thereof adipate-based plasticizers such as but not limited to bis(2-ethylhexyl)adipate, dimethyl adipate, monomethyl adipate, dioctyladipate and mixtures thereof sebacate based plasticizers such as but not limited to dibutyl sebacate, and maleate type plasticizers such as but not limited to dibutyl maleate, diisobutyl maleate and mixtures thereof; polyalkylene glycols such as but not limited to polyethylene glycol, polypropylene glycol and mixtures thereof. Other plasticizers which may be used include but are not limited to benzoates; epoxidized vegetable oils; sulfonamides such as but not limited to N-ethyl toluene sulfonamide, N-(2 -hydroxypropyl) benzene sulfonamide, and N-(n-butyl)benzene sulfonamide; organophosphates such as but not limited to tricresyl phosphate and tributyl phosphate; glycols / polyethers such as but not limited to triethylene glycol dihexanoate, tetraethylene glycol diheptanoate and mixtures thereof; alkyl citrates such as but not limited to triethylcitrate, acetyl triethylcitrate, tributylcitrate, acetyl tributyl citrate, trioctyl citrate, acetyltrioctyl citrate, trihexylcitrate, acetyl trihexylcitrate, butyryl trihexyl citrate, and trimethylcitrate; and alkyl sulphonic acid phenyl ester and mixtures thereof.

[0045] Dispersants which may be employed in formation of the slurry or dry-mixed powder include but are not limited to oxidized Menhaden fish oil (MFO), dicarboxylic acids such succinic acid, ethanedioic acid, propanedioic acid, pentanedioic acid, hexanedioic acid, heptanedioic acid, octanedioic acid, nonanedioic acid, decanedioic acid, sorbitan monooleate, o-phthalic acid, p- phthalic acid and mixtures thereof.

[0046] In certain embodiments, particularly when BN pre-forms 655 are intended to be planar parts having a thickness less than about 2 millimeters, or about 1 millimeter, a slurry containing seed crystals 111 and nutrient 113 is tape-cast onto a flexible carrier film using a tape casting or doctor blade technique using methods that are known in the art. In certain embodiments, the flexible carrier film includes or consists of Mylar™, which is then removed after the slurry has been dried to form a green body.

[0047] BN pre-forms 655 may be formed from a mixed blend of seed crystals 111 and particles of the nutrient 113 by one or more of granulation, tableting, roller compaction, uniaxial pressing, isostatic pressing, or the like. BN pre-forms 655 may have a porosity between about 1% and about 80%, between about 3% and about 50%, or between about 4% and about 25%.

[0048] In certain embodiments, BN pre-forms with more complex shapes may be prepared by one or more of injection molding or green machining. Green machining may include one or more of milling, turning, grinding, and drilling.

[0049] FIG. 3D illustrates another configuration of the growth chamber 101 that consists substantially of a sealable container 600 and is intended for growth of a single-crystal cBN layer on seed crystals 111, which are suspended from furniture 143. The sealable container 600 may include or consist of a capsule, an autoclave, or a liner within an autoclave. The capsule or liner may include one or more of fill tube or upper inlet 623 and lower inlet 625. While polycrystalline hBN or pBN can be used as nutrient, in certain embodiments cBN is used as nutrient 113, so that the supersaturation during processing can be controlled by a temperature difference between lower zone 107 and upper zone 105 rather than by the difference in free energy between cBN and hBN at a given temperature and pressure. In certain embodiments nutrient 113 includes or consists of mesh cBN, which may be single-crystalline, polycrystalline, or a mix of the two. However, for growth of intentionally doped cBN, pBN that has been doped with Be, Mg, S, or Si, as described above, may be preferred as a nutrient.

[0050] The configuration shown in FIG. 3D is appropriate for ammonothermal growth of singlecrystal cBN when the solubility with a given mineralizer system is normal, that is, the solubility increases with increasing temperature. With some of the mineralizers disclosed below the solubility may be retrograde, that is where the solubility decreases with increasing temperature. In the case of growth with a mineralizer exhibiting retrograde solubility for BN, the configuration shown in FIG. 3D is reversed, so that seed crystals 111 are placed in lower zone 107 and nutrient 113 is placed in upper zone 105.

[0051] In some embodiments, the seed crystals 111 are positioned in either the lower zone 107 or the upper zone 105 and the nutrient 113 is placed in the opposite zone, such as the upper zone 105 or the lower zone 107, respectively, and are separated by a separation distance and / or a baffle 109. As shown in FIG. 3D, the separation distance is in a vertical direction, which, by controlling the temperature in each zone, will enable supercritical fluid-containing convection loops to form during the ammonothermal growth process.

[0052] In preferred embodiments, nutrient 113 is substantially oxygen-free, with an oxygen concentration less than one percent by weight, less than 100 parts per million by weight, or less than 10 parts per million by weight. Without wishing to be bound by theory, the inventors believe that B2O3 may inhibit the dissolution and / or the crystallization of BN in supercritical ammonia, which may have been a factor in conventional processes being unable to form cBN at pressures significantly below 5 GPa. In addition, the presence of oxygen in the B-N system may shift the cBN-hBN equilibrium boundary to the left, as shown schematically in FIG. ID, which, depending on the temperature and pressure, can cause a growth process to favor the formation hBN versus cBN. The inventors also note that hot-pressed BN, which has been used in conventional processes as a raw material, typically contains B2O3, used as a sintering aid. In addition, as noted above, the presence of oxygen in the growth system may shift the phase boundary between cBN and hBN to higher pressures and lower temperatures. In certain embodiments, a weight of added carbon within the nutrient, for example, in the form of graphite or carbon black, may be within a factor of 5 or within a factor of two of the weight of oxygen within polycrystalline nutrient 113, for example, as B2O3. The added carbon may be able to remove oxygen from the BN system, as CO, for example, thereby creating more favorable conditions for formation or recrystallization of cBN.

[0053] After preparation, one or more of seed crystals 111, nutrient 113, granules 645, BN preforms 655 and, optionally baffle 109 or 635 and other furniture, are placed within interior 103 of growth chamber 101 or interior 603 of sealable container 600. The sealable container 600 may then be closed and sealed except for one or more connections to a fluid manifold that includes at least one of a gas, liquid, or vacuum manifold. The sealable container 600 may then be evacuated, so as to remove air, moisture, and other volatile contaminants. In some embodiments, the sealable container 600 is heated during evacuation, to a temperature between about 25 degrees Celsius and about 1200 degrees Celsius, between about 100 degrees Celsius and about 1000 degrees Celsius, between about 200 degrees Celsius and about 800 degrees Celsius, or between about 300 degrees Celsius and about 700 degrees Celsius, depending in part on the composition of sealable container 600 (i.e., the maximum temperature should remain well below its melting point). In some embodiments the sealable container is subjected to at least two, at least three, at least five, or at least ten cycles of evacuation followed by back-filling with an inert gas such as argon or nitrogen. In certain embodiments, referring again to FIGs. 2B, 3A, and 3D, the sealable container is provided with at least a lower inlet 625, which may function as a gas-phase inlet, and an upper inlet 623, which may function as a gas-phase outlet, so that the sealable container can be purged by a continuous flow of gas. Purging may provide for superior removal of air, moisture, and other volatile contaminants, relative to evacuation, because of the limited conductance through a tube to the interior of the sealable container. The efficiency of purging may be enhanced by causing purge gas to flow from one end of the interior volume of the sealable container to the other. The sealable container may be coupled to a gas source within the fluid manifold by means of at least one fill tube or purge tube, preferably without exposing the contents of the sealable container to air, according to a specific embodiment. The gas source may comprise at least one of nitrogen, argon, hydrogen, helium, and ammonia, among others. When the purging gas is ammonia, residual oxide, for example, B2O3, within the sealable container and within granules 645 or BN preforms 655, for example, may be reduced to BN and H2O vapor formed by chemical reaction may be removed. The presence of graphite or carbon black in granules 145 or BN preforms 655 may help in removal of oxygen, for example, as CO, during purging with ammonia, particularly if the sealable container is heated to a temperature of 700 degrees Celsius or above. The evacuation, pump / purge, and / or flow-purge operations may be carried out at elevated temperature for a duration between about one hour and about one week, or between about 4 hours and about 96 hours.

[0054] A mineralizer composition may be added to sealable container 600. In certain embodiments, the mineralizer composition includes one or more of an alkali element, an alkaline earth element, or a halogen. In certain embodiments, the mineralizer composition includes one or more of Li3N, LiNH2, NaNH2, NaN3, KNH2, KN3, Mg3N2, Ca3N2, HF, HC1, HBr, HI, or a reaction product of one or more of these with NH3and / or with BN. The mineralizer composition may consist of or include an alkali metal such as Li, Na, K, Rb, or Cs, an alkaline earth metal, such as Mg, Ca, Sr, or Ba, or an alkali or alkaline earth hydride, amide, imide, amido-imide, nitride, or azide. The mineralizer may consist of or include an ammonium halide, such as NH4F, NH4CI, NH4Br, or NH4I, a boron halide, such as BF3, BC13, BBr3, BI3, or any compound that may be formed by reaction of one or more of F, Cl, Br, I, HF, HC1, HBr, HI, B, BN, and NH3. In certain embodiments, the mineralizer composition is added to sealable container 600 prior to closing of sealable container 600, for example, within a glove box or under an atmosphere containing less than 10 parts per million, less than 5 parts per million, less than 2 parts per million, or less than 1 part per million of water vapor. In preferred embodiments, the mineralizer composition is added to sealable container 600 after the sealable container 600 has been closed, evacuated, and baked and / or purged at elevated temperature, as described further below.

[0055] One or more embodiments of the disclosure provided herein includes a pressure vessel pressurization process that utilizes a simplified and robust method of achieving the desirable processing pressures to enable the formation of cBN crystalline layers, films, or materials. In some embodiments, after the pump-purge and / or flow-purge process is completed, the sealable container 600 may be cooled and filled with ambient temperature or chilled ammonia (NH3) to a specified level within the internal volume. In certain embodiments, the sealable container 600 is cooled to a dry ice temperature, for example, by immersion in a dry ice solvent bath or by use of a cryogenic heat exchanger, and a controlled quantity of gaseous ammonia is flowed into the sealable container from the fluid manifold and condensed into a liquid phase. In other embodiments, a controlled amount of liquid ammonia is flowed into the sealable container 600 at an elevated pressure from a fluid assembly in the fluid manifold, for example, above approximately seven atmospheres. In certain embodiments, the fill percentage of ammonia, that is, the fraction of free volume within sealable container 600, that is, excluding the nutrient 113, seed crystals 111, and any furniture, that is filled with ammonia is between about 10% and about 100%, between about 20% and about 90%, or between about 30% and about 85%. The fill percentage is calculated as the ratio of the weightof ammonia within sealable container 600 to the free volume within sealable container 600, divided by 0.6 g / cm3(the density of liquid ammonia at equilibrium with its vapor at room temperature) and multiplied by 100. By chilling sealable container 600 to a temperature between room temperature and dry ice temperature and allowing liquid ammonia to completely fill sealable container 600, fills between 100% and up to and above about 120% may be achieved. For example, at water ice temperature the equilibrium density of liquid ammonia is about 0.634 g / cm3(enabling a fill of 105.7%), and at dry ice temperature the equilibrium density of liquid ammonia is about 0.729 g / cm3(enabling a fill of 121.6%). Ammonia freezes, at atmospheric pressure, at about approximately -77.7 degrees Celsius. Even higher percent fills of ammonia may be achieved by means of external pressurization of liquid ammonia. Of course, when ammonia is supplied to the sealable container to a level of a 100% or greater fill percentage, as sealable container 600 is warmed back to room temperature, significant pressure will be generated, so it is important that sealable container 600 be able to handle such internally-generated pressures safely. The pressure of ammonia as a function of temperature, for selected values of % fill (that is, density relative to 0.6 g / cm3), is shown in FIG. 8, where the data have been obtained from the public-domain NIST fluids database [https: / / webbook.nist.gov / chemistry / fluid / ] or by a simple polynomial interpolation or extrapolation of the tabulated data.

[0056] Referring again to FIGs. 1A, IB, and 1C, we see that there is widespread agreement that the boundary between the cBN-stable phase and the hBN-stable phase at about 2000 degrees Celsius is between about 5 and about 6 GPa but that there is substantial disagreement about the extrapolation of the phase boundary to the zero-pressure axis or whether cBN is even the stable phase at ambient pressure. Also included in FIG. 8 are “low”, “medium”, and “high” cBN-to-hBN phase boundaries where, in each case the boundary is assumed to cross a pressure of 5.25 GPa at a temperature of 2000 degrees Celsius and to cross the zero-pressure axis at temperatures of 150, 250, or 350 degrees Celsius, respectively. While the inventors have not yet determined the precise position of the low-pressure phase boundary, it is believed to be within the ranges of the latter boundary lines. As described further in the Examples, the inventors have found that, although the cubic phase is stable under ambient conditions, the inter-conversion rate between the hexagonal and cubic phases is vanishingly slow at temperatures below about 300 degrees Celsius, and still quite slow at temperatures below about 400 degrees Celsius or about 450 degrees Celsius. Although there are embodiments where bonding of a hBN phase to cBN or diamond seed crystals(such as mesh crystals or powder) adds utility, typically one will prefer formation of the cubic phase, or at least minimize back-conversion of the cubic phase to the hexagonal phase. As a consequence of the usefulness of temperatures above about 350 degrees Celsius, above about 400, or above about 450 degrees Celsius and the position and slope of the phase boundaries, the inventors have found that it is useful to utilize an ammonia density above about 0.42 g / cm3(70% fill), above about 0.54 g / cm3(90% fill), above about 0.6 g / cm3(100% fill), above about 0.63 g / cm3(105% fill), above about 0.66 g / cm3(110% fill), or above about 0.69 g / cm3(115% fill).

[0057] In certain embodiments, the mineralizer is added to sealable container 600 together with liquid ammonia, for example, in solution by use of a mixed-fluid delivery system, as shown in Figure 4. For example, referring to FIG. 4, a mineralizer composition may be weighed and added to a mineralizer vessel 951 within a glove box (not shown) and then mineralizer vessel 951 may be sealed and removed from the glove box. Mineralizer vessel 951 and flush vessel 953 may be attached to an ammonia manifold 961 through valve 957. With valves 955 and 957 open, mineralizer vessel 951 may be chilled to dry ice temperature and filled with a predetermined quantity of ammonia. Then, with valve 957 open and valve 955 closed, flush vessel 953 may be chilled and filled with a predetermined quantity of ammonia. With valve 957 closed, flush vessel 953 and mineralizer vessel 951 may be disconnected from the ammonia manifold and warmed to room temperature, generating a solution of mineralizer in ammonia within mineralizer vessel 951, and connected to sealable container 600, which has been pre-evacuated. Valve 959 may then be opened, along with any additional valves between mineralizer vessel 951 and sealable container 600, causing the liquid-ammonia-mineralizer solution to be injected into sealable container 600. If desired, sealable container 600 may be chilled, or mineralizer vessel 951 heated, for example by 5 to 25 degrees Celsius, to cause the last residue of liquid ammonia to be transferred to sealable container 600. Valve 959 may then be closed and valve 955 opened, causing ammonia to transfer from flush vessel 953 to mineralizer vessel 951. If desired, mineralizer vessel 951 may be chilled, or flush vessel 953 heater, for example, by 5 to 25 degrees Celsius, to cause the last residue of liquid ammonia to be transferred from flush vessel 953 to mineralizer vessel 951. Mineralizer vessel 951 may be warmed to room temperature, causing re-dissolution of any traces of mineralizer left behind from the first ammonia transfer from mineralizer vessel 951 to sealable container 600. Valve 959 may then be opened, along with any additional valves (e.g., V4 and FV) between mineralizer vessel 951 and sealable container 600, causing the liquid ammonia withtraces of dissolved mineralizer to be injected into sealable container 600. This process can be repeated additional times as desired. Additional ammonia can be added to sealable container 600 as described above. After processing any residual ammonia may be evacuated through an outlet 965. This method is readily capable of providing ammonia fills greater than 100%, for example, to 105%, to 110%, to 115%, or to 120% (again, expressed with respect to 0.60 g / cm3). In preferred embodiments, the density of ammonia within sealable container 600 before and during the ammonothermal crystal growth process is between about 0.42 g / cm3and about 0.75 g / cm3, between about 0.54 g / cm3and about 0.72 g / cm3, or between about 0.60 g / cm3and about 0.69 g / cm3.

[0058] In certain embodiments, a mineralizer composition may be formed in situ in sealable container 600 by reaction of ammonia with a hydrogen halide. In certain embodiments, with sealable container connected to a gas manifold, HF vapor is transferred in a vapor phase from an HF cylinder to a transfer vessel, and then a measured quantity of HF is transferred from the transfer vessel to sealable container 600. The measured quantity of HF may be determined by a volume or height measurement within the transfer vessel, gravimetrically, or by integration of the signal from a mass flow controller. The measured quantify of HF may be transferred to sealable container 600 by a vapor phase, for example, with the sealable container 600 chilled to dry ice temperature, prior to condensation of ammonia within sealable container 600. NH4F may be formed in situ within sealable container 600 once ammonia is condensed over previously-transferred HF. In certain embodiments, one or more of HC1, HBr, or HI is transferred from a gas cylinder to sealable container 600 through a mass flow controller, with one or more of NH4CI, NH4Br, or NH4I being formed in situ by reaction with ammonia within sealable container 600. In certain embodiments, the HC1, HBr, or HI is passed through a point-of-use purifier prior to admitting to sealable container 600.

[0059] The molar ratio of the mineralizer composition and the ammonia may be between about 0.1% and about 75%, between about 1% and about 50%, between about 2% and about 25%, or between about 3% and about 15%.

[0060] After the desired amount of ammonia and mineralizer has been added to the sealable container 600, the sealable container 600 may be closed and sealed. The sealing process may include one or more of closing a valve, ultrasonically welding a fill tube, such as upper inlet 623and / or lower inlet 625, and tungsten-inert-gas welding of a fill tube, such as upper inlet 623 and / or lower inlet 625.

[0061] In certain embodiments, the ammonia-filling process is performed while the sealable container is enclosed within a pressure vessel (or is the pressure vessel, in the case where the sealable container is an autoclave). In certain embodiments, the sealable container 600 is placed within a high-pressure apparatus or pressure vessel after filling with ammonia and sealing. The high-pressure apparatus is capable of supporting pressure internally generated by the ammonia, after heating, but does not actively supply pressure to the sealable container.

[0062] In certain embodiments, the pressure vessel is an autoclave and the sealable container 600 is a liner or capsule 211 within autoclave 200, as shown schematically in FIG. 5 A. The autoclave may be capable of processing a material in a fluid at a pressure above about 5 MPa and below about 1000 MPa, below about 800 MPa, below about 500 MPa, below about 300 MPa, or below about 200 MPa, at temperatures between about 50 degrees Celsius and about 900 degrees Celsius, between about 100 degrees Celsius and about 600 degrees Celsius, between about 150 degrees Celsius and about 500 degrees Celsius, or between about 200 degrees Celsius and about 400 degrees Celsius. Referring again to FIG. 5A, autoclave 200 includes an autoclave body 201. The upper portion of autoclave body 201 may be surrounded by an upper heater 205 and the lower portion of autoclave body may be surrounded by a lower heater 207, each of which may include insulation. Upper heater 205 may include one, two, or more independently-controllable hot zones, for example, top tail zone 205a and top main zone 205b. Lower heater 207 may include one, two, or more independently-controllable hot zones, for example, bottom main zone 207a and bottom tail zone 207b. Upper heater 205 and lower heater 207 may be physically joined into a unitary component but are typically independently controllable. In certain embodiments, a liner 211 is placed within a cavity of autoclave body 201. Liner 211 may be formed from or may include one or more of platinum, palladium, iridium, a Pt / Ir alloy, gold, or silver. Liner 211 may also include or be formed from one or more of titanium, rhenium, copper, stainless steel, zirconium, tantalum, molybdenum, niobium, alloys thereof, and the like.

[0063] In certain embodiments, autoclave 200 further includes autoclave cap 217 and closure fixture 219, as shown schematically, plus a gasket (not shown). The configuration shown in FIG.5A is a schematic representation of a Grayloc™ seal. In other embodiments, autoclave 200 includes one or more of an unsupported Bridgman seal, an o-ring seal, a confined gasket seal, a cone seal, a bolted closure, an AE™ closure, an EZE-Seal™, a Keuntzel closure, a ZipperClave™ closure, a threadless pin closure, or a Gasche™ gasket seal. In certain embodiments, autoclave 200 further includes a cap, closure fixture, and seal on the lower end, in addition to the cap, closure fixture, and seal on the upper end.

[0064] Autoclave body 201, autoclave cap 217, and closure fixture 219 may each be fabricated from a material selected from a group consisting of steel, low-carbon steel, SA723 steel, SA266 carbon steel, 4340 steel, A-286 steel, iron based superalloy, nickel based superalloy, cobalt based superalloy, Inconel 718, Rene 41, 304 stainless steel, 310 stainless steel, 316 stainless steel, 340 stainless steel, 410 stainless steel, and 17-4 precipitation hardened stainless steel, zirconium and its alloys, titanium and its alloys, and other materials commonly known as Monel, Inconel, Hastelloy, Udimet 500, Stellite, Rene 41, and Rene 88. One or more of the components comprising autoclave body 201, autoclave cap 217, and closure fixture 219 may undergo a heat treatment operation. In certain embodiments, autoclave body 201 includes a demountable seal at the bottom as well as at the top.

[0065] Autoclave 200 may further comprise a bottom end heater 231 that is thermally coupled to the bottom portion of autoclave body 201 and includes thermal insulation 232. Bottom end heater 231 generates a power distribution that is approximately azimuthally uniform about the axis of autoclave body 201. The power level in bottom end heater 231, relative to the power level in lower heater 207 and upper heater 205, along with the radial dependence of the power density within bottom end heater 231, is chosen so as to maintain a temperature distribution along bottom surface 215 that is uniform to within 10 degrees Celsius, within 5 degrees Celsius, within 2 degrees Celsius, within 1 degree Celsius, within 0.5 degree Celsius, or within 0.2 degree Celsius. In certain embodiments, the power level in bottom end heater 231, relative to the power level in lower heater 207 and upper heater 205, along with the radial dependence of the power density within bottom end heater 231, is chosen so as to maintain an average temperature of bottom surface 215 that is equal to the average temperature within a specified height, measured with respect to bottom surface 215, of the inner surface of liner 211, or of the inner surface of autoclave body 201 if the liner 211 is not present, to within 20 degrees Celsius, within 10 degrees Celsius,within 5 degrees Celsius, within 2 degrees Celsius, or within 1 degree Celsius. In certain embodiments the specified height is approximately 1 centimeter, 5 centimeters, 10 centimeters, 20 centimeters, or 25 centimeters. In certain embodiments, the bottom end heater 231 is configured with at least two or at least three independently-controllable hot zones.

[0066] In certain embodiments, autoclave 200 further includes a top insulator / heater 209. In certain embodiments, top insulator / heater 209 includes or consists of a load-bearing thermal insulator, for example, zirconia or another ceramic material with a low thermal conductivity. In certain embodiments, top insulator / heater also has capability to generate heat, for example, by means of electrical connections through autoclave cap 217. In certain embodiments, top insulator / heater 209 includes one or more of a cartridge heater, a cable heater, a disk heater, or the like. Top insulator / heater 209 may have finished surfaces so that it fits snugly against a lower surface of autoclave cap 217 and against top surface 245 of liner 211 and sufficient radial clearance with respect to an inner surface of autoclave body 201 for easy insertion and removal without enabling extrusion of an upper portion of liner 211 into a radial gap during high pressure operation. The dimensions of top insulator / heater 209 and its power level, if present, along with the power levels in lower heater 207 and upper heater 205, including a top zone within upper heater 205, along with the radial dependence of the power density within top insulator / heater 209, may be chosen so as to maintain a temperature distribution along top surface 245 that is uniform to within 10 degrees Celsius, within 5 degrees Celsius, within 2 degrees Celsius, or within 1 degree Celsius. In addition, the dimensions of top insulator / heater 209 and the power levels of upper heater 205 and lower heater 207 may be chosen to maintain top surface 245 at an average temperature that is equal to the average temperature within a specified height, measured with respect to top surface 245, of the inner surface of liner 211, or of the inner surface of autoclave body 201, if liner 211 is not present, to within 20 degrees Celsius, within 10 degrees Celsius, within 5 degrees Celsius, within 2 degrees Celsius, or within 1 degree Celsius. In certain embodiments the specified height is approximately 1 centimeter, 5 centimeters, 10 centimeters, 20 centimeters, or 25 centimeters. In certain embodiments, the top insulator / heater 209 is configured with at least two or at least three independently-controllable hot zones.

[0067] In certain embodiments, sealable container 600 is placed within an internally-heated high- pressure apparatus 300 as capsule 307, as shown schematically in FIG. 5B. The internally-heatedhigh-pressure apparatus 300 provides adequate containment in all directions which, for a typical cylindrical vessel, can be classified as radial and axial. Furthermore, depending on the specifics of the design parameters, the apparatus is capable of operating at temperatures between 200 degrees Celsius and 1500 degrees Celsius, pressures between about 5 MPa and about 2000 MPa, for between about 1 hour and about 365 days. The internally-heated high-pressure apparatus 300 may include a stack of one or more ring assemblies to provide radial confinement, comprising a high strength enclosure ring 301 and a ceramic ring 303. The stack may include greater than 2, greater than 5, greater than 10, greater than 20, greater than 30, greater than 50, or greater than 100 ring assemblies. The stack surrounds heater or heating member 305 and capsule 307 and may be supported mechanically by at least one support plate (not shown). In other words, the heating member or heater may be positioned between the capsule and one or more radial restraint structures comprise a high strength enclosure ring and a ceramic ring 303. The stack may provide radial confinement for pressure generated within capsule 307 and transmitted outward through heater 305. Heater 305 includes an upper heater 305a and a lower heater 305b. Each of upper heater 305a and lower heater 305b may include one, two, or more independently-controllable hot zones. Upper heater 305a and lower heater 305b may be physically joined into a unitary component but are typically independently controllable. The interior of heater 305 may define a processing chamber, into which capsule 307 may be placed. In the case that the ring assemblies in the die stack are comprised of high strength enclosure ring 301 and ceramic ring 303, there may be an interference fit between the two members in each ring assembly. Means for external cooling of the one or more ring assemblies or radial restraints may be provided. In certain embodiments, capsule 307 includes an inner capsule member and an outer capsule member (not shown).

[0068] Axial confinement of pressure generated within capsule 307 may be provided by end plugs 311, crown members 317, and tie rods or tie rod fasteners 315. End plugs 311 may comprise zirconium oxide or zirconia. Alternative end plug materials may include magnesium oxide, aluminum oxide, silicon oxide, silicon carbide, tungsten carbide, steel, nickel alloys, titanium alloys, salts, and phyllosilicate minerals such as aluminum silicate hydroxide or pyrophyllite, according to a specific embodiment. End plugs 311 may be surrounded by end plug jackets 313. End plug jackets may provide mechanical support and / or radial confinement for end plugs 311. End plug jackets 313 may also provide mechanical support and / or axial confinement for heater305. End plug jackets 313 may comprise steel, stainless steel, an iron-based alloy, a nickel-based alloy, or the like. In certain embodiments, tie rod fasteners 315 are arranged in a configuration that provides axial loading of two or more ring assemblies. Further details are provided in US patents 9,724,666 and 10,174,438, which are incorporated by reference herein.

[0069] Crown members 317 and tie rod fasteners 315 may comprise a material selected from a group consisting of steel, low-carbon steel, SA723 steel, SA266 carbon steel, 4340 steel, A-286 steel, iron based superalloy, 304 stainless steel, 310 stainless steel, 316 stainless steel, 340 stainless steel, 410 stainless steel, 17-4 precipitation hardened stainless steel, zirconium and its alloys, titanium and its alloys, and other materials commonly known as Monel, Inconel, Hastelloy, Udimet 500, Stellite, Rene 41, and Rene 88.

[0070] Internally-heated high-pressure apparatus 300 may include a pressure transmission medium 309 proximate to the axial ends of capsule 307 and to end plugs 311 according to a specific embodiment. Pressure transmission medium 309 may include multiple components, for example, one or more disks. The pressure transmission medium may comprise sodium chloride, other salts, or phyllosilicate minerals such as aluminum silicate hydroxide or pyrophyllite, or other materials, according to a specific embodiment. In certain embodiments, pressure transmission medium 309 may comprise one or more of metal halides, such as NaCl, NaBr, AgCl, AgBr, CaF2, SrF , graphite, hexagonal boron nitride, talc, soapstone, gypsum, limestone, alabaster, molybdenum disulfide, calcium carbonate, magnesium oxide, zirconium oxide, merylinite clay, bentonite clays, or sodium silicate.

[0071] Internally -heated high-pressure apparatus 300 may further comprise a bottom end heater 331 and / or a top end heater 341 that are thermally coupled to the bottom portion and the top portion of capsule 307, respectively. Bottom end heater 331 generates a power distribution that is approximately azimuthally uniform about the axis of heater 305 and the relative power level in bottom end heater 331, relative to the power level in lower heater 305b and upper heater 305a, along with the radial dependence of the power density within bottom end heater 331, is chosen so as to maintain a temperature distribution along bottom surface 215 that is uniform within 10 degrees Celsius, within 5 degrees Celsius, within 2 degrees Celsius, or within 1 degree Celsius. In certain embodiments, the relative power level in bottom end heater 331, relative to the powerlevel in lower heater 305b and upper heater 305a, along with the radial dependence of the power density within bottom end heater 331, is chosen so as to maintain an average temperature of bottom surface 215 that is equal to the average temperature within a specified height, measured with respect to bottom surface 215, of the inner surface of capsule 307 to within 10 degrees Celsius, within 5 degrees Celsius, within 2 degrees Celsius, or within 1 degree Celsius. In certain embodiments the specified height is approximately 1 centimeter, 5 centimeters, 10 centimeters, 20 centimeters, or 25 centimeters. Top end heater 341 generates a power distribution that is approximately azimuthally uniform about the axis of heater 305 and the relative power level in top end heater 3 1, relative to the power level in lower heater 305b and upper heater 305a, along with the radial dependence of the power density within top end heater 341, is chosen so as to maintain a temperature distribution along top surface 345 that is uniform within 10 degrees Celsius, within 5 degrees Celsius, within 2 degrees Celsius, or within 1 degree Celsius. In certain embodiments, the relative power level in top end heater 341, relative to the power level in lower heater 305b and upper heater 305a, along with the radial dependence of the power density within bottom end heater 331, is chosen so as to maintain an average temperature of top surface 345 that is equal to the average temperature within a specified height, measured with respect to top surface 345, of the inner surface of capsule 307, to within 10 degrees Celsius, within 5 degrees Celsius, within 2 degrees Celsius, or within 1 degree Celsius.

[0072] In certain embodiments, particularly for work with ammonia fills near or above 100% where highest purity is required, sealable container 600 includes or consists of a dual capsule, with a process capsule contained within a support capsule. For example, as shown schematically in FIG. 6, a process capsule 214 may be disposed within a support capsule having a support capsule wall 212, a support capsule end (closed end) 210, and a support capsule end (sealed end) 304. The support capsule provides structural support for the process capsule. Furthermore, process capsule 214 may also be provided with at least one baffle 109 within internal volume 103, the one or more baffles 109 serving to create separate regions within the internal volume 103. In one embodiment, as shown in FIG. 6, the support capsule comprises a support capsule closed end 210, at least one support capsule wall 212 adjoining the support capsule closed end 210 and extending therefrom, and a support capsule sealed end 304 adjoining the at least one support capsule wall 212 and opposite of the support capsule closed end 210. The components of the support capsule may be joined to one another by welding, by interlocking threads, by separatefasteners, or the like. “Support capsule closed end”, “support capsule wall”, and “support capsule sealed end” are terms of convenience and should not be considered limiting terms. The support capsule closed end 210, at least one support capsule wall 212, and the support capsule sealed end 304 define an internal volume capable of receiving and containing a process capsule. The process capsule includes a process capsule closed end 110, at least one process capsule wall 106 adjoining the process capsule closed end 110 and extending therefrom, and a process capsule sealed end 104 adjoining the at least one process capsule wall and opposite of the process capsule closed end 110. The components of the process capsule may be joined to one another by welding, by brazing, or the like. The process capsule closed end 110, at least one process capsule wall 106, and the process capsule sealed end 104 define an internal volume 103 within the process capsule capable of containing at least one material and at least one solvent that becomes a supercritical fluid at a high-temperature and high-pressure condition (also referred to as “HPHT”). HPHT conditions encompass temperatures greater than about room temperature (about 20° C.) and pressures greater than about 1 atmosphere. As also shown in FIG. 6, the dual capsule may include a first support capsule closed end 210 integrally coupled to the process capsule closed end 110, a second support capsule sealed end 304 integrally coupled to the process capsule sealed end 104, and a third support capsule wall 212 integrally coupled to the process capsule wall 106. In a specific embodiment, the first support capsule closed end, second support capsule sealed end, and third support capsule wall are configured to maintain a cylindrical shape of the process capsule free from any substantial deformation. In one embodiment, the support capsule ends (e.g., support capsule sealed end 304 and support capsule closed end 210) are chosen to integrally couple or mate with the process capsule.

[0073] Referring again to FIG. 6, the process capsule has at least one fill tube 102 disposed on a portion of the process capsule sealed end. In a specific embodiment, the fill tube 102 has an opening operably coupled to the interior region (e.g., internal volume) 103 of the process capsule. In a specific embodiment, a fill tube support tube 302 is provided to provide radial support for fill tube 102. Fill tube support tube 302 may be fabricated from similar materials as those of the support capsule components described above, and is similar to that described in U.S. Patent Application PubL No. 2024 / 0158949. The dual capsule described above is similar to that described in U.S. Patent 10,029,955 but incorporates hemispherical ends for greater strength. The axial ends of support capsule closed end 210 and support capsule sealed end 304 may beapproximately planar, for easy integration with internally-heated high pressure apparatus 300, as shown schematically in FIG. 5B.

[0074] The structural support capsule may be required to prevent substantial deformation, strain, cracks, leaks, and failure of the process capsule due to the axial and radial stresses that result from heating the process capsule after fdling the process capsule with a solvent, including warming to room temperature (e.g., with an ammonia fill greater than 100%). Pressure generated by the solvent (e.g., ammonia), based on its equation of state can result in significant stresses on the process capsule, especially for capsules with one or more large dimensions. For example, at a fill of 105% (0.63 g / cm3) the pressure at room temperature will be approximately 35 MPa, or 5, 000 pounds per square inch, and at a fill of 120% (0.72 g / cm3) the pressure at room temperature will be approximately 254 MPa, or 37,000 pounds per square inch. The outer support capsule may comprise steel, stainless steel, carbon steel, nickel, nickel-based alloy, Inconel 718®, Inconel 625®, Rene 41®, or other compositions, as known in the art. The process capsule may include or consist of copper, copper-based alloy, silver, silver-based alloy, palladium, platinum, platinumbased alloy, nickel, nickel-based alloy, or other compositions that are known in the art. The composition and thickness of support capsule wall 212, support capsule end (closed end) 210, and support capsule end (sealed end), may be selected to safely contain internal pressure from the solvent, for example, at or near room temperature. For example, with an internal pressure of 254 MPa, a support capsule with an inner diameter of 0.625 inch and an outer diameter of 1 inch has a Von Mises stress at the inner diameter of 722 MPa, less than the 0.2% yield strength of half- hard stainless steel 316 (758 MPa). Similarly, for an internal pressure of 254 MPa, a support capsule with an inner diameter of 3.75 inches and an outer diameter of 6 inches has a Von Mises stress at the inner diameter of 722 MPa, less than the 0.2% yield strength of half-hard stainless steel 316. As the target ammonia fill is reduced, the internal pressure at room temperature is reduced, and the thickness of the support capsule wall can be reduced. In certain embodiments, for example, where the mineralizer does not attack the composition of the support capsule or a modest level of metallic impurities in the ammonothermal BN layer can be tolerated, the support capsule can be used as a process capsule, that is, a separate process capsule as shown in FIG. 6 can be omitted.

[0075] The pressure vessel, for example, autoclave 200 (FIG. 5A) or internally-heated high- pressure apparatus 300 (FIG. 5B), is then closed and sealable container 600 is then heated to a temperature above about 400 degrees Celsius and pressurized (i.e., self-pressurized by the equation of state of the ammonia) above about 200 MPa, causing the ammonia within sealable container 600 to become a supercritical fluid. In certain embodiments, the temperature is initially raised to a first, intermediate value, for example, between about 100 degrees Celsius and about 400 degrees Celsius, to enable reaction of boron, lithium, magnesium, calcium, and / or other metals within sealable container 600 to form hydrogen, and for an azide mineralizer, if present, to decompose into amide plus nitrogen in a controlled way, prior to formation of an ammonothermal BN material. The temperature may then be raised to a second value, for example, between about 400 degrees Celsius and about 1200 degrees Celsius, between about 450 degrees Celsius and about 1000 degrees Celsius, or between about 500 degrees Celsius and about 800 degrees Celsius, and a pressure between about 200 MPa and about 2000 MPa, between about 250 MPa and about 1500 MPa, or between about 300 MPa and about 1100 MPa. In certain embodiments, referring again to FIG. 6, the power levels in bottom end heater 331, top end heater 341, upper heater 305a and lower heater 305b are adjusted so as to maintain a temperature within capsule 307 (same as sealable container 600) that is uniform to within about 20 degrees Celsius, within about 10 degrees Celsius, within about 5 degrees Celsius, within about 2 degrees Celsius, or within about 1 degree Celsius.

[0076] In certain embodiments, for example, growth of single-crystal cBN layers using a configuration similar to that shown schematically in FIG. 3D, lower zone 107 may be heated to a higher temperature than upper zone 105, by a temperature difference AT that is between about 2 degrees Celsius and about 150 degrees Celsius, between about 3 degrees Celsius and about 100 degrees Celsius, between about 4 degrees Celsius and about 50 degrees Celsius, or between about 5 degrees Celsius and about 30 degrees Celsius.

[0077] The temperature distribution may be maintained at the higher temperature values for a period between about one hour and about 364 days, or between about 2 hours and about 240 days, or between about 3 hours and about 90 days.

[0078] During the time that sealable container 600 is at elevated temperature and pressure, portions of nutrient 113 that are etched by chemical reaction with the mineralizer composition become dissolved within the supercritical ammonia and may be transported by free convection within sealable container 600 (growth chamber 101). A reverse chemical reaction will cause deposition of BN on seed crystals 111 and / or, in some cases on other surfaces within sealable container 600. A volume change occurs within sealable container 600 as hBN is converted to cBN, since the density of hBN ph is approximately = 2.1 g / cm3, while the density of cBN pcis approximately 3.45 g / cm3. Assuming complete conversion of hBN to cBN during the high- temperature soak, the ratio of the final ammonia fill percentage f to the initial fill percentage f may be calculated to be / / * = [1 + / ^(l- Ph I Pc)]’1, whereh° is the ratio of the initial volume of hBN to the initial free volume in sealable container 600, as shown in FIG. 7. The self-generated pressure of supercritical ammonia is a strong function of percentage fill, as shown in FIG. 8. Referring again to the phase diagrams in FIGs. 1A-1D, a decrease in pressure may reduce the driving force for conversion of hBN to cBN. As the driving force is reduced, the rate of the recrystallization process may decrease or stop. Therefore, it is desirable to prepare sealable container 600 such that, with reference to FIGs. 7 and 8, the ratio of the initial volume of hBN to the initial free volume in sealable container 600 is below 2, below 1, below 0.5, below 0.2, below 0.1 , or below 0.05 to ensure that a driving force for conversion of hBN to cBN will exist at or near the final fill percentage created by the volume reduction due to the conversion of hBN to cBN during processing.

[0079] After removal from sealable container 600, the single-crystal or polycrystalline material formed, for example, on seed crystals 111 or from BN pre-forms 655, may be subjected to finishing operations. Finishing operations may include one or more of grinding, polishing, drilling, cleaning, metallizing, or the like.

[0080] In certain embodiments, a free-standing cubic boron nitride crystal, cubic boron nitride layer, or polycrystalline cubic boron nitride material may be characterized by a zincblende structure substantially free from any hexagonal or wurtzite entities or other crystal structures, the other structures being less than about 0.1% in volume in reference to the substantially zincblende structure. In certain embodiments, a free-standing cubic boron nitride crystal, cubic boron nitride layer, or polycrystalline cubic boron nitride material may further include hexagonal boron nitride(hBN), directly bonded to the cubic boron nitride (cBN), having a volume fraction between about 0.1% and about 50%, or between about 0.5% and about 25%, or between about 1% and about 10%, in reference to the substantially zincblende structure of the cBN. In certain embodiments, a freestanding cubic boron nitride crystal, cubic boron nitride layer, or polycrystalline cubic boron nitride material may further include rhombohedral boron nitride (rBN), directly bonded to the cubic boron nitride (cBN), having a volume fraction between about 0.01% and about 10%, or between about 0.05% and about 5%, or between about 0.1% and about 1%, in reference to the substantially zincblende structure of the cBN.

[0081] A free-standing cubic boron nitride crystal, cubic boron nitride layer, or polycrystalline cubic boron nitride material formed by the inventive process may be characterized by unique properties or characteristics not found in boron nitride materials formed by conventional boron nitride formation processes. Free-standing cubic boron nitride crystals, cubic boron nitride layers, or polycrystalline cubic boron nitride material formed by the processes described herein can be characterized by an infrared spectrum having an absorbance per unit thickness of at least 0.01 cm'1for a least one peak falling in a range between about 3000 cm'1and about 3400 cm'1or between about 2100 cm'1and about 2500 cm'1. Without wishing to be bound to theory, the inventors believe these infrared absorption features are uniquely associated with point defects found in the ammonothermally-grown cubic boron nitride that are due to partially-hydrogenated boron vacancies (i.e., N-H bonds) or partially-hydrogenated nitrogen vacancies (i.e., B-H bonds), respectively. In certain embodiments, boron nitride compositions, including a free-standing cubic boron nitride crystal, a boron nitride layer, or polycrystalline boron nitride material formed by the inventive process may be characterized by impurity concentrations of H and O that are each between about 1016cm'3and about 1022cm'3, and, optionally, at least one of the impurity concentrations of H or O is between about 1017cm'3and about 1021cm'3, or between about 1018cm'3and about IO20cm'3, as quantified by calibrated secondary ion mass spectrometry (SIMS). In certain embodiments, a free-standing cubic boron nitride crystal, boron nitride layer, or polycrystalline boron nitride material formed by the inventive process may be characterized by an impurity concentration of one or more of Li, Na, Mg, F, or Cl between about 1015cm'3and about 1022cm'3, or between about 1016cm'3and about 1021cm'3, or between about 1017cm'3and about IO20cm'3, as quantified by calibrated secondary ion mass spectrometry (SIMS). In certain embodiments, a free-standing cubic boron nitride crystal, boron nitride layer, or polycrystallineboron nitride material formed by the inventive process may be characterized by a dopant impurity concentration of one or more of Be, Mg, S, or Si between about 1015cm'3and about 1021cm'3, between about 1016cm'3and about IO20cm'3, or between about 1017cm'3and about 1019cm'3, as quantified by calibrated secondary ion mass spectrometry (SIMS).

[0082] Embodiments of the disclosure provided herein can be used to form near- net- shape polycrystalline cubic boron nitride containing components that are useful for use in ceramic packages and thermal management components due to the high-thermal-conductivity, ultra-hard, and chemical-inertness properties of polycrystalline cubic boron nitride. In certain embodiments, the polycrystalline cubic boron nitride containing components further include significant quantities of diamond, for example, diamond micron powder that had been utilized as seed crystals, conveying advantages from diamond’s outstanding thermal conductivity and ultra-high hardness. Polycrystalline cubic boron nitride material formed by the inventive process may have a maximum dimension, such as a length or diameter, between about 100 micrometers and about 450 millimeters, between about 250 micrometers and about 100 millimeters, or between about 500 micrometers and about 25 millimeters, and a minimum dimension, such as a thickness, between about 1 micrometer and about 25 millimeters, between about 5 micrometers and about 5 millimeters, or between about 25 micrometers and about 2 millimeters. In certain embodiments, polycrystalline cubic boron nitride material formed by the inventive process have a simple geometry, such as a disk or a plate, or a more complicated shape. Polycrystalline cubic boron nitride material formed by the inventive process may be characterized by a porosity between about 0.1% and about 50%, between about 1% and about 40%, between about 2% and about 30%, or between about 3% and about 20%. A maximum dimension of a polycrystalline cubic boron nitride part formed in the inventive process may change, relative to a maximum dimension of the BN preform 655 from which it originated, by less than about 50%, by less than about 30%, by less than about 20%, by less than about 10%, or by less than about 5%. A minimum dimension of a polycrystalline cubic boron nitride part formed in the inventive process may change, relative to a minimum dimension of the BN preform 655 from which it originated, by less than about 50%, by less than about 30%, by less than about 20%, by less than about 10%, or by less than about 5%.

[0083] Polycrystalline cubic boron nitride material formed by the inventive process may be characterized by a thermal conductivity between about 50 W / m-K and about 1600 W / m-K (withisotopically enriched B), between about 25 W / m-K and about 850 W / m-K (with natural isotopic abundances B and N), between about 50 W / m-K and about 800 W / m-K, or between about 100 W / m-K and about 700 W / m-K.

[0084] A cubic boron nitride single-crystalline layer may be characterized by a large area surface having a lateral dimension of at least about 1 millimeter, at least about 3 millimeters, at least about 10 millimeters, at least 25 millimeters, at least 50 millimeters, at least 100 millimeters or as large as 200 millimeters. The cubic boron nitride single-crystalline layer may characterized by a zincblende structure substantially free from any hexagonal or wurtzite entities or other crystal structures, the other structures being less than about 0.1% in volume in reference to the substantially zincblende structure. The cubic boron nitride layer may be characterized by a thickness between about 1 micrometer and about 25 millimeters, between about 5 micrometers and about 10 millimeters, or between about 10 micrometers and about 5 millimeters. The cubic boron nitride layer may be characterized by a dislocation density that is below about 1010cm'2, below about 109cm'2, below about 108cm'2, below about 106cm'2, below about 105cm'2, or below about 104cm'2. In certain embodiments, the cubic boron nitride single-crystalline layer is characterized by a crystallographic orientation that is mis-oriented from {001 } in a <110> direction by between 0 degree and about 5 degrees or between about 0.1 degree and about 3 degrees and in an orthogonal <110> direction by less than about 1 degree, less than about 0.5 degree, less than about 0.2 degree, less than about 0.1 degree, or less than about 0.05 degree.

[0085] A method of synthesis according to a specific embodiment is briefly outlined below. The method will include providing an apparatus for high-pressure crystal growth or material processing, such as the ones described above, the apparatus comprising an interior region (for example, cylindrical in shape) surrounded by radial and axial restraint structures, and a closable opening region to the interior region. Next, provide one or more boron-containing raw materials to the interior region and close and seal the opening region. Then provide a solvent, such as ammonia, to the interior region, and provide the apparatus with thermal energy to cause an increase in temperature within the interior region to greater than 350 degrees Celsius to cause the solvent to be superheated to form a crystalline cubic boron nitride material from a process of the superheated solvent. Then, remove thermal energy from the apparatus to cause a temperature of the capsule to change from a first temperature to a second temperature, which is lower than thefirst temperature. Then release the solvent from the interior region, open an opening region to the interior region of the high-pressure apparatus, remove the crystalline material from the interior region, and perform other steps, as desired.

[0079] The above sequence of steps provides a method according to an embodiment of the present disclosure. In a specific embodiment, the present disclosure provides a method and resulting crystalline material provided by a high-pressure apparatus where an elevated temperature is applied directly to seed crystals. Other alternatives can also be provided where steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein. Details of the present method and structure can be found throughout the present specification and more particularly below.

[0080] FIG. 10 is a simplified flow diagram 1000 of a method of processing a material within a supercritical fluid. This diagram is merely an example, which should not unduly limit the scope of the claims herein.

[0081] In some embodiments, the method begins with step 1001. The method begins by providing an apparatus for high-pressure crystal or material processing (see step 1003), such as the ones shown schematically in FIGs. 5A, 5B, and 6 and described above. In certain embodiments, the apparatus has an interior region (for example, cylindrical in shape) surrounded by radial and axial restraint structures. In certain embodiments, the opening region to the interior region are closable by lid closure or welded structures. In certain embodiments, the apparatus is capable of safely supporting self-generated pressures above 50 MPa, above 100 MPa, or above 250 MPa at room temperature. In certain embodiments, the apparatus is capable of safely supporting selfgenerated pressures of at least about 200 MPa, at least about 500 MPa, at least about 1000 MPa, at least 150 MPa, or at least about 2000 MPa at temperatures between 400 degrees Celsius and about 1000 degrees Celsius, between about 500 degrees Celsius and about 900 degrees Celsius, or between about 550 degrees Celsius and about 800 degrees Celsius.

[0082] In a specific embodiment, the method provides at least one boron-containing raw material, a mineralizer, and a solvent such as ammonia, for example, to the interior region (see step 1005), followed by closing an opening region (see step 1007). In some embodiments, the ammonia has a density, relative to the free volume in the interior region, of at least 0.42 g / cm3, atleast 0.54 g / cm3, at least 0.60 g / cm3, at least 0.63 g / cm3., or at least 0.66 g / cm3. In a specific embodiment, the raw materials include seed crystals, where the seed crystals include or consist of at least one of cubic boron nitride crystals or diamond crystals, and nutrient material. The nutrient material includes boron and may include or consist essentially of pyrolytic boron nitride, hexagonal boron nitride powder, or cubic boron nitride crystals. In certain embodiments, the seed crystals consist essentially of at least one of cubic boron nitride micron powder particles or diamond micron powder particles, the nutrient consists essentially of hexagonal boron nitride powder, and the two are blended and formed into a BN pre-form, with the volume of the seed crystals significantly exceeding the volume of the nutrient. In certain embodiments, the seed crystals consist essentially of at least one of cubic boron nitride micron powder particles or diamond micron powder particles, the nutrient consists essentially of hexagonal boron nitride powder, and the two are blended and formed into a granule, where the net volume of the nutrient significantly exceeds the net volume of the seed crystals. In certain embodiments, the seed crystals consist essentially of at least one of cubic boron nitride mesh crystals and diamond mesh crystals and the nutrient consists essentially of pyrolytic boron nitride. In certain embodiments, the seed crystals consist essentially of at least one of cubic boron nitride single crystals, diamond single crystals, or a cubic boron nitride crystalline layer on a diamond single crystal having a maximum dimension of at least 1 millimeter, and the nutrient consists essentially of at least one of pyrolytic boron nitride or cubic boron nitride mesh crystals. The method heats the interior region (see step 1011) with thermal energy to cause an increase in temperature within the interior region to greater than 350 degrees Celsius to cause the solvent to be superheated and process the at least one raw material in the interior region.

[0083] Referring again to FIG. 10, the method forms a boron and nitrogen-containing ammonothermal crystalline material (see step 1013) from a process of the superheated solvent. In certain embodiments, the ammonothermal crystalline material comprises a cubic boron nitride material. In certain embodiments, the crystalline material comprises a hexagonal boron nitride material. In certain embodiments, the ammonothermal crystalline material includes impurities of hydrogen, oxygen, and at least one of Li, Na, Mg, F, and Cl. In a specific embodiment, the method removes thermal energy from the capsule (see step 1015) to cause a temperature within the interior region to change from a first temperature to a second temperature, which is lower than the firsttemperature. Once the energy has been removed and temperature reduced to a suitable level, the method removes a solvent from the interior region (step 1017).

[0084] In a specific embodiment, the interior region is opened, step 1019. In a specific embodiment, the crystalline material is removed from the interior region, step 1021. Depending upon the embodiment, there can also be other steps, which can be inserted or added, or certain steps can also be removed. In a specific embodiment, the method ends at stop, step 1023.

[0085] The above sequence of steps provides a method according to an embodiment of the present disclosure. In a specific embodiment, the present disclosure provides a method and resulting ammonothermal crystalline material provided by a high-pressure apparatus where an elevated temperature is applied directly to seed crystals. Other alternatives can also be provided where steps are added, one or more steps are removed, or one or more steps are provided in a different sequence without departing from the scope of the claims herein.EXAMPLES

[0086] Embodiments provided by the present disclosure are further illustrated by reference to the following examples. It will be apparent to those skilled in the art that many modifications, both to materials and methods, may be practiced without departing from the scope of the disclosure.Comparative Example 1

[0087] A cylindrical rod of pyrolytic BN (pBN), having a hBN crystal structure and dimensions of approximately 0.05 inch diameter x 0.75 inch long, was placed in the bottom of an autoclave along with approximately 0.56 g of 40 / 50 commercial cBN mesh crystals. The pBN had an oxygen content of 35 parts per million, as measured by Interstitial Gas Analysis, and its Raman spectrum was characterized by a single peak at approximately 1366 cm'1, as shown in FIG. 9A. The cBN mesh crystals were characterized by a Raman spectrum having two sharp peaks at approximately 1056 cm'1and 1304 cm'1, as shown in FIG. 9B. The autoclave was fabricated from 316 stainless steel, had inner and outer diameters of approximately 0.0625 inch and 0.25 inch, respectively, and was about 10 inches long. The autoclave was connected to a gas manifold and the autoclave was evacuated and heated to a temperature of approximately 250 degrees Celsius under vacuum, held at this temperature for approximately 24 hours, and cooled.An aliquot of L1NH2 was scooped from a reagent bottle that was inserted into a glove box having an atmosphere containing nitrogen and less than 1 part per million each of O2 and H2O and opened there, weighed, added to a small stainless-steel vessel within the glove box, and sealed. The LiNH2 mineralizer, along with a pre- weighed quantity of liquid ammonia, was connected to the autoclave in a configuration similar to that shown schematically in FIG. 4. The autoclave was chilled to a temperature of approximately 7 degrees Celsius, and both the LiNfC mineralizer and the ammonia were transferred to the capsule without any air exposure. The initial ammonia fill was approximately 103.5% and the molar ratio of LiNFh to ammonia was approximately 4%.

[0088] The autoclave was inserted into a heater and heated to soak temperature in approximately one hour. The autoclave was heated to approximately 300 degrees Celsius through most of its length, with a valve connected to the top of the autoclave and protruding from the heater reaching a temperature of approximately 70 degrees Celsius. Based on measurements from multiple thermocouples at various heights along the length of the autoclave, the pressure was estimated as approximately 567 MPa (see “Comp. Ex.” item label illustrated in Figure 8), using polynomial fits to the equation of state for pure ammonia from the NIST fluids database. After holding at the soak temperature for 72 hours, the autoclave was cooled, vented, and opened.

[0089] Upon careful inspection, no changes to either the pBN or cBN starting materials were evident. Referring to FIG. 8, it is believed that this experiment was performed under cBN-stable conditions. It is concluded that 300 degrees Celsius is too low a temperature for any useful ammonothermal reaction of BN to take place.Example 1

[0090] One example of the processes performed using method 1000 includes suspending two plates of pyrolytic BN (pBN), having a hBN crystal structure and dimensions of approximately 50 mm x 10 mm x 1 mm in a silver capsule having a wall thickness of about 1 mm, an outer diameter of 1.0 inch and a length of 9.0 inches, in a configuration similar to that shown schematically in FIG. 2A. The silver process capsule was surrounded by a support capsule wall fabricated from 304 stainless steel and having a thickness of 0.002 inch. The pBN had an oxygen content of 35 parts per million, as measured by Interstitial Gas Analysis, and its Raman spectrum was characterized by a single peak at approximately 1366 cm'1, as shown in FIG. 9A.Approximately 5 g of 40 / 50 commercial cBN mesh crystals were placed in each of two silver wire-cloth baskets, also in a configuration similar to that shown schematically in FIG. 2A, and the capsule was welded closed, with a single fdl tube left open. The cBN mesh crystals were characterized by a Raman spectrum having two sharp peaks at approximately 1056 cm'1and 1304 cm'1, as shown in FIG. 9B. The fill tube of the capsule was connected to a gas manifold and the capsule was evacuated and heated to a temperature of approximately 250 degrees Celsius under vacuum, held at this temperature for approximately 24 hours, and cooled. An aliquot of LiNFh was scooped from a reagent bottle that was inserted into a glove box having an atmosphere containing nitrogen and less than 1 part per million each of O2 and H2O and opened there, weighed, added to a small stainless-steel vessel within the glove box, and sealed. The LiNFh mineralizer, along with a pre-weighed quantity of liquid ammonia, was connected to the capsule in a configuration similar to that shown schematically in FIG. 4. Both the LiNFh mineralizer and the ammonia were transferred to the capsule without any air exposure. The initial ammonia fill was approximately 79.5% and the molar ratio of LiNFh to ammonia was approximately 4.02%.

[0091] The capsule was inserted into an internally-heated pressure vessel similar to that shown schematically in FIG. 5B and heated to a soak temperature in approximately one hour. The upper portion, or upper chamber, of the capsule was heated to 675 degrees Celsius and the bottom portion, or lower chamber, to 700 degrees Celsius. Based on measurements from multiple thermocouples at various heights along the length of the capsule, the average temperature within the capsule during soak was approximately 687 degrees Celsius. Based on the phase diagram of ammonia (FIG. 8), neglecting any possible partial decomposition of ammonia, the pressure is estimated to have been about 438 MPa, as illustrated by item label Ex. 1 in Figure 8. After holding at these temperatures for 90 hours, the capsule was cooled, removed from the internally-heated high-pressure apparatus, vented, and opened.

[0092] A scanning electron micrograph of a portion of a BN coating formed on a cBN crystal containing seed, from which a small portion has delaminated, on a representative crystal from the upper basket in the capsule is shown schematically in FIG. 9C. The coating is seen to be considerably rougher than the original seed crystal (see the surface within the spalled area). Several of the crystals from the lower basket were fractured by crushing with a hammer, and a scanning electron micrograph from a fractured crystal is shown schematically in FIG. 9D.Inspecting the interface between the BN coating and the cBN seed crystal, one can clearly see that the formed BN coating is strongly adherent to the cBN seed crystal. After washing in deionized water, a portion of the coating on a cBN crystal was analyzed by micro-Raman spectroscopy; the spectrum is shown in FIG. 9E. The presence of a large peak near 1366 cm'1, which was very similar to that of the as-received pBN, indicates that the coating consists primarily ofhBN, based on published data for hBN [T. Kuzuba, etal., Solid State Commun. 25, 863 (1978]. The appearance of a small peak near 790 cm'1suggests the additional presence of a small fraction of rhombohedral boron nitride (rBN), based on published data for rBN [T. Sato, Proc. Japan Acad. 61B, 459 (1985); J. Liu, et al., Phys. Rev. B 51, 8591 (1995)], as was previously reported by Maruyama and co-workers [Y. Maruyama, et al., Mater. Lett. 232, 110 (2018)]. A portion of the coating on another cBN seed crystal was analyzed by secondary ion mass spectrometry and compared to results from a similar analysis on the pBN starting material. In the case of the pBN starting material, impurity concentrations of 0, H, and Li had all decayed to background levels by a depth of 1 micrometer. In the case of the ammonothermal BN coating on the cBN seed crystal, the concentrations of 0, H, and Li were measured as 2.4xlO20cm'3, 2.7xlO20cm'3, and LlxlO21cm'3, respectively, averaged over a depth between approximately 1 micrometer and approximately 5 micrometers.

[0093] Portions of the pyrolytic BN plates were also covered with a coating having a distinct morphology (rough). A portion of the coating on a pBN plate was analyzed by micro-Raman spectroscopy; the spectrum is shown in FIG. 9F. Again, the coating appears to consist mainly of hBN, with a minor rBN component. The coatings appeared to be polycrystalline, with a root- mean-square surface roughness on the order of 5 to 10 micrometers. Referring again to FIG. 8, we see that this process condition clearly lies on the hBN-stable side of the equilibrium line. The coatings are strongly adherent to the cBN seed crystals, as indicated by retention on the surface even after fracture of the free-standing cBN crystal (FIG. 9D). It is expected, therefore, that retention of cBN crystals with a polycrystalline BN coating would exhibit superior retention in vitreous, single-layer, metallic, or resin bonds, for example, in a grinding wheel or in an abrasive tool.Example 2

[0002] In another example, the processes performed using method 1000 included placing a cylindrical rod of pyrolytic BN (pBN), having a hBN crystal structure and dimensions of approximately 0.05 inch diameter x 0.75 inch long in the bottom of an autoclave along with approximately 0.58 g of 40 / 50 commercial cBN mesh crystals. The pBN had an oxygen content of 35 parts per million, as measured by Interstitial Gas Analysis, and its Raman spectrum was characterized by a single peak at approximately 1366 cm'1, as shown in FIG. 9A. The cBN mesh crystals were characterized by a Raman spectrum having two sharp peaks at approximately 1056 cm'1and 1304 cm'1, as shown in FIG. 9B. The autoclave was fabricated from 316 stainless steel, had inner and outer diameters of approximately 0.0625 inch and 0.25 inch, respectively, and was about 10 inches long. The autoclave was connected to a gas manifold and the autoclave was evacuated and heated to a temperature of approximately 250 degrees Celsius under vacuum, held at this temperature for approximately 24 hours, and cooled. An aliquot of LiNH was scooped from a reagent bottle that was inserted into a glove box having an atmosphere containing nitrogen and less than 1 part per million each of O2 and H2O and opened there, weighed, added to a small stainless- steel vessel within the glove box, and sealed. The LiNFF mineralizer, along with a preweighed quantity of liquid ammonia, was connected to the autoclave in a configuration similar to that shown schematically in FIG. 4. The autoclave was chilled to a temperature of approximately 0 degrees Celsius, and both the LiNFF mineralizer and the ammonia were transferred to the capsule without any air exposure. The initial ammonia fill was approximately 105% and the molar ratio of LiNfF to ammonia was approximately 8%.

[0003] The autoclave was inserted into a heater and heated to soak temperature in approximately one hour. The autoclave was heated to temperatures between approximately 375 degrees Celius and approximately 475 degrees Celsius through most of its length, with a valve connected to the top of the autoclave and protruding from the heater reaching a temperature of approximately 90 degrees Celsius. Based on measurements from multiple thermocouples at various heights along the length of the autoclave, the pressure was estimated as approximately 597 MPa (see item label Ex. 2 in Figure 8), using polynomial fits to the equation of state for pure ammonia from the NIST fluids database. After holding at the soak temperature for 300 hours, the autoclave was cooled, vented, and opened.

[0004] Upon careful inspection, the surface of some of the facets on the cBN crystals was slightly rougher than that of the starting crystals. A portion of the coating on a cBN crystal was analyzed by micro-Raman spectroscopy; the spectrum is shown in FIG. 9G. In this case, unlike that in Example 2, the spectrum is indistinguishable from that of the starting material (cf. FIG. 9B), with sharp peaks at 1052 and 1303 cm'1, small peaks near 760 and 948 cm'1, and no trace of the hBN peak at 1366 cm'1. Based on the observed surface morphology, the coating thickness is estimated as at most a few micrometers. Referring again to FIG. 8, it appears that this process condition is just slightly on the cBN-stable side of the equilibrium line.Example 3

[0005] In another example, the processes performed using method 1000 included providing a cBN micron powder, having a D50 diameter of approximately 20 micrometers, that is blended at a ratio of 0.1% with hBN powder having an average particle size below 1 micrometer and an oxygen concentration of approximately 0.1 % by weight. The powders are added to a powder mixer along with 0.5% ethylene glycol by weight and mixed thoroughly. The agglomerated powder is then pressed into granules, approximately 2 mm in diameter, using a roll compactor. The granules have a porosity of approximately 25%. The granules are then placed into a process capsule fabricated from pure silver, placed within a support capsule fabricated from 316 stainless steel. The process capsule has a wall thickness of 0.04 inch and the support capsule has a wall thickness of 0.05 inch, an outer diameter of 1.0 inch and a length of 9.0 inches, in a configuration similar to that shown schematically in FIGs. 2B and 6. The ratio of the initial volume of hBN to free volume in the capsule is approximately 0.2.

[0006] The capsule is connected to a gas manifold, evacuated, back-filled with Ar, and heated to a temperature of approximately 700 degrees Celsius, with pure ammonia flowing at a rate of approximately 0.5 standard liter per minute. The capsule is held at this temperature for approximately 48 hours and then cooled. The oxygen content in the hBN is reduced from about 0.1% to about 100 parts per million. An aliquot of LiNH? is scooped from a reagent bottle that was inserted into a glove box having an atmosphere containing nitrogen and less than 1 part per million each of O2 and H2O and opened there, weighed, added to a small stainless-steel vessel within the glove box, and sealed. The LiNFE mineralizer, along with a pre- weighed quantity of liquid ammonia, is connected to the capsule in a configuration similar to that shown schematicallyin FIG. 4. The capsule has a dual-capsule construction, similar to that shown in FIG. 6, with a process capsule fabricated from pure silver contained within a support capsule fabricated from 304 stainless steel. Both the LiNFh mineralizer and the ammonia are transferred to the capsule, held in a dry-ice-alcohol bath, without any air exposure. The initial ammonia fill is approximately 107.9% and the molar ratio of LiNFh to ammonia is approximately 10%. After warming to room temperature, the capsule has an internal pressure of approximately 63 MPa and the support capsule has a Von Mises stress at the inner diameter of approximately 576 MPa, neglecting any support provided by the process capsule, well less than the 0.2% yield strength of half-hard stainless steel 316 (758 MPa).

[0007] The capsule is then inserted into an internally-heated pressure vessel similar to that shown schematically in FIG. 5B and heated to soak temperature in approximately one hour. The upper portion, or upper chamber, of the capsule is heated to 400 degrees Celsius and the bottom portion, or lower chamber, to 400 degrees Celsius. Based on the equation-of- state data shown in FIG. 8, the pressure during the soak process is approximately 720 MPa, as illustrated by item label Ex. 3 in Figure 8. After holding at these temperatures for 240 hours, the capsule is cooled, removed from the internally-heated high-pressure apparatus, vented, and opened.

[0008] Approximately 0.4% of the hBN is converted to cBN, and the average diameter of the cBN particles is increased from approximately 20 micrometers to approximately 30 micrometers.Example 4

[0009] In another example, the processes performed using method 1000 included providing a capsule is prepared with cBN-in-hBN granules as in Example 3, except that the wall thickness of the support capsule is increased to 0.0625 inch. However, in this case the LiNH mineralizer and the ammonia are transferred to the capsule, held at dry-ice temperature, without any air exposure. The initial ammonia fill is approximately 110% and the molar ratio of LiNH2 to ammonia is approximately 10%. After warming to room temperature, the capsule has an internal pressure of approximately 88 MPa and the support capsule has a Von Mises stress at the inner diameter of approximately 651 MPa, neglecting any support provided by the process capsule, well less than the 0.2% yield strength of half-hard stainless steel 316 (758 MPa).

[0010] The capsule is inserted into an internally-heated pressure vessel similar to that shown schematically in FIG. 5B and heated to soak temperature in approximately one hour. The upper portion, or upper chamber, of the capsule is heated to 450 degrees Celsius and the bottom portion, or lower chamber, to 450 degrees Celsius. Based on the equation-of-state data shown in FIG. 8, the pressure during the soak process is approximately 857 MPa, as illustrated by item label Ex. 4 in Figure 8. After holding at these temperatures for 240 hours, the capsule is cooled, removed from the internally-heated high-pressure apparatus, vented, and opened.

[0011] Approximately 1% of the hBN is converted to cBN, and the average diameter of the cBN particles is increased from approximately 20 micrometers to approximately 40 micrometers.Example 5

[0012] In another example, the processes performed using method 1000 included providing a capsule that includes cBN-in-hBN granules as in Examples 3 and 4. However, in this case the support capsule has a wall thickness of 0.188 inch, an outer diameter of 1.0 inch and a length of 9.0 inches, in a configuration similar to that shown schematically in FIGs. 2B and 6. The LiNH2 mineralizer and the ammonia are transferred to the capsule, immersed in a dry-ice-ethanol bath, without any air exposure. The initial ammonia fill is approximately 120% and the molar ratio of LiNHi to ammonia is approximately 10%. After warming to room temperature, the capsule has an internal pressure of approximately 254 MPa and the support capsule has a Von Mises stress at the inner diameter of approximately 722 MPa, neglecting any support provided by the process capsule, less than the 0.2% yield strength of half-hard stainless steel 316 (758 MPa).

[0013] The capsule is inserted into an internally-heated pressure vessel similar to that shown schematically in FIG. 5B and heated to soak temperature in approximately one hour. The upper portion, or upper chamber, of the capsule is heated to 650 degrees Celsius and the bottom portion, or lower chamber, to 650 degrees Celsius. Based on the equation-of-state data shown in FIG. 8, the pressure during the soak process is approximately 1590 MPa, as illustrated by item label Ex. 5 in Figure 8. After holding at these temperatures for 240 hours, the capsule is cooled, removed from the internally-heated high-pressure apparatus, vented, and opened.

[0014] Approximately 50% of the hBN is converted to cBN, and the average diameter of the cBN particles has increased from approximately 20 micrometers to approximately 160 micrometers.Example 6

[0015] In another example, the processes performed using method 1000 included providing a cBN micron powder, having a D50 diameter of approximately 20 micrometers, cBN micron powder, having a D50 diameter of approximately 5 micrometers, and hBN powder having a D10 diameter of approximately 10 micrometers, a D50 diameter of approximately 30 micrometers, a D90 diameter of approximately 50 micrometers and a total oxygen concentration of about 0.3 weight % are blended at a ratio of approximately 8:2:1 by weight. The powders are added to a powder mixer along with 0.5% ethylene glycol by weight and mixed thoroughly. The agglomerated powder is then pressed into disk-shaped BN preforms having a diameter of approximately 125 mm in diameter and a thickness of approximately 1 mm, using a punch-die set in a Carver press. The BN preform disks have a porosity of approximately 15%. The granules are then placed into a silver process capsule within a 316 stainless- steel support capsule. The process capsule has a wall thickness of 0.04 inch and the support capsule has a wall thickness of 0.0625 inch, an outer diameter of 1.0 inch and a length of 9.0 inches, in a configuration similar to that shown schematically in FIGs. 2B and 6. The ratio of the initial volume of hBN to free volume in the capsule is approximately 0.05.

[0016] The capsule is connected to a gas manifold, evacuated, back-filled with Ar, and heated to a temperature of approximately 700 degrees Celsius, with pure ammonia flowing at a rate of approximately 0.5 standard liter per minute. The capsule is held at this temperature for approximately 48 hours, and cooled. The oxygen content in the hBN is reduced from about 0.3% to about 100 parts per million. An aliquot of LiNFh is scooped from a reagent bottle that was inserted into a glove box having an atmosphere containing nitrogen and less than 1 part per million each of O2 and H2O and opened there, weighed, added to a small stainless- steel vessel within the glove box, and sealed. The LiNFh mineralizer, along with a pre-weighed quantity of liquid ammonia, is connected to the capsule in a configuration similar to that shown schematically in FIG. 4. Both the LiNFh mineralizer and the ammonia are transferred to the capsule, held at dryice temperature, without any air exposure. The initial ammonia fill is approximately 110% andthe molar ratio of L1NH2 to ammonia is approximately 10%. After warming to room temperature, the capsule has an internal pressure of approximately 88 MPa and the support capsule has a Von Mises stress at the inner diameter of approximately 651 MPa, neglecting any support provided by the process capsule, well less than the 0.2% yield strength of half-hard stainless steel 316 (758 MPa).

[0017] The capsule is inserted into an internally-heated pressure vessel similar to that shown schematically in FIG. 6 and heated to soak temperature in approximately one hour. The upper portion, or upper chamber, of the capsule is heated to 450 degrees Celsius and the bottom portion, or lower chamber, to 450 degrees Celsius. Based on the equation-of-state data shown in FIG. 8, the pressure during the soak process is approximately 857 MPa, as illustrated by item label Ex. 6 in Figure 8. After holding at these temperatures for 240 hours, the capsule is cooled, removed from the internally-heated high-pressure apparatus, vented, and opened.

[0018] Approximately 90% of the hBN is converted to cBN, and the average diameters of the polycrystalline cBN disks has decreased by approximately 5% and the average thicknesses of the disks have also decreased by approximately 5%. The porosity of the polycrystalline cBN disks is approximately 15%.

[0019] By comparison to Examples 3, 4, and 5, it is seen that with ammonothermal processing of BN pre-forms in which most of the volume consists of cBN or diamond powder, with a modest volume fraction of hBN powder that facilitates compaction and densification of the BN pre-form as a green body, even with the modest conversion rate achieved under relatively mild temperatures and pressures it is possible to fabricate near-net- shape ceramic parts having outstanding properties, including high thermal conductivity, high hardness, and good chemical inertness.Example 7

[0002] In another example, the processes performed using method 1000 included providing a three single-crystal diamond seed crystals, each consisting of a homoepitaxial CVD layer deposited on a type lb diamond synthesized by a high-pressure high-temperature method and having a crystallographic orientation tilted from (001) by approximately 4 degrees toward

[0110] and a single-domain (2x1) reconstructed surface, are placed in into a silver process capsule withina 316 stainless- steel support capsule. The process capsule has a wall thickness of 0.04 inch and the support capsule has a wall thickness of 0.0625 inch, an outer diameter of 1.0 inch and a length of 9.0 inches, in a configuration similar to that shown schematically in FIGs. 2B and 6, along with approximately 10 grams of 40 / 50 commercial cBN mesh crystals that are placed in a silver wirecloth basket as nutrient material. The capsule is welded closed, with two single fill tubes left open.

[0003] The capsule is connected to a gas manifold, evacuated, back-filled with Ar, and heated to a temperature of approximately 700 degrees Celsius, with pure ammonia flowing at a rate of approximately 0.5 standard liter per minute. The capsule is held at this temperature for approximately 48 hours and then cooled. An aliquot of LiNH is scooped from a reagent bottle that was inserted into a glove box having an atmosphere containing nitrogen and less than 1 part per million each of O2 and H2O and opened there, weighed, added to a small stainless-steel vessel within the glove box, and sealed. The LiNH mineralizer, along with a pre- weighed quantity of liquid ammonia, is connected to the capsule in a configuration similar to that shown schematically in FIG. 4. Both the LiNFF mineralizer and the ammonia are transferred to the capsule, held at water-ice temperature, without any air exposure. The initial ammonia fill is approximately 110% and the molar ratio of LiNFh to ammonia is approximately 10%. After warming to room temperature, the capsule has an internal pressure of approximately 88 MPa and the support capsule has a Von Mises stress at the inner diameter of approximately 651 MPa, neglecting any support provided by the process capsule, well less than the 0.2% yield strength of half-hard stainless steel 316 (758 MPa).

[0004] The capsule is inserted into an internally-heated pressure vessel similar to that shown schematically in FIG. 6 and heated to soak temperature in approximately one hour. The upper portion, or upper chamber, of the capsule is heated to 440 degrees Celsius and the bottom portion, or lower chamber, to 460 degrees Celsius. Based on the equation-of-state data shown in FIG. 8, the pressure during the soak process is approximately 857 MPa, as illustrated by item label Ex. 7 in Figure 8. After holding at these temperatures for 400 hours, the capsule is cooled, removed from the internally-heated high-pressure apparatus, vented, and opened.

[0005] A layer of single-crystal cBN is formed on the diamond seed crystals, having a thickness of approximately 20 micrometers and a surface crystallographic oriented that is offset from (001) by about 1 degree toward

[0110] .

[0006] Although the above is a full description of specific embodiments, various modifications, alternative constructions and equivalents may be used. Therefore, the above description and illustrations should not be taken as limiting the scope of the present disclosure which is defined by the appended claims.

Claims

What is claimed is:

1. A boron nitride (BN) composition, comprising a boron nitride layer overlying a seed crystal, wherein: the boron nitride layer comprises boron and nitrogen; and impurity concentrations of each of H and 0 between about 1016cm'3and about 1022cm'3, as quantified by calibrated secondary ion mass spectrometry; and the seed crystal comprises at least one of cubic boron nitride and diamond and is characterized by a maximum dimension of between 40 micrometers and 450 millimeters,2. The boron nitride composition of claim 1 , wherein the boron nitride layer further comprises an impurity concentration of one or more of Li, Na, Mg, F, Cl, Be, S, or Si between about 1015cm'3and about 1022cm'3.

3. The boron nitride composition of claim 1, wherein the boron nitride layer comprises: a zincblende crystal structure; and point defects characterized by an infrared spectrum having an absorbance per unit thickness of at least 0.01 cm'1for at least one peak falling in a range between about 3000 cm'1and about 3400 cm'1or between about 2100 cm'1and about 2500 cm'1.

4. The boron nitride composition of claim 3, wherein the boron nitride layer is characterized by a zincblende structure substantially free from any hexagonal or wurtzite entities or other crystal structures, the other structures being less than about 0.1% in volume in reference to the substantially zincblende structure.

5. The boron nitride composition of any of claims 1 to 4, wherein a surface of the boron nitride layer comprises polycrystalline grains of boron nitride, and the boron nitride layer has a root-mean- square surface roughness between about 3 micrometers and about 250 micrometers.

6. The boron nitride composition of claim 3, wherein boron nitride layer is characterized by a thickness, in a third direction that is orthogonal to the first direction and to the second direction,that is between about 1 micrometer and about 25 millimeters and by a crystallographic orientation that is mis-oriented from {001 } in a <011> direction by between 0 degree and 5 degrees.

7. A polycrystalline cubic boron nitride composition, comprising boron and nitrogen, wherein the polycrystalline cubic boron nitride composition comprises: a zincblende crystal structure; a maximum dimension between 100 micrometers and 450 millimeters; a minimum dimension between 1 micrometer and 25 millimeters; a porosity between 0.1% and 50% ; and an impurity concentration of each of H and O between 1016cm'3and 1022cm'3, as quantified by calibrated secondary ion mass spectrometry.

8. The polycrystalline cubic boron nitride composition of claim 7, further comprising an impurity concentration of one or more of Li, Na, Mg, F, or Cl between 1015cm'3and 1022cm'3, as quantified by calibrated secondary ion mass spectrometry.

9. The polycrystalline cubic boron nitride composition of claims 7 or 8, further comprising point defects characterized by an infrared spectrum having an absorbance per unit thickness of at least 0.01 cm'1for at least one peak falling in a range between about 3000 cm'1and about 3400 cm'1or between about 2100 cm'1and about 2500 cm'1.

10. A method for forming a boron nitride composition, comprising: placing a plurality of seed crystals and a nutrient material inside a sealable container, wherein the plurality of seed crystals comprise at least one of cubic boron nitride and diamond, and have a maximum dimension between about 5 micrometers and about 200 millimeters, and the nutrient material comprising boron; adding a mineralizer composition and ammonia to the sealable container, the mineralizer composition comprising at least one of Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, F, Cl, Br, or I; andheating the sealable container to a temperature greater than or equal to 350 degrees Celsius for a period greater than or equal to one hour, wherein the heating of the sealable container causes growth of a boron nitride layer on at least one of the plurality of seed crystals, wherein: a weight ratio between the seed crystals and the nutrient is between about one part per million and about 0.999; the ammonia within the sealable container has a density between 0.42 g / cm3and0.75 g / cm3; and a molar ratio of the mineralizer composition and the ammonia is between about 0.01% and about 75%.

11. The method of claim 10, wherein the nutrient consists substantially of pyrolytic boron nitride particles or cubic boron nitride particles characterized by a particle size distribution having a D10 value between about 10 micrometers and about 2 millimeters and a D90 value between about 25 micrometers and about 10 millimeters.

12. The method of claim 11, wherein the nutrient further comprises a dopant, selected from at least one of Be, Mg, S, and Si and having a concentration between 1015cm'3and 1021cm'3.

13. The method of claim 10, wherein at least a portion of the seed crystals and nutrient are provided in the form of boron nitride pre-forms, wherein the weight ratio between the seed crystals and the nutrient is between about 0.25 and about 0.999 and the boron nitride pre-forms are characterized by a porosity between 5% and 80%.

14. The method of any of claims 10 to 13, wherein an initial ratio of a volume of nutrient to the free volume is less than about 2.

15. An apparatus for forming a boron nitride (BN) composition, comprising: a sealable container comprising one or more walls that define an internal volume;one or more seed crystals disposed within a first region of the internal volume, wherein the one or more seed crystals comprise a material selected from a group consisting of cubic boron nitride (cBN) or diamond; ammonia (NH3) disposed within the internal volume; a mineralizer disposed within the internal volume, wherein the mineralizer comprises a material selected from a group consisting an alkali element, an alkaline earth element, or a halogen; and a nutrient disposed within a second region of the internal volume, wherein the nutrient comprises boron.

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