Method for producing multiphase composite materials using microwave plasma processing

Abstract

To provide a method for generating particles with generally uniform size and uniform thermal history for a variety of applications.SOLUTION: There is disclosed herein a method to produce multiphase composite materials directly from solution precursor droplets by a fast pyrolysis process using a microwave plasma embodiment containing a microwave generating source 1, a dielectric plasma torch 3, and a droplet maker 4. Here, using homogenous solution precursors, droplets are generated with a narrow size distribution, and are injected and introduced into the microwave plasma torch with generally uniform thermal path. The generally uniform thermal path in the torch is achieved by axial injection of droplets into an axisymmetric hot zone with laminar flows. Upon exposing to high temperature within the plasma with controlled residence time, the droplets are pyrolyzed and converted into particles by quenching with a controlled rate of the exhaust gas in a gas chamber. The particles generated have generally uniform sizes and uniform thermal history, and can be used for a variety of applications.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This application is a continuation-in-part of Application No. 13,673,737, filed Dec. 4, 2012, by inventors Kamal Hadidi and Makhlouf Redjdal, entitled "Method for Making Amorphous Particles Using a Uniform Melt-state in a Microwave Generated Plasma Torch," which is incorporated herein by reference in its entirety. This application also claims priority to U.S. Provisional Application No. 61,802,769, filed Mar. 18, 2013, by inventors Makhlouf Redjdal and Kamal Hadidi, entitled "Single-Step Synthesis Method for the Production of Multiphase Oxide Ceramics Using Microwave Plasma Process," which is incorporated herein by reference in its entirety. [Background technology]

[0002] The present invention generally relates to a method for producing multiphase composite materials directly from solution precursor droplets by rapid pyrolysis processing using microwave-generated plasma.

[0003] In recent years, interest in the emergence of multiphase nanostructured composites of metal oxide ceramics has surged as a natural improvement of the coarse-grained or even single-phase nanostructure of these materials. It has been found that the reduction of grain size from the coarse micrometer scale to the nanometer scale, typically with grain sizes less than 100 nanometers (nm), can significantly improve the mechanical, thermal, optical, chemical, electrical and magnetic material properties. Furthermore, these nanocomposites exhibit much more stable phases than their single-phase counterparts. The presence of multiple phases in a matrix tends to inhibit grain growth during thermal heating. The properties of these new materials are also influenced by nanoscale grain boundaries, which are susceptible to site pinning and are responsible for the stability of the phase microstructure. Another stringent condition for achieving phase stability is to produce these multiphase nanocomposites with fine and uniform distribution of phase domains in the nanocomposite matrix.

[0004] Many synthetic methods have been used to synthesize these nanocomposites to control the microstructural length scale and distribution of elements in the composition. Most methods are unable to achieve both conditions due to the complex chemical, thermal and nucleation kinetics of the matrix components, plus the even more challenging physical and chemical properties of the involved solvents. Some methods can achieve both, but require multiple heat treatment steps to achieve nanoscale grains and phase homogeneity of the component matrix. Jordan et al. (US Patent Publication No. 20120322645, 2012) used a sol-gel esterification technique to produce magnesia-yttrium particles suitable for the infrared window. This invention uses three main steps. Step 1 consists of low temperature and moderate heating to evaporate the water and form a foam consisting of a complex network of organic acids and alcohols necessary to obtain a homogeneous dispersion of metal oxide cations. Step 2 consists of thermal heating up to 400° C. to remove all carbon embedded in the foam while maintaining the particle size below 20 nanometers (nm). Step 3 uses heat treatment up to 1100°C to achieve full crystallinity of magnesia-yttrium nanocomposite with particle size of about 100 nm. The main drawbacks of such an approach include that it is not easily scalable due to the need for large furnaces, and that thermal heating is required for hours, if not days, to remove the solvent and achieve full crystallization of the final product.

[0005] A method to achieve ultrafine and somewhat homogeneous metal oxide nanocomposites is liquid-fed flame pyrolysis by R. Laine et al. (US Pat. No. 7,770,152, 2010). This method, similar to the present invention, injects atomized droplets of precursors into a combustion flame to produce nanocomposite particle powders in a few milliseconds. However, this method suffers from several drawbacks, including non-uniform particle size and size distribution due to atomization, and non-uniform thermal heating due to large temperature gradients in flames where the temperature does not exceed 2000° C. This leads to phase microstructural heterogeneity in the composition distribution of the final product. Post-processing steps involving cyclones and ceramic filters are necessary to separate large agglomerates from nanoscale particles.

[0006] Another method that features a one-step approach for the production of nanocomposites uses radio frequency plasma to treat atomized droplets of metal precursors (Boulos, US Pat. No. 6,919,527 B2, 2005). Although the high temperature and axial symmetry of the physical embodiment to contain the plasma are realized, this method still suffers from compositional inhomogeneity, in part due to the injection of the atomized liquid precursor with variable diameter, but also due to the inhomogeneity of the plasma, which exhibits a hollow core due to the skin effect. Particles that pass through the core of the plasma tend to be less well treated compared to particles that pass through the periphery of the crystal. This leads to inhomogeneity in particle processing and production of particles with homogeneous phase microstructures.

[0007] From the above, it can therefore be seen that a need exists in the art to overcome the deficiencies and limitations set forth hereinabove. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Application Publication No. 2012 / 0322645 [Patent Document 2] U.S. Patent No. 7,770,152 [Patent Document 3] U.S. Patent No. 6,919,527 Summary of the Invention [Problem to be solved by the invention]

[0009] The shortcomings of the prior art are overcome and additional advantages are provided by the direct fabrication of multiphase composites from solution precursor droplets by rapid pyrolysis processing using microwave-generated plasma. The method solves two major problems that have plagued the materials heat processing industry: compositional non-uniformity of the feedstock and non-uniform thermal path. Here, by using a homogenous solution precursor, droplets are produced with a narrow size distribution and are injected and introduced into the microwave plasma torch with a generally uniform thermal path. The generally uniform thermal path within the torch is achieved by axial injection with a laminar flow of droplets into an axisymmetric hot zone. [Means for solving the problem]

[0010] In one aspect, multiphase composite materials were produced by first preparing a salt solution in water, in an organic solvent, or in a mixture of water and an organic solvent, followed by generating precursor droplets from the salt solution using a feed jet device, then introducing the droplets axially into a microwave plasma torch using a gas flow toward the microwave-generated plasma, where the droplets are pyrolyzed and converted to particles by quenching with a controlled rate of exhaust gas in a gas chamber when exposed to high temperatures with a controlled residence time in the plasma, and finally filtering and extracting the exhaust gas particles.

[0011] The salt solutions were produced by different methods. In one example, the salt solutions were prepared by further including an acid in the solution. In another example, the salt solutions were prepared by combining a) water and an organic solvent (e.g. water and ethylene glycol), b) water and an acid (e.g. water and citric acid) or c) a solution of water, an organic solvent and (e.g. water, ethylene glycol and citric acid) with another solution of a) water and a salt or b) water, a salt and an organic solvent. The organic solvent was selected from a solvent that is miscible with water, such as ethanol, methanol, 1-propanol, 2-propanol, tetrahydrofuran or a mixture of these solvents.

[0012] In another embodiment, the composition of the resulting particles is adjusted by selecting salts with different cations, the cations being selected from alkali metals, alkaline earth metals, transition metals, post-transition metals, lanthanides, actinides, metalloids, non-metallic elements and mixtures of such elements.

[0013] For example, to produce yttrium (and / or scandium)-aluminum-garnet product particles, the cations of the salt solution are aluminum, yttrium (and / or scandium) and other dopants such as lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thallium, ytterbium, lutetium, and combinations thereof. The product particles can be used as active materials for lasers or phosphors and other applications.

[0014] Other examples of cations are selected from a.) post-transition metals and transition metal mixtures, b.) magnesium and yttrium, c.) magnesium and aluminum, d.) lanthanum, magnesium and aluminum, e.) zirconium and yttrium (and / or samarium). Product particles from these selections are used as active materials for a variety of applications such as catalysts, infrared transparent materials, transparent exteriors, thermal barrier coatings and solid oxide fuel cells.

[0015] In another embodiment, the anion of the salt is selected from nitrate, acetate, citrate, sulfate, carbonate, chloride, phosphate, alkoxide, atlane, tetraethyl orthosilicate, metal borohydrides, and mixtures of these anions.

[0016] In another embodiment, the salt solution droplets are entrained using at least two coaxial laminar flows, such laminar flows being generated using air, oxygen, argon, methane, ammonia, nitrogen gases and any combination of these gases.

[0017] In another embodiment, the exhaust gas from the microwave plasma is 3 Kelvin / second (K / s) or higher 10 6 The quench is achieved by selecting a quench rate of less than or equal to 100 K / s, and the quench is achieved using a controllable atmosphere chamber.

[0018] It is therefore an object of the present invention to produce particles having a generally uniform size and uniform thermal history for a wide variety of applications.

[0019] Additional features and advantages are achieved through the techniques of the present invention.Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention.

[0020] The recitation herein of desirable objectives satisfied by various embodiments of the invention is not meant to imply or suggest that any or all of these objectives are present as essential features, either individually or collectively, in the most general embodiment of the invention, or in any of its more specific embodiments.

[0021] The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification, however the invention, both as to organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description read in connection with the accompanying drawings. [Brief description of the drawings]

[0022] [Figure 1] A method of producing particles is shown using a microwave plasma embodiment containing a microwave source, a dielectric plasma torch, and a droplet generator that dispenses precursor droplets, as described in US Patent Application Publication No. 2008 / 0173641. [Diagram 2] FIG. 1 shows a schematic diagram of several routes used to prepare salt solutions for generating precursor droplets. [Diagram 3] 1 shows a scanning electron microscope (SEM) image of yttrium-aluminum-garnet (YAG) particles prepared according to the method of the present disclosure using yttrium and aluminum salts along with citric acid and ethylene glycol. [Figure 4] 1 shows the X-ray diffraction (XRD) and selected area diffraction (SAD) patterns of YAG particles produced by the method of the present disclosure, suggesting an amorphous microstructure. [Diagram 5] 1 shows a comparison between the XRD pattern of calcined yttrium aluminum garnet and an XRD powder diffraction file (PDF) reference from a database showing the pure YAG phase produced according to the methods of the present disclosure. [Figure 6] 1 shows an SEM image of magnesia-yttrium particles prepared according to the method of the present disclosure using magnesium and yttrium salts along with citric acid and ethylene glycol. [Figure 7] 1 shows SEM images of spinel particles prepared according to the method of the present disclosure using magnesium and aluminum salts along with citric acid and ethylene glycol. [Figure 8] 1 shows an XRD pattern of lanthanum-magnesium-hexaaluminate product particles quenched onto a heated substrate exhibiting a nanocomposite phase microstructure produced according to the method of the present disclosure. [Figure 9] 1 shows a flow chart of one embodiment according to the method of the present disclosure, a precursor metal salt mixed with a reagent and an accompanying heating treatment with microwave plasma. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] A method is disclosed for directly producing multiphase composites from solution precursor droplets by rapid pyrolysis processing using microwave plasma embodiments containing a microwave generating source as described in US 2008 / 0173641, a dielectric plasma torch as described in other patent applications, and a droplet generator for dispensing uniform precursor droplets as described in other patents. Using a homogeneous solution precursor, droplets are generated with a narrow size distribution and are injected and introduced into the microwave plasma torch by a generally uniform thermal path. The generally uniform thermal path in the torch is achieved by axial injection of the droplets in a laminar flow into an axisymmetric hot zone. When exposed to high temperatures with a controlled residence time in the plasma, the droplets are pyrolyzed and converted into particles by quenching with a controlled rate of exhaust gas in a gas chamber. The particles generated have generally uniform size and uniform thermal history and can be used in a wide variety of applications.

[0024] Referring to FIG. 1, the method for making metal oxide nanocomposite ceramics consists of an apparatus including a microwave radiation generating device 1, a microwave chamber 2, a dielectric sheath plasma torch 3, a droplet generator 4, and a gas flow communication scheme 5. The microwave generating device 1 is combined with the microwave chamber 2 and the dielectric plasma torch sheath 3 to ignite a stable plasma in a high temperature zone 6 inside the dielectric torch 3. A homogeneous solution of salt and metal solvent is injected into the droplet generator 4 under constant stirring and pressure in a tank 7. A piezoelectric element 8 is actuated to produce uniform droplets 9, which are injected axially into the plasma torch 3 and are entrained as particles 10 by the gas laminar flow due to the gas flow communication scheme 5. In the high temperature zone 6 containing the stable plasma 11, the particles 10 undergo homogeneous heat treatment to produce spherical product particles. 12 and is collected in a stainless steel or ceramic filter.

[0025] Referring to FIG. 2, a schematic diagram of the preparation of the metal precursor is shown. The high level of precursor homogeneity is dependent on the molecular species, its high miscibility in the liquid phase and its low melting point. Other factors that influence the final morphology and microstructural homogeneity include molar concentration, solvent evaporation rate, solute diffusion and associated thermodynamics involved during thermal treatment. The present invention employs three routes for precursor preparation. Route 1 (FIG. 2a) incorporates an organic acid, e.g., citric acid, and an organic alcohol, e.g., ethylene glycol, to produce a composite network for optimal dispersion of the solute in the solution. This route is used to prepare MgO-Y 2 O 3 Porous particles of MgAl 2 O 4 (Spinel) Shell and Y 3 Al 5 O 12 Route 2 (Figure 2b) involves an alcohol, such as ethanol, methanol or propanol, mixed with a high molar concentration of a water-soluble metal salt. This method has been used to produce solid particles of MgO. Finally, route 3 (Figure 2c) involves the use of more expensive precursors using alkoxides diluted in alcohol to provide a metal source for producing metal oxide ceramics. This method has been used to produce LaMgAl 11 O 19 All three mixtures were thoroughly mixed in a pressurized tank to produce a homogenous solution precursor.

[0026] Disclosed herein are compositions of metal oxide ceramics suitable for laser, phosphor, catalyst, exterior and visible to infrared window applications. Some compositions include yttrium aluminum garnet (YAG), monoclinic YAM, perovskite YAP, magnesium aluminum spinel (MgAl 2 O 4 ) and magnesia-yttria (MgO-Y 2 O 3The composites are based on binary and ternary stoichiometric ratios of, for example, aluminum, magnesium, and yttrium to produce ZnO, FeO, FeNb ...

[0027] In one specific embodiment, a solution precursor consisting of a stoichiometric composition of aqueous aluminum nitrate and yttrium nitrate, distilled or deionized water, citric acid, and ethylene glycol is prepared to produce yttrium-aluminum-garnet oxide ceramic. An exemplary solution is Al(NO 3 ) 3 9H 2 1250 ml of a 0.5 molar solution of O, Y(NO 3 ) 3 6H 2 The mixture consisted of 750 ml of a 0.5 molar solution of O, 1798 ml of a 0.5 molar solution of citric acid, and 17.77 ml of ethylene glycol. The precursors were thoroughly mixed using a magnetic mixer for at least 1 hour to ensure complete molecular mixing of the composition. The precursors were then dispersed in a 1-5 mm volume as uniform droplets with characteristic diameters varying from tens of micrometers to 130 micrometers, produced by a radio frequency driven, pressure actuated droplet maker. liter The plasma is injected at an injection flow rate between 1000 and 1000 ml / min. A total gas flow of not more than 80 SCFH for particle entrainment and cooling of the inner wall of the dielectric is used to stabilize the plasma at a relatively low microwave radiation power of 5.5 KW. The YAG powder particles are collected using nylon, ceramic or stainless steel filters housed in a device inserted in the path of the powder collection heat rejection system. The microstructure, grain size and morphology are investigated using Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) techniques.

[0028] SEM was used to investigate the particle size, particle size distribution and morphology of the amorphous yttrium-aluminum-garnet particles 12 in FIG. 1. Referring to FIG. 3, it can be seen that the obtained YAG particles are approximately spherical, shell-like and have a porous texture on the surface. The diameter varies from 300 to 400 micrometers or four times the particle size of the jetted precursor droplets. The obtained particles tend to expand and are fluffy, mainly due to the explosive nature of the solvent expelled during the thermal drying process of the nitrate-containing precursor droplets.

[0029] 4, a detailed analysis of the internal microstructure of the YAG powder product particles 12 using XRD techniques is shown. This reveals that the phase microstructure of the particle product was found to be completely amorphous. This amorphous state indicates the presence of high quench rates as the processed material exits the plasma hot zone according to this specific embodiment.

[0030] The amorphous product particles were subsequently calcined at 1200° C. for 1 hour and analyzed using XRD technique. Referring to FIG. 5, the resulting crystalline structure is compared to that of YAG using the XRD database PDF-33-40 (reference intensities have been scaled accordingly for better visual comparison at comparable angles). It can be clearly seen that there is a perfect match of most of the major and minor peaks in the XRD plots of the UniMelt treated and calcined YAG and the crystalline YAG used as a reference. The perfect match of all peaks is consistent with the binary YAG structure. 2 O 3 -Al 2 O 3 This shows the phase purity of the obtained YAG without any other phases of YAM and YAP in the oxide system.

[0031] In another embodiment using the apparatus shown in Figure 1, a one-step heat treatment can be used to produce treated metal oxide particles having a nanocrystalline microstructure by extending the residence time of the particles at the high temperature zone. Such an extension of the residence time can be achieved by increasing the size of the plasma plume within the dielectric tube containing the microwave plasma. amount This is achieved by increasing the microwave power in the plasma source. The elongated plasma plume allows complete evaporation of the solvent, drying of the solute, melting and further sintering of the particle product, achieving a nanocrystalline microstructure in situ before the particles exit the dielectric tube containing the plasma. This allows for an additional step of in situ sintering for crystallization, eliminating the need for the post-processing step of sintering the amorphous product described in this paragraph.

[0032] The modification of the composition of yttrium and aluminum elements involves the addition of rare earth dopants in the amount of several weight percents to modify the basic properties of the nanocomposite metal oxide YAG. In this case, rare earth salts are added to yttrium and aluminum salts and the solution is heat treated using microwave plasma. The rare earth elements considered include neodymium (Nd), erbium (Er), terbium (Tr), ytterbium (Yb), holmium (Ho) and thulium (Tm). The doping levels range from 0.5 to 3 (mol) percent. The nanocomposite YAG powder produced acts as a host material for laser applications.

[0033] Another modification of the composition of yttrium and aluminum elements involves the addition of dopants of other groups of rare earth elements in amounts of several weight percent to modify the basic properties of the nanocomposite metal oxide YAG. Rare earth elements considered include cerium (Ce), dysprosium (Dy), samarium (Sm) and terbium (Tb). This is done by adding appropriate precursor sources of rare earth elements to the initial aluminum and yttrium solution precursors and injecting them into the microwave plasma. Similar doping levels are used, i.e., 0.5 to 3 (mol) percent. The rare earth doped nanocomposite YAG is suitable for use as a phosphor.

[0034] In another embodiment, a solution precursor consisting of a composition of aqueous aluminum nitrate and yttrium nitrate, distilled or deionized water, citric acid, and ethylene glycol is used to prepare nickel-alumina (Ni-Al 2 O 3 ) oxide ceramics. A typical solution is prepared using Ni(NO 3 ) 2 7 2H 2 22 ml of a 0.82 molar solution of Al(NO 3 ) 3 9H 2 The mixture consisted of 847 ml of a 0.82 molar solution of 1,000 ml of a 0.82 molar solution of citric acid and 14.5 ml of ethylene glycol. 2 O 3 This corresponds to a 5 mol% ratio of the complex. Other ratios between 2 and 10 mol% can also be considered. The precursors are thoroughly mixed using a magnetic mixer for at least 1 hour to ensure complete molecular mixing of the composition. The precursors are then dispersed in 1 to 5 mm particles as uniform droplets with diameters of tens of micrometers to 100 micrometers produced by a radio frequency-driven, pressure-actuated droplet generator. literThe plasma is injected at an injection flow rate between 1000 and 1500 ml / min. A gas flow of at least 40 SCFH but not exceeding 120 SCFH total for particle entrainment and cooling of the dielectric inner walls is used to stabilize the plasma at a relatively low microwave radiation power of 5.5 KW. The nickel-alumina nanocomposite powder particles are collected using nylon, ceramic or stainless steel filters housed in a device inserted in the path of the powder collection heat rejection system.

[0035] Other embodiments of the composition may include, instead of nickel salts, other metal salts including platinum, palladium, nickel, silver, and gold, added individually in small amounts to dope the aluminum cations. These compositions are suitable for catalytic applications. Platinum-doped alumina is used in the petrochemical industry for the dehydrogenation of hydrocarbons, whereas palladium- and nickel-doped alumina is used for the hydrogenation of hydrocarbons and fats. Silver-doped alumina is used to convert ethylene to ethylene oxide.

[0036] In another embodiment, a solution precursor consisting of a composition of aqueous magnesium nitrate and yttrium nitrate, distilled or deionized water, citric acid, and ethylene glycol is used to prepare magnesium-aluminum-spinel (MgO-Y 2 O 3 ) oxide ceramics. A typical solution is prepared using Mg(NO 3 ) 2 9H 2 1744 ml of a 0.5 molar solution of O, Y(NO 3 ) 3 6H 2 The mixture consisted of 218 ml of a 0.5 molar solution of O, 1798 ml of a 0.5 molar solution of citric acid, and 17.17 ml of ethylene glycol. The precursors were thoroughly mixed using a magnetic mixer for at least 1 hour to ensure complete molecular mixing of the composition. The precursors were then dispersed as uniform droplets with characteristic diameters ranging from tens of micrometers to 130 micrometers, produced by a radio-frequency-driven, pressure-actuated droplet generator. , MThe plasma is injected at an injection flow rate between 1000 and 2000 liters per minute (ml / min). Gas flows of at least 40 SCFH, but not exceeding a total of 120 SCFH, for particle entrainment and cooling of the inner walls of the dielectric are used to stabilize the plasma at a relatively low microwave radiation power of 5.5 KW. The YAG powder particles are collected using nylon, ceramic, or stainless steel filters housed in a device inserted in the path of the powder collection heat rejection system.

[0037] SEM was used to examine the particle size, particle size distribution and morphology of the magnesium-yttrium nanocomposite oxide ceramic particles. 2 O 3 It can be seen that the particles are roughly spherical, shell-like, and have a porous honeycomb-like structure on the surface. The average diameter of the typical shell is about 100 micrometers, which is relatively comparable to the diameter of the jetted precursor droplets. The resulting particles are fluffy and porous, mainly due to the explosive nature of the solvents expelled during the thermal drying process of the nitrate-containing precursor droplets.

[0038] The magnesium yttrium oxide ceramic (MgO-Y 2 O 3 ) can be consolidated using sinter / HIP, hot press and hot press / HIP to produce transparent bodies suitable for infrared transmission. Powders produced using the present invention have been found to sinter at lower temperatures, thus lowering the cost of processing into 3D solid bodies that can be made into infrared domes or windows.

[0039] In one specific embodiment, a solution precursor consisting of a stoichiometric composition of aqueous magnesium nitrate and yttrium nitrate, distilled or deionized water, citric acid, and ethylene glycol is used to prepare magnesium-aluminum-spinel (MgAl 2 O 4 ) nanocomposite oxide ceramics. A typical solution is prepared using Al(NO 3 ) 2 9H 21333 ml of a 0.5 molar solution of Mg(NO 3 ) 2 6H 2 The mixture consists of 666 ml of a 0.5 molar solution of O, 1798 ml of a 0.5 molar solution of citric acid, and 17.77 ml of ethylene glycol. The precursors are thoroughly mixed using a magnetic mixer for at least 1 hour to ensure complete molecular mixing of the composition. The precursors are then dispersed in a 1-5 mm diameter solution as uniform droplets with characteristic diameters of tens of micrometers to 130 micrometers, produced by a radio frequency-driven, pressure-actuated droplet generator. liter The gas flow is injected at an injection flow rate of between 1000 and 1000 ml / min. Gas flows of more than 40 SCFH, but not exceeding a total of 120 SCFH, for particle entrainment and cooling of the inner walls of the dielectric are used to stabilize the plasma at a relatively low microwave radiation power of 5.5 KW. 2 O 4 The nanocomposite spinel powder particles were collected using nylon, ceramic or stainless steel filters housed in a device inserted in the path of the powder collection heat rejection system.

[0040] SEM was used to examine the grain size, grain size distribution and morphology of the magnesium-aluminum nanocomposite spinel oxide ceramic. 2 O 4 It can be seen that the particles are roughly spherical, shell-like, and have a porous texture on the surface. The average diameter of a typical shell is about 300 micrometers or three times the diameter of the jetted precursor droplets. The resulting particles tend to expand and are fluffy, mainly due to the explosive nature of the solvent expelled during the thermal drying process of the nitrate-containing precursor droplets.

[0041] The magnesium aluminate spinel (MgAl 2 O 4) can be consolidated using sinter / HIP, hot press and hot press / HIP to produce transparent bodies suitable for visible to infrared transmission or as transparent cladding. Powders produced using the present invention have been found to sinter at lower temperatures, thus lowering the cost of processing into 3D solids that can be made into domes or transparent cladding panels.

[0042] In one specific embodiment, a solution precursor consisting of a stoichiometric composition of aqueous lanthanum nitrate or acetate, magnesium nitrate or acetate, and aluminum nitrate, distilled or deionized water, is used to prepare lanthanum-magnesium-hexaaluminate (LaMgAl 11 O 19 ) nanocomposite oxide ceramic powders. A typical solution is prepared using Al(NO 3 ) 2 9H 2 The precursors consist of 676.4 ml of water with 100 grams of O, 61.50 ml of water with 8.31 grams of magnesium acetate, and 61.70 ml of water with 5.20 grams of lanthanum acetate. The precursors are thoroughly mixed using a magnetic mixer for at least 1 hour to ensure complete molecular mixing of the composition. The precursors are then dispersed in a 1 to 5 mm solution as uniform droplets with characteristic diameters of tens of micrometers to 130 micrometers, produced by a radio frequency driven, pressure actuated droplet generator. liter The gas flow is injected at an injection flow rate of between 1000 and 1000 ml / min. Gas flows of at least 40 SCFH, but not exceeding a total of 120 SCFH for particle entrainment and cooling of the inner walls of the dielectric, are used to stabilize the plasma at a relatively low microwave radiation power of 5.5 KW. 11 O 19 The nanocomposite powder particles were collected using nylon, ceramic, or stainless steel filters housed in a device inserted into the path of the powder collection and exhaust system. These LaMgAl 11 O 19 The nanocomposite powders are suitable for thermal barrier coating or catalytic applications.

[0043] Referring to FIG. 8, the LaMgAl11 O 19 A detailed analysis of the internal microstructure of the lanthanum-magnesium-aluminum oxide nanocomposite phase is shown. This figure shows the results of quenching into different environments other than the ambient atmosphere as described in paragraph

[0016] . In fact, the particle product after the UniMelt process is quenched into a heated substrate (typical temperature of about 450°C). This results in a lower quenching rate compared to quenching into the ambient atmosphere. As a result, the XRD spectrum shown in FIG. 8 is defined by a series of sharp peaks (black curve) indicating the presence of a lanthanum-magnesium-aluminum oxide nanocomposite phase microstructure.

[0044] In one specific embodiment, a solution precursor consisting of a stoichiometric composition of aqueous zirconyl nitrate and yttrium nitrate, distilled or deionized water, citric acid, and ethylene glycol is prepared to produce 8 wt% yttria-stabilized zirconia (8YSZ) nanocomposite oxide ceramic powder. A representative solution consists of 251.24 ml water with 50.24 grams of zirconium nitrate hydrate, 23.84 ml water with 7.32 grams of yttrium nitrate, 251.24 ml water with 38.72 grams of citric acid, and 3.78 ml ethylene glycol. The precursor solution is thoroughly mixed for at least 1 hour using a magnetic mixer to ensure complete molecular mixing of the composition. The precursor is then dispersed in a 1 to 5 mm diameter solution as uniform droplets with characteristic diameters of tens of micrometers to 130 micrometers produced by a radio frequency-driven, pressure-actuated droplet generator. liter The plasma is injected at an injection flow rate between 1000 and 1000 ml / min. A gas flow of at least 40 SCFH, but not exceeding 120 SCFH total, for particle entrainment and cooling of the inner wall of the dielectric is used to stabilize the plasma at a relatively low microwave radiation power of 5.5 KW. The 8YSZ nanocomposite powder particles are collected using nylon, ceramic or stainless steel filters housed in a device inserted in the path of the powder collection heat rejection system. These 8YSZ nanocomposite powders are suitable as electrolytes for solid oxide fuel cell (SOFC) applications.

[0045] In one specific embodiment, to produce magnesium-aluminum-oxynitride (MgALON) nanocomposite oxide ceramic powder, a solution precursor consisting of a stoichiometric composition of aqueous magnesium nitrate or acetate and aluminum nitrate or acetate and distilled or deionized water is prepared and then injected into a nitrogen microwave plasma gas. The precursor solution is thoroughly mixed for at least one hour using a magnetic mixer to ensure complete molecular mixing of the composition. The precursor is then dispersed as uniform droplets with characteristic diameters of tens of micrometers to 130 micrometers, ranging from 1 to 5 millimeters, produced by a radio frequency-driven, pressure-actuated droplet generator. liter The plasma is injected at an injection flow rate between 1000 and 1500 ml / min. A gas flow consisting of nitrogen at no less than 40 SCFH but no more than 120 SCFH total for particle entrainment and cooling of the dielectric inner wall is used to stabilize the plasma at a relatively low microwave radiation power of 5.5 KW. The MgALON nanocomposite powder particles are collected using nylon, ceramic or stainless steel filters housed in a device inserted in the path of the powder collection heat rejection system. These MgALON nanocomposite powders are suitable for clear exterior applications.

[0046] Referring to FIG. 9, amorphous or nanocrystalline metal oxide particles are made according to the homogeneous solution droplets described therein. The desired chemical composition is first mixed according to the specified ratio of reactants. The reactants are then thoroughly stirred to produce a homogeneous molecular mixture of reactants. The solution is then pumped inside the reservoir of the droplet making device using a peristaltic pump or pressurized tank. Once the reservoir is full, a piezoelectric transducer is actuated using high frequency drive electronics to apply a suitable perturbation to the solid ceiling or membrane of the solution reservoir. This in turn creates a disturbance in the volume of the solution in the reservoir. If the perturbation satisfies Rayleigh's breakdown law, the solution will emerge through the capillary nozzle as a continuous stream of uniform droplets exiting at a constant rate for a given frequency of electronic drive. The nature of the droplet stream is particularly noteworthy because the droplet stream is not in a burst mode, but instead in the form of a jet with uniform droplets. Prior to this, referring to the right side of FIG. 9, microwave radiation is introduced into a wave guide towards a plasma chamber in which a dielectric plasma torch is positioned and arranged perpendicular to the wave guide. Two annular flows are introduced: one to introduce the ejected droplets and the other to protect the inner wall of the outer tube of the plasma torch from melting under the effect of the high heat from the plasma. Once both annular flows are introduced in place, a plasma is ignited inside the dielectric plasma torch. To stabilize the plasma, a suitable combination of entrainment and cooling flows is chosen. These flows are also chosen to smoothly circulate the droplets towards the plasma and to avoid turbulences that may cause recirculation or backflow of the droplets above the hot zone. When the droplets reach the plasma now present in the hot zone, they are subjected to a uniform melting condition characterized by a uniform thermal path together with a uniform temperature profile of the plasma in the hot zone. The droplets are volumetrically and uniformly processed since all the solvent is burned off. The treated particles exit into a controlled atmosphere quench chamber below the plasma exit nozzle. The particle product was collected in nylon, ceramic or stainless steel filters and analyzed for its microstructure as well as its mechanical, optical and thermal properties.

[0047] Although the present invention has been described in detail according to certain preferred embodiments thereof, many modifications and variations therein may be made by those skilled in the art. It is therefore intended by the appended claims to cover all such modifications and variations which fall within the spirit and scope of the present invention.

Claims

1. 1. A method for making crystalline multiphase composite particles from a solution precursor, comprising: dispersing the solution precursor in the form of droplets using a droplet generator, wherein the solution precursor comprises a salt dissolved in a solvent; entraining the droplets in a microwave-generated plasma using a gas, wherein the droplets are entrained using a laminar flow of the gas; controlling the amount of said microwave generated plasma to control the residence time of said droplets in said microwave generated plasma to convert said salt into multi-phase composite particles, and sintering said multi-phase composite particles before they exit the microwave generated plasma, wherein the amount of microwave plasma is controlled by varying microwave power at a plasma generation source; and quenching and recovering said multiphase composite particles. The method includes:

2. The method of claim 1 , wherein the droplets are entrained using at least two coaxial laminar flows.

3. 3. The method of claim 2, wherein the coaxial laminar flow is generated using the following gases: oxygen, argon, methane, ammonia, nitrogen, and any combination of these gases.

4. The method of claim 1 , wherein the droplets are converted into multiphase composite particles by a pyrolysis process.

5. 5. The method of any one of claims 1 to 4, wherein the solution precursor comprises one or more salts selected from the group consisting of lithium, sodium, potassium, rubidium, magnesium, calcium, strontium, barium, scandium, yttrium, nickel, zirconium, palladium, silver, platinum, gold, aluminum, thallium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, boron, silicon, germanium, arsenic, antimony, tellurium, carbon, phosphorus, sulfur, and selenium, and combinations thereof.

6. The solution precursor comprises: aluminum; Yttrium, scandium, and any combination thereof; and Dopants selected from the group consisting of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and combinations thereof.

6. The method of claim 1 , wherein the compound is prepared by dissolving a salt containing a cation of

7. The solution precursor comprises: Dissolving salts containing cations of aluminum, zirconium, silicon, magnesium and manganese and any combination thereof or cerium of the lanthanides; and Doping the phosphorus with a transition metal or nonmetal selected from the group consisting of palladium, platinum, nickel, silver, gold, ruthenium, rhodium, vanadium, molybdenum, cobalt, tungsten, and any combination thereof. The method according to any one of claims 1 to 5, wherein the compound is prepared by:

8. 6. The method of claim 1, wherein the solution precursor is prepared by dissolving a salt containing magnesium and yttrium cations.

9. 6. The method of claim 1, wherein the solution precursor is prepared by dissolving a salt containing magnesium and aluminum cations.

10. 6. The method of claim 1, wherein the solution precursor is prepared by dissolving a salt containing lanthanum, magnesium, and aluminum cations.

11. The solution precursor comprises: Zirconium, and yttrium or samarium, 6. The method of claim 1 , wherein the compound is prepared by dissolving a salt containing a cation of

12. 12. The method of claim 1, wherein the residence time of the droplets in the microwave-generated plasma is extended by increasing the volume of a plasma plume of the microwave-generated plasma.

13. A method for making crystalline multiphase composite particles directly from solution precursor droplets, comprising: providing a solution precursor, where the solution precursor comprises a salt dissolved in a solvent; generating droplets from the solution precursor using a droplet generator; injecting the droplets into a microwave-generated plasma; entraining the droplets with a gas in a microwave-generated plasma using a laminar flow of the gas; entraining the droplets in a microwave-generated plasma while pyrolyzing the salt into multiphase composite particles; sintering the multiphase composite particles before they exit the microwave-generated plasma, wherein pyrolysis and sintering are performed by controlling the residence time of the droplets in the microwave generated plasma by controlling the amount of the microwave plasma, wherein the amount of microwave plasma is controlled by varying microwave power at a plasma generation source; Controlling the quench rate of the microwave generated plasma using exhaust gas from the microwave generated plasma; and extracting multiphase composite particles from said exhaust gas; The method includes:

14. The method of claim 13, wherein the solution precursor is a salt solution in water, an organic solvent, or a salt solution in a mixture of water and an organic solvent.

15. 15. The method of claim 13 or 14, wherein the solution precursor comprises one or more salts selected from the group consisting of lithium, sodium, potassium, rubidium, magnesium, calcium, strontium, barium, scandium, yttrium, nickel, zirconium, palladium, silver, platinum, gold, aluminum, thallium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, thorium, boron, silicon, germanium, arsenic, antimony, tellurium, carbon, phosphorus, sulfur, and selenium, and combinations thereof.

16. 16. The method of any one of claims 13 to 15, wherein the droplets are entrained using coaxial laminar flows of at least two gases.

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