Rotary Seal Ring Materials

Abstract

The present invention relates to a green composite powder composition of silicon carbide and aluminum nitride, a sintering method and a silicon carbide sintered body obtained or obtained therefrom, as well as a SiC-AlN composite ceramic, its uses and molded articles containing the same. In one aspect, the present invention provides a green composite powder composition comprising 90.0% to 99.9% by weight of silicon carbide and 0.1% to 10% by weight of aluminum nitride. In another aspect, the present invention provides a green composite powder composition of the formula x (SiC) 1-x (AlN), wherein 0.999≧x≧0.900, and the composite ceramic material has a thermal conductivity of 4.5 MPa.m 1 / 2 and thermal conductivity exceeding 120 W / mK.

Description

[Background technology]

[0001] Exemplary embodiments relate to the art of rotary seals, and in particular to seal rings used in rotary seals. In particular, the present invention relates to green composite powder compositions comprising silicon carbide and aluminum nitride, sintering processes, and silicon carbide sintered materials obtained or obtainable therefrom, and SiC-AlN composite ceramics, uses thereof, and articles including same.

[0002] There are several types of seals that can be used to seal between the rotating shaft of a rotary machine and the stationary housing of a pump, compressor, or turbine. One example is the end face mechanical seal. Such a seal includes a seal contact surface formed by two rings, each having a face, arranged so that the two faces are in slidable contact with each other.

[0003] During operation, one of the rotating rings rotates with the rotating shaft and the other is held in a fixed position. The rotating ring is sometimes called the "mating ring" because it is mated to the rotating shaft / rotor. The rotating ring may be mated to the rotor via a shaft sleeve. The fixed ring is sometimes called the primary ring and does not rotate during operation.

[0004] Frictional wear between the sealing faces of the rings can cause gaps to form between the two faces, resulting in excessive leakage. Such seals therefore require periodic adjustment to maintain the proper position or axial location of the faces relative to one another to account for wear, while still maintaining a relatively leak-free seal. Of course, no matter how well the faces are operated, some leakage will occur.

[0005] A variety of biasing mechanisms have been devised to automatically compensate for wear and provide a closing force that presses the seal faces together. Such biasing mechanisms include single and multiple coil springs, metal bellows, etc. Those skilled in the art will appreciate that the combination of the hydraulic force from the sealed fluid and the force provided by the biasing mechanism is in fact the total closing force.

[0006] Silicon carbide is a non-oxide ceramic material that has excellent thermo-mechanical properties such as high strength, high thermal conductivity, high hardness, high stiffness, excellent wear resistance, and also excellent chemical resistance, which has led to its widespread use in tribological applications, especially as a component of the mechanical seal faces.

[0007] Silicon carbide based ceramic seals are commercially available in a variety of forms such as reaction bonded silicon carbide, solid phase silicon carbide (SS SiC) and liquid phase silicon carbide (LP SiC). Summary of the Invention

[0008] The inventors have discovered that the materials currently used in ceramic seals have shortcomings that limit their use in certain applications. For example, self-sintered SiC has reasonable strength (about 450 MPa) but low fracture toughness (about 4 MPa.m 1 / 2 ), limiting its use under high PV conditions. Similarly, liquid phase sintered SiC has higher strength (about 650 MPa) and high fracture toughness (about 6 MPa.m, as measured, for example, by the single edge notch bending (SENB) method, according to ASTM D5045). 1 / 2 ), but has low thermal conductivity (about 90 W / mK) and low resistance to contact wear.

[0009] To overcome these limitations, the present specification discloses details of improved silicon carbide compositions and methods for making same that have higher strength, higher fracture toughness, higher thermal conductivity and higher contact wear resistance than known silicon carbide compositions.

[0010] In one embodiment, the present invention provides a green composite powder composition comprising 90.0% to 99.9% by weight silicon carbide and 0.1% to 10% by weight aluminum nitride.

[0011] In another aspect, the present invention provides a SiC-AlN composite ceramic material obtained or obtainable by sintering the green composite powder composition described herein.

[0012] In yet another aspect, the present invention provides a method for the preparation of a compound of formula x (SiC) 1-x (AlN), wherein 0.999≧x≧0.900, and wherein the composite ceramic material has a SiC-AlN composite strength of 4.5 MPa.m 1 / 2 It has greater fracture toughness and a thermal conductivity greater than 120 W / mK.

[0013] In a further aspect, the present invention provides a process for producing the green composite powder described herein, the process comprising combining silicon carbide powder and aluminum nitride powder in amounts of 90.0% to 99.9% by weight silicon carbide and 0.1% to 10% by weight aluminum nitride to form a green composite powder composition.

[0014] In yet another aspect, the present invention provides an article comprising a component formed of the SiC-AlN composite ceramic material described herein.

[0015] In yet another aspect, the invention relates to a mechanical seal face formed of the SiC-AlN composite ceramic material described herein.

[0016] In yet another aspect, the present disclosure relates to the use of a SiC-AlN composite ceramic material as described herein in a mechanical seal, bearing or wear part.

[0017] Major applications for these materials include, but are not limited to, mechanical seal faces, bearings, and wear parts (both dry and wet applications).

[0018] Additional technical features and advantages are realized by the techniques of the present invention. Embodiments and aspects of the present invention are described in detail herein and are considered a part of the claimed subject matter. For a better understanding, reference should be made to the detailed description and drawings. [Brief description of the drawings]

[0019] The particular subject matter of the exclusive rights disclosed herein is particularly pointed out and distinctly claimed in the claims at the end of the specification. The foregoing and other features and advantages of embodiments of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 shows a flow chart of a process by which a SiC—AlN composite ceramic material may be prepared. [Diagram 2] FIG. 2 shows the steady state coefficient of friction (CoF) test results of example materials in air with 60% humidity. [Diagram 3] FIG. 3 shows a comparison of coefficient of wear (CoW) test results of example materials in air with 60% humidity. [Figure 4] FIG. 4 shows the coefficient of wear (CoW) test results measured using the ball-on-disk (BoD) method under dry conditions (-40° C. dew point temperature) under nitrogen for the example materials.

[0020] The figures depicted herein are exemplary. Many variations are possible in the figures or the operations described therein without departing from the spirit of the invention. For example, operations can be performed in a different order, or operations can be added, deleted, or modified. Additionally, the term "coupled" and variations thereof describe that there is a communication path between two elements, and do not imply a direct connection between the elements without an intervening element / connection between the elements. All of these variations are considered part of this specification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] [Detailed Description of the Invention] In one aspect, the present invention provides an unsintered composite powder composition comprising 90.0% to 99.9% by weight of silicon carbide and 0.1% to 10% by weight of aluminum nitride. The unsintered composition of the present invention is particularly useful as a precursor of a SiC-AlN composite ceramic material, and has been found to be particularly advantageous in applications requiring both high fracture toughness and high thermal conductivity. The compatibility of high fracture toughness and high thermal conductivity has not been achieved in conventional SiC or AlN ceramics.

[0022] SiC-AlN composite ceramic materials that may be formed from the green composite powder compositions described herein have been found to be particularly useful in forming seals for turbomachinery applications. For example, the outboard seal of a two-seal system in a centrifugal gas compressor typically operates at low pressure but high speed. Materials used under such conditions must have high tensile strength to withstand the hoop stresses from the high speed rotation of the shaft and high thermal conductivity combined with a low coefficient of thermal expansion to minimize thermal coning or tapering of the seal interface that would impair the ability of the seal face grooves to form a stable fluid film. The inboard seal of such a system operates at high pressure and seals the process gas at high speed. Materials exposed to such conditions must have high mechanical strength to minimize deformation of the parts due to pressure and abutment loads, and high thermal conductivity combined with a low coefficient of thermal expansion to also minimize thermal deformation of the seal parts. As with the outboard seal, a "form stabile" seal interface gap is important for fluid film stability, but is equally important for limiting leakage across the seal gap.

[0023] The inventors have demonstrated that conventional gas seal ceramics (SiC and Si 3 N 4 ) found that even before the stress levels in the components become critically high, these materials suffer from excessive thermal interface taper at high speeds, which limits their maximum rated speed. The reason is that the viscous shear of the seal interface increases with speed, so high thermal gradients within the components cause "thermal coning," or increase the taper of the seal interface, causing the interfacial gas seal grooves to generate less hydrodynamic lift. The result is that the fluid film gap "collapses" at high speeds, causing catastrophic failure of the entire gas seal.

[0024] SiC-AlN composite ceramic materials preparable from the green powder composite compositions described herein can reduce or minimize the change in seal interface flatness with speed experienced by seals formed from conventional materials. The fluid film gap can be maintained up to the maximum speed and hoop stress that the material can withstand. As an example, conventional SiC materials may be limited to a rotational speed of 140 m / s due to thermal coning, while SiC-AlN composite ceramic materials with similar mechanical strength can reach speeds of over 250 m / s.

[0025] The presence of 0.1-10 wt% aluminum nitride in the green composite powder composition has been found to be an important feature in forming a ceramic material having particularly advantageous properties, which is believed to be the result of a modification of the microstructure of the resulting ceramic not exhibited by pure silicon carbide ceramics or pure aluminum nitride ceramics. In a preferred embodiment, the green composite powder composition comprises 95.0-99.9 wt% silicon carbide and 0.1-5.0 wt% aluminum nitride. More preferably, the green composite powder composition comprises 95.0-99.9 wt% silicon carbide and 0.1-5.0 wt% aluminum nitride.

[0026] The present invention also provides green composite powder compositions and processes for producing the SiC-AlN composite ceramics described herein.

[0027] In conventional solid synthesis methods for producing ceramic materials, milling of starting powders is usually followed by shaping and, optionally, firing, before sintering to produce the desired ceramic product. Milling can be wet or dry. High energy vibration milling can be used, for example, to mix the starting powders and, if utilized, for milling after demineralization. When wet milling is employed, the powders are mixed with a suitable liquid (e.g., ethanol or water, or a combination thereof) to form a slurry and wet milled with a suitable high density grinding media (e.g., yttria stabilized zirconia (YSZ) beads, or silicon carbide balls). The milled powders can be optionally fired and / or optionally shaped into a desired shape (e.g., pellets) before being sintered to produce a ceramic product, preferably with a high sintered density. Once a composite ceramic material is prepared after sintering, post-sintering machining and surface treatment can also be performed as necessary. See also FIG. 1, which is a flow chart of the process by which a SiC-AlN composite ceramic material is prepared.

[0028] It will therefore be appreciated that the green composite powder compositions described herein may result, for example, from milling and other process steps carried out prior to sintering to form a composite ceramic. Thus, the green composite powder compositions described herein may include additional components related to subsequent steps to form a composite ceramic material. For example, the green composite powder compositions may include stabilizers, binders and / or sintering promoters, although these are preferably minimized or eliminated entirely. Common sintering promoters include, for example, Y 2 O 3 , CaO, SiO 2 , La 2 O 3 , CEO 2 , SiO 2 , Al 2 O 3 , and TiO 2 Examples include:

[0029] Thus, in some embodiments, the green composite powder composition comprises less than 5 wt.%, preferably less than 3 wt.%, less than 2 wt.%, less than 1 wt.%, or even less than 0.1 wt.%, or even less than 0.01 wt.%, of additional components such as the sintering promoters. In particularly preferred embodiments, the green composite powder composition consists or consists essentially of silicon carbide and aluminum nitride.

[0030] As will be appreciated by those skilled in the art, high purity silicon carbide and aluminum nitride starting powders are commercially available with a variety of particle size specifications. α-Silicon carbide (α-SiC) is the most common crystalline form (polymorphic form) of silicon carbide and has a hexagonal crystal structure, although other polymorphic forms are known, such as β-Silicon carbide (β-SiC). In some embodiments, silicon carbide materials that may be used in connection with the present invention include or contain α-Silicon carbide (α-SiC).

[0031] Average particle size (D 50 ) may be used in forming the green composite powder composition of the present invention. In some embodiments, the silicon carbide component in the green composite powder composition has an average particle size of 0.1 μm to 5 μm, preferably less than or equal to 3 μm, such as 0.2 μm to 2 μm, more preferably 0.2 μm to 1 μm. The particle size of the silicon carbide component can be measured, for example, using known light scattering techniques and instruments such as Zetasizer 1000HS, M / s Malvern Instruments Ltd, UK, etc.

[0032] Average particle size (D 50 Although aluminum nitride powders with different average particle sizes can be used in forming the green composite powder composition of the present invention, it is preferred that the aluminum nitride powder component have a smaller average particle size than the silicon carbide powder component. In a preferred embodiment, the aluminum nitride in the green composite powder composition is aluminum nitride nanoparticles (e.g., having an average particle size (D) of 1.0 nm to 1,000 nm). 50Preferably, the aluminum nitride particles in the unsintered composite powder composition have an average particle size (D 50 ) is 10 nm to 500 nm. The particle size of the aluminum nitride component can be measured, for example, by using a known transmission electron microscope (TEM) technique.

[0033] The green composite powder composition described herein can be obtained by mixing silicon carbide and aluminum nitride starting powders, including any of those described herein, and milling (and optionally drying) to form a green composite powder composition. As mentioned above, as part of the preparation of a ceramic composite material, it is common for a mixture of starting powders to be dry milled or preferably wet milled (i.e., as part of a slurry in a liquid medium). Thus, the silicon carbide and aluminum nitride powders described above can be mixed in a selected weight ratio (which can be selected to ultimately obtain a SiC-AlN composite ceramic material having a desired component molar ratio) and then contacted with a suitable liquid medium (shown in the first step of the flow chart in FIG. 1) to provide a slurry that can be wet milled. Liquid media suitable for this purpose are those in which the silicon carbide and aluminum nitride are insoluble and / or non-reactive, and include liquid media selected from C1-C5 aliphatic monohydric alcohols such as methanol, ethanol, iso-propanol, n-butanol or n-heptanol, water, or combinations thereof. Preferably, when a slurry is formed for wet milling, a liquid medium is used that comprises or consists of ethanol, as shown in Figure 1. In a preferred embodiment, the slurry is formed from silicon carbide powder having an average particle size less than or equal to 3 μm, for example 0.2 μm to 3 μm, and / or the slurry is formed from aluminum nitride nanoparticle powder having an average particle size of 10 nm to 500 nm.

[0034] The particular form of milling is not particularly limited, and examples of suitable milling techniques include roller milling, ball milling, attrition milling, and centrifugal / planetary milling. In some embodiments, ball milling is used, and the milling media is optionally comprised of YSZ beads, silicon nitride balls, or silicon carbide balls. The use of silicon carbide balls as the milling media is advantageous in avoiding contamination or leaching of unwanted components from alternative milling media in order to maximize the purity of the milled product obtained before sintering. Such contamination by leaching from the milling media is not an issue when the milling media itself is formed from silicon carbide. A person skilled in the art can select a particular form of milling, such as roller milling, based on the form of milling (i.e., dry or wet), the intended particle size of the components of the resulting milled product, and the time scale over which the milling may be performed (e.g., 15-25 hours), but typical milling time scales typically range from 6 to 48 hours, preferably 12 to 36 hours, more preferably 15 to 25 hours, e.g., 18 to 20 hours, depending on the scale of production.

[0035] As shown in the flow chart of FIG. 1, if a wet milling step is used, the next step in the process is typically a drying step, which may be utilized to produce a green composite powder composition. The particular form of drying is not particularly limited and may utilize drying under vacuum, oven drying, or spray drying. In some embodiments, the slurry is dried under vacuum at 80° C. to 100° C. In some embodiments, the slurry is spray dried at 100° C. to 140° C. Examples of suitable lab-scale spray dryers include the Buchi mini B-290 spray dryer or the Okawara Kakoki L-8i spray dryer, depending on the scale.

[0036] Following the optional drying step, the green composite powder composition may be screened / sieved to obtain a powder composite of the desired particle size distribution, as shown in the flow chart of Figure 1. In some embodiments, after milling, and drying if performed, the green composite powder is passed through a screen with pores between 250 μm and 350 μm, e.g., 275 μm and 325 μm, e.g., a screen with pores of 300 μm.

[0037] According to another aspect, the present invention provides a SiC-AlN composite ceramic material obtained or obtainable by sintering the green composite powder composition described herein. The sintering step may be pressure assisted and may consist of, for example, high temperature pressing, spark plasma sintering, hot isostatic pressing (HIP), gas pressure sintering, or any combination thereof, as shown in the flow chart of FIG.

[0038] There is no particular limit to the temperature of the sintering step, since lower temperatures may be appropriate under certain pressure-assisted conditions, provided that adequate sintering is achieved, which can be readily determined by microstructural analysis of the product. For example, scanning electron microscopy (SEM) analysis, transmission electron microscopy (TEM) analysis can be used to quantify grain size and grain size distribution, and evaluate grain boundaries. The density and porosity of the product can also be readily measured by known methods, such as ASTM C373-88. Suitable sintering temperatures, for example, are typically 1800°C or higher, and suitable pressures to employ in pressure-assisted sintering systems are at least 5MPa.

[0039] In some embodiments, the SiC-AlN composite ceramic material is obtained or obtainable from sintering of the green composite powder composition at a temperature between 1800° C. and 2100° C., preferably between 1800° C. and 2000° C., more preferably between 1850° C. and 1950° C. When pressure assisted sintering is employed, a suitable pressure range at which sintering occurs is between 5 MPa and 75 MPa, preferably between 10 MPa and 60 MPa, more preferably between 30 MPa and 50 MPa.

[0040] In some embodiments, the SiC-AlN composite ceramic material obtained or obtainable from sintering the green composite powder compositions described herein comprises sintered α-silicon carbide. In some embodiments, the SiC-AlN composite ceramic material obtained or obtainable from sintering the green composite powder compositions described herein comprises sintered silicon carbide having a grain size of 2.0-3.0 μm.

[0041] After sintering, the obtained SiC-AlN composite ceramic material can be subjected to machining (i.e., shaping for different applications) or final surface treatment (such as polishing or grooving), as shown in Figure 1.

[0042] The SiC-AlN composite ceramic materials obtained or obtainable from sintering the green composite powder compositions described herein have been found to exhibit a combination of several advantageous properties that make them particularly suitable for sealing applications that are subject to high speeds, high thermal gradients, and high hoop stresses, such as turbomachinery applications (e.g., inbound or outboard seals in two-seal systems in centrifugal gas compressors). Such advantageous properties include high thermal conductivity along with a low coefficient of thermal expansion (e.g., to minimize thermal coning or tapering of sealing interfaces), and high mechanical strength (to minimize distortion of parts due to pressure and abutment loads).

[0043] A combination of features that has been found to be particularly surprising in the SiC-AlN composite ceramic materials obtained or obtainable from the sintered and unsintered composite powder compositions described herein is high fracture toughness (e.g., 4.5 MPa.m 1 / 2 The combination of high thermal conductivity (e.g., 120 W / mK or more) and high thermal conductivity (e.g., 120 W / mK or more) is a particular feature that is difficult to overcome, for example, in conventional sealing materials of choice such as SiC ceramic or silicon nitride (Si 3 N 4) never before seen in ceramics. Fracture toughness can be measured using ASTM C1421 (chevron notch method), and thermal conductivity can be measured using ASTM E1461.

[0044] The presence of AlN in the required concentrations in the composite ceramic materials described herein is believed to be particularly advantageous in modifying the ceramic microstructure (e.g., compared to conventional SiC ceramics). The substantial absence of components other than SiC and AlN in forming the ceramic composite is also believed to be particularly advantageous in maximizing the favorable interaction of SiC and AlN in the composite ceramic resulting from sintering the green composite powder compositions described herein.

[0045] Thus, in yet another aspect, the present invention also provides a compound of formula x (SiC) 1-x (AlN), where 0.999≧x≧0.900, and where the composite ceramic material has a thermal conductivity of 4.5 MPa.m 1 / 2 It has greater fracture toughness and a thermal conductivity greater than 120 W / mK.

[0046] In a preferred embodiment, the SiC-AlN composite ceramic material has the formula x (SiC) 1-x (AlN), where 0.999≧x≧0.950.

[0047] In some embodiments, the SiC-AlN composite ceramic materials described herein have a strength of 5 MPa.m 1 / 2 Greater than or equal to 5.0-6.0 MPa.m 1 / 2 It has a fracture toughness of

[0048] In some embodiments, the SiC—AlN composite ceramic materials described herein have a thermal conductivity of 110 W / mK to 150 W / mK, preferably 115 W / mK to 150 W / mK, and more preferably 120 W / mK to 145 W / mK.

[0049] In some embodiments, the SiC-AlN composite ceramic materials described herein have a thermal expansion coefficient of 4×10 compared to that of sintered silicon carbide materials. -6 / K. The coefficient of thermal expansion may suitably be measured using ASTM E228.

[0050] In some embodiments, the SiC-AlN composite ceramic materials described herein have a flexural strength greater than or equal to 600 MPa, preferably between 600 MPa and 850 MPa, more preferably between 700 MPa and 850 MPa. Flexural strength may suitably be measured using ASTM C1161 (4 points).

[0051] In some embodiments, the SiC-AlN composite ceramic materials described herein have an elastic modulus of 400 GPa to 450 GPa, preferably 420 GPa to 450 GPa. The elastic modulus may be suitably measured using ASTM E494.

[0052] In some embodiments, the SiC—AlN composite ceramic materials described herein have one or more of the following properties: (a) 3.0-3.3 g / cm 3 density of, (b) a porosity of less than 5%, preferably less than 2.5%, and more preferably less than 1%; and (c) A Poisson's ratio of 0.10 to 0.20, preferably 0.14 to 0.18.

[0053] Density and porosity are suitably measured using ASTM C373-88, while Poisson's ratio is suitably measured using ASTM E494.

[0054] In some embodiments, the SiC-AlN composite ceramic materials described herein have a coefficient of friction in gaseous fluids (such as air, nitrogen, carbon dioxide, etc.) at relative humidities of less than 60% that is less than 0.5, preferably less than 0.4, and most preferably less than 0.3.

[0055] In some embodiments, the SiC-AlN composite ceramic materials described herein have a melting point of 0.00001 mm in a gaseous fluid (e.g., air, nitrogen, carbon dioxide, etc.) with a relative humidity of less than 60%. 3 Wear coefficient less than 0.000005mm / Nm, preferably 0.000005mm 3 / Nm and / or 0.0001mm 3 / Nm, preferably under dry conditions, 0.000005mm 3 / Nm.

[0056] Friction and wear coefficients may suitably be measured by the ball-on-disk method in accordance with ASTM G-99, where a disk of a particular material is rotated at a constant speed and a ball of a mating material is moved against the disk until it contacts the disk and a known force is applied for a particular period of time. During the test, the normal and lateral loads are measured and the coefficient of friction can be determined from these two forces. After the test is completed, the volume of material removed from the disk and ball is measured and the wear coefficient can be determined.

[0057] In some embodiments, the SiC—AlN composite ceramic materials described herein have a tensile strength greater than 300 MPa, preferably greater than 350 MPa, and more preferably between 375 MPa and 450 MPa.

[0058] In some embodiments, the process for preparing the SiC—AlN composite ceramic material described herein further comprises further processing the silicon carbide sintered material into an article or part thereof.

[0059] Thus, in a further aspect, the present invention provides an article comprising a component formed of the SiC-AlN composite ceramic material described herein. As discussed herein, the particular combination of properties exhibited by the SiC-AlN composite ceramic material makes it useful in different applications, particularly those subject to high speeds, high thermal gradients, and high hoop stresses, such as turbomachinery applications (e.g., inbound or outboard seals in a two-seal system of a centrifugal gas compressor).

[0060] Thus, in yet another aspect, the present invention provides a mechanical seal face formed from the SiC-AlN composite ceramic material described herein.

[0061] In yet another aspect, the present disclosure provides for the use of a SiC-AlN composite ceramic material as described herein in a mechanical seal, bearing or wear part.

[0062] In another aspect, the present disclosure provides for the use of a SiC-AlN composite ceramic material as described herein to improve resistance to centrifugal stresses (eg, hoop stresses) in mechanical seal face components.

[0063] A detailed description of one or more embodiments of the disclosed apparatus and method is illustrated by way of example and not by way of limitation with reference to the figures.

[0064] Various embodiments are described herein with reference to the associated drawings, and alternative embodiments may be devised without departing from the scope of the disclosure.

[0065] Turning now to an overview of the technology more specifically related to aspects of the present invention, we disclose a newly developed SiC-AlN composite ceramic material, “JC-SiC,” having the composition shown below: α-Silicon carbide (average particle size 0.7μm) = 95.0~99.9wt% Aluminum nitride (nanoparticles) = 0.1 to 5.0 wt%

[0066] In one embodiment, the material can be formed as described below.

[0067] Silicon carbide and aluminum nitride powders are added to ethanol (200 proof) in a plastic container. Silicon nitride balls are used as the grinding media. The slurry is milled using a roller mill for 18-20 hours and dried at 90°C under vacuum. The powder thus obtained is sieved through a 300 micrometer screen. The powder is then consolidated using a combination of pressure (10-50 MPa) and temperature (1800-2100°C). The consolidated parts are machined and given a final surface finish.

[0068] A flow chart of this process is shown in FIG.

[0069] The proposed seal may address one or more of the problems identified below for the following seals: For example, the outboard seal of a two-seal system typically operates at low pressure but high speed. Materials exposed to such conditions must have high tensile strength to withstand hoop stresses due to high shaft rotational speeds, and high thermal conductivity combined with a low coefficient of thermal expansion to minimize thermal coning or tapering of the seal interface that would impair the ability of the seal surface grooves to generate a stable fluid film. The inboard seal of such a system operates at high pressure and seals process gases at high speeds. Materials exposed to such conditions must have high mechanical strength to minimize deformation of the parts due to pressure and abutment loads, and also high thermal conductivity combined with a low coefficient of thermal expansion to minimize thermal deformation of the seal parts. As with the outboard seal, a "form stable" seal interface gap is important for fluid film stability, but is also important for limiting leakage across the seal gap.

[0070] Simulation of the performance of the outboard seal of a turbo gas seal shows that the conventional gas seal ceramics (SiC and Si3 N 4 ) appear to suffer from excessive thermal interface taper at high speeds, limiting the maximum rated speed of these materials even before component stress levels become critically high. The reason is that high thermal gradients within the components increase the "thermal coning", or taper of the thermal sealing interface, as the viscous shear of the seal interface increases with speed, causing the interfacial gas seal grooves to generate less hydrodynamic lift. The result is that the fluid film gap "collapses" at high speeds, causing catastrophic failure of the entire gas seal.

[0071] However, the improved thermal properties of the JC-SiC material disclosed herein can reduce or minimize the change in flatness of the seal interface with speed. The fluid film gap can be maintained up to the maximum speed and hoop stress that the material can withstand. As an example, a conventional SiC material may be limited to a rotational speed of 140 m / s due to thermal coning, while a JC-SiC-S material with similar mechanical strength can reach speeds of over 250 m / s.

[0072] The present invention will now be further described with reference to the following examples, which are illustrative and should not be construed as limiting. EXAMPLES

[0073] [Example 1] Preparation of sintered silicon carbide material ("JC-SiC") Silicon carbide and aluminum nitride powders are added to ethanol (200 proof) in a plastic container. Silicon nitride balls are used as grinding media. The slurry is milled in a roller mill for 18-20 hours and dried at 90°C under vacuum. The powder thus obtained is sieved through a 300 micrometer screen. The powder is then consolidated using a combination of pressure (10-50 MPa) and temperature (1800-2100°C). The joined parts are then machined to size and given a final surface finish. The "JC-SiC-S" material was consolidated using the Spark Plasma Sintering (SPS) method, while the "JC-SiC-H" material was consolidated using the Hot Pressing (HP) method.

[0074] [Example 2] Characterization of SiC-AlN composite ceramics ("JC-SiC") and comparative ceramics

[0075] Furthermore, a performance simulation of the inboard seal of a turbo gas seal showed that the conventional gas seal ceramics (SiC and Si 3 N 4 It is clear that the JC-SiC face seal does not maintain the seal interface flatness well with increasing shaft speed. The reason is very similar to that of the outboard seal, where viscous heating of the gas at the seal interface and local cooling by expanding gas at the seal gap exit cause temperature gradients that affect the flatness (coning). As the shaft speed increases, these factors are amplified. The change in face flatness affects the stability of the fluid film or gap, which is expressed as film stiffness. Most importantly, the face flatness affects the seal leakage (increase). However, the improved thermal properties of the SiC-AlN composite ceramic (JC-SiC) material limit the change in interface flatness with speed. The fluid film gap can be maintained up to the highest speeds (limited only by the stress limits of the outboard seal components) without significant impact on the film stability and leakage.

[0076] For further illustration, Table 1 is provided below. Table 1 shows the key thermomechanical properties of JC-SiC materials (JC-SiC-S and JC-SiC-H) in comparison with commercially available solid phase sintered and liquid phase sintered materials, measured according to ASTM methods as described above unless otherwise noted. It can be seen that the JC material has the best of both self-sintered (SS SiC) and liquid phase sintered (LP SiC) silicon carbide properties.

[0077] [Table 1]

[0078] [Example 3] Tribological property evaluation To evaluate the tribological properties of JC materials and commercial SS SiC and LP SiC materials, a ball-on-disk (BoD) test was used (e.g., according to ASTM G-99). Figure 2 shows the steady coefficient of friction (CoF) of the above materials in air with a humidity of 60%. It can be seen that the CoF of JC SiC-S is about 1 / 3 of that of LP SiC and less than 1 / 2 of that of SS SiC.

[0079] A comparison of the coefficient of wear (CoW) in air with 60% humidity is shown in Figure 3. Here, the CoW of JC-SiC-S is approximately 2 1 / 2 lower than that of LP SiC and significantly lower than that of SS SiC.

[0080] To evaluate the CoW in a dry state, a BoD test was performed in a nitrogen atmosphere with a dew point temperature of -40°C. The results are shown in Figure 4.

[0081] Again, it is clear that the CoW of JC-SiC-S is the lowest compared to the commercially available SiC materials.

[0082] Tribological evaluations clearly highlight the advantages of the SiC-AlN composite ceramic (JC-SiC) material over other commercially available materials used for these applications under both wet and dry conditions.

[0083] [Example 4] Tensile strength evaluation Tensile strength was tested by spinning ring-shaped samples (outer diameter = 230 mm, inner diameter = 172, thickness = 17 mm) in a high-speed testing machine. The speed was increased in stages until the material broke. Based on the speed at break, the stress developed at that speed was calculated. Table 2 compares the spin test results of JC-SiC-S and commercial LP sintered SiC.

[0084] [Table 2]

[0085] The results show that JC-SiC-S is approximately 10% stronger than LP sintered SiC.

[0086] The term "about" is intended to include the degree of error associated with measurement of the particular quantity based on the equipment available at the time of filing.

[0087] The terms used herein are only for describing certain embodiments and are not intended to limit the disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly indicates otherwise. It will be further understood that as used herein, the terms "comprises" and / or "comprising" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0088] Additionally, the terms "coupled," "connected," and variations thereof describe having a path between two elements and do not imply a direct connection between the elements without an intervening element / connection between them. All of these variations are considered part of this specification. However, if specifically recited in the appended claims, any connection / coupling described may be a direct connection / coupling.

[0089] Connections and / or location relationships can be direct or indirect unless otherwise specified, and the invention is not intended to be limited in this respect. Thus, coupling of entities can refer to either direct couplings or indirect couplings, and location relationships between entities can be direct or indirect location relationships. Additionally, various tasks and process steps described herein can be combined into a more comprehensive procedure or process having additional steps or functionality not described in detail herein.

[0090] Although the present disclosure has been described with reference to exemplary embodiments or embodiments, those skilled in the art will recognize that various changes can be made and equivalents can be substituted for the elements without departing from the scope of the present disclosure. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope of the present disclosure. Therefore, it is not intended that the disclosure be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the disclosure, but rather that the disclosure includes all embodiments falling within the scope of the claims.

Claims

1. An unsintered composite powder composition comprising 90.0 wt% to 99.9 wt% (preferably 95.0 wt% to 99.9 wt%) of α-silicon carbide having an average particle size of 0.2 μm to 3 μm, and 0.1 wt% to 10 wt% (preferably 0.1 wt% to 5.0 wt%) of aluminum nitride nanoparticles having an average particle size of 10 nm to 500 nm.

2. An SiC-AlN composite ceramic material obtained by sintering the unsintered composite powder composition according to Claim 1, wherein the sintering includes hot pressing, spark plasma sintering, hot isostatic pressing (HIP), gas pressure sintering, or any combination thereof, and the composite ceramic material has the formula x(SiC) - 1 - x(AlN), where 0.999 ≥ x ≥ 0.900, a fracture toughness exceeding 4.5 MPa·m1 / 2, a thermal conductivity exceeding 120 W / mK, and the silicon carbide sintered body material having a particle size of 2.0 to 3.0 μm.

3. In the SiC - AlN composite ceramic material according to Claim 2, the SiC - AlN composite ceramic material has the formula ｘ (SiC) - １－ｘ (AlN), where 0.999 ≥ x ≥ 0.950, a SiC - AlN composite ceramic material.

4. In the SiC-AlN composite ceramic material according to Claim 2, the silicon carbide sintered body material has a fracture toughness of 5 MPa·m １／２ greater than or equal to. Preferably, the silicon carbide sintered body material has a fracture toughness of 5.0 to 6.0 MPa·m1 / 2, and the SiC-AlN composite ceramic material.

5. In the SiC-AlN composite ceramic material according to Claim 2, the silicon carbide sintered body material has a thermal conductivity of 110 W / mK to 150 W / mK, preferably 115 W / mK to 150 W / mK, more preferably 120 W / mK to 145 W / mK.

6. In the SiC-AlN composite ceramic material according to any one of Claims 2 to 5, the coefficient of thermal expansion of the silicon carbide sintered body material is less than 4×10 －６ / K, the SiC-AlN composite ceramic material.

7. In the SiC-AlN composite ceramic material according to Claim 2, the silicon carbide sintered body material has a flexural strength greater than or equal to 600 MPa, preferably 600 MPa to 850 MPa, more preferably 700 MPa to 850 MPa.

8. In the SiC-AlN composite ceramic material according to Claim 2, the silicon carbide sintered body material has an elastic modulus of 400 GPa to 450 GPa, preferably 420 GPa to 450 GPa.

9. In the SiC-AlN composite ceramic material according to Claim 2, the silicon carbide sintered body material has the following properties: (a) A density of 3.0 to 3.3 g / cm ３ and (b) A porosity of less than 5%, preferably less than 2.5%, more preferably less than 1%, and (c) A Poisson's ratio of 0.10 to 0.20, preferably 0.14 to 0.18 having one or more of the above.

10. The SiC - AlN composite ceramic material according to Claim 2, wherein the silicon carbide sintered body material has a coefficient of friction of less than 0.5, preferably less than 0.4, and most preferably less than 0.3 in a gaseous fluid (such as air, nitrogen, carbon dioxide, etc.) with a relative humidity of less than 60%. SiC - AlN composite ceramic material.

11. In the SiC - AlN composite ceramic material according to Claim 2, the silicon carbide sintered body material has a wear coefficient of less than 0.00001 mm ３ / Nm, preferably less than 0.000005 mm ３ / Nm, and / or a wear coefficient under dry conditions of less than 0.0001 mm ３ / Nm, preferably less than 0.000005 mm ３ / Nm, being the SiC - AlN composite ceramic material.

12. The SiC - AlN composite ceramic material according to Claim 2, wherein the silicon carbide sintered body material has a tensile strength of more than 300 MPa, preferably more than 350 MPa, and more preferably 375 MPa to 450 MPa. SiC - AlN composite ceramic material.

13. A process for manufacturing the unsintered composite powder composition according to Claim 1, comprising combining the α - silicon carbide powder having particles with an average particle size of 0.2 μm to 3 μm and the aluminum nitride nanopowder having particles with an average particle size of 10 nm to 500 nm in an amount of 90.0 wt% to 99.9 wt% (preferably 95.0 wt% to 99.9 wt%) of silicon carbide and 0.1 wt% to 10 wt% (preferably 0.1 wt% to 5.0 wt%) of aluminum nitride to form the unsintered composite powder composition. A process for manufacturing an unsintered composite powder composition.

14. The process according to Claim 13, wherein combining the silicon carbide powder and the aluminum nitride powder includes forming a slurry of the powders in a liquid medium, and the liquid medium includes a C1 - C5 aliphatic monohydric alcohol such as ethanol. Process.

15. The process according to Claim 14, wherein the process further includes grinding the slurry, and optionally, grinding the slurry includes using a roller mill, and preferably, grinding the slurry includes grinding the slurry by using silicon carbide balls as a grinding medium. Process.

16. The process according to Claim 13, further including drying the slurry, and drying the slurry in a vacuum and / or drying the slurry at a temperature of 80°C to 140°C. Process. **Claim 17**: A process for manufacturing the SiC—AlN composite ceramic material according to claim 2, the process comprising sintering the unsintered composite powder composition according to claim 1, wherein sintering the unsintered composite powder composition includes hot pressing, spark plasma sintering, hot isostatic pressing (HIP), gas pressure sintering, or any combination thereof. **Claim 18**: The process according to claim 17, wherein the sintering includes sintering at a temperature of 1800° C. or higher, preferably the sintering includes sintering at a temperature of 1800° C. to 2100° C., and / or the sintering includes sintering at a pressure of 5 MPa to 75 MPa, preferably the sintering includes sintering at a pressure of 10 MPa to 60 MPa. **Claim 19**: A molded article including a component formed of the SiC—AlN composite ceramic material according to claim 2, the molded article including a mechanical seal, a bearing, or a wear part, preferably the molded article is the mechanical seal, and the component is a mechanical seal surface. **Claim 20**: Use of the SiC—AlN composite ceramic material according to claim 3 for improving the resistance of a component of a mechanical seal surface to centrifugal stress (e.g., hoop stress).

Images