Microwave catalyst support and its preparation method

Abstract

This invention relates to the field of microwave catalysts, and discloses a microwave catalyst support and its preparation method. The microwave catalyst support has a columnar structure, and along the height direction of the support, the support is divided into n layers of honeycomb structure, wherein n≥4, and each layer of honeycomb structure has a pore density of 3-23 pores / cm². 2 The honeycomb structure has through-holes; wherein the through-holes of any two adjacent honeycomb structures are staggered; wherein the carrier is selected from one or more of carbon, alloy materials, metals, and ceramics. This invention uses 3D printing to prepare catalyst carriers, which have a wide range of material coverage, designable microstructures, and facilitate control and optimization of the material structure and the stepwise distribution of active sites. The preparation process is simple, controllable, and highly stable. The carrier bed has high porosity, low bed pressure drop, and high heat transfer efficiency with inert gas.

Description

Technical Field

[0001] This invention relates to the field of microwave catalysts, and more specifically to a microwave catalyst support and its preparation method. Background Technology

[0002] Microwaves are electromagnetic waves. When molecules in a substance are exposed to microwave irradiation, locally charged dipole molecules vibrate rapidly in the rapidly changing electromagnetic field of the microwaves. The collisions and friction between molecules raise the temperature of the substance itself, making it a highly efficient and clean heating energy source. By focusing high-intensity continuous or pulsed microwave radiation onto specific solid catalyst beds, microwaves can excite the active sites in the catalyst to generate energy. This not only catalyzes the reaction but also provides the necessary energy from within the reaction system. This effectively lowers the reaction temperature and provides a green and efficient solution to the high energy and material consumption of catalytic reactions in existing technologies.

[0003] Currently, catalyst supports used in the petrochemical industry are typically in the form of plates, rings, spheres, etc. To overcome the shortcomings of traditional catalyst supports, such as small bed porosity and large pressure drop, CN201871380U discloses a design of a hollow toothed spherical support. While this can increase the catalyst bed porosity and reduce the catalyst bed pressure drop, it also reduces the mass and heat transfer between the catalyst and reactants during the reaction process. Therefore, there is an urgent need to find a novel catalyst support suitable for microwave catalysis, with high bed porosity, low pressure drop, and favorable mass and heat transfer between the catalyst and reactants. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of small porosity and large pressure drop in the catalyst support bed and poor mass and heat transfer between the catalyst and reactants in the prior art, and to provide a microwave catalyst support and its preparation method.

[0005] To achieve the above objectives, the present invention provides a microwave catalyst support, wherein the support has a columnar structure and is divided into n layers of honeycomb structure along its height, wherein n≥4, and each layer of honeycomb structure has a pore density of 3-23 pores / cm². 2 through holes;

[0006] In this structure, the through holes of any two adjacent honeycomb layers are staggered with each other;

[0007] The carrier is selected from one or more of carbon, alloy materials, metals, and ceramics.

[0008] Another aspect of the present invention provides a method for preparing the above-mentioned carrier, wherein the carrier is prepared by 3D printing technology, comprising: designing a three-dimensional model of a carrier having a multi-layered honeycomb structure and writing a program, adding printing base material into the material cylinder of a 3D printer, and 3D printing the carrier according to the program;

[0009] The printing base material is selected from at least one of thermoplastic plastics, alloy materials, metals, and ceramic powders.

[0010] The microwave catalyst support provided by this invention is divided into n-layer honeycomb structure, with high bed porosity, low bed pressure drop, and high heat transfer efficiency with inert gas.

[0011] This invention uses 3D printing to prepare catalyst supports, which have a wide range of material coverage, designable microstructures, and facilitate the control and optimization of the material structure and the stepwise distribution of active sites. The preparation process is simple, controllable, and highly stable. Attached Figure Description

[0012] Figure 1 This is a schematic diagram showing the layer-by-layer disassembly of the microstructure of the catalyst support prepared by 3D printing in Example 1;

[0013] Figure 2 This is a schematic diagram of the pore offset structure of the upper and lower honeycomb structures of the catalyst support prepared by 3D printing in Example 1, viewed from the top of the support. Detailed Implementation

[0014] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0015] In this invention, unless otherwise stated, the term "height direction" in the specification refers to the direction of extension of the central axis of the column of the carrier, "top of the carrier" refers to the two ends of the column perpendicular to the central axis of the column, and directional terms such as "upper" and "lower" refer to the relative positions along the height direction.

[0016] This invention provides a microwave catalyst support, wherein the support has a columnar structure and is divided into n layers of honeycomb structure along its height, wherein n≥4, and each layer of honeycomb structure has a pore density of 3-23 pores / cm². 2 through holes;

[0017] In this structure, the through holes of any two adjacent honeycomb layers are staggered with each other;

[0018] The carrier is selected from one or more of carbon, alloy materials, metals, and ceramics.

[0019] The carrier provided in this invention is divided into n-layer honeycomb structures. Each honeycomb structure has vertically distributed through-holes, and the through-holes of adjacent honeycomb structures are staggered to form tortuous microchannels. For example, along the height direction, the carrier is divided into 6-layer honeycomb structures. A schematic diagram of layer-by-layer disassembly is shown below. Figure 1 As shown, the pore density of each layer of the honeycomb structure is 14-15 pores / cm². 2 In any two adjacent honeycomb structures, the center of the hole in the lower honeycomb structure is offset relative to the corresponding center of the hole in the upper honeycomb structure along the length of the hole side. The offset is 0.1-0.8 times the length of the hole side. For example, the hole offset of the upper and lower honeycomb structures visible from the top of the carrier is as follows: Figure 2 As shown. By increasing the porosity of the carrier and utilizing the staggered pore walls of each honeycomb structure to provide more active sites, segmented and regional reactions in the bed can be achieved, preventing local overheating.

[0020] According to a preferred embodiment of the present invention, the number of layers n in the honeycomb structure is 4-12, preferably 6-10. Under the above preferred conditions, it is beneficial to improve the contact efficiency between the catalyst and the material.

[0021] According to the present invention, the through-holes of the honeycomb structure can be selected as any regular opening shape. Preferably, the through-holes of the honeycomb structure are selected from one or more of the following: circular, equilateral triangular, square, and regular hexagonal cross-sections. In the above preferred cases, a larger specific surface area can be obtained, further increasing the active sites of the carrier.

[0022] According to the present invention, there is no specific limitation on the direction in which the through holes of any two adjacent honeycomb structures are staggered, as long as the above-mentioned structural requirements are met. Specifically, in any two adjacent honeycomb structures, the offset direction of the hole center of the lower honeycomb structure relative to the corresponding hole center of the upper honeycomb structure can be the same or different. For example, along the height direction of the carrier, the hole centers of each honeycomb structure layer can be offset sequentially in the same direction to form a stepped, partially overlapping honeycomb hole structure. Preferably, in any two adjacent honeycomb structures, the hole center of the through hole in the lower honeycomb structure is offset along the side length or diameter direction of the through hole relative to the corresponding hole center in the upper honeycomb structure.

[0023] According to a preferred embodiment of the present invention, the offset of the center of the hole in the honeycomb structure is 0.1-0.9 times the side length or diameter of the hole, preferably 0.1-0.5 times, and more preferably 0.1, 0.125, 0.25, 0.33, or 0.5 times.

[0024] According to the present invention, the size of the support can be controlled according to the specific catalytic reaction requirements. For example, the support can be filled as an integral honeycomb support or filled with small-sized support particles. When filled with small-sized support particles, the diameter of the support is preferably 5-10 mm and the height is 5-10 mm; more preferably, the diameter of the support is 6-8 mm and the height is 6-8 mm. In the above preferred cases, it is beneficial to increase the porosity of the overall catalytic system and reduce the packing density, which further helps to reduce the reactor pressure drop and increase the reaction space velocity.

[0025] According to the present invention, the range of selection for the carrier material is relatively wide. Preferably, the alloy material is selected from one or more of titanium alloy, aluminum alloy, copper alloy, zinc alloy, lead-tin alloy, ferromanganese alloy, carbon steel alloy, ferrosilicon alloy, potassium-sodium alloy, and nickel alloy; more preferably, it is selected from at least one of titanium alloy, copper alloy, and nickel alloy.

[0026] According to a preferred embodiment of the present invention, the metal is selected from one or more of Group VIII or IB metals; preferably one or more of iron, cobalt, nickel, copper, palladium, silver, gold, platinum, rhodium, and ruthenium; more preferably at least one of nickel, copper, palladium, and platinum.

[0027] According to a preferred embodiment of the present invention, the ceramic is selected from one or more of alumina, zirconium oxide, magnesium oxide, calcium oxide, beryllium oxide, titanium dioxide, and silicon carbide; preferably silicon carbide.

[0028] Another aspect of the present invention provides a method for preparing the above-mentioned carrier, wherein the carrier is prepared by 3D printing technology, comprising: designing a three-dimensional model of a carrier having a multi-layered honeycomb structure and writing a program, adding printing base material into the material cylinder of a 3D printer, and 3D printing the carrier according to the program; wherein the printing base material is selected from at least one of thermoplastic plastics, alloy materials, metals, and ceramic powders.

[0029] This invention offers a wide range of 3D printing technologies, and commonly used 3D printing technologies can be applied to this invention. Preferably, the 3D printing technology includes one or a combination of several of fused deposition modeling (FDM), selective laser melting (SLM), selective laser sintering (SLS), and selective thermal sintering (SLS); more preferably, it includes at least one of fused deposition modeling (FDM), selective laser melting (SLM), and selective laser sintering (SLS).

[0030] This invention does not impose any particular limitations on the parameters and conditions for 3D printing; any conditions known in the art can be used as long as the aforementioned carrier can be formed. According to a preferred embodiment of this invention, the 3D printing conditions include: a printing temperature of 150-1700℃ and a printing speed of 10-200 mm / s.

[0031] According to a preferred embodiment of the present invention, when the printing base material is thermoplastic, the carrier particles also need to undergo post-processing; wherein, the post-processing includes: placing the carrier particles in a quartz tube for calcination under vacuum conditions; preferably, the calcination conditions include: holding at 140-300°C for 1-4 hours, then raising the temperature to 700-1700°C and holding for 10-15 hours.

[0032] According to the present invention, the range of selection for the printing base material is relatively wide. Thermoplastic plastic refers to a polymer material that can flow when heated and maintain a certain shape after cooling. Preferably, the thermoplastic plastic is selected from one or more of polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), acrylonitrile-butadiene-styrene (ABS), nylon, polycarbonate (PC), polyurethane (PU), polytetrafluoroethylene (PTFF), polyethylene terephthalate (PET), and polylactic acid (PLA), and more preferably at least one of polypropylene, polylactic acid, and nylon.

[0033] According to a preferred embodiment of the present invention, the alloy material may be selected from easily formable alloy materials. Preferably, the alloy material is selected from one or more of titanium alloys, aluminum alloys, copper alloys, zinc alloys, lead-tin alloys, ferromanganese alloys, carbon steel alloys, ferrosilicon alloys, potassium-sodium alloys, and nickel alloys; more preferably, it is selected from at least one of titanium alloys, copper alloys, and nickel alloys.

[0034] According to a preferred embodiment of the present invention, the metal is selected from one or more of Group VIIIB or Group IB metals; preferably one or more of iron, cobalt, nickel, copper, palladium, silver, gold, platinum, rhodium, and ruthenium.

[0035] According to a preferred embodiment of the present invention, the ceramic is selected from one or more of alumina, zirconium oxide, magnesium oxide, calcium oxide, beryllium oxide, titanium dioxide, and silicon carbide; preferably silicon carbide.

[0036] The present invention will be described in detail below through embodiments.

[0037] Example 1

[0038] The 3D structure of the catalyst support was modeled using SolidWorks software. The catalyst support has a diameter of 6 mm, a length of 6 mm, and is cut into 6 layers along the height direction, with a layer height of 1 mm. Each layer has four circular through holes with a cross-sectional diameter of 2 mm, forming a honeycomb structure. Starting from the bottom, the center of the holes in the upper layer is offset by 1.66 mm relative to the center of the holes in the lower layer along any diameter direction. A schematic diagram of the layer-by-layer disassembly of the support is shown below. Figure 1 As shown. The 3D model is converted into an STL format file for layer stacking using the export module in the software. The obtained STL model file is then provided to the MakerBot Replicator R2 fused deposition modeling 3D printer. Polypropylene filament is added to the material cylinder of the 3D printer, and the printing temperature is set to 185℃ and the printing speed is 60mm / s to print catalyst carrier particles.

[0039] The printed catalyst support particles were placed in a quartz boat and then placed in a quartz tube. Dry nitrogen gas was introduced to replace the air in the tube for 30 minutes. The quartz tube was then evacuated to a vacuum of 1 mmHg using a vacuum pump. The quartz tube was heated to 145°C and held for 3 hours. After the catalyst support in the quartz boat turned black, the heating temperature was increased to 750°C and held for 12 hours. The catalyst support was completely carbonized, and microwave catalyst support S1 was obtained.

[0040] Example 2

[0041] The 3D structure of the catalyst support was modeled using SolidWorks software. The catalyst support was 8mm in diameter and 8mm in length, cut into 8 layers along the height direction, with a layer height of 1mm. Each layer had four through holes with a square cross-section of 2mm side length, forming a honeycomb structure. Starting from the bottom, the center of the holes in the upper layer was offset by 0.50mm relative to the center of the holes in the lower layer along any side. The constructed 3D model was converted into an STL format file for layer stacking using the software's export module. The obtained STL model file was provided to a MakerBot Replicator R2 fused deposition modeling 3D printer. Polylactic acid filament was added to the material cylinder of the 3D printer, and the printing temperature was set to 225℃ and the printing speed to 100mm / s to print the catalyst support particles.

[0042] The printed catalyst support particles were placed in a quartz boat and then placed in a quartz tube. Dry nitrogen gas was introduced to replace the air in the tube for 30 minutes. The quartz tube was then evacuated to a vacuum of 1 mmHg using a vacuum pump. The quartz tube was heated to 170°C and held for 3 hours. After the catalyst support in the quartz boat turned black, the heating temperature was increased to 1200°C and held for 12 hours. The catalyst support was completely carbonized, and microwave catalyst support S2 was obtained.

[0043] Example 3

[0044] The 3D structure of the catalyst support was modeled using SolidWorks software. The catalyst support was 6mm in diameter and 6mm in length, cut into 6 layers along the height direction, with a layer height of 1mm. Each layer had four through holes with a cross-section of regular hexagons and a side length of 2mm, forming a honeycomb structure. Starting from the bottom, the center of the holes in the upper layer was offset by 0.3mm relative to the center of the holes in the lower layer along any side. The constructed 3D model was converted into an STL format file of layer stacking using the software's export module. The obtained STL model file was provided to an EOSINT P760 selective laser sintering 3D printer. Nylon powder was added to the material cylinder of the 3D printer, and the printing temperature was set to 265℃ and the printing speed to 150mm / s to print the catalyst support particles.

[0045] The printed catalyst support particles were placed in a quartz boat and then placed in a quartz tube. Dry nitrogen gas was introduced to replace the air in the tube for 30 minutes. The quartz tube was then evacuated to a vacuum of 1 mmHg using a vacuum pump. The quartz tube was heated to 250°C and held for 3 hours. After the catalyst support in the quartz boat turned black, the heating temperature was increased to 1500°C and held for 12 hours. The catalyst support was completely carbonized, and microwave catalyst support S3 was obtained.

[0046] Example 4

[0047] The 3D structure of the catalyst support was modeled using SolidWorks software. The catalyst support was 6mm in diameter and 6mm in length, cut into 6 layers along the height direction, with a layer height of 1mm. Each layer had four through holes with a square cross-section of 2mm side length, forming a honeycomb structure. Starting from the bottom, the center of the holes in the upper layer was offset by 1.0mm relative to the center of the holes in the lower layer along any side. The constructed 3D model was converted into an STL format file of layer stacking using the software's export module. The obtained STL model file was provided to an EOSINT P760 selective laser sintering 3D printer. Silicon carbide ceramic powder was added to the material cylinder of the 3D printer, and the printing temperature was set to 1450℃ and the printing speed to 20mm / s, printing catalyst support particles S4.

[0048] Example 5

[0049] The 3D structure of the catalyst support was modeled using SolidWorks software. The catalyst support was 6 mm in diameter and 6 mm in length, cut into 6 layers along the height direction, with a layer height of 1 mm. Each layer had four circular through holes with a cross-sectional diameter of 2 mm, forming a honeycomb structure. Starting from the bottom, the center of the holes in the upper layer was offset by 1.0 mm relative to the center of the holes in the lower layer along any diameter direction. The constructed 3D model was converted into an STL format file of layer stacking using the software's export module. The obtained STL model file was provided to an EOSINT P760 selective laser sintering 3D printer. Titanium alloy microspheres were added to the material cylinder of the 3D printer, and the printing temperature was set to 1660℃ and the printing speed to 15 mm / s, printing catalyst support particles S5 were produced.

[0050] Comparative Example 1

[0051] 1 kg of polypropylene plastic granules were extruded into thin strips with a diameter of 5 mm using a strip press, and then cut into granules with a length of 5 mm. The granular carrier particles were placed in a quartz boat and then placed in a quartz tube. Dry nitrogen gas was introduced to replace the air in the tube for 30 minutes. The quartz tube was then evacuated to a vacuum of 1 mmHg using a vacuum pump. The quartz tube was heated to 145°C and held for 3 hours. After the catalyst carrier in the quartz boat turned black, the heating temperature was increased to 750°C and held for 12 hours. The catalyst carrier was completely carbonized, and catalyst carrier DS1 was obtained.

[0052] Comparative Example 2

[0053] 1 kg of polypropylene plastic granules were extruded into pentagonal strips with a diameter of 5 mm using a strip press, and then cut into granules with a length of 5 mm. The granular carrier particles were placed in a quartz boat and a quartz tube was placed inside. Dry nitrogen gas was introduced to replace the air in the tube for 30 minutes. The quartz tube was then evacuated to a vacuum of 1 mmHg using a vacuum pump. The quartz tube was heated to 145°C and maintained for 3 hours. After the catalyst carrier in the quartz boat turned black, the heating temperature was increased to 750°C and maintained for 12 hours. The catalyst carrier was completely carbonized, and the catalyst carrier DS2 was obtained.

[0054] Measure 10 mL of each of the catalyst supports S1-S5 and DS1 and DS2 using a graduated cylinder, and place them into quartz tubes with an inner diameter of 20 mm, a wall thickness of 6 mm, and a length of 500 mm. Fill the middle portion of the quartz tubes with catalyst support particles, and insert 5 mm diameter Al2O3 ceramic rings into both ends of the catalyst support. Fix the filled quartz tubes in the microwave radiation cavity of a microwave reactor, and control the flow rate of high-purity nitrogen gas to 15000 h⁻¹. -1The microwave radiation source was turned on and the power was adjusted to bring the temperature of the catalyst support to 300℃. After the system stabilized for 30 minutes, the fluid pressure and temperature before and after the catalyst support were measured. The pressure drop of the catalyst bed and the temperature rise of the inert fluid were calculated. The pressure drop of the catalyst bed and the temperature rise of the inert fluid after the experiment are shown in Table 1.

[0055] The porosity of the catalyst support was determined by the water injection method.

[0056] Table 1

[0057]

[0058]

[0059] The catalyst supports prepared by 3D printing in Examples 1-5 showed at least a 90% increase in catalyst porosity compared to the conventional configuration of Comparative Example 1. The catalyst bed pressure drop was essentially the same as in Comparative Example 2, but lower than in Comparative Example 1. However, the heat transfer of Examples 1-5 was higher than that of Comparative Example 2, reaching or even exceeding the level of Comparative Example 1. In summary, the catalyst supports prepared by 3D printing can improve the heat transfer efficiency between the catalyst and the inert gas while effectively reducing the catalyst bed pressure drop.

[0060] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A microwave catalyst support for reducing bed pressure drop and improving mass and heat transfer between the catalyst and reactants in microwave catalysis, characterized in that, The carrier has a columnar structure, and along its height, it is divided into n layers of honeycomb structure, where n ≥ 4, and each layer of honeycomb structure has a pore density of 3-23 pores / cm². 2 through holes; In this configuration, the through holes of any two adjacent honeycomb structures are staggered with each other; in any two adjacent honeycomb structures, the center of the through hole of the lower honeycomb structure is offset relative to the center of the corresponding through hole in the upper honeycomb structure along the side length or diameter of the through hole, and the offset is 0.25-0.5 times the side length or diameter of the through hole. The diameter of the carrier is 6-8 mm and the height is 6-8 mm; The carrier is selected from one or more of carbon, alloy materials, metals, and ceramics; the metal is selected from one or more of Group VIII or IB metals.

2. The carrier according to claim 1, wherein, The number of layers n in the honeycomb structure is 4-12; And / or, the through holes of the honeycomb structure are selected from one or more through holes with a cross-section of a circle, an equilateral triangle, a square, or a regular hexagon.

3. The carrier according to claim 2, wherein, The number of layers n in the honeycomb structure is 6-10.

4. The carrier according to any one of claims 1-3, wherein, The alloy material is selected from one or more of the following: titanium alloy, aluminum alloy, copper alloy, zinc alloy, lead-tin alloy, ferromanganese alloy, carbon steel alloy, ferrosilicon alloy, potassium-sodium alloy, and nickel alloy.

5. The carrier according to claim 4, wherein, The alloy material is selected from at least one of titanium alloys, copper alloys, and nickel alloys.

6. The carrier according to claim 1, wherein, The metal is selected from one or more of iron, cobalt, nickel, copper, palladium, silver, gold, platinum, rhodium, and ruthenium.

7. The carrier according to claim 6, wherein, The metal is selected from at least one of nickel, copper, palladium, and platinum.

8. The carrier according to any one of claims 1-3, wherein, The ceramic is selected from one or more of alumina, zirconium oxide, magnesium oxide, calcium oxide, beryllium oxide, titanium dioxide, and silicon carbide.

9. The carrier according to claim 8, wherein, The ceramic is silicon carbide.

10. A method for preparing a carrier according to any one of claims 1-9, characterized in that, The carrier is prepared by 3D printing technology, including: designing a three-dimensional model of a carrier with a multi-layered honeycomb structure and writing a program, adding printing base material into the material cylinder of a 3D printer, and 3D printing the carrier according to the program; The printing base material is selected from at least one of thermoplastic plastics, alloy materials, metals, and ceramic powders, and the metal is selected from one or more of group VIIIB or IB metals.

11. The method according to claim 10, wherein, The conditions for 3D printing include: a printing temperature of 150-1700℃ and a printing speed of 10-200mm / s.

12. According to claim 10, when the printing substrate is thermoplastic, the carrier further requires post-processing; in, The post-processing includes: calcining the carrier particles in a quartz tube under vacuum conditions; The roasting conditions include: holding at 140-300℃ for 1-4 hours, then raising the temperature to 700-1700℃ and holding for 10-15 hours.

13. The method according to claim 10, wherein, The thermoplastic is selected from one or more of polyethylene, polypropylene, polyvinyl chloride, polystyrene, acrylonitrile-butadiene-styrene, nylon, polycarbonate, polyurethane, polytetrafluoroethylene, polyethylene terephthalate and polylactic acid.

14. The method according to claim 13, wherein, The thermoplastic is at least one of polypropylene, polylactic acid, and nylon.

15. The method according to claim 10, wherein, The alloy material is selected from one or more of the following: titanium alloy, aluminum alloy, copper alloy, zinc alloy, lead-tin alloy, ferromanganese alloy, carbon steel alloy, ferrosilicon alloy, potassium-sodium alloy, and nickel alloy.

16. The method according to claim 15, wherein, The alloy material is at least one of titanium alloy, copper alloy, and nickel alloy.

17. The method according to claim 10, wherein, The metal is selected from one or more of iron, cobalt, nickel, copper, palladium, silver, gold, platinum, rhodium, and ruthenium.

18. The method according to claim 10, wherein, The ceramic is selected from one or more of alumina, zirconium oxide, magnesium oxide, calcium oxide, beryllium oxide, titanium dioxide, and silicon carbide.

19. The method according to claim 18, wherein, The ceramic is silicon carbide.

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