Method for rapidly preparing ZrO2 core toughened ZrC blocky ceramic material at low temperature

Abstract

The invention discloses a preparation method of a ZrO2 core toughened ZrC blocky ceramic material, zirconium nitrate, starch, urea and yttrium nitrate are used as raw materials for hydrothermal reaction to obtain a hydrothermal precursor of the ceramic material, and the hydrothermal precursor is subjected to freeze drying and SPS sintering to obtain the blocky ZrO2 toughened ZrC ceramic material with ZrO2 as a core and ZrC as a surface layer. According to the method, the size of the core ZrO2 can be changed by changing the ratio of the zirconium source to the carbon source in the raw materials, and the toughening effect is coordinated. The precursor powder is subjected to SPS sintering, amorphous carbon on the surface layer and ZrO2 completely react to generate ZrC, the core part is still ZrO2, finally, a unique core-shell structure with the core part being ZrO2 and the surface layer being ZrC is obtained, and the obvious effect on improving the toughness of the ZrC ceramic material is achieved. In addition, the controllability of the ZrO2 toughening effect can be realized by changing the size of ZrO2 at the core part.

Description

Technical Field

[0001] The invention relates to a method for rapidly preparing a ZrC ceramic material at low temperature. The ZrC ceramic material has a core-shell structure with ZrO2 in the core and ZrC in the surface. Background Art

[0002] With the rapid development of aerospace, military defense and industrial applications, the demand for ultra-high temperature ceramic materials is growing. Such materials have attracted much attention due to their excellent high-temperature stability, excellent oxidation resistance and good thermal shock resistance. ZrC ceramic materials have high melting point, low density, wear resistance, excellent temperature resistance and oxidation and ablation resistance. They are capable of serving in the nose cone, wing leading edge and aviation ramjet nozzle of hypersonic aircraft. As one of the candidate materials for extreme thermal components of hypersonic aircraft, it has become a research hotspot.

[0003] Although ZrC has the above advantages, its high sintering temperature, low density and high brittleness limit its application in extreme environments. The toughening phase of the ceramics prepared by conventional processes is easily enriched, reducing the toughening effect and leading to a decrease in mechanical properties, resulting in fracture failure. In order to ensure and improve its mechanical properties such as fracture toughness and optimize the preparation process, researchers have been exploring a scientific and effective method to improve the brittleness of ZrC ceramic materials. Summary of the invention

[0004] The present invention realizes the simultaneous completion of reaction and preparation, has a simple raw material production process, strong controllability, and an obvious ceramic toughening effect, which solves the brittleness limitation of ZrC ceramics in extreme environments such as high temperature. The toughening phase of the ceramics prepared by conventional processes is easily enriched, which reduces the toughening effect and leads to a decrease in mechanical properties, resulting in fracture failure, high energy consumption, and complex preparation process. Further, a preparation method for a ZrO2 core-toughened ZrC block ceramic material is proposed. The preparation method is a new type of "core toughening" mechanism. Through special precursor design and sintering process, a special core-shell structure with a core of ZrO2 and a surface of ZrC is formed inside the ZrC ceramic material to ensure and improve the overall toughness of the material.

[0005] The purpose of the present invention can be achieved by the following technical scheme: a preparation method of a ZrO2 core toughened ZrC bulk ceramic material, using zirconium nitrate, starch, urea, and yttrium nitrate as raw materials for hydrothermal reaction, freeze-drying the hydrothermal precursor to obtain a mixed powder of zirconium oxide and amorphous carbon, and SPS sintering the mixed powder to obtain a bulk ceramic material with a core of ZrO2 and a surface of ZrC. The preparation method of the ZrO2 core toughened ZrC bulk ceramic material comprises the following steps: Step 1: Raw material mixing: zirconium nitrate, starch, urea, and yttrium nitrate are used as raw materials, mixed evenly with 100 ml of deionized water according to a certain proportion, and then placed into the polytetrafluoroethylene lining of a stainless steel hydrothermal reactor; Step 2: hydrothermal reaction: subjecting the mixed raw materials in step 1 to a hydrothermal reaction at 200° C. for 20 h to obtain a precursor solution of the ceramic material, centrifuging the precursor solution, removing the supernatant to obtain a precursor mixed solution of zirconium oxide and amorphous carbon, and freeze-drying to obtain a mixed powder of zirconium oxide and amorphous carbon; Step 3: Spark plasma (SPS) sintering: The mixed powder after drying in step 2 is sintered using SPS technology.

[0006] A further technical improvement of the present invention is that in step 1, zirconium nitrate, starch, urea and yttrium nitrate are used as raw materials, and the zirconium-carbon ratio is 1:4 or 1:5 or 1:6 or 1:7.

[0007] A further technical improvement of the present invention is that the step of mixing zirconium nitrate, starch, urea and yttrium nitrate specifically includes: Step S11: zirconium nitrate, starch, urea and yttrium nitrate are accurately weighed according to the required ratio, wherein starch serves as a carbon source and urea provides an alkaline environment for the solution; Step S12: weighing zirconium nitrate, yttrium nitrate, starch and 100 ml of deionized water, mixing them with magnetic stirring for 30 minutes, and adding them into the polytetrafluoroethylene liner; Step S13: adding urea to the solution prepared in step S12, and mixing with magnetic stirring for 30 minutes to obtain a mixed solution; Step S14: fully stirring the mixed solution.

[0008] A further technical improvement of the present invention is that the specific steps of the hydrothermal reaction in step 2 include: Step S21: placing the polytetrafluoroethylene liner containing the mixed raw material solution in step 1 into a stainless steel hydrothermal reactor; Step S22: placing the reactor in a drying oven and setting the constant temperature at 200° C. Step S23: Maintaining the set temperature, the mixture is allowed to react under these conditions for 20 hours to obtain a hydrothermal precursor.

[0009] A further technical improvement of the present invention is that in the hydrothermal reaction of step 2, the hydrothermal precursor is repeatedly centrifuged three to five times with deionized water and anhydrous ethanol, and the supernatant is removed to obtain a mixed solution of zirconium oxide and amorphous carbon precursors, which is then freeze-dried in a freeze dryer, and the freeze dryer parameters are set to -50°C and 24h. After drying, a mixed powder of zirconium oxide and amorphous carbon is obtained.

[0010] A further technical improvement of the present invention is that in step 3, the specific steps of spark plasma (SPS) sintering include: Step S31: selecting a mixed powder of zirconium oxide and amorphous carbon with a suitable zirconium-carbon ratio, and setting SPS equipment parameters, including sintering temperature, pressure, heating rate and holding time; Step S32: placing the mold containing the mixed powder in step S31 into the SPS equipment with set parameters, and starting the sintering program; Step S33: performing SPS sintering under vacuum; Step S34: After the sintering in step S33 is completed, the ZrC block ceramic material is quickly cooled to room temperature to obtain a ZrO2 core toughened ZrC block ceramic material.

[0011] The further technical improvement of the present invention is that the parameters of the SPS equipment in S31 are: the sintering temperature is controlled at 1900°C, the pressure is controlled at 50MPa, the heating rate is controlled at 150-200°C / min, and the holding time is controlled at 10min.

[0012] A further technical improvement of the present invention is that in step S34, after sintering is completed, a vacuum environment is maintained for cooling.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) In the present invention, the preparation method adopts a core toughening method as a new type of toughening method for ZrC ceramic materials proposed for the first time. What is different from the existing toughening methods is that the mixed powder of zirconium oxide and amorphous carbon in the preparation method is directly prepared by a hydrothermal method, and the mixed powder has a carbon-coated core-shell structure, in which the core is ZrO2 and the surface is amorphous carbon. In addition, the prepared ZrO2 particles are so fine that they reach the nanometer level. During sintering, they can fully contact with the carbon on the surface and react smoothly to form ZrC. After SPS sintering, the amorphous carbon on the surface reacts with ZrO2 to form ZrC, thereby forming a unique core-shell structure with ZrO2 as the core. The thickness of the ZrC layer can be changed by the zirconium-carbon ratio of the raw materials to achieve core toughening, which helps to improve the fracture toughness of the material; (2) In the present invention, the mixed powder of zirconium oxide and amorphous carbon in the preparation method is obtained by changing the zirconium-carbon ratio, hydrothermal reaction and then drying, and the thickness of the ZrC layer is controlled by changing the zirconium-carbon ratio of the raw material to achieve optimization of the mechanical properties of the material; (3) The present invention proposes a method for preparing ZrC bulk ceramic materials with ZrO2 core toughening. Through innovative precursor design, precise hydrothermal synthesis process and SPS sintering technology, ultra-high temperature ceramic materials with excellent performance are successfully prepared. This method not only improves the fracture toughness and reliability of the material, but also opens up a new path for the further research and application of ultra-high temperature ceramic materials. DETAILED DESCRIPTION

[0014] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Embodiment 1

[0015] A method for preparing a ZrO2 core-toughened ZrC bulk ceramic material, the method for preparing a ZrO2 core-toughened ZrC bulk ceramic material comprising the following steps: Step 1: Mixing raw materials: Zirconium nitrate, starch, urea and yttrium nitrate are used as raw materials. The zirconium-carbon ratio of zirconium nitrate, starch, urea and yttrium nitrate is 1:5. Zirconium nitrate and yttrium nitrate are accurately weighed according to the required ratio, wherein starch is used as a carbon source and urea provides an alkaline environment for the solution. The weighed zirconium nitrate, yttrium nitrate, starch and 100 ml of deionized water are mixed with magnetic stirring for 30 minutes to obtain a mixed solution; urea is added to the mixed solution, and the mixture is mixed with magnetic stirring for 30 minutes, and the solution is added to the polytetrafluoroethylene liner.

[0016] Step 2: hydrothermal reaction: the polytetrafluoroethylene liner containing the mixed raw materials in step 1 is placed in a stainless steel hydrothermal reactor, the drying oven is set to a constant temperature of 200°C, the set temperature is maintained, and the mixture is allowed to react under these conditions for 20 hours, the hydrothermal precursor is centrifuged, the supernatant is removed to obtain a mixed solution of zirconium oxide precursor and amorphous carbon, and freeze-dried to obtain a mixed powder of zirconium oxide and amorphous carbon; Step 3: Spark plasma sintering (SPS): The mixed powder (zirconium-carbon ratio of 1:5) dried in step 2 is placed in an SPS sintering mold, and the SPS equipment parameters are set. The sintering temperature is controlled at 1900°C, the pressure is controlled at 50MPa, the heating rate is controlled at 150°C / min, and the holding time is controlled at 10min. The mold containing the mixed powder is placed in the SPS equipment with set parameters, and the sintering program is started. SPS sintering is performed under vacuum. After sintering, the vacuum environment is maintained for cooling to obtain a ZrO2 core-toughened ZrC block ceramic material. Embodiment 2

[0017] A method for preparing a ZrO2 core-toughened ZrC bulk ceramic material, the method for preparing a ZrO2 core-toughened ZrC bulk ceramic material comprising the following steps: Step 1: Mixing raw materials: Zirconium nitrate, starch, urea and yttrium nitrate are used as raw materials. The zirconium-carbon ratio of zirconium nitrate, starch, urea and yttrium nitrate is 1:6. Zirconium nitrate and yttrium nitrate are accurately weighed according to the required ratio, wherein starch is used as a carbon source and urea provides an alkaline environment for the solution. The weighed zirconium nitrate, yttrium nitrate, starch and 100 ml of deionized water are mixed with magnetic stirring for 30 minutes to obtain a mixed solution; urea is added to the mixed solution, and the mixture is mixed with magnetic stirring for 30 minutes, and the solution is added to the polytetrafluoroethylene liner.

[0018] Step 2: hydrothermal reaction: the polytetrafluoroethylene liner containing the mixed raw materials in step 1 is placed in a stainless steel hydrothermal reactor, the drying oven is set to a constant temperature of 200°C, the set temperature is maintained, and the mixture is allowed to react under these conditions for 20 hours, the hydrothermal precursor is centrifuged, the supernatant is removed to obtain a mixed solution of zirconium oxide precursor and amorphous carbon, and freeze-dried to obtain a mixed powder of zirconium oxide and amorphous carbon; Step 3: Spark plasma sintering (SPS): The mixed powder (zirconium-carbon ratio of 1:6) dried in step 2 is placed in an SPS sintering mold, and the SPS equipment parameters are set. The sintering temperature is controlled at 1900°C, the pressure is controlled at 50MPa, the heating rate is controlled at 200°C / min, and the holding time is controlled at 10min. The mold containing the mixed powder is placed in the SPS equipment with set parameters, and the sintering program is started. SPS sintering is performed under vacuum. After the sintering is completed, the vacuum environment is maintained for cooling to obtain a ZrO2 core-toughened ZrC bulk ceramic material.

[0019] After experiments, it is more appropriate to use a mixed powder with a zirconium-carbon ratio of 1:5, 200°C, 20h, and freeze-dried as a precursor powder for ZrO2 core toughening ZrC bulk ceramic materials.

[0020] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a ZrO2 core toughened ZrC bulk ceramic material, wherein zirconium nitrate, starch, urea, and yttrium nitrate are used as raw materials for hydrothermal reaction to obtain a hydrothermal precursor of the ceramic material, the hydrothermal precursor is freeze-dried, and SPS sintered to finally obtain a bulk ceramic material with a ZrO2 core and a ZrC surface layer, characterized in that: The preparation process of the bulk ceramic material comprises the following steps: Step 1: Raw material mixing: zirconium nitrate, starch, urea, and yttrium nitrate are used as raw materials, mixed evenly with 100 ml of deionized water according to a certain proportion, and then placed in a polytetrafluoroethylene liner in a stainless steel hydrothermal reactor; Step 2: hydrothermal reaction: subjecting the mixed raw materials in step 1 to a hydrothermal reaction at 200° C. for 20 h to obtain a hydrothermal precursor of the ceramic material, subjecting the hydrothermal precursor to multiple centrifugation, removing the supernatant to obtain a mixed solution of zirconium oxide and amorphous carbon precursors, and subjecting the mixed solution to freeze-drying treatment to obtain a mixed powder of zirconium oxide and amorphous carbon; Step 3: Spark plasma sintering (SPS): The mixed powder after drying in step 2 is sintered using SPS technology.

2. The method for preparing a ZrO2 core toughened ZrC bulk ceramic material according to claim 1, characterized in that: In step 1, the zirconium-to-carbon ratio of zirconium nitrate, starch, urea and yttrium nitrate is 1:4 or 1:5 or 1:6 or 1:

7.

3. The method for preparing a ZrO2 core toughened ZrC bulk ceramic material according to claim 2, characterized in that: The steps of mixing zirconium nitrate, starch, urea and yttrium nitrate specifically include: Step S11: zirconium nitrate, starch, urea and yttrium nitrate are accurately weighed according to the required ratio, wherein starch serves as a carbon source and urea provides an alkaline environment for the solution; Step S12: Mix the weighed zirconium nitrate, yttrium nitrate, starch and 100 ml of deionized water with magnetic stirring for 30 minutes, and add the mixture into the polytetrafluoroethylene liner; Step S13: adding urea to the solution prepared in step S12, and mixing by magnetic stirring for 30 minutes to obtain a mixed solution.

4. The method for preparing a ZrO2 core toughened ZrC bulk ceramic material according to claim 1, characterized in that: The specific steps of the hydrothermal reaction in step 2 include: Step S21: placing the polytetrafluoroethylene liner containing the mixed raw materials in step 1 into a stainless steel hydrothermal reactor; Step S22: placing the reactor in a drying oven and setting the constant temperature at 200° C. Step S23: Maintaining the set temperature, the mixture is allowed to react under these conditions for 20 hours to obtain a hydrothermal precursor.

5. The method for preparing a ZrO2 core toughened ZrC bulk ceramic material according to claim 1, characterized in that: In the hydrothermal reaction of step 2, the hydrothermal precursor is repeatedly centrifuged three to five times with deionized water and anhydrous ethanol, and the supernatant is removed to obtain a mixed solution of zirconium oxide and amorphous carbon precursors, which is then freeze-dried in a freeze dryer. The freeze dryer parameters are set to -50°C and 24h. After drying, a mixed powder of zirconium oxide and amorphous carbon is obtained.

6. The method for preparing a ZrO2 core toughened ZrC bulk ceramic material according to claim 1, characterized in that: In step 3, the specific steps of spark plasma sintering (SPS) include: Step S31: Select a mixed powder of zirconium oxide and amorphous carbon with a suitable zirconium-carbon ratio and put it into an SPS sintering mold, and set SPS equipment parameters, including sintering temperature, pressure, heating rate and holding time; Step S32: placing the mold containing the mixed powder in step S31 into the SPS equipment with set parameters, and starting the sintering program; Step S33: performing SPS sintering under vacuum; Step S34: After the sintering in step S33 is completed, the ZrC block ceramic material is quickly cooled to room temperature to obtain a ZrO2 core toughened ZrC block ceramic material.

7. The method for preparing a ZrO2 core toughened ZrC bulk ceramic material according to claim 6, characterized in that: The parameters of the SPS equipment in S31 are: sintering temperature is controlled at 1900°C, pressure is controlled at 50MPa, heating rate is controlled at 150-200°C / min, and holding time is controlled at 10min.

8. The method for preparing a ZrO2 core toughened ZrC bulk ceramic material according to claim 6, characterized in that: In step S34, after sintering is completed, the vacuum environment is maintained for cooling.