CN1240640C - Method preparing BN/SiO2 composite ceramics through dipping, and cracking precursor body - Google Patents

Abstract

The present invention relates to a method for preparing BN/SiO2 composite ceramics by immersing and cracking precursors, which belongs to a method for preparing ceramic material. The existing hot-pressing sintering method has the disadvantages of directional arrangement of tissue, anisotropic performance, etc. The method of the present invention comprises: a) B powder and BN powder are used as raw material to be processed and shaped; b) the shaped material is sintered in the atmosphere of nitrogen with one atmospheric pressure to obtain porous boron nitride ceramics, wherein the sintering temperature is from 1500 DEG C to 1600 DEG C, and the heat preservation time is from 4 hours to 5 hours; c) the porous boron nitride ceramics are immersed in poly carbon silicon alky solution for 32 hours to hours at room temperature under the condition of vacuum; d) the immersed product is oxidized and cracked at the temperature of 800 DEG C; e) the oxidized and cracked product is sintered for 2 hours at the temperature of 1300 under the protection of nitrogen with one atmospheric pressure, and the BN/SiO2 composite material is obtained. The BN/SiO2 composite material prepared by the method of the present invention has the advantages of uniform tissue, dispersive distribution, no directional arrangement and good comprehensive performance; because pressure is not applied in the whole reaction sintering process, the present invention has the advantages that the rate of finished products is improved, the sintering temperature is reduced by 300 DEG C to 500 DEG C than hot-pressed sintering temperature, and the cost is reduced.

Description

Method for Preparing BN/SiO2 Composite Ceramics by Impregnation and Cracking of Precursor

Technical field:

The invention relates to a method for preparing a ceramic material, in particular to a method for preparing a BN/ _SiO2 composite material by impregnating a porous BN ceramic substrate with a precursor polycarbosilane and then cracking it.

Background technique:

BN and SiO ₂ ceramics are excellent high-temperature wave-transmitting materials due to their low dielectric constant and low dielectric loss, excellent thermal conductivity, thermal shock resistance, and chemical stability. In the past, hot pressing sintering was often used to prepare BN/SiO ₂ composite materials. The typical hot pressing sintering process is a pressure of 10-30Mpa, a temperature of 1600-1800°C, and a density of 95%. However, the existing hot-pressing sintering method has the following problems: the structure after hot-pressing sintering presents directional arrangement, and the performance is anisotropic. For large-scale component materials, the higher the density, the worse the thermal shock resistance, especially when using hot-pressing The sintering method is too expensive to prepare large-scale and complex-shaped components, and there are still great difficulties.

Invention content:

The purpose of the present invention is to provide a method for preparing BN/SiO ₂ composite ceramics by impregnating and pyrolyzing a precursor, which is suitable for pressureless sintering and for the preparation of large and complex components. The operation steps of the present invention are: a. using B and BN powders with a particle size of 3 to 5 μm as raw materials, and the mass ratio of B and BN is 5 to 20: 80 to 95, for mixing, granulating and molding; b. Then place the compact with a density of 1.4-1.6g/ ^cm3 in a sintering furnace, sinter in a nitrogen atmosphere at an atmospheric pressure, the sintering temperature is 1500-1600°C, and the holding time is 4-5 hours to obtain porous boron nitride ceramics; c. impregnating porous boron nitride ceramics in the precursor polycarbosilane solution, immersing them at room temperature under vacuum for 32 to 40 hours, and drying to obtain prefabricated blocks; ^d . The prefabricated block is oxidized and cracked in an air furnace at 800°C, and the holding time is 3 to 4 hours; e. Then sintered in a vacuum sintering furnace at 1300°C and an atmospheric pressure of nitrogen for 2 hours to obtain BN/SiO ₂ composite materials. The effect of the present invention is that: the BN/ _SiO2 composite material tissue prepared by the method of the present invention is uniformly dispersed and distributed without directional arrangement, and has good comprehensive performance; because the whole process of reaction sintering does not apply pressure, the yield of finished products is improved, and the specific heat of sintering temperature Pressing and sintering reduces the temperature by 300-500°C, reducing the cost.

Detailed ways:

Specific embodiment one: the operating steps of this embodiment are: a. be raw material with B and BN powder of 3～5 μ m in particle diameter, by mass ratio, the mass ratio of B and BN is (5～20): (80 ~95), according to the conventional process of mixing, granulation, molding; b. Then put the green compact with a density of 1.4 ~ 1.6g/cm ³ in a sintering furnace, and sinter in a nitrogen atmosphere at an atmospheric pressure, and the sintering temperature is 1500 ~1600°C, holding time 4-5 hours, to obtain porous boron nitride ceramics; c. impregnate the porous boron nitride ceramics with the precursor polycarbosilane solution, and impregnate them at room temperature for 32-40 hours under vacuum conditions, after drying Obtain a prefabricated block; d. Oxidize and crack the prefabricated block with a density not exceeding 1.75g/ ^cm3 in an air furnace at 800°C for 3 to 4 hours; e. Then oxidize and crack the prefabricated block at 1300°C and one atmospheric pressure under nitrogen protection conditions. Then sinter in a vacuum sintering furnace for 2 hours to obtain the BN/SiO ₂ composite material.

Specific embodiment two: the operation steps of this embodiment are: a. use B and BN powders with a particle size of 3 to 5 μm as raw materials, and in terms of mass ratio, the mass ratio of B and BN is 5:95, and then pour the powder containing In the 120# gasoline of 1% styrene-butadiene rubber binding agent, after fully mixing, dry pressing molding, by controlling the stroke of pressure head, the density of controlling compact is 1.40g/cm ; ^b . put compact into multi-functional Sinter in a vacuum sintering furnace, vacuumize before 600°C, the vacuum degree is 3×10 ^-2 Pa, heat up slowly at a rate of 200°C/h, keep warm at 200°C for 1 hour, keep warm at 600°C for 1 hour, and then pass Nitrogen gas was introduced, the nitrogen pressure was 1.1-1.2 atmospheres, the temperature was raised to 1500°C at a rate of 100°C/h and kept for 4 hours to obtain a porous BN ceramic matrix with a density of 1.40g/cm ³ and a porosity of 38.4%. c: Porous BN ceramics impregnated with polycarbosilane/n-hexane solution, the mass ratio of polycarbosilane and n-hexane is 50:100, soaked at room temperature for 40 hours under vacuum conditions, then taken out and dried; d. The prefabricated blocks exceeding 1.75g/ ^cm3 are placed in an air heating furnace and slowly heated to 800°C for oxidative cracking, and the holding time is 3 hours. The BN/SiO ₂ ceramics were prepared by keeping the temperature for 2 hours under nitrogen protection condition at atmospheric pressure. According to experiments, the obtained BN/SiO ₂ ceramic has a density of 1.52g/cm ³ , a bending strength of 62Mpa, a dielectric constant of 3.50, and a dielectric loss of 2.0×10 ^-3 .

Specific embodiment three: the operation steps of this embodiment are: a. take B and BN powders with a particle size of 3 to 5 μm as raw materials, and in terms of mass ratio, the mass ratio of B and BN is 10:90, and pour the powder containing 1 In 120# gasoline of % styrene-butadiene rubber binding agent, after fully mixing dry pressing molding, the density that obtains green compact by controlling the stroke of pressure head is 1.45g/cm ; ^b . put green compact in multifunctional vacuum sintering Sintering in the furnace, vacuum before 600°C, the vacuum degree is 3×10 ^-2 Pa, slowly raise the temperature, the heating rate is 200°C/h, keep warm at 200°C for 1 hour, keep warm at 600°C for 1 hour, and then pass nitrogen , the nitrogen pressure is 1.1 to 1.2 atmospheres, and the temperature is raised to 1550°C at a speed of 100°C/h and kept for 5 hours to obtain a porous BN ceramic matrix with a density of 1.42g/cm ³ and a porosity of 37.5%; c. Porous BN ceramics are impregnated with polycarbosilane/n-hexane solution, the mass ratio of polycarbosilane and n-hexane is 50:100, soaked at room temperature under vacuum conditions for 36 hours and then taken out and dried; d. Then the density does not exceed 1.75g/cm The prefabricated block of ³ is placed in an air heating furnace and slowly heated to 800°C for oxidative cracking, and kept for 3.5 hours. e. It is further densified in a vacuum sintering furnace under an atmosphere of nitrogen protection at an atmospheric pressure, and kept at 1300°C for 2 hours. , that is, BN/SiO ₂ ceramics are obtained, the density of the obtained BN/SiO ₂ ceramics is 1.56g/cm ³ , the bending strength is 64Mpa, the dielectric constant is 3.56, and the dielectric loss is 4.4×10 ^-3 .

Specific embodiment four: a. be the B and BN powder of 3～5 μm with particle diameter as raw material, by mass ratio, the mass ratio of B and BN is 15: 85, pour into the powder that contains 1% styrene-butadiene rubber binding agent 120# gasoline, dry press molding after fully mixing, by controlling the stroke of the pressure head, the density of the compact is 1.45g/cm ³ , b. Sinter the compact in a multi-functional vacuum sintering furnace, before 600℃ Vacuumize, the vacuum degree is 3×10 ^-2 Pa, slowly raise the temperature, the heating rate is 200°C/h, keep warm at 200°C for 1 hour, keep warm at 600°C for 1 hour, then feed nitrogen, nitrogen pressure is 1.1～1.2 Atmospheric pressure, heat up to 1550°C at a rate of 100°C/h and keep warm for 5 hours to obtain a porous BN ceramic matrix with a density of 1.50g/cm ³ and a porosity of 33.9%; c. Porous BN ceramics impregnated with polycarbosilane/n-hexane alkane solution, the mass ratio of polycarbosilane and n-hexane is 50:100, soak at room temperature under vacuum for 36 hours, then take it out and dry it; d. Then place the prefabricated block with a density not exceeding 1.75g/ ^cm3 in an air heating furnace Slowly heat up to 800°C for oxidative cracking, holding time for 4 hours, e. Put it in a vacuum sintering furnace under an atmosphere of nitrogen protection at an atmospheric pressure for further densification, and keep it at 1300°C for 2 hours to prepare BN/SiO ₂ ceramics. According to experiments, the density of the obtained BN/SiO ₂ ceramics is 1.65g/cm ³ , the bending strength is 78Mpa, the dielectric constant is 3.78, and the dielectric loss is 3.4×10 ^-3 .

Specific embodiment five: the operation steps of this embodiment are: a. take B and BN powders with an average particle size of 3 to 5 μm as raw materials, and in terms of mass ratio, the mass ratio of B and BN is 20:80, and pour the powder containing 1 In the 120# gasoline of % styrene-butadiene rubber binding agent, after fully mixing dry pressing molding, by controlling the stroke of pressure head, the density that obtains green compact is 1.45g/cm ; ^b . green compact is placed in multifunctional vacuum Sintering in a sintering furnace, vacuum before 600°C, the vacuum degree is 3×10 ^-2 Pa, slowly heat up, the heating rate is 200°C/h, keep warm at 200°C for 1 hour, keep warm at 600°C for 1 hour, and then pass through Nitrogen, the nitrogen pressure is 1.1-1.2 atmospheric pressure, the temperature is raised to 1550°C at a speed of 100°C/h and kept for 5 hours, and a porous BN ceramic matrix is obtained. The density of the BN ceramic matrix is 1.54g/cm ³ , and the porosity is 32%; C .Porous BN ceramics are impregnated with polycarbosilane/n-hexane solution, the mass ratio of polycarbosilane and n-hexane is 50:100, soaked at room temperature under vacuum conditions for 32 hours, then taken out and dried; d. Then placed in an air heating furnace Slowly heat up to 800°C for oxidative cracking, holding time for 4 hours, e. Place it in a vacuum sintering furnace under an atmosphere of nitrogen protection at an atmospheric pressure for further densification, and hold at 1300°C for 2 hours to prepare BN/SiO ₂ ceramics, the density of the obtained BN/SiO ₂ ceramics is 1.69g/cm ³ , the bending strength is 94Mpa, the dielectric constant is 3.73, and the dielectric loss is 3.0×10 ^-3 .

Specific embodiment six: In this embodiment, the specific parameters in the operation process are optimized to the following results: a. The B and BN powders with a particle size of 3 to 5 μm are used as raw materials, and the mass ratio of B and BN is 5:95 or 10: 90 or 15:85 or 20:80, mix, granulate, and shape according to the conventional process; b. Then place the compact with a density of 1.4 to 1.6g/cm ³ in a sintering furnace, in an atmosphere of nitrogen at an atmospheric pressure Sintering, the sintering temperature is 1550°C, the holding time is 4.5 hours, and the porous boron nitride ceramics are obtained; c. The porous boron nitride ceramics are impregnated with the precursor polycarbosilane solution, and immersed at room temperature for 36 hours under vacuum conditions, and dried Finally, the prefabricated block is obtained; d. The prefabricated block with a density not exceeding 1.75g/ ^cm3 is oxidized and cracked in an air furnace at 800°C, and the holding time is 3 to 4 hours; e. Then, the prefabricated block is protected at 1300°C and an atmospheric pressure of nitrogen. Sinter in a vacuum sintering furnace for 2 hours under the same conditions to obtain the BN/SiO ₂ composite material.

In practical operation, it is impossible to control each specific numerical value to be absolutely consistent with the numerical value described in the present invention, so even if in practice each numerical value deviates slightly from the numerical value described in the present invention, such as "one atmosphere", in the specific embodiment, it is "1.1-1.2 atmospheric pressure" can also achieve the purpose of the present invention, which should also be within the protection scope of the present invention.

Claims (3)

1, a kind of precursor infiltration and pyrolysis prepares BN/SiO ₂The method of composite ceramics is characterized in that its operation steps is: a. is that B and the BN powder of 3～5 μ m is raw material with particle diameter, and the mass ratio of B and BN is 5～20: 80～95, carries out batch mixing, granulation, moulding; B. be 1.4～1.6g/cm with density then ³Pressed compact place sintering oven, sintering in an atmospheric nitrogen atmosphere, sintering temperature is 1500～1600 ℃, soaking time 4～5 hours obtains the porous boron nitride ceramics; C. the porous boron nitride ceramics be impregnated in the precursor Polycarbosilane solution, the room temperature dipping is 32～40 hours under the condition of vacuumizing, and gets prefabricated section after the drying; D. density is no more than 1.75g/cm ³Prefabricated section under 800 ℃ of conditions in air furnace oxicracking, soaking time 3～4 hours; E. then under 1300 ℃, one atmospheric nitrogen protection condition in vacuum sintering furnace sintering 2 hours, promptly get BN/SiO ₂Matrix material.

2, precursor infiltration and pyrolysis according to claim 1 prepares BN/SiO ₂The method of composite ceramics is characterized in that precursor Polycarbosilane solution is Polycarbosilane/hexane solution in the c step, and the mass ratio of Polycarbosilane and normal hexane is 50: 100.

3, precursor infiltration and pyrolysis according to claim 1 and 2 prepares BN/SiO ₂The method of composite ceramics is characterized in that in the operating process that concrete parameter is: a. is that B and the BN powder of 3～5 μ m is raw material with particle diameter, and the mass ratio of B and BN is 5: 95 or 10: 90 or 15: 85 or 20: 80, carries out batch mixing, granulation, moulding; B. be 1.4～1.6g/cm with density then ³Pressed compact place sintering oven, sintering in an atmospheric nitrogen atmosphere, sintering temperature is 1550 ℃, soaking time 4.5 hours obtains the porous boron nitride ceramics; C. the porous boron nitride ceramics be impregnated in the precursor Polycarbosilane solution, the room temperature dipping is 36 hours under the condition that vacuumizes, and gets prefabricated section after the drying; D. density is no more than 1.75g/cm ³Prefabricated section under 800 ℃ of conditions in air furnace oxicracking, soaking time 3～4 hours; E. then under 1300 ℃, one atmospheric nitrogen protection condition in vacuum sintering furnace sintering 2 hours, promptly get BN/SiO ₂Matrix material.