阅读说明：本技术 高强度透明氮化硅陶瓷的高温高压制备方法 (High-temperature high-pressure preparation method of high-strength transparent silicon nitride ceramic ) 是由 马帅领 崔田 陶强 朱品文 包括 于 2020-06-09 设计创作，主要内容包括：本发明的高强度透明氮化硅陶瓷的高温高压制备方法属于透明氮化硅陶瓷材料制备的技术领域,以微米α-Si<Sub>3</Sub>N<Sub>4</Sub>和纳米β-Si<Sub>3</Sub>N<Sub>4</Sub>混合物为原料,经过原料混合、压块、组装、高温高压合成、冷却卸压的工艺过程制得β-Si<Sub>3</Sub>N<Sub>4</Sub>透明陶瓷材料。本发明工艺流程简单,不需要添加烧结助剂；简化了透明陶瓷材料的制备流程,缩短了材料制备周期和烧结时间；通过温度和压力来调节氮化硅(β-Si<Sub>3</Sub>N<Sub>4</Sub>)的形貌和性能,制备出了高强度的透明氮化硅(β-Si<Sub>3</Sub>N<Sub>4</Sub>)陶瓷。(The invention relates to a high-temperature high-pressure preparation method of high-strength transparent silicon nitride ceramic, belonging to the technical field of preparation of transparent silicon nitride ceramic materials, and the high-temperature high-pressure preparation method is characterized in that micron α -Si is used 3 N 4 And nano β -Si 3 N 4 The β -Si is prepared by using the mixture as raw material and through the processes of raw material mixing, briquetting, assembling, high-temperature high-pressure synthesis, cooling and pressure relief 3 N 4 The method has simple process flow, does not need to add sintering aids, simplifies the preparation process of the transparent ceramic material, shortens the preparation period and the sintering time of the material, and regulates the silicon nitride (β -Si) by temperature and pressure 3 N 4 ) The appearance and the performance of the silicon nitride are adopted to prepare the high-strength transparent silicon nitride (β -Si) 3 N 4 ) A ceramic.)

1. A high-temp and-pressure process for preparing high-strength transparent silicon nitride ceramics (micron α -Si)₃N₄And nano β -Si₃N₄The β -Si is prepared by using the mixture as raw material and through the processes of raw material mixing, briquetting, assembling, high-temperature high-pressure synthesis, cooling and pressure relief₃N₄A transparent ceramic material; the pressing block is formed by pressing the raw materials of the mixture into a cylinder shape according to the size of the synthesis cavity by using a hydraulic machine; the assembly is that the blocky cylindrical raw materials are put into a heating container and then are put into a synthesis cavity; the high-temperature high-pressure synthesis is carried out for 15-60 min under the conditions that the pressure is 3.0-5.5 GPa and the temperature is 1400-2000 ℃; and the step of cooling and pressure relief is that the sample is naturally cooled to normal temperature after the electrification and the heating are stopped, and then the pressure is relieved to normal pressure.

2. The high-temperature high-pressure preparation method of high-strength transparent silicon nitride ceramic according to claim 1, wherein the high-temperature high-pressure synthesis is carried out at a synthesis temperature of 1800 ℃ and a synthesis pressure of 5.5 GPa.

3. The high-temperature high-pressure preparation method of high-strength transparent silicon nitride ceramic according to claim 1 or 2, characterized in that α -Si is contained in the raw material₃N₄The particle size of the β -Si is 1-10 microns and accounts for 90 percent of the total mass of the mixture₃N₄The particle size of (A) is 100nm, which accounts for 10% of the total mass of the mixture.

Technical Field

The invention belongs to the technical field of preparation of transparent silicon nitride ceramic materials, and particularly relates to silicon nitride (β -Si)₃N₄) The high-temperature high-pressure preparation method.

Background

Transparent ceramics are a novel optical material, and the transparent ceramic material has the advantages of high strength, high temperature resistance, wear resistance, acid and alkali corrosion resistance and the like besides the optical properties which are comparable to those of common optical materials (such as single crystals and glass), shows incomparable flexibility in the aspect of optical system design, and is an irreplaceable optical material in the modern society. When the ceramic is used as key components such as infrared windows and fairings in the fields of transparent armor, high-pitch missile and aerospace, the transparent ceramic is required to have higher mechanical strength, shock resistance, lower density and stronger chemical stability, so that the research of special transparent materials under the condition of super-long service becomes a hot spot of domestic and foreign research gradually. The silicon nitride has a series of excellent performances of low density, high specific strength, thermal shock resistance, creep resistance, corrosion resistance, wear resistance and the like, is a ceramic material with high strength, chemical stability and good optical transmittance, is a potential system for preparing novel transparent ceramic materials, and has important significance for the performance research and even development and application of the prepared transparent nano silicon nitride ceramic.

The sintering process is the key for preparing the transparent silicon nitride ceramic, is the densification process of a silicon nitride blank under certain temperature and pressure conditions, and mainly relates to the processes of blank particle bonding, substance transfer and diffusion, volume shrinkage, air hole removal and the like. Common sintering methods include reactive sintering (RB), atmospheric sintering (PLS), re-sintering (PS), Gas Pressure Sintering (GPS), hot press sintering (HP), hot isostatic pressing sintering (HIP), and microwave sintering and explosive forming. Silicon nitride is a covalent ceramic material, has very low self-diffusion coefficient, leads to harsh sintering conditions (T is more than or equal to 1800 ℃) and is easy to decompose at high temperature, so that a sintering aid is usually added for liquid phase sintering to reduce the free energy of a grain boundary and promote the densification process. The sintering aid for preparing silicon nitride ceramic at present stage mainly comprises metal oxide, nitride, fluoride and chloride, and MgO and Y are added₂O₃The sintering aid can obtain silicon nitride ceramics with the density higher than 99 percent and the transparency reaching about 25 percent. But the addition of the sintering aid causes the impurities in the powder, large and uneven particle size and the impurities to be enriched at the grain boundary, and a glass phase is formed after cooling; leading to the phenomena of grain coarsening, grain boundary embrittlement, grain fracture and the like, and seriously reducing the mechanical and optical properties of the silicon nitride ceramics. It is difficult to eliminate internal non-uniform structure, inhibit grain growth and achieve high densification without adding a sintering aid, and therefore, there is a need to develop a sintering method for transparent silicon nitride ceramics, which can control grain growth and eliminate non-uniform structure without adding a sintering aid.

Disclosure of Invention

The invention aims to solve the technical problem of preparing the silicon nitride ceramic with high transparency by using a high-temperature and high-pressure method. According to the method, a sintering aid is not required to be added, a complex preparation process is not required, and the crystal structure and the transparency of the silicon nitride ceramic are directly adjusted by adjusting the synthesis pressure and the temperature to prepare the high-transparency silicon nitride material.

The technical scheme of the invention is as follows:

a high-temp and-pressure process for preparing high-strength transparent silicon nitride ceramics (micron α -Si)₃N₄And nano β -Si₃N₄The β -Si is prepared by using the mixture as raw material and through the processes of raw material mixing, briquetting, assembling, high-temperature high-pressure synthesis, cooling and pressure relief₃N₄A transparent ceramic material; the pressing block is formed by pressing the raw materials of the mixture into a cylinder shape according to the size of the synthesis cavity by using a hydraulic machine; the assembly is that the blocky cylindrical raw materials are put into a heating container and then are put into a synthesis cavity; the high-temperature high-pressure synthesis is carried out for 15-60 min under the conditions that the pressure is 3.0-5.5 GPa and the temperature is 1400-2000 ℃; and the step of cooling and pressure relief is that the sample is naturally cooled to normal temperature after the electrification and the heating are stopped, and then the pressure is relieved to normal pressure.

Preferably, the high-temperature high-pressure synthesis is carried out at the synthesis temperature of 1800 ℃ and the synthesis pressure of 5.5 GPa.

Preferably, α -Si is contained in the raw material₃N₄The particle size of the β -Si is 1-10 microns and accounts for 90 percent of the total mass of the mixture₃N₄The particle size of (A) is 100nm, which accounts for 10% of the total mass of the mixture.

In order to ensure the uniformity of the temperature of the cavity of the synthesized sample, the heating mode adopted by the method is the indirectly heated mode of an electrified graphite tube; in order to ensure that the sample does not react with the graphite tube generating heat, hexagonal boron nitride is adopted to protect the synthesized sample.

Has the advantages that:

the invention has simple process flow, does not need complex processes such as adding sintering aid and the like, and regulates β -Si by regulating temperature and pressure₃N₄And crystal structure and transparency, to produce a highly transparent mass β -Si₃N₄A ceramic. The method greatly shortens the preparation period and the cost of the traditional method, and the synthesized transparent silicon nitride ceramic is beneficial to optimizing the optical and mechanical properties.

Drawings

FIG. 1 is β -Si prepared at different temperatures in example 1₃N₄Compound X-ray diffractogram.

FIG. 2 is β -Si prepared under different pressures for example 2₃N₄Compound X-ray diffractogram.

FIG. 3 is β -Si prepared at different temperatures in example 1₃N₄Hardness versus load for the compounds.

FIG. 4 is β -Si prepared under different pressures for example 2₃N₄Hardness versus load for the compounds.

FIG. 5 shows β -Si prepared in examples 1 and 2₃N₄Optical photographs.

Detailed Description