Method for preparing porous nano silicon nitride ceramics by combining gas solid reaction with liquid sintering method

Abstract

The invention discloses a method for preparing porous nano silicon nitride ceramics by combining a gas solid reaction with a liquid sintering method, which comprises the following steps: 1, after carrying out die-pressing forming on mixed powder of 20 to 85 weight percent of carbon nano tubes, 0 to 70 weight percent of alpha-Si3N4 and 10 to 20 weight percent of rare earth oxide in percentage by mass, forming a green body, placing SiO powder at the bottom of a crucible, placing the green body at the middle part of the crucible, then placing the crucible in a multifunctional sintering furnace, filling in nitrogen, carrying out heat preservation for 1 to 6 hours at a temperature of 1,500 DEG C to 1,700 DEG C, and performing a carbothermal reduction nitridation reaction to generate a silicon nitride body, wherein a mass ratio of SiO to the carbon nano tubes is 10:1; and 2, continuously warming to a temperature of 1,750 DEG C to 1,850 DEG C to carry out liquid sintering for 0.5 to 2 hours,and in such process, generating phase transformation so as to obtain the porous nano silicon nitride ceramics. The silicon nitride porous ceramics obtained by the method disclosed by the invention canbe widely applied to the fields of a high-temperature filter, a catalyst carrier, or the like.

Description

technical field [0001] The invention relates to a method for preparing porous nano-silicon nitride ceramics by gas-solid reaction combined with a liquid-phase sintering method, which is suitable for various high-temperature filter separators, catalyst carriers, sound-absorbing materials, and wave-transmitting materials. Background technique [0002] Porous silicon nitride ceramics are widely used in high temperature metal filters, radiation burners, heat exchangers, catalyst carriers, radar and missile radomes due to their excellent room temperature and high temperature strength. Porous silicon nitride composed of β-silicon nitride rod-shaped grains overlapped with each other has excellent mechanical properties, good thermal shock resistance, and damage resistance. However, since the transformation process of α to β silicon nitride is often accompanied by densification, it is very difficult to directly prepare porous silicon nitride with a porosity higher than 50% by liquid ...

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Problems solved by technology

Among them, the porosity of porous silicon nitride prepared by partial sintering method is difficult to be higher than 60%. Although the porosity can be further improved by freeze-drying and adding pore-forming agents, there are usually defects such as macropores in its microstructure, and Inhomogeneous pore structure and pore size distribution, resulting in lower strength

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