Microstructure and properties of porous Si3N4 ceramics by gelcasting-self-propagating high-temperature synthesis (SHS)

Shile Chen,Gang He,Jiangtao Li,Liang Wang,Chang-An Wang

doi:10.1007/s40145-021-0525-7

Abstract

Porous silicon nitride ceramics have attracted a considerable attention due to their excellent overall performance, but poor porosity homogeneity and structural shrinkage induced by prolonged high temperature sintering limit its further application. Herein, as a three-in-one solution for the above issues, for the first time we develop a novel approach that integrates the merits of gelcasting-SHS (self-propagating high-temperature synthesis) to prepare porous Si3N4 ceramics to simultaneously achieve high porosity, high strength, high toughness, and low thermal conductivity across a wide temperature range. By regulating the solid content, porous Si3N4 ceramics with homogeneous pore structure are obtained, where the pore size falls inbetween 1.61 and 4.41 µm, and the elongated grains are interlaced and interlocked to form micron-sized coherent interconnected pores. At the same time, porous Si3N4 ceramics with porosity of 67.83% to 78.03% are obtained, where the compressive strength reaches 11.79 to 47.75 MPa and fracture toughness reaches 1.20 to 6.71 MPa·m1/2.

Highlights

Si3N4 ceramics boasting superior mechanical properties, thermal stability, chemical stability, and oxidation resistance, are among the best materials for structural ceramics in terms of integrated performance [1,2,3]
The porous Si3N4 ceramics prepared by the pore-former–SHS method [9] have high porosity, the homogeneity of the porous structure is difficult to be guaranteed
The fracture toughness of porous Si3N4 ceramics was loaded in the same way as the three-point bending test, and the test specimen size is 4 mm × 2 mm × 20 mm with a notch width of less than 0.2 mm, the span of this test is 16 mm, and the loading rate is selected 0.05 mm/min

Summary

Introduction

Si3N4 ceramics boasting superior mechanical properties, thermal stability, chemical stability, and oxidation resistance, are among the best materials for structural ceramics in terms of integrated performance [1,2,3]. The porous Si3N4 ceramics prepared by the pore-former–SHS method [9] have high porosity, the homogeneity of the porous structure is difficult to be guaranteed. Based on our previous research [21,22,23], gelcasting process using tert-butyl alcohol (TBA) as the medium can enable porous ceramics with homogeneous and dimensionally adjustable pore structure, which has obvious advantages over the pore former and foaming methods. Sintering at high temperatures for long time consumes a lot of energy and tends to cause structural shrinkage of porous ceramics. We have integrated the advantages of the gelcasting–SHS process for the first time to achieve porous Si3N4 ceramic structure with high porosity and high toughness. It offered a new perspective to obtain porous ceramics with high porosity and high performance and quickly

Experimental

Results and discussion

Conclusions