期刊
CERAMICS INTERNATIONAL
卷 47, 期 6, 页码 8113-8122出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.ceramint.2020.11.166
关键词
Highly porous ceramics; beta-Si3N4; Carbothermal reduction nitridation; Ultrafine fibrous grains
资金
- National Key R&D Program of China [2017YFB0310300, 2017YFB0903803]
- National Natural Science Foundation of China [51672209]
- Shaanxi Innovation Capacity Support Program [2018TD-031]
This study successfully developed highly porous Si3N4 ceramic monoliths composed of ultrafine fibrous grains with high flexural strength through a novel vapor-solid carbothermal reduction nitridation reaction. By controlling the content of alpha-Si3N4 diluents and density of CNT green bodies, porous Si3N4 monoliths with porosity ranging from 61-78% were achieved.
Si3N4 ceramic with ultrafine fibrous grains are expected to exhibit remarkable mechanical properties. In this work, highly porous Si3N4 ceramic monoliths composed of ultrafine fibrous grains were developed via a novel vapor-solid carbothermal reduction nitridation (V-S CRN) reaction between SiO vapor and green bodies comprised of carbon nanotubes (CNTs), alpha-Si3N4 diluents and Y2O3 in a N-2 atmosphere. The unique fibrous grains interconnected structure was developed through in-situ formation of Si3N4 and following liquid phase sintering. The porous Si3N4 monoliths with porosity of 61-78% was developed by controlling the contents of alpha-Si3N4 diluents and densities of the CNT green bodies. With increasing of the alpha-Si3N4 contents, Si3N4 fibrous grains with an aspect ratio of approximate or higher than 20 could be achieved, and the grains were gradually refined. For the samples with 40 wt% alpha-Si3N4, the minimum mean grain diameter and pore size of 164 nm and 0.79 mu m were achieved, respectively, and the resultant porous Si3N4 monolith exhibited a flexural strength of as high as 73-102 MPa with the porosity of 61-73%, which is much higher than that of the reported in literature. The improvement of mechanical strength could be attributed to the densely interconnected bird's nests structure formed by the ultrafine fibrous grains. The effects of the alpha-Si3N4 diluents on the resulting porous Si3N4 monolith via this method were analyzed.
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