以松木炭化后形成的多孔木炭为模板, 经Y2O 3/SiO2混合溶胶浸渍生物碳模板形成Y2O 3/SiO2/C复合体, 在高压氮气氛下(0.6MPa), 1600℃碳热还原氮化制备出生物形态多孔氮化硅陶瓷. 借助XRD、SEM研究了烧结助剂、烧结温度、反应时间和烧结气氛对烧结产物显微结构和晶相的影响, 探讨了多孔Si3N4陶瓷的反应过程和机理. 结果表明, 多孔Si3N4陶瓷是由主晶相β-Si3N4和少量晶间玻璃相Y8Si4N4O14组成; 多孔Si3N4 不仅保留了松木的管胞结构, 还在孔道中生长出纤维状形貌的β-Si3N4颗粒; Si3N4的反应烧结过程包括α-Si3N4的形成、晶形转变(α-β相变)和晶粒生长三个阶段. 在1450℃烧结的机理是气-固和气-气反应机理, 在1600℃通过液相烧结的溶解-沉淀机理形成纤维状的多孔Si3N4陶瓷.
Porous silicon nitride ceramics with a biomorphic microstructure were manufactured by
carbothermal reduction and nitridation of Y2O3/SiO2/charcoal composites in high concentration nitrogen atmospheres(0.6MPa) at 1600℃. These
composites were prepared from pine-derived charcoal impregnated with yttrium-incorporated silica mixed sol by vacuum/pressure infiltration
process. The influences of sintering temperature, reaction time, additive and sintering atmosphere on microstructure and phase composition were studied by XRD, SEM. The formation mechanism of Si3N4 was analyzed. XRD analysis shows that mainly \β-Si3N4 and minor glass component of
Y8Si4N4O{14 are detected. SEM observation reveals that the resulting porous Si3N4 retains the microcellular morphology of original pinewood tissue, and the remarkable rod-like \β-Si3N4 grains grow from the internal walls of macroscopic pores. The sintering process of porous \β-Si3N4 consists of three stages, namely, formation of α-Si3N4, transformation of α-\β and grain growth, respectively. Nitridation is based on gas-solid and gas-gas reaction among SiO(g), N2(g), C(s) or CO(g) for the samples treated at 1450℃. Porous ceramics with elongated fibrous \β-Si3N4 grain is developed by solution-reprecipitation mechanism at 1600℃.
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