氧化钴掺杂对溶胶凝胶法合成莫来石微观结构和烧结性能的影响

Effect of Cobalt Oxide Addition on the Microstructure and Sinterability of Mullite Synthesized by Sol-gel Method

以分析纯Al(NO 3)3·9H 2O和正硅酸乙酯为原料,调控体系pH值为8,采用溶胶凝胶法制备莫来石前驱体,研究氧化钴加入量对莫来石前驱体烧结得到莫来石物相的形成和致密化行为的影响。结果表明:加入过渡族金属氧化物氧化钴能显著降低莫来石物相的形成温度,其物相的形成温度较未添加氧化钴的试样降低了约100℃。溶胶凝胶法制备莫来石前驱体的高温烧结性能显示,添加氧化钴的试样致密化速度较未添加的试样明显快。1400℃烧结2 h,添加10%(质量分数)氧化钴制备莫来石前驱体的高温烧结试样体积密度最大可达2.912 g/cm^3。试样中大量针状莫来石晶粒形成,其长径比最大可达14。针状莫来石晶粒相互交织在一起,形成空间致密的网状结构。加入氧化钴对莫来石前驱体烧结制备莫来石物相生成温度和致密化行为的影响可能归因于钴离子部分取代莫来石[AlO 6]八面体中铝离子,导致莫来石晶体发生畸变,使其晶格得到活化,从而有助于低温下莫来石的形成及致密化,促进材料烧结。

Mullite precursor powders were prepared by a sol-gel method by using aluminum nitrate nonahydrate and ethyl orthosilicate as raw materials,as pH value of reaction solution is about 8.The effect of cobalt oxide addition on the phase compositions and densification of mullite cera-mics obtained by sintering of mullite precursor were investigated.The results show that the formation temperature of mullite was significantly reduced,and it was about 100℃lower than that of the sample without cobalt oxide addition.The sinterability of mullite precursors prepared by sol-gel method shows that the densification rate of the sample with cobalt oxide is faster than that of the sample without cobalt oxide.The maximum bulk density of the sample can reach to 2.912 g/cm 3,as the mullite precursors with 10wt%cobalt oxide addition were sintered at the temperature of 1400℃for 2 h.And a large number of needle-like mullite grains with the ratio of length to diameter of^14 were obtained in the sample.Needle-like mullite grains interweave with each other to form a dense network structure.The effect of cobalt oxide addition on the phase compositions and densification behavior of mullite ceramics maybe attributed to Al 3+in mullite[AlO 6]octahedron structure may be replaced by Co 2+,which cause its grain lattice distortion and activate its grain lattice.And mullite was formed and sintered at the lower sintering temperature.