凝胶陈化对ZrB_2粉末制备的影响

Effects of Gel Aging on Synthesis of ZrB_2 Powders

以正丙醇锆、硼酸、醋酸和D．果糖为原料，采用溶胶-凝胶法，结合高温碳热还原反应制备得到了长柱状单相ZrB2粉末。反应体系中，D-果糖不仅提供碳热还原反应的碳源，同时作为化学修饰剂，起到抑制正丙醇锆快速水解的作用。通过对比未陈化和陈化的凝胶制备得到的产物，探讨了陈化过程对于ZrB2粉末制备的影响。结果表明，凝胶陈化有利于ZrO2向ZrB2的完全转化。当起始原料满足n（B）／n（Zr）=3．5~4，n（C）／n（Zr）=7时，采用室温陈化7d的凝胶在1550℃保温2h可获得长度为4～7I．tm，横截面等效直径约为1岬1，长径比约为4～7，比表面积为2．53m。儋，D50=6．46μm的单相长柱状ZrB2粉末。

ZrB2 particles were synthesized by a Sol-Gel method using zirconium n-propoxide, boric acid, acetic acid and D-fructose. D-Fructose acts as both a modifier and a carbon source for carbothermal reduction reaction. For com- parison, both nascent state gel and aged gel were used to clarify the aging-time-dependent mechanism for ZrB2 synthe- sis. As a result, a single phase ZrB2 powder with a uniform size and shape distribution can be obtained from the aged gel with a boron and carbon to zirconium molar ratio of 3.5-4 and 7, respectively, after reduced at 1550 ~C for 2 h. Besides, the synthesized ZrB2 particles exhibit prism-like morphology with average particle size of ca. 4-7 pm in length, 1 μm in diameter of excircle of the cross-section and 4--7 in aspect ratio, when initial raw materials ratio n（B）/n（Zr） is 3.5-4 and n（C）/n（Zr） is 7. The median diameter Ds0 is 6.46 μm and specific surface area is about 2.53 m2/g. Furthermore, a complete carbothermal reduction of ZrO2 can be achieved using the aged gel.