高纯SiO_2玻璃纤维析晶性能的研究

Crystallization Behavior of Silica Fibers

本文用 X 射线衍射系统地研究了石英熔融法、酸沥滤法和溶胶凝胶法等三种方法所制备的 SiO_2玻璃纤维的析晶性能;Al_2O_3.B_2O_3和 Na_2O 含量对 SiO_2纤维析晶性能的影响以及 Al_2O_3和 B_2O_3的交互作用。用 Raman 光谱、核磁共振和 X 射线径向分布函数分析等手段研究了各种纤维的结构.研究结果表明,各因素对 SiO_2玻璃纤维析晶规律的影响在许多方面不同于块状石英玻璃。又根据纤维形成的特点和结构分析结果,对各种纤维的析晶规律进行了讨论.

Up to now,no systematic research report on the crystallization behavior of silica fibers has been found in the open literature. The authors concentrate on crystallization behavior of high purity silica fibers.There are three types of such fibers used in experiment:type A contains 99.69% SiO_2 prepared by the authors with acid leach- ing method,type B contains 99.95% SiO_2 prepared by the authors with sol-gel method,and type C,made by high purity silica fusion method,is purchased. The authors concentrate further on the individual effects of impurities Al_2O_3,B_2O_3 and Na_2O and coupled effect of Al_2O_3 and B_2O_3 on the crystallization of silica fibers.The structure of the silica fibers is investigated by using X-ray diffraction,Raman spectrum,nuclear magnetic resonance,and X-ray radial distribution function. Results indicate that fibers made by different methods possess different crystallization tendencies. Contrary to previous results from bulk silica glasses,type C fiber possesses much higher crystallization tendency than types A and B,though it contains much less broken bond and its network structure is much better linked.Type B silica fiber is the most crystallization resistant one regardless of its high OH content. Small amount of Al_2O_3 in the fibers is mainly in the form of [AlO_4] with a H^+ neutralizing the extra nega- tive charge.This [AlO_4] promotes the crystallization of the fibers,and its effect grows stronger at higher temperatures.A model that such [AlO_4] will break down at high temperatures by combination of H^+ and OH in the fibers is proposed,which can be used to explain satisfactorily the effect of [AlO_4] on the crystallization of the fibers.Small amount of B_2O_3 up to at least 0.9wt% has an effect of resisting the crystallization of type B silica fiber and up to at least 0.8wt% does not affect the crystallization of type A silica fibers.For silica fibers containing 1～2wt% Al_2O_3,the effect of B_2O_3 is to promote intensely the crystallization of the fibers.This is due to the change of the structure state of B_2O_3 from [BO_4] to [BO_3] caused by the addition of Al_2O_3.Small amount of Na_2O possesses great effect of promoting the cyrstallization of the silica fibers.