Preparation of Oxide Fibers by Unidirectional Freezing

Titania和Alumina Fibers是由凝胶的单向冻结准备的。纤维素的制备条件、形成机理、结构和性质被调查了。一种钛盐是由氢化钛<Cl_4>和五种氧化铝盐作为起始材料准备的。该气体将其放入长度为120毫米的蜂窝管，直径为20或8毫米，并将其在分散的水中进行2-30天的转换成凝胶。凝胶，放置在一个聚乙烯圆柱体中，被插入到一个单一的冻结-78 ° C冷浴中，在1.0厘米和13厘米/小时之间的速率。冰冻的身体在房间的温度下被冻结。About 10 cm long titania fibers were formed when the Ti <O_2>concentration of the sol was 1.0 and 2.0 M and the rate of insertion was 2.0 and 4.5 cm/h。一至5厘米长的氧化铝纤维是由凝胶制成的，只有从含有太阳的羽毛状颗粒中提取出来的。泰坦尼亚和氧化铝纤维都形成了，只有在凝胶中的细胞生长的时候。冰纤维晶体的细胞增长的情况已被发现取决于冻结速率R和温度梯度G，在单方向冻结期间。Fiber diameters were found to be in an inverse proportion to the product of G and R. The fibers thus prepared were both porous and charaterized by large specific surface area of 350 &lt;m ^2&gt;/g in Ti <O_2>and 240 &lt;m^2&gt;/g in <Al_2><O_3>and high water contents after dried at 110 c。铝纤维的张力强度增加到约180兆帕，加热到1000 ° C。这些结果表明，钛和氧化铝纤维可以用作催化剂、催化剂载体和强化纤维。

Titania and alumina fibers were prepared by unidirectional freezing of gels. Preparation conditions, formation mechanism, structure and properties of the fibers were investigated.A titania sol prepared by hydrolyzing Ti <Cl_4> and five kinds of alumina sols were used as starting materials. The sols were put into a cellulose tube 120mm in length and 20 or 8mm in diameter, and dialyzed in distilled water for 2-30 days to convert to gel. The gels, placed in a polyethylene cylinder, were unidirectionally frozen by inserting into -78゜C cold bath from the bottom at a rate between 1.0 and 13cm/h. Frozen bodies were thawed at room temperature. About 10cm long titania fibers were formed when the Ti <O_2> concentration of the sol was 1.0 and 2.0M and the rate of insertion was 2.0 and 4.5cm/h. One to 5cm long alumina fibers were formed only from the gels derived from the sols containing feather-like particles. Both titania and alumina fibers were formed only when the cellular growth of ice took place in gels. The occurrence of the cellular growth of ice fibrous crystals was found to depend on freezing rate R and temperature gradient G during unidirectional freezing. Fiber diameters were found to be in an inverse proportion to the product of G and R.The fibers thus prepared were both porous and charaterized by large specific surface area of 350 <m^2> /g in Ti <O_2> and 240 <m^2> /g in <Al_2> <O_3> and high water contents after dried at 110゜c. The tensile strength of alumina fibers increased to about 180MPa on heating to 1000゜C. These results indicate that titania and alumina fibers could be used as catalyst, catalyst carrier, and reinforcing fibers.