Preparation of GRIN Glass Rods of Large Diameter

为了制备直径大于10 mm的r-GRIN玻璃棒，研究了用Sol-Gel法制备PbO-K2O-B203-SiO_2系玻璃棒的各种处理条件。(1)将醋酸和醋酸铅水溶液的混合物加入到由正硅氧基硅烷、四甲氧基硅烷和乙二醇硼组成的前驱体溶液用pH=2的盐酸水解制得的溶胶中，可以得到大尺寸的无泡凝胶。(2)在形成铅浓度梯度之前，凝胶的前处理应在模具中60℃老化，浸泡在水-异丙醇体系的溶液中，然后依次浸泡在异丙醇-丙酮体系(异丙醇/丙酮=8/2，5/5，0/10)的溶液中，以去除不必要的水和醋酸，并在凝胶的微孔壁上沉淀细小的铅晶体。(3)将直径约35 mm、长度约50 mm的预处理凝胶在醋酸钾乙醇溶液中浸泡4h，可形成中心与周长相差4%的铅浓度差。(4)在丙酮饱和气氛中干燥凝胶，然后在580℃下烧结，可得到直径约13 mm、长约20 mm、中心与周长折射率差约0.05的透明无气泡GRIN玻璃棒。

On the purpose of preparing r-GRIN glass rods having a diameter larger than 10mm, the conditions on the various treatments for the preparation of the rods of PbO-K2O-B203-SiO2 system by sol-gel process have been studied.The results obtained were summarized as follows; (1) A bubble free gel of large size can be prepared by adding the mixture of acetic acid and aqueous lead acetate solution to a sol obtained by hydrolyzing a precursor solution consisted of tetraethoxysilane, tetramethoxysilane, and boronethoxide with aqubous hydrochloric acid of pH=2. (2) The pretreatment of the gel prior to the formation of concentrational gradient of lead should be made by aging the gel at 60 C in the mold, soaking in a solution of water-isopropanol system, and subsequent successive soaking in the solutions of isopropanol-acetonsystem (isopropanol/aceton=8/2, 5/5,0/10), in order to remove unnecessary water and acetic acid and to precipitate fine lead crystals on the micropore walls of the gel. (3) Formation of concentrational difference of lead in 4% between center and perimeter can be made by soaking the pretreated gel of about 35mm in diameter and 50mm in length in an ethanolic solution of potassium acetate for 4h. (4) A transparent bubble free GRIN glass rod of about 13mm in diameter and 20mm in length having a refractive index difference of about 0.05 between center and perimeter can be obtained by drying the gel in an atmosphere saturated with aceton, followed by sintering at 580 C.