Preparation of GRIN Glass Rods of Large Diameter

以制备直径大于10 mm的r-GRIN玻璃棒为目的，研究了用溶胶-凝胶法制备PbO-K_2 O-B_2 O_3-SiO_2系玻璃棒的各种处理条件，得到如下结果：（一）通过将乙酸和乙酸铅水溶液的混合物添加到通过水解前体获得的溶胶中，可以制备大尺寸的无气泡凝胶溶液由四乙氧基硅烷、四甲氧基硅烷和乙醇硼与pH=2的盐酸水溶液组成。(2)在形成铅浓度梯度之前，凝胶的预处理应先在模具中于60 ℃老化，然后在水-异丙醇体系中浸泡，再在异丙醇-丙酮体系中连续浸泡（异丙醇/丙酮=8/2，5/5，0/10），以除去不必要的水和乙酸，并在凝胶的内壁上沉淀细的铅晶体。(3)将直径约35 mm、长约50 mm的预处理凝胶在醋酸钾乙醇溶液中浸泡4 h，可使铅在中心和周边形成4%的浓度差。(4)通过在丙酮饱和的气氛中干燥凝胶，然后在580 ℃下烧结，可以获得直径约13 mm、长度约20 mm、中心和周边之间折射率差约为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.