Patent GB-1431352-A (GB)
Title: Method of making a glass body
IPC: C03C3/06
Filed: 1973-03-20
Abstract: 1431352 Glass body CORNING GLASS WORKS 20 March 1973. [30 March 1972] 13282/73 Heading C1M A method of making a glass body comprises the steps of: depositing at least two oxides produced by flame hydrolysis on a support to form a porous body thereon, which body contains oxygen and residual water (defined as H 2 O and the dissociation products H and OH); establishing an atmosphere surrounding the said body, the said atmosphere containing (a) gaseous hydrogen and/or water vapour at a lower level than in the said body, or (b) gaseous oxygen at a higher level than in the said body, or (c) gaseous hydrogen and/or water vapour at a lower level than in the said body and gaseous oxygen at a higher level than in the said body, or (d) gaseous hydrogen and/or water vapour at a lower-level than in the said body and gaseous oxygen at a lower level than in the said body; maintaining the gas level(s) in the said atmosphere while heating the said body to a temperature below the sintering temperature of the glass; maintaining the said temperature until an equilibrium is reached; heating the said body to at least the sintering temperature of the glass for such a time as to consolidate the said porous body to form a dense, non-porous glass body; and subsequently removing the resulting consolidated glass body which preferably contains not more than 20 p.p.m. residual water from the said atmosphere. The support may be removed from the consolidated body prior to shaping and the consolidated body may be formed to the desired configuration within the controlled atmosphere. The deposited oxides comprise silica and at least one dopant in amounts up to 15% by weight selected from titanium oxide, tantalum oxide, tin oxide, niobium oxide, zirconium oxide, aluminium oxide, lantharium oxide and germanium oxide, e.g. 95% by weight SiO 2  and 5% by weight TiO 2 . In particular the porous body is formed by depositing a layer of oxide on said support and then depositing an oxide coating of different composition on the said deposited oxide layer. The support on to which the oxides are deposited may be glass having a composition and coefficient of expansion compatible with the deposited glass. Alternatively the support may be graphite. The mixed oxides are applied to the substrate using a conventional flame hydrolysis technique. In one embodiment the porous body is disposed in an atmosphere maintained by vacuum means at a degree of dryness corresponding to 20 p.p.m. or less of water vapour thus causing hydrogen and residual water to be removed from the porous body until an equilibrium is reached. In another embodiment the porous body is disposed in an atmosphere of oxygen and again an equilibrium is reached between the gas in the structure and the gas in the atmosphere. Thereafter while maintaining the atmosphere the porous body is heated to at least 1400‹ C. to sinter the root particles. The fused quartz support is then removed by a diamond reamer and the tubular member so formed is rinsed with hydrofluoric acid before being heated to about 2000‹ C. at which temperature it is drawn. As the tube is drawn the central hole collapses. If an optical waveguide is to be formed from the consolidated non-porous glass body a coating of glass having an index of refraction lower than that of the consolidated glass body may be applied to the exterior surface of the body, e.g. by flame hydrolysis. The glass body may also be used for lenses and prisms.