GB1222119A - Processes for strengthening vitreous, vitrocrystalline and ceramic bodies - Google Patents

Abstract

1,222,119. Coated glass bodies. GLAVERBEL. 11 March, 1968 [27 April, 1967], No. 11797/68. Heading C1M. A coated vitreous, vitrocrystalline or ceramic body is chemically strengthened by ionexchange through the coating between a liquid or gaseous medium and the surface-layers of the body, so producing compressive stresses in said surface-layers; the coating layer is, or is converted during or after the chemically strengthening to, an at least partially crystalline coating with surface hardness greater than that of the coated surface. The coating layer may result from the reaction in situ of constituents applied separately to the body. The final chemical composition of the coating may result from a reaction during the ion-exchange treatment between a coating constituent, present before ion-exchange, and another substance. Crystallization-promoters may be used. The coating may contain Al, Zr, Si, or Ti, and crystallization-promoters may be Li, Ti, Mn, Mg, Co, Cu, Ni, Zn, Cr. Fe, Ca, rare earths, halogens, Cd, Bi, Ni, Al, or water-vapour. The final coating may comprise at least one crystalline phase formed by: Al 2 O 3 (corundum), SiC, SiO 2 , ZrB 2 , TiN, TaC, ZrC, TiC, A1B, B 1 C, TiO 2 , ZrSiO 4 (zircon), Al 2 Be 3 Si 6 O 18 (beryl), or Al 2 SiO 3 (F.OH) 2 (topaz). The promoter may be added to a molten saltbath used for the ion exchange, either as such, or as compounds, e.g. sulphates, chlorides, or oxides. The coating may be performed by vacuum deposition, cathodic sputtering or hydrolysis. The body may be of glass formed from silica, soda, lime, and/or feldspar. Two exemplified bodies comprise, in wt. per cent: SiO 2 , 72.4/72.9; Na 2 O, 13.7/9.8; CaO, 12À0/0À9; Al 2 O 3 , 1.9/6.2; K 2 O, -/0À1; B 2 O 3 , -/10À4. The ions exchanged may be alkali-metal ions, e.g. K<SP>+</SP>, Cs<SP>+</SP>, or Li<SP>+</SP>, which are present in a molten salt-bath, e.g. of KNO 3 , OsNO 3 , or LiNO 3 . The ion-exchange may be promoted by a direct or alternating electric field, e.g. of 60-200 v. The exchange may be promoted by use of a substance which weakens the diffusion-barrier, e.g. by countering the diffusion-inhibiting effects of ions which diffuse into the ion-exchange medium from the body; such substances include halogens, alkaline earth metal ions, e.g. Ca<SP>++</SP> or Mg<SP>++</SP>, and substances which form complexes with ions migrating from the body, e.g. Fe, Ni, NH 4 <SP>+</SP>, CN-.