Patent GB-1407515-A (GB)
Title: Foamed glass body
IPC: C04B14/24
Filed: 1973-06-18
Abstract: 1407515 Cellulated glass CORNING GLASS WORKS 18 June 1973 [2 Aug 1972] 28827/73 Heading C1M A batch consisting of particles substantially all passing a standard U.S. 200 mesh screen and at least 10% by weight thereof being finer than 5 microns in diameter suitable for making a cellulated glass body consists essentially of, in weight per cent on an anhydrous basis: (a) A rock selected from volcanic ash, weathered volcanic ash, clay, and mixtures thereof in an amount of at least 50% by weight; (b) A cellulating agent selected from carbon, an organic compound which thermally decomposes to yield carbon at a temperature below the cellulating temperature, and mixtures thereof, the amount of carbon available for cellulation being 0À1-2% by weight of the batch; (c) A flux consisting of at least one alkali metal compound containing the elements of alkali metal oxide in an amount of 3-10%, by weight, of the batch, at least 60% by weight of said elements being K 2 O; and (d) B 2 O 3  in an amount of 7-18%, by weight, of the batch or a boron compound containing from 7-18%, by weight, of the batch of the elements B 2 O 3 ; said batch consisting essentially, calculated by weight on the oxide basis, of 3-10% alkali metal oxide, 7-18% B 2 O 3 , 10-20% Al 2 O 3  and 50-80% SiO 2 , wherein the SiO 2  : Al 2 O 3  weight ratio is from 3 : 1-7 : 1, and the total of alkali metal oxide, B 2 O 3 , Al 2 O 3  and SiO 2  constitutes at least 90% by weight of the batch. The rock, cellulating agent, flux and B 2 O 3  or boron-containing compound preferably constitutes at least 75% by weight of the anhydrous batch with up to 25% of the batch being silica, alumina or " grog " added to adjust the SiO 2  : Al 2 O 3  ratio. The clay may contain an illite and/or smectite mineral and in particular smectite clays containing beidellite, nontronite and/or montmorillonite. The boron containing compound may be borax. The flux is preferably KOH but K 2 CO 3  and K 2 SiO 3  may be substituted in whole or in part thereof, minor amounts of Li 2 O and/or Na 2 O being tolerated. The cellulating agent used in the specific examples is sodium acetate. The batch is shaped to form an article of the desired configuration, fixed by heating the body to the cellulating temperature (normally 875-1000 C.) and by holding thereat for a sufficient time to attain minimum density (e.g. less than 0À5 gm./c.c.), and finally annealed. The body after foaming may be fired without restraint. The glass body formed may have the following properties: (a) a density less than 0À5 gm./c.c.; (b) a modulus of rupture in excess of 200 p.s.i.; (c) an essentially uniform, closed cell structure wherein the cells are generally spherical in shape and do not exceed 1 mm. in diameter; and (d) a coefficient of thermal expansion less than 50 x 10<SP>-7</SP>/ C. In the specific Example (I) the finished glass has the following compositions in per cent by weight: (I) 63À5% SiO 2 , 13À8% Al 2 O 3 , 12-4% B 2 O 3 , 1À6% Na 2 O, 4À2% K 2 O, 2À5% MgO, 1À3% CaO and 0À7% Fe 2 O 3 . A comparative Example (II) discloses a glass comprising 63À7% SiO 2 , 13À9% Al 2 O 3 , 12À4% B 2 O 3 , 3À1% Na 2 O, 2À4% K 2 O, 2À5% MgO, 1À3% CaO, and 0À7% Fe 2 O 3 .