GB718132A - Vitreous phosphate enamels and their use - Google Patents

Abstract

718,132. Vitreous enamel frits. DU PONT DE NEMOURS & CO, E.I. Feb. 18, 1952, [March 22, 1951.] No. 4289/52. Class 56. A vitreous enamel frit comprises, in mole percentages, P 2 O 5 20-50, Al 2 O 3 10-45, alkali metal oxide 20-50 of which at least half is Na 2 O and the balance K 2 O and/or Li 2 O, the K 2 O being 0-25 and Li 2 O 0-15, B 2 O 3 0-20, TiO 2 0-15, and ZrO 2 0-5, with or without ceramic pigment. Preferred mole per cent ranges are P 2 O 5 25-45, Al 2 O 3 15-40, alkali oxide 25-45, together totalling at least 60 per cent, B 2 O 3 0-10, TiO 2 3-6, and ZrO 2 0-3, the K 2 O being 5-15, and the Li 2 O 0-10. If the enamel is required to have a coefficient of expansion near that of aluminium, B 2 O 3 is omitted or does not exceed 3 mol per cent. Minor amounts of other ingredients may be present, but the SiO 2 content is not more than 2 per cent. The frits are used for the porcelain enamelling of aluminium and aluminium with alloys, e.g. at least 80 per cent Al and 1-20 per cent of ingredients such as Mn, Mg, Cu, Cr, Zn, Si. The ingredients are fired at about 480-540‹C. and fritted, and the frit dried at about 150‹C. or less, and ground with water or other desired liquid with the addition of up to about 10 per cent by weight of opacifying agents, e.g. TiO 2 or ceramic pigments, e.g. cobalt, aluminate blue. A small amount of phosphoric acid is advisably added. The firing temperature of the enamel is not above about 580‹C., and is 'preferably 500-560‹C. The alloys to be enamelled are preferably prepared by treating with an alkaline aqueous solution of a chromate and heating at 350-600‹C. Examples, showing the compositions in mole percentages, are:-(1) Na 2 O 40, Al 2 O 3 30, P 2 O 5 30 milled with 130 c.c. water and 2 c.c. of 85 per cent H 3 PO 4 , fired at 560‹C., (2) Na 2 O 29.1, K 2 O 9.7, Al 2 O 3 24.2, P 2 O 5 29.1, B 2 O 3 4.9, TiO 2 3.0, fritted, dried, milled, and fired at 520-540‹C., (3) Na 2 O 30.4, K 2 O 10.0, Al 2 O 3 21.8 P 2 O 5 34.8, TiO 2 3.0, fritted, &c., and fired at 540‹C., (4) 150 gm. of glass at (2) milled with 60 c.c. water, 1 c.c. of 85 per cent orthophosphoric acid, and 9.0 gm. of cobalt silicate blue pigment, fired at 520-540‹C., (5) Na 2 O 32, K 2 O 10, Al 2 O 3 24, P 2 O 5 24, TiO 2 3, B 2 O 3 5, ZrO 2 2, (6) Na 2 O 32.8, Li 2 O 10.0, Al 2 O 3 24.6, P 2 O 5 24.6, TiO 2 3.0, B 2 O 3 5.0. The batch compositions and results of firing these examples are given. Frits containing alkali oxide 35-45, Al 2 O 3 20-30, P 2 O 5 30-40, B 2 O 3 0-3 have coefficients of expansion near those of aluminium and alloys. Specification 642,228 is referred to.