GB711068A - Improvements in or relating to fluorescent materials - Google Patents

Abstract

711,068. Luminescent materials. DERBY & CO., Ltd. Nov. 7, 1952 [Aug. 31, 1951], No. 20621/51. Class 39(1) A process for the manufacture of a lead-activated barium silicate sulphate having an emission in the long U.V. region when excited by short U.V. radiation, such as 2537A in a discharge lamp, comprises heating to a temperature of at least 1000‹C, but below the temperature of fusion, preferably between 1100 and 1125‹C, a mixture containing silica, barium oxide or a compound forming barium oxide on heating, such as barium carbonate, a lead compound and barium sulphate or substances forming barium sulphate on heating, such as barium carbonate and ammonuim sulphate Barium fluoride and/or barium chloride may also be present in the mixture. The mixture can contain per mol. of barium carbonate 2.2 to 3.5 mols. of silica, 0.05 to 0.5 mol. of barium sulphate and 0.5 to 3 per cent by weight of the mixture, of a lead compound (calculated as lead), with or without a small proportion of barium fluoride and/or barium chloride. In one example the mixture contains 1 mol. of barium carbonate, 3 mols of silica, 0.12 mol. of barium sulphate, 1.5 per cent by weight of the mixture of a lead compound (calculated as lead), 2¢ per cent by weight of barium chloride dihydrate and 5 per cent by weight of barium fluoride. The lead may be added as the oxide, peroxide, sulphate, nitrate or fluoride. Other examples are described. Further examples are described in the Provisional Specification. The ingredients are ball-milled dry, filled into silica crucibles, fired for four hours in air at 1125‹C, removed from the crucible, ground with water, washed free from any soluble salts, dried and sieved. According to the Provisional Specification the ingredients are ball-milled with acetone, filtered, dried and filled into silica crucibles, &c. Specifications 572,771, 646,575 and 672,516 are referred to.