GB1198250A - Calcium Silicate Phosphor - Google Patents

Abstract

1,198,250. Luminescent materials and uses thereof. W. R. GRACE & CO. 2 May, 1969 [6 May, 1968], No. 22640/69. Heading C4S. Finely divided fluorescent calcium silicate with divalent Pb and Mn activators is made by (a) mixing Pb, Ca, Mn compounds decomposable to oxides and volatile components, with a silica hydrogel, (b) decomposing and dehydrating in a fluid energy mill (e.g. steam) operated at above about 500‹ F., e.g. 600‹ to 1500‹ F., and (c) calcining and recovering the phosphor, e.g. of Wollastonite structure, Ca 0 . 96 Mn 0 . 033 Pb 0 . 007 SiO 3 being instanced. The Mn and Pb may be in amounts 0À005 to 0À20 and 0À001 to 0À10 gm. moles, respectively, per gm. moles of Ca. The calcining temperature may be not less than 1600‹ F., e.g. 1900‹ to 2100‹ F. in an inert atmosphere. The hydrogel may be crushed and slurried with solutions of Pb, Mn and Ca such as hydroxides, nitrates, sulphates, or carboxylic acid salts, e.g. formates and acetates, precipitated as oxalates, malonates or succinates in a slightly acidic medium to maintain the Mn in a +2 state and filtered. Alternatively, Pb, Mn and Ca compounds may be mixed dry with previously acidified hydrogel. The hydrogel, prepared by gelling sodium silicate with sulphuric acid for instance, may contain 10 to 90% by wt., e.g. 30 to 40% by wt., of water. Fluorescent lamp, C.R.T., display and postage stamp applications are instanced. U.V., X-ray and cathode-ray excitation is mentioned.