GB936251A - Method of and apparatus for making phosphors - Google Patents

Abstract

936,251. Luminescent materials. SYLVANIA ELECTRIC PRODUCTS Inc. Dec. 9, 1959 [Dec. 10, 1958 (2)], No. 41942/59. Drawings to Specification. Class 39 (1). Method of making a phosphor, e.g. a calcium halo-phosphate phosphor activated by trivalent antimony and manganese, comprises preheating the starting materials at a temperature between 1000 ‹ and 1600 ‹ F. sufficient to remove undesired ingredients such as water and carbon dioxide but below that at which phosphorproducing reaction between the materials occurs and firing the materials at a temperature substantially above 1600‹ F. immediately following the pre-heating and without an intermediate cooling. There may be two pre-heating zones, one at about 1150‹ F., and the other at about 1350‹ F., a firing zone at between 1900‹ and 2150‹ F., for example at about 2050‹ F., and a final cooling zone at well below 1000‹ F. Part of the cooling zone can be kept at about 660‹ F. and the remainder at about 360‹ F. The firing can take place at two temperatures, only the second higher one of which causes the formation of the phosphor. The materials can be moved through zones heated to different temperatures, and a flow of gas inert with respect to the materials, such as nitrogen, can be maintained over them, the direction of flow being the same as that of the movement during the pre-heating and opposite to that of the movement during the firing. The starting materials can be placed in an open silica boat, on a ceramic plate on rails, to a level between two-thirds and three-quarters of the inside height of the boat. When the starting materials contain compounds of antimony and chlorine, the atmosphere of antimony chloride accumulated above the materials during the firing is kept below atmospheric pressure.