GB529127A - Magnesium carbonate composition and process for the preparation thereof - Google Patents

Abstract

529,127. Magnesium carbonate; setting-compositions. PLANT RUBBER & ASBESTOS WORKS. May 22, 1939, No. 15210. Convention date, June 9, 1938. [Class 1 (iii)] [Also in Group V] Self setting normal magnesium carbonate is produced by decomposing magnesium bicarbonate in solution by vigorous agitation and controlled heating. The product is stated to be in the form of minute elongated crystals. The heating must not be above 120‹F. The solution of magnesium bi-carbonate is preferably obtained by gassing an aqueous suspension of calcined dolomitic material, the insoluble calcium carbonate so produced being removed. The agitation may be mechanical or by the introduction of fine streams of compressed air together with live steam when the solution is also heated. Seeding with previously formed crystals assists the reaction. After suitable reinforcing material such as asbestos fibre has been added to the suspension it is filtered and may be washed although any magnesium bicarbonate remaining in the slurry may be removed by the addition thereto of magnesium oxide or calcined dolomite. The filtered material is then poured into moulds and compressed if a more dense product is required. Setting proceeds on the application of heat at from 140 to 195‹ F. Heating may be by live steam passing through the space in which the moulds are placed. To assist setting 1 to 5 per cent. of magnesium oxide 1 to 2 per cent. of borate or 0.1 to 1 per cent. of sodium hydroxide may be added this serving to absorb any carbon dioxide given off by the setting product which tends to decompose slightly. After setting, which takes place without shrinkage, the blocks are dried in an oven at from 155 to 395‹F. to remove any uncombined water and then trimmed if necessary. The specific gravity of the product is stated to be from 14 to .19. The periods of precipitation, setting and drying are 1 to 1¢ hours, ¢ to 3 hours and 24 to 72 hours respectively.