| 摘要 |
<p>Building units, e.g. bricks tiles, blocks slabs, floors &c. are prepared by casting in a mould and allowing to set a composition prepared by admixing reactive magnesia, at least 75% of which passes a 100 B.S.S. sieve, with at least one of a water-soluble chloride or sulphate (not magnesium) or sulphuric acid, and with a fibrous material and water. The sulphate may be of Fe, Al, Cu, Zn, Na, K, NH4, or an alum and preferably reacts with magnesium hydroxide to produce a substantially water-insoluble oxide or hydroxide. Magnesium chloride, if used, may comprise up to 96,5% of the composition may include magnesium nitrate besides the chloride. The fibrous strengthening material e.g. wood wool of flour, timber, cane, asbestos, may be impregnated with an aqueous solution of the chloride, sulphate or sulphuric acid and excess of the latter removed before mixing with the reactive magnesia, e.g. magnesite of dolomite calcined at 750 DEG C. to 850 DEG C. Suitable fillers which may be incorporated include sand, quartz, marble fragments, granite, pulverised chert, diatomaceous earth, calcium carbonate, burnt clay, coke breeze, cinders, ashes, powdered pumice, kaolin, talc, barytes, glass, plaster, powdered slag or metal mineral ores, or pigments, the preferred particle size of these aggregates being greater than 100 B.S.S. mesh but smaller than 8 B.S.S. mesh. The composition can include colouring matter or a metallic finish can be imparted to the slab by giving it a wash with a solution of a metallic salt which reacts with a metal salt already included in the composition; the resultant metallic film may be thickened by electro deposition and lacquered to resist oxidation. By substitution of 7 1/2 to 20% of the magnesium chloride solution with a 7 1/2 to 15% alcoholic shellac solution a glazed finish may be obtained.</p> |
