| 摘要 |
In the production of plaster articles, for example, dental dies and moulds, powdered gypsum (calcium sulphate) is mixed with an aqueous solution of boric acid and/or silicic acid. By incorporating boric acid and/or silicic acid in the mix, the hardness and setting characteristics of the mix are improved. In a typical application the concentration of boric acid in the aqueous solution is from 0.3 to 1.1 grams boric oxide per liter of solution and the preferred concentration of silicic acid in the aqueous solution is within the range of from 75 mls to 300 mls concentrated silicic acid per liter of aqueous solution. |
