PROCESS FOR THE PREPARATION OF Aqueous CALCIUM SULFATE SEMI-HYDRATE SUSPENSIONS AND THEIR USE

摘要

1. Process for making aqueous calcium sulfate semihydrate suspensions setting under control, the setting being inhibited by the addition of at least one alkaline earth metal and/or alkali metal hydroxide and/or ammonia and/or an organic amine and at least one polycarboxylic acid in a total proportion of 0.2 to 2 weight %, based on calcium sulfate semihydrate, characterized in that an aqueous calcium sulfate semihydrate suspension capable of setting and having been obtained by subjecting calcium sulfate dihydrate to hydrothermal treatment is used, and in that the setting of the suspension is initiated at any moment deemed desirable by reducing the pH-value of the suspension to less than 8 by the addition of mineral acids or their acid salts.