Homogeneous mixt. of synthetic anhydrite and gypsum - obtd. by mixing activators and small amt. of water with neutralised anhydrite, then compacting and milling the mixt.

摘要

Fine synthetic anhydrite (SA) is neutralised followed by adding 0.5-2.5 wt. % activators (I) which cause the absorption of water of crystallisation and hardening. The free water content of the mixt. is adjusted to 2-4.5%, and the mixt. is then compacted and stored for min. 20 hours followed by milling to 0.16mm size with distribution:- 10-40% below 0.2 mm; 20-45% at 0.2-1 mm; 15-40% at 1-3.15 mm; and 5-30% at 3.15-15 mm. The milled prod. contains 70-92% SA and 8-25%, esp. 10.20% CaSO4, 2H2O(CSDH) and has an initial thickening time below 12 minutes. The fine SA is pref. obtd. during the mfr. of HF; or from CSDH or CaSO4 1/2 H2O obtd. e.g. during the mfr. of H3PO4 or esp. by washing waste gases, using dehydration. The prod. pref. has max size 8 mm and initial setting time below 10 minutes. Activator (I) is pref. K2SO4 or Ca(OH)2. Used esp. in coal mining for the mfr. of dams, tunnels, support pillars etc. made by pneumatic laying or transport of the mixt.