Abstract: A glass forming compound having in its melted glass phase the formula Si.sub.2 AlO (PO.sub.4).sub.3 or 4 SiO.sub.2.Al.sub.2 O.sub.3.3P.sub.2 O.sub.5 is provided together with grain mixtures for producing refractory thermally insulating bricks adapted for use in the preheating zone of a rotary cement kiln operating in an atmosphere containing alkali chlorides, particularly KCl. The bricks develop a glass layer on the kiln exposed face thereof which resists penetration by alkalis, particularly KCl.

Abstract: A glass forming compound having in its melted glass phase the formula Si.sub.2 AlO (PO.sub.4).sub.3 or 4 SiO.sub.2.Al.sub.2 O.sub.3.3P.sub.2 O.sub.5 is provided together with grain mixtures for producing refractory thermally insulating bricks adapted for use in the preheating zone of a rotary cement kiln operating in an atmosphere containing alkali chlorides, particularly KCl. The bricks develop a glass layer on the kiln exposed face thereof which resists penetration by alkalis, particularly KCl.

Abstract: Low carbon, white husk ash suitable for use in manufacturing building materials, more particularly refractory building materials are prepared by first removing volatile constituents by heating the husks, normally rice husks but alternatively, for example, wheat, oats or barley husks, to a first relatively low temperature below the ignition point of the husks. Fixed carbon is then oxidized in the presence of a reagent by heating the husks to a second temperature above the separation temperature but below the crystallization temperature of the SiO.sub.2 in the husks, following by a heat treatment at a third temperature above the crystallization temperature of the SiO.sub.2, to produce a uniform SiO.sub.2 crystal structure.