Process for preparing bonded reconstituted mica

A silica-bonded reconstituted mica mat is made by impregnating a reconstituted mica mat with an aqueous solution of ammonium silicate, drying to remove ammonia, and pressing at a temperature of 75 DEG to 200 DEG C. The initial mica mat may be prepared by cleavage and grinding of mica and incorporation of the mica particles into a mat using well-known paper-making methods. The mat may be impregnated by immersion, spraying, or brushing with an aqueous solution containing from 5% to 30% ammonium silicate and may be dried at a temperature of from 20 DEG to 100 DEG C. The dried mat may be subjected to a pressure of 25 to 2000 p.s.i. at a temperature from 75 DEG to 200 DEG C. for a time exceeding half an hour and, if desired, may be pressed again at the same or different pressure within the above range but at a temperature from 100 DEG to 200 DEG C. Cooling may be effected under pressure. Two or more mats may be placed in layers either prior to the impregnation stage or prior to the pressing stage. The final product may be used as an electrical insulator, and particularly as a spacer in electronic tubes.