A glass-bonded crystalline mineral is prepared from a synthetic mineral selected from mica, amphiboles, humites, spinel, zirconia, norbergite, and titania and glass compositions free of b. For example, the raw materials for producing fluor-phlogopite were weighed as mgo 28.7, Al2o3 7.44, Sio2 19, k2sif6 19.33, and feldspar 25.53 pct. The raw materials for the glass-forming composition were weighed as pbo 55, al2o3 9.3, and sio2 35.7 pct. The combined raw materials were mixed for 30 min in a 50:50 ratio. A pressure of 2 tons/sq in was used to cold press the mixture into preforms, which were placed in a kiln, heated to 1,100 deg c, and maintained at this temperature for 1 h. During heating, at 800 deg c the material was dry, the glass components formed a glass, and initial crystal development occurred. At 800 deg-1,000 deg c, crystals of synthetic mineral reached 1-2 micrometers in size and were increasing. At 1,000 deg-1,100 deg c, fluor-phlogopite, mica, lead mica, fibrous humite, minute spinel particles, and crystalline norbergite continued to grow. At 1,100 deg c the crystal size increased to 3-5 micrometers during a 1-h soak. The preform was rapidly cooled to 880 deg c, molded at a pressure of 2-5 tons/sq in for 1-3 min in a mold heated to 625 deg c, then cooled in an annealing furnace from 625 deg c to room temperature in 12 h. The product was impervius with increased impact strength; dielectric constant 7.55, Dissipation factor (ASTM) 0.0013, Loss factor (ASTM) 0.0098, Flexural strength 17,000 psi, and density 3.65.
U.S. Pat. 3,516,810; June 23, 1970; Chem. Abstr. 73:80,149A