Abstract
The composites consisting of α-quartz crystallites and amorphous SiO2 were prepared by HIP technique, imitating the structure of natural agate which is practically strong and is widely used in the industry, α-quartz and SiO2 glass powders with 5μm in average grain size were used as starting materials. These powders were mixed with the composition of 0, 5, 10, 25, 50 in wt% of α -quartz. This mixture was pressed into a compact with φ12mm×20mm in size. The Pyrex glass capsule containing the compact was hipped at 800-1200°C for 30-240 minutes under the pressure of 50-200MPa. The specimens with the appearance of agate were obtained at 1200°C under 100 and 200MPa. The polarization microphotograph showed that the crystallites were in the amorphous SiO2 matrix. α-quartz was confirmed as the crystalline phase by x-ray powder diffraction method. The composition of α-quartz increased slightly after hipping. Therefore, chemical bonds may be formed between crystallites of α-quartz and amorphous SiO2. Using the starting mixture with 25wt% of α-quartz, the maximum density of 2.50g/cm3 was obtained at 1200°C for 120 minutes under 200MPa. In the case, the maximum bending strength was obtained to be 9.2Kg/mm2, corresponding to 70% of that in the natural agate.
