Quartz, geology terminology, generally refers to low temperature quartz (α-quartz), is the most widely distributed mineral minerals in quartz. Generalized quartz also includes high temperature quartz (β-quartz), coesite and so on. The main ingredient is SiO2, colorless and transparent, often containing a small amount of impurities, and become translucent or opaque crystals, hard texture. Quartz is a physical property and chemical properties are very stable mineral resources, crystal is a triad of oxide minerals.
Quartz stone at room temperature is a stable mineral, insoluble in water and sulfuric acid, hydrochloric acid, nitric acid. Hardness 7, specific gravity of about 2.65, melting point 1713 ℃. Glossy glassy, sometimes fat-like. Texture is purely colorless; with impurities are red, yellow, blue, black, brown, purple, green; Quartz transparent to opaque, brittle Fracture was shell-like or staggered. Crystal was hexagonal columnar, column with stripes. There is a difference between left and right crystals. Twin crystals are common. Quartz is a non-plastic material, and its clay in the high temperature generated mullite crystal to give porcelain higher mechanical strength and chemical stability, Quartz and can increase the translucent body, is the preparation of white glaze good raw materials.
The role of quartz in porcelain billet
(1) quartz raw materials are barren raw materials, it has a ceramic body in the normal temperature heating has an important impact. Before sintering, the quartz in the blank material on the plasticity of the plastic from the role of conditioning, and can reduce the shrinkage in dry, Quartz shorten the drying time and prevent the deformation of the body (including deformation and collapse).
(2) quartz in the firing process, the emergence of crystal transformation, volume expansion, can offset the partial shrinkage of the body. As the quartz crystal transition will cause changes in volume, so in the heating and cooling process should be carefully controlled cooling and heating rate, Quartz to avoid cracking products.
(3) When firing, the heating expansion of quartz properly counteracts the sintering of the billet, and when the glass phase is present in large quantities, the quartz becomes the skeleton of the ceramic, which prevents the body from bending during firing And other defects.
(4) high temperature chemical affinity is very strong, Quartz with a variety of other oxide compounds, high temperature liquid viscosity is very high, increase the green body binding capacity.
(5) to increase the mechanical strength and transparency of the body.
The role of quartz in enamel
(1) Quartz in the glaze, the more fusible CaO, Na2O, K2O, MgO melt to produce transparent quartz glass, so that glazed bright, improve the glaze gloss.
(2) quartz in the glaze in the thermal expansion coefficient is small, good heat resistance.
(3) quartz softening temperature is high, high temperature liquid viscosity.
(4) quartz can increase the mechanical strength of glazed, improve the glaze hardness, Quartz so that porcelain wear, and chemical stability Ye Hao, not affected by the erosion of acid.
(5) can make the glaze transparent light.
In the production of glazed tiles, the amount of quartz in the green body is generally 10-20%, in a firing glazed tile body in the amount of less, usually 10-15%, in the amount of glaze frit 20-40%. White billet for quartz purity requirements are higher, while the colored body can be used less pure quartz. In a burnt wall tiles of the body is often not directly added to the quartz, but by the introduction of clay with clay.