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), Ke Shiying and so on
The The main ingredient is SiO2, colorless and transparent, often contain a small amount of impurity composition, and become Quartz translucent or opaque crystal, hard texture. Quartz is a kind of physical and chemical properties are very stable
Of the mineral resources, the 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 faty. texture
Pure to colorless; with impurities are red, yellow, blue, black, brown, purple, green; transparent to opaque, brittle Fracture was shell-like or mixed. Crystal was hexagonal columnar, column with stripes. Have left
The difference between crystal and right crystal. Twin crystals are common. Quartz is a non-plasticizable material that Quartz imparts high mechanical strength and chemical stability to porcelain with mullite crystals produced at high temperatures and can increase
The translucent body is a good raw material for the preparation of white glaze.
First, the role of quartz in porcelain billet
(1) quartz raw materials are barren raw materials, it has a ceramic body in the heating at room temperature have an important impact. Before firing, the quartz in the blank material on the plasticity of the role of adjusting the role, and can be dry
Reduce shrinkage, shorten drying time and prevent 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. Since the quartz crystal form changes can cause volume changes, so in the heating and cooling process
Should be carefully controlled cooling and heating rate, to avoid cracking products.
(3) In the firing, due to the heating expansion of quartz to properly offset the baking of the billet; and when the glass phase appears, quartz has become a skeleton of ceramics, can prevent the green body in the firing
The occurrence of bending deformation and other defects.
(4) high temperature chemical affinity is very strong, 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.
Second, the role of quartz in the 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, so that porcelain wear, and chemical stability Ye Hao, not affected by the erosion of acid.
(5) make the glaze transparent and bright.
In the production of glazed tiles, the amount of quartz in the green body is generally 10-20%, in a firing glazed tile body Quartz in the amount of less, usually 10-15%, in the amount of glaze frit 20-40%. White
The color of the green body requires a higher purity for quartz, while the colored body can be made of less pure quartz. In a burnt wall tiles of the body is often not directly added to the quartz, but by the use of clay to lead
Third, the crystal in the firing process of crystal transformation
(1) low-temperature rapid transformation of quartz crystal: the conversion temperature is low, the crystal table at the same time transformation, conversion speed, reversible reversible direction, before and after transformation of the body volume changes little, the body heated
The effect of cracking is greater:
A, β-quartz reversible into α-quartz, the conversion temperature is 573 ℃, the volume expansion is 0.82%;
B, γ-scale quartz reversible into β-squamous quartz, the conversion temperature is 117 ℃, the volume expansion is 0.20%;
C, β-scale quartz reversible into α-scale quartz, the conversion temperature is 163 ℃, the volume expansion of 0. 20%;
D, β-square quartz reversible into α-cristobalite, the conversion temperature is 180-270 ° C, the volume is expanded by 2.80%;
(2) quartz crystal high temperature slow conversion: high conversion temperature, from the surface to the internal transformation, the transformation process is slow