ceramic raw materials
The raw materials of coarse pottery, fine pottery, stone ware, semi Ceramic China and even porcelain are from coarse to fine, the blank body is from coarse to porous, gradually to dense, sintered, and the firing temperature is gradually from low to high.
Rough pottery is the most primitive and low-level ceramic ware, which is generally made of a kind of fusible clay. In some cases, clinker or sand can also be added to clay to mix with it to reduce shrinkage. The firing temperature of these products varies greatly, which depends on the nature and amount of impurities contained in the chemical composition of clay. If the porosity of brick and tile is too high, the frost resistance of the body is not good, and the low fork is not easy to catch the mortar, so the water absorption should be kept between 5% and 15%. The color of the green body after firing is determined by the content of the colored oxide in the clay and the firing atmosphere. It is mostly yellow or red in the oxidation flame and blue or black in the reduction flame.
The blue brick in the building materials of our country is made of yellow or red clay containing Fe ₂ O3, which is calcined in the reduction flame near the fire stop, so that Fe 203 can be reduced to FeO and become blue. The pottery can be divided into ordinary pottery and fine pottery. Ordinary pottery refers to earthenware pots, pots, jars, urn, and refractory bricks with porous colored body products. The water absorption rate of the body of fine pottery is still 4-12%, so it has permeability, no translucency, generally white and colored. Most of the glazes are fusible glazes containing lead and boron. Compared with stoneware, it is not fully sintered due to less fluxes and firing temperature less than 1300 ℃; compared with porcelain, it has lower requirements for raw materials, greater plasticity of blank and lower firing temperature. It is not easy to deform, so it can simplify the forming, filling and other processes of products. However, the mechanical strength and impact strength of fine pottery are smaller than that of porcelain and stoneware, and its glaze is softer than that of the above-mentioned products. When its glaze layer is damaged, the porous body is easy to contaminate, which affects the health.
According to the composition of the body, fine pottery can be divided into four types: clay, calcareous, feldspar and clinker. Clay fine pottery is close to common pottery. Limestone is used as the flux in the manufacturing process of calcareous fine pottery, which is similar to that of feldspar fine pottery, but its quality is not as good as that of feldspar fine pottery. In recent years, it has been rarely produced and replaced by feldspar fine pottery. Feldspar fine pottery is also called hard fine pottery, with feldspar as the flux. It is the most perfect and widely used pottery. In modern times, many countries use it to mass produce tableware (cups, dishes, etc.) and sanitary pottery instead of expensive porcelain. Hot material fine pottery is to add a certain amount of clinker into the blank of fine pottery, in order to reduce shrinkage and avoid waste products. This kind of blank is mostly used in large and thick tire products (such as bathtub, too washbasin, etc.).
Stoneware is called "stoneware" in ancient Chinese books. The body of stoneware is dense and has been completely sintered, which is close to porcelain. However, it has not been vitrified yet. It still has a water absorption of less than 2%. The green body is opaque and white. Most of them are allowed to show color after firing. Therefore, the purity of raw materials is not as high as that of porcelain, and it is easy to get raw materials. Stoneware has high strength and good thermal stability, which is very suitable for modern mechanical washing, and can smoothly pass through the rapid change of temperature from refrigerator to oven. In the international market, due to the development of tourism and the socialization of diet, stoneware has a larger sales volume than enamel.
The blank of semi porcelain is close to that of porcelain, but it still has 3-5% water absorption after firing (true porcelain, water absorption is below 0.5%), so its performance is not as good as that of porcelain, which is better than that of fine ceramics.
Porcelain is a higher stage in the development of ceramics. It is characterized by complete sintering and vitrification of the body, so it is very dense, and has no permeability to liquid and gas. The tire is thin and translucent, with a shell shaped cross section, licking with the tongue, and feels smooth without being stuck. Hard porcelain has the best performance in ceramics.