In building sanitary ceramic products, magnesium silicate ceramic raw materials play an important role in ceramic blanks and glazes. For example, it can improve the glaze of the product
With regard to the performance of the billet, it plays an important role. At present, domestic and foreign markets have increased requirements for the appearance of building sanitary ceramic products. Especially in improving the whiteness, translucency and thermal stability of building sanitary ceramic products, magnesium silicate ceramic raw materials are essential additive raw materials. This article discusses and introduces the commonly used magnesium silicate mineral ceramic raw materials, such as talc, serpentine, forsterite, etc., in building sanitary ceramic products.
I. alc (3MgO · 4SiO2 · H2O)
1.Physical and chemical properties of talc raw materials
As we all know, the raw material of natural talc is hydrous magnesium silicate mineral, its chemical formula is 3MgO · 4SiO2 · H2O. Its theoretical chemical composition is: MgO content is 31.7%, SiO2 content is 63.5%, and H2O content is 4.8%. A natural talc mineral, it is white or pinkish in appearance, and is generally coarse scale-like. The dense, fine scale-like shape is called block talc, which has a slippery feel and a bulk density of 2.6 to 2.8 g / cm3. The hardness of the natural talc raw material is relatively small, only 1 to 1.5, which can be scored by fingernails. The thermal properties of natural talc raw materials are: when heated to 870 ° C, talc begins to remove crystal water, and when 950 ° C is completely dehydrated. The melting point of natural talc is 1550 ° C. Talc has good heat resistance, lubricity, acid resistance, and insulation in ceramics, and has a strong adsorption effect on glazes. Due to the above excellent properties, talc is widely used in daily-use ceramics, building sanitary ceramics and special ceramic products. In particular, it has played an extremely important role in improving the whiteness, expansion coefficient and preventing product cracking.
2. Application of talc in ceramic industry
Talc has a wide range of applications in the ceramic industry, such as making talc daily porcelain with high whiteness and high transparency, and producing high-frequency porcelain (also known as device porcelain) in the electric porcelain industry, or used in building sanitary ceramic products Colored glaze wall tiles and other glazes. Adding a small amount of talc to the feldspar porcelain blank can reduce the firing temperature, expand the firing range, reduce the content of free quartz in the porcelain tire, and improve the translucency and thermal stability of the product. A certain proportion of talc is added to some high-grade daily-use porcelain varieties in the northern porcelain district of China. In the raw materials of ceramic products, talc is used instead of feldspar, which can reduce the hygroscopic expansion and cracking defects of the product at the same time, and can reduce the dry knot, knot and firing shrinkage. For example, talc is introduced into glazed tiles and interior wall tiles in building hygiene products to improve the appearance and intrinsic quality of products.
The role of vermiculite in the glaze of sanitary ceramic products is more important and extensive. It can reduce the expansion coefficient of glaze during firing and prevent the glaze from cracking. Because talc can form a prism-shaped crystal substance in the glaze that enhances the ability to reflect light, it can enhance the opacifying effect of the glaze and help improve the whiteness of the glaze. In the color glaze wall and floor tile glaze, talc and apatite can form a phosphate-magnesium opacifying agent and a whitening agent, and the firing temperature is low and the range is wide, and the cost of the opalescent glaze can be reduced. In addition, a diopside crystal-like milky glaze can also be formed in the high-magnesium lime glaze. This type of opalescent glaze without the addition of opacifying agent (zircon) can act on its own to form a opalescent effect. In addition, talc can also increase the firing temperature range of the glaze to avoid smoky firing defects. Before being used as a formula, the raw material of natural talc must be calcined at a temperature of about 1200 ° C to improve the technological performance of talc.
3. Overview of the distribution of talc resources
China's talc resources are very rich, and the quality and quality of minerals are also very good. Among them, the most famous ones are Liaoning Haicheng, Shandong Yuyang, and Guangxi Longsheng, all of which are the main sources of talc. In addition, talc is also produced in Qixia, Shandong, Taiyuan, Shanxi, Lijiang, Yunnan, and Gaozhou, Guangdong.
Second, serpentine (3MgO · 2SiO2 · 2H2O)
In ceramic technology, serpentine belongs to the magnesium silicate class. Its chemical formula is 3MgO · 2SiO2 · 2H2O. The theoretical mineral chemical composition is: MgO content is 43.0%, SiO2 content is 44.1%, and H2O is 12.9%. Among natural minerals, serpentine has a higher impurity content, which often contains compounds such as Fe, Ni, Mu, Ti, Co, Cr and other elements. The appearance of serpentine is green, light green, yellow green, dark green and even black. The hardness is 2.5 to 3.5, and its thermal performance is decomposition at 1557 ° C. According to the internal structure and shape of serpentine, it is divided into serpentine and fiber serpentine, and the mixed concomitants of both serpentine and fiber serpentine are collectively called colloidal serpentine.
2. Changes of serpentine in calcination
① Serpentine dehydration temperature is earlier than talc. It starts dehydration at 400-600 ℃ and reaches full dehydration at 700 ℃. The minerals formed are forsterite and MgO · SiO2. The reaction process is: 3MgO · 2SiO2 · 2H2O2MgO · SiO2 (forsterite) + MgO · SiO2 + 2H2O.
② When the firing temperature is about 1000 ° C, MgO · SiO2 forms refractory pyroxene, and then increases with temperature to form oblique refractory. 2MgO · SiO2 + MgO · SiO2 (amorphous) 1000 ° C 2MgO · SiO2 + MgO · SiO2 (cavite-type pyroxene).
③ When the firing temperature of serpentine reaches 1300-1400 ℃, the material shrinks violently, and the shrinkage rate can reach 10-25%.
④ At 1400-1500 ℃, serpentine forms complete sintering. The main minerals are forsterite and oblique opalite. In addition, there are magnetite and spinel inclusions.
Application of Serpentine in Ceramics
Since serpentine contains more impurities than talc, raw materials with low iron content can be used as ceramic blanks. Serpentine can be used to produce serpentine daily porcelain. This has been trial-produced in the Handan porcelain district of Hebei in the past. Its product properties, such as whiteness and translucency, are similar to talc porcelain. In addition, serpentine raw materials can be used in mid-range products of porcelain, building ceramic products, floor tiles, and industrial ceramics. At present, serpentine mineral raw materials are mainly used for refractory materials, such as used to make cordierite boxes. Serpentine minerals are widely distributed in the north of China, such as Jilin Ji'an, Xiuyan in Liaoning, Chengde in Hebei, Da'an in Shaanxi, Yilan in Heilongjiang, and Pengxian in Sichuan.
With the rapid and high-quality development of China's building sanitary ceramic industry and the use of high-tech technology, magnesium silicate ceramic raw materials will show a wider range of uses, and will continue to increase the value of raw materials in use, and achieve more Good economic benefits.