How to adjust the glaze of ceramics?

There are many kinds of ceramic glazes, which are described as follows:

1, lead glaze and lead-free glaze

In the lead glaze formula used in building ceramics and sanitary ceramics products, the source of lead is lead metasilicate or boron lead silicate frit. In actual production, the typical formula of lead metasilicate is: Segur type 1.00 lead oxide, 0. 10 alumina, 1.89 silica, weight ratio: lead oxide 64%, alumina 3%, silica 33%). Glaze can have the lowest solubility. If the content of basic oxide and boron oxide increases, the solubility of lead in glass frit will increase. The Netherlands and other countries have no restrictions on lead-free solubility, so lead silicate and lead borate frit glazes with low melting point or high solubility are used. The difference between lead glaze and lead-free glaze relates to the quality of products. However, when the temperature is higher than 1 150℃, lead is obviously volatilized. When the temperature is higher than this limit, lead glaze is usually no longer used. Lead-free glaze refers to the kind with lead oxide content less than 1 wt%. With more and more strict environmental protection requirements, the building ceramics industry in various countries has gradually turned to lead-free glaze, lead-free flux and lead-free pigment.

Strontium glaze has shown good effect in replacing lead glaze. Besides wide firing range, low firing temperature and glossy glaze, it also has good wear resistance. Therefore, strontium glaze becomes a good lead-free glaze. When used in combination with under-glaze colorant, it has little adverse effect on colorant. However, when it is used with chrome tin red, a certain amount of calcium oxide must be added to the glaze to stabilize the timbre.

2. Raw glaze and frit glaze

Because frit is not used in the composition of ceramic raw glaze, it is only used when the highest firing temperature is greater than 1 150℃. Generally, it can be used to glaze hard porcelain, vitrified sanitary porcelain, stoneware, electric porcelain and various low expansion blanks. Raw glaze contains mineral solvents, such as feldspar or nepheline syenite, and clay, timing, calcium carbonate, dolomite, zinc oxide and zirconium silicate are added as common raw materials. Low expansion raw glaze also uses petalite as flux. Raw glaze will not have any form of glass phase, so it must take enough time to exhaust the gas from the raw materials when firing. After the glaze is melted, a smooth and bubble-free glaze can be obtained. So the firing time of green glaze is longer than that of frit glaze. When the firing temperature is lower than 1 150℃, frit glaze should be used. In addition, the content of frit in the glaze needs to be increased when the low temperature and fast firing process is adopted.

3. Primary firing and secondary firing.

For ceramic enterprises, the first firing of glazed products is more energy-saving and economical than the second firing, which greatly reduces the product cost and is beneficial to environmental protection. One-time firing is very beneficial to high value-added products, such as large sanitary ware or large insulators. The main advantage of secondary firing is that you can choose to eliminate some defective semi-finished products, and you can also produce high-quality and low-cost products. In the process of one firing, the glaze and the green body mature at the same time, and the formation of the intermediate layer between the green body and the glaze can often increase the strength of the product, and the complete vitrification of the green body is also obvious. In the process of primary firing, glaze often contains binder, which can not only control the evaporation rate of water from glaze slurry, but also control the movement of water into porous body. Glaze binder can increase the hardness of dry glaze.

4. Colored glaze and colorless glaze

Building sanitary ceramic products are generally decorated with colored glaze, which makes them feel beautiful when used and improves the added value of the products. The application of colorless glaze is limited to a very small product range (such as special purpose ceramic tile products). In Europe, the color glazes of ceramic building and sanitary ceramics use metal oxide pigments, and inorganic compounds of transition metals such as vanadium, chromium, manganese, iron, cobalt, nickel and copper are commonly used pigments. The effect of colored glaze depends on the chemical composition of basic glaze, the amount of pigment added, the thickness and uniformity of glaze application and the kiln gas during firing. For example, the introduced iron oxide is usually red ferric oxide, and melting the green body into the glaze can produce subtle decorative effects. Iron can produce light yellow, honey color and brown color in ceramic glaze in oxidation flame atmosphere. Light blue, gray, green, blue or black can be formed in reducing flame atmosphere; Cobalt black oxide is the strongest colorant in glaze. When the content is lower than 1%, bright blue can be formed. Cobalt is easily melted in the glass glaze matrix and added into the enamel structure; Chromium oxide can make some glazes appear green, while others can form red, yellow, pink or brown. Nickel oxide has a wide range of colors in glaze, which can form brown, green and dark blue glaze. When the glaze contains barium carbonate, it will form pink purple. Manganese dioxide can form black in glass, but it can also form red, pink and brown. The high alkali glaze containing manganese will produce light blue after firing at high temperature; Copper oxide glaze is green in oxidation flame and red in reducing flame. Vanadium pentoxide can produce brown or yellow, but even if the dosage is increased, it will only show medium-intensity yellow. Vanadium and zirconium can be made into stable colored glaze, such as Vanadium Zirconium Yellow and Vanadium Zirconium Blue. In addition, cadmium sulfide and selenium pigments can be made into yellow, orange and red glazes.

5, transparent glaze and opaque glaze

Opaque glaze is widely used in building sanitary ceramics. Due to the insufficient hiding power of transparent glaze, it is difficult to cover the unclean brick surface, and the environmental protection work requires the use of low-quality raw materials as much as possible, so the application scope of transparent glaze becomes narrow. The glaze opacifier used by ceramic enterprises has gone through the processes of tin oxide, zinc oxide, titanium dioxide, phosphate and zirconium silicate. However, as a sunscreen, tin oxide is used less and less because of its high cost. In the 1920s, zircon was introduced as opacifier of glaze, and then zircon was used instead of tin oxide, which reduced the cost of glaze products for ceramic tile decoration. However, if 5% tin oxide is added to the conventional glaze, the hue of white glaze and blue glaze can be produced; Zinc oxide is widely used in zircon glaze, which can improve whiteness and opacity. Zinc oxide has a strong solubility in the glaze of high-temperature sanitary ware products, which can significantly reduce the viscosity of the glaze, so it is still partially used at present and it is difficult to completely eliminate it in the future; Adding titanium oxide to glaze can make high-grade white opaque glaze, which has been proved to be a feasible formula. The functions of phosphorus compounds in glaze are as follows: first, as opacifier, the glaze is opaque; Second, increase the refractive index of glaze to light and increase the luster of glaze. Calcium phosphate, ashes and apatite can be mixed into the glaze in proper amount as appropriate, so that the glaze can form a good opaque and bright effect. In addition, lithium compounds such as lithium limestone and diopside are also good raw materials for opaque glaze.

6. Glossy glaze, semi-dull glaze, dull glaze and broken glaze

Various glazes have different light absorption, which can be divided into glossy glaze, semi-dull glaze, dull glaze and broken glaze. The above-mentioned glazes are rich in color and there are many kinds of glazes. The development trend of ceramic tile glaze will gradually shift to semi-matte and matte glaze series. There are not many color forming elements in matte glaze, but the glaze color is very rich, and there are many kinds of matte glaze, such as kaolinite matte glaze, alkaline matte glaze and silica matte glaze. Among them, barium matte glaze, zinc matte glaze and magnesium matte glaze are its main representatives. In addition, there are crystalline matt glaze, spodumene crystalline matt glaze and insoluble matt glaze. Broken glaze is a kind of reticulate turtle crack produced by glaze surface, which is suitable for tile decoration. It originated from China's broken porcelain products, and was later used for tile decoration in western countries, and received particularly beautiful results. Cracks occur due to different expansion coefficients of blank glazes, and there are five methods to prepare broken glazes: for example, two glazes with different shrinkage rates are used, and the glaze with high shrinkage rate is applied to ordinary glazes, and the upper glaze cracks after firing, so that the lower glaze can be seen through; Increase the solubility of glaze and increase the shrinkage of glaze, such as increasing the dosage of feldspar and boric acid; Increase glaze shrinkage and reduce body shrinkage; Therefore, the product will also produce broken glaze during quenching; Some glazes will form broken glazes after being left for many years. For example, France adopts the method of adding silica, bauxite or alkali to ordinary glaze to make broken glaze varieties. Some use a variety of firing methods to form different broken lines and color effects.

7. crystalline glaze refers to the glaze with obviously coarse crystals. It is a highly decorative artistic glaze, which originated from the ancient colored glaze in China. Crystalline glaze is different from ordinary glaze, it contains a certain number of visible crystals (that is, we can see the crystal flowers on or in the glaze).

Crystalline glaze's crystal flowers can be large or small, more or less. The large ones can be seen by naked eyes, and the small ones need a microscope to distinguish. The distribution of crystal flowers can also be reasonably controlled by artificial methods. Shapes are star-shaped, needle-shaped or flower-leaf-shaped. As a kind of advanced ceramic art glaze, crystalline glaze's beautiful and novel natural crystal flowers, with its diverse appearance and colorful colors, give people a strong artistic effect and are deeply welcomed by users at home and abroad.

In addition, the building sanitary ceramics industry has accelerated the adoption of high and new technology to promote the development of new glaze technology and develop new glaze varieties, and has made many progress. Such as the application of nano-material technology in glaze technology, a large number of new products are introduced every year. Generally speaking, attaching importance to glaze technology innovation and new product development can improve the grade and added value of products. With the increasing variety of building sanitary ceramics, many new requirements are put forward for the improvement of glaze. Therefore, the research and development of ceramic glaze will be more and more important in the future, and will occupy an increasingly important position in the competition of international ceramic industry. China's ceramic industry should accelerate the absorption of advanced technology, continue to improve the grade and scientific content of products, and gradually form its own glaze product system and decorative characteristics.

Low temperature: about 800 degrees, medium temperature about 1 100 degrees, high temperature: 1280- 1400 degrees, and cracked glaze is fired at high temperature. Shadow glaze is high temperature. Cracked glaze and sapphire glaze can't be mixed together. Pay attention to operation. If crack glaze is mixed, there may be no cracks.