Three main chemical composition of refractory materials

Three main chemical composition of refractory materials

The chemical composition of a refractory material is its basic characteristic. Whether a refractory material can form a certain phase under certain conditions, why this phase appears, and has certain specific properties, as well as how to essentially change certain specific properties of the material, all first depend on its chemical composition . According to the content and function of various chemical components in refractory materials, they are usually divided into three categories: main components, impurities and additional components.

A .Principal component

The main components in refractory materials refer to the vast majority of chemical components that play a decisive role in the high-temperature properties of the material. The reason why refractory materials have good resistance to high temperature effects, and many refractory materials have their own characteristics, completely or basically depends on the main components. Usually, the classification of refractory materials according to their chemical composition and the classification of many refractory materials of the same material into several grades are or mostly based on the type of their main components and their content.

The main components of refractory materials are simple substances or compounds with high lattice energy, high melting point or high decomposition temperature. It is required to form stable minerals with good properties during the production or service of refractory materials. It has high reserves in nature and is easier to extract and utilize. It is widely distributed in the earth's crust and can be used as refractory materials. The main component is mainly oxide. In addition, there are some carbides, nitrides, silicides and borides, which can also be used as the main components of refractory materials. 

Nowadays, the main components of refractory materials that are widely produced and used are mainly oxides- such as A1203, BeO, Cr2O3, MgO, CaO, Si02, ThO2, UO2, ZrO2, carbides- such as SiC, WC, B4C, and nitride-A1N, Si3N4, etc. .

B. Impurities

Impurities refer to chemical components in refractory materials that are different from the main components, have a small content, and often cause harm to the high-temperature resistance properties of refractory materials. This chemical component is mostly entrained from the raw materials containing the main component.

Some of the impurities in refractory materials are fusible substances, and some have high melting points themselves, but when they coexist with the main components, they can produce fusible substances. Therefore, the presence of impurities often exerts a strong fluxing effect on the main component. Although the fluxing effect sometimes helps the liquid phase sintering of the material, it has serious harm to the material's resistance to high temperature. The stronger the fluxing effect, that is, due to the presence of impurities, the lower the temperature at which the liquid phase begins to form in the system, or the greater the amount of liquid phase formed, or the faster the amount of liquid phase increases as the temperature increases, and the amount of liquid formed is The lower the phase viscosity and the better the wettability, the more serious the risk. For example, for materials whose main component is SiO2, if it contains any oxide among Na20, A120, TiO2, CaO and FeO, except for Na2O, which has a lower melting point, other oxides have higher melting points, but they are not the same as SiO2 Although they coexist, they both have a fluxing effect. It can be seen that if Na20 and SiO2 coexist, the temperature at which the liquid phase begins to form is very low. Therefore, if the refractory material with Si02 as the main component contains a small amount of Na20, its high-temperature properties can be improved. to cause serious harm. If the refractory material with SiO2 as the main component contains A1203 and Ti02 respectively, although the eutectic temperatures of the Si02-Al203 and Si02-TiO2 systems are similar, 1595°C and 1550°C respectively, at the eutectic temperature every 1 % impurity chloride in the liquid phase is quite different, the former is about 1.9 times the latter. Moreover, as the temperature increases, the difference becomes larger. For example, at 1600°C, it is about 2.3 times. Therefore, the impurity A1203 has a stronger flux effect on Si02 than TiO2. Alumina is very harmful to the high temperature performance of silicon refractory materials.

In addition, when impurities coexist with the main components, if the viscosity of the generated liquid is lower, and the viscosity decreases faster as the temperature increases and the wettability is better, the harm to the refractory materials will be more serious. Therefore, it is necessary to improve the resistance of the refractory materials to high temperatures. performance, the content of impurities must be strictly controlled.

C.Additional ingredients

Additional ingredients, often called admixtures, are small amounts of ingredients added for specific purposes in the production of refractory products. For example, mineralizers are added to promote the formation and transformation of certain phases in the material; inhibitors or stabilizers are added to inhibit the formation of certain phases in the material; additives are added to promote the sintering of the material. Flux etc. In short, in the production of refractory materials, adding a small amount of additives can change the composition and structure of the material to a certain extent, thereby facilitating production and making the product obtain certain expected characteristics. However, care must be taken not to seriously affect its basic properties of resisting high temperature.

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