In industrial production and high-temperature technology applications, refractories play a crucial role. They can withstand extremely high temperatures, protecting equipment and personal safety. So, what raw materials are these amazing refractories made of?
Alkaline refractory
① magnesium raw material
(1) magnesite
There are two main types of magnesite: crystalline magnesite and amorphous magnesite. The main impurity of this mineral is talc, and some magnesite also contains relatively high CaO, followed by dolomite mineral composition. In order to obtain high purity magnesia, two-step flotation and two-step calcination are often used for preparation. Using the high purity magnesia obtained by this method, many high-performance refractory products can be further developed to meet the needs of various high temperature processes.
(2) Other minerals containing magnesium
In the field of magnesium refractories, magnesium olivine products are highly respected for their unique mineral composition and excellent performance. This kind of product is mainly composed of magnesium olivine (2MgO·SiO2) and magnesite (MgO), the combination of these two minerals, making the product in the fire resistance has been significantly improved. In particular, it is worth mentioning that magnesium olivine products have excellent erosion resistance to molten iron oxide, and their thermal shock stability is significantly better than that of ordinary magnesium bricks, which enables them to maintain stable performance in high temperature and highly corrosive working environments. The main raw materials for the production of this high-performance product are carefully selected peridotite and serpentine rock, the purity and mineral composition of which have a crucial impact on the performance of the final product.
② white marble raw material
Dolomite, the refractory raw material mainly composed of magnesium carbonate (MgCO3) and calcium carbonate (CaCO3) double salt, its chemical formula can be expressed as CaMg(CO3)2 or MgCO3·CaCO3. In terms of theoretical composition, it contains 30.41% CaO, 21.87% MgO and 47.72% CO2, showing a specific chemical composition ratio, in which the ratio of CaO to MgO is 1.39. In addition, the hardness of dolomite is 3.54, showing its good physical properties.
Raw materials for zirconium products
① Zircon stone
Zircon stone, chemical formula ZrO2·SiO2 or ZrSiO4, is an indispensable raw material for the manufacture of zirconium products and zircon products. In terms of theoretical composition, zircon contains 67.01% ZrO2 and 32.99% SiO2. Notably, it also often contains TiCfe as well as other trace rare earth oxides. The presence of these elements makes zircon stone have a certain degree of radioactivity, therefore, appropriate protective measures must be taken during the production process to ensure safety. Zircon has a low thermal conductivity of 3.72W/(m.K) between 20 ° C and 1000 ° C. In addition, its coefficient of expansion is low compared to other crystalline phases, only 4.6 x 10-6 ° C at 1000 ° C. Zircon’s chemical properties are extremely stable, with high chemical inertness, and it is difficult to react with acids. Although it will react with glass melt to a lesser extent, this does not prevent it from being widely used as a refractory in the metallurgical and glass industries.
② Oblique zircon
Natural zircon (ZrO2) often occurs in irregular clumps and varies in color, including black, brown, yellow, or colorless. However, natural plagiozircon ore bodies are relatively rare. ZrO2, which is widely used in industry, is actually a chemical raw material, which is a white or slightly yellow powder extracted from zircon stone (ZrO2·SiO2) by chemical methods. Under atmospheric pressure, pure ZrO2 exhibits three distinct crystal forms: monoclinic, tetragonal, and cubic as the temperature goes from low to high. In addition, stable ZrO2 can be further subdivided into partially stable ZrO2 and fully stable ZrO2 according to its degree of stability. It is worth noting that although the fully stable ZrO2 performs well in some respects, its thermal shock stability is not as good as that of the partially stable ZrO2 due to its relatively large coefficient of thermal expansion. Because of this, partially stable ZrO2 is more commonly used as a toughening material for ceramics and refractories.
③ Desiliconized zirconium
In the production process of fused cast zirconium corundum (AZS) refractory, foreign manufacturers in addition to the use of zircon concentrate, but also generally add a certain amount of “desilicated zirconium” raw materials. The purpose of this practice is mainly in two aspects: first, to adjust and optimize the formula to ensure the accurate control of product ingredients; The second is to further improve and optimize the performance of the product through the addition of desiliconized zirconium, so that it has better stability and durability in high temperature environment. This refined raw material ratio not only improves the overall quality of refractories, but also meets the stringent requirements of refractories in various complex industrial environments.
Zirconium corundum mullite is a kind of refractory material with high performance. The preparation process of zirconium corundum mullite requires selective raw materials and strict control of process parameters. The raw materials include industrial alumina, high purity kaolin and zirconite, which are finely ground and evenly mixed and pressed into spheres by semi-dry process. Subsequently, calcination is carried out in the temperature range of 300 to 1700 ° C, and through this series of fine processes, high-quality zirconium corundum mullite materials can be produced. The results show that with the increase of zircon content, the sintering temperature will increase, the total shrinkage will decrease, and the number of closed pores will increase. These reactions combine to produce sintered zirconium corundum mullite with high density and strength, as well as excellent thermal shock stability to meet the demanding demands of refractory materials in high-temperature industries.
Raw materials for chrome products
The production of chrome products, such as chrome brick, chrome magnesia brick, magnesia chrome brick and other refractory materials, cannot be separated from a key raw material – chromium ore or chromite. Chromite is not a single mineral, but a mixture of many minerals. This mixing characteristic makes the mineral composition of chromite fluctuate greatly, which results in significant changes in its chemical composition and physical properties. Chromite is mainly composed of chromic grains and gangue minerals, which are mostly magnesium silicate, such as serpentine, magnesium olivine and olivine. In addition to the main component Cr2O3, chromite also contains other oxides such as Al2O3, Fe2O3 and MgO. Therefore, the general chromite composition is often expressed in the form of (Mg, Fe) Cr2O3, which also reflects the important presence of magnesium and iron in it. This complex chemical composition gives chrome products unique fire resistance and makes them perform well in high temperature environments.
The above are commonly used refractory raw materials, with the innovation of refractory technology, the types of raw materials are more diverse, especially in recent years, because of a series of reasons such as environmental problems and raw ore resources, and continue to develop better performance of artificial synthetic materials and more environmentally friendly resource renewable raw materials.