Differences Between Magnesia Bricks and High Alumina Bricks

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Magnesia bricks and high alumina bricks are two common types of refractory materials widely used in high-temperature industrial fields such as metallurgy, construction materials, and chemical industries. Although both types can be used in high-temperature kilns, they are made from different materials and have distinct properties. Many customers find it difficult to distinguish between the two types when choosing refractory bricks. In fact, magnesia bricks and high alumina bricks differ significantly in terms of composition, performance, and application scenarios.

different kinds of magnesia bricks

Magnesia Bricks

Composition: Magnesia bricks are MgO products and are classified as basic refractory bricks because magnesium oxide is a basic oxide. They are white or grayish-white powders, odorless, tasteless, and non-toxic, and are typical alkaline earth metal oxides. The main component of magnesia bricks is magnesium oxide (MgO), usually with a content of over 80%, and in some cases, up to 95%. They are made by firing magnesite or fused magnesia. The melting point is 2852°C, the boiling point is 3600°C, and the density is 3.58g/cm³ (at 25°C).

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Performance of Magnesia Bricks

  • High Refractoriness: The refractoriness of magnesia bricks is typically above 2000°C, making them suitable for high-temperature environments.
  • Alkali Resistance: Due to their basic composition, magnesia bricks have excellent resistance to alkali slags and substances.
  • Thermal Expansion: They have a high coefficient of thermal expansion, which makes them prone to cracking when heated.
  • Thermal Conductivity: They have high thermal conductivity, allowing for quick heat dissipation.

Application: Mainly used in high-temperature furnace linings under basic conditions, such as steelmaking electric furnaces, open-hearth furnaces, and non-ferrous metal smelting furnaces.

Production Process: The main raw material for producing magnesia bricks is magnesite. The production process involves pressing calcined magnesia (with particle sizes from 5mm to fine powder) with an appropriate amount of sulfite pulp waste liquid or caustic magnesia as a binder. The components of magnesia bricks include metallurgical magnesia, sulfite pulp waste liquid, and caustic magnesia.

magnesia bricks and high alumina bricks

High Alumina Bricks

Composition: High alumina bricks belong to the Al2O3-SiO2 system, often referred to as alumina-silica products or neutral refractory bricks. The main component is aluminum oxide (Al2O3), usually with a content above 48%, and in some cases, exceeding 80%. The raw materials are often bauxite, corundum, etc. The main oxides are Al2O3 and SiO2, where Al2O3 is a trivalent oxide (R2O3), and SiO2 is a tetravalent oxide (RO2). The combination of these oxides allows for the formation of mullite at high temperatures.

Performance of High Alumina Bricks

  • High Refractoriness: The refractoriness of high alumina bricks is above 1750°C, higher than that of ordinary clay bricks.
  • Acid Resistance: High alumina bricks have good resistance to acidic slags and substances.
  • High Compressive Strength: They possess high compressive strength and good wear resistance.
  • Thermal Stability: They have good thermal stability and are less prone to thermal expansion-induced cracking.

Application: Mainly used in high-temperature furnace linings under acidic conditions, such as glass kilns, ceramic kilns, and cement rotary kilns. They are also widely used in electric furnace roofs and blast furnace linings.

high alumina refractory materials
magnesia spinel refractory bricks

Properties of High Alumina Bricks

  • Low-grade high alumina bricks have a load softening temperature of around 1450°C.
  • Al2O3 is an amphoteric oxide, reacting as a base with strong acids and as an acid with strong bases, forming salts and water, making high alumina bricks neutral refractory products.

Magnesia bricks and high alumina bricks are essential products for kiln construction and repair. It is crucial to analyze and confirm the material and properties of the bricks before use to avoid selection errors and potential losses. The main differences between magnesia bricks and high alumina bricks lie in their chemical composition, corrosion resistance, and suitability for different high-temperature environments. Magnesia bricks are suitable for basic conditions with magnesium oxide as the main component, while high alumina bricks are suitable for acidic conditions with aluminum oxide as the main component. When choosing refractory materials, consider specific operating conditions such as temperature, chemical nature, and mechanical stress to select the appropriate material.

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Refractory Brick Price Analysis

Refractory bricks are a niche product within the refractory materials industry, essential in industrial production but not a primary industrial product. Their market price reflects their necessity in industrial applications. Refractory bricks come in various types and specifications, with no uniform pricing. Prices can vary significantly, from clay bricks at 600 yuan/ton to corundum bricks at over 20,000 yuan/ton. It is important to choose based on specific needs rather than blindly opting for cheaper options, considering kiln design and working environment to select suitable, reasonable, and qualified refractory bricks.

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