Among refractory materials, magnesia bricks and high-alumina bricks are both high-temperature protective products, yet they differ significantly. Understanding the differences between the two can help companies accurately select the right bricks and avoid losses. This analysis is based on the following three dimensions.
1. Core Composition: Determines the Basic Material Properties
Magnesia bricks are primarily composed of magnesium oxide (MgO), typically exceeding 80%. Some high-purity magnesia bricks can contain over 95% MgO. These bricks are primarily derived from magnesite, which is calcined, formed, and then sintered at high temperatures. Due to their high MgO content, they possess exceptional resistance to alkaline corrosion.
High-alumina bricks: With aluminum oxide (Al₂O₃) as their core component, they can be divided into Type I (Al₂O₃ ≥ 75%), Type II (60% ≤ Al₂O₃ < 75%), and Type III (48% ≤ Al₂O₃ < 60%), depending on the alumina content. The primary raw material is high-alumina bauxite, supplemented with binders such as clay. The higher the alumina content, the greater the high-temperature resistance and strength of the high-alumina brick.
2.Differences in High-Temperature Resistance: Applicable Temperature Ranges
Magnesia bricks: They offer exceptionally high-temperature resistance, with long-term operating temperatures reaching 1600°C-1800°C and short-term maximum operating temperatures exceeding 2000°C. Due to the melting point of magnesium oxide at 2800°C, magnesia bricks maintain structural stability even in ultra-high-temperature environments and are not susceptible to softening or deformation, making them suitable for use in extreme high-temperature environments.
High-alumina bricks: High-temperature resistance varies with alumina content. Class I high-alumina bricks have a long-term operating temperature of approximately 1500°C-1700°C, while Class II and Class III have slightly lower operating temperatures, at 1400°C-1600°C and 1300°C-1500°C, respectively. While lower than magnesia bricks, high-alumina bricks offer a more cost-effective performance in the medium- to high-temperature range (1300°C-1700°C), making them a common choice for most medium- and high-temperature industrial furnaces.
3.Corrosion Resistance Differences: Different Compatibility with Different Media
Magnesia bricks: Primarily resistant to alkaline corrosion, they offer exceptional resistance to alkaline slag, molten steel, and other molten metals. Because magnesium oxide is an alkaline oxide, it forms a stable compound with alkaline media, making it resistant to corrosion and flaking. Therefore, it is widely used in alkaline equipment such as steelmaking converters and alkaline open-hearth furnaces. However, its acid resistance is weak, making it susceptible to severe corrosion in acidic slag environments, shortening its service life.
High-alumina bricks offer medium corrosion resistance and are generally resistant to both acidic and alkaline media, but without a bias towards either. Because aluminum oxide is an amphoteric oxide, it can withstand mildly acidic slags, such as acidic volatiles in glass furnaces, and moderately alkaline corrosion, such as in the transition zone of cement rotary kilns. However, in strongly acidic and alkaline environments, its performance is inferior to that of magnesium bricks (strongly alkaline) or silica bricks (strongly acidic).