What are the differences between high-alumina bricks, clay bricks, and magnesia bricks?
2025-11-11 10:01:49
In high-temperature industrial furnaces, refractory bricks are the most basic and crucial materials. Different types of refractory bricks, due to differences in raw material composition, chemical properties, and service temperature, are widely used in metallurgy, building materials, power, and chemical industries. Among them, high-alumina bricks, clay bricks, and magnesia bricks are the three most common types. Although they all belong to shaped refractory materials, their performance and applications differ significantly. This article will analyze the differences between the three in detail from the aspects of composition, performance, refractoriness, and applications.
I. Different Compositions and Raw Materials
Clay Bricks: Clay bricks use natural soft clay or hard kaolin as the main raw material. The alumina (Al?O?) content is generally between 30% and 48%, with a relatively high amount of impurities. The main chemical components are SiO? and Al?O?, belonging to the aluminosilicate refractory material family.
High-alumina bricks are refractory products made primarily from high-alumina bauxite, fused alumina, or mullite. Their Al?O? content is above 48%, with common grades including 55%, 65%, 75%, and 80%. Higher alumina content results in higher refractoriness and better slag resistance.
Magnesia bricks are made primarily from fused or sintered magnesia, with magnesium oxide (MgO) as the main component, typically ranging from 85% to 97%. They are alkaline refractory materials and incompatible with acidic slag.
II. Differences in Refractoriness and Service Temperature
Clay bricks have a refractoriness of approximately 1580–1750℃ and are commonly used low-grade refractory bricks, suitable for furnace linings at relatively low temperatures.
High-alumina bricks have a refractoriness of over 1770–1790℃, higher than clay bricks, and can withstand higher temperatures, making them suitable for medium- and high-temperature applications.
Magnesium bricks have the highest refractoriness, reaching over 2000℃, and also possess good high-temperature volume stability and resistance to alkaline slag erosion, making them an important material in high-temperature smelting.
III. Chemical Properties and Slag Erosion Performance
Clay bricks are weakly acidic refractory materials, offering good resistance to acidic slags, but are easily eroded by alkaline slags.
High-alumina bricks are neutral or slightly acidic refractory materials, resisting both acidic and alkaline slags, exhibiting superior slag resistance compared to clay bricks.
Magnesium bricks are typical alkaline refractory materials, exhibiting extremely strong resistance to alkaline slags, molten iron, and steel slags, but are unsuitable for contact with acidic media.
IV. Comparison of Thermal Shock Stability and Mechanical Properties
Clay bricks: Good thermal shock stability, not easily spalling under heating and cooling cycles; however, their high-temperature strength is relatively low.
High-alumina bricks: High strength and good wear resistance, but slightly inferior thermal shock resistance compared to clay bricks.
Magnesium bricks: Although possessing outstanding high-temperature resistance, they have poor thermal shock resistance and are prone to cracking; therefore, they are mostly used in temperature-stable areas.
V. Comparison of Main Application Areas
Refractory Brick Types | Main Applications | Characteristics
Clay Bricks | Metallurgical furnaces, hot blast stoves, lime kilns, boiler linings | Low price, easy construction, suitable for low-temperature zones
High-alumina bricks | Cement rotary kilns, heating furnaces, glass kilns, upper part of hot blast stoves | High strength, good slag resistance, suitable for medium-high temperature zones
Magnesium Bricks | Converters, electric arc furnaces, refining furnaces, ladles, etc. | High temperature resistance, resistant to alkaline slag, suitable for high-temperature metallurgical zones
VI. Price and Service Life
Clay bricks: Widely available raw materials, low price, easy to process, but shorter service life.
High-alumina bricks: Superior performance, medium to high price, longer service life.
Magnesium bricks: Highest price, suitable for critical high-temperature areas; service life depends on furnace conditions.
From a cost-performance perspective, clay bricks are suitable for low-temperature applications; high-alumina bricks are suitable for medium-temperature applications requiring high wear resistance and slag resistance; and magnesia bricks are used in extremely high-temperature or strongly alkaline environments.
VII. Summary: How to Choose the Right Refractory Bricks?
When selecting refractory bricks, factors such as furnace type, operating temperature, slag properties, mechanical impact, and cost budget should be considered comprehensively:
If the temperature is below 1700℃ and the environment is relatively stable, clay bricks can be selected;
If the temperature is around 1750℃ and the slag properties are complex, high-alumina bricks are recommended;
If the temperature exceeds 1800℃ and the slag environment is strongly alkaline, magnesia bricks should be selected.
Different refractory bricks each have their advantages; a reasonable combination and use can ensure furnace safety while achieving energy saving, consumption reduction, and extended service life.