Magnesia chrome refractory is a type of basic refractory material widely used in metallurgical industries due to its exceptional resistance to high-temperature corrosion, superior mechanical strength, and thermal stability. Comprised primarily of magnesium oxide (MgO) and chromium oxide (Cr2O3), these refractories are designed to withstand harsh environments in steelmaking, non-ferrous metal smelting, cement kilns, and other high-temperature industrial processes.
What is Magnesia Chrome Refractory?
Magnesia chrome refractories are based on dead-burned magnesite (MgO) combined with chrome-containing materials, such as chrome ore (chromite). Depending on the chromium content, these refractories are classified into three main types:
Magnesia chrome refractory: less than 30% Cr2O3
Chrome-magnesia refractory: more than 30% Cr2O3
Picro-chromite refractory: more than 75% Cr2O3
These materials are called “basic refractories” because they resist chemical attack from basic slags, dusts, and fumes at high temperatures. Certain modern formulations, particularly direct bonded chrome magnesite bricks used in copper smelting, also show resistance to mildly acidic slags, expanding their range of applications.
Composition and Raw Materials
The primary raw materials for magnesia chrome refractory are:
Dead-burned magnesia (MgO): Provides high melting point, thermal stability, and chemical resistance.
Chrome ore (chromite, FeO·Cr2O3): Serves as a source of chromium, improving slag resistance and thermal shock properties.
High-purity magnesia and chromite enable the formation of direct bonded bricks, where a ceramic bond forms between MgO and chromite particles. The interaction between magnesia and chromite during firing produces a stable spinel phase, magnesio-ferrite (MgO·Fe2O3), which enhances hot strength and reduces redox-related deterioration.
Chromite and Its Role
Chromite used in refractory applications typically contains:
30–50% Cr2O3
13–30% Al2O3
12–24% Fe2O3
14–20% MgO
<10% SiO2
Its spinel structure contributes to high melting point, thermal stability, and resistance to corrosive slags, especially silica-rich fayalite slags common in non-ferrous smelting.
Types of Magnesia Chrome Refractory Bricks
Magnesia chrome refractory bricks are classified based on their bonding and production methods:
1. Silicate-Bonded Bricks
These bricks use silicate minerals to bond magnesia and chromite grains. They offer good thermal shock resistance but limited refractoriness compared to direct bonded alternatives.
2. Direct-Bonded Magnesia Chrome Bricks
Direct bonded bricks, introduced in the late 1950s, eliminate the silicate bond. High-purity magnesia and chromite are fired at elevated temperatures to form a strong spinel bond. Benefits include:
High hot strength
Superior slag resistance
Excellent spalling resistance
The ratio of magnesia to chrome ore affects properties: higher chrome content generally increases corrosion resistance, while higher magnesia content enhances resistance to alkali environments.
3. Rebonded Bricks
Rebond bricks are produced by fusing magnesia and chromite in an electric arc furnace, then crushing, pressing, and firing. They have excellent corrosion resistance but are more expensive.
4. Chemically Bonded Bricks
These bricks use magnesium salts instead of firing to bond magnesia and chromite. While cost-effective, they have lower hot strength and slag resistance.
5. Fused and Co-Burned Bricks
Fused or co-burned bricks are made by melting or sintering magnesia and chromite before brick forming. These bricks exhibit low porosity, high corrosion resistance, and are used in demanding applications like argon oxygen decarburization (AOD) furnaces and non-ferrous metal smelting.
Microstructure and Performance
Magnesia chrome bricks consist of:
Aggregates: Larger grains (>1 mm) of fused magnesia-chrome particles
Matrix/Binding System: Smaller particles (<1 mm) that densify during sintering and bond aggregates together
The matrix is the first component exposed to corrosive slags, so its composition and sintering behavior are critical. High-quality bricks feature a fully dense matrix with spinel crystal structures that bond well with aggregates, enhancing strength, thermal stability, and slag resistance.
Spinels in Magnesia Chrome Refractories
Spinel solid solutions like MgCr2O4, MgAl2O4, and MgFe2O4 form during firing. These spinels:
Resist high temperatures (>1300°C)
Provide thermal shock resistance
Improve chemical stability against liquid slags
Firing temperature, atmosphere, and cooling rate influence the formation of secondary spinels, which fill grain boundaries and strengthen the brick.
Applications of Magnesia Chrome Refractories
Due to their chemical and thermal properties, magnesia chrome refractories are used in:
Steelmaking: Vacuum degassing furnaces, electric arc furnaces, secondary steel refining
Non-ferrous metal smelting: Copper, nickel, and platinum group metal converters
Cement industry: Kiln linings
Foundries: Electric-arc furnace linings
Glass melting and incinerators: High-temperature corrosion-resistant linings
Their resistance to acidic and basic slags, combined with high hot strength, makes them preferred over other basic refractories in many applications.
Advantages of Magnesia Chrome Refractories
Excellent slag resistance: Especially against silica-rich fayalite slags
High thermal stability: Low thermal expansion reduces spalling
Superior mechanical strength: Maintains integrity at elevated temperatures
Corrosion resistance: Effective against both basic and mildly acidic slags
Versatility: Suitable for steel, non-ferrous, cement, and glass industries
Conclusion
Magnesia chrome refractory is a cornerstone material for high-temperature metallurgical and industrial applications. Its unique combination of magnesia and chromite, advanced production techniques, and the formation of spinel structures provide excellent resistance to corrosion, thermal shock, and mechanical stress. While environmental concerns over hexavalent chromium have prompted alternative materials in some applications, magnesia chrome refractories remain a highly effective and reliable choice for industries requiring durable, high-performance refractory linings.
For professional advice and competitive magnesia chrome refractories price quotes, feel free to contact Xintai Refractory. We are committed to providing high-quality products and tailored solutions to meet your specific needs.
