Introduction
Direct-bonded magnesia-chrome bricks are refractory materials that form a ceramic bonding phase through the direct reaction of high-purity magnesium oxide (MgO) and chromium oxide (Cr₂O₃), with little to no low-melting-point impurities. These bricks are made from high-purity sintered magnesia (with SiO₂ < 2%) and chromite concentrate through high-temperature sintering. The degree of direct bonding increases with decreasing SiO₂ content and increasing firing temperature.
Due to their high strength, excellent resistance to high temperatures, and erosion resistance, direct-bonded magnesia-chrome bricks are widely used in extreme environments such as the firing zones of cement kilns and high-temperature zones of glass furnaces. Despite their higher cost and the environmental risks associated with chromium content, they remain a preferred choice in high-performance applications. Practical use requires assessment based on kiln conditions, budget, and environmental regulations, with a gradual shift recommended toward chromium-free alternatives.
Advantages
High-temperature strength: Maintains high strength (compressive strength ≥50 MPa) at 1600°C, suitable for extreme high-temperature environments.
Thermal shock resistance: Low coefficient of thermal expansion (~1.0×10⁻⁶/°C); withstands 10–15 cycles of rapid heating and cooling (1000°C → room temperature → 1000°C).
Erosion resistance:
Alkali Resistance: Cr₂O₃ reacts with alkali to form high-melting compounds (e.g., K₂CrO₄), reducing penetration.
Sulfur/Chlorine Resistance: Superior to ordinary magnesia-chrome bricks.
Abrasion resistance: Dense structure resists particle wear.
Zinfon Refractory Technology Co.,Ltd.
We provide one-stop services from technical consultation to design, production, and after-sales support.
Raw Materials
Magnesium Oxide (MgO): ≥80%, provides refractoriness and alkali erosion resistance.
Chromium Oxide (Cr₂O₃): 15–30%, enhances strength, thermal shock resistance, and creep resistance.
Bonding Agent: No traditional clay; relies on direct sintering between high-purity magnesia grains.
Physical and Chemical Specifications
| Grade / Specifications | YXDMGe-10 | YXDMGe-12 | YXDMGe-16 | YXDMGe-18 | YXMGe-20 | |
| Chemical Composition (%) | MgO % | 72 | 70 | 68 | 63 | 58 |
| SiO2 % | 2.5 | 2.5 | 2.5 | 2.5 | 3 | |
| Cr2O3 % | 10 | 12 | 16 | 18 | 20 | |
| Apparent Porosity (%) | 18 | 18 | 18 | 18 | 18 | |
| Bulk Density (g/cm3) | 3.05 | 3.1 | 3.1 | 3.15 | 3.18 | |
| Cold Crushing Strength (MPa) | 40 | 40 | 40 | 40 | 40 | |
| Refractoriness under Load ºC @0.2MPa | 1650 | 1650 | 1700 | 1700 | 1700 | |
| Thermal Shock Resistance 950ºC (Times) | 5 | 5 | 5 | 5 | 6 | |
Process
1.Raw Material Preparation
MgO: High-purity fused magnesia (≥98% MgO, CaO/SiO₂ ≥ 2.0), 5–0.088 mm particle size.
Cr₂O₃: Chromite concentrate (Cr₂O₃ ≥ 50%, Fe₂O₃ ≤ 15%), ≤0.045 mm fineness.
Additives: Optional 5% Al₂O₃ or 3% ZrO₂ for enhanced performance.
Pretreatment:
Magnesia: Magnetic separation to reduce Fe₂O₃ ≤ 0.5%.
Chrome ore: Pre-fired at 1200°C for 2 hours to reduce volatiles.
2.Dosing and Mixing
Particle Gradation:
Coarse (5–3 mm): 30–40%
Medium (3–1 mm): 35–45%
Fine (≤0.088 mm): 20–30%
Mixing:
Dry mix for 20–30 min.
Optional 2–5% phosphate solution (e.g., aluminum dihydrogen phosphate) for better initial strength.
3.Molding
High-pressure hydraulic press ≥200 MPa.
Multi-layer pressing to avoid delamination.
Size tolerance ≤±1 mm; surface flatness ≤0.5 mm.
Natural curing for 24–48 hours post-demolding.
4.Drying and Sintering
Drying: Tunnel dryer at 110–150°C for 12–24 hours, moisture ≤1%.
Sintering:
Heat rate: 10–15°C/min
Temperature: 1600–1700°C
Holding time: 4–6 hours
Reaction: MgO + Cr₂O₃ → MgCr₂O₄ spinel (ceramic bond)
Protective atmosphere (N₂ or Ar) to prevent Cr₂O₃ oxidation to CrO₃.
5.Post-Processing and Testing
Trimming: Precision cutting/polishing (flatness error ≤0.1 mm).
Performance Testing:
Compressive strength ≥50 MPa (RT), ≥30 MPa (1600°C)
Apparent porosity ≤20%
Thermal shock resistance ≥15 cycles (1000°C water cooling)
Environmental test: Cr⁶⁺ content ≤0.5%
Comparison of direct bonded magnesium-chromium bricks and normal bonded magnesium-chromium bricks process
|
Process Steps |
Direct-Bonded Bricks | Ordinary Bonded Bricks |
|
Raw material purity |
MgO ≥ 98%, Cr₂O₃ ≥ 50% | MgO ≥ 85%, Cr₂O₃ ≤ 30% |
|
Granularity |
Fine (5–0.088 mm) | Coarse (5–1 mm) |
|
Binding agent |
Clay-free; direct bonding | 5–10% refractory clay (e.g., kaolin) |
|
Forming pressure |
≥200 MPa | 100–150 MPa |
|
Sintering temperature |
1600–1700°C | 1500–1600°C |
|
Binding phase |
MgCr₂O₄ (no low-melting impurities) | MgO-Al₂O₃-SiO₂ (contains glassy phase) |
application
Cement Kilns
Firing Zone: 1400–1600°C, direct contact with clinker and flame.
Advantage: Superior resistance to erosion; lifespan 2× that of ordinary bricks (approx. 2–3 years).
Glass Furnaces
Melting Section (Front Wall): 1500–1600°C, exposure to alkali vapor and molten glass.
Advantage: Improved resistance to glass infiltration; reduces spalling risk.
Non-Ferrous Metal Furnaces
Ladle Refining Furnaces: Resistance to steel and alkali slag erosion.
Advantage: Excellent thermal shock resistance and strength at high temperatures.
Comparison with ordinary bonded magnesium-chromium bricks
| Indicator | Direct-Bonded Bricks | Ordinary Bonded Bricks |
|---|---|---|
| Fire Resistance | ≥1750°C | ≥1700°C |
| High-Temperature Strength | ≥50 MPa (1600°C) | ≤30 MPa (1600°C) |
| Thermal Shock Resistance | Excellent (≥15 cycles) | Moderate (≤8 cycles) |
| Erosion Resistance | Strong (alkali/S/Cl) | Moderate (mainly alkali) |
| Cost | High (2–3× ordinary bricks) | Low |
| Environmental Impact | Contains Cr (waste handling required) | Same risks |
Why chooes us?
01/Customized dimensions and shapes
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Customized Brick Shape
Provide Sample Sheets
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Mold Opening & Quotation
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Mold Opening & Sample Making
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Bulk Production Quotation
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Contract Signing
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Bulk Production
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02/Delivery cycle and logistics
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Sea freight, land freight. Determine the mode of transportation according to the needs
About 30 days, customized products delivery time depends on the actual situation.
03/Customized packaging
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Customize your brand
Logo customization, custom fonts, taglines and messages for packaging, signage, websites or printed materials.
Take your brand to the next level, contact us today to discuss your project!
04/Purchase ZINFON refractory Bricks at Reasonable Prices
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The price of refractory bricks is a known key factor influencing customers' purchasing decisions. Therefore, we offer affordable refractory bricks for sale. Here are several reasons why ZINFON provides refractory bricks at competitive prices:
Factory price
By collaborating with ZINFON, we ensure that customers enjoy the ex-factory price of refractory bricks, reducing costs from middlemen or distributors. This allows customers to obtain the most cost-effective pricing directly from the source.
Low raw material cost
ZINFON is surrounded by abundant mineral resources. With these high-quality materials, customers can obtain products that are both affordable and excellent in performance.
Mass production
ZINFON possesses advanced production equipment and technologies, enabling the factory to achieve economies of scale and reduce unit production costs. Meanwhile, it ensures a continuous supply of high-quality products at preferential prices.
It is worth noting that while price is an important factor, it should not be the sole determinant of your purchasing decision. When buying refractory bricks from ZINFON, quality, reliability, and technical support are equally important considerations.
By choosing ZINFON as your supplier, you can access high-quality refractory bricks, a wide range of other refractory materials, and comprehensive support. Contact ZINFON Refractories immediately to discuss your specific requirements and obtain customized solutions!
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