Sintered magnesia is divided into dead-burned magnesia, medium-grade magnesia and high-purity magnesia according to the preparation process and the mass fraction of magnesium oxide.
Sintered magnesia is generally made by directly calcining magnesite in a vertical kiln or a rotary kiln. The grade of sintered magnesia is calibrated by the mass fraction of MgO, and the highest grade can generally reach w(MgO)=98%. The main impurities in the raw materials are SiO2 and CaO, and the mass fraction of Fe2O3 is not high.
| Type | w(MgO)/% | w(SiO2)/% | w(CaO)/% | CaO/SiO2 molar ratio | Volume density/g·cm3 |
|---|---|---|---|---|---|
| MS98A | ≥97.7 | ≤0.3 | / | ≥3 | ≥3.40 |
| MS98B | ≥97.7 | ≤0.4 | / | ≥2 | ≥3.35 |
| MS98C | ≥97.5 | ≤0.4 | / | ≥2 | ≥3.30 |
| MS97A | ≥97.0 | ≤0.5 | / | ≥2 | ≥3.40 |
| MS97B | ≥97.0 | ≤0.6 | / | ≥2 | ≥3.35 |
| MS97C | ≥97.0 | ≤0.8 | / | / | ≥3.30 |
| MS96A | ≥96.0 | ≤1.0 | / | / | ≥3.30 |
| MS96B | ≥96.0 | ≤1.5 | / | / | ≥3.25 |
| MS95A | ≥95.0 | ≤2.0 | ≤1.6 | / | ≥3.25 |
| MS95B | ≥95.0 | ≤2.2 | ≤1.6 | / | ≥3.20 |
| MS93A | ≥93.0 | ≤3.0 | ≤1.6 | / | ≥3.20 |
| MS93B | ≥93.0 | ≤3.5 | ≤1.6 | / | ≥3.18 |
| NS90A | ≥90.0 | ≤4.0 | ≤1.6 | / | ≥3.20 |
| NS90B | ≥90.0 | ≤4.8 | ≤2.0 | / | ≥3.18 |
Heavy burned magnesite sand is sintered at 1600 – 1900℃ from magnesite, seawater/magnesium hydroxide. China uses >46% MgO magnesite lump with solid fuel in vertical kiln, yielding 89% – 98% MgO dead burn magnesite sand.
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Volume density/g·cm-3 |
| 0.27 | 3.87 | 1.86 | 92.48 | 0.62 | 0.90 | 3.16 |
Using MgO mass fraction greater than 46.5% of magnesite, lightly burned by the reflection furnace, and then finely ground, mixed with water, ball pressed, mixed with solid fuel blocks into the vertical kiln calcined production of magnesium sand.MgO mass fraction of about 95%, also known as mid-range magnesium sand.
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Bulk density/g-cm-3 |
| 0.50 | 1.95 | 1.58 | 94.63 | 0.34 | 1.00 | 3.17 |
The use of MgO mass fraction greater than 47% of magnesite, lightly burned to obtain a good high purity of lightly burned magnesium powder as raw material, by fine grinding, dry ball pressing, into the ultra-high temperature oil vertical kiln calcination production of magnesium sand MgO mass fraction of 96.5% to 98%, known as high purity magnesium sand.
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Volume density/g·cm-3 |
| 0.30 | 0.70 | 1.35 | 96.90 | 0.25 | 0.80 | 3.20 |
China’s abundant magnesite reserves have long led metallurgical firms to mainly produce low-grade magnesium sand from magnesite. Two-step calcination can make high-purity magnesium sand with ~97% purity, but ≥99% ultra-high-purity sand via heavy firing remains tough. Producing ≥98%/≥99% sand from seawater/brine is easier, with MgO up to 99.5%.
| IL | SiO2 | CAO | MgO | Al2O3 | Fe2O3 | Volume density/g·cm-3 |
| 0.25 | 0.23 | 0.53 | 98.85 | 0.03 | 0.11 | 3.20 |
In steel industry, sintered magnesia makes refractory bricks/linings to resist high temps & corrosion. In non-ferrous smelting, it protects equipment. For coatings/castables, it boosts heat resistance & strength. Also used in ceramics/abrasives for hardness/stability.
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