Magnesia bricks are made from high-purity sintered magnesia and fired to a direct periclase bond, giving the highest refractoriness and the strongest resistance to alkali of any material in the XZK magnesia range. Their weakness is thermal shock: magnesia expands more than most refractories when...
Magnesia bricks are made from high-purity sintered magnesia and fired to a direct periclase bond, giving the highest refractoriness and the strongest resistance to alkali of any material in the XZK magnesia range. Their weakness is thermal shock: magnesia expands more than most refractories when heated and cannot be cycled rapidly, so the brick is placed in stable, high-temperature zones rather than in positions that see reversal or steep gradients.
XZK Group supplies high-purity magnesia bricks with MgO content of 95% and above. In a glass furnace they are the top-course and hot-zone material in the regenerator, exactly where alkali attack and temperature are highest and the thermal regime is steady.
The brick is made from sintered magnesia of high purity, with the lime-to-silica ratio and the level of B2O3 and other fluxes held under close control, and fired at high temperature to develop a direct bond between periclase crystals. Periclase, the mineral form of MgO, melts at around 2800°C and is stable against alkali and iron oxides. Keeping the silicate and borate content low is what gives a magnesia brick its hot strength, because those fluxes form low-melting phases that soften the bond.
That chemical stability makes magnesia the reference material for the hottest, most alkali-laden part of a regenerator. In the top courses and hot zone the checkerwork meets flue gas carrying alkali vapour at the highest temperature in the chamber, and a high-purity magnesia brick resists both the chemistry and the heat. It also carries load well, which matters where the courses above press down on a structure that runs for years.
Thermal shock is the limitation. Magnesia has a relatively high coefficient of thermal expansion, so a brick that is cycled quickly or placed across a steep temperature gradient will crack. The material therefore belongs in a stable regime, and where cycling is unavoidable its place is taken by a spinel-bonded grade, whose microcracked spinel bond absorbs the thermal strain that would otherwise open a crack.
| Project | M - 98 | M - 97A | M - 97B | M - 95A | M - 95B | M - 93 | M - 91 | M - 89 | M - 87 |
| ω(MgO)/% ≥ | 97.5 | 97 | 96.5 | 95 | 94.5 | 93 | 91 | 89 | 87 |
| ω(SiO₂)/% ≤ | 1 | 1.2 | 1.5 | 2 | 2.5 | 3.5 | — | — | — |
| ω(CaO)/% ≤ | — | — | — | 2 | 2 | 2 | 3 | 3 | 3 |
| Apparent Porosity /% | 16 | 16 | 18 | 16 | 18 | 18 | 18 | 20 | 20 |
| Bulk Density /(g/cm³) | 3.00 - 3.20 | 3.00 - 3.20 | 2.95 - 3.15 | 2.90 - 3.10 | 2.85 - 3.02 | ||||
| Compressive Strength at Normal Temperature /MPa ≥ | 60 | 60 | 60 | 60 | 60 | 60 | 60 | 50 | 50 |
| Initial Softening Temperature under 0.2MPa Load / °C ≥ | 1700 | 1700 | 1650 | 1620 | 1560 | 1550 | 1540 | ||
| Permanent Linear Change after Heating (1650 °C × 2h) /% | -0.2 - 0 | -0.2 - 0 | -0.3 - 0 | -0.4 - 0 | -0.5 - 0 | -0.6 - 0 | — | ||
Grades are separated by purity and by bond. A high-purity grade of 95% MgO or above with a direct periclase bond is the reference material for the hottest, most alkali-bearing courses. Lower-purity grades with more silicate bond are economical substitutes where the temperature and alkali load are lower, but they soften earlier under load.
The choice within the magnesia family is set by the duty. Steady high temperature and strong alkali attack call for a pure magnesia brick. Where the lining must also tolerate thermal cycling, a magnesia alumina spinel brick or a magnesium iron spinel brick is preferred. Where the atmosphere is reducing and a slag is present, a magnesia carbon brick is used instead.
High-purity magnesia bricks are used in the steady, hot, alkali-bearing parts of a furnace:
Manufacturing is controlled from raw material through to finished brick. Four automatic batching lines feed 20 CNC presses ranging from 630 to 2000 tonnes, so density is set by press force rather than operator judgement, and firing runs through four 108-metre fully automatic tunnel kilns and five ultra-high-temperature shuttle kilns for a uniform soak.
Every batch is tested for bulk density, apparent porosity, cold crushing strength and refractoriness under load, and ships with a certificate of analysis. XZK Group holds ISO 9001, ISO 14001, ISO 45001 and ISO 50001 certification and operates the Henan Provincial Engineering Technology Research Center for Sintered Refractories for Glass Furnaces.
High-purity magnesia bricks are supplied as part of a zoned regenerator refractory system with magnesia chrome bricks, magnesia alumina spinel bricks, chrome corundum bricks and sillimanite bricks. See the magnesia range or browse all refractory products.
MgO:85-88%;
Bulk Density:2.95g/cm³;
Cold Crushing Strength:≥80MPa;
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