Magnesia Series Refractory Bricks

Magnesia Alumina Spinel Brick

Name: Magnesia Alumina Spinel Brick
Brand: XZK

MgO:70-80%

Al₂O₃:8-20%

Bulk Density:2.85-3.15g/cm³

Cold Crushing Strength:≥40MPa

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Magnesia Alumina Spinel Brick Overview

Magnesia alumina spinel bricks are built on a periclase matrix bonded by magnesium aluminate spinel, a chrome-free bond that gives the brick good thermal shock resistance together with strong resistance to alkali vapour and sulphate condensates. This combination is what makes the grade the standard choice for the condensation zone and bottom courses of a glass furnace regenerator, where sulphate attack and thermal cycling are both severe.

XZK Group supplies the grade as XZK-MA. Because the spinel bond contains no chrome, it also avoids the handling and disposal issues of a chrome-bearing refractory.

What Is a Magnesia Alumina Spinel Brick?

The brick combines high-purity magnesia with alumina, either as a pre-formed spinel added to the mix or as alumina that reacts with the magnesia during firing to form spinel in situ. Spinel is made up of MgO and Al₂O₃ in roughly equal parts, so the brick is mainly periclase with a spinel bond: MgO typically 75–88% and Al₂O₃ about 8–20%. The spinel content is the main grade variable, and with it the balance between thermal shock resistance and refractoriness.

Spinel formation is accompanied by a slight volume expansion, and that expansion is the source of the material's thermal shock resistance. As the spinel forms it creates a network of fine microcracks around the periclase grains, and those microcracks absorb thermal strain instead of letting it propagate as a through-crack. The result is a brick that tolerates the cycling of a regenerator far better than a pure magnesia brick, while keeping a high enough hot strength to carry the load of the courses above.

The chemistry also suits a regenerator. Between roughly 800 and 1100°C, alkali vapour in the flue gas reacts with sulphur oxides to form sulphate condensates that attack and swell many refractories; spinel is resistant to those condensates and to alkali vapour generally. Because it contains no chrome, it can be used and disposed of without the restrictions that apply to a chrome-bearing brick, which is why it has become the default material for the condensation zone and bottom courses, working alongside chrome corundum bricks and sillimanite bricks.

Key Properties

Composition: MgO about 75–88% with Al₂O₃ about 8–20% as magnesium aluminate spinel.
Bond: spinel bond with a microcracked structure; pre-formed or in-situ spinel.
Thermal shock resistance: good for a magnesia brick, from the microcracked spinel bond.
Alkali and sulphate resistance: strong, which is why it suits the regenerator condensation zone.
Hot strength: adequate for load-bearing checkerwork and chamber courses.
Chrome-free: no hexavalent chromium formation, so handling and disposal are straightforward.

Technical Specifications

Project	MLJ - 80	MLJ - 75	MLJ - 70
ω(MgO)/% ≥	80	75	70
ω(Al₂O₃)/%	8 – 20	8 – 20	8 – 20
Apparent Porosity /% ≤	17	19	20
Bulk Density /(g/cm³)	2.85 – 3.15	2.85 – 3.15	2.85 – 3.10
Compressive Strength at Normal Temperature /MPa ≥	40	40	40
Initial Softening Temperature under 0.2 MPa Load / °C ≥	1700	1650	1600
Thermal-shock Resistance (1100 °C, water-cooled) / times ≥	10	10	8

Test methods follow GB/T and ISO practice; ASTM equivalents and full certificates of analysis are issued with every shipment.

Available Grades and How to Choose

Grades are set mainly by spinel content, commonly in steps around 10%, 20% and 30%. A higher spinel content raises thermal shock resistance and alkali resistance but reduces the magnesia fraction and slightly lowers refractoriness; a lower spinel content keeps more of the pure-magnesia performance at lower cost. The right grade balances the thermal cycling of the position against the temperature and load it must carry.

The choice within the magnesia family is set by the duty. The condensation zone of a regenerator, with its combined sulphate attack and thermal cycling, is the classic application for a spinel brick. Where the temperature is highest and steady and alkali attack dominates, a high-purity magnesia brick is used. Where the environment is basic and slag-bearing rather than a flue gas, a magnesia chrome brick or magnesia carbon brick is the appropriate grade.

Industry Applications

Cement Industry: Core parts such as the firing zone and transition zone of cement rotary kilns.
Glass Industry: High-temperature areas such as the regenerators of glass melting furnaces.
Steel Industry: High-temperature and erosion - resistant scenarios such as ladle linings and tundish.

Where Magnesia Alumina Spinel Bricks Are Used in a Glass Furnace

Magnesia alumina spinel bricks are used in the parts of a furnace where alkali, sulphate and thermal cycling combine:

Regenerator condensation zone. Between about 800 and 1100°C, sulphate condensates attack the checkerwork; the spinel bond resists them without the chrome of a magnesia chrome brick.
Regenerator bottom courses, where the brick carries load and resists chemical attack from the condensates above.
Regenerator chamber walls, where alkali vapour passes continuously and the brick must resist it at temperature.
Target wall and port areas, where radiant heat and alkali load are high and a chrome-free material is preferred.
Cement rotary kiln transition and upper transition zones, where the spinel bond tolerates the cycling between coated and uncoated conditions.
Steel ladle linings, where spinel-bonded magnesia resists slag and thermal shock without carbon pickup.

Manufacturing and Quality Control

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.

Related Refractory Products

Magnesia alumina spinel bricks are supplied as part of a zoned regenerator refractory system with magnesia bricks, magnesia chrome bricks, chrome corundum bricks and sillimanite bricks. See the magnesia range or browse all refractory products.

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About XZK Group

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Specializing in premium zircon, corundum, sintered AZS, and monolithics. With a $70M+ annual output, we deliver durable linings for global high-temp industries.

Capacity

✔ 4 automated microcomputer batching systems.

✔ 4 ultra-high-temp tunnel kilns & 5 shuttle kilns.

✔ 20+ CNC hydraulic presses (630-1500T).

✔ Digitalized workshops with 100,000T annual capacity.