Introduction to Spinel Products‌

Spinel is a mineral composed of magnesium aluminum oxide, which may contain elements such as magnesium, iron, zinc, and manganese. Depending on the elements present, spinel can be classified into various types, including aluminum spinel, iron spinel, zinc spinel, manganese spinel, and chromium spinel. Different spinels exhibit different colors due to their varying compositions. For example, magnesium spinel can appear in red, blue, green, brown, or colorless forms; zinc spinel is dark green; and iron spinel is black. Spinel typically forms hard, glassy octahedral crystals, granules, or massive aggregates. It occurs in igneous rocks, granitic pegmatites, and metamorphic limestones. Some transparent and beautifully colored spinels are used as gemstones, while others serve as iron-containing magnetic materials. Over 200 varieties of spinel have been artificially synthesized.

Magnesium aluminum spinel (MgAl₂O₄) is a type of magnesium aluminum oxide, primarily composed of alumina and magnesia. It exists in both natural and synthetic forms. Naturally occurring magnesium spinel is extremely rare, so industrial applications rely entirely on synthetic magnesium aluminum spinel. The two main methods for synthesizing magnesium aluminum spinel are sintering and electric melting. Most spinel materials are produced from high-purity synthetic alumina and chemically pure magnesia, either through shaft kiln sintering or electric arc furnace melting.

Both spinel and garnet are isotropic and exhibit anomalous extinction under polarized light. However, spinel has a significantly lower refractive index than garnet, and their absorption spectra differ. Additionally, spinel often contains single or aligned octahedral inclusions, while pyrope garnet typically contains rounded inclusions.

Spinel can undergo heat treatment to enhance its color. For example, blue spinel turns green when heated to 900°C and yellow at 1200°C, with stable color modification effects. There are also reports of red spinel being heat-treated to remove brown tones, resulting in a purer red hue.

‌Physical Properties of Spinel‌

• ‌Chemical Formula:‌ MgAl₂O₄

• ‌Crystal System:‌ Cubic (isometric)

• ‌Crystal Habit:‌ Commonly forms octahedral crystals, sometimes in combination with rhombic dodecahedrons or cubes.

• ‌Luster:‌ Vitreous to sub-adamantine

• ‌Transparency:‌ Transparent to opaque

• ‌Refractive Index:‌ 1.718 (may vary up to 2.000 depending on trace elements)

• ‌Birefringence:‌ None

• ‌Pleochroism:‌ None

• ‌Special Optical Effects:‌ Star effect (four or six rays), color-changing effect (rare).

‌Applications of Spinel‌

Sintered magnesium aluminum spinel is used in cement rotary kilns, not only avoiding chromium pollution but also providing excellent spalling resistance. When used in ladle castables, it significantly enhances the erosion resistance of refractory linings, making sintered magnesium aluminum spinel widely applicable in steelmaking refractories. High-quality pre-synthesized spinel provides a new raw material for producing high-purity unshaped and shaped refractory materials.

Fused magnesium aluminum spinel is an ideal material for manufacturing slide gates, nozzle bricks, and open-hearth furnace bricks. Spinel-based products exhibit excellent high-temperature mechanical properties and serve as fundamental materials for large cement kilns, neutral kiln filter belts, refractory castables, and high-temperature kiln furniture. Fused magnesium aluminum spinel is also used in steel smelting and glass industry furnaces.