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Xiaoyi City Jingang Refractory Materials Co., Ltd. was established in 2019. It is a provincial-level specialized, refined, distinctive, and innovative enterprise, a national high-tech enterprise, an innovative small and medium-sized enterprise, and a municipal technology center.

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Product Description

Commodity name: Natural Sintered Mullite

Alumina-based sintered mullite is a high‑end refractory aggregate whose primary crystalline phase is acicular mullite, produced by high‑temperature solid‑state sintering at 1700–1780°C using natural high‑alumina bauxite, kaolin, kyanite, and other aluminosilicate minerals as raw materials.

Refractory Raw Materials · Technical Manual

Natural sintering Mullite

3Al₂O₃ · 2SiO₂ | Al₂O₃ = 71.8% SiO₂ = 28.2% Melting point 1870°C

Sintering temperature 1700 – 1780°C

Main crystalline phase Acicular mullite

Typical grade M45 · M60 · M70 · M75

Coefficient of thermal expansion 5.3 × 10⁻⁶ /°C

Definition and Distinction

Natural native mullite

Natural volcanic and metamorphic primary deposits are extremely rare, with highly variable impurity levels, and are virtually unused in industry.

Natural sintered mullite (the industry’s mainstream term)

With Natural high-alumina bauxite, kaolin, kyanite / andalusite Using natural aluminosilicate minerals as raw materials, after ore blending and homogenization… High-temperature solid-state sintering at 1700–1780°C , a refractory aggregate synthesized artificially with needle-like mullite as the primary crystalline phase. It belongs to Synthetic Sintered Mullite Category , as the raw material is derived from natural minerals, it is commonly referred to in the industry as “natural sintered mullite.”

Production Process Flow

Natural bauxite/kaolinite raw ore →

Crushing and iron removal →

Precise ore blending and homogenization →

Wet fine grinding to produce mud →

Compaction / Granulation →

Drying →

Sintering at 1750°C →

Crushing and Screening →

Aggregate / Fine Powder Product

Physical and Chemical Specifications of Mainstream Grades

Grade	Al₂O₃	SiO₂	Fe₂O₃ ≤	TiO₂ ≤	Alkali metal R₂O ≤	Bulk density ≥	Refractoriness	Main crystalline phase
M45	44~46%	50~53%	0.8%	0.4%	0.3%	2.50 g/cm³	1770°C	Mullite + Cristobalite
M60	58~62%	35~38%	0.7%	0.4%	0.2%	2.65 g/cm³	1850°C	Mainly composed of mullite.
M70	69~73%	22~26%	0.6%	0.35%	0.15%	2.78 g/cm³	1850°C	Acicular mullite 85%+
M75	74~77%	19~22%	0.6%	0.3%	0.1%	2.82 g/cm³	1860°C	Mullite + a small amount of corundum

Core Performance Advantages

Thermal shock resistance, rolled and homogenized bauxite

Mullite needle-like crystals interpenetrate to form a reticular framework, exhibiting an extremely low thermal expansion coefficient (5.3 × 10⁻⁶/°C) and resisting cracking under rapid heating and cooling, making it well suited for kilns subject to frequent temperature cycling.

Extremely low high-temperature creep

It maintains its structural integrity under long-term high-temperature loading at 1600°C, with a load‑softening temperature of ≥ 1630°C, making it well suited for prolonged high‑temperature service in hot blast stoves and glass furnaces.

Acid-resistant slag erosion

It exhibits stability toward glass melts, acidic flue gases, and ceramic glazes, with virtually no chemical reactions occurring. High-alumina bauxite, on the other hand, contains abundant iron and titanium impurities, which readily form low-melting-point glassy phases at elevated temperatures.

Low porosity, stable structure

Sintering is thorough, with a high density of closed pores, ensuring dimensional stability at elevated temperatures and minimal thermal expansion or contraction; however, the presence of residual free corundum in the calcined alumina results in significant volumetric fluctuations under high‑temperature conditions.

Attention

Weakness: Poor resistance to alkaline slag.

Alumina content not exceeding 77%, with low pure corundum content, It is less resistant to the highly alkaline slag of molten steel than high-alumina homogenizing material. ; At the same aluminum content, the price is higher than that of calcined alumina.

Main application areas

Refractory materials Maximum use

Shaped refractory products: mullite bricks, hot-blast stove bricks, regenerative bricks for glass furnaces, kiln shelves and saggers for ceramic firing, and crucibles.
Unshaped refractory materials: medium- and high-temperature thermal-shock-resistant castables, wear-resistant ramming masses, kiln‑mouth wear‑resistant linings, and heat‑treatment furnace linings.
Blast furnace ancillary equipment: the upper section of the hot blast stove, the mid-temperature zone of the furnace body, and the lining of the tapping spout.

Precision casting

Mullite powder is used as a surface coating for casting; it does not react with molten steel or alloy steels, resulting in castings with smooth surfaces and no sand adhesion.

Ceramics / Building Materials

High-grade sanitary ceramic bodies, high-temperature kiln furniture, electrical porcelain refractory components, and roller‑kiln roller‑head protective materials.

Other

Low-thermal-conductivity insulating refractory composite aggregate, abrasive additives, and high-temperature electronic substrate filler

Natural Sintered Mullite vs. Homogenized Alumina Bauxite

Comparison item

Natural Sintered Mullite (M70)

Homogenized Bauxite (GL-88)

Main crystalline phase

Acicular mullite (70%–90%)

Corundum-dominated, with minor mullite.

Al₂O₃ range

45% ~ 77%

83% ~ 88%

Refractoriness

1850 ~ 1870°C

1790 ~ 1820°C

Thermal shock resistance

Excellent—resists cracking even with alternating hot and cold temperatures.

Generally, large temperature differences can cause peeling.

High-temperature creep

Extremely low; does not deform at 1600°C.

Moderate; prone to deformation under prolonged high temperatures.

Acid-resistant slag

Excellent

General

Alkali-resistant steel slag

General

Excellent

Typical operating conditions

Glass kilns, ceramic kilns, hot-air furnaces, and heat-treatment furnaces

Ladle, taphole, cement kiln, metallurgical wear-resistant lining

Cost

Slightly high

Better value for money

Supply Specification

Aggregate particle size

0-1 mm · 1-3 mm
3-5 mm · 5-8 mm

Fine powder mesh count

200 mesh · 325 mesh
400 mesh · 800 mesh fine powder

Packaging method

25 kg woven bag
1-ton bulk bag

Storage Requirements

Moisture-proof storage
Avoid mixing with other ingredients.

Additional note: Differences of electrofused mullite

Sintered vs Fused Mullite

Although both belong to the mullite family, their manufacturing processes differ: Electrofused mullite It is an electric arc furnace‑melted, water‑cooled product with coarse grains, higher density, and greater purity, and its price is significantly higher than… Natural Sintered Mullite , commonly used in high-end specialty refractories. Sintered mullite It is a solid-phase low-temperature sintering material with moderate costs, making it a widely used industrial base material.