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Calcined Alumina (α-Alumina)

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Calcined Alumina (α-Alumina)
Calcined alumina is a functional powder produced by calcining industrial aluminum hydroxide or alumina at approximately 1300~1500°C to achieve complete conversion to the stable α-Al₂O₃ phase. Unlike the interlocking platelet structure of tabular alumina, calcined alumina typically exhibits an equiaxed or near-spherical crystal morphology. Primary crystal size can be tailored within 0.3~100 μm, α-phase conversion reaches 93%~97% or higher, and true density ranges from 3.92~3.98 g/cm³. It offers high purity, stable high-temperature performance, and controllable sintering activity.

Product Specifications

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Item Typical Range
Crystal Form α-Al₂O₃, equiaxed / near-spherical
Primary Crystal Size 0.3~100 μm (microcrystalline <1μm; coarse crystalline >10μm; ultra-coarse >50μm)
α-Phase Conversion ≥93% ~ ≥97% (varies by grade)
True Density (Effective Density) 3.92~3.98 g/cm³
Loss on Ignition (L.O.I) ≤0.1% ~ ≤0.2% (typical low-soda original powder)
Specific Surface Area (BET) 0.3~25 m²/g (microgrit; finer size yields higher surface area)
Key Properties High purity, stable α-phase, adjustable crystal size, controllable sintering activity, high-temperature volume stability

Chemical Composition

Typical chemical composition by soda grade (applicable to both original powder and microgrit):

Constituent Ordinary Soda (%) Low Soda (%) Ultra-Low Soda (%)
Al₂O₃ ≥99.0 ~ ≥99.6 ≥99.5 ~ ≥99.7 ≥99.5 ~ ≥99.7
Na₂O ≤0.35 ≤0.10 ≤0.05
SiO₂ ≤0.10 ~ ≤0.20 ≤0.05 ~ ≤0.10 ≤0.05 ~ ≤0.10
Fe₂O₃ ≤0.04 ~ ≤0.05 ≤0.02 ~ ≤0.04 ≤0.02
Loss on Ignition (L.O.I) ≤0.2 ≤0.2 ≤0.2

Ordinary soda values reference commercial standard-grade calcined alumina; low-soda and ultra-low-soda values are based on published technical parameters for low-soda calcined α-alumina and microgrit. Microgrit products may show slightly relaxed upper limits for SiO₂ and Fe₂O₃ due to grinding media wear, while Na₂O remains strictly controlled to the corresponding soda grade.

Production Specifications

Calcined alumina is supplied as original powder and microgrit, with customizable particle size specifications:

Specification Type Common Range Notes
Original Powder (A-C Series) Primarily 80~120 mesh; D50 adjustable by grade Direct calcination product, unground or coarse-crushed only
Microgrit (A-CG Series) D50 1±0.5μm, 3±0.5μm, 5±0.5μm, etc.; -325 mesh (-0.045mm) Ball-milled or jet-milled, controllable particle size distribution
Fine Powder Common Meshes -100#, -200#, -320#, -325# Common in refractories and ceramics
Section Sand (companion supply) 0-1mm, 1-3mm, 3-5mm, 5-8mm Used with fine powder for castable/ramming mix grading

Original powder grades such as A-C-03, A-C-05, and A-C-10 are available per YS/T 89, and microgrit is supplied under the A-CG series.

Application Scenarios

The three principal application areas of calcined alumina are ceramics, refractories, and abrasive/polishing applications.

Ceramics:

Electronic Ceramics: Low-soda and ultra-low-soda calcined alumina are used in electronic substrates, spark plugs, high-frequency insulating ceramics, headers, and housings, leveraging high α-phase content and low soda content for superior electrical insulation and dielectric properties.

Structural and Wear-Resistant Ceramics: Used in wear-resistant ceramic parts, ceramic cutting tools, valves, pump components, and high-alumina ceramic grinding media (beads and balls).

Functional and Thermally Conductive Ceramics: Serve as high-purity fillers in thermally conductive composites, metal-ceramic composites, and functional ceramic systems.

Refractories:

Refractory Castables and Ramming Mixes: Used as fine powder or matrix components in grading with section sand, providing high-temperature volume stability and sintering performance.

Corundum Bricks, Crucibles, Kiln Furniture, Ceramic Rollers: Utilize high refractoriness and α-phase stability for high-temperature kiln linings and load-bearing components.

High-Grade Refractory Base Materials: Low-soda calcined alumina microgrit is suitable for advanced refractories, zirconia-alumina composites, and high-purity structural ceramics.

Abrasive and Polishing:

Grinding Media and Abrasives: Raw material for grinding wheels, abrasive tools, wear-resistant fillers, and high-alumina grinding media.

Polishing Materials: Suitable for lapping and polishing of precision workpieces, glass, and ceramics. Microgrit grades offer stable cutting performance due to uniform particle size and high α-phase content.

Other Extended Applications:

Investment Casting: Low-soda calcined alumina is used in investment casting slurry systems; low Na₂O content helps stabilize slurry pH and flowability.

Glass and Daily-Use Ceramics: Used as a functional raw material in specialty glass and daily-use ceramic formulations.

Our Facilities

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FAQ

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Q1: Is your company a trading firm or a manufacturing plant? Where are your facilities located?
We are an export-oriented enterprise that integrates manufacturing and sales; we are not an intermediary. Our headquarters—handling international sales, order processing, documentation, and after-sales service—is located in the Liaocheng Economic and Technological Development Zone, serving as the hub for global client relations, order negotiations, and cross-border services. Our production facility is situated in Chiping District, Liaocheng City, and specializes in the R&D, smelting, processing, and testing of white fused alumina, brown fused alumina, and other fused alumina products. This allows us to manage the entire supply chain—from primary production and rigorous quality control to direct export.


Q2: What is your production capacity and supply capability? Can you ensure a stable, long-term supply?
Our production base in Chiping features mature production lines and comprehensive processing equipment, enabling large-scale, continuous manufacturing. We offer a stable supply of our full range of white fused alumina, brown fused alumina, and related fused alumina products. With ample inventory and well-organized production scheduling, we are fully equipped to handle bulk orders, recurring annual orders, and urgent requests during peak seasons, ensuring a reliable, long-term supply for our global clients.


Q3: What are your primary export products, and what are your core offerings?
Our core exports consist of three main series of fused alumina materials: brown fused alumina, white fused alumina, and other fused alumina products. We offer a comprehensive range of specifications and particle sizes that meet various international procurement standards. Brown fused alumina is our flagship product for cost-effective industrial abrasives and refractory raw materials; white fused alumina is designed for high-purity, high-precision grinding and polishing applications; and our broader fused alumina line serves high-end refractory, specialty ceramic, and precision abrasive tool sectors—covering the full spectrum of procurement needs across all market tiers.


Q4: What are the specific applications for these three types of fused alumina, and how should one choose the right product? 1. Brown Fused Alumina: Characterized by high toughness, excellent wear and impact resistance, and a strong price-performance ratio. It is suitable for general industrial applications such as metal sandblasting (rust removal), hardware grinding, the manufacturing of grinding wheels and sandpaper, metallurgical castable refractories, and lining materials for standard industrial furnaces. It serves as a versatile, all-purpose abrasive and refractory raw material.

2. White Fused Alumina: Features high purity, high hardness, and excellent self-sharpening properties, with a pure white appearance free from impurities. It is ideal for high-precision and high-cleanliness applications, including the polishing of precision molds, grinding of aerospace components, finishing of electronic materials, and the production of high-end refractory products and precision ceramics.

3. Fused Alumina (High-Purity/Specialized): Possesses a dense structure, exceptional thermal stability, and high resistance to both heat and corrosion. It serves as a core raw material for high-end, specialized refractories, structural ceramics, precision grinding media, and linings for high-temperature industrial kilns, making it well-suited for demanding, high-performance operating environments.

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