Black Fused Alumina

Product Overview

Black fused alumina, also known as low-alumina corundum, is a gray-black crystalline abrasive made by high-temperature arc fusion of bauxite. Its main phases are α-Al₂O₃ and iron spinel. Iron oxide, approximately 10% Fe₂O₃, together with silica, titania and other impurities, gives it a black appearance. Alumina content is lower than brown or white fused alumina at 70%-85%, but it offers moderate hardness, high toughness, temperature resistance and stable hot performance. Available in F8-F220, it is widely used for stainless steel polishing, metal finishing, resin-bonded abrasives and blasting.

Technical Specifications

Black fused alumina has relatively low Al₂O₃ content and requires less smelting energy than brown fused alumina.

Chemical Composition

Key Features

1. Moderate hardness and toughness help prevent scratches

Black fused alumina combines moderate hardness and good toughness with the cutting ability of alumina abrasives. It is less likely to scratch workpieces and produces a high polish, particularly on stainless steel and optical glass requiring high surface quality.

2. Strong self-sharpening and low grinding heat

Dulled grains continuously fracture to expose fresh edges. Low grinding heat helps prevent workpiece burns and maintain surface quality.

3. Good adhesion and wettability

The particle surface provides good wettability and bond adhesion, facilitating application to grinding discs and improving resin-bonded tool strength.

4. Economical and cost-effective

Lower alumina content reduces smelting energy requirements compared with brown fused alumina, offering a cost advantage for applications that are price-sensitive and do not require high abrasive purity.

5. Scratch-free finishing and high polishing quality

Its distinctive properties provide strong grinding and polishing performance, with more than twice the polishing capability of brown fused alumina and an improvement of over two finish grades.

Available Grit Sizes

Typical Applications

Stainless steel polishing: polishing and blasting workpieces, tableware, cookware and hardware; the most typical application

Metal finishing: polishing before electroplating, rust and scale removal, deburring, and polishing bicycle, motorcycle, sewing-machine, watch and lighting components

Blasting: metal and non-metal surfaces, rust removal, decorative glass blasting and stone etching

Resin-bonded abrasives: manufacturing cut-off wheels, angle grinder discs and grinding wheels

Coated abrasives: manufacturing abrasive cloth and sandpaper

Non-metals: grinding and polishing optical glass, ceramics, bamboo and wood products, plastics and composite panels

Packaging

Standard bags: 25 kg woven bags with liners

Bulk bags: 1,000 kg per bag (1 ton), plastic woven

Pallet packaging: 25 kg bags stacked on pallets and secured with stretch film

Custom packaging: special packaging on request

Neutral or branded packaging is available on request.

Storage Recommendations

To maintain black fused alumina quality during storage, observe the following conditions:

Store in a cool, dry, ventilated warehouse away from direct sunlight. Relative humidity should preferably be ≤60% to prevent caking and mold on packaging.

Stack bags no more than 10 layers high to prevent packaging damage or grain fracture. Use wooden or plastic pallets to keep them off the ground.

Keep separate from acids, alkalis, organic solvents and other corrosive substances. Clearly label and separate grit sizes to prevent mixing.