Abrasives are substances both natural and synthetic that are used to grind, polish, abrade, scour, clean, or otherwise remove solid material usually by rubbing action (as in a grinding wheel), but also by impact (pressure blasting). The most important physical properties of materials that qualify as abrasives are hardness, toughness (or rigidity), grain shape and size, character of fracture (or cleavage), and purity (or uniformity).
In the final analysis, the choice of a high-grade abrasive depends upon the quality and quantity of work performed by the abrasive per unit of cost. Initial cost of an artificial abrasive may be much greater than that of a natural abrasive, but the artificial mineral may do so much better work and do it so much faster that the ultimate cost is less. It is for this reason that artificial abrasives have largely replaced natural abrasives.
- Synonyms:iron spinel, hercynite
- Chemical Formula: Al2O3 + an iron bearing mineral + trace impurities such as mullite, titania, silica, and magnesia
- Description: A natural occurring mineral having its broadest use as an abrasive in polishing applications. An intimate mix of corundum and magnetite. The higher amounts of impurities and weaker internal structure than naturally occurring minerals has restricted its growth in new applications.
- Nominal Chemical Properties: Al2O3= 58.0%, Fe2O3= 24.0%, SiO2= 4.0%, TiO2= 3.0%, CaO= 2.0%
- Synonyms: aluminum oxide, activated alumina, calcined alumina, dispersing alumina, infiltrating alumina, reactive alumina, tabular alumina, ground alumina
- Formula: Al2O3
- Description: Native alumina is found as the mineral corundum. Most bauxite is refined by the Bayer process to remove impurities and produce a nominal 99.5% Al2O3 product. Four types of alumina are generally utilized: calcined, tabular, hydrated, and synthetic boehmite
- Typical Chemical Properties Available: Purities available from 98% (industrial grade) to 99.999% (high purity grade)
- Typical Physical Properties Available: Sintered pieces, targets, tumbling media, colloidal dispersion, and numerous powder granulations as small as nanoparticles
- Typical Applications: Refractories, abrasives, cement, slag adjusters, traditional & advanced ceramics (lamp components, nuclear insulation, magnetic recording media, IC packages, & tool bits), aluminum chemicals, flame retardants, fillers, welding fluxes, adsorbents, adhesives, coatings, and detergent zeolites
- Synonyms: Silicon carbide powder, fused silicon carbide, SiC, fused, synthetic, powder, grit, crystals, wafers, granule, fabrications
- Formula: SiC
- Description: Produced in electric resistance furnaces with a mixture of coke, sand, sawdust, and a small amount of salt. It is blocky and sharp edged. It is extremely hard, has a high thermal conductivity and low thermal expansion. Not attacked by most acids and alkaline solutions. It dissociates in molten iron and steel. It oxidizes slowly in air above 800 deg.C.
- Typical Chemical Properties Available: Various purities available from a low purity metallurgical grade (90.0%) to 99.0% (black), 99.2% (black), 99.5% (dark green), and 99.7% (light green)
- Typical Physical Properties Available: Available as irregular shaped powder, crystals, platelets, and wafers. Numerous size distributions available from very coarse grits (1/2" pieces) all the way down to 20-100 nanometer particles
- Typical Applications: Bonded abrasive products, abrasive grits, blasting, lapping & honing compounds, semiconductor wafers, quartz crystals, hard metals, refractories, metallurgical purposes, production of exponential resistors, wire sawing, construction industry, a filler in plastics and composites, ceramic sintered parts, ferrites, soft metals, gettering, electric heating elements, and lightning arresters