White fused alumina

Identity and material boundaries

Sanhui’s WA-F and WA-P macro ranges list at least 99.40% Al₂O₃, while the listed micro ranges give at least 99.0%. Use the grade and size family when reading the limit. White fused alumina is produced by electric-arc fusion of high-purity alumina. Sanhui identifies its grain as alpha alumina and SRL describes calcined feedstock and block-method fusion. Sanhui product information, p. 1 SRL Dental, 06-23_en

Alpha alumina has the corundum structure. NIST’s measurements concern grown single crystals. Grain beds require separate measurements. NIST SRD 30, Z00627

The following alumina forms have different processing histories.

These descriptions come from Almatis's refractory-material brochure, PDF pp. 5 and 17–19. They do not define all polishing powders or demonstrate interchangeability with fused grains. Almatis brochure

Explanatory synthesis. A grain family is also distinct from a finished suspension, polishing compound, coated belt or bonded wheel. The finished product introduces a carrier, bond, backing or other formulation. Grain properties alone do not describe that product's behavior. FEPA identifies grains as ingredients of bonded and coated abrasives and as materials for separate industrial applications. FEPA grain overview

Chemistry depends on grade and reporting basis

A Washington Mills sheet marked updated 11-12, preserved by distributor Fintec, gives this typical analysis for DURALUM Special White. Al₂O₃ is 99.77% by difference, with SiO₂ 0.02%, Fe₂O₃ 0.01% and Na₂O 0.20%. The sheet explicitly disclaims specification status and warns of variation and unlisted trace elements. It is historical product evidence, not a current lot certificate. Washington Mills sheet

Explanatory synthesis. Here, subtracting the three listed minor oxides from 100% gives 99.77%. That arithmetic explains the reported balance. It does not independently measure Al₂O₃ or establish a quantitative alpha-phase fraction.

Sanhui's separate chemistry table distinguishes size families. The table below retains its numerical limits, read as percentages. The source prints a percent sign only beside some Al₂O₃ entries and supplies neither an analytical method nor an explicit mass basis. Sanhui, p. 1

Sanhui also offers custom chemistry. Its published table therefore does not establish one purity threshold for every WFA size or order. Sanhui, p. 1

SRL Dental's average typical analysis instead lists Al₂O₃ 99.7%, Na₂O 0.14%, Fe₂O₃ 0.03%, SiO₂ 0.01%, CaO 0.02%, TiO₂ 0.02% and MgO 0.01%. Although the sheet calls the material iron-free, it reports nonzero Fe₂O₃ and supplies no separate free-metallic-iron result. White color and that wording do not prove absence of every iron species or contamination-free use. SRL Dental

Shape, treatment and fracture

The historical DURALUM sheet describes blocky grains with sharp edges. The current Washington Mills page calls DURALUM Special White friable, meaning susceptible to grain fracture. Neither supplies a numerical fracture index. Washington Mills sheet Current Special White page

The current CA and CP page attributes comparatively rapid fracture to high purity and large crystals. Its superlative friability claim supplies no comparison protocol. SK has an added silane coating, with claimed improvements in resin-bonded wheels. The SK page provides no numerical wheel-life comparison or common test conditions. These claims concern named products and applications. They do not establish a universal toughness ranking against brown fused alumina, or equal performance among untreated and treated white grains. CA and CP SK

Density, hardness and temperature values

The historical DURALUM sheet reports specific gravity 3.96, Knoop₁₀₀ hardness 2000, and grain bulk density under ANSI B74.4-1992, reaffirmed 2007. Example typical bulk densities are 1.78 g/cc at grit 46 and 1.54 g/cc at grit 220. Its hardness row supplies no explicit unit. Those entries retain their original reporting basis. Washington Mills sheet

SRL Dental reports bulk density 1.4–2.1 g/cm³ depending on grain size, Mohs hardness 9, and Knoop 1800/2100 without a test load or unit. It labels 3.98 g/cm³ as specific gravity. SRL Dental

Explanatory synthesis. Mass per bulk volume includes spaces between grains. It differs from material density. Specific gravity conventionally expresses a dimensionless density ratio, so SRL's unit-bearing label remains a source ambiguity. A packing-density comparison also depends on size distribution, grain shape and filling or compaction method. Mohs scratch hardness and Knoop indentation hardness are separate scales. Neither alone measures fracture toughness or friability.

Published melting points also disagree. SRL gives 2,040 °C. Sanhui gives 2,150 °C. The Zhengzhou Haixu sheet gives 2,250 °C under typical physical properties. None of these sheets supplies a melting-point test method. These values remain separate source claims, not an averaged WFA constant or an abrasive operating-temperature limit. SRL Dental Sanhui, p. 1 Zhengzhou Haixu technical sheet

Grain size is a distribution

The public standard scopes distinguish the application and designation.

FEPA's overview cites its 2006 F standards for F4–F220 macrogrits and F230–F2000 microgrits. It distinguishes sieving for macrogrits from sedimentation for microgrits, and warns that illustrative mean diameters do not replace the specified distributions. Its P discussion cites separate coated-abrasive standards and sedimentation equipment. These are the editions and methods named by that overview, not a claim that every present supplier uses those methods. FEPA

The Zhengzhou Haixu sheet illustrates the distribution concept with F60. Its sieve row gives +425 µm at 0%, +300 µm at ≤30%, +250 µm at ≥40%, combined 250 and 212 µm fractions at ≥65%, and −180 µm at ≤3%. This is that supplier's sieve table, not a reproduced normative standard. Zhengzhou Haixu technical sheet

Explanatory synthesis. An unprefixed grit number cannot establish equivalence among FEPA F, FEPA P, ANSI and JIS designations. A laser-diffraction d50 is a method-dependent median, not a maximum size or a complete distribution. Grain diameter is also distinct from workpiece roughness. Neither the grit label nor d50 alone establishes removal rate, finish, reuse life or substrate compatibility.

Source coverage and limits

Reviewed 29 October 2026 PDT. The Washington Mills sheet is a distributor-hosted historical copy. Its current pages are undated snapshots. Their technical-sheet links now lead to a request form, so this reference does not treat the historical chemistry as a verified current specification. Historical sheet Current page

SRL's sheet is marked 06-23_en. Sanhui and Zhengzhou Haixu sheets supply no visible revision date. Complete short sheets, their tables and disclaimers, relevant Almatis sections, current Washington Mills product descriptions, and public FEPA and ISO scopes were read. Paid standard requirements were not reviewed or reproduced.

The evidence does not establish lot-specific phase purity, free-iron limits, quantitative grain toughness, approved substrate conditions, wheel strength or a guaranteed finish. It also supplies no operating recipe or customer capability. Finishing process references describes the separate process context.