How to Read an Alumina Technical Data Sheet

Why This Matters

An alumina technical data sheet (TDS) or certificate of analysis (COA) lists a dozen or more parameters — particle size, surface area, chemistry, phase composition. Knowing which numbers matter for your application saves time, reduces trial batches, and helps you compare suppliers on a like-for-like basis. This guide explains the most common parameters and what they actually tell you.

Chemical Composition

Al₂O₃ Content

The headline number. For calcined and tabular grades, typical values range from 99.3% to 99.7%. Higher Al₂O₃ generally means lower impurities, but for many refractory applications, impurity type matters more than total purity.

Na₂O (Sodium Oxide)

The most practically important impurity in alumina. Na₂O content affects:

Sintering behavior — sodium can act as a flux, lowering the sintering temperature but potentially reducing hot strength.
Beta-alumina formation — at high temperatures, Na₂O reacts with Al₂O₃ to form beta-alumina (NaAl₁₁O₁₇), which has a different crystal structure and can cause volume instability.

Typical calcined and tabular grades specify Na₂O ≤ 0.25–0.30%. Reactive grades for advanced ceramics often require ≤ 0.10%.

Fe₂O₃ and SiO₂

Iron and silica are the other routinely reported impurities. Fe₂O₃ affects color (whiteness) and can reduce refractoriness. SiO₂ can form low-melting phases with alkalis. Both are typically below 0.10% in high-purity grades.

Physical Properties

Particle Size: D50 and Top Cut

D50 is the median particle size — half the particles are smaller, half are larger. It’s the most commonly quoted single number, but it doesn’t tell the full story.

Top cut (often reported as D90, D97, or D100) is equally important: it tells you how many coarse particles are present. Two powders with the same D50 can behave very differently if one has a long tail of coarse particles.

For refractory castables, D50 ranges from sub-micron (reactive alumina) to 80 μm (coarse calcined). For polishing grades, D50 spans from 3.5 μm (mirror finishing) to 65 μm (heavy stock removal).

BET Specific Surface Area

Measured by nitrogen adsorption, BET surface area (m²/g) reflects both particle size and internal porosity:

Low BET (0.5–3 m²/g): calcined and tabular grades. Low surface area means low water demand — critical for castable workability.
Medium BET (3–8 m²/g): reactive alumina. Higher surface area drives sintering activity.
High BET (up to 12 m²/g): polishing grades with high internal porosity, designed for controlled breakdown during use.

BET is more informative than particle size alone for predicting how a powder will behave in a formulation. Two powders with the same D50 can have different BET if their primary crystallite size or porosity differ.

Alpha-Al₂O₃ Phase Content

Alpha (α) is the thermodynamically stable corundum phase of alumina. The alpha content tells you what fraction of the material is in this stable form:

≥ 92–98%: calcined and tabular grades. High alpha means dimensional stability — the material won’t undergo phase transformation or associated volume change in service.
~70%: some polishing grades where controlled breakdown during use is desirable.
50–96%: reactive grades, where lower alpha means more transition alumina phase available for sintering.

Bulk Density

For tabular alumina, bulk density (≥ 3.50 g/cm³ on pellets) reflects the density of individual aggregate particles and is a measure of how well-sintered the material is. For calcined and reactive powders, bulk density (typically 0.55–1.00 g/cm³) is primarily a function of particle size and morphology, not material density.

Reading Between the Lines

What the TDS Won’t Tell You

A standard TDS reports typical or guaranteed values. What it typically won’t show:

Batch-to-batch variation — consistency matters more than a single data point. Ask for multiple-lot data.
Sintering curve — the TDS gives you the starting powder. How it behaves during heat-up depends on your formulation and firing schedule.
Rheology — water demand and flow properties depend on particle packing, not just individual powder specs. Small-scale trials are essential.

Questions to Ask Your Supplier

What is the typical D10/D90 spread (not just D50)?
Is the reported BET a typical or guaranteed value?
What is the lot-to-lot variation on key parameters?
Can you provide a multi-lot trend chart?

For product-specific data, refer to the individual product pages:

Contact our technical team if you need detailed COA data for a specific lot or grade.