GP-985, GP-991, and GP-993 are all alumina powders, but they are not the same material in use.

GP-985 is our industrial alumina grade. Its typical Al2O3 content is about 98.7%. The BET surface area is around 60–80 m²/g, while alpha-alumina is controlled below 10%. The LOI is about 0.5–1%.

For you, this means GP-985 is not simply a lower-purity version of calcined alumina. It has a much higher surface area and a different phase condition. It is more active than a fully developed, low-surface-area alumina grade.

GP-985 is worth checking when the formula needs a general industrial Al2O3 source, especially where surface activity matters more than fired whiteness or a defined calcined particle size.

GP-991 and GP-993 belong to the calcined alumina powder direction.The tested calcined grade contains about 99.54% Al2O3. Its LOI is only 0.13%, with Fe2O3 around 0.01% and Na2O around 0.22%. The fired whiteness reaches 97.1 after firing at 1200°C for 30 minutes.

This is the cleaner choice when the ceramic formula needs:

low firing loss
high fired whiteness
stable Al2O3 input
better control in white or light-colored systems

The next choice is particle size.

GP-991 is the 100 mesh grade.It is mainly considered for ceramic bodies, refractory formulas, kiln furniture, and wear-resistant ceramic trials where a coarser alumina powder is acceptable.

GP-993 is the 325 mesh grade.The finer powder is easier to distribute in a glaze or fine ceramic formula. It is the more practical grade when dispersion, surface uniformity, or a finer Al₂O₃ addition is needed.

So do not choose only by purity.

GP-985 is the industrial grade in this series. Its high surface area is the main reason to consider it.GP-991 and GP-993 are calcined alumina powder grades.

For a body or refractory formula, I would look at GP-991 first. The 100 mesh powder is often enough for an initial trial.

Working with glaze or a finer ceramic body? Then GP-993 may be easier to use. Its 325 mesh size gives you a finer and more even alumina addition.

Item	GP-985	GP-991	GP-993
Product type	Industrial alumina	Calcined alumina	Calcined alumina
Al2O3	98.5% min 98.7% typical	About 99.54%	About 99.54%
BET surface area	60–80 m²/g	Not provided	Not provided
Alpha content	Max. 10%	Not provided	Not provided
LOI	0.5–1%	About 0.13%	About 0.13%
Fe2O3	About 0.01%	About 0.01%	About 0.01%
Fired whiteness	Not provided	About 97.1	About 97.1
Particle size	Standard industrial supply	100 mesh	325 mesh
Better starting direction	High-surface-area Al2O3 input	Body,refractory, wear-resistant ceramic	Glaze, fine body, better dispersion

Which Alumina Grade Fits the Job?

When the formula needs a general Al₂O₃ source. GP-985 is the grade to check first when the main goal is to bring more alumina into a ceramic formula.

Its high surface area makes it different from the two calcined grades. It may suit formulas where material activity matters more than very high fired whiteness or a fixed fine particle size.

Use it as an industrial alumina input, not as a direct substitute for GP-991 or GP-993.

When a ceramic body needs more hardness or high-temperature support,GP-991 is the 100 mesh calcined grade.It is mainly considered in refractory ceramic bodies, kiln furniture, crucibles, spark plug insulator formulas, and wear-resistant ceramic parts.

In these products, alumina becomes part of the fired structure. The result still depends on the full formula, forming pressure, particle packing, and firing curve.

When the glaze needs a finer alumina addition,GP-993 is the 325 mesh grade.The finer powder is easier to spread through a glaze slurry. It is useful when you need to adjust Al₂O₃ input without bringing a visibly coarse material into the glaze.

This is where calcined alumina for ceramic glaze makes more sense, especially when surface uniformity, glaze hardness, or controlled viscosity matters.

When whiteness matters in a light-colored formula.The tested calcined alumina reaches a fired whiteness of about 97.1. That makes GP-991 and GP-993 more suitable than GP-985 when the body or glaze must stay clean and light after firing.

It will not cover iron or other coloring impurities already in the formula. But it gives you a cleaner alumina source to work with.

When the product must resist wear

Grinding media, liners, wear tiles, and similar ceramic parts need more than a high Al₂O₃ number on paper.GP-991 can be tested in these body systems, but wear resistance comes only after the body is properly formed and fired.

The alumina grade matters. So do density, porosity, and the final fired structure.

One Point Before You Choose

Purity is only the first number to check.Also look at the alumina phase, particle size, surface area, and where the powder will be used.

GP-985, GP-991, and GP-993 may show similar Al₂O₃ values, but they should not be treated as interchangeable grades.

The particle size should follow the application, not only the price.

Your Need	Better Starting Point
General Al2O3 addition	GP-985 industrial alumina powder
Higher fired strength	GP-991 calcined alumina powder
Glaze formulation and better dispersion	GP-993 calcined alumina
Refractory ceramic body	GP-991 / GP-993 depending on formula
Wear resistant ceramic body	Calcined alumina, usually higher Al2O3 system
Fine glaze adjustment	GP-993 325 mesh

If the issue is basic alumina input, GP-985 may be enough.

If the issue is fired stability, strength, whiteness, or glaze surface control, calcined alumina is usually worth testing first.

FAQ

Q: Can GP-985 replace GP-991 or GP-993?

A: Not directly.GP-985 is a high-surface-area industrial alumina. GP-991 and GP-993 are calcined alumina grades.
Their Al2O3 levels look close, but the phase condition, surface area, and particle size are different. Treat them as separate raw materials, not interchangeable grades.

Q: 100 mesh or 325 mesh - where should I start?

A: Where will you put it?
In a ceramic body, refractory part, or wear-resistant formula, start by looking at GP-991.For glaze or a formula that does not accept coarse particles well, GP-993 is usually the better one to compare.The mesh number gives you a direction. The fired sample gives you the answer.

Q: Will calcined alumina make the ceramic whiter?

A: Not automatically. The tested calcined alumina has a fired whiteness of about 97.1 and low Fe2O3. That gives you a clean alumina source.
But it cannot hide iron, titanium, or other coloring impurities already present in the body or glaze.
Bring the Formula, Not Just the Al2O3 Number