Alumina

Technical Information

PACE Technologies

Alumina Polishing Abrasives

Considerations for proper Alumina lapping or polishing

• Particle grit size • Alumina hardness • Carrier vehicle • Polishing pad or lapping

surface • Applied grinding load • Grinding lubricant

Inside this brochure:


1

Calcined and Fussed Alumina

2

Polycrystalline Alumina 3

Specifications 4

Product Numbers 5

Precision Alumina Abrasives

Alumina polishing powders, slurries and suspensions

There are a number of different types of alumina polishing abrasives. These abrasive are classified by there manufacturing process, crystal structure (hardness) and there classification process. The main types of alumina’s produced for polishing are either calicned or polycrystalline aluminas. Calcined powders can also be characterized as either fused, levigated or plately alumina depending upon the grain shape, purity and classification process. There is a major difference in the performance between calcined and polycrystalline alumina abrasives, especially for the submicron particle sizes. The two common crystal structures are the harder alpha alumina (mohs hardness 9) and the softer gamma crystal structure (mohs hardness 8).

Alumina / property

Polycrystalline Calcined Fused Levigated

Crystal structure

Polycrystalline alpha alumina

Monocrystalline alpha alumina

Alpha alumina Monocrystalline

Shape Hexagonal platelets

Hexagonal platelets

Particle size 0.05 micron Submicron up to 30 microns

5-70 micron 3-5 micron (air classified)

pH 4 and 10 8-11 9.0-10.5

% solids 15-25%

Specific gravity 1.6 gms/cc (liquid)

3.95 gms/cc 3.95 gms/cc 3.95 gms/cc

Hardness Knoop 2000 (Mohs 9)

Knoop 2000 (Mohs 9)

Knoop 2000 (Mohs 9)

Mohs 8,9

Applications pH 4 – metal polishing pH 10 – ceramic polishing

-Metal lapping and polishing -Lapping films -Glass lapping

-Lapping compounds -Wear resistant coating

General purpose alumina -Polishing and buffering abrasive -Additive for heat sinks -Abrasion resistant coatings

Precision Surface Finishing Applications

Page 2

“Polishing depends upon the alumina particle shape and purity.”


Calcined and Fused Alumina Calcined alumina powders are typically used for metal lapping and polishing, as well as have been the traditional rough and final polishing abrasive for many years and is relatively inexpensive and readily available. Calcined alumina grains consist of single platey crystals, whereas fused alumina is more blocky in shape. A perfect clacined alumina particle would be a six-sided disk, with a thickness of about 1/5 of its diameter. Calcined alumina are typically very pure (>99%) , whereas the purity of fused alumina can vary from i96% to 99+%.. The issue with the calcined powders is the agglomeration issue created by processing these type of alumina’s as dry powders creates agglomeration of the particles. For larger particles (>600 grit), the agglomeration is not too much of an issue, however for smaller particles the agglomeration issue can be significant. For example, the agglomerated or standard version of a 0.05 um aluimina crystal can form an agglomerate size as large as 40 um. When polishing hard samples these agglomerates can often be broken down, however for soft materials such as aluminum, copper, zinc, etc. these fine agglomerated abrasives can form large random scratches. Agglomerated vs. Deagglomerated The term agglomeration refers to the electrostatic attraction of small particles to each other. This arises from the fact that all surfaces have an unbalanced surface charge. When the surface area of small alumina particle becomes large compared to its volume, then it becomes nearly impossible to keep the particle from attracting each other in a dry processing state. The term deagglomeration refers to the process by which a dry agglomerated particle is milled or broken down. The process for deagglomeration of dry powders is to blast the agglomerated powder at each other at high velocities, thus breaking down the agglomerate size. The process is only moderately successful.

Calcined Alumina

Fused Alumina

Polycrystalline or nanometer alumina is a colloidal alumina processed by a proprietary process which produces a polycrystalline alumina crystal. This processing offers two significant improvements over conventional alumina calcining processes:

• Tighter more controlled particle size distributions

• Harder alpha alumina phase

A tighter more controlled particle size distribution is a result of less particle aggregation. For example, standard calcined 0.05 um gamma alumina products form aggregate sizes as large as 5 um. These aggregates can be broken down during polishing with harder specimens. However, these large aggregates have been known to cause significant scratching in soft metals such as aluminum, tin, lead, copper and soft steels. Nanometer alumina is specifically milled to produce a much smaller aggregate particle size distribution (<0.5 um). Nanometer alumina is also the harder alpha alumina particle, therefore making it a more efficient cutting abrasive. Thus nanometer alumina is a much more controlled polishing abrasive than calcined gamma alumina.

Advantages and Features of Nanometer Alumina

• Improved surface finishes over gamma alumina

• Less random scratching

• Higher cutting rates than gamma alumina

• Much more uniform surface finish

• Tighter particle size distributions than gamma alumina

• Low viscosity for easy dispensing

• Semi-permanent suspensions

Application of Nanometer Alumina

• The most efficient application is to initially wet the

polishing cloth with Nanometer alumina and then to slowly drip or spray the suspension onto the polishing cloth

• It is recommended that water be continuously applied

to the polishing cloth for several seconds prior to completion of the polishing step. This aids in removing the fine particles which may be electrostatically attracted to the specimen surface. This phenomena occurs because of the deagglomeration characteristics of the alumina.

0.20 um Calcined gamma alumina

0.20 um polycrystalline alumina

Polycrystalline Alumina

Alumina Polishing Abrasives Page 3

Polycrystalline Alumina

Chemical Analysis

Chemical Analysis

Chemical Analysis

0.05 µm and 0.3 µm deagglomerated alumina powders

0.3 µm high density alumina, 0.5 µm, 1.0 µm, 3 µm, 5µm alumina

Page 4 Alumina Polishing Abrasives

Crystal Form Monocrystalline alpha alumina

Shape Hexagonal platelets, deagglomerated

Hardness Knoop - 2000

pH (recommended) 9.0 - 10.5

Specific gravity 3.95 gm/cc

Al2O3 99% min.

SiO2 0.06% max

Fe2O3 0.03% max

Na2O 0.60% max

TiO2 0.02% max

CaO 0.07% max

MgO 0.05% max

240, 400, 600 grit alumina powders

Crystal Form Monocrystalline alpha alumina

Shape Hexagonal platelets, deagglomerated


pH (recommended) 9.0 - 10.5

Specific gravity 3.95 gm/cc

Al2O3 98.70% min.

SiO2 0.06% max

Fe2O3 0.03% max

Na2O 0.60%ax

TiO2 0.02% max

CaO 0.07% max

MgO 0.05% max

Particle size 0.05 µm 0.3 µm

Crystal Form Gamma Alpha

Shape Cubic, deagglomerated

Hexagonal, deagglomerated

Surface area, m2/gm 100 15

Hardness, Mohs 8 9

pH in distilled water 7.5-8 7.5-8

Specific gravity 3.67 gm/cc 3.98 gm/cc

0.05 µm Nanometer alumina slurry

Crystal Form Polycrystalline alpha alumina

Size 0.05 - 0.10 µm crystals


pH 4 or 10

% solids 15% for pH 4 25% for pH 10

NANO alumina suspension

Crystal Form Alpha alumina

Size 0.05 - 5 µm


pH 10

% solids 20%

Al2O3 >98%

Ca <5 ppm

Fe <10 ppm

K <60 ppm

Na <20

Si <45

Page 5 Alumina Polishing Abrasives

Alumina Slurries

Fine Alumina Powders

Coarse Alumina Powders

Product Name Catalog Number Packaging

Nanometer 0.05 micron alpha alumina (pH 10)

NA-1005-16 NA-1005-64 NA-1005-128

16 oz 64 oz (1/2 gallon) 1 gallon

Nanometer 0.05 micron alpha alumina (pH 4)

NA-1020-16 NA-1020-64 NA-1020-128

16 oz 64 oz (1/2 gallon) 1 gallon

Alumina Suspensions Product Name Catalog Number Packaging

NANO 0.05 micron suspension NANO-1005-06 NANO-1005-128

6 oz 1 gallon


6 oz 1 gallon


6 oz 1 gallon


6 oz 1 gallon

NANO 3 micron suspension NANO-1030-06 NANO-1030-128

6 oz 1 gallon

NANO 5 micron suspension NANO-1050-06 NANO-1050-128

6 oz 1 gallon


240 grit alumina powder ALR-0240-05 5 lbs




0.05 micron deagglomerated alumina powder ALR-0105-01 ALR-0105-05

1 lb 5 lbs

0.3 micron deagglomerated alumina powder ALD-0103B-01 ALD-0103B-05

1 lb 5 lbs

0.3 micron high density alumina powder ALR-0103-01 ALR-0103-05

1 lb 5 lbs

0.5 micron alumina powder ALR-1005-01 ALR-1005-05

1 lb 5 lbs

1.0 micron alumina powder ALR-1010-01 ALR-1010-05

1 lb 5 lbs

3 micron alumina powder ALR-1030-01 ALR-1030-05

1 lb 5 lbs

5 micron alumina powder ALR-1050-01 ALR-1050-05

1 lb 5 lbs

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Alumina