Final Polishing Abrasives

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FINE POLISHING ABRASIVES

Nanometer Alumina

Final polishing abrasives are selected based upon specimen hardness and chemical reactivity. The most common polishing abrasives are alumina and colloidal silica. Alumina abrasives are primarily used as mechanical abrasives because of their high hardness and durability. They also exist in either the softer gamma (mohs 8) or harder alpha (mohs 9) phases.

Colloidal Silica

Colloidal silica's are relatively soft final polishing abrasives with a high chemical activity. They are ideal for chemical mechanical polishing (CMP). The chemical activity of colloidal silica results from the electrochemical balance (zeta potential) required to keep the fine particles from aggregating. This chemical balance produces a surface phenomena which makes the specimen surface more reactive. This reacted layer is consequently removed by the colloidal silica abrasives themselves or by a mechanical scrubbing of the surface with other abrasives and/or the polishing pad.

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NANOMETER ALPHA ALUMINA DESCRIPTION

Nanometer alumina is a colloidal alumina processed by a proprietary process which produces a polycrystalline alumina crystal. This processing offers two significnat improvements over conventional alumina calcining processes:

1. Tighter more controlled particle size distributions
2. 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.

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COLLODIAL SILICA DESCRIPTION

Colloidal silica is a very unique polishing suspension because it provides a chemical mechanical polishing (CMP) action for materials such as ceramics, composites and soft metals. Colloidal silica has particle size distribution between 0.05 um and 0.07 um and is stabilized at alkaline pH values (typically >9.5).

Ceramics and Minerals - At higher pH values colloidal silica is held in nearly perfect suspension by the electrochemical repulsive forces of the fine particles themselves. This chemical balance electrochemcially attacks the surface of a ceramic or mineral surface to form a thin reacted layer on the specimen surface. This reacted layer can then be removed via the mechanical action of the polishing cloth or another abrasive (e.g. diamond). Polishing rates and surface finishes are significantly better for ceramics and minerals as compared with straight mechanical abrasives such as diamond. Thus the highest removal rates and the most reliable action for removing both surface and subsurface damage on ceramics and minerals is via chemical mechanical polishing with colloidal silica.

As with other exothermic chemical reactions the chemical contribution can be enhanced by increasing the temperature of the polishing action. This can be accomplished by increasing the polishing pressure which increases the friction between the polishing cloth, colloidal silica and the specimen.

Cleaning of the surface is best accomplished by running water on the surface for the final 10-15 seconds of the polishing cycle and then immediately rinsing the specimen surface with water. This allows the cloth to mechanically remove the reacted layer and any residual colloidal silica.

Application of Colloidal Silica

• The most efficient application is to initially wet the polishing cloth with SIAMAT Colloidal Silica and then to slowly drip or spray the suspension onto the polishing cloth
• It is recommended that water be applied continuously to the polishing cloth for 10-15 seconds prior to completion of the polishing step. This aids in removing the fine particles which may be electrostatically attracted to the specimen surface.

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TROUBLE SHOOTING GUIDE for NANOMETER ALUMINA

Symptom	Cause	Action
Agglomerate particles	Bacterial growth in suspending agent	Replace product
Specimen has a fine matte like finish	Thin layer of particles on the surface	Clean surface with 100% cotton swab and alcohol Clean specimen by flushing specimen and polishing pad with water for last 10-15 seconds of the polishing operation
Excessive relief in surface finish	Overpolishing	Repeat step prior to final polish and shorten final polishing time
Scratches in specimen	Improper selection of polishing pad Contaminated pad Removal of secondary phases	Review application guideline chart for polishing pads or select a softer pad Replace polishing pad Alternate between polishing and etching
Etching of specimen	Alumina abrasive pH too high	Use lower pH alternative abrasives

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TROUBLE SHOOTING GUIDE for COLLOIDAL SILICA

Symptom	Cause	Action
Crystallized residue on specimens	Improper cleaning of specimen	Repolish specimens and apply rinse water to pad and specimen for last 10-15 seconds
Etching of specimen	Too high a polishing pH	Use an alternative polishing suspension
Excessive scratching on specimen	Crystallization of silica	Keep bottle closed when not in use and filter colloidal silica through a filtering cloth

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FINE ABRASIVES PRODUCT SELECTION GUIDE

ALUMINA Abrasive Slurry (pH 10)
Description	Quantity	Catalog Number
Nanometer 0.05 um micron Alpha alumina	16 oz (0.475 ml)	NA-1005-16
Nanometer 0.05 um micron Alpha alumina	64 oz (1.9 l)	NA-1005-64
Nanometer 0.05 um micron Alpha alumina	128 oz (3.8 l)	NA-1005-128

ALUMINA Abrasive Slurry (Acidic-pH 4)
Description	Quantity	Catalog Number
Nanometer Acid Alumina Slurry (0.05 micron)	16 oz (0.475 ml)	NA-1020-16
Nanometer Acid Alumina Slurry (0.05 micron)	64 oz (1.9 l)	NA-1020-64
Nanometer Acid Alumina Slurry (0.05 micron)	128 oz (3.8 l)	NA-1020-128

ALUMINA Abrasive Suspension
Description	Quantity	Catalog Number
NANOPOLISH 0.05 um micron suspension	6 oz (0.475 ml)	NANO-1005-06
NANOPOLISH 0.30 um micron suspension	6 oz (0.475 ml)	NANO-1003-06
NANOPOLISH 0.5 um micron suspension	6 oz (0.475 ml)	NANO-1105-06
NANOPOLISH 1.0 um micron suspension	6 oz (0.475 ml)	NANO-1010-06
NANOPOLISH 5.0 um micron suspension	6 oz (0.475 ml)	NANO-1050-06

Fine ALUMINA Polishing Powders
Description	Quantity	Catalog Number
0.05 um Alumina Powder	1 lb 5 lbs	ALP-0105-01 ALP-0105-05
0.3 um Alumina Powder (high density)	1 lb 5 lbs	ALP-0103-01 ALP-0103-05
0.3 um Alumina Powder (Deagglomerated)	1 lb 5 lbs	ALD-0103B-01 ALD-0103B-05
0.5 um Alumina Powder	5 lbs	ALR-0150-05
1.0 um Alumina Powder	1 lb 5 lbs	ALR-0110-01 ALR-0110-05
3 um Alumina Powder	5 lbs	ALR-0130-05
5.0 um Alumina Powder	5 lbs	ALR-0150-05

Coarse ALUMINA Powders
Description	Quantity	Catalog Number
240 grit Alumina Suspension	5 lbs	ALR-0240-05
400 grit Alumina Suspension	5 lbs	ALR-0400-05
600 grit Alumina Suspension	5 lbs	ALR-0600-05

Colloidal Silica (0.05 micron)
Description	Quantity	Catalog Number
SIAMAT Colloidal Silica	16 oz (500 ml)	SI-100A-16
SIAMAT Colloidal Silica	64 oz (1.9 l)	SI-100A-64
SIAMAT Colloidal Silica	128 oz (3.8 l)	SI-100A-128

Colloidal Silica (0.02 micron)
Description	Quantity	Catalog Number
SIAMAT2 Colloidal Silica	16 oz (500 ml)	SI2-100A-16
SIAMAT2 Colloidal Silica	64 oz (1.9 l)	SI2-100A-64
SIAMAT2 Colloidal Silica	128 oz (3.8 l)	SI2-100A-128