Metallographic Final Polishing Abrasives

Introduction

Alumina Powders and Suspensions

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 and CMP Slurries

Colloidal silica and CMP slurries are a 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.

Alumina Polishing Abrasives

There are a number of different types of alumina polishing abrasives. These abrasive are classified by their manufacturing process, crystal structure (hardness) and their classification process. The main types of alumina’s produced for polishing are either calcined or polycrystalline alumina. Calcined powders can also be characterized as either fused, platey or levigated (air classified / sized) 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 gamma or alpha Shape Hexagonal platelets Hexagonal platelets Particle size 0.05 microns Submicron up to 30 microns 5-70 micron 3-5 micron

(air classified) pH 4 and 10 Range from 8-11 9.0-10.5 % solids 20-30% Specific gravity 3.95 gms/cc 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 (acidic) – metal polishing

pH 10 (basic)- ceramic polishing Linde A, Linde B and Linde C alumina polishes

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 96% to 99+%https://www.metallographic.com 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.

Nanometer Polycrystalline Alumina





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:

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.

Colloidal Silica and CMP Slurry Descriptions

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 electrochemically 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.

Trouble Shooting Guidelines 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

Trouble Shooting Guidelines 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

Final Polishing Abrasives Product Selection Guidelines

Polycrystalline Alumina Abrasive Slurries (pH 10)

Description Quantity Catalog Number Product Image Nanometer 0.05 micron

Alpha alumina 16 oz (475 ml) NA-1005-16 Nanometer 0.05 micron

Alpha alumina 32 oz (950 ml) NA-1005-32 Nanometer 0.05 micron

Alpha alumina 1/2 gallon (1.9 l) NA-1005-64 Nanometer 0.05 micron

Alpha alumina 1 gallon (3.8 l) NA-1005-128

Polycrystaline Alumina Abrasive Slurries (Acidic-pH 4)

Description Quantity Catalog Number Product Image Nanometer Acid Alumina Slurry

(0.05 micron) 16 oz

(475 ml) NA-1020-16 Nanometer Acid Alumina Slurry

(0.05 micron) 32 oz

(950 ml) NA-1020-32 Nanometer Acid Alumina Slurry

(0.05 micron) 1/2 gallon

(1.9 l) NA-1020-64 Nanometer Acid Alumina Slurry

(0.05 micron) 1 gallon

(3.8 l) NA-1020-128

Deagglomerated Electronic Polishing Grade Alumina Suspensions

Description Quantity Catalog Number Product Image 0.05 micron Electronics Graded Deagglomerated Alumina Suspensions 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1005-06E

NANO2-1005-16E

NANO2-1005-32E

NANO2-1005-128E 0.30 micron Electronics Graded Deagglomerated Alumina Suspensions 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1003-06E

NANO2-1003-16E

NANO2-1003-32E

NANO2-1003-128E 1 micron Electronics Graded Deagglomerated Alumina Suspensions 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1010-06E

NANO2-1010-16E

NANO2-1010-32E

NANO2-1010-128E

ALUMINA NANO Low Viscosity Abrasive Slurry

Description Quantity Catalog Number Product Image NANO 0.05 micron slurry 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO-1005-06

NANO-1005-16

NANO-1005-32

NANO-1005-128 NANO 0.30 micron slurry 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO-1003-06

NANO-1003-16

NANO-1003-32

NANO-1003-128 NANO 0.50 micron slurry 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO-1105-06

NANO-1105-16

NANO-1105-32

NANO-1105-128 NANO 1 micron slurry 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO-1010-06

NANO-1010-16

NANO-1010-32

NANO-1010-128 NANO 3 micron slurry 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO-1030-06

NANO-1030-16

NANO-1030-32

NANO-1030-128 NANO 5 micron slurry 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO-1050-06

NANO-1050-16

NANO-1050-32

NANO-1050-128

ALUMINA NANO2 High Viscosity Abrasive Susupension

Description Quantity Catalog Number Product Image NANO2 0.05 micron suspension 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1005-06

NANO2-1005-16

NANO2-1005-32

NANO2-1005-128 NANO2 0.30 micron suspension 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1003-06

NANO2-1003-16

NANO2-1003-32

NANO2-1003-128 NANO2 0.50 micron suspension 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1105-06

NANO2-1105-16

NANO2-1105-32

NANO2-1105-128 NANO2 1 micron suspension 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1010-06

NANO2-1010-16

NANO2-1010-32

NANO2-1010-128 NANO2 3 micron suspension 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1030-06

NANO2-1030-16

NANO2-1030-32

NANO2-1030-128 NANO2 5 micron suspension 6 oz (0.475 ml)

16 oz (475 ml)

32 oz (950 ml)

1 gallon (3.8 l) NANO2-1050-06

NANO2-1050-16

NANO2-1050-32

NANO2-1050-128

Alumina Polishing Powders

Electronics Graded Deagglomerated Fine ALUMINA Polishing Powders

Description Quantity Catalog Number Product Image 0.05 micron Electronics Graded Alumina Powder (Deagglomerated) 1 lb

5 lbs ALR-1005-01E

ALR-1005-05E 0.30 micron Electronics Graded Alumina Powder (Deagglomerated) 1 lb

5 lbs ALR-1003-01E

ALR-1003-05E 1 micron Electronics Graded Alumina Powder (Deagglomerated) 1 lb

5 lbs ALR-1010-01E

ALR-1010-05E

Fine Standard Deagglomerated Colloidal Alumina Polishing Powders (<1 micron)

Description Quantity Catalog Number Product Image 0.05 micron Alumina Powder (Deagglomerated) 1 lb

5 lbs ALR-1005-01

ALR-1005-05 0.30 micron Alumina Powder (Deagglomerated) 1 lb

5 lbs ALR-1003-01

ALR-1003-05 0.50 micron Alumina Powder (Deagglomerated) 1 lb

5 lbs ALR-0105-01

ALR-0105-05

Alumina Polishing Powders

Description Quantity Catalog Number Product Image 1 micron Alumina Powder 1 lb

5 lbs ALR-1010-01

ALR-1010-05 3 micron Alumina Powder 5 lbs ALR-0130-05 5 micron Alumina Powder 5 lbs ALR-0150-05

Coarse Alumina Grinding Powders

Description Quantity Catalog Number Product Image 9 micron Alumina Powder 5 lbs ALR-0190-05 12 micron Alumian Powder 5 lbs ALR-1200-05 15 micron Alumina Powder 5 lbs ALR-1500-05 20 grit Alumina Powder 5 lbs ALR-2000-05 30 grit Alumina Powder 5 lbs ALR-3000-05 40 grit Alumina Powderon 5 lbs ALR-4000-05 240 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 Polishing Abrasives

Colloidal Silica (0.05 micron)

Description Quantity Catalog Number Product Image SIAMAT Colloidal Silica 16 oz

(475 ml) SI-100A-16 SIAMAT Colloidal Silica 32 oz

(950 ml) SI-100A-32 SIAMAT Colloidal Silica 1/2 gallon

(1.9 l) SI-100A-64 SIAMAT Colloidal Silica 1 gallon

(3.8 l) SI-100A-128 SIAMAT Colloidal Silica 5 gallons

(19 l) SI-100A-640

Low-Crystallizing Colloidal Silica (0.02 micron)

Description Quantity Catalog Number Product Image SIAMAT2 Low Crystallizing Colloidal Silica 16 oz

(475 ml) SI-100A-16 SIAMAT2 Low Crystallizing Colloidal Silica 32 oz

(950 ml) SI-100A-32 SIAMAT2 Low Crystallizing Colloidal Silica 1/2 gallon

(1.9 l) SI-100A-64 SIAMAT2 Low Crystallizing Colloidal Silica 1 gallon

(3.8 l) SI-100A-128 SIAMAT2 Low Crystallizing Colloidal Silica 5 gallons

(19 l) SI-100A-640

Colloidal Silica - Blue (0.05 micron)

Description Quantity Catalog Number Product Image SIAMAT Blue Colloidal Silica 16 oz

(475 ml) SI-100B-16 SIAMAT Blue Colloidal Silica 32 oz

(950 ml) SI-100B-32 SIAMAT Blue Colloidal Silica 1/2 gallon

(1.9 l) SI-100B-64 SIAMAT Blue Colloidal Silica 1 gallon

(3.8 l) SI-100BA-128 SIAMAT Blue Colloidal Silica 5 gallons

(19 l) SI-100B-640

Chemical Mechanical Polishing Suspensions

Chemcial Mechanical CMP Polycystalline Alumina / Colloidal Silica Suspension

Description Quantity Catalog Number Product Image Chemical Mechanical Alumina-Silica Slurry (pH 10) 16 oz

(475 ml) CMP-1005-16 Chemcial Mechanicl Alumina-Silica Slurry (pH 10) 32 oz

(0.95 l) CMP-1005-32 Chemical Mechanical Alumina-Silica Slurry (pH 10) 1/2 gallon

(1.9 l) CMP-1005-64 Chemical Mechanical Alumina-Silica Slurry (pH 10) 1 gallon

(3.8 l) CMP-1005-128







CMP2 High Viscosity Chemical Mechanical Polishing Suspension



Description Quantity Catalog Number Product Image High Viscosity CMP Suspension 16 oz

(475 ml) CMP2-1005-16 High Viscosity CMP Suspension 32 oz

(0.95 l) CMP2-1005-32 High Viscosity CMP Suspension 1/2 gallon

(1.9 l) CMP2-1005-64 High Viscosity CMP Suspension 1 gallon

(3.8 l) CMP2-1005-128

PACE TECHNOLOGIES CONTACT

PACE Technologies

3601 E. 34th St.

Tucson, Arizona 85713

+1-520-882-6598

FAX +1-520-882-6599

email: pace@metallographic.com

https://www.metallographic.com

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