Alumina
Aluminum oxide (alumina) polishing abrasives for metallographic and materials preparation, in ready-to-use suspension and dry powder. Supplied in graded alpha and gamma grades — including Linde A (0.3 micron), Linde B (0.05 micron), and Linde C (1 micron), plus coarser sizes for lapping — comparable to the alumina products from Buehler (MicroPolish), Struers, and Allied High Tech, typically 20 to 40 percent lower in price. Alumina is a durable, purely mechanical oxide abrasive with good edge retention, used across metallography, ceramics, optics, and semiconductor substrate preparation.
Alumina Grade Selection
Alumina comes in two crystalline phases. Alpha alumina is the harder, more angular form used for intermediate and final polishing where cut rate and edge retention matter; gamma alumina is softer and finer, used for the final deformation-reducing step. The traditional Linde designations map to these phases and sizes:
| Grade | Micron | Phase | Step |
|---|---|---|---|
| Linde C | 1.0 micron | Alpha | Coarser polishing / high removal on soft alloys |
| Linde A | 0.3 micron | Alpha | Intermediate / general polishing |
| Linde B | 0.05 micron | Gamma | Final deformation-reducing polish |
Coarser powder sizes (up to 50 micron) are available for lapping and high-removal work. The suspension is supplied in 0.05, 0.3, 1, and 3 micron.
Powder or Suspension?
Alumina suspension is pre-dispersed and ready to dispense onto the cloth (8 oz, 16 oz, 32 oz, and 1 gallon) — the convenient, consistent choice for automated systems. Alumina powder (1, 5, and 10 lb) lets you mix your own slurry to a chosen concentration and is more economical in bulk. Both are the same graded alpha and gamma alumina.
Alumina or Colloidal Silica for the Final Polish?
Alumina is purely mechanical with good edge retention. It is preferred for BCC metals (ferritic steels, molybdenum, tungsten), optical glass, ceramics, and coatings, and for high-removal final polishing of soft alloys such as lead and magnesium, where a durable oxide abrasive gives a flat, scratch-free surface for optical and SEM examination. Colloidal silica is chemo-mechanical and is preferred for a deformation-free finish for EBSD on FCC and HCP metals. Many labs keep both and choose by material.
Frequently Asked Questions
What is the difference between Linde A, B, and C alumina?
Linde C is 1.0 micron alpha alumina (a coarser polishing and high-removal step), Linde A is 0.3 micron alpha alumina (the general intermediate step), and Linde B is 0.05 micron gamma alumina (the finest, for the final deformation-reducing step). Alpha is harder for cut rate and edge retention; gamma is finer for the last step.
Should I use alumina powder or suspension?
Use the ready-to-use suspension (0.05, 0.3, 1, 3 micron) for automated polishing and consistent dispensing. Use the powder (1, 5, or 10 lb) when you want to mix your own slurry to a specific concentration or buy in bulk for a lower cost per use. Both are the same alpha and gamma alumina grades.
When do I use alumina instead of colloidal silica?
Use alumina for a mechanical final polish with good edge retention, and for BCC metals, optical glass, ceramics, and high-removal polishing of soft alloys, where colloidal silica can attack grain boundaries. Use colloidal silica for a deformation-free finish for EBSD on FCC and HCP metals such as titanium, aluminum, and austenitic stainless steels.
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