Frequently Asked Questions — Metallographic and Petrographic Sample Preparation

The following questions are answered by Beta Diamond Products' application team. For questions not covered here, or for application-specific guidance on your material or preparation system, contact us directly or request a complimentary sample.

Diamond Abrasives — Suspension and Compound

What is the difference between diamond compound and diamond suspension?

Diamond compound is a viscous, oil-based or water-based paste applied manually to a polishing cloth or lapping plate. Diamond suspension is a liquid dispersion (water-based or oil-based) dispensed directly onto a rotating polishing cloth. Suspensions are the standard choice for automated polishing systems with integral dispensers (Buehler Burst, Struers DiaDuo-2) because they provide a consistent, measured abrasive delivery with each dispense cycle. Compounds are preferred for manual polishing operations, for lapping on precision flat lapping plates, and when extended working time is required without re-application. Both formats deliver equivalent surface finish quality at equivalent micron sizes when paired with an appropriate polishing cloth and lubricant.

 

Is monocrystalline or polycrystalline diamond suspension better for my application?

Monocrystalline diamond suspension contains intact diamond crystals with defined facets, producing a high, consistent material removal rate. It is the correct choice for hard, brittle materials: cemented carbides (WC-Co), alumina and zirconia ceramics, hardened tool steels above HRC 60, and silicon carbide-reinforced composites. Polycrystalline diamond suspension contains multi-faceted particles that self-sharpen during polishing by progressive fracture, exposing fresh cutting edges and producing a finer scratch pattern at equivalent micron sizes. Polycrystalline is preferred for all intermediate and final polishing of metals and alloys (titanium, stainless steel, nickel superalloys, aluminum), and is mandatory for applications requiring a deformation-minimized surface — specifically EBSD/EBSP, TEM cross-section preparation, and orientation imaging microscopy.

 

What micron diamond suspension should I use for final polishing?

The standard final diamond polishing step for most metallographic applications is 1 micron (1μm) polycrystalline diamond suspension. Where the highest possible surface quality is needed before microscopy — particularly for optical metallography at high magnification, SEM backscattered electron imaging, or hardness testing of fine microstructures — a 0.25 micron (0.25μm) final diamond step is recommended. For EBSD analysis on deformation-sensitive materials (titanium, magnesium, zirconium alloys, Al alloys, austenitic stainless steels), the diamond polishing sequence should be followed by a final oxide polishing step using 0.06 micron colloidal silica or 0.05 micron high-purity alumina on a chemomechanical polishing cloth.

 

Can I use Beta Diamond suspensions with my Buehler Ecomet, Struers LaboPol, or LECO polisher?

Yes. All Beta Diamond diamond suspensions and compounds are fully compatible with Buehler (AutoMet 250, Ecomet 30/60, Vector Power Head), Struers (LaboPol-5, LaboPol-21, Tegrapol-21/31, Tegramin-20/25/30), LECO (VP-160, VP-50), and all other major automated and manual grinder-polisher systems. The products are drop-in replacements for Buehler MetaDi Supreme, Struers DiaPro and DP-Suspension, and LECO diamond suspensions. Contact us to confirm connector compatibility if you are using an automated dispensing system.

 

Silicon Carbide Grinding Papers

What SiC grit sequence should I use for metallographic preparation?

The correct grit sequence depends on the hardness of your material and the condition of the surface after sectioning. Standard sequences: Soft metals (Al alloys, Cu alloys, soft brass): 320 → 600 → 1200 → 2400 grit. Annealed carbon and low-alloy steel: 180 → 320 → 600 → 1200 grit. Medium-hard steels (HRC 30–50): 120 → 240 → 320 → 600 → 1200 grit. Hard alloys and Ni superalloys (HRC 50+): 80 → 120 → 240 → 320 → 600 grit, then 9μm diamond grinding. Titanium alloys: 240 → 400 → 600 → 1200 grit. Ceramics and carbides: Bypass SiC papers; begin with 15μm or 9μm diamond grinding disc. Each step must completely eliminate the scratch pattern from the previous step — verify at 50–100× reflected light magnification — before advancing.

 

What is the difference between PSA and plain-back grinding paper?

PSA (pressure-sensitive adhesive) papers have a factory-applied adhesive on the back and adhere directly to the platen surface without additional accessories. They are the standard choice in high-throughput labs for speed and convenience. Plain-back papers are adhesive-free and require either a separate PSA adhesive disc, a magnetic backing system, or water-adhesion onto a glass or epoxy lapping surface. Plain-back papers are preferred when the same paper must be repositioned, when using non-standard platen materials incompatible with PSA adhesive, or when preparing for manual lapping on flat glass plates.

 

Petrographic Supplies

What is the standard size and thickness of a petrographic thin section slide?

The internationally accepted standard for a petrographic thin section slide is 27 mm × 46 mm × 1.0–1.2 mm thickness (the European/ISO standard), or 2 inches × 3 inches (50 mm × 76 mm) in the larger American format. Beta Diamond Products produces both sizes from premium Swiss glass, cut and ground to tight dimensional tolerances at our USA facility. Slide thickness is held to 1.2 mm ± 0.05 mm for compatibility with standard petrographic microscope stage clips and specimen holders.

 

What cover glass should I use for petrographic thin section analysis?

The correct cover glass for petrographic thin section analysis is No. 1.5 borosilicate glass, with a nominal thickness of 0.16–0.19 mm. No. 1.5 is the standard specification because it is the thickness for which most high-numerical-aperture petrographic objectives (40×, 63×) are corrected. Using thinner cover glass (No. 1, 0.13–0.16 mm) or thicker cover glass (No. 2, 0.19–0.23 mm) introduces spherical aberration at high magnification and compromises interference color accuracy under crossed polarizers. Beta Diamond cover glass is manufactured from colorless borosilicate glass, precision-cut and edge-ground for uniform dimensions and freedom from optical striations.

 

What is the difference between a petrographic slide and a standard laboratory microscope slide?

Petrographic slides are manufactured to significantly tighter tolerances than standard laboratory microscope slides. The critical difference is thickness uniformity: petrographic slides are ground to a flatness of less than 10 micrometers total thickness variation across the slide surface, whereas standard laboratory slides have thickness tolerances of ±100 micrometers or more. At the working magnifications of polarized light petrographic microscopy (40×–200×), any thickness variation introduces parallax errors and birefringence artifacts that can be mistaken for features of the specimen. Additionally, petrographic slides are specified for freedom from optical striations, stress birefringence, and bubbles — all of which would interfere with polarized light analysis. Beta Diamond petrographic slides are made in the USA from Swiss-sourced glass and are tested for optical homogeneity.

 

Mounting Consumables

When should I use hot (compression) mounting vs. cold cure epoxy mounting?

Hot compression mounting uses thermosetting (phenolic, diallyl phthalate) or thermoplastic resins cured at 150–180°C under 150–300 bar pressure in a mounting press. It is the preferred method for high-throughput labs processing large numbers of similar, temperature-stable specimens: most steels, cast irons, aluminum alloys, and copper alloys. Cycle time is 5–8 minutes per mount. Hot mounting is not suitable for temperature-sensitive specimens including: electronic components (PCBs, semiconductors, wire bonds), lead-based alloys, zinc alloys, specimens with pre-applied adhesive or polymer coatings, and specimens where residual stress from the mounting press would affect subsequent analysis. Cold cure epoxy mounting uses two-part epoxy or acrylic systems cured at room temperature in open molds. It is required for all temperature-sensitive specimens and is the standard approach for petrographic thin section preparation. Cure times range from 30 minutes (fast-cure acrylics) to 8–12 hours (standard epoxies). Low-viscosity cold cure epoxies can be used for vacuum impregnation of porous specimens — an essential step before preparation of powder metallurgy parts, porous ceramics, or rock specimens with open porosity.

 

Ordering & Samples

Can I get a complimentary sample before placing an order?

Yes. Beta Diamond Products offers a complimentary sample of any product in our catalog — including specific micron sizes and formulations that may not be listed as standard items on the website. To request a sample, fill out our sample request form with the product name, micron size or grit, your material and application, your preparation equipment, and your shipping address. Most sample requests are processed and shipped within 2 business days. There is no purchase obligation, and we do not follow up with unsolicited sales calls.

 

Do you supply custom micron sizes or blade dimensions?

Yes. Beta Diamond Products manufactures diamond suspensions and compounds in any particle size from 0.05 to 120 microns on request. We also manufacture diamond wafering blades in non-standard diameters, arbor hole sizes, blade thicknesses, and bond types (sintered metal, resin, nickel electroplate) to customer specification. Please contact us with your specification for a quotation — standard lead times for custom products are 2–4 weeks depending on specification.