A test report (Certificate of Analysis) is the main document confirming diamond micron powder quality. But for a non-specialist, it looks like a set of confusing numbers and abbreviations. This article breaks down each parameter: what it means, how it's measured, and what values are considered good.
Section 1: Particle Size Distribution
This is the most important section. It shows the actual grain size distribution, not just the nominal W10 marking.
| Parameter | Meaning | Good value (W10) |
|---|---|---|
| D10 | 10% of grains smaller than this size | 4–6 μm |
| D50 | Median size (50% smaller, 50% larger) | 8–10 μm |
| D90 | 90% of grains smaller than this size | 12–16 μm |
| D90/D10 | Distribution narrowness indicator | ≤2.5 (PCD-grade ≤2.0) |
What to watch: if D90 significantly exceeds nominal (e.g., for W10 D90=25 μm), the powder has many coarse grains that can scratch surfaces during polishing. If D90/D10 >3, distribution is too wide for PCD.
Section 2: Chemical Composition (Impurities)
| Parameter | Method | PCD-grade | Industrial |
|---|---|---|---|
| Fe (ppm) | Atomic absorption spectrometry | ≤40 | 100–500 |
| Ni (ppm) | Atomic absorption spectrometry | ≤15 | 50–300 |
| Co (ppm) | Atomic absorption spectrometry | ≤10 | 30–200 |
| Total Fe+Ni+Co | — | ≤65 | 500–2000 |
| Magnetic impurities (%) | Magnetic separation + weighing | ≤0.1 | 0.5–2.0 |
Section 3: Morphology (Grain Shape)
Usually presented as SEM photos at 1000–5000× magnification and qualitative assessment. The report specifies shape class (AAA/AA/A/B) and spherical grain ratio. PCD requires AA or AAA class with spherical ratio ≥70%. If the report only has photos without quantitative assessment, ask the manufacturer to specify the spherical grain ratio.
Section 4: Thermal Stability
Presented as thermogravimetric analysis (TGA) data: oxidation onset temperature and mass loss at 850°C for 1 hour in air. PCD-grade: oxidation onset ≥750°C, mass loss at 850°C ≤1%. If the report does not contain TGA data, it means thermal stability was not tested — unacceptable for PCD.
Section 5: Physical Properties
- Bulk density (g/cm³): usually 1.2–2.0 depending on fraction. Affects packaging volume calculation.
- Moisture (%): ≤0.3%. High moisture indicates poor drying after acid treatment.
- Water extract pH: 6.5–7.5 (neutral). Acidic reaction (pH<5) means residual acid after washing.
Checklist: What to Verify in the Report
- Report issued by third-party center (CNAS/CMA accredited), not by manufacturer
- Batch number and test date specified — report tied to specific batch
- All key parameters measured, not marked "N/A"
- Values match declared grade (PCD vs industrial)
- Center signature and stamp, report number for verification
Rule: don't take it on faith — require a report. And don't trust a report without a batch number: it may have been issued on a 2-year-old sample and not reflect current batch quality.
Frequently Asked Questions
Which parameters are mandatory in a test report?
A standard diamond micron powder test report must contain: particle size distribution (D10, D50, D90, D99 max), magnetic inclusion content (%), Fe+Ni+Co impurity content (ppm), bulk density (g/cm³), grain shape (sphericity grade), batch number and test date. Absence of any of these parameters makes the report incomplete.
What is D99 max and why is it important?
D99 max is the maximum size of 99% of grains (i.e., only 1% of grains are larger). For polishing, D99 max is critical: even 1% oversized grains can cause scratches on optical surfaces. Good PCD-grade micron powder has D99 max ≤ 1.5 × D50. If a report only specifies D50 without D90/D99 — it is insufficient for quality assessment.
How to verify report authenticity?
An official Chinese state lab report has: unique report number, testing center seal, responsible person signature, issue date, accreditation indication (CMA/CNAS). You can verify authenticity by contacting the center directly with the report number. Reports issued by manufacturers independently (without state lab involvement) have less legal validity.
Related Articles
Practical tip
For a first purchase we recommend a trial batch from 1 kg: test the fraction on your equipment before a bulk order. Every trial batch comes with a report (particle size, Fe+Ni+Co). Standard W5/W10/W20 fractions are always in stock — ships within 48 hours.
What a "Good" vs "Suspicious" Distribution Looks Like
On the distribution curve, a good product shows a narrow, symmetric peak near D50 and a very short right tail toward the coarse side. A suspicious product shows either a second hump on the coarse particles (inadequate sieving), a long shallow tail to D90 and D99, or two peaks — a sign of mixed fractions. D10/D50/D90 are just points on that curve: buying blind from a single D50 line hides the distribution shape. If the supplier sends only a numeric table without the curve, ask for the plot — it answers questions more often than the numbers themselves.
Two Reports on the Same W10 Inquiry, Compared
Compare two reports for the same W10 request. Report A: D50=8.2 μm, D90=13 μm, D90/D10=1.9, Fe+Ni+Co=48 ppm. Report B: D50=9.1 μm, D90=21 μm, D90/D10=3.1, Fe+Ni+Co=520 ppm. Both are nominally "W10", but A is a narrow PCD-grade fraction while B is a broad industrial powder with noticeable metallic contamination. A yields a predictable surface; B brings scratch and sintering-stability risk. That is why suppliers are compared on the full D10/D50/D90 set and total Fe+Ni+Co, not on the fraction name.
How an In-house COA Differs from a Third-party Report
Many manufacturers issue an in-house quality certificate from internal control. It is useful as operational information, but its data are not independently verified. For critical supply (PCD, optics, semiconductors), require an accredited laboratory report — with a unique number, a seal and a CMA/CNAS accreditation reference. On request we provide such a report per batch; an internal certificate with D10/D50/D90 accompanies every shipment automatically.
Do I need a third-party report on every batch?
For serial production, an in-house certificate with D10/D50/D90 and Fe+Ni+Co per batch is enough. An official third-party report makes sense at incoming inspection of a new line, in quality disputes, or when your end customer requires it.
Conclusion
A report is not a formality but a control tool. Learn to read D90 and D99, total Fe+Ni+Co, the presence of TGA and the batch number; demand the distribution plot and compare numbers across suppliers. Then the choice stops being a lottery. Start with a trial batch from 1 kg and its attached report, so you know in advance what our documentation looks like.
Quick Glossary of Report Abbreviations
| Abbreviation | Meaning |
|---|---|
| COA | Certificate of Analysis — quality certificate for a specific batch |
| D10 / D50 / D90 / D99 | Particle-size percentiles: the size below which 10/50/90/99% of particles fall |
| ppm | Parts per million: 1 ppm = 0.0001% — the impurity unit |
| TGA | Thermogravimetric analysis — sample mass vs temperature, the basis for thermal stability |
| SEM | Scanning electron microscope — the basis for grain morphology |
| CMA / CNAS | National accreditation systems for Chinese testing laboratories |
Keep this glossary handy on your first review: most "unclear" lines in a report are explained by these six abbreviations. If a report uses a term not listed here and its meaning matters for acceptance, simply ask the supplier for a note — a competent manufacturer answers such questions promptly.
Product inquiry
Fill in 4 fields — we reply within 1 business day. Or message us directly on VK / MAX.
Request a quote