The parameters and how they are usually tested
| Parameter | What it tells you | Common method |
|---|---|---|
| Al₂O₃, SiO₂, Fe₂O₃, TiO₂, K₂O + Na₂O, CaO + MgO | Chemical composition; purity; colouring oxides; flux content | XRF (or ICP) |
| Loss on ignition (LOI) | Combined water and organics lost on heating; separates hydrous from calcined | Heating to a stated temperature |
| Kaolinite content, free quartz | Mineral purity | XRD |
| ISO brightness (R457) / whiteness | Colour of the powder | ISO 2470; spectrophotometer |
| Fired whiteness | Colour after firing, for ceramics | Test piece fired at an agreed temperature |
| % < 2 µm, D50 | Fineness; affects gloss, opacity, viscosity, plasticity | Sedimentation (Sedigraph) or laser diffraction |
| 325-mesh (45 µm) residue | Coarse grit | Wet sieving |
| Brookfield viscosity | Slurry flow behaviour at high solids, for coating | Brookfield viscometer at stated solids and rpm |
| Oil absorption | Filler demand for binder | ISO 787-5 |
| pH, moisture | Slurry pH; as-packed moisture | pH meter; drying to constant weight |
Results can differ between methods — for example laser diffraction and sedimentation give different particle sizes — so always agree the method with the supplier.
Typical reference values for PTMS grades
These are typical reference ranges taken from our grade pages. They are not guaranteed specifications; final values, methods and tolerances are agreed with each customer, usually after sample testing.
| Grade | Typical reference values |
|---|---|
| Ceramics | Al₂O₃ 34 – 38 %; SiO₂ 45 – 50 %; Fe₂O₃ ≤ 0.8 %; TiO₂ ≤ 0.5 %; K₂O + Na₂O ≤ 2.5 %; CaO + MgO ≤ 0.8 %; Loss on ignition (LOI) 11 – 14 %; Fired whiteness (1250–1300 °C) ≥ 85 %; Particles < 2 µm 40 – 75 %; 325 mesh (45 µm) residue ≤ 0.5 %; Moisture ≤ 2 % |
| Catalyst | Kaolinite content ≥ 85 %; Al₂O₃ 37 – 40 %; SiO₂ 44 – 48 %; Fe₂O₃ ≤ 0.8 %; TiO₂ ≤ 1.5 %; K₂O + Na₂O ≤ 0.5 %; CaO + MgO ≤ 0.5 %; Free quartz ≤ 2 %; Loss on ignition (LOI) 13 – 14.5 %; Particles < 2 µm ≥ 75 %; 325 mesh (45 µm) residue ≤ 0.1 %; Moisture ≤ 1.5 % |
| Paper | ISO brightness (R457) 85 – 92 %; Particles < 2 µm 80 – 98 %; Median particle size D50 0.3 – 1 µm; 325 mesh (45 µm) residue ≤ 0.05 %; Fe₂O₃ ≤ 1 %; TiO₂ ≤ 1 %; Brookfield viscosity (70 % solids, 100 rpm) ≤ 500 mPa·s; pH (slurry) 4.5 – 7.5 –; Moisture (dry product) ≤ 1.5 % |
| Fillers | Whiteness (dry powder) 88 – 95 %; Median particle size D50 0.8 – 5 µm; Particles < 2 µm 50 – 90 %; Oil absorption 30 – 65 g/100 g; 325 mesh (45 µm) residue ≤ 0.05 %; Fe₂O₃ ≤ 1 %; pH (10 % slurry) 4.5 – 8 –; Moisture ≤ 1 %; Loss on ignition (hydrous / calcined) ≤ 14 % |
| Fiberglass | Al₂O₃ 36 – 39 %; SiO₂ 44 – 48 %; Fe₂O₃ ≤ 0.4 %; TiO₂ ≤ 0.8 %; K₂O + Na₂O ≤ 0.5 %; CaO + MgO ≤ 0.6 %; Loss on ignition (LOI) 13 – 14.5 %; 325 mesh (45 µm) residue ≤ 5 %; Moisture ≤ 1 % |
What to write in your RFQ
- Grade or application and, if relevant, hydrous or calcined.
- Target and limits per parameter — minimum, maximum or both — rather than a single number.
- Test method for each critical parameter (brightness, particle size, residue, viscosity).
- Moisture basis: as-packed or dry basis.
- Packaging (25 kg bags, 1 t jumbo bags or bulk), quantity and destination port.
- Certificate of analysis per lot, and whether you will test arrival samples yourself.
The Spec Builder pre-fills reference values by industry and sends your RFQ by WhatsApp or email. Free samples are available on request.
Frequently asked questions
Are the values on this website guaranteed?
No. They are typical reference values. Final specifications, test methods and tolerances are agreed per customer, usually after sample testing.
Why do two suppliers quote different particle sizes for similar kaolin?
Different measuring principles — sedimentation versus laser diffraction — and different sample preparation give different results. Compare only results measured by the same method.
Which parameters matter most for an RFQ?
It depends on the industry: fired whiteness and Fe₂O₃ for ceramics; ISO brightness, % < 2 µm and viscosity for paper; D50, oil absorption and grit for fillers; Al₂O₃/SiO₂ stability and Fe₂O₃ for fiberglass; kaolinite content and alkalis for catalysts.
Related guides
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