How to read a fused silica COA — what actually matters
A Certificate of Analysis is only useful if you know which numbers decide whether the batch will run. Here is what we put on every Chemsize COA, and what to look at first.
1. SiO₂ — but check the method
SiO₂ looks like the headline number, yet it varies with test method and laboratory. The same material can read 99.9% by one method and up to 99.96% by another. What matters is consistency: a COA should state the method and lab, so you can compare shipments on equal terms.
2. Fe₂O₃ — the number that affects your color and electronics
For Grade A we guarantee Fe₂O₃ <50 ppm. Iron shows up as color drift in ceramics and unstable dielectric behaviour in EMC/CCL. Because our powder is ground iron-free (alumina-ceramic media and linings), the Fe₂O₃ on the COA is the Fe₂O₃ in your batch — it is not added back during processing.
3. Amorphous content — the anti-crack factor
Thermal-shock resistance comes from the amorphous structure. Grade A targets >99% amorphous (SGS). If your application is thermal-shock critical, this number matters more than SiO₂. We grade out cristobalite-rich material by hand and can supply third-party XRD verification on request.
4. Particle size — one number is not enough
We report PSD by Malvern plus standard sieves — typically D10 / D50 / D90, not a single mesh label. Two lots with the same mesh name can behave differently in slurry viscosity or packing density; D50 plus distribution width catches that.
5. What we test on every batch
- Chemical composition — XRF / ICP (SiO₂, Fe₂O₃, Al₂O₃, TiO₂, alkalis)
- Particle size — Malvern + standard sieves
- Whiteness, pH, moisture
Every batch is sampled and tested before shipment, and the COA matches your purchase specification. Incoming inspection becomes confirmation, not discovery.