SiO₂ and Fe₂O₃ are often the first figures reviewed in an industrial silica quotation, but they cannot be interpreted correctly without knowing the sample, test method and end use. A high or low number does not establish universal quality. Suitability means that the measured result falls within the operating requirement of a specific process.
What does SiO₂ tell you?
SiO₂ reports the proportion of silicon dioxide measured in the test sample. Higher purity is desirable in many uses, but it is not always the only decision criterion. Grading, moisture, particle shape and the identity of the impurities may be equally important. The report should also state whether the result is expressed on a dry basis or as received.
Why can Fe₂O₃ matter?
Iron oxide may influence colour or appearance in applications such as clear glass and selected ceramic products. Other processes can have a different sensitivity to iron. General terms such as “low iron” or “white” are therefore insufficient for purchasing; request a numeric result, an agreed test method and a written acceptance limit.
Do not ignore the rest of the analysis
Depending on source and application, a report may include Al₂O₃, CaO, MgO, alkalis or other constituents. Their significance is process-specific: a component that is unimportant in one use can be limiting in another. Two COAs should be compared using a consistent set of parameters and comparable test methods.
Moisture and loss on ignition are not the same as chemistry
Moisture measures water removed under defined test conditions and may affect dry-material yield and flow. Loss on ignition (LOI) is the mass reduction at a specified temperature and can include moisture plus other volatile or decomposable components. The two values should not be interchanged without reviewing the method and test temperature.
Why might two laboratories report slightly different results?
- Samples may have been collected from different parts of the shipment.
- Drying, grinding or preparation may not have been identical.
- Instrumentation, calibration and detection limits may differ.
- One result may be dry-basis and the other as-received.
- Rounding and decimal precision may differ.
Reduce disputes by agreeing the sampling and test method in the purchase specification and retaining a reference sample where appropriate.
COA review checklist
- The product and batch number match the received shipment.
- Sampling and test dates are stated.
- Units and dry/as-received basis are clear.
- The test method or laboratory reference is identifiable.
- Results are compared with contractual limits, not a general claim.
Conclusion
Chemical analysis is a decision tool, not a marketing label. State the critical impurities, acceptance limits and preferred test method in the enquiry. Then review the result for the identified batch alongside particle-size and moisture data to make a complete selection.
