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D605-82 – Standard Test Method Technical Guide
📐 Composition and Chemical Requirements
ASTM D605-82 establishes the criteria for magnesium silicate pigment (talc) used in paint applications. The pigment must consist predominantly of natural hydrous magnesium silicate processed to paint pigment quality. The chemical composition must adhere to the following limits:
| 🟦 Component | 📏 Minimum (%) | 📐 Maximum (%) |
|---|---|---|
| Combined Magnesium and Calcium Silicates (MgO + SiO₂ + CaO) | 88 | — |
| Calcium Oxide (CaO) | — | 10 |
| Aluminum and Iron Oxides (R₂O₃) | — | 6 |
| Loss on Ignition | — | 7 |
| Moisture and Other Volatile Material | — | 1 |
These limits ensure the pigment achieves adequate purity and consistency for use in coatings, with the combined MgO, SiO₂, and CaO content representing the primary active silicate fraction.
⚙️ Testing and Specification Tolerances
Beyond chemical composition, D605-82 specifies physical properties that are evaluated against a reference sample agreed upon between purchaser and seller. Key requirements include:
| 🎯 Property | ⚡ Requirement |
|---|---|
| Color | Within agreed tolerances of reference sample |
| Coarse Particles (45-µm No. 325 sieve) | ≤ 2% retained |
| Water-Soluble Matter | ≤ 1% |
| Oil Absorption | Within agreed tolerances of reference sample |
| Consistency (when specified) | Within agreed tolerances of reference sample |
| Paint Fineness | Within agreed tolerances of reference sample |
Per Section 4, two random samples from different packages must be taken per lot or production unit for testing, ensuring representative quality assessment.
⚠️ Safety Note: The standard includes a hazard caveat for test methods. Users must establish appropriate safety, health, and environmental practices and comply with regulatory limitations prior to use.
💡 Tip: Consult referenced ASTM standards (D280, D281, D562, D717, D1208, D1210) for detailed test procedures on hygroscopic moisture, oil absorption, consistency, and fineness of dispersion.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D605-82?
This specification covers pigments composed substantially of natural hydrous magnesium silicate, processed to paint pigment quality and conforming to prescribed chemical limits. It applies to minerals that can be suitably processed for commercial paint pigment use.
💡 What are the mandatory chemical limits for talc pigment?
The combined MgO, SiO₂, and CaO must be at least 88%, with CaO capped at 10%, aluminum and iron oxides (R₂O₃) at 6%, loss on ignition at 7%, and moisture at 1%.
⚡ How is sampling conducted under this standard?
Two samples are taken at random from different packages for each lot, batch, or day’s pack in a shipment. When production units are not distinguishable, samples are taken in a 2:1 ratio per lot.
📌 What physical properties are evaluated for acceptance?
Key properties include color, coarse particles (≤2% on No. 325 sieve), water-soluble matter (≤1%), oil absorption, consistency, and paint fineness. All are compared against a reference sample with agreed tolerances.