Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D604-91 – Standard Test Method Technical Guide
ASTM D604 – 81 (Reapproved 1996) defines the standard specification for diatomaceous silica pigments processed for paint and coating applications. The standard classifies pigments into two distinct types based on fineness and specific physical properties, providing a comprehensive framework for manufacturers, purchasers, and quality control laboratories.
🧪 Composition and Physical Properties
The pigment must be a specially produced diatomaceous silica processed through chemical, thermal, and mechanical grading. Section 3 of the standard establishes the strict limits governing purity and physical behavior.
| 🟦 Requirement | 📏 Type A (Standard Fineness) | 📐 Type B (Extra Fine) |
|---|---|---|
| Loss on Ignition, max % | 1.0 | 1.0 |
| Matter Soluble in HCl (1+2), max % | 3.0 | 3.0 |
| Moisture and Other Volatile Matter, max % | 1.0 | 1.0 |
| Settled Volume in Petroleum Spirits (1 h), min mL | 35 | 25 |
| Coarse Particles (retained on 45 µm No. 325 sieve), % | 5.0 to 15.0 | 1.0 max |
⚠️ Color Compliance: Section 3.2 specifies that the color must not be assessed against a universal standard. Instead, it must conform to a mutually agreed-upon reference sample between the purchaser and the seller.
📂 Classification and Sampling Protocol
The standard explicitly differentiates between Type A, intended for general paint use, and Type B, an extra fine grade for specialized applications. Both types must meet the identical chemical purity thresholds but diverge significantly on physical performance criteria such as settled volume and sieve residue.
To ensure representative testing, Section 4 mandates a rigorous sampling procedure: two samples must be selected at random from separate packages per production unit. For unmarked shipments exceeding 10,000 lb (4,540 kg), the sample ratio is fixed at two per 10,000 lb. Purchasers have the option to test these samples separately or combine them into a composite sample for analysis.
💡 Practical Insight: The “settled volume” requirement is a direct indicator of the pigment’s bulking value, which is critical for achieving the desired flatting and rheological properties in paint systems. The higher minimum for Type A (35 mL) reflects its standard coarser particle structure compared to Type B.
🔬 Test Methods and Compliance
Testing against this specification must be performed using specific referenced ASTM standards to ensure procedural consistency across different laboratories.
- Coarse Particles: Determined via Test Methods D 185 (Coarse Particles in Pigments, Pastes, and Paints).
- Loss on Ignition and Moisture: Conducted in accordance with Test Methods D 1208 (Common Properties of Certain Pigments).
- General Analysis: The standard also references Test Methods D 719 for supplementary analytical procedures.
Any testing requirements not explicitly detailed by these ASTM methods must be subject to mutual agreement between the involved parties.
❓ Frequently Asked Questions
🔍 What differentiates Type A from Type B diatomaceous silica pigment?
Type A is the standard fineness grade formulated for general paint use, while Type B is an extra-fine grade for specialized applications. The primary distinctions are the coarse particle content (5.0–15.0% for Type A vs. 1.0% max for Type B on a 45 µm sieve) and the minimum settled volume (35 mL for Type A vs. 25 mL for Type B).
💡 What are the maximum allowable levels for chemical impurities?
Both types must meet identical chemical purity standards: a maximum loss on ignition of 1.0%, a maximum moisture and volatile matter content of 1.0%, and a maximum of 3.0% matter soluble in hydrochloric acid (1+2).
📌 How is sampling conducted for this pigment standard?
Section 4 requires two random samples from distinct packages for each lot, batch, or day’s pack. For large shipments without production marks, the sample ratio is two per 10,000 lb (4,540 kg). Buyers may test samples separately or combine them into a composite sample.
⚡ Which ASTM test methods are referenced for quality assurance?
The standard specifically references Test Methods D 185 for coarse particles, D 1208 for ignition loss and moisture, and D 719 for general diatomaceous silica pigment analysis.