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D602-81 – Standard Test Method Technical Guide
📜 Standard Overview and Scope
ASTM D602-81 (Reapproved 2019) provides the standard specification for barium sulfate pigments, specifically the naturally occurring barytes and the chemically precipitated blanc fixe. This specification is critical for industries such as paints, coatings, plastics, and rubber where these pigments are valued for their high density, chemical inertness, and consistent opacity.
The standard defines strict limits for chemical purity, physical properties, and standardized test methods to ensure quality and uniformity. All values stated in SI units are regarded as the standard for compliance.
🧪 Chemical Composition and Physical Properties
To conform to the standard, the pigment must consist entirely of barium sulfate (BaSO₄) without admixture of other materials in the case of blanc fixe, and without any materials not naturally occurring in barite ore for barytes. The following requirements must be met:
| 📊 Property | 🎯 Barytes | 🎯 Blanc Fixe |
|---|---|---|
| Barium sulfate (BaSO₄), min % | 94 | 97 |
| Ferric oxide (Fe₂O₃), max % | 0.05 | 0.02 |
| pH, min | 3.5 | 3.5 |
| Matter soluble in water, max % | 0.2 | 0.2 |
| Moisture and other volatile matter, max % | 0.5 | 0.5 |
| Coarse particles (total residue on No. 325 / 45 µm sieve), max % | 0.5 | 0.5 |
| Free silica (quartz, clays, or other foreign materials), max % | 2.0 | 2.0 |
⚠️ Strict Composition Rules: Blanc fixe must be pure barium sulfate with no other materials added. Barytes cannot contain any synthetic extenders or materials not naturally occurring in the mined barite ore. Matching a mutually agreed-upon reference sample for physical properties is also required when specified by the purchaser.
⚙️ Sampling and Test Methods
Reliable evaluation requires standardized sampling and rigorous testing. The standard provides clear protocols for lot sampling and mandates specific ASTM methods for verifying compliance.
📐 Sampling Protocol
Two random samples must be taken from different packages for each production unit (lot, batch, or day’s pack). For larger shipments, the ratio is two samples for every 5,000 kg (10,000 lb), with a minimum of two samples for smaller shipments. At the purchaser’s option, samples may be tested individually or blended into a composite sample for analysis.
📋 Mandated Test Methods
| 🛠️ Test Parameter | 📄 ASTM Method |
|---|---|
| Coarse Particles in Pigment | D185 |
| Moisture and Other Volatile Matter | D280 |
| Analysis of Barium Sulfate, Ferric Oxide, and Free Silica | D715 |
| Hydrogen Ion Concentration (pH) and Matter Soluble in Water | D1208 |
💡 Purchaser-Seller Agreement: For any test procedures not explicitly covered by the listed ASTM methods, the standard requires that the specific testing protocol be mutually agreed upon in advance by the purchaser and the seller.
❓ Frequently Asked Questions
🔍 What classes of pigments are covered by ASTM D602?
This specification covers both natural and synthetic barium sulfate pigments: barytes (ground natural barite ore) and blanc fixe (chemically precipitated barium sulfate).
💡 What is the maximum allowable free silica content?
Both barytes and blanc fixe must have a maximum free silica content of 2.0%, including quartz, clays, or other foreign materials.
⚡ What is the sampling procedure for large shipments?
For shipments exceeding 10,000 lb (5,000 kg), the standard requires two random samples to be taken from different packages for every 5,000 kg (10,000 lb) of product.
📌 How is the pH of the pigment determined?
The hydrogen ion concentration (pH) and matter soluble in water are tested in accordance with ASTM D1208. The minimum pH for both pigment types is 3.5.