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D2218-67 – Standard Test Method Technical Guide
The ASTM D2218-67 (Reapproved 2019) specification establishes the standard requirements for Molybdate Orange pigments used in paints and coatings. This article details the critical compliance areas including chemical composition, sampling protocols, and performance testing criteria.
📐 Specification Scope and Chemical Composition
Per the Scope (Section 1.1), this standard covers the dry pigment known as molybdate orange. Chemically defined in Section 3.1 as a product of the co-precipitation of lead chromate and lead molybdate, the specification allows for the addition of stabilizers or other insoluble lead compounds to control specific properties such as shade and durability. The standard mandates that the mass color, tint characteristics, and strength must match a mutually agreed-upon standard between the purchaser and the seller (Section 3.2). All values are stated in SI units as the primary standard.
⚠️ Safety Hazard Caveat: As specified in Section 1.3, the test method portions of this standard do not address all safety concerns. It is the responsibility of the user to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
📏 Sampling and Referenced Test Methods
Quality assurance relies heavily on a robust sampling plan. Section 4 requires two samples to be taken at random from different packages for each lot, batch, or day’s pack. For shipments where production units are not distinguished, the sampling frequency is based directly on shipment weight.
| 🟦 Lot or Shipment Size | 🧪 Minimum Samples Required |
|---|---|
| ≤ 4,540 kg (10,000 lb) | 2 samples |
| > 4,540 kg (10,000 lb) | 2 samples per 4,540 kg (10,000 lb) |
Conformance testing relies on several key ASTM standards including D126 for chemical analysis, D387 for color and strength using a mechanical muller, and D523 for specular gloss measurements.
💡 Critical Reference: When evaluating weatherability (Section 3.3), the pigment is incorporated into a vehicle system conforming to TT-R-266 and exposed per Practice D822. This accelerated testing is essential for applications demanding long-term color and gloss retention.
⚙️ Performance Testing and Measured Properties
Molybdate Orange pigments must meet strict criteria for mass color, tinting strength, and durability. When mutually agreed upon by the purchaser and seller as essential to the end use (Section 3.3), the pigment must pass rigorous weatherability tests. The following table summarizes the acceptance criteria for exposed panels.
| 🎯 Measured Property | 📊 Acceptance Criterion |
|---|---|
| Loss of Specular Gloss (D523) | ≤ 10 % of original value |
| Chalking Resistance | None permitted |
| Color Change Difference | ≤ 3 units |
The pigment must also conform to the chemical composition requirements prescribed in Table 1 of the standard, ensuring batch-to-batch consistency for industrial manufacturing.
❓ Frequently Asked Questions
🔍 What is the scope of ASTM D2218-67?
This specification covers the dry pigment known as molybdate orange, defining its chemical composition, physical properties, and the test methods required to verify conformance.
💡 What is the chemical basis for Molybdate Orange?
It is a co-precipitated product of lead chromate and lead molybdate. The standard allows for the addition of other insoluble compounds to control specific properties like shade and stability.
⚡ How many samples are needed for a large shipment?
For shipments exceeding 10,000 lb (4,540 kg), two samples must be taken from different packages for every 10,000 lb increment, ensuring the sample is statistically representative of the whole.
📌 What are the main weather resistance criteria?
The exposed panel must show no chalking, a gloss loss of no more than 10 % of the original value, and a color change difference of not more than three units when tested per Practice D822.