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D3718-85 – Standard Test Method Technical Guide
ASTM D3718-85a (Reapproved 2022) specifies a standard test method for determining low concentrations of chromium in paint by atomic absorption spectroscopy. This method is applicable for chromium content in the range of 0.005% to 1.0% in the solids of liquid coatings or dried films.
🔬 Test Method Scope and Summary
The test method covers the determination of chromium, including chromium oxide, in the range of 0.005% to 1.0% in paint solids. The sample is prepared by dry ashing at 500 °C, followed by digestion with potassium permanganate and sulfuric acid in a PTFE-lined acid decomposition vessel at elevated temperature. Chromium in the filtered digestion mixture is then determined by atomic absorption spectroscopy. This method is significant for regulatory compliance regarding heavy metals in coatings, providing a fully documented procedure for both water- and solvent-reducible coatings.
⚙️ Apparatus and Procedure
The required apparatus includes an atomic absorption spectrophotometer with nitrous oxide-acetylene flame, a muffle furnace maintained at 500 ± 10°C, a force-draft oven at 105 ± 2°C, an acid decomposition vessel with PTFE cup, and volumetric flasks.
| 🔧 Equipment | 📏 Specification |
|---|---|
| Muffle Furnace | 500 ± 10°C |
| Force-Draft Oven | 105 ± 2°C |
| Atomic Absorption Spectrophotometer | N₂O-acetylene flame, chromium hollow cathode lamp |
| Acid Decomposition Vessel | PTFE-lined, for elevated temperature digestion |
The procedure involves dry ashing the sample at 500°C, digesting with potassium permanganate and sulfuric acid in the PTFE vessel, and analyzing by atomic absorption spectroscopy. Dilutions may be necessary for concentrations above 1.0%.
| 📊 Parameter | 🎯 Value |
|---|---|
| Chromium Concentration Range | 0.005% to 1.0% |
| Ashing Temperature | 500 ± 10°C |
| Digestion Acid | KMnO₄ and H₂SO₄ |
| Sample Preparation | Dry ashing followed by acid digestion |
💡 For concentrations above 1.0%, appropriate dilutions and adjustments in specimen size and reagent quantities should be made as per the standard.
⚠️ Specific hazard statements are given in Section 7 of the standard. Users must establish appropriate safety, health, and environmental practices before use.
❓ Frequently Asked Questions
🔍 What is the concentration range for chromium detection in this test method?
The test method covers chromium content between 0.005% and 1.0% in the solids of liquid coatings or dried films.
💡 What is the summary of the test method?
The sample is dry ashed at 500°C, digested with potassium permanganate and sulfuric acid in a PTFE-lined vessel, and analyzed by atomic absorption spectroscopy.
⚡ What apparatus is required for this test method?
Key apparatus includes an atomic absorption spectrophotometer, muffle furnace, force-draft oven, acid decomposition vessel, and volumetric flasks.
📌 Why is this test method significant?
It provides a documented procedure for determining low chromium concentrations in coatings to ensure compliance with regulatory limits on heavy metals.