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D1325-94 – Standard Test Method Technical Guide
🛡️ Scope and Material Overview
This specification, ASTM D1325-94 (Reapproved 2000), covers the compositional and property requirements for Ammoniacal Copper Arsenate (ACA) and Ammoniacal Copper Zinc Arsenate (ACZA) solutions. These waterborne preservatives are specifically formulated for the pressure treatment of wood, providing long-term protection against decay, fungi, and insect attack. The standard is under the jurisdiction of ASTM Committee D07 on Wood.
🧪 Chemical Composition and Active Ingredients
The standard strictly defines the nominal and minimum percentage limits for the active ingredients in the preservative concentrates. The ingredients must be dissolved in a specific aqueous ammonia solution to ensure stability and penetration.
💡 Key Ratio for ACA: The ammonia content must be strictly maintained at exactly 1.38 times the copper content (calculated as CuO). For ACZA, this same ammonia-to-copper ratio applies, but ammonium bicarbonate must also be added at a weight of at least 0.92 times the weight of the copper oxide.
Ammoniacal Copper Arsenate (ACA) Composition
| 🧪 Ingredient | ⚖️ Minimum (%) | 🎯 Nominal (%) |
|---|---|---|
| Copper (calculated as CuO) | 47.7 | 49.8 |
| Arsenic (calculated as As2O5) | 47.6 | 50.2 |
Ammoniacal Copper Zinc Arsenate (ACZA) Composition
| 🧪 Ingredient | ⚖️ Minimum (%) | 🎯 Nominal (%) |
|---|---|---|
| Copper (calculated as CuO) | 45.0 | 50.0 |
| Arsenic (calculated as As2O5) | 22.5 | 25.0 |
| Zinc (calculated as ZnO) | 22.5 | 25.0 |
📏 Purity Standards and Analytical Verification
Section 3.5 mandates that all water-soluble source compounds utilized in the formulation must exceed 95% purity on an anhydrous basis. Acceptable precursors specifically listed include bivalent copper (e.g., cupric hydroxide), pentavalent arsenic (e.g., arsenic acid), and zinc oxide.
⚠️ Additive Limit: While glacial acetic acid may be added to aid in dissolving the ingredients for ACA, its quantity must not exceed 1.7% of the total active ingredients (CuO + As2O5).
To ensure full compliance with this specification, the chemical composition of the final treating solution must be rigorously verified. The required analytical procedures are detailed in the companion standard ASTM D1326, the Test Method for Chemical Analysis of Ammoniacal Copper Zinc Arsenate.
❓ Frequently Asked Questions
🔍 What is the primary difference between ACA and ACZA?
ACZA introduces zinc oxide (ZnO) into the formulation, replacing roughly half of the arsenic content found in ACA while maintaining a similar copper loading for efficacy.
💡 Why is the specific ammonia-to-copper ratio critical?
The 1.38:1 ratio of ammonia to copper oxide is essential for achieving complete dissolution of the active ingredients and ensuring the long-term chemical stability and penetration properties of the treating solution.
⚡ What is the required purity for the raw materials?
The standard requires that all raw materials (copper, arsenic, zinc compounds) be water-soluble and have a purity exceeding 95% on an anhydrous basis to ensure consistent preservative quality.
📌 How is the final solution composition verified?
Conformance to this specification must be verified through chemical analysis conducted strictly in accordance with ASTM D1326, which defines the analytical methods for these specific solutions.