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D4350-16 – Standard Test Method Technical Guide
🔬 Scope and Significance of the Corrosivity Index
This test method, designated D4350 −16 (Reapproved 2022), is designed for obtaining the specific conductance of a water extract of plastics and fillers. The magnitude of this conductance is defined as the Corrosivity Index, which serves as an indicator of the likelihood that metal surfaces in contact with these materials can be corroded by galvanic action or direct chemical attack in a humid atmosphere.
Standard Uniqueness: As stated in the scope, there is no known ISO equivalent to this standard. It is issued under the fixed designation D4350 and is under the jurisdiction of ASTM Committee D20 on Plastics.
The values stated in SI units are regarded as standard. According to Section 4 (Significance and Use), this test method provides a means for comparing the corrosive potential of plastics and fillers and is intended for research and evaluation purposes. Users must also refer to Section 7 for specific precautionary statements regarding safety, health, and environmental practices.
⚙️ Essential Apparatus and Equipment Specifications
Section 5 of the standard details the specific apparatus required for conducting the test. Achieving the required ±2% accuracy depends heavily on the precision of these components.
| 🟦 Component | 📏 Specification / Requirement |
|---|---|
| Conductance Bridge | Wheatstone type; Range 1-250,000 Ω; Oscillator 1000±50 Hz; Accuracy ±2% |
| Conductivity Cell | Dip-type, micro; Cell constant ~1.0 cm⁻¹; Borosilicate glass |
| Electric Drill | Capable of holding a 10.54 mm drill bit; Max speed 500 r/min |
| Laboratory Mill | Wiley cutting mill or equivalent for sample preparation |
| Standard Sieves | 425 µm (No. 40) and 250 µm (No. 60) per Specification E11 |
Critical Dimensional Data: The conductivity cell is highly specific. Per Section 5.2, it must have a maximum outside tube diameter of 12.7 mm, an overall length of 177.8 mm, a chamber inside diameter of 9.5 mm, and a chamber depth of 50.8 mm.
📐 Key Test Parameters and Material Preparation
Sample preparation is critical to the test. The material is processed using the specified mill and sieves to achieve a standardized particle size distribution. The conductance of the water extract is then measured, providing the Corrosivity Index. Conditioning and reagent water must conform to the relevant ASTM standards, such as D618 and D1193.
| 📐 Parameter | 🎯 Required Value / Specification |
|---|---|
| Cell Constant | ~1.0 cm⁻¹ |
| Cell Outer Diameter | 12.7 mm (max) |
| Cell Overall Length | 177.8 mm |
| Cell Chamber ID | 9.5 mm |
| Cell Chamber Depth | 50.8 mm |
| Primary Sieve Designation | 425 µm (No. 40) |
| Secondary Sieve Designation | 250 µm (No. 60) |
| Bridge Oscillator Frequency | 1000 ± 50 cycles per second |
Regulatory Compliance: This test method was developed in accordance with internationally recognized principles on standardization established by the World Trade Organization Technical Barriers to Trade (TBT) Committee. Users must follow all regulatory limitations and safety protocols referenced in Section 1.3 and detailed in Section 7.
❓ Frequently Asked Questions
🔍 What exactly is the Corrosivity Index?
The Corrosivity Index is the specific conductance value of a water extract of plastics and fillers. It is an index of the likelihood of corrosion on metal surfaces in a humid atmosphere due to galvanic action or direct chemical attack.
💡 What type of conductivity cell is specified?
A dip-type, micro conductivity cell for solutions of medium conductance is required. It must be made of borosilicate glass and possess a cell constant of approximately 1.0 cm⁻¹, along with specific dimensional tolerances defined in Section 5.2.
⚡ What are the required specifications for the conductance bridge?
The standard requires a Wheatstone-type bridge with a range from 1 to 250,000 Ω measured resistance. It must include a 1000 ± 50 cycles per second oscillator and be capable of measuring resistance with an accuracy of ±2%.
📌 What sieve sizes are required for sample preparation?
Section 5.5 specifies the use of standard sieves in accordance with Specification E11: a 425 µm sieve (No. 40) and a 250 µm sieve (No. 60) for sizing the milled material.