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D2318-20 – Standard Test Method Technical Guide
🔬 Scope and Method Summary
ASTM D2318-20 covers the determination of quinoline-insoluble matter (QI) in tar and pitch. This test method is strictly empirical, requiring absolute adherence to every procedural detail to ensure reliable and reproducible results. In practice, a representative sample is digested in hot quinoline at a tightly controlled temperature. The solution is then filtered through a fine-porosity porcelain crucible, and the retained insoluble residue is thoroughly washed, dried, and weighed to determine the gravimetric QI content. The standard utilizes SI units throughout.
⚠️ Strict Adherence Required: Because this is an empirical test, even minor deviations in digestion time, temperature stability, or washing technique can significantly alter the final reported QI value. Operators must follow the standard exactly.
⚙️ Apparatus and Reagent Specifications
The accuracy of this method depends on the use of tightly specified apparatus and high-purity reagents. The standard provides exact requirements for the filtering crucibles, sieves, heating equipment, and the quinoline solvent to guarantee consistency across different laboratories.
🔧 Key Equipment Requirements
| 🛠️ Component | 📐 Specification | 🎯 Required Value |
|---|---|---|
| Filtering Crucible | Material & Porosity | Porcelain, fine-porosity (max 7 µm) |
| Filtering Crucible | Capacity (High-Form) | 25 mL to 40 mL |
| Test Sieve (No. 30) | Opening (per E11) | 600 µm |
| Test Sieve (No. 60) | Opening (per E11) | 250 µm |
| Heating Bath / Hot Plate | Temperature Control | 75 °C ± 5 °C |
| Total Immersion Thermometer | Type & Range | ASTM 69C (195 °C to 305 °C) |
🧪 Reagent Purity: Refined Quinoline
The quinoline must be refined and meet strict distillation criteria as determined by Test Method D850. The distillation range from 5 % to 95 % recovered must fall within a span of 2 °C and must include the fully corrected temperature of 237.4 °C.
| ⚗️ Parameter | ⚡ Requirement |
|---|---|
| Distillation Range (5% to 95%) | Within a 2 °C range |
| Range Position | Must include 237.4 °C (corrected) |
| Reference Thermometer | Thermometer 69C (0.5 °C divisions) |
💡 Alternative Temperature Devices: The standard permits the use of precision thermocouples or resistance temperature detectors (RTDs) as alternatives to the specified Thermometer 69C, provided they demonstrate equal or better accuracy in the required temperature range.
❓ Frequently Asked Questions
🔍 What does the QI content represent in tar and pitch?
The Quinoline-Insoluble (QI) content represents the fraction of insoluble matter, primarily free carbon and refractory solids, within the sample. It is a critical quality parameter that directly influences the binding properties and baked density of carbon anodes and other manufactured products.
💡 Why are the 600 µm and 250 µm sieves specified for sample preparation?
These sieves are used to standardize the particle size of the sample before digestion. Consistent particle size distribution is essential for ensuring uniform and complete dissolution of the soluble fraction in the hot quinoline, which directly enhances the reproducibility of the test results.
⚡ Why is D2318-20 classified as an “empirical” test method?
An empirical test method means the result is inherently defined by the specific procedure used. Deviations in variables such as digestion time, filtration temperature, or washing cycles will change the measured QI value. Strict compliance is therefore mandatory for generating comparable data across different laboratories or over time.
📌 What is the maximum allowable pore diameter for the filtering crucible?
The standard specifies a high-form, fine-porosity porcelain crucible. The critical requirement is a maximum pore diameter of 7 µm, which ensures the effective retention of insoluble particles while allowing the dissolved pitch fraction to pass through efficiently during filtration.