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D5061-19 – Standard Test Method Technical Guide
🔬 Scope and Terminology for Microscopical Component Analysis
ASTM D5061-19 provides a standardized test method for the microscopical determination of textural components in metallurgical coke. Specifically, it covers the equipment and procedures to determine the types and amounts of coke carbon forms and associated coal- and process-derived textural components, reported in volume percent. The method relies on reflected light microscopy to distinguish components based on their optical properties, specifically excluding structural features such as coke pores or wall dimensions.
Important Scope Limitation: This test method explicitly excludes the measurement of structural components such as coke pores, coke wall dimensions, or other structural associations. The analysis is strictly focused on the carbonaceous textural components derived from the organic portion of the coal.
| 🟦 Term | 📏 Definition / Criterion |
|---|---|
| Anisotropic | Exhibiting optical properties of different values when viewed with mutually exclusive polarized light, for example, crossed nicols. |
| Binder Phase | A continuous solid carbon matrix formed during the thermoplastic deformation of reactive and semi-inert coal macerals. Inert macerals and minerals are partly or wholly incorporated into this phase. |
| Carbon Form | Microscopically distinguishable carbonaceous textural components of coke, excluding mineral carbonates. Recognized by reflectance, anisotropy, and morphology. |
| Coke Pore | A microscopically distinguishable void created by the entrapment of gaseous volatiles during solidification. Not counted as a textural component in this method. |
⚙️ Circular Anisotropic Phases and Measurement Categories
A key classification within the standard is the “Circular Anisotropic Phase,” a group of binder-phase anisotropic carbon textures distinguished by approximately circular domains where length equals width. The standard defines specific size categories for these domains, which are essential for accurate microscopical determination under crossed nicols.
| 🎯 Category | 📐 Size Range (Domain Diameter) |
|---|---|
| Fine Circular | 0.5 µm to 1.0 µm |
| Medium Circular | 1.0 µm to 1.5 µm |
| Coarse Circular | 1.5 µm to 2.0 µm |
Technical Recognition Criteria: Recognition of carbon forms is based on their reflectance, anisotropy, and morphology. The binder phase material is formed from the thermoplastic deformation of reactive (vitrinite and liptinite) and semi-inert (semifusinite) coal macerals. Most of the coke pores are located in the binder phase, although they are classified separately from textural components.
🛠️ Referenced Standards and Methodology
The test method relies on several key ASTM and ISO standards to ensure consistency and accuracy. Sample preparation is governed by Practice D3997/D3997M (Preparing Coke Samples for Microscopical Analysis by Reflected Light). The precision and trueness of the measurement method follow the guidelines outlined in ISO 5725-6:1994 (Accuracy of Measurement Methods and Results).
All values stated in the standard are in SI units, which are regarded as the standard. The procedure utilizes an optical microscope equipped with polarized light capabilities (crossed nicols) to distinguish between isotropic and anisotropic components. For additional definitions of generalized terms (e.g., “vitrinite”), the standard directs users to refer to Terminology D121 (Coal and Coke).
❓ Frequently Asked Questions
🔍 What is the primary purpose of ASTM D5061-19?
It provides a standardized procedure for determining the types and amounts of coke carbon forms and textural components in metallurgical coke using reflected light microscopy, reported in volume percent.
💡 How does the standard define an “anisotropic” carbon form?
A carbon form is considered anisotropic if it exhibits different optical properties when viewed under mutually exclusive polarized light (crossed nicols).
⚡ What are the specific size ranges for the circular anisotropic phase?
The standard defines three categories based on domain diameter: Fine Circular (0.5 – 1.0 µm), Medium Circular (1.0 – 1.5 µm), and Coarse Circular (1.5 – 2.0 µm).
📌 Are coke pores included as textural components in this test method?
No. The test method explicitly excludes structural components like coke pores, coke wall dimensions, and other structural associations. The analysis is focused entirely on the carbonaceous textural components.