Measurement of reflectance of coal macerals: its automation and significance
A prime objective of the Pennsylvania State University's DOE program is the characterization of 1,300 samples of U.S. coals. Reflectance determination plays a major role in meeting this objective, because it is used as an accurate rank index both to select coals for testing and to investigate property-behavior interrelationships using the Penn State/DOE Coal Data Base. Reflectances of coal macerals are related to their refractive and absorptive indices by the Beer equation; the refractive index of the medium and the wavelength of light need to be specified. Determinations usually are made in immersion oil at 546 nm. Properties of vitrinite make it the most suitable maceral for these measurements, but the variety of vitrinite selected may depend upon the intended application. Vitrinite reflectance is considered to be dependent upon the degree of aromatization of its structural units. Although some of the earlier investigators believed that the reflectance of coals increased in a discontinuous, stepped manner as their rank increased, the bulk of assembled data suggests that the change is continuous. Some recent results indicate that there may be more than one coalification track for coals with different geological histories, resulting in displacement from the general trend. Several techniques have been employed to determine the optical properties of coal constituents. Usual comparative method involves the use of a microscope photometer to compare the intensity of light reflected by particles within a polished pellet of coal to that of a glass or synthetic mineral standard. Because coal is anisotropic it is common to measure either maximum reflectance in polarized light or random reflectance in non-polarized light. Various eqipment modifications and accessories have been used to improve the ease of measuring maximum reflectance.
- Research Organization:
- Pennsylvania State Univ., University Park (USA). Coal Research Section
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- EX-76-C-01-2030
- OSTI ID:
- 6074074
- Report Number(s):
- FE-2030-TR10
- Country of Publication:
- United States
- Language:
- English
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