Sławomira Pusz

On the optically biaxial character and heterogeneity of anthracites

Abstract The results of the study of optical properties of 13 anthracites from different parts of the world are presented in this paper. Measurements of reflectance values were made on non-oriented vitrinite grains for a minimum of 300 points per sample. The reconstruction of Reflectance Indicating Surfaces (RIS) were made by Kilbys method [Kilby, W.E., 1988. Recognition of vitrinite with non-uniaxial negative reflectance characteristics. Int. J. Coal Geol. 9, 267–285; Kilby, W.E., 1991. Vitrinite reflectance measurement — some technique enhancements and relationships. Int. J. Coal Geol. 19, 201–218]. It was found that the use of Kilbys method for strongly anisotropic materials like anthracites did not give unambiguous results. Some improvement in Kilbys method, consisting of the division of the cumulative cross-plot into several elemental components, is suggested. Each elemental cross-plot corresponds to a textural class of anthracite, which is characterized by the values of RIS main axes RMAX(k), RINT(k) and RMIN(k) (k=1,2,…n; n — number of classes). The global texture of anthracite is characterized as a RIS with main axes calculated as the weighted means of R MAX , R INT and R MIN for each class of this anthracite. The division of cumulative Kilbys cross-plot on elemental components makes possible the calculation of new coefficients Ht and H10 characterizing the heterogeneity of the structure and texture of anthracites. The results of our study show that all anthracites have biaxial negative textures, but their heterogeneity varies in a wide range of Ht and H10 coefficients depending upon the individual coal basin.

Textural transformation of thermally treated anthracites

Abstract The organic matter of anthracites consists of turbostratic (two-dimensional crystalline order) stacks of three to five aromatic layers called the Basic Structural Units (BSU). The arrangement of BSU forms the texture of anthracites, which corresponds to their chemical and physical properties including optical properties (reflectance values). Thermal treatment leads to the changes in the arrangement of BSU. The character of structural and textural transformation of anthracites during heating can be determined based on the changes of reflectance values of anthracites. Several anthracites of various ranks were thermally treated over the temperature range of 400 (673 K)–1000 °C (1273 K) in an inert atmosphere (N2), at atmospheric pressure. The reflectance indicating surfaces (RIS) were reconstructed and reflectance indicatrix parameters were calculated according to the Kilby method specially modified for the study of anthracites. It was found that the relative increase of reflectance values (Rmax, Rmin) was greater for the lower metamorphosed samples than for the higher ones. However, the higher rank of initial samples, the greater their final reflectance values and the anisotropy of the texture attained at 1000 °C. It indicates that the texture of the higher metamorphosed anthracites (meta-anthracites) is more flexible for rearrangement during heating, than the texture of the lower metamorphosed anthracites. Moreover, the difference in the changes of reflectance values versus temperature for the higher and for the lower rank anthracites suggests that meta-anthracites have undergone stronger natural metamorphism equivalent to about 200 °C in comparison with the other anthracites. It could be said that the character of textural transformations of individual anthracites results from the degree of their metamorphism and, in a consequence, from the texture of parent sediments.

The study of textural and structural transformations of carbonized anthracites

Abstract Specific physical and chemical properties of anthracites may be explained by the differences in chemical structure of basic structural units (BSUs) and in various spatial arrangements of BSUs, that is, the texture. The structure and the texture of anthracites correspond with their optical properties. Thermal treatment causes the changes in the structure of BSUs and rearrangement of the texture of anthracites. The character of structural and textural transformation could be determined based on the reflectance values of anthracites. Various anthracites were thermally treated to the temperature of 1800 °C. Maximum ( R max ) and minimum ( R min ) reflectance values were measured and reflectance indicatrix parameters ( R ev , R st and R am ) were calculated for initial and heated samples. It was found that R max , R min and R ev values increase together with the temperature up to 1200–1400 °C. In higher temperatures, they start to decrease, while R am parameter depending on anisotropy of the texture still increases to the final temperature of 1800 °C. That indicates gradual and soft transformation of the structure and the texture of anthracites up to the temperature 1200–1400 °C (arrangement of turbostratic structure) and some disturbances in textural order before the stage of graphitization.

Review: tailoring the properties of macroporous carbon foams

Carbon foams are non-toxic, highly porous, light materials which demonstrate a wide range of properties. That fact allows carbon foams to be applied in many areas of life, ranging from electronics industry, through machinery, car and construction industry, to environmental protection. The properties of carbon foams are closely connected with their density, and its value is especially influenced by their internal structure, i.e. mainly size and number of pores, pore wall thickness and structural order of solid matrix. That is why it is possible to design the properties of carbon foams by controlling their growth. The main control factors are selecting the suitable raw material, the process parameters (temperature and pressure) and the suitable production method. Additionally, the properties of carbon foams may be modified by doping them with carbon or mineral fillers. The second method is the enrichment of carbon matrix with heteroatoms, mainly of boron and nitrogen. This paper presents the review of the possibilities of tailoring the structure and properties of carbon foams, based on the current level of knowledge available in the literature.

Microporosity and optical properties of some activated chars

Abstract The aim of this work was to understand the structural and microtextural changes responsible for microporosity formation in saccharose-based chars activated with CO 2 at 850 °C. High-resolution transmission electron microscopy (HRTEM) and optical microscopy (reflectance measurements) allow to follow the changes in the chars organisation from nanometric to micrometric scales. Quantitative structural and microtextural data can now be extracted from the HRTEM images with an in-house image analysis procedure. Our results allow to suggest that the development of the microporosity with an increasing burn-off could be due to the development of slit-shaped pores. Such changes in pore shape and dimensions affect optical properties; a relationship was established between BET surface area and mean reflectance. By coupling these experimental data and a theoretical approach, a model of activated carbons is proposed to explain the reflectance changes during activation.

Interactions between organic matter and minerals in two bituminous coals of different rank

Abstract The association between specific mineral and organic constituents in two Asturian bituminous coals of different rank was studied. For this, raw coals were fractionated by density and the variation of a number of parameters was followed in parallel. Results of coal chemical analyses, including analyses for 22 elements, were used to establish the elemental association with coal organic matter. Petrographic analyses determined the distribution of macerals among densimetric fractions, vitrinite reflectance being at a minimum in the intermediate density fractions. Mineral species were identified by X-ray diffraction, FT-IR spectroscopy and Mossbauer spectroscopy. Comparison of trends for different parameters determined using this set of techniques allowed classification of the various minerals according to their association with organic matter. Carbonates seem to be specifically associated with the organic matter of the low-volatile bituminous coal whereas sulfides concentrate in the organic matter of the high-volatile bituminous coal. Vitrinite is the maceral exhibiting the most probable association with inorganic matter. The possibility of a merely physical association of fine-grained detrital minerals with organic matter cannot be excluded; nevertheless, one must bear in mind that even this type of interaction is important due to its effect on various coal preparation and utilization processes.