Coal Macerals Research Articles

The investigation of chemical structure of coal macerals via transmitted-light FT-IR microscopy by X. Sun

A recent paper by Sun [X. Sun, Spectrochim. Acta A 62 (1–3) (2005) 557] attempts to characterize a variety of liptinite, termed “barkinite”, from Chinese Permian coals. The component identified does not appear to fundamentally differ from previously-described liptinite macerals included in the International Committee for Coal and Organic Petrology's system of maceral nomenclature. Further, chemical comparisons made with macerals from coals of different rank and age are flawed because the author did not account for changes in chemistry with rank or for the chemical changes associated with botanical changes through geologic time. The author has not satisfactorily proved his hypothesis that the component differs morphologically or chemically from known liptinite-group macerals.

Evolution of optical properties of vitrinite, sporinite and semifusinite in response to heating under inert conditions

Abstract The objective of the study was to characterize changes of reflectance, reflectance anisotropy and reflectance indicating surface (RIS) shape of vitrinite, sporinite and semifusinite subjected to thermal treatment under inert conditions. Examination was performed on vitrinite, liptinite and inertinite concentrates prepared from channel samples of steam coal ( R r = 0.70%) and coking coal ( R r = 1.25%), collected from seam 405 of the Upper Silesian Coal Basin. The concentrates were heated at temperatures of 400–1200 °C for 1 h time in an argon atmosphere. All components examined in this study: vitrinite, sporinite and semifusinite as well as matrix of vitrinite and liptinite cokes, despite of rank of their parent coal, show, in general, the most important changes of reflectance value and optical anisotropy when heated at 500 °C, 800 °C (with the exception of bireflectance value of sporinite) and 1200 °C. After heating the steam coal at 1200 °C, the vitrinite and the semifusinite reveal similar reflectances, whereas the latter a slightly stronger anisotropy. Sporinite and matrix of liptinite coke have lower reflectances but anisotropy ( R bi and R am values) similar to those observed for vitrinite and semifusinite. However, at 1000 °C sporinite and matrix of liptinite coke have the highest reflectivity of the studied components. The RIS at 1200 °C is the same for all components. The optical properties of the three macerals in the coking coal become similar after heating at 1000 °C. Coke obtained at 1200 °C did not contain distinguishable vitrinite grains. At 1200 °C semifusinite and vitrinite coke matrix have highest R r values among the examined components. Maximum reflectance ( R max ) reach similar values for vitrinite and sporinite, slightly lower for semifusinite. Matrix of liptinite coke and matrix of vitrinite coke have considerably stronger anisotropy ( R bi and R am values) than other components. RIS at 1200 °C is also similar for all components.

Occurrence of non-mineral inorganic elements in low-rank coal macerals as shown by electron microprobe element mapping techniques

Significant proportions of inorganic elements (up to 1.5% Ca, up to 0.5% Al and up to 0.7% Fe) are consistently found in electron microprobe studies of such otherwise ‘clean’ coal macerals, especially vitrinite macerals, without any visible minerals or mineral inclusions in the macerals concerned. Detailed mapping of the concentration of these elements in visibly ‘clean’ macerals of several low-rank coals reveals that a majority of inorganic elements (Al, Ca and Fe) occur as non-mineral entities rather than discrete mineral particles, and are intimately distributed throughout the macerals; the distribution of the these elements is very similar to that of organic S, particularly in the collotelinite and fusinite of the same coal samples. The baseline concentrations seen in the inorganic element maps (Al, Ca, Fe and S) normally agree with the averaged concentrations derived from more general microprobe analysis of the same macerals in the coals, indicating that the elemental mapping technique provides a consistent basis and a powerful tool for evaluating the modes of inorganic element occurrence in coal macerals. The overall consistency in the baseline levels, instead of spike-like peaks expected from micron-sized mineral inclusions, suggests that these elements occur as an inherent part of the organic structure in the macerals concerned, possibly as a combination of exchangeable ions, carboxylates, chelates and other organometallic compounds; they may also be held by physical absorption and adsorption mechanisms. Better understanding the mode of occurrence of these non-mineral inorganic elements may provide important insights into a number of coal utilisation processes, such as catalyst reactions, slagging and fouling, and emission generation associated with combustion and carbonisation operations.

Application of attenuated total reflectance micro-Fourier transform infrared (ATR-FTIR) spectroscopy to the study of coal macerals: Examples from the Bowen Basin, Australia

Attenuated total reflectance micro-Fourier transform infrared (ATR-FTIR) spectrometry has been successfully used to characterise coal macerals, in particular telocollinite, and to investigate changes in the aromatic and aliphatic functional groups in the telocollinite, over a wide rank range (Rvmax from 0.39 to 3.52%) in coals from the Bowen Basin, Queensland, Australia. The results show that ATR-FTIR is very sensitive to the increasing aromaticity (the fraction of carbon atoms involved in aromatic units) of the telocollinites, and thus is a very useful tool to study the evolution of aromatic and aliphatic functional groups with maturation of telocollinite, and also to differentiate and characterise the various macerals in coal samples. In comparison with other micro-FTIR techniques, ATR-FTIR has many advantages: (1) no difficult and time-consuming procedures are required to obtain “pure” maceral separations, or for preparation of thin coal slices; (2) the ATR-FTIR spectra have better signal-to-noise ratio and increased sensitivity; (3) the ATR-FTIR spectra are similar to absorption spectra, but without significant spectral distortion.

Devolatilization Characteristics of Shenmu Coal Macerals and Kinetic Analysis

The pyrolysis of Shenmu coal macerals was performed in TG151 thermobalance. The volatile matter evolved in primary and secondary devolatilization and devolatilization kinetics were studied. The volatile matter evolved during primary devolatilization is the major part of the total volatile matter, especially for vitrinite. The percentage of volatile matter evolved during primary and secondary devolatilization suggested that inertinite have higher thermal stability. Though the heating rate can affect the percentage of volatile matter evolved during primary and secondary devolatilization, the order of volatile matter in all the temperature range is the same: vitrinite > parent coal > inertinite. The kinetic analysis of devolatilization using distributed activation energy model (DAEM) shows that the activation energy existed relatively large error at the conversion of initial 10% and final 10%. And the conversion of 10% to 90% was used to describe the variation of activation energy during pyrolysis. The activation energy of vitrinite appeared a minimum of about 50% conversion, but that of inertinite always increased as pyrolysis went on, indicating the different structure and chemical composition between them. Inertinite has higher activation energy and lower pyrolysis rate than vitrinite.

Organic facies and palynofacies: Nomenclature, classification and applicability for petroleum source rock evaluation

Abstract The basic aim of the investigation presented in this paper was to determine all relevant petrographical and geochemical characteristics of organic facies and their correlation with the lithological composition, sedimentation conditions and paleoenvironments. Application of geological and geochemical methods gives new insight into problems concerning determination of the potential and efficiency of petroleum source rocks. In making the qualitative and quantitative analyses of organic matter in this study various analytical methods were used (whole rock samples, kerogen concentrates; transmitted and reflected normal and fluorescent light). The type of organic facies was used as a criterion for the identification, accumulation and transformation of the organic matter. Paleobotanical studies of organic facies and palynofacies were used to identify types of vegetation and draw conclusions concerning the sedimentary environment. Various types of organic facies and palynofacies were classified in relation to the origin of the organic matter. All sedimentary organic constituents of continental (huminite/vitrinite, inertinite, cuticle, wood fragments, tracheids, spores and pollen) and marine (mostly autochthonous-dinocysts, algae, foraminifera test linings, acritarchs and amorphous organic matter) origin have been grouped according to different classification systems. A summary of these classifications is proposed, with remarks on approximate corresponding coal macerals and selected kerogen types.

Chlorine in coal: A review

This review embraces approximately 100 publications on chlorine (Cl) in coal. Topics reviewed in this paper include: (a) historical introduction; (b) some peculiarities of Cl environmental geochemistry; (c) estimation of the Cl coal Clarke value; (d) occurrence of high-Cl coals; (e) mode of Cl occurrence in coal; (f) factors influencing the distribution of Cl in coal; and (g) origins of Cl in coal. 1. The world average Cl contents in coals (coal Clarke of Cl) for hard and brown coals are, respectively, 340 ± 40 and 120 ± 20 ppm. The average Cl content on an ash basis is 1435 ppm which is much more than the Clarke value for sedimentary rocks (150 ppm); hence, chlorine is, on average, a highly coalphile element. Just this alone shows that the authigenic sorption fraction, Clsorb, must be dominant in coals. Aside from “normal” coals with average Cl contents, there are “saline” coals, strongly enriched in Cl, up to 1 wt.% and more. Although there are different genetic concepts, it seems that such coals were mainly formed in epigenesis — when coal beds were influenced by basinal chloride brines (often by hot ore-forming brines, containing also some ore elements such as As, Pb, Zn, etc.). The modes of Cl occurrence in coal are surprisingly varied. Among them are found inorganic salt-like Na and other chlorides, as well as the Cl-bearing silicates, carbonates, sulfides, as well as dissolved chlorides in pore moisture. Organic-associated Cl seems to predominate in coal. It may consist of two different types. One (minor) site (“true” Clorg) may be as covalent-bonded Cl in coal organic macromolecules. The major organic Cl is represented by “semi-organic” Cl, as anion Cl−, sorbed on the coal organic surface in pores and being surrounded by pore moisture. These are HCl-complexes bonded with bases, such as quaternary nitrogen. If Cl in coal is mainly of syngenetic origin, a “true” Clorg form may be of value, and Cl is concentrated in low-ash gelified coal macerals. If coals were submerged by epigenetic impact from basinal brines, Clmin (NaCl and other salts) and “semi-organic” Clsorb forms have to be dominant. In such instances, Cl may be enriched in fusain and in high-ash coals. There is a complicated relationship between Cl-contents in coal and coal rank. On the one hand, the coals subjected to epigenetic brine influence are, as a rule, bituminous coals that have been submerged to considerable depths where basinal brines exist. On the other hand, if coals have a rank higher than low volatile bituminous A (Cdaf more than 86%), the Cl content decreases due to decreasing sorption capacity of the high carbonized coal organic matter.

The role of sulphide and carbonate minerals in the concentration of chalcophile elements in the bituminous coal seams of a paralic series (Upper Carboniferous) in the Upper Silesian Coal Basin (USCB), Poland

Sulphide and carbonate minerals from nine bituminous coal seams of a Paralic Series were investigated by means of polished-section microscopy, scanning electron microscopy and absorption spectral analyses. In addition to syngenetic accumulations of kaolinite, illite and quartz, diagenetic veinlets of subhedral pyrite and marcasite most often occur in vitrinite clast fissures and in post-tectonic fissures, nests and lenses with fusinite. Epigenetic anhedral and subhedral grains of ankerite, dolomite, siderite and calcite are also frequently found in post-tectonic veins. Pyrite replaced some of the marcasite grains and it dominates in older coal seams in the Flora Beds as compared with the Grodziec Beds. Occasionally there are anhedral and subhedral galena, sphalerite and chalcopyrite grains among coal macerals as well as cerussite among post-tectonic carbonate veins. They all represent the only minerals that are abundant in definite chalcophile elements (Cd, Co, Cu, Ni, Pb, Zn). In addition to the minerals just mentioned, the elements occurred in pyrite and ankerite grains, which contained inclusions of fusinite and other minerals (among others, clay and carbonate minerals in pyrite, pyrite in carbonates). Although there is a low content of minerals accumulating Cd, Co, Cu, Ni, Pb and Zn, the minerals significantly influence the average concentration of elements in the coal seams. In the Grodziec Beds, mineral matter, especially carbonates and sulphides, determines (>50%) the concentration of Cd, Cu, Pb and Zn in coal. The basic part of Cd, Co and Ni in the coal seams of the Grodziec Beds and of Co, Cu, Ni, Pb and Zn in coal seams of the Flora Beds originates from organic matter. These regularities can be important, from an ecological perspective, in stating whether the coals investigated are useful for combustion and in chemical processing.

05/01944 Formation of HCN and NH 3 during coal macerals pyrolysis and gasification with CO 2

05/01944 Formation of HCN and NH 3 during coal macerals pyrolysis and gasification with CO 2

Measuring surface properties and oxidation of coal macerals using the atomic force microscope

Early microscopic examination of coals and coal macerals began with the use of transmitted and then reflected light microscopy. These methods were limited by the resolution and optical quality of the microscopes used. Improved microscope technology and the development of oil immersion techniques led to advancements in coal petrology. Introduction of the atomic force microscope (AFM) has led to higher resolution (angstrom and nanometer scale) imaging of various inorganic and organic surfaces with ability to quantitatively measure surface features and forces, but the use of AFM for measuring coal surfaces has been limited by a lack of a method to identify the macerals being analyzed. This paper describes a method using AFM to identify individual macerals and precisely measure their surface properties through the use of various AFM modes and analyses. This method has the potential to yield useful information about the physical properties of coal macerals (e.g. topography, roughness, hardness, and elastic modulus), and also about the effects of natural oxidation on coal macerals and the intentional oxidation of individual macerals to enhance either optical properties or surface porosity.

Partitioning of minerals and elements during preparation of Taixi coal, China

Mineralogy, sulfur and 40 other element contents were determined on eight samples of the Taixi coal and its preparation products from the Rujigou mining district, China. INAA, ICP-AES, CV-AAS, GAAS, XRD, SEM/EDX, conventional chemical and maceral analysis were carried out on the samples. This study is focused on the partitioning behavior of the minerals and elements during the coal cleaning, and the main factors influencing the partitioning behavior of elements were also discussed. The clay minerals (kaolinite, illite, montmorillonite and chlorite), quartz and, to a lesser extent, carbonate minerals (calcite, dolomite and siderite) dominate the mineralogy of Taixi coal. There is also minor amounts of pyrite and trace amounts of gypsum and feldspar. The quartz is dominantly epigenetic in origin, and clay minerals were modified by the thermal metamorphism. They are easily liberated from the coal by cleaning. However, although the majority of carbonate minerals are also mainly epigenetic in origin, its degree of removal is relatively low, especially with respect to dolomite and siderite, which are often finely dispersed in coal macerals, so that they are mostly retained in cleaned coal. Most of the elements studied could be removed effectively during the cleaning processes, especially for the elements predominantly hosted in coarse, epigenetic minerals. Compared with other sized cleaned coals, the coarse-grained cleaned coal is cleanest and has a relatively low potential of environmental risk. The majority of the potentially hazardous elements are notably enriched in the coal waste so that the waste is not feasible to be used as fuel. The partitioning of elements during the coal cleaning processes is essentially controlled by some factors such as the modes of occurrence of elements, maceral type, grain size and textural relation of minerals, and types of cleaning technique used.

Inorganic chemistry, petrography and palaeobotany of Permian coals in the Prince Charles Mountains, East Antarctica

Sampled outcrops of Permian coal seams of the Bainmedart Coal Measures in the Lambert Graben, eastern Antarctica, have been analysed for their proximates, ultimates, ash constituents and trace elements. A similar series of samples has been analysed for their principle maceral and microlithotype components and vitrinite reflectance. The coals are sub-bituminous to high volatile bituminous in rank; maturity increases markedly in southern exposures around Radok Lake where the oldest part of the succession is exposed and some strata have been intruded by mafic dykes and ultramafic sills. The coal ash is mostly silica and aluminium oxides, indicating that the mineral ash component is mostly quartz and various clay minerals. The ratio of silica to aluminium oxides appears to increase in an upward stratigraphic direction. The coal macerals include a relatively high liptinite content (mainly sporinite) that is significantly higher than for typical Gondwana coals. Greater degrees of weathering within the floodbasin/peat mire environments associated with climatic drying towards the end of the Permian might account for both preferential sporopollenin preservation and increased silica:aluminium oxide ratios up-section. Correlation of the coal maceral components to adjacent peninsula India coals indicates the closest comparative coals of similar age and rank occur within the Godavari Basin, rather then the Mahanadi Basin, which is traditionally interpreted to have been contiguous with the Lambert Graben before Gondwanan breakup. The petrological characteristics suggest that either previous interpretations of Palaeozoic basin alignments between Antarctica and India are incorrect, or that environmental settings and post-Permian burial histories of these basins were strongly independent of their tectonic juxtaposition. A permineralized peat bed within the succession reveals that the coals predominantly comprise wood- and leaf-rich debris derived from low-diversity forest-mire communities dominated by glossopterid and noeggerathiopsid gymnosperms.

The synergistic effect between macerals of different coals during coking

The synergistic effect between macerals of different coals during coking

The investigation of chemical structure of coal macerals via transmitted-light FT-IR microspectroscopy

The Late Permian coals from South China are characterized by high content of the unique maceral “barkinite” and elemental hydrogen, typically produce high yields of tar, and exhibit significant oil-producing potential. “Barkinite” has been identified as suberinite for a long time, but now many Chinese workers have concluded that “barkinite” is not suberinite, rather it is a distinct maceral. The term “barkinite” was formally certified and named by the State Bureau of Technical Supervision of PR China in 1991, 1995, and 1999, however, it has not been recognized as a scientific term by international coal geologists and the ICCP. Transmitted-light FT-IR microspectroscopy and curve-fitting analysis were used to investigate the chemical structure of “barkinite”; at the same time, parallel studies were also carried out on vitrinite, fusinite, and sporinite. In comparison with other maceral types, the micro-FT-IR spectra of “barkinite” are characterized by very strong intensities of aliphatic CH x stretching vibrations at 3000–2800 cm −1 and deformations at 1460–1450 cm −1, less intense bands from aromatic C C ring stretching at 1610–1600 cm −1 and aromatic CH out-of-plane deformations at 900–700 cm −1. The aliphatic side-chains in the molecular structure of “barkinite” are longer and less branched. In addition, there also appear intense aliphatic ether C O C and alcohol C O stretching bands at 1100–1000 cm −1, notable aromatic CH stretching vibrations at 3050–3030 cm −1, weak OH stretching bands of water in the 3600–3200 cm −1 range, and rare acid C O group absorption at 1740–1700 cm −1. Collectively the IR spectral characteristics indicate that “barkinite” is composed of great numbers of long chain aliphatics, a fewer of aromatics and rare of oxygenate components. The chemical structure of “barkinite” show that the high tar yields and the relatively high oil-producing potential of the Late Permian coals from South China are attributable to the high “barkinite” content in the Leping coals and the great numbers of long chain aliphatic substances contained in this maceral.

Effects of Pressure on Hydrogen Transfer from Tetralin to Coal Macerals

The influence of pressure (within a range of 5−100 MPa) on the rate of hydrogen transfer from tetralin to various coal macerals has been studied. Ten maceral concentrates (five vitrinites, three in...

04/02654 Elemental and functional composition of macerals of brown coal from the Uryup field: Shulyakovskaya, L. V. et al. Khimiya Tverdogo Topliva, 2003, 3, 3–2. (In Russian)

The coal measures of the Orange Free State Coalfield occur in post-glacial Permo-Carboniferous sedimentary environments of the Karoo Basin. Pre-Karoo geology and palaeotopography are the overriding controls on sedimentation and coal distribution. The more important coal-bearing sediments occur within the Vryheid Formation of the Karoo Sequence in paralic depositional environments. Sedimentation is cyclothemic in character and foru regressive cycles are recognized. Each basinward progradation is separated from the following one by a major coal seam.The basal Dwyka coal has a moderate to extremely high inertinite content and the Bottom, Middle and Top coals have high vitrinite contents. The petrographic distinction between the coals is also evident in their microlithotype compositions, the Dwyka coal having less than 40% vitrite plus clarite, the others, more than 50% vitrite plus clarite. This major variation in petrographic type may be due to climatically controlled diversity in sedimentary environments and plant type. The Dwyka seam was deposited in cold conditions associated with glaciation in the Early Permian; the overlying coals were deposited in a more temperate climate. However, within these two major climatic subdivisions, petrographic compositions vary with depositional environment.Comparison has been made of the Orange Free State coals with Permian coals from the Cooper Basin, Australia, that have formed in a post-glacial, cratonic environment. The Cooper Basin coals were similar, petrographically, to those of the Dwyka seam, irrespective of palaeodepositional environment.

Formation of HCN and NH 3 during coal macerals pyrolysis and gasification with CO 2

Three coal macerals with high purities were separated from Pingshuo gas coal. The formation rules of HCN and NH 3 during macerals pyrolysis and gasification were investigated. Experiments were carried out in a tubular quartz reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a prespecified period of time at a peak temperature. The amount of HCN and NH 3 were quantified by ion chromatography. The influence of temperature and macerals type on the formation rules of HCN and NH 3 was discussed. Results showed that the formation of HCN was mainly due to the thermal cracking of volatile, and NH 3 formed both from the thermal cracking of volatile and the cracking of nascent char. The HCN yield increased with an increase in pyrolysis temperature. For three coal macerals (liptinite, vitrinite and inertinite), the yield of HCN depended not only on their volatile contents but also nitrogen-containing functional groups, in which more pyrrole-type nitrogens would form more amount of HCN at lower temperature. The yield of NH 3 depended on the ability of forming ‘H’ radical. Under the experiment condition in this study, inertinite could convert more nitrogen into NH 3 than vitrinite and liptinite. The yield of HCN during gasification was almost the same as that during pyrolysis, the yield of NH 3 during gasification was little higher than that during pyrolysis.

04/01719 Identification of chemical structures in barkinite, vitrinite and fusinite using pyrolysis gas spectrometry: Sun, X. et al. Dizhi Xuebao, 2003, 77, (1), 135–143. (In Chinese)

The Permian Lepingian coal is known for its high content of , which is a unique liptinite macer-al located only in the Late Permian coals, South China. In this paper, Rock-Eval pyrolysis and pyrolysis gas chromatographic analyses were used to investigate the pyrolysate composition and the chemical structure of barkinite. At the same time, paralleled studies were also carried out on vitrinite and fusinite. The results show that at low temperatures, the pyrolyzates of and vitrinite are dominated by heteroatomic compounds, followed by aliphatic compounds, lower molecular (one- and two-ring) aromatic compounds (such as benzene and naphthalene), and alkyl aromatics (toluene and xylenes). However, the pyrolysis products of fusinite are mostly composed of aliphatic compounds. With increasing temperature, the proportion of aliphatic compounds from the three macerals increases, whereas the aromatic compounds and the heteroatomic compounds from barkinite and vitrinite decrease. At high temperatures, the pyrolysis products from these macerals sre dominated by low-chain aliphatic compounds. On the basis of these results, we can deduce that the chemical structures of these macerals are mainly composed of four kinds of function groups: (1) aliphatic compounds; (2) lower molecular (one- and two-ring) aromatic compounds, and alkyl aromatics; (3) heteroatomic function groups,- (4) multi-ring aromatics. The outlayers of the chemical structures of these coal macerals are mostly composed of heteroatomic compounds, lower molecular aromatic compounds and alkyl aromatics. The nucleus of the chemical structures of these coal macerals are dominated by multi-ring aromatic compounds. Between the outlayer and the nucleus, the chemical structures of these macerals are mainly composed of aliphatic compounds. The ways of hydrocarbon generation from coal macerals are based on the values of band energy. The smaller the bond energy function groups, the earlier they break off from coal macerals. Because heteroatomic compounds, benzene, naphthalene, toluene, xylenes, and long-chain aliphatic compounds have relatively low band energy, they were broken off from coal macerals first, then the higher-bond energy short-chain aliphatic compounds, and the remaining function groups in coal macerals are the multi-ring aromatic compounds of the highest bond energy.

Precombustion Cleaning of Coal By Triboelectric Separation of Minerals

In one method of electrostatic beneficiation, pulverized coal is tribocharged by contact with electrically grounded copper. Coal maceral and mineral particles charge with positive and negative polarities, respectively. The charged particles are passed through a separator consisting of two plate electrodes, across which a high voltage is applied, and the positively charged coal particles are separated from the negatively charged mineral particles. The efficiency of separation is dependent upon coal bulk and surface composition, and fineness of grind. Analyses of total sulfur and ash content of the charge-separated particles were used to evaluate beneficiation success of the Illinois No. 6 and Pittsburgh No. 8 coals studied. Two-stage beneficiation demonstrated improved separation. Exposing coal powders to chemical vapors of SO 2 , NH 3 , or acetone prior to beneficiation did not enhance beneficiation.

Influence of microwave power on EPR spectra of coal macerals

The paper contains a numerical analysis of the electron paramagnetic resonance (EPR) spectra of coal macerals (exinite, vitrinite, inertinite) obtained from Polish medium-rank coal (85.6 wt% C). We determine the lineshapes and the parameters of the component lines, i.e., the intensities and linewidths. As a result, we find that the EPR spectra of the studied macerals are superpositions of broad Gaussian, broad Lorentzian 1 and narrow Lorentzian 3 lines for vitrinite and exinite and two narrow Lorentzian 2 and Lorentzian 3 lines for inertinite. The influence of microwave power on the component lines of the EPR spectrum is studied. A comparison of the results obtained at 223 and 293 K shows that the EPR lines at both temperatures saturate at the same microwave power. It also indicates similar changes of the linewidths with changes of microwave power at both temperatures, a slight increase with increasing microwave power.