Anthracite properties

Anthracite. Anthracite is preferred to other forms of coal (qv) in the manufacture of carbon products because of its high carbon-to-hydrogen ratio, its low volatile content, and its more ordered stmcture. It is commonly added to carbon mixes used for fabricating metallurgical carbon products to improve specific properties and reduce cost. Anthracite is used in mix compositions for producing carbon electrodes, stmctural brick, blocks for cathodes in aluminum manufacture, and in carbon blocks and brick used for blast furnace linings. 

The properties of the coals mined in the United Kingdom vary from the high carbon anthracites to the lower rank non-... 

Many other fuels such as soot, turf, corkmeal, powdered anthracite, woodmeal, carbene (polymerized acetylene), calcium hydride, and spongy aluminum have been tried. Physical and chemical properties of many LOX fuels are given by Howell et al (Ref 3) and O Neil Van Fleet (Ref 5a)... 

Reflectance. The optical properties (reflectance) are not in accord with the chemical properties for these coal samples, and the maximum reflectance of the coals indicates that they are higher in rank than would be concluded from the chemical data alone. These discrepancies are not surprising since these coals are thermally metamorphosed and may not follow the normal coalifica-tion curve (8). For the subject samples, it was decided that chemical data did not suitably indicate rank or the degree of thermal metamorphism, particularly in those instances where the samples contained so much ash that they were not suitable for routine chemical tests. The maximum reflectance in oil of these coals ranges from 2.6% to 11.5% (Table I). The lower reflectance is similar to that encountered in some semianthracites and anthracites, whereas the upper reflectance is more nearly that of graphite or long term, high tern-... 

In on effort to establish the mechanism of coal flotation and thus establish the basis for an anthracite lithotype separation, some physical and chemical parameters for anthracite lithotype differentiation were determined. The electrokinetic properties were determined by streaming potential methods. Results indicated a difference in the characteristics of the lithotypes. Other physical and chemical analyses of the lithotypes were mode to establish parameters for further differentiation. Electron-microprobe x-ray, x-ray diffraction, x-ray fluorescent, infrared, and density analyses were made. Chemical analyses included proximate, ultimate, and sulfur measurements. The classification system used was a modification of the Stopes system for classifying lithotypes for humic coals. 

From the foregoing it is evident that the lithotypes of anthracite are different. Differences in adsorption characteristics, surface structure, physical properties, and chemical composition conclusively demonstrate that the anthracite lithotypes are unalike and are distinct entities. It is also evident that to interpret research results of anthracite coals correctly, a petrographic knowledge of the coal is necessary. Anthracite cannot be regarded as a homogeneous substance. 

Generally, the decrepitation resistance of anthracites increases with decreasing volatile matter content, but in some cases differences in physical properties of the coals appear to nullify this relation. 

Semianthracile Coal. Coal having a fixed-carbon content of between 86 and 92%. It is between bituminous coal and anthracite coal in metamorphic rank, although its physical properties more closely resemble those of anthracite. 

The standard test method for proximate analysis (ASTM D-3172) covers the methods of analysis associated with the proximate analysis of coal and coke and is, in fact, a combination of the determination of each of three of the properties and calculation of a fourth. Moisture, volatile matter, and ash are all determined by subjecting the coal to prescribed temperature levels for prescribed time intervals. The losses of weight are, by stipulation, due to loss of moisture and, at the higher temperature, loss of volatile matter. The residue remaining after ignition at the final temperature is called ash. Fixed carbon is the difference of these three values summed and subtracted from 100. In low-volatile materials such as coke and anthracite coal, the fixed-carbon value equates approximately to the elemental carbon content of the sample. 

Several of the minor components of coal are of importance, because of the quantity present on occasion, but more so in some cases by virtue of the special properties they possess which are undesirable when the coal is used for certain purposes. For example, to arrive at a correct figure for the combustible carbon in coal, it is necessary to apply a correction for the quantity of carbonate associated with the sample. Combustion analyses determine only the total carbon. Again, coking coals should have low phosphorus content, and anthracites used for malting should contain only very small quantities of arsenic, so that the determination of these elements becomes necessary in certain cases. Since both are found normally in small amounts, they are not included in the general statement of the ultimate analysis but are reported separately. 

When wet coal is exposed to higher temperatures (0 to 200°C, 32 to 392°F), an increase in electrical resistivity (with a concurrent decrease of dielectric constant) is observed. This is due to moisture loss. After moisture removal, a temperature increase results in lower resistivity (and higher dielectric constant). The dependency of conductive properties on temperature is mainly exponential, as in any semiconductor. At lower temperatures, the effect of temperature on electrical properties is reversible. The onset of irreversible effects is rank dependent and starts at 200 to 400°C (392 to 752°F) for bituminous coal and at 500 to 700°C (932 to 1292°F) for anthracite. 

The agglomerating for agglutinating) tendency of coal may also be determined by the Roga test (ISO 335), and the Roga index (calculated from the abrasion properties when a mixture of a specific coal and anthracite is heated) is used as an indicator of the agglomerating tendencies of coals (Table 7.4). 

Rank property of coal that is descriptive of degree of coalification (i.e., the stage of metamorphosis of the original vegetal material in the increasing sequence peat, lignite, subbituminous, bituminous, and anthracite) (ASTM D-388). Anthracite rank of coal such that on a dry, mineral-matter-free basis, the volatile matter content of the coal is greater than 2% but equal to or less... 

Activated carbons [171-182] are amorphous materials showing highly developed adsorbent properties. These materials can be produced from approximately all carbon-rich materials, including wood, fruit stones, peat, lignite, anthracite, shells, and other raw materials. The properties of the produced adsorbent materials will depend not merely on the preparation technique but as well on the carbonaceous raw material used for their production. Actually, lignocellulosic materials account for 47% of the total raw materials used for active carbon production [178],... 

The preparation, manufacture, and reactions of SiC have been discussed in detail in Gmelin, as have the electrical, mechanical, and other properties of both crystalline and amorphous of SiC. Silicon carbide results from the pyrolysis of a wide range of materials containing both silicon and carbon but it is manufactured on a large scale by the reduction of quartz in the presence of an excess of carbon (in the form of anthracite or coke), (Scheme 60), and more recently by the pyrolysis of polysilanes or polycarbosUanes (for a review, see Reference 291). Although it has a simple empirical formula, silicon carbide exists in at least 70 different crystalline forms based on either the hexagonal wurtzite (ZnS) structme a-SiC, or the cubic diamond (zinc blende) structme /3-SiC. The structmes differ in the way that the layers of atoms are stacked, with Si being fom-coordinate in all cases. 

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