Zuzana Weishauptová

Experimental weathering of marlstone from Přednı́ Kopanina (Czech Republic)—historical building stone of Prague

Abstract Romanesque builders favoured marlstones because of their easy workability. Unfortunately, this rock rapidly deteriorates when exposed to the external atmospheric conditions. Artificial weathering experiments were conducted on marlstone from Předni Kopanina quarry near Prague (Czech Republic) in order to determine: (A) which weathering factor presents major danger to this rock type, and (B) which of the test methods provide the most reliable measure of the intensity of rock disintegration. Rock specimens prepared from fresh rock were subjected to standardized freeze–thaw cycles and salt crystallization tests, and to the accelerated weathering in climatic chamber using SO 2 and a combination of freeze–thaw and SO 2 cycles. Stone properties were evaluated by non-destructive and destructive techniques including ultrasonic velocity measurements, determination of water uptake by capillary action, mechanical testing, detailed porosimetric analysis and microscopic study.

Bound forms of methane in the porous system of coal

The total quantity of methane present in a coal bed at temperatures above the critical temperature was divided into four basic forms of bonding: the part adsorbed in micropores, the part adsorbed on the meso- and macropores surface, the part freely moving in the pore space which is not filled with water, and finally the part dissolved in the water present in the pores. The sum of the partial volumes mentioned was interpreted as the theoretical isotherm of the total amount of methane occluded in coal; for its evaluation Dubinins low-pressure isotherm extrapolated to the range of true in situ pressures and the volume and surface of meso- and macropores were used. Isotherms computed in this way were in very good agreement with experimental high-pressure isotherms measured up to 10 MPa. For the estimation of methane amount occluded in coal under real mining conditions the theoretical isotherms will be modified by the introduction of correction terms characterizing the changes of the porous system of coal due to water content and overburden pressure. It has been shown that the presence of water content has on the restriction of methane amount a greater effect than the overburden pressure.

Microstructures and physical properties of “backfill” clays: comparison of residual and sedimentary montmorillonite clays

Hydrophysical behaviour of a backfill material produced as a mixture of montmorillonite-rich clays (fine-grained fraction) and ballast material (coarse-grained fraction) is studied. Two different genetic types of clays are evaluated—bentonite, representing the residual weathering type, and sedimentary montmorillonite-rich clay. Hydrophysical properties (liquid and plastic limits, permeability and swelling pressure) were determined for mixtures of mixing ratios from 0% to 100% by weight. The microstructural study focused mainly on pore space and specific surface determination that were employed for the interpretation of the hydrophysical properties. The most favourable results were obtained for activated Ca-bentonite but sedimentary montmorillonite-rich clays yielded good quality backfilling mixtures as well. The transition from fine to coarse-fraction dominated behaviour was established for mixtures containing about 20% of clayey admixture.

The microporous phase of carbonaceous substances and its fractal dimension

The microporous phase of carbonaceous materials is characterized by means of fractal dimension D, determined on the principle of the coverage of microporous body of ideal shape with a monolayer of molecules of various sizes. A part of molecules remains lying on the external surface of the solid phase characterizing it with the dimension D=2 and another part enters into the micropores (with dimension D=3) respecting their size distribution. The combination of both dimensions gives the resulting value of fractal dimension within interval 2<D<3. The fractal dimension of bituminous coal, cokes and carbonization products prepared at different temperatures of heat treatment were determined. The characteristic parameters of the microporous structure necessary for D evaluation were obtained from carbon dioxide isotherm, for active carbon they were calculated from the isotherms of CO2 and some hydrocarbons.

Relationship between properties and conversions of North Bohemian coals during coal/oil coprocessing

Abstract Eleven low rank coals from North Bohemian mines were comprehensively characterized by using a number of analytical methods. Along with common proximate and ultimate analysis, spectroscopic techniques, porosity measurement, extractability and swelling in organic solvents were used. Although coals were of similar geological origin, some of their characteristics largely differed from one coal to another. Coals were coprocessed with petroleum vacuum residue at 440°C for 1 h and yields of reaction products and coal conversions were determined. Despite the differences in composition and properties, the coals provided similar conversions and yields of distillable reaction products. A small positive effect on coal conversion was found for ash content and microporosity of coals. However, a small negative effect was found for carbon content, optical reflectance and solvent extractability of coals.

Determination of resistivity of solids in powdered form

Abstract Changes in the electrical resistance of some powdered substances during compaction have been studied. Two limiting states were introduced for the description of the powder-column resistance: in the first state it equals the resistivity of the solid phase; in the second its resistance equals zero. Contacts between particles forming the conducting cross-section were expressed as a function of the powder column height. Two mechanisms for the change of the column height were proposed: (a) shifting of particles; (b) particle deformation. The dependence of the resistance on the height of the powder column and on its conducting cross-section was mathematically described. The validity of the equations was experimentally verified using carbonaceous substances with different conductivities. Special enamel was used as an insulating liner, which enabled measurements to be made at pressures of up to 1500 MPa.

Relation between texture and rheological properties of mesophase pitch

Abstract The type and extent of plastic deformation of mesophase pitch (MPP) prepared from coal tar pitch free of quinoline-insoluble matter (QI) at temperatures

Composition and properties of North Bohemian coals

Abstract This work presents the mean chemical, micropetrographic, surface and other characteristics of coal seams from western, central, and eastern parts of the North Bohemian brown coal basin. Attention was especially paid to the elemental composition, ash content, content and forms of sulphur, occurrence of syngenetic and epigenetic sulphides, maceral composition, and degree of gelification and decomposition of components in the huminite maceral group. Some other coal characteristics were also assessed, such as pore texture, extractability and solvent swelling of the coals. The coals examined were huminitic with a variable xylite and detrite content. Huminite reflectance varied between 0.33 and 0.39%. Substantial differences in pore texture of the coals were found in the range of meso- and macropores. These differences largely affected the extractability of the North Bohemian coals. The coals also exhibited extremely high swelling ratios in basic solvents, such as pyridine.

HYDROGEN CHARGING OF FUEL CLADDING METHODOLOGY

Hydrogen content is a very important parameter for mechanical properties of fuel cladding, especially after LOCA transients. Therefore, it is necessary to take into account the amount of hydrogen absorbed in the fuel cladding during normal operation (before a hypothetical LOCA). The required value of hydrogen content is possible to reach by a long-term pre-oxidation test or a much shorter hydrogen charging experiment. The methodology of hydrogen charging developed in UJP is described in this contribution. Results of experiments aiming to prepare samples with uniform hydrides and samples with a rim-layer and other hydrides are shown.

Influence of chemical changes of the isotropic matrix on physical properties of mesophase pitch

Abstract The temperature dependence of average molecular mass and carbon content of the isotropic matrix prepared by heat treatment of coal tar pitch exhibits distinct local minima at 400°C. This temperature agrees approximately with the position of local extremes on viscosity curves, designated as maximum/minimum. The anomalies were attributed to accelerated mesophase formation affecting the chemical and rheological properties of the isotropic matrix. For this study samples of mesophase pitch were prepared at 250, 300, 350, 400 and 450°C. After removal of anisotropic QI substances by extraction with quinoline the portions of isotropic matrix were further separated by solvent fractionation into groups of maltenes, asphaltenes plus preasphaltenes (APA) and carboids (CA). The soluble samples of APA and CA have been obtained by means of non-reductive alkylation. Their ‘average molecule’ was characterized by elemental composition, n.m.r. spectroscopy and vapour osmometry.