Papers by Keyword: Specific Surface

Abstract: The continuous tightening of emission limits for the production of harmful substances into the air and the rising price of emission allowances gradually force construction material producers to limit the use of binders with a high content of Portland clinker. In the production of concrete, this is achieved by using admixtures, which make it possible to reduce Portland cement doses. However, the single European market uses a method that maximises the use of blened cements, making it easier for cement plants to meet emission limits while not reducing cement production. The performed experiment focused on the possibility of using CEM II and CEM III cements and their comparison with CEM I cement not only in terms of the physical–mechanical parameters of concrete but also in terms of the stability of concrete mixtures made from these cements. The stability of concrete mixtures was monitored using the water separation value in the pressure method. In the experiment, the relationship between water separation and physical parameters of cement was explored.

Abstract: The features of the use of waste foundry sand to obtain secondary products are presented. The properties of the surface of mineral particles of waste molding sand are described. It is shown that on the surface of the particles there is a porous layer capable of increasing the adhesion forces of mineral particles with bitumen in the production of asphalt concrete. It has been established that the modified surface of the waste foundry sand contains up to 40% carbon, which provides an increase in the adhesion force between the mineral particles of the waste foundry sand and bitumen. It has been experimentally proven that the use of waste foundry sand in the composition of asphalt concrete can improve its physical and mechanical properties.

Abstract: The paper provides a flow sheet of the phosphorus slag processing to produce precipitated silica (white soot). The process conditions for opening phosphorus slag at the I stage of leaching have been selected: the nitric acid concentration is 3.5 mol/dm³; the ratio S:L = 1:3.5; the temperature is 60 oС; and the process duration is 1 hour. The parameters of the white soot production II stage have been determined: the HNO₃ concentration is 6.5 mol/dm³; the ratio S:L = 1:3.5; the temperature is 50 oС; and the process duration is 1 hour. The temperature effect on the white soot structure and the specific surface have been established. At optimal process parameters, the white soot batches have been obtained with the main SiO₂ component content of 88.2 and 90.5 %, and a specific surface of 170 and 182 m²/g, respectively. The through recovery of silicon into a commercial product is 98.0 % of its initial content in slag.

Abstract: For the development of new compositions of modified powder mixtures a comprehensive analysis of the technical characteristics of powder additives is required. The specific surfaces of nanosized powders of "Tarkosil" silicone dioxide were determined by the experimental method. Therefore, at present, the estimating relationships of sizes, particles shapes and specific surface area of nanosized powder is relevant scientific and practical task. And the particles shape was evaluated by the values of these surfaces. Using the method of small-angle scattering the functions of distribution of the modifying powders particles on their sizes were estimated, and the average values of particles size of "Tarkosil" powder were specified The particle shape of the modifying powders has been estimated according to the specific surface values. The particle shapes of T50 powders are close to isometric (a ball, a cube); particle shapes of T150 powders correspond to a tetrahedron, the particle size T80 and T110 corresponds to the intermediate value of the specific surface area.

Abstract: The structure of martensite obtained by quenching steel under the action of a constant magnetic field was studied. The kinetic changes of the martensitic transformation, caused by the action of a magnetic field, are expressed in the structure by an increase in the dispersity of the transformation products. Samples of steels C45, 100CrMn6 and 30HGSA were investigated. Dispersity was evaluated statistically in images obtained on light and electron microscopes. The specific surface area was measured and the parameters of the surface relief caused by martensitic transformation were studied. Experimental data show that after quenching in a magnetic field, a decrease in the volumetric strain of the transformation, an increase in the dispersity of packets of martensitic crystals and components of the packets are observed. It is concluded that an increase in dispersion and a fragmentation of the structure of martensite are mainly the result of multiplicative nucleation.

Abstract: The physical and chemical properties of "loose" manganese ore of Ulu-Telyak Deposit of the Republic of Bashkortostan for the possibility of its use as an effective sorbent for purification of exhaust gases of metallurgical, chemical, oil refining, mining and other industries are studied. Analyses were carried out on the phase composition, chemical composition, determined the specific surface area of the pores and thermogravimetric method of water content. The process of sorption of a gas mixture containing hydrogen sulfide, methyl and ethyl mercaptans was also studied. The results of the experiments concluded that the prospects of using this "loose" manganese ore for the sorption of sulfur-containing gases.

Abstract: After laser ablation treatment, there are grooves on the surfaces of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3δ (BSCFO) membranes. These grooves with width about 150μm and depth about 25μm increase the specific surface of these membranes. The oxygen permeation fluxes through these membranes, which sides were treatment by laser ablation, were measured. Comparing with the membrane without laser ablation treatment, the oxygen permeation fluxes through the membranes with cross grooves pattern decorated on both sides after laser ablation treatment can increase by 34.7%.

Abstract: The objective of this study was to examine microstructural changes of cement mortar due to elevated temperature from 105 to 500°C. Changes at the meso and microscopic levels were followed by nitrogen adsorption desorption isotherms, from which the pores size distributions and specific surface areas were determined. The results show a decrease in volume of micropores and an increase in volume of mesopores which reflect clearly the shrinkage and structural transformation of the calcium silicate hydrate due to high temperature.

Abstract: The adsorption of monovalent organic cationic dye, methylene blue, on the natural and modified with hydrochloric acid and sodium hydroxide Latvian clay samples from water solutions has been studied. It was established, that alkali and acidic treatment of Latvian clay samples changes their sorption characteristics. It was found that increasing concentration of hydrochloric acid from 5 mass % until 15 mass %, decreases adsorption of clay samples proportionally to the acid concentration. Increasing concentration of sodium hydroxide from 5 mass % to 15 mass %, BET specific surface area of the modified clay samples is lower than BET specific surface area of the natural clay sample. The studies have proven that adsorption ability of Latvian clays is sufficient for using them in waste water purification from admixtures of organic dyes.

Abstract: This study investigated the effect of mechanical grinding of the residual sugar cane bagasse ash on its theoretical reactive capacity. The independent variables were: type of ball mill (rotary and centrifugal crusher), and milling time. The analyzed dependent variables were: specific surface, by Blaine equipment; and mineralogy, assessed by X-ray diffraction and infrared. The results indicate that the specific surface of the ball mill type centrifugal crusher was more efficient than the rotary, achieving an increase of 500% for an optimal grinding time of 60 min. The diffraction spectra X-ray and infrared were not altered due to the grinding process. Despite the degree of finess increase, it can be concluded that the used milling conditions were not able to modify their mineralogical characteristics. Both refinement processes were capable of enhancing the material reactivity while provided a significant increase in its specific surface. Longer milling times becomes unnecessary, because would cause little change in size distribution curve, at a high energy cost.