Papers by Keyword: Composition

Abstract: The current paper introduces a case study dealing with the problem of pumpability of the ready-mix concrete of grade of C16/20-X0v (H)-24-F3 []. During solving a practical industrial problem we have worked out a modified composition of the related concrete material in order to improve the pumpability. After describing some possible theoretical and practical methods the authors give suggestion for a practical solution. The characteristic feature of the method consists in modifying the recipe of the given grade of concrete without altering the additive structure, and to assure the pulp saturation. The paper reports the results of standardised physical and mechanical tests, executed on the novel concrete material. Based on these results it has been proved, that besides solving the original practical problem of pumpability, the new concrete material possesses better application and technological performance, and is more economical to produce.

Abstract: Humic substances are the major components of soil, peat and brown coal. They can be fractionating into fulvic acids (FA), brown humic acids (BHA) and gray humic acids (GHA). In this work we investigated the influence of mechanochemical modifications on structural composition of HAs main fractions using the methods of IR and ¹H MRS spectroscopy. The IR spectroscopy results has shown that HA has different chemical composition in comparison with GHA and BHA. Potentiometric titration showed that mechanoactivation (MA) with thiourea increases the amount of oxygen-containing groups up to 2.5. For the first time we studied the impact of modifying agent of thiourea on the structural composition and acid-base properties of HAs major fractions - GHA and BHA during the mechanoactivation process.

Abstract: In modern society, due to the improvement of industrialized and development of marine economy, pollutants in the atmosphere and water aggravation corrosion of steel structure, annual worldwide economic losses due to corrosion is astronomical figures. Hence, atmospheric corrosion resistance of weathering steel has a broad market prospect. In addition, it also has excellent mechanics, welding and other properties. This paper mainly discusses the structure, production process, performance organization and the effect of various alloying elements on weathering steel.

Abstract: Pyrolysis mechanism of nitrogen in carbon fibers, heat-treated at various temperatures, was investigated, in relation to the nitrogen chemical bonding states. Nitrogen content shows exponential decreasing with increased temperature and extended time. The pyrolysis of nitrogen exhibited time-temperature equivalence. Nitrogen atoms containing hydrogen in the amorphous region and at the edge of microcrystalline, and the double-bonded nitrogen in pyridine rings are easily pyrolyzed, while nitrogen atoms in the six-member ring of the graphite sheets are difficult to be pyrolyzed.

Abstract: Arthroplasty is a surgery that aims to replace the defective joint surfaces, aiming to restore their functions. Is employed in this type of surgery that metallic materials play a key role in the constitution of orthopedic prostheses. In this context, we studied the chemical composition, mechanical and structural behavior of stainless steel developed for applications as biomaterials used in the manufacture of orthopedic implants. In this paper, two prostheses were analyzed established brands in the market. Proceeded through the chemical Spectroscopy Energy Dispersive X-ray (EDX) analysis. Characterized the crystal structures of these materials by diffraction of X-ray and mechanical behavior using tensile test. We compared the results of chemical composition and strength of the samples according to ASTM F-138 (2008). The results of EDX showed the presence of chloride in stainless steel alloys as an impurity that can compromise the durability of the prosthesis. The XRD patterns showed the presence in austenitic stainless steel alloys. As the tensile strength of the alloys analyzed, values that are consistent with those presented in the standards were recorded. In a general analysis, it became apparent incompatibility of assessed as biomaterials for use in prosthetic alloys, although meets the structural and mechanical requirements.

Abstract: We present a new Al-Cu-Mn system to fabricate nanoporous copper ribbons by dealloying. The microstructures of the nanoporous copper ribbons are characterized using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis. The results show that the compositions of the melt-spun Al-Cu-Mn alloys have an important effect on the dealloying process and microstructures of the nanoporous copper ribbons. The melt-spun Cu₃₀Al₄₀Mn₃₀, Cu₃₀Al₃₅Mn₃₅, Cu₃₀Al₃₀Mn₄₀ and Cu₃₀Al₂₅Mn₄₅ (at.%) alloys can completely form a bicontinuous interpenetrating ligament-channel structure. Compared with other alloys, the dealloying of Cu₃₀Al₄₀Mn₃₀ alloys is more difficult. In addition, for Cu₃₀Al₃₅Mn₃₅ and Cu₃₀Al₃₀Mn₄₀ alloys, porous structures are relatively uniform. But for the Cu₃₀Al₂₅Mn₄₅ alloys, porous structure is not uniform, occurring aggregation phenomenon.

Abstract: The growth of microarc oxidation (MAO) coatings on aluminum substrates was controlled via changing solution temperature from 10 to 60 °C. The results show that an elevation of the temperature lowers the applied voltage and the coating thickness. The coating formed in low-temperature solution demonstrates large-sized pores and contains lots of elements only originating from solute such as P, W, and V. On the contrary, numerous small-sized pores disperse homogeneously on the coating synthesized in high-temperature solution. It is assumed that the variation of solution temperature affects the dissolving capacity of the alkaline solution and the adsorptive capacity of solute anions, thus dominating the growth behaviors of MAO coating.

Abstract: The work shows the main results on the development at NRNU MEPhI of rapidly quenched amorphous and nanocrystalline ribbon-type and powder brazing filler metals based on Al, Cu, Ni, Ti and Zr and their application for brazing of a wide range of materials in nuclear, thermonuclear, aerospace, automotive, aircraft and other industries: from steels, alloys and refractory metals to various ceramics without metallization of their surfaces.

Abstract: The treated palm oil fuel ash (POFA) is used as a substitute material in producing an improved porcelain ceramics. Most of the POFA is posed as waste in landfills, causing environmental and other problems. The POFA is grounded in a ball mill until the particle size is reduced to about 50 μm. Then it is heated at a temperature of 600 oC for 1.5 h in an electric furnace. About 5 wt% to 25 wt% of POFA is used to substitute quartz in porcelain composition. The mixed powder is then pressed into pellets at pressure of 91 MPa. All the pellets are sintered at a temperature of 1000 oC, 1100 oC, 1200 oC and 1280 oC for 2.0 h soaking times. It is found that the highest compressive strength, 45 MPa is obtained at 15 wt% of POFA and sintered at 1100 oC. The improvement in the properties could be attributed to the changes in the microstructural features as a result of an increase in mullite and cristobalite simultaneously.

Abstract: One of the characteristic features of Armenian architecture is a logical, sustained process of development for thousands of years. In the past two centuries in a national architecture is a trend of active influence of the international styles, which, together with socio-economic, cultural, industrial and construction and design innovations contribute to changes in all areas of architectural and construction activities. At the same time the spectrum of traditional concepts based on regional factors are crystallized, including climate, landscape, building stone, functional and aesthetic priorities. The important role is played individual creative activity of galaxy of talented artists.