查看更多>>摘要：The impact of low temperature pre-aging on the artificial age-hardening of AA 6061 (Al-1.1Mg-0.63Si) has been investigated using differential scanning calorimetry (DSC) as well as by measuring the electrical resistivity, and confirmed by microstructure observation using scanning electron microscopy and transmission electron microscopy (TEM). Tensile tests were performed to determine the mechanical properties of the samples. During the pre-aging treatment GP zones I formed at 0-30 deg C. These GP zones I retarded the precipitation of the intermediate beta' phase during artificial aging and led to a decrease in the strength of the alloy. During the pre-aging treatment beta" precipitates formed at 40-70 deg C. Increasing the pre-aging temperature significantly increases the strength after artificial aging. On the other hand, increasing the pre-aging temperature decreases the size of the precipitation-free zones (PFZ) adjacent to the grain boundaries. It was found that the tensile strength was greater if the PFZs were smaller than if they were larger. Grain boundary precipitates (GBP) did not significantly contribute to the hardening or strengthening. The specimens subjected to a lower pre-aging temperature followed by the same artificial aging step had better bendability than did the specimens subjected to a higher pre-aging temperature.
查看更多>>摘要：Since the 1980s, Nippon Steel has been developing multistage refining processes, mainly in the area of hot metal pre-treatment, due to increasing demand for high-purity steels. In recent years, in order to cope with the new problems that have arisen with the changing business environment, e.g. raw material conditions and environmental regulations and establishing a more efficient process with respect to productivity, resources and energy, several rearrangements have been carried out with emphasis on primary refining. The major change in the new process comprises (1) high-efficiency hot metal desulfurization and (2) desiliconization and dephosphorization using basic oxygen furnaces. Consequently, high-speed treatment, fluoride-free refining, decrease in CaO consumption and waste slag and improvement of heat balance have been accomplished. Some of the metallurgical phenomena concerning the new process are discussed and future works are suggested.
查看更多>>摘要：The aim of this study was to build a thermodynamic model to extrapolate the system NiSO_4-(NH_4)_2SO_4-NH_3-H_2O which exists in aqueous hydrogen reduction processes of nickel. These solutions are relatively concentrated, and the temperature for solution preparation and reduction stages might range from room temperature up to 180-200 deg C. Temperature has a great effect on solution equilibria and the equilibrium solubility of simple and complex crystalline salts such as sulphates and hydroxides known to exist in the system. In this work, the role of kinetics is recognized, but only equilibrium phenomena reconsidered. The main focus of the study was on the modeling of salt solubility. In cases of a process solution where the precipitation of solid crystalline salts is highly undesirable it is important to know the safe limits for a 'clear solution' to operate even if the kinetics are unfavorable. Relatively concentrated solutions are strongly non-ideal and realistic calculations on solution equilibria necessitate the modeling of excess thermodynamic properties of these solutions. The excess model selected for aqueous species was Pitzer's ion-interaction model and for the gas phase Tsonopoulos' model. Emphasis in data assessment was on the thermodynamic modeling of various binaries and ternaries to create a substantial database for the approximation of the quaternary system.
查看更多>>摘要：In this work, the techniques of physical modeling for optimization, control and improvement of metallurgical processes, such as RH degassing, continuous casting, IR-UT, etc with special reference to Brazilian steel plants such as Usiminas, CST, Belgo-Mineira etc. are discussed. Many of these have been industry-sponsored projects, involving development of physical models of laboratory scale, considering similarity principles and carrying over the results of experiments to the industrial unit, for optimizing the processes or suggesting alternative techniques for improved efficiency.
查看更多>>摘要：This paper presents calculations on the separation times for solid spherical, octahedral and plate-like micro-inclusions across interfaces between molten low carbon steel and ladle, tundish, and mold slags. The effect of inclusion shape on the interfacial capillary force that arises due to the dynamic inter-facial energy change during separation has been investigated and it is shown that this has a significant effect on whether the inclusion separates rapidly or settles at the interface. In the case of settled particles, the inclusion dissolution time was computed based on experimental data. For the slags considered, the most significant physical property was found to be the slag viscosity that resulted in fast separation and dissolution times for the mold and ladle slag when compared to the tundish slag.
查看更多>>摘要：The paper reviews work on copper deposition onto porous, fluidized and spouted bed electrodes and discusses the phenomena that are important in governing electrode behavior. An ongoing investigation into the use of ion exchange and electrodeposition to recover copper and water from semiconductor industry waste streams is described. These waste streams, and the associated fresh water consumption, appear to be a growing problem as the semiconductor industry moves to copper metallization (by electrolytic and electroless deposition). Copper metallization also implies the generation of significant waste streams from copper removal by chemical-mechanical planarization (CMP). The quantity of copper to be recovered is still small but its removal from the waste stream will facilitate disposal and, perhaps, reuse of the large volume of water entailed. Extended surface area electrodes may play a role in this task and results using porous carbon electrodes are presented. Recent results on the growth of copper particles in spouted electrodes and the deposition of copper from electrolytes containing other metal salts are presented.
查看更多>>摘要：The physicochemical properties of lanthanides, and of their derivatives, contribute essential functions to a range of modern-day materials and processes. Some fundamental thermodynamic and electrochemical features of lanthanide halide melts are presented. They are illustrated by a few selected examples of relevance for applications ranging from pyroreprocessing of spent nuclear fuel to electrochemical molten salt synthesis of materials.
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