Papers by Keyword: Supersaturation

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Authors: Xiao Ni Zhang, Wen Long Wu, Dong Mei Li, Guang Jin Zhao
Abstract: A new rapid evaluation method of reverse osmosis (RO) scale inhibitors based on pH measurement has been reported. Five scale inhibitors, Amino Trimethylene Phosphonic Acid (ATMP), Hydrolyzed Polymaleic Anhydride (HPMA), GE-Argo, PTP-0100 and TPTO-150, each at the dose of 1 ppm was added for evaluating the performance of CaCO3 scale controlling. Brine pH was the only measured parameter at periodic time intervals. The criterion was that the pH drops, the precipitate occurs. We can compare the efficacy against CaCO3 by calculating the supersaturation value of CaCO3. The test results show that Argo is the best effective inhibitor and HPMA is the worst of all. This method with high sensitivity and accuracy is fit for screening out scale inhibitors before RO dynamic test.
Authors: Alexey O. Rodin, D. Prokoshkina, A. Itckovitch, N. Dolgopolov
Abstract: It is generally agreed that during diffusion process between two phases e.g. matrix/diffusant layer the thermodynamic equilibrium state is fulfilled and the supersaturated solid solutions can not formed by diffusion. Nevertheless, in many cases the formation of equilibrium phases does not occur due to kinetic and other reasons, and metastable phases can be formed. The analysis of the concentration profiles for bulk diffusion obtained at low temperatures consistent with B-regime for grain boundary diffusion in systems Cu/Al, Fe and Co/Cu is performed. It is shown that in these systems the supersaturated solutions are formed and the extent of supersaturation is the more as the diffusion temperature is lower. The concentration of diffusant may be 5-10-times greater than solubility according to phase diagram.
Authors: Ignacy Wierszyłłowski, Sebastian Wieczorek
Abstract: Studies of transformation kinetics during ageing of Al-4.7 % Cu were performed with use of dilatometric and DTA methods. The dilatometric method was used for studies of isothermal ageing, DTA for studies of ageing during isochronal heating. In order to determine isothermal transformation kinetics the JMA (Johnson – Mehl – Avrami) equation was applied, for isochronal heating transformation kinetics Kissinger method was used. Ageing of Al- Cu alloys consist of precipitation processes and dissolution processes that overlap each other. These processes, during isothermal ageing were distinguished with help of the time exponent n of JMA equation that is very sensitive to change of the transformation mechanism. During isochronal ageing, precipitation processes produce heat, dissolution processes consume heat. That helps to distinguish them. Results obtained during isothermal studies were in agreement with isochronal heating studies. Activation energies for precipitation processes 324-530 K temperature range varied from about 50 kJ/mol to about 100 kJ/mole and complied with the values obtained before. For precipitation processes at 650- 735 K temperature range, activation energies varied from 226 to 300 kJ/mole. The results obtained were discussed with literature data.
Authors: Paula A.A.P. Marques, M.C.F. Magalhães, Rui N. Correia, A.I. Martin, Antonio J. Salinas, Maria Vallet-Regí
Authors: Erwin Schmitt, Michael Rasp, Arnd Dietrich Weber, M. Kölbl, Robert Eckstein, L. Kadinski, M. Selder
Authors: Da Hui Chen, Li Qun Hou, Jin Jun Tang, Zheng Ren, Liang Jun Fei, Zhen Yu Kang
Abstract: In order to obtain the directional microstructure of different supersaturation and growing velocity, three simulations is calculated with different initial temperature. When the initial temperature is 1576K, and the supersaturation and growing velocity are smaller. The average space length of columnar crystals is bigger, and microsegregation is smaller. when the initial temperature is 1574K, the supersaturation and growing velocity increase. The average space length of columnar crystals decreases, and microsegregation increase; when the initial temperature falls to 1566K, the supersaturation and growing velocity reach 1.176 and 3.238 cm per second. The microsegregation decreases rapidly. The average space length of columnar crystals is the smallest. The solute curve of columnar crystal is like a “U” figure. When the growing velocity is bigger than VA, the phenomenon of solute trapping takes place.
Authors: D.D. Nolte, I. Lahiri, R. Guersen, M.R. Melloch, J.M. Woodall
Authors: Alexey Rodin, Nataliya Goreslavets
Abstract: The study of diffusion processes in the aluminum - copper system was carried out at the temperature 350 and 520 °C. Special attention was paid on the chemical composition of the system near Al/Cu interface. It was determined that the intermediate phases in the system, corresponding to the equilibrium phase diagram, were not formed at low temperature. At high temperature the intermediate phases forms starting with Cu - rich phases. In both cases supersaturated solid solution of copper in aluminum could be observed near the interface.
Authors: Matthias Arzig, Michael Salamon, Norman Uhlmann, Bertil A. Johansen, Peter J. Wellmann
Abstract: Two 3inch SiC boules were grown in a PVT setup using source material of different packing density. During the growth, in-situ computed tomography of the growing boules showed differences in the development of the growth interface. A slightly bent growth interface was found for the smaller packing density. For the higher packing density the resulting crystal exhibits the onset of 6 pyramidal facets on its flanks. Besides that, strong anisotropic lateral growth was found on its (000-1) facet. Numerical simulations show an impact of the powder on the thermal gradient in the growth cell and therefore on the supersaturation. It is discussed that a higher supersaturation can account for the anisotropy in the growth rate of the [1-100] and the [11-20] direction.
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