Nucleation of gaseous hydrogen bubbles is the initial stage of GASAR process. Through the theoretical analysis, it has been identified that heterogeneous nucleation of bubbles as caps on the solid surfaces of impuriti...Nucleation of gaseous hydrogen bubbles is the initial stage of GASAR process. Through the theoretical analysis, it has been identified that heterogeneous nucleation of bubbles as caps on the solid surfaces of impurities is impossible and only the heterogeneous nucleation in pits and cracks in impurities is the most feasible way in the GASAR process. The results also show that the probability of bubble nucleation progressively decreases from Al, Cu and Ni to Fe molten metal, which is the result of the increasing adhesion work of liquid metal on alumina.展开更多
This paper presents the general mathematical model on gasar eutectic growth in directional solidification. Using multiple scale expansion and matching method, we obtain the global steady solution of gasar eutectic gro...This paper presents the general mathematical model on gasar eutectic growth in directional solidification. Using multiple scale expansion and matching method, we obtain the global steady solution of gasar eutectic growth as the Peclet number ε≤1, where ε is defined as the ratio of half an inter-pore spacing and solutal diffusion length. We also give the interfacial shape and predict the porosity of gasar eutectic growth. Results show that porosity is mainly dependent on gas pressure above the metal melt, but independent of pulling velocity. Our predicted results are in agreement with experimental data.展开更多
A single-mold Gasar technique was developed to produce lotus-type porous micro-channel copper with uniform porous structure. In this paper the effect of withdrawal rate on the solid/liquid interface morphology and the...A single-mold Gasar technique was developed to produce lotus-type porous micro-channel copper with uniform porous structure. In this paper the effect of withdrawal rate on the solid/liquid interface morphology and the corresponding porous structure was systematically investigated, especially the pore morphology, pore growth direction, porosity, and pore diameter of porous copper ingots. In addition, a temperature fi eld simulation was carried out based on Pro Cast software to investigate the shape and movement velocity of the solidifying solid/liquid interface. The experimental results show that the solidifi cation interface changes from convex to planar, then to concave shape with an increase in withdrawal rate. The average porosities of copper ingots are constant and independent of the withdrawal rate. The average pore diameter decreases with an increase in withdrawal rate.展开更多
The Lake Zowla-Aného lagoon hydro system, located on the southeast coast of Togo, is very exposed to metal contamination as it receives a huge amount of untreated domestic and industrial effluents from Aného...The Lake Zowla-Aného lagoon hydro system, located on the southeast coast of Togo, is very exposed to metal contamination as it receives a huge amount of untreated domestic and industrial effluents from Aného City and the phosphorite treatment plant at Kpémé. This study aims to assess the concentrations of seven heavy metals and their bioaccumulation status in soft tissues and shells of the mangrove oyster (<i>Crassostrea gasar</i>) collected from this aquatic environment. Samples were collected in January, April and July 2017 at two stations and analyzed using flame atomic absorption spectrophotometry. Results indicate that the waters are contaminated by Cd, Pb and Cr with average concentrations that are significantly above WHO standards. At both locations, the contents of the trace elements (except Cr) in oysters’ soft tissues were significantly higher than those in the shells. In the soft tissues, the concentration of Cr, Cu, Zn, As, Cd, Hg, and Pb ranged (in mg·kg<sup>-1</sup>) from 4.33 to 23.14, 93.4 to 366.7, 455.68 to 1384.15, 0.11 to 1.34, 16.42 to 62.6, 0.05 to 0.473 and 0.39 to 21.08, respectively. Furthermore, statistical analyses showed marked differences in mean concentrations between sampling time on the one hand, and between sampling locations on the other hand (p < 0.05). The highest metal concentrations were recorded in oysters collected in June at Zalivé whereas the lowest values were recorded in April at Zowla. Based on BCF results in the lagoon system, the oyster <i>C. gasar</i> can be used as a biomonitor of Zn, Cd, Cu and Hg exposure. Finally, the Cd, Pb, As, Zn and Cu concentrations in soft tissues and were found to be significantly higher than the permissible limit for human consumption according to WHO and FAO and thus pose a threat to human health.展开更多
文摘Nucleation of gaseous hydrogen bubbles is the initial stage of GASAR process. Through the theoretical analysis, it has been identified that heterogeneous nucleation of bubbles as caps on the solid surfaces of impurities is impossible and only the heterogeneous nucleation in pits and cracks in impurities is the most feasible way in the GASAR process. The results also show that the probability of bubble nucleation progressively decreases from Al, Cu and Ni to Fe molten metal, which is the result of the increasing adhesion work of liquid metal on alumina.
基金the National Natural Science Foundation of China(Grant Nos.51201078,51164018,and u0837603)
文摘This paper presents the general mathematical model on gasar eutectic growth in directional solidification. Using multiple scale expansion and matching method, we obtain the global steady solution of gasar eutectic growth as the Peclet number ε≤1, where ε is defined as the ratio of half an inter-pore spacing and solutal diffusion length. We also give the interfacial shape and predict the porosity of gasar eutectic growth. Results show that porosity is mainly dependent on gas pressure above the metal melt, but independent of pulling velocity. Our predicted results are in agreement with experimental data.
基金financially supported by the National Natural Science Foundation of China(No.51271096)the Program for New Century Excellent Talents in University,Ministry of Education,China(NCET-12-0310)
文摘A single-mold Gasar technique was developed to produce lotus-type porous micro-channel copper with uniform porous structure. In this paper the effect of withdrawal rate on the solid/liquid interface morphology and the corresponding porous structure was systematically investigated, especially the pore morphology, pore growth direction, porosity, and pore diameter of porous copper ingots. In addition, a temperature fi eld simulation was carried out based on Pro Cast software to investigate the shape and movement velocity of the solidifying solid/liquid interface. The experimental results show that the solidifi cation interface changes from convex to planar, then to concave shape with an increase in withdrawal rate. The average porosities of copper ingots are constant and independent of the withdrawal rate. The average pore diameter decreases with an increase in withdrawal rate.
文摘The Lake Zowla-Aného lagoon hydro system, located on the southeast coast of Togo, is very exposed to metal contamination as it receives a huge amount of untreated domestic and industrial effluents from Aného City and the phosphorite treatment plant at Kpémé. This study aims to assess the concentrations of seven heavy metals and their bioaccumulation status in soft tissues and shells of the mangrove oyster (<i>Crassostrea gasar</i>) collected from this aquatic environment. Samples were collected in January, April and July 2017 at two stations and analyzed using flame atomic absorption spectrophotometry. Results indicate that the waters are contaminated by Cd, Pb and Cr with average concentrations that are significantly above WHO standards. At both locations, the contents of the trace elements (except Cr) in oysters’ soft tissues were significantly higher than those in the shells. In the soft tissues, the concentration of Cr, Cu, Zn, As, Cd, Hg, and Pb ranged (in mg·kg<sup>-1</sup>) from 4.33 to 23.14, 93.4 to 366.7, 455.68 to 1384.15, 0.11 to 1.34, 16.42 to 62.6, 0.05 to 0.473 and 0.39 to 21.08, respectively. Furthermore, statistical analyses showed marked differences in mean concentrations between sampling time on the one hand, and between sampling locations on the other hand (p < 0.05). The highest metal concentrations were recorded in oysters collected in June at Zalivé whereas the lowest values were recorded in April at Zowla. Based on BCF results in the lagoon system, the oyster <i>C. gasar</i> can be used as a biomonitor of Zn, Cd, Cu and Hg exposure. Finally, the Cd, Pb, As, Zn and Cu concentrations in soft tissues and were found to be significantly higher than the permissible limit for human consumption according to WHO and FAO and thus pose a threat to human health.
基金This research was supported by the National Natural Science Foundation of China （No. 50404002）National Program on Key Basic Research Projects （No. 2004CCA05100）.
基金National Natural Science Foundation of China(51864026,51964030)Kunming University of Science and Technology Research Start-up Fund(KKSY201765025)Fund of Yunnan Provencal Education Department(2021J0048)。
