A comprehensive heat and mass transfer model of dissolution process of non-agglomerated and agglomerated alumina particles was established in an aluminum reduction cell. An appropriate finite difference method was use...A comprehensive heat and mass transfer model of dissolution process of non-agglomerated and agglomerated alumina particles was established in an aluminum reduction cell. An appropriate finite difference method was used to calculate the size dissolution rate, dissolution time and mass of alumina dissolved employing commercial software and custom algorithm based on the shrinking sphere assumption. The effects of some convection and thermal condition parameters on the dissolution process were studied. The calculated results show that the decrease of alumina content or the increase of alumina diffusion coefficient is beneficial for the increase of size dissolution rate and the decrease of dissolution time of non-agglomerated particles. The increase of bath superheat or alumina preheating temperature results in the increase of size dissolution rate and the decrease of dissolution time of agglomerated particles. The calculated dissolution curve of alumina（mass fraction of alumina dissolved） for a 300 k A aluminum reduction cell is in well accordance with the experimental results. The analysis shows that the dissolution process of alumina can be divided into two distinct stages： the fast dissolution stage of non-agglomerated particles and the slow dissolution stage of agglomerated particles, with the dissolution time in the order of 10 and 100 s, respectively. The agglomerated particles were identified to be the most important factor limiting the dissolution process.展开更多
The Box–Behnken design and desirability approach were used to investigate and optimize the process parameters for aluminum reduction cells related to alumina dissolution. The bath temperature, alumina content, curren...The Box–Behnken design and desirability approach were used to investigate and optimize the process parameters for aluminum reduction cells related to alumina dissolution. The bath temperature, alumina content, current and alumina temperature were chosen as the design parameters. The content of cumulative dissolved alumina(CCDA) and the relative deviation from the target content(RDTC) were adopted as the responses. The interactive influence results show that increasing the bath temperature and alumina temperature, as well as decreasing the alumina content, can increase CCDA. Increasing the bath temperature and lowering the current are beneficial for obtaining a more uniform alumina distribution. The optimal operating parameters were determined to be as follows: bath temperature of 958.8 ℃, alumina content of 2.679 wt.%, current of 300 kA and alumina temperature of 200 ℃.展开更多
A wave flume simulator was used to study internal nitrogen release from the surface sediment collected from Taihu Lake, China. Particulate nitrogen concentrations were positively correlated with the concentrations of ...A wave flume simulator was used to study internal nitrogen release from the surface sediment collected from Taihu Lake, China. Particulate nitrogen concentrations were positively correlated with the concentrations of suspended solids, primarily from surface erosion related to the shear stress and duration of wave action. In response to 4 cm- and 10 cm-high wave production representing waves generated in Taihu Lake by gentle and gusty winds, respectively, the mean dynamic release rate of ammonium （NH4＋） from the sediment to the overlying water was 1 × 10-3 mg/（m2.s） and the NH4＋ concentration in the overlying water increased by 0.016 mg/L, indicating that waves resulting from strong wind can induce the rapid release of dissolved nitrogen from Taihu Lake sediments. The decrease in interstitial NH4＋ concentrations at all sediment depths was associated with an increase in NH4＋ concentrations in the overlying water by 0.01 mg/L, showing that sediment below the eroded layer was the main source of internal nitrogen release. Changes in the interstitial dissolved oxygen and NH4＋ concentrations showed that wave-induced pore water movement can greatly increase the diffusion rate, and that these 15 cm. Diffusion induced by pore water movement sediment layer in Taihu Lake. effects can influence the sediment to a depth of at least may be very important for the formation of an active展开更多
Aiming at understanding how intermetallic phases response when AA2024-T3 aluminium alloy is exposed to chloridecontainingaqueous medium, scanning electron microscopy was employed to provide morphological information o...Aiming at understanding how intermetallic phases response when AA2024-T3 aluminium alloy is exposed to chloridecontainingaqueous medium, scanning electron microscopy was employed to provide morphological information on alloy surfacebefore and after corrosion testing. Energy dispersive X-ray spectroscopy was carried out to determine compositional change inintermetallic particles. Atomic force microscopy was used to examine topographical variation introduced by the reactions ofintermetallic phases. Transmission electron microscopy combined with ultramicrotomy was carried out on dealloyed Al2CuMgparticles and their periphery region. It is found that dealloyed Al2CuMg particles exhibited porous, polycrystalline structurecomprised of body-centred cubic copper particles with sizes of 5 to 20 nm. Aluminium matrix started to trench in the periphery ofAl2CuMg particles at the early stage of dealloying. Development of trenching in Al.Cu.Fe.Mn.（Si） particle’s periphery was notuniform and took longer time to initiate than Al2CuMg dealloying. Localized corrosion at a cluster of Al2CuMg and Al2Cu particleswas mainly associated with Al2CuMg particles.展开更多
基金Project(2010AA065201)supported by the High-tech Research and Development Program of ChinaProject(2013zzts038)supported by the Fundamental Research Funds for the Central Universities of Central South University,ChinaProject(ZB2011CBBCe1)supported by the Major Program for Aluminum Corporation of China Limited
文摘A comprehensive heat and mass transfer model of dissolution process of non-agglomerated and agglomerated alumina particles was established in an aluminum reduction cell. An appropriate finite difference method was used to calculate the size dissolution rate, dissolution time and mass of alumina dissolved employing commercial software and custom algorithm based on the shrinking sphere assumption. The effects of some convection and thermal condition parameters on the dissolution process were studied. The calculated results show that the decrease of alumina content or the increase of alumina diffusion coefficient is beneficial for the increase of size dissolution rate and the decrease of dissolution time of non-agglomerated particles. The increase of bath superheat or alumina preheating temperature results in the increase of size dissolution rate and the decrease of dissolution time of agglomerated particles. The calculated dissolution curve of alumina（mass fraction of alumina dissolved） for a 300 k A aluminum reduction cell is in well accordance with the experimental results. The analysis shows that the dissolution process of alumina can be divided into two distinct stages： the fast dissolution stage of non-agglomerated particles and the slow dissolution stage of agglomerated particles, with the dissolution time in the order of 10 and 100 s, respectively. The agglomerated particles were identified to be the most important factor limiting the dissolution process.
基金Project(2010AA065201)supported by the High Technology Research and Development Program of ChinaProject(2018zzts157)supported by the Fundamental Research Funds for the Central Universities of Central South University,China。
文摘The Box–Behnken design and desirability approach were used to investigate and optimize the process parameters for aluminum reduction cells related to alumina dissolution. The bath temperature, alumina content, current and alumina temperature were chosen as the design parameters. The content of cumulative dissolved alumina(CCDA) and the relative deviation from the target content(RDTC) were adopted as the responses. The interactive influence results show that increasing the bath temperature and alumina temperature, as well as decreasing the alumina content, can increase CCDA. Increasing the bath temperature and lowering the current are beneficial for obtaining a more uniform alumina distribution. The optimal operating parameters were determined to be as follows: bath temperature of 958.8 ℃, alumina content of 2.679 wt.%, current of 300 kA and alumina temperature of 200 ℃.
基金Supported by the National Natural Science Foundation of China(Nos.41101458, 40825004,40871095,40801200)the Major Project for National Science and Technology Development(No.2010ZX03006-006)the "100-Talent Project" of Chinese Academy of Sciences,China(No.YOBROB045)
文摘A wave flume simulator was used to study internal nitrogen release from the surface sediment collected from Taihu Lake, China. Particulate nitrogen concentrations were positively correlated with the concentrations of suspended solids, primarily from surface erosion related to the shear stress and duration of wave action. In response to 4 cm- and 10 cm-high wave production representing waves generated in Taihu Lake by gentle and gusty winds, respectively, the mean dynamic release rate of ammonium （NH4＋） from the sediment to the overlying water was 1 × 10-3 mg/（m2.s） and the NH4＋ concentration in the overlying water increased by 0.016 mg/L, indicating that waves resulting from strong wind can induce the rapid release of dissolved nitrogen from Taihu Lake sediments. The decrease in interstitial NH4＋ concentrations at all sediment depths was associated with an increase in NH4＋ concentrations in the overlying water by 0.01 mg/L, showing that sediment below the eroded layer was the main source of internal nitrogen release. Changes in the interstitial dissolved oxygen and NH4＋ concentrations showed that wave-induced pore water movement can greatly increase the diffusion rate, and that these 15 cm. Diffusion induced by pore water movement sediment layer in Taihu Lake. effects can influence the sediment to a depth of at least may be very important for the formation of an active
基金Project(51201157)supported by the National Natural Science Foundation of ChinaProject(H052013A003)supported by the National Defense Technology Foundation,ChinaProject supported by the UK-ESPRC LATEST2 Program
文摘Aiming at understanding how intermetallic phases response when AA2024-T3 aluminium alloy is exposed to chloridecontainingaqueous medium, scanning electron microscopy was employed to provide morphological information on alloy surfacebefore and after corrosion testing. Energy dispersive X-ray spectroscopy was carried out to determine compositional change inintermetallic particles. Atomic force microscopy was used to examine topographical variation introduced by the reactions ofintermetallic phases. Transmission electron microscopy combined with ultramicrotomy was carried out on dealloyed Al2CuMgparticles and their periphery region. It is found that dealloyed Al2CuMg particles exhibited porous, polycrystalline structurecomprised of body-centred cubic copper particles with sizes of 5 to 20 nm. Aluminium matrix started to trench in the periphery ofAl2CuMg particles at the early stage of dealloying. Development of trenching in Al.Cu.Fe.Mn.（Si） particle’s periphery was notuniform and took longer time to initiate than Al2CuMg dealloying. Localized corrosion at a cluster of Al2CuMg and Al2Cu particleswas mainly associated with Al2CuMg particles.
