The leaching kinetics of niobium from a low-grade niobium-tantalum ore by concentrated KOH solu-tion under atmospheric pressure has been studied. Significant effects of reaction temperature, KOH concentration, stirrin...The leaching kinetics of niobium from a low-grade niobium-tantalum ore by concentrated KOH solu-tion under atmospheric pressure has been studied. Significant effects of reaction temperature, KOH concentration, stirring speed, particle size and inass ratio of alkali-to-ore on the dissolution rate of niobium were examined. The experimental data of the leaching rates and the observed effects of the relevant operating variables were well in-terpreted with a shrinking core model under diffusion control. By using the Arrhenius expression, the apparent activation energy for the dissolution of niobium was evaluated. Finally, on the base of the shrinking core model, the rate equation was established.展开更多
Electromagnetic levitation technique was used to undercool bulk samples of Co-20% Cu and Co-60% Cu alloys and high undercoolings up to 303 and 110 K were achieved,respectively.The dendritic growth velocities were meas...Electromagnetic levitation technique was used to undercool bulk samples of Co-20% Cu and Co-60% Cu alloys and high undercoolings up to 303 and 110 K were achieved,respectively.The dendritic growth velocities were measured as a function of undercooling.The dendrite growth velocity of the Co-20% Cu alloy was much higher than that of the Co-60% Cu alloy.The experimental data were analyzed on the basis of the LKT/BCT dendritic growth model by taking into account non-equilibrium interface kinetics.It has been revealed that a transition from solute diffusion controlled dendritic growth to thermal diffusion controlled dendritic growth occurs at an undercooling of about 66 K for the Co-20% Cu alloy,whereas the dendrite growth in Co-60% Cu alloy proceeds in a solute diffusion controlled mode within a large solidification temperature range,and the solutal undercooling plays a dominant role.It is thus deduced that certain distinct solidification temperature ranges may be responsible for the different solidification modes for the two alloys.展开更多
Integral imaging is a three dimensional(3D)display technology without any additional equipment.A new system is proposed in this paper which consists of the elemental images of real images in real mode(RIRM)and the one...Integral imaging is a three dimensional(3D)display technology without any additional equipment.A new system is proposed in this paper which consists of the elemental images of real images in real mode(RIRM)and the ones of virtual images in real mode(VIRM).The real images in real mode are the same as the conventional integral images.The virtual images in real mode are obtained by changing the coordinates of the corresponding points in elemental images which can be reconstructed by the lens array in virtual space.In order to reduce the spot size of the reconstructed images,the diffuser in conventional integral imaging is given up in the proposed method.Then the spot size is nearly1/20 of that in the conventional system.And an optical integral imaging system is constructed to confirm that our proposed method opens a new way for the application of the passive 3D display technology.展开更多
基金Supported by the National Natural Science Foundation of China (No. 50234040 and No. 20306031).
文摘The leaching kinetics of niobium from a low-grade niobium-tantalum ore by concentrated KOH solu-tion under atmospheric pressure has been studied. Significant effects of reaction temperature, KOH concentration, stirring speed, particle size and inass ratio of alkali-to-ore on the dissolution rate of niobium were examined. The experimental data of the leaching rates and the observed effects of the relevant operating variables were well in-terpreted with a shrinking core model under diffusion control. By using the Arrhenius expression, the apparent activation energy for the dissolution of niobium was evaluated. Finally, on the base of the shrinking core model, the rate equation was established.
基金supported by the National Natural Science Foundation of China (Grant No.50871088)NPU-FFR and the Foundation of Key Laboratory for Liquid-Solid Structural Evolution and Processing of Materials,Ministry of Education,Shandong University,China
文摘Electromagnetic levitation technique was used to undercool bulk samples of Co-20% Cu and Co-60% Cu alloys and high undercoolings up to 303 and 110 K were achieved,respectively.The dendritic growth velocities were measured as a function of undercooling.The dendrite growth velocity of the Co-20% Cu alloy was much higher than that of the Co-60% Cu alloy.The experimental data were analyzed on the basis of the LKT/BCT dendritic growth model by taking into account non-equilibrium interface kinetics.It has been revealed that a transition from solute diffusion controlled dendritic growth to thermal diffusion controlled dendritic growth occurs at an undercooling of about 66 K for the Co-20% Cu alloy,whereas the dendrite growth in Co-60% Cu alloy proceeds in a solute diffusion controlled mode within a large solidification temperature range,and the solutal undercooling plays a dominant role.It is thus deduced that certain distinct solidification temperature ranges may be responsible for the different solidification modes for the two alloys.
基金supported by the National Natural Science Foundation of China(No.11474169)
文摘Integral imaging is a three dimensional(3D)display technology without any additional equipment.A new system is proposed in this paper which consists of the elemental images of real images in real mode(RIRM)and the ones of virtual images in real mode(VIRM).The real images in real mode are the same as the conventional integral images.The virtual images in real mode are obtained by changing the coordinates of the corresponding points in elemental images which can be reconstructed by the lens array in virtual space.In order to reduce the spot size of the reconstructed images,the diffuser in conventional integral imaging is given up in the proposed method.Then the spot size is nearly1/20 of that in the conventional system.And an optical integral imaging system is constructed to confirm that our proposed method opens a new way for the application of the passive 3D display technology.
