Search1998 Vol. 5, No. 4
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1998, vol. 5, no. 4, pp.
185-191.
Abstract:
A rate equation of small particle-air bubble attachment in the turbulent now of flotation cells has been derived. The equation, integrating both the collision probability and adhesion probability together, represents the probability of attachment between particle and bubble in the turbulent flow. “Capture efficiency” f(α) is introduced into the rate equation to reflect the influence of energy hairier on the attachment rate. Three typical situations of particle-bubble interaction in flotation process have been discussed. For a completely hydrophobic particle-bubble system,f(α) = 1. This means that all collision leads to attachment. Whereas for hydrophilic particle-bubble systems,.f(α) = 0. Thus no adhesion of particle on bubble occurs at all. In real notation circumstances, however, there always exists a certain energy barrier between the particle and the bubble. Therefore, f(α) = 0~1. In such cases, not all collisions result in particle-bubble attachment.
A rate equation of small particle-air bubble attachment in the turbulent now of flotation cells has been derived. The equation, integrating both the collision probability and adhesion probability together, represents the probability of attachment between particle and bubble in the turbulent flow. “Capture efficiency” f(α) is introduced into the rate equation to reflect the influence of energy hairier on the attachment rate. Three typical situations of particle-bubble interaction in flotation process have been discussed. For a completely hydrophobic particle-bubble system,f(α) = 1. This means that all collision leads to attachment. Whereas for hydrophilic particle-bubble systems,.f(α) = 0. Thus no adhesion of particle on bubble occurs at all. In real notation circumstances, however, there always exists a certain energy barrier between the particle and the bubble. Therefore, f(α) = 0~1. In such cases, not all collisions result in particle-bubble attachment.
1998, vol. 5, no. 4, pp.
192-202.
Abstract:
Some fundamental studies related to the production of high carbon ferrochromium were summarized using melt circulation technology carried out in the School of Chemical Engineering at the University of Birmingham. These studies focused on the kinetics of chromite reduction in Fe-C(-Cr-Si) melts. The effects of feed mode,fluxes, amount and particle size of reductant, particle size of chromite, melt composition and the reduction temperature were investigated. The reduction mechanisms were discussed. The results showed that (1) the reduction rates of sintered chromite Pellets and non-compacted chromite powder in Fe-C(-Cr-Si) melts was generally very low,(2) addition of carbon in the non-compacted chromite feed greatly improved the reduction kinetics, (3) compaction of the carbon-chromite mixtures into composite Pellets further improved the reduction kinetics and (4) addition of lime in the composite Pellets increased the reduction rate, while the addition of silica may suppress the posihve effect of lime. It can be concluded that solid-state reduction, smelting reduction and dissolution proceed simultaneously during the reduction of compacted compostite pellets or non-compacted composite mixtures in Fe-C(-Cr-Si) melts,and the early stage of reduction is very likely to be controlled by either or both solid-state and/or gas diffusion through the oxide phases and/or the product layers.
Some fundamental studies related to the production of high carbon ferrochromium were summarized using melt circulation technology carried out in the School of Chemical Engineering at the University of Birmingham. These studies focused on the kinetics of chromite reduction in Fe-C(-Cr-Si) melts. The effects of feed mode,fluxes, amount and particle size of reductant, particle size of chromite, melt composition and the reduction temperature were investigated. The reduction mechanisms were discussed. The results showed that (1) the reduction rates of sintered chromite Pellets and non-compacted chromite powder in Fe-C(-Cr-Si) melts was generally very low,(2) addition of carbon in the non-compacted chromite feed greatly improved the reduction kinetics, (3) compaction of the carbon-chromite mixtures into composite Pellets further improved the reduction kinetics and (4) addition of lime in the composite Pellets increased the reduction rate, while the addition of silica may suppress the posihve effect of lime. It can be concluded that solid-state reduction, smelting reduction and dissolution proceed simultaneously during the reduction of compacted compostite pellets or non-compacted composite mixtures in Fe-C(-Cr-Si) melts,and the early stage of reduction is very likely to be controlled by either or both solid-state and/or gas diffusion through the oxide phases and/or the product layers.
1998, vol. 5, no. 4, pp.
203-207.
Abstract:
The mechanism of cathode process of B(Ⅲ) at molybdenum and platinum electrodes in LiF-NaF-KBF4 melt was studied and the transferred electron number of the reaction was calculated by means of cyclic voltammetry.The effect of adsorption of electroactive component on the electrochemical response (e.g., the voltammetric i─E curves) was analyzed and discussed. The "electrochemical spectra" for linear sweep voltammetry was used to elucidate the electrode reaction accompanied by a following transform process. The results show that the reduction of B(Ⅲ) to B(0) proceeds in reversible one step three-electron reaction and the cathode process of B(Ⅲ) is affected by product adsorbed strongly at the electrode surface. It is assumed that the reduction and deposition of B(Ⅲ) at molybdenum and platinum electrodes proceed in two kinds of mechanism: (1) B(Ⅲ)+ 3e = Bads→ B (surface diffusion deposition mechanism) and (2) B(Ⅲ) + 3e = B (direct deposition mechanism).
The mechanism of cathode process of B(Ⅲ) at molybdenum and platinum electrodes in LiF-NaF-KBF4 melt was studied and the transferred electron number of the reaction was calculated by means of cyclic voltammetry.The effect of adsorption of electroactive component on the electrochemical response (e.g., the voltammetric i─E curves) was analyzed and discussed. The "electrochemical spectra" for linear sweep voltammetry was used to elucidate the electrode reaction accompanied by a following transform process. The results show that the reduction of B(Ⅲ) to B(0) proceeds in reversible one step three-electron reaction and the cathode process of B(Ⅲ) is affected by product adsorbed strongly at the electrode surface. It is assumed that the reduction and deposition of B(Ⅲ) at molybdenum and platinum electrodes proceed in two kinds of mechanism: (1) B(Ⅲ)+ 3e = Bads→ B (surface diffusion deposition mechanism) and (2) B(Ⅲ) + 3e = B (direct deposition mechanism).
1998, vol. 5, no. 4, pp.
208-211.
Abstract:
Based on the phase diagram, the coexistence theory of the metallic melt structure involving compound formation and the regularity of melts containing saturated phase, a calculating model of mass action concentrations for Mn-C melts was formulated. According to the activities (or activity coefficients γMn and γC), obtained by the Unified Interaction Parameter Model (UIPM), the thermodynamic parameters △GMn3C⊝ and △GMn5C2⊝ at higher temperatures (1628~1873 K) were optimized by the repeated try and error method. It is testified that △GMn23Cn⊝, △GMn15C4⊝(873~1273 K) and △GMn7C3⊝ (298~1623 K), obtained at lower temperatures, can also be used at the above-mentioned higher temperatures. The calculated NMn and NC agree well with αMn and αC obtained by UIPM. This result shows that the deduced model can reflect the structural reality of Mn-C melts.
Based on the phase diagram, the coexistence theory of the metallic melt structure involving compound formation and the regularity of melts containing saturated phase, a calculating model of mass action concentrations for Mn-C melts was formulated. According to the activities (or activity coefficients γMn and γC), obtained by the Unified Interaction Parameter Model (UIPM), the thermodynamic parameters △GMn3C⊝ and △GMn5C2⊝ at higher temperatures (1628~1873 K) were optimized by the repeated try and error method. It is testified that △GMn23Cn⊝, △GMn15C4⊝(873~1273 K) and △GMn7C3⊝ (298~1623 K), obtained at lower temperatures, can also be used at the above-mentioned higher temperatures. The calculated NMn and NC agree well with αMn and αC obtained by UIPM. This result shows that the deduced model can reflect the structural reality of Mn-C melts.
1998, vol. 5, no. 4, pp.
212-218.
Abstract:
The thermodynamic properties and the phase diagrams of the systems Ga-M (M = In, Sb, Ph) were critically re-assessed and optimized employing the software package ChemSage for the calculation of thermodynamic equilibria. The Redlich-Kister/Margules formalism was employed for all solution phases and sets of self-consistent thermodynamic parameters were obtained. The results of re-assessment and optimization are compared with previous work, they are in excellent agreement with most experimental data.
The thermodynamic properties and the phase diagrams of the systems Ga-M (M = In, Sb, Ph) were critically re-assessed and optimized employing the software package ChemSage for the calculation of thermodynamic equilibria. The Redlich-Kister/Margules formalism was employed for all solution phases and sets of self-consistent thermodynamic parameters were obtained. The results of re-assessment and optimization are compared with previous work, they are in excellent agreement with most experimental data.
1998, vol. 5, no. 4, pp.
219-222.
Abstract:
In the thermodynamic evaluation Y was selected as a typical heavy rare earth metal for reducing the detrmental effects of tramp elements in the petroleum pipe steel. The possibilities of reactions between Y and tramp elements such as Sn, Sb, As, etc. after deoxidation and desulphurization were estimated by calculating the Gibbs free energies of formation. The equilibrium content of Y for eliminating the detrimental effects of tramp elements in the steel was recommended from the results of thermodynamic calculation.
In the thermodynamic evaluation Y was selected as a typical heavy rare earth metal for reducing the detrmental effects of tramp elements in the petroleum pipe steel. The possibilities of reactions between Y and tramp elements such as Sn, Sb, As, etc. after deoxidation and desulphurization were estimated by calculating the Gibbs free energies of formation. The equilibrium content of Y for eliminating the detrimental effects of tramp elements in the steel was recommended from the results of thermodynamic calculation.
1998, vol. 5, no. 4, pp.
223-227.
Abstract:
By contrast of microstructure and boron distribution in the same area of samples, the behavior of boron during ferrite reaction in Nb-B microalloyed steel was studied. Boron atoms have segregated to original austenite boundaries betfore ferrite reaction starts during isothermal treatment. The concentration of boron in small Pieces of ferrite foming along austenite boundaries may be remarkably higher than that in austenite matrix, but it will reduce gradually when the ferrite continuously grows. There is no obvious boron segregation on interface of γ/α and α/α.These facts indicate that ferrite growth is not controlled by diffusion of boron in austenite.
By contrast of microstructure and boron distribution in the same area of samples, the behavior of boron during ferrite reaction in Nb-B microalloyed steel was studied. Boron atoms have segregated to original austenite boundaries betfore ferrite reaction starts during isothermal treatment. The concentration of boron in small Pieces of ferrite foming along austenite boundaries may be remarkably higher than that in austenite matrix, but it will reduce gradually when the ferrite continuously grows. There is no obvious boron segregation on interface of γ/α and α/α.These facts indicate that ferrite growth is not controlled by diffusion of boron in austenite.
1998, vol. 5, no. 4, pp.
228-232.
Abstract:
Eight kinds of nonclasslcal periodic lattices with locally 8-fold rotational symmetries are introduced.They can be described via nonclassical Planc-crystallographic groups. The periodic lattices may be interpreted by the projections on the plane of the corresponding unit cells consisting of embedding polyhedrons, respectively. The Fourier-transform patterns of the Periodic lattices have striking approximate "8-fold rotational symmetries", some of which are similar to those displaying in the electrton-diffraction patterns of so-called quasicrystals.
Eight kinds of nonclasslcal periodic lattices with locally 8-fold rotational symmetries are introduced.They can be described via nonclassical Planc-crystallographic groups. The periodic lattices may be interpreted by the projections on the plane of the corresponding unit cells consisting of embedding polyhedrons, respectively. The Fourier-transform patterns of the Periodic lattices have striking approximate "8-fold rotational symmetries", some of which are similar to those displaying in the electrton-diffraction patterns of so-called quasicrystals.
1998, vol. 5, no. 4, pp.
233-236.
Abstract:
The mixture of Fe and Al powder was mechanically activated and sintered to study a non-melting method of producing the intermetallics Fe3Al. High-energy ball milling was used as an activation method, X-ray diffraction and SEM were chosen to analyze the materials variation before and after activation and sintering, and hot press of Fe-Al powder was inveshgated to compare mechanical activation with sintering. The results show that combining mechanical activation with reaction sintering can complete the transformation from pure Fe and Al powder to intermetallics. It is difficult to do the transformation by either mechanical activation or hot press.
The mixture of Fe and Al powder was mechanically activated and sintered to study a non-melting method of producing the intermetallics Fe3Al. High-energy ball milling was used as an activation method, X-ray diffraction and SEM were chosen to analyze the materials variation before and after activation and sintering, and hot press of Fe-Al powder was inveshgated to compare mechanical activation with sintering. The results show that combining mechanical activation with reaction sintering can complete the transformation from pure Fe and Al powder to intermetallics. It is difficult to do the transformation by either mechanical activation or hot press.
1998, vol. 5, no. 4, pp.
237-240,250.
Abstract:
hased on both the wrinkle model and fracturc model, the wrinkle critical tangent pressure and the fracture on critical radial tensile stress are calculated respectively. The maximum tangent pressure formula in the flange deformation zone and the maximum radial tensile stress formula in the cylinder-wall pass force zone are given, and both the no-wrinkle limitl criterion and no-fracture limit criterion are put froward. The prediction and control criterion and diagram of both the wrinkle limit and fracture limit on cylindrical cup deep-drawing, the most suitable forming zone and the limit deep-drawing coefficient are obtained. Comparing with present experience formulae and actual product's production, this prediction and control are quite accurate.
hased on both the wrinkle model and fracturc model, the wrinkle critical tangent pressure and the fracture on critical radial tensile stress are calculated respectively. The maximum tangent pressure formula in the flange deformation zone and the maximum radial tensile stress formula in the cylinder-wall pass force zone are given, and both the no-wrinkle limitl criterion and no-fracture limit criterion are put froward. The prediction and control criterion and diagram of both the wrinkle limit and fracture limit on cylindrical cup deep-drawing, the most suitable forming zone and the limit deep-drawing coefficient are obtained. Comparing with present experience formulae and actual product's production, this prediction and control are quite accurate.
1998, vol. 5, no. 4, pp.
241-244.
Abstract:
C60 High Performance Concrete (HPC) was prepared by limiting cement content and adopting composite superplasticizer, low-alkalinity expansive agent and high-quality line mixture. The results showed that the performance of the prepared C60 HPC was excellent. By adopting some advanced construction techniques such as using secondary vibration and secondary face compaction, controlling temperature difference and paying special attention to early curing in the construction process, the prepared C60 HPC had been successfully applied in the monolithic structure of huge building.
C60 High Performance Concrete (HPC) was prepared by limiting cement content and adopting composite superplasticizer, low-alkalinity expansive agent and high-quality line mixture. The results showed that the performance of the prepared C60 HPC was excellent. By adopting some advanced construction techniques such as using secondary vibration and secondary face compaction, controlling temperature difference and paying special attention to early curing in the construction process, the prepared C60 HPC had been successfully applied in the monolithic structure of huge building.
1998, vol. 5, no. 4, pp.
245-250.
Abstract:
An algorithm for the computation of the unstructured real stability radius of high dimensional linear system is presented. Using the accurate formula of the real stability radius of 2-dimensional system linear system checks the algorithm. The result shows that the algorithm is reliable and efficient. As applications, the unstructured real stability radii of 2-dimensional Chua's circuit and 3-dimensional piecewise-linear system are calculated, the dynamical orbits of the corresponding perturbed systems are simulated.
An algorithm for the computation of the unstructured real stability radius of high dimensional linear system is presented. Using the accurate formula of the real stability radius of 2-dimensional system linear system checks the algorithm. The result shows that the algorithm is reliable and efficient. As applications, the unstructured real stability radii of 2-dimensional Chua's circuit and 3-dimensional piecewise-linear system are calculated, the dynamical orbits of the corresponding perturbed systems are simulated.
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