Search2000 Vol. 7, No. 2
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2000, vol. 7, no. 2, pp.
79-81.
Abstract:
The difference between the systems of CaO-SiO2,-H2O and CaO-SiO2-Al(OH)3,-H2O, was studied, especially the effect of Al3+ on the crystallinity of tobermorite was focussed. As a result, in the system of CaO-SiO2-H2O, tobermorite formed early, however, with reaction time forward, tobermorite was replaced by xonotlite. So far as CaO-SiO2-Al(OH)3,-H2O was concemed, hydrothermal reaction was cdried out under the same condition as CaO-SiO2-H2O to study the morphological changes of tobermorite crystals. It was found that Al3+ accelerated the crystal growth of tobermorite to some extent and was in favor of platy crystals. Moreover, with the Al3+ content increasing in the starting material, the morphology of tobermorite did not change magnificently, but platy crystals became more and more eminent. As soon as the Al2O3 content was over 15.6%, synthetic mineral greatly changed in structure and haled into hibschite different from 1.1 nm tobermorite. Obviously, xonotlite was not apt to form in the presence of Al3+.
The difference between the systems of CaO-SiO2,-H2O and CaO-SiO2-Al(OH)3,-H2O, was studied, especially the effect of Al3+ on the crystallinity of tobermorite was focussed. As a result, in the system of CaO-SiO2-H2O, tobermorite formed early, however, with reaction time forward, tobermorite was replaced by xonotlite. So far as CaO-SiO2-Al(OH)3,-H2O was concemed, hydrothermal reaction was cdried out under the same condition as CaO-SiO2-H2O to study the morphological changes of tobermorite crystals. It was found that Al3+ accelerated the crystal growth of tobermorite to some extent and was in favor of platy crystals. Moreover, with the Al3+ content increasing in the starting material, the morphology of tobermorite did not change magnificently, but platy crystals became more and more eminent. As soon as the Al2O3 content was over 15.6%, synthetic mineral greatly changed in structure and haled into hibschite different from 1.1 nm tobermorite. Obviously, xonotlite was not apt to form in the presence of Al3+.
2000, vol. 7, no. 2, pp.
82-85.
Abstract:
Experiments were carried out at 1873 K in a double-temperature zone furnace using vapor pressure method. The equilibrium tests of barium vapor with liquid iron were conducted in CaO crucibles sealed in a Mo chamber. As a result, the experiments obtained the relation between the dissolved content of Ba in liquid iron and the vapor pressure of Ba and the standard Gibbs energies for the reactions Ba(g)=[Ba] and Ba(l)=[Ba].
Experiments were carried out at 1873 K in a double-temperature zone furnace using vapor pressure method. The equilibrium tests of barium vapor with liquid iron were conducted in CaO crucibles sealed in a Mo chamber. As a result, the experiments obtained the relation between the dissolved content of Ba in liquid iron and the vapor pressure of Ba and the standard Gibbs energies for the reactions Ba(g)=[Ba] and Ba(l)=[Ba].
2000, vol. 7, no. 2, pp.
86-91.
Abstract:
An empirical equation of carbon solubility in Fe-Cr-C melts is regressed based on the experimental data from references. A calculating model of mass action concentrations for these melts is formulated on the basis of the coexistence theory of metallic melts involving compound formation, the phase diagram of Cr-C system as well as thermodynamic data of Fe-Cr-C melts. According to the model, the standard Gibbs free energies of formation of CrC and Cr3C2 are obtained. Satisfactory agreement between the calculated and measured values shows that the model can reflect the structural characteristics of Fe-Cr-C melts.
An empirical equation of carbon solubility in Fe-Cr-C melts is regressed based on the experimental data from references. A calculating model of mass action concentrations for these melts is formulated on the basis of the coexistence theory of metallic melts involving compound formation, the phase diagram of Cr-C system as well as thermodynamic data of Fe-Cr-C melts. According to the model, the standard Gibbs free energies of formation of CrC and Cr3C2 are obtained. Satisfactory agreement between the calculated and measured values shows that the model can reflect the structural characteristics of Fe-Cr-C melts.
2000, vol. 7, no. 2, pp.
92-95.
Abstract:
With the self-made equipment, the behavior of the splashed slag coating was studied by the thermo-simulation. The influence of TFe, basicity and heating rate of slag on the occurrence of fractional melting was investigated. Furthermore, the composition variation of slag in different stages of the heating process was also discussed, and the mechanism of fractional melting was explained. In addition,the exploitation of this phenomenon in practice was also discussed.
With the self-made equipment, the behavior of the splashed slag coating was studied by the thermo-simulation. The influence of TFe, basicity and heating rate of slag on the occurrence of fractional melting was investigated. Furthermore, the composition variation of slag in different stages of the heating process was also discussed, and the mechanism of fractional melting was explained. In addition,the exploitation of this phenomenon in practice was also discussed.
2000, vol. 7, no. 2, pp.
96-98.
Abstract:
The slag-resistance and microstructural changes after the slag tests of MgAlON spinel containing different amount of nitrogen were studied by means of crucible slag-resistant experiment, SEM and EDS in the work. The results show that the slag-resistance of MgAlON is dependent on the nitrogen content, and the optimum amount is 2.88%. The structure is not changed although the grains have been permeated by some silicon, calcium and iron. A glass phase which contained nitrogen formed in the metamorphic layer. The glass can improve the ability of the slag-resistance of MgAlON because of its higher viscosity.
The slag-resistance and microstructural changes after the slag tests of MgAlON spinel containing different amount of nitrogen were studied by means of crucible slag-resistant experiment, SEM and EDS in the work. The results show that the slag-resistance of MgAlON is dependent on the nitrogen content, and the optimum amount is 2.88%. The structure is not changed although the grains have been permeated by some silicon, calcium and iron. A glass phase which contained nitrogen formed in the metamorphic layer. The glass can improve the ability of the slag-resistance of MgAlON because of its higher viscosity.
2000, vol. 7, no. 2, pp.
99-102.
Abstract:
The microstructural formation of the semi-solid AlSi7Mg alloy stirred by electromagnetic field is investigated together with the tempeatre field of the stirred melt at continuously cooling. A important kinetic factor for primary α-Al nucleation is proposed. It is found that a low temperature gradient exists in the electromagnetic stirred melt. This is why the first dendritic arms and secondary dendritic arms are refined. Experimental results also show that the root remelting of secondary dendritic arms is an important mechanism for the primary α-Al refmement. Strong electromagnetic stirring greatly reduces the composition supercooling in the melt and eliminates preferring growth of the first dendritic arms. Therefore, many rosettes or spherical Primary α-Al phase particles form finally.
The microstructural formation of the semi-solid AlSi7Mg alloy stirred by electromagnetic field is investigated together with the tempeatre field of the stirred melt at continuously cooling. A important kinetic factor for primary α-Al nucleation is proposed. It is found that a low temperature gradient exists in the electromagnetic stirred melt. This is why the first dendritic arms and secondary dendritic arms are refined. Experimental results also show that the root remelting of secondary dendritic arms is an important mechanism for the primary α-Al refmement. Strong electromagnetic stirring greatly reduces the composition supercooling in the melt and eliminates preferring growth of the first dendritic arms. Therefore, many rosettes or spherical Primary α-Al phase particles form finally.
2000, vol. 7, no. 2, pp.
103-106.
Abstract:
In order to develop super-board and super-thick slabs, the flow and temperature fields were studied in slab continuous casting molds under different practical conditions, such as slab dimensions, with-drawing slab speed, design of nozzles, and superheat temperature. The results showed that it is preferred to incline nozzle bores downwards and the submerged depth of the nozzles is best kept between 250-300 mm. In addition, the solidified shell is thicker at the wide face than that at the narrow face, while the thin points along the wide face exist both in the center and in the some area toward each respective end.
In order to develop super-board and super-thick slabs, the flow and temperature fields were studied in slab continuous casting molds under different practical conditions, such as slab dimensions, with-drawing slab speed, design of nozzles, and superheat temperature. The results showed that it is preferred to incline nozzle bores downwards and the submerged depth of the nozzles is best kept between 250-300 mm. In addition, the solidified shell is thicker at the wide face than that at the narrow face, while the thin points along the wide face exist both in the center and in the some area toward each respective end.
2000, vol. 7, no. 2, pp.
107-109.
Abstract:
Textures in different layers of superconductors based on YBCO system are analyzed using the methods of pole figure and conventional φ scans. It is shown that the φ scanning technology has only 1-dimensional description and could omit some information of 3-dimensional orientation distribution, which will influence the superconductor quality The pole figure method, in contrast, demonstrates the orientation distribution 2-dimensionally and gives a comprehensive view of thin film textUr, which is a much better method for texture analysis in superconducting films, in which there is commonly an unique high sharpness texture component.
Textures in different layers of superconductors based on YBCO system are analyzed using the methods of pole figure and conventional φ scans. It is shown that the φ scanning technology has only 1-dimensional description and could omit some information of 3-dimensional orientation distribution, which will influence the superconductor quality The pole figure method, in contrast, demonstrates the orientation distribution 2-dimensionally and gives a comprehensive view of thin film textUr, which is a much better method for texture analysis in superconducting films, in which there is commonly an unique high sharpness texture component.
2000, vol. 7, no. 2, pp.
110-114.
Abstract:
The effect of ZrO2, content on the fracture toughness, flexural strength and Vickers hardness as well as the erosive wear resistant properties of zirconia toughened Al2O3-TiC ceramic composites has been investigated. The results showed that the improvement in fracture toughness and flexure strength of composites with the content of zirconia less than 50% and 10% in mass fraction respectively,is primarily attributed to stress-induced transformation toughening by the analyse of X-ray diffraction. The dependance of erosion wear resistance on the attack angle and the content of ZrO2, panicles of the composites was also revealed. It is found that the erosion rate of the composites has a sharp rise at a attack angle over 65°. This phenomenon is due to a brittle response to the erosion test by microsmictural observation on eroded surface.
The effect of ZrO2, content on the fracture toughness, flexural strength and Vickers hardness as well as the erosive wear resistant properties of zirconia toughened Al2O3-TiC ceramic composites has been investigated. The results showed that the improvement in fracture toughness and flexure strength of composites with the content of zirconia less than 50% and 10% in mass fraction respectively,is primarily attributed to stress-induced transformation toughening by the analyse of X-ray diffraction. The dependance of erosion wear resistance on the attack angle and the content of ZrO2, panicles of the composites was also revealed. It is found that the erosion rate of the composites has a sharp rise at a attack angle over 65°. This phenomenon is due to a brittle response to the erosion test by microsmictural observation on eroded surface.
2000, vol. 7, no. 2, pp.
115-117.
Abstract:
The effects of different firing temperatures on the stability of perovskite phase, grain size, and dielectric properties were investigated by XRD, TEM, SEM and dielectric measurements. The dielectric ceramics of Pb(Mg1/3Nb2/3)O3-PbTiO3-BaTiO3 system were obtained by chemical coprecipitation in water. The ceramics have higher dielectric constant (7003-9714), lower firing temperature(950-1150℃), quite uniform microstructure with grain size less than 2.5 mp, and lower temperature coefficients of capacitance. As a result, it was confirmed that the simple and low cost chemical route used namely coprecipitation in water is a desired method for preparing high property dielectric materials applicable to multilayer capacitors.
The effects of different firing temperatures on the stability of perovskite phase, grain size, and dielectric properties were investigated by XRD, TEM, SEM and dielectric measurements. The dielectric ceramics of Pb(Mg1/3Nb2/3)O3-PbTiO3-BaTiO3 system were obtained by chemical coprecipitation in water. The ceramics have higher dielectric constant (7003-9714), lower firing temperature(950-1150℃), quite uniform microstructure with grain size less than 2.5 mp, and lower temperature coefficients of capacitance. As a result, it was confirmed that the simple and low cost chemical route used namely coprecipitation in water is a desired method for preparing high property dielectric materials applicable to multilayer capacitors.
2000, vol. 7, no. 2, pp.
118-121.
Abstract:
The oxygen permeabilities of polypropylene films are reduced by adding a minor percentage of a polyisobutene ionomer. The polyisobutene ionomers were prepared by in situ salt exchange of magnesium acetate with maleated polyisobutenes of commercially available low relative molecular mass. The more polar magnesiurn salts aided phase separaion during crystallization from the molten polypropylene mixtusre. Scanning electron microscope photographs revealed that the polyisobotene ionomer is largely concentratd in the amorphous regions between the polypropylene spherulites, where the ionomer tends to concentrate during crystallization. The influence of the polyisobutene ionomer on the oxygen permeability of polypropylene was found to be slightly dependent upon the relative molecular mass of the polyisobutene precursor. Under optimum conditions, the oxygen permeability of polypropylene is reduced by 20% with only 1% additive.
The oxygen permeabilities of polypropylene films are reduced by adding a minor percentage of a polyisobutene ionomer. The polyisobutene ionomers were prepared by in situ salt exchange of magnesium acetate with maleated polyisobutenes of commercially available low relative molecular mass. The more polar magnesiurn salts aided phase separaion during crystallization from the molten polypropylene mixtusre. Scanning electron microscope photographs revealed that the polyisobotene ionomer is largely concentratd in the amorphous regions between the polypropylene spherulites, where the ionomer tends to concentrate during crystallization. The influence of the polyisobutene ionomer on the oxygen permeability of polypropylene was found to be slightly dependent upon the relative molecular mass of the polyisobutene precursor. Under optimum conditions, the oxygen permeability of polypropylene is reduced by 20% with only 1% additive.
2000, vol. 7, no. 2, pp.
122-125.
Abstract:
W/Cu Functionally Graded Materials (FGM) was designed not only for reducing the thermal stress caused by the mismatch of thermal expansion coefficients, but also for combining the features of W, Mo-high plasma-erosion resistance and the advantages of Cu-high heat conductivity and ductility. Four different fabrication processes for W/Cu or Mo/Cu, including hot-pressing, Cu infiltration of sintered porosity-graded W skeleton, spark plasma sintering and plasma spraying, were investigated and compared. It was found that the hot-pressing process is difficult to keep the designed composition gradient, while the other three processes are successful in making W/Cu or Mo/Cu FGM. Meanwhile, microstructures and composition gradients are analyzed with SEM and EDAX.
W/Cu Functionally Graded Materials (FGM) was designed not only for reducing the thermal stress caused by the mismatch of thermal expansion coefficients, but also for combining the features of W, Mo-high plasma-erosion resistance and the advantages of Cu-high heat conductivity and ductility. Four different fabrication processes for W/Cu or Mo/Cu, including hot-pressing, Cu infiltration of sintered porosity-graded W skeleton, spark plasma sintering and plasma spraying, were investigated and compared. It was found that the hot-pressing process is difficult to keep the designed composition gradient, while the other three processes are successful in making W/Cu or Mo/Cu FGM. Meanwhile, microstructures and composition gradients are analyzed with SEM and EDAX.
2000, vol. 7, no. 2, pp.
126-131.
Abstract:
A technique for recycling spent nickel-cadmium batteries, which makes separaion of cadmium and nickel possible, is developed by laboratory-scale experiments. NH3-H2CO3 aqueous solution was used in this leaching technique. Since neutralization and/or solvent extraction were not required in the separation procedure of nickel and cadmium, the closed systemizaion of the process becomes possible. Experimental results show that, (1) if the NH3 concentraion of leaching solution is sufficiently high and the ratio of H2CO3 to NH3 is properly adjusted, both Ni(OH)2 and Cd(OH)2 react with NH, and quickly dissolve into leaching solution, and (2) Ni(OH)2 can be converted into insoluble NiO by calcination at 500℃, and CdO from Cd(OH)2 by calcination maintains good solubility in NH3-H2CO3 aqueous solution. As a conclusion, the recycling technique characterized by two step leaching can be developed based on such changes in dissolution behavior by calcination. Meanwhile, the yields of 99.8% for nickel and 97.6% for cadmium are obtained, and the purities of recovered nickel and cadmium are 99.9% and 98.6%, respectively.
A technique for recycling spent nickel-cadmium batteries, which makes separaion of cadmium and nickel possible, is developed by laboratory-scale experiments. NH3-H2CO3 aqueous solution was used in this leaching technique. Since neutralization and/or solvent extraction were not required in the separation procedure of nickel and cadmium, the closed systemizaion of the process becomes possible. Experimental results show that, (1) if the NH3 concentraion of leaching solution is sufficiently high and the ratio of H2CO3 to NH3 is properly adjusted, both Ni(OH)2 and Cd(OH)2 react with NH, and quickly dissolve into leaching solution, and (2) Ni(OH)2 can be converted into insoluble NiO by calcination at 500℃, and CdO from Cd(OH)2 by calcination maintains good solubility in NH3-H2CO3 aqueous solution. As a conclusion, the recycling technique characterized by two step leaching can be developed based on such changes in dissolution behavior by calcination. Meanwhile, the yields of 99.8% for nickel and 97.6% for cadmium are obtained, and the purities of recovered nickel and cadmium are 99.9% and 98.6%, respectively.
2000, vol. 7, no. 2, pp.
132-134.
Abstract:
Sodium chromate solubility is determined in the range of NaOH concentrations from 450 to 810 g/L and solution temperatures from 30 to 110℃. The optimized conditions to separate sodium chromate from NaOH in leached solution are resolved. It is first found the method to efficiently separate sodium chromate from NaOH and sodium aluminate in crude sodium chromate. Bench-scale studies on the separating are performed. Finally, good separation results are achieved.
Sodium chromate solubility is determined in the range of NaOH concentrations from 450 to 810 g/L and solution temperatures from 30 to 110℃. The optimized conditions to separate sodium chromate from NaOH in leached solution are resolved. It is first found the method to efficiently separate sodium chromate from NaOH and sodium aluminate in crude sodium chromate. Bench-scale studies on the separating are performed. Finally, good separation results are achieved.
2000, vol. 7, no. 2, pp.
135-138.
Abstract:
The electrochemical behavior of the medical Stainless steel 317L which is used as in vivo fixation materials has been investigated at different passivated states in several candidate-testing solutions. The potentiodynamic scanning polarizaion technique was employed to measure the polarizaion curves of 317L in 0.9%NaCl solution at 37℃. The results showed that the electrochemical behavior in 0.9% NaCl solution at 37℃ and in 2% NaCl solotion at 30℃ can be better used to detect and evaluate passivated states and corrosion resistance of 317L. In addition,the pitting potential Eb can be used as a criterion and itS lower limit could be 0.85 V(SEC) for this system.
The electrochemical behavior of the medical Stainless steel 317L which is used as in vivo fixation materials has been investigated at different passivated states in several candidate-testing solutions. The potentiodynamic scanning polarizaion technique was employed to measure the polarizaion curves of 317L in 0.9%NaCl solution at 37℃. The results showed that the electrochemical behavior in 0.9% NaCl solution at 37℃ and in 2% NaCl solotion at 30℃ can be better used to detect and evaluate passivated states and corrosion resistance of 317L. In addition,the pitting potential Eb can be used as a criterion and itS lower limit could be 0.85 V(SEC) for this system.
2000, vol. 7, no. 2, pp.
139-146.
Abstract:
The theorems for testing the local in one-port cellular neural/nonlinear network (CNN) cells with four local state variables are presented. Using the theorems computes the bifurcation diagrams of the cardiac Purkinje fiber (CPE) equations Which describe the long-lasting action and pace-maker potentials of the Purkinje fiber of the heart. The computer simulation shows that periodic trajectories or convergent trajectories of the CPF Equations can be foun if the cormsponing cell Parameters are located in a positive domain but nearby edge of chaos. In particular a heart with approximate normal frequency of heartbeat but non-normal electrocardiogram may suddenly stop by slightly perturbing the parameters of the corresponding CPF Equations when the Paramders are located nearby the edge of chaos in the bifurcation diagrams. This research seems to interpret reasonably the phenomena that patients with cardiac diseases might suddenly die without warning.
The theorems for testing the local in one-port cellular neural/nonlinear network (CNN) cells with four local state variables are presented. Using the theorems computes the bifurcation diagrams of the cardiac Purkinje fiber (CPE) equations Which describe the long-lasting action and pace-maker potentials of the Purkinje fiber of the heart. The computer simulation shows that periodic trajectories or convergent trajectories of the CPF Equations can be foun if the cormsponing cell Parameters are located in a positive domain but nearby edge of chaos. In particular a heart with approximate normal frequency of heartbeat but non-normal electrocardiogram may suddenly stop by slightly perturbing the parameters of the corresponding CPF Equations when the Paramders are located nearby the edge of chaos in the bifurcation diagrams. This research seems to interpret reasonably the phenomena that patients with cardiac diseases might suddenly die without warning.
2000, vol. 7, no. 2, pp.
147-150.
Abstract:
A new intelligent control scheme for hot strip coiling temperature is presented. In this scheme, the prediction model of finishing temperature and the presetting model of main cooling zone are establish based on BP neural network, the feed-forward open-loop control model of main cooling zone is constructed based on T-S fuzzy neural network, a new improved structure of T-S fuzzy neural network is developed, and the feedback close-loop control model of precision cooling zone is obtained based on fuzzy control. The effectiveness of the proposed scheme has been demonstrated by computer simulation with a satisfactory result.
A new intelligent control scheme for hot strip coiling temperature is presented. In this scheme, the prediction model of finishing temperature and the presetting model of main cooling zone are establish based on BP neural network, the feed-forward open-loop control model of main cooling zone is constructed based on T-S fuzzy neural network, a new improved structure of T-S fuzzy neural network is developed, and the feedback close-loop control model of precision cooling zone is obtained based on fuzzy control. The effectiveness of the proposed scheme has been demonstrated by computer simulation with a satisfactory result.
2000, vol. 7, no. 2, pp.
151-153.
Abstract:
A set of device is designed based on PC to realize the functions of traditional potentiostats in the phase analysis of galvanochemistry. In the device, A/D and D/A conversion is used to measure the electrode potential and convert the voltage for outPut; specific program runs in the PC to regulate and control the system. The effect of the proportion factor Kp on the control variation is researched through certain experiment. Two experiments, the control of electrolysis in constant poteniial and the determination of polarization curves, are designed to test and evaluate the effectiveness of the device. The experimemel results show that the variation between the actual anode potential and the target potential could be controlled to below 1 mV if Kp is set to an appropriate value.
A set of device is designed based on PC to realize the functions of traditional potentiostats in the phase analysis of galvanochemistry. In the device, A/D and D/A conversion is used to measure the electrode potential and convert the voltage for outPut; specific program runs in the PC to regulate and control the system. The effect of the proportion factor Kp on the control variation is researched through certain experiment. Two experiments, the control of electrolysis in constant poteniial and the determination of polarization curves, are designed to test and evaluate the effectiveness of the device. The experimemel results show that the variation between the actual anode potential and the target potential could be controlled to below 1 mV if Kp is set to an appropriate value.
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