Search2012 Vol. 19, No. 5
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2012, vol. 19, no. 5, pp.
377-383.
https://doi.org/10.1007/s12613-012-0567-5
Abstract:
Metal leaching from a low-grade nickel ore was investigated using an ammonium sulfate roasting-water leaching process. The nickel ore was mixed with ammonium sulfate, followed by roasting and finally leaching with water. During the process the effects of the amount of ammonium sulfate, roasting temperature, and roasting time on the leaching recovery of metal elements were analyzed. The optimum technological parameters were determined as follows:ammonium sulfate/ore ratio, 0.8 g/g; roasting temperature, 400℃; and roasting time, 2 h. Under the optimum condition the leaching recoveries of Ni, Cu, Fe, and Mg were 83.48%, 76.24%, 56.43%, and 62.15%, respectively. Furthermore, the dissolution kinetics of Ni and Mg from the nickel ore was studied. The apparent activation energies for the leaching reaction of Ni and Mg were 18.782 and 10.038 kJ·mol-1, which were consistent with the values of diffusion control reactions. Therefore, the results demonstrated that the leaching recoveries of Ni and Mg were controlled by diffusion.
Metal leaching from a low-grade nickel ore was investigated using an ammonium sulfate roasting-water leaching process. The nickel ore was mixed with ammonium sulfate, followed by roasting and finally leaching with water. During the process the effects of the amount of ammonium sulfate, roasting temperature, and roasting time on the leaching recovery of metal elements were analyzed. The optimum technological parameters were determined as follows:ammonium sulfate/ore ratio, 0.8 g/g; roasting temperature, 400℃; and roasting time, 2 h. Under the optimum condition the leaching recoveries of Ni, Cu, Fe, and Mg were 83.48%, 76.24%, 56.43%, and 62.15%, respectively. Furthermore, the dissolution kinetics of Ni and Mg from the nickel ore was studied. The apparent activation energies for the leaching reaction of Ni and Mg were 18.782 and 10.038 kJ·mol-1, which were consistent with the values of diffusion control reactions. Therefore, the results demonstrated that the leaching recoveries of Ni and Mg were controlled by diffusion.
2012, vol. 19, no. 5, pp.
384-390.
https://doi.org/10.1007/s12613-012-0568-4
Abstract:
The reduction of ilmenite concentrate by hydrogen gas was investigated in the temperature range of 500 to 1200℃. The microstructure and phase transition of the reduction products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical microscopy (OM). It was found that the weight loss and iron metallization rate increased with the increase of reduction temperature and reaction time. The iron metallization rate could reach 87.5% when the sample was reduced at 1150℃ for 80 min. The final phase constituents mainly consist of Fe, M3O5 solid solution phase (M=Mg, Ti, and Fe), and few titanium oxide. Microstructure analysis shows that the surfaces of the reduction products have many holes and cracks and the reactions take place from the exterior of the grain to its interior. The kinetics of reduction indicates that the rate-controlling step is diffusion process control with the activation energy of 89 kJ·mol-1.
The reduction of ilmenite concentrate by hydrogen gas was investigated in the temperature range of 500 to 1200℃. The microstructure and phase transition of the reduction products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical microscopy (OM). It was found that the weight loss and iron metallization rate increased with the increase of reduction temperature and reaction time. The iron metallization rate could reach 87.5% when the sample was reduced at 1150℃ for 80 min. The final phase constituents mainly consist of Fe, M3O5 solid solution phase (M=Mg, Ti, and Fe), and few titanium oxide. Microstructure analysis shows that the surfaces of the reduction products have many holes and cracks and the reactions take place from the exterior of the grain to its interior. The kinetics of reduction indicates that the rate-controlling step is diffusion process control with the activation energy of 89 kJ·mol-1.
2012, vol. 19, no. 5, pp.
391-398.
https://doi.org/10.1007/s12613-012-0569-3
Abstract:
Rapid thick strip casting (RTSC) by Anton Hulek, Inventmetall®, is an innovative concept for the production of hot strips with a final as-cast thickness of about 25 mm before rolling. The innovation of the mechanism consists in a vertical mould performing a caterpillar motion. This moving mould has an unconventional parallelogram-shaped cross-section. The conventional rectangular shape is formed in the shaping machine, which is placed straight below the mould. Further elements of the technology are state-of-the-art. For the investigation of this new casting system theoretical calculations were complemented with practical experiments. The investigation focused mainly on two key aspects:the characteristics of the mould and the shaping process. For the practical analysis a static mould with three pairs of elements in laboratory scale was developed and commissioned by the Dept. of Ferrous Metallurgy @ RWTH Aachen University. The shaping experiments were carried out in model scale with two different materials and in variable boundary conditions. The results of these experiments delivered important mechanical as well as thermal informations about the casting system.
Rapid thick strip casting (RTSC) by Anton Hulek, Inventmetall®, is an innovative concept for the production of hot strips with a final as-cast thickness of about 25 mm before rolling. The innovation of the mechanism consists in a vertical mould performing a caterpillar motion. This moving mould has an unconventional parallelogram-shaped cross-section. The conventional rectangular shape is formed in the shaping machine, which is placed straight below the mould. Further elements of the technology are state-of-the-art. For the investigation of this new casting system theoretical calculations were complemented with practical experiments. The investigation focused mainly on two key aspects:the characteristics of the mould and the shaping process. For the practical analysis a static mould with three pairs of elements in laboratory scale was developed and commissioned by the Dept. of Ferrous Metallurgy @ RWTH Aachen University. The shaping experiments were carried out in model scale with two different materials and in variable boundary conditions. The results of these experiments delivered important mechanical as well as thermal informations about the casting system.
2012, vol. 19, no. 5, pp.
399-403.
https://doi.org/10.1007/s12613-012-0570-x
Abstract:
Auger electron spectroscopy (AES) was used to investigate the grain boundary segregation of arsenic and nitrogen in a kind of microalloyed steel produced by a compact strip production (CSP) technology at 950 to 1100℃, which are similar to the hot working temperature of the steel on a CSP production line. It was discovered that arsenic segregated on grain boundaries when the steel was annealed at 950℃ for 2 h. When the annealing temperature increased to 1100℃, arsenic was also found to have segregated on grain boundaries in the early annealing stage, for instance, within the first 5 min annealing time. However, if the holding time of the steel at this temperature increased to 2 h, arsenic diffused away from grain boundaries into the matrix again. Nitrogen was not found to have segregated on grain boundaries when the steel was annealed at a relatively low temperature, such as 950℃. But when the annealing temperature increased to 1100℃, nitrogen was detected to have segregated at grain boundaries in the steel.
Auger electron spectroscopy (AES) was used to investigate the grain boundary segregation of arsenic and nitrogen in a kind of microalloyed steel produced by a compact strip production (CSP) technology at 950 to 1100℃, which are similar to the hot working temperature of the steel on a CSP production line. It was discovered that arsenic segregated on grain boundaries when the steel was annealed at 950℃ for 2 h. When the annealing temperature increased to 1100℃, arsenic was also found to have segregated on grain boundaries in the early annealing stage, for instance, within the first 5 min annealing time. However, if the holding time of the steel at this temperature increased to 2 h, arsenic diffused away from grain boundaries into the matrix again. Nitrogen was not found to have segregated on grain boundaries when the steel was annealed at a relatively low temperature, such as 950℃. But when the annealing temperature increased to 1100℃, nitrogen was detected to have segregated at grain boundaries in the steel.
2012, vol. 19, no. 5, pp.
404-408.
https://doi.org/10.1007/s12613-012-0571-9
Abstract:
Interface morphology has important influence on the bond quality of titanium clad steel plates. The mechanical properties of titanium clad steel plates with wavy and straight interfaces were investigated by tensile-shear tests and bending tests. The interface morphology of the plates was examined by optical microscopy (OM) and scanning electron microscopy (SEM). The experimental results show that the shear strength of a wavy interface is higher than that of a straight interface. A wavy interface is the guarantee for obtaining high shear strength to provide a greater shear resistance. During the macrobending process, cracks appear in the swirl of the wave tip and ferrotitanium intermetallics. For in-situ observing the bending process by SEM, the wave tip of a wavy interface and the massive ferrotitanium intermetallics of a straight interface are places where cracks initiate and propagate. The results are the same as those observed in the macrobending process. Because of high hardness, the wave tip and the massive ferrotitanium intermetallics are hard in terms of compatible deformation.
Interface morphology has important influence on the bond quality of titanium clad steel plates. The mechanical properties of titanium clad steel plates with wavy and straight interfaces were investigated by tensile-shear tests and bending tests. The interface morphology of the plates was examined by optical microscopy (OM) and scanning electron microscopy (SEM). The experimental results show that the shear strength of a wavy interface is higher than that of a straight interface. A wavy interface is the guarantee for obtaining high shear strength to provide a greater shear resistance. During the macrobending process, cracks appear in the swirl of the wave tip and ferrotitanium intermetallics. For in-situ observing the bending process by SEM, the wave tip of a wavy interface and the massive ferrotitanium intermetallics of a straight interface are places where cracks initiate and propagate. The results are the same as those observed in the macrobending process. Because of high hardness, the wave tip and the massive ferrotitanium intermetallics are hard in terms of compatible deformation.
2012, vol. 19, no. 5, pp.
409-420.
https://doi.org/10.1007/s12613-012-0572-8
Abstract:
Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway service. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fracture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation after fracture and percentage reduction of area) and the toughness indices (Charpy impact energy Ak and plane-strain fracture toughness KIC) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and KIC values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.
Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway service. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fracture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy (SEM) on the fracture surfaces of the tested specimens. The ductility indices (percentage elongation after fracture and percentage reduction of area) and the toughness indices (Charpy impact energy Ak and plane-strain fracture toughness KIC) of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and KIC values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.
2012, vol. 19, no. 5, pp.
421-427.
https://doi.org/10.1007/s12613-012-0573-7
Abstract:
The fracture of a drilling tail made of 18CrNi3MoA steel in the exchanging water hole was analyzed in terms of inclusions, prior austenite grain size, carburized layers, and fatigue fracture morphology by means of optical microscopy, quantitative metallography, and scanning electron microscopy (SEM). Fatigue crack initiation and propagation on the drilling tail were also studied. The results showed that the fracture on the drilling tail was not induced by inclusions and the distribution inhomogeneity of prior austenite grain size. Instead, because the outside surface of the exchanging water hole was not continuously geometric, there was a great deal of stress concentration in those areas under continuous twisting, axial impact, and corrosion of mineral water. Thus three crack sources emerged in these areas. Initial cracks centered on these sources spread from the outside surface to the inside surface, and eventually the drilling tail ruptured. Furthermore, the fractograph of the region around the crack sources exhibited a typical ductile dimple fracture pattern, and cracks initiated on the outside surface of the carburized layers of the exchanging water hole. Three crack sources could be the sources of fatigue crack propagation. Based on the analysis of fatigue crack propagation, it was further demonstrated that fatigue damage originated from the outside surface of the exchanging water hole.
The fracture of a drilling tail made of 18CrNi3MoA steel in the exchanging water hole was analyzed in terms of inclusions, prior austenite grain size, carburized layers, and fatigue fracture morphology by means of optical microscopy, quantitative metallography, and scanning electron microscopy (SEM). Fatigue crack initiation and propagation on the drilling tail were also studied. The results showed that the fracture on the drilling tail was not induced by inclusions and the distribution inhomogeneity of prior austenite grain size. Instead, because the outside surface of the exchanging water hole was not continuously geometric, there was a great deal of stress concentration in those areas under continuous twisting, axial impact, and corrosion of mineral water. Thus three crack sources emerged in these areas. Initial cracks centered on these sources spread from the outside surface to the inside surface, and eventually the drilling tail ruptured. Furthermore, the fractograph of the region around the crack sources exhibited a typical ductile dimple fracture pattern, and cracks initiated on the outside surface of the carburized layers of the exchanging water hole. Three crack sources could be the sources of fatigue crack propagation. Based on the analysis of fatigue crack propagation, it was further demonstrated that fatigue damage originated from the outside surface of the exchanging water hole.
2012, vol. 19, no. 5, pp.
428-433.
https://doi.org/10.1007/s12613-012-0574-6
Abstract:
A mixed-control model was developed to study the transformation character of ferrite formation by a ledge mechanism. A numerical two-dimensional diffusion-field model was combined to describe the evolution of the diffusion field ahead of the migrating austenite/ferrite interface. The calculation results show that the bulk diffusion-controlled model leads to a deviation from experimental results under large solute supersaturation. In the mixed-control model, solute supersaturation and a parameter Z together determine the transformation character, which is quantified by the normalized concentration of carbon in austenite at the austenite/ferrite interface. By comparing with experimental data, the pre-exponential factor of interface mobility, M0, is estimated within the range from 0.10 to 0.60 mol·m·J-1·s-1 for the alloys with 0.11wt%-0.49wt% C at 700-740℃. For a certain Fe-C alloy, the trend of the transformation character relies on the magnitude of M 0 as the transformation temperature decreases.
A mixed-control model was developed to study the transformation character of ferrite formation by a ledge mechanism. A numerical two-dimensional diffusion-field model was combined to describe the evolution of the diffusion field ahead of the migrating austenite/ferrite interface. The calculation results show that the bulk diffusion-controlled model leads to a deviation from experimental results under large solute supersaturation. In the mixed-control model, solute supersaturation and a parameter Z together determine the transformation character, which is quantified by the normalized concentration of carbon in austenite at the austenite/ferrite interface. By comparing with experimental data, the pre-exponential factor of interface mobility, M0, is estimated within the range from 0.10 to 0.60 mol·m·J-1·s-1 for the alloys with 0.11wt%-0.49wt% C at 700-740℃. For a certain Fe-C alloy, the trend of the transformation character relies on the magnitude of M 0 as the transformation temperature decreases.
2012, vol. 19, no. 5, pp.
434-440.
https://doi.org/10.1007/s12613-012-0575-5
Abstract:
(Al65Cul20Fe15)100-x Snx (x=0, 12, 20, 30) and Al57Si10Cu18Fe15 powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al65Cul20Fe15 sample were crystalline λ-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of θ-Al2Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al65Cul20Fe15)100-x Snx samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al57Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.
(Al65Cul20Fe15)100-x Snx (x=0, 12, 20, 30) and Al57Si10Cu18Fe15 powders were cladded on a medium carbon steel (45# steel) substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the Al65Cul20Fe15 sample were crystalline λ-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of θ-Al2Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the (Al65Cul20Fe15)100-x Snx samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded Al57Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.
2012, vol. 19, no. 5, pp.
441-445.
https://doi.org/10.1007/s12613-012-0576-4
Abstract:
Biphasic calcium phosphate (BCP) nanopowders were synthesized by using microwave and non-microwave irradiation assisted processes. The synthesized powders were pressed under a pressure of 90 MPa, and then were sintered at 1000-1200℃ for 1 h. The mechanical properties of the samples were investigated. The formed phases and microstructures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the synthesis time was shorter, along with a more homogeneous microstructure, when the microwave irradiation assisted method was applied. The compression strength and the Young's modulus of the samples synthesized with microwave irradiation were about 60 MPa and 3 GPa, but those of the samples synthesized without microwave irradiation were about 30 MPa and 2 GPa, respectively. XRD patterns of the microwave irradiation assisted and non-microwave irradiation assisted nanopowders showed the coexistence of hydroxyapatite (HA) and tricalcium phosphate (TCP) phases in the system.
Biphasic calcium phosphate (BCP) nanopowders were synthesized by using microwave and non-microwave irradiation assisted processes. The synthesized powders were pressed under a pressure of 90 MPa, and then were sintered at 1000-1200℃ for 1 h. The mechanical properties of the samples were investigated. The formed phases and microstructures were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the synthesis time was shorter, along with a more homogeneous microstructure, when the microwave irradiation assisted method was applied. The compression strength and the Young's modulus of the samples synthesized with microwave irradiation were about 60 MPa and 3 GPa, but those of the samples synthesized without microwave irradiation were about 30 MPa and 2 GPa, respectively. XRD patterns of the microwave irradiation assisted and non-microwave irradiation assisted nanopowders showed the coexistence of hydroxyapatite (HA) and tricalcium phosphate (TCP) phases in the system.
2012, vol. 19, no. 5, pp.
446-452.
https://doi.org/10.1007/s12613-012-0577-3
Abstract:
Carbon nanotubes (CNTs) were coated by tungsten using metal organic chemical vapor deposition. Magnetic stirring was employed to disperse the W-coated CNTs (W-CNTs) in a Cu matrix, and then, the mixed powders were consolidated by spark plasma sintering. The W-CNTs obtained a uniform dispersion within the Cu matrix when the W-CNT content was less than 5.0vol%, but high content of W-CNTs (10vol%) resulted in the presence of clusters. The W-CNT/Cu composites containing low content of W-CNTs (<5.0vol%) exhibited a higher thermal conductivity than the sintered pure Cu, while the CNT/Cu composites exhibited no increase in thermal conductivity after the incorporation of uncoated CNTs. The W-CNT content was found to play a crucial role in determining the thermal conductivity of the W-CNT/Cu composites. The thermal conductivity of the W-CNT/Cu composites increased first and then decreased with the W-CNT content increasing. When the W-CNT content was 2.5vol%, the W-CNT/Cu composite obtained the maximum value of thermal conductivity. The thermal resistance of the (W-CNT)-Cu interface was predicted in terms of Maxwell-Garnett effective medium approximation, and its calculated value was about 3.0×10-9 m2·K·W-1.
Carbon nanotubes (CNTs) were coated by tungsten using metal organic chemical vapor deposition. Magnetic stirring was employed to disperse the W-coated CNTs (W-CNTs) in a Cu matrix, and then, the mixed powders were consolidated by spark plasma sintering. The W-CNTs obtained a uniform dispersion within the Cu matrix when the W-CNT content was less than 5.0vol%, but high content of W-CNTs (10vol%) resulted in the presence of clusters. The W-CNT/Cu composites containing low content of W-CNTs (<5.0vol%) exhibited a higher thermal conductivity than the sintered pure Cu, while the CNT/Cu composites exhibited no increase in thermal conductivity after the incorporation of uncoated CNTs. The W-CNT content was found to play a crucial role in determining the thermal conductivity of the W-CNT/Cu composites. The thermal conductivity of the W-CNT/Cu composites increased first and then decreased with the W-CNT content increasing. When the W-CNT content was 2.5vol%, the W-CNT/Cu composite obtained the maximum value of thermal conductivity. The thermal resistance of the (W-CNT)-Cu interface was predicted in terms of Maxwell-Garnett effective medium approximation, and its calculated value was about 3.0×10-9 m2·K·W-1.
2012, vol. 19, no. 5, pp.
453-456.
https://doi.org/10.1007/s12613-012-0578-2
Abstract:
A Y-type hexaferrite rod with the composition of Ba2Co1.8Cu0.2Fe12O22 was presented as an absorbing material with high absorbance. Its high absorbance and wide absorption band result from ferromagnetic resonance (FMR) that is self-biased by strong shape and magnetocrystalline anisotropy fields. Around the FMR frequency the specimen of the ferrite rods exhibits very high absorbance and the FMR frequency can be tuned by the rod dimension. In addition to the high absorbance and the wide tunable absorption band, the microwave absorber has another advantage of light weight due to the use of the ferrite rods instead of ferrite slabs.
A Y-type hexaferrite rod with the composition of Ba2Co1.8Cu0.2Fe12O22 was presented as an absorbing material with high absorbance. Its high absorbance and wide absorption band result from ferromagnetic resonance (FMR) that is self-biased by strong shape and magnetocrystalline anisotropy fields. Around the FMR frequency the specimen of the ferrite rods exhibits very high absorbance and the FMR frequency can be tuned by the rod dimension. In addition to the high absorbance and the wide tunable absorption band, the microwave absorber has another advantage of light weight due to the use of the ferrite rods instead of ferrite slabs.
2012, vol. 19, no. 5, pp.
457-460.
https://doi.org/10.1007/s12613-012-0579-1
Abstract:
Spinel compounds LiNi0.5Mn1.3Ti0.2O4 (LNMTO) and Li4Ti5O12 (LTO) were synthesized by different methods. The particle sizes of LNMTO and LTO are 0.5-2 and 0.5-0.8 μm, respectively. The LNMTO/LTO cell exhibits better electrochemical properties at both a low current rate of 0.2C and a high current rate of 1C. When the specific capacity was determined based on the mass of the LNMTO cathode, the LNMTO/LTO cell delivered 137 mA·h·g-1 at 0.2C and 118.2 mA·h·g-1 at 1C, and the corresponding capacity retentions after 30 cycles are 88.5% and 92.4%, respectively.
Spinel compounds LiNi0.5Mn1.3Ti0.2O4 (LNMTO) and Li4Ti5O12 (LTO) were synthesized by different methods. The particle sizes of LNMTO and LTO are 0.5-2 and 0.5-0.8 μm, respectively. The LNMTO/LTO cell exhibits better electrochemical properties at both a low current rate of 0.2C and a high current rate of 1C. When the specific capacity was determined based on the mass of the LNMTO cathode, the LNMTO/LTO cell delivered 137 mA·h·g-1 at 0.2C and 118.2 mA·h·g-1 at 1C, and the corresponding capacity retentions after 30 cycles are 88.5% and 92.4%, respectively.
2012, vol. 19, no. 5, pp.
461-466.
https://doi.org/10.1007/s12613-012-0580-8
Abstract:
In-situ pure TiO2 and Fe-doped TiO2 thin films were synthesized on Ti plates via the micro-arc oxidation (MAO) technique. The as-fabricated anatase TiO2 thin film-based conductometric sensors were employed to measure the gas sensitivity to ethanol. The results showed that Fe ions could be easily introduced into the MAO-TiO2 thin films by adding precursor K4(FeCN)6·3H2O into the Na3PO4 electrolyte. The amount of doped Fe ions increased almost linearly with the concentration of K4(FeCN)6·3H2O increasing, eventually affecting the ethanol sensing performances of TiO2 thin films. It was found that the enhanced sensor signals obtained had an optimal concentration of Fe dopant (1.28at%), by which the maximal gas sensor signal to 1000 ppm ethanol was estimated to be 7.91 at 275℃. The response time was generally reduced by doped Fe ions, which could be ascribed to the increase of oxygen vacancies caused by Fe3+ substituting for Ti4+.
In-situ pure TiO2 and Fe-doped TiO2 thin films were synthesized on Ti plates via the micro-arc oxidation (MAO) technique. The as-fabricated anatase TiO2 thin film-based conductometric sensors were employed to measure the gas sensitivity to ethanol. The results showed that Fe ions could be easily introduced into the MAO-TiO2 thin films by adding precursor K4(FeCN)6·3H2O into the Na3PO4 electrolyte. The amount of doped Fe ions increased almost linearly with the concentration of K4(FeCN)6·3H2O increasing, eventually affecting the ethanol sensing performances of TiO2 thin films. It was found that the enhanced sensor signals obtained had an optimal concentration of Fe dopant (1.28at%), by which the maximal gas sensor signal to 1000 ppm ethanol was estimated to be 7.91 at 275℃. The response time was generally reduced by doped Fe ions, which could be ascribed to the increase of oxygen vacancies caused by Fe3+ substituting for Ti4+.
2012, vol. 19, no. 5, pp.
467-472.
https://doi.org/10.1007/s12613-012-0581-7
Abstract:
A novel photocatalyst, bismuth oxychloride (BiOCl) micro-nano particles with a fine ferrite plate structure, was prepared by a low-cost, simple hydrolytic method. The as-prepared BiOCl was characterized by scanning electron microscopy (SEM), thermogravimetric analysis-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD), and UV-vis diffuse reflectance spectra (DRS). The effects of preparation conditions such as sodium dodecyl benzene sulfonate (SDBS) dispersant, HCl concentration, and heat treatment temperature on BiOCl performances were investigated. Moreover, its photocatalytic activity was evaluated on the degradation of methylene orange (MO) and was compared with that of TiO2 (P25). The experimental results confirmed that BiOCl micro-nano particles prepared with SDBS, the HCl concentration of 1.5 mol/L, and the heat treatment temperature of 80℃ exhibited the best performance for the photodegradation of MO solution, and they showed good stability and better photocatalytic activity than P25 photocatalyst.
A novel photocatalyst, bismuth oxychloride (BiOCl) micro-nano particles with a fine ferrite plate structure, was prepared by a low-cost, simple hydrolytic method. The as-prepared BiOCl was characterized by scanning electron microscopy (SEM), thermogravimetric analysis-differential thermal analysis (TGA-DTA), X-ray diffraction (XRD), and UV-vis diffuse reflectance spectra (DRS). The effects of preparation conditions such as sodium dodecyl benzene sulfonate (SDBS) dispersant, HCl concentration, and heat treatment temperature on BiOCl performances were investigated. Moreover, its photocatalytic activity was evaluated on the degradation of methylene orange (MO) and was compared with that of TiO2 (P25). The experimental results confirmed that BiOCl micro-nano particles prepared with SDBS, the HCl concentration of 1.5 mol/L, and the heat treatment temperature of 80℃ exhibited the best performance for the photodegradation of MO solution, and they showed good stability and better photocatalytic activity than P25 photocatalyst.
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