Search2010 Vol. 17, No. 3
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2010, vol. 17, no. 3, pp.
251-256.
https://doi.org/10.1007/s12613-010-0301-0
Abstract:
Jajarm’s bauxite deposits are mainly diasporic, and they have a low mass ratio of Al2O3/SiO2. It is necessary to increase the run-of-mine mass ratio before feeding the material to the Bayer process. Chemical analysis indicated that the low-grade bauxite sample from Jajarm contained 43.9wt% Al2O3 and 13.35wt% SiO2, resulting in a mass ratio of 3.29. According to mineralogical studies, the presence of aluminosilicate minerals such as kaolinite, illite, and quartz was the main reason for the decrease of the mass ratio. Microscopic observations revealed that, with the size reduction from -1000+710 to -38 μm, the liberation degree of diaspore increased from 10% to 60%, and that of aluminosilicates increased from 20% to 85%. Heavy liquids with the densities of 2.8, 3.0, 3.2, and 3.4 g/cm3 were used to evaluate the heavy media separation in three sizes, i.e., -3350+710, -710+212, and -212+125 μm. Laboratory studies confirm that the density of 3.2 g/cm3 can produce the concentrates (in sunk fractions) with recoveries of 89.09%, 91.24%, and 84.68% with the Al2O3/SiO2 mass ratios of 5.03, 5.16, and 5.15 for the -3350+710, -710+212, and -212+125 μm sizes, respectively.
Jajarm’s bauxite deposits are mainly diasporic, and they have a low mass ratio of Al2O3/SiO2. It is necessary to increase the run-of-mine mass ratio before feeding the material to the Bayer process. Chemical analysis indicated that the low-grade bauxite sample from Jajarm contained 43.9wt% Al2O3 and 13.35wt% SiO2, resulting in a mass ratio of 3.29. According to mineralogical studies, the presence of aluminosilicate minerals such as kaolinite, illite, and quartz was the main reason for the decrease of the mass ratio. Microscopic observations revealed that, with the size reduction from -1000+710 to -38 μm, the liberation degree of diaspore increased from 10% to 60%, and that of aluminosilicates increased from 20% to 85%. Heavy liquids with the densities of 2.8, 3.0, 3.2, and 3.4 g/cm3 were used to evaluate the heavy media separation in three sizes, i.e., -3350+710, -710+212, and -212+125 μm. Laboratory studies confirm that the density of 3.2 g/cm3 can produce the concentrates (in sunk fractions) with recoveries of 89.09%, 91.24%, and 84.68% with the Al2O3/SiO2 mass ratios of 5.03, 5.16, and 5.15 for the -3350+710, -710+212, and -212+125 μm sizes, respectively.
2010, vol. 17, no. 3, pp.
257-261.
https://doi.org/10.1007/s12613-010-0302-z
Abstract:
A new route of impurity rejection to remove ferric iron from a synthetic nickel leach solution was introduced, which simulated the chemical composition of a typical acid leach solution of nickel laterites under atmospheric pressure. The synthetic solution underwent a stepwise neutralization process, with each step adopting different pH value-temperature combinations. In a conventional nickel atmospheric leach (AL) process, the nickel loss could be as high as 10wt%, which was a longstanding issue and prevented this process from commercialization. The new impurity rejection route is the first step towards resolving this issue. The results show that, the best neutralization performance is achieved at the nickel loss of 3.4wt% in the neutralization scheme that employs ethylenediaminetetraacetic acid as a nickel stabilizer (pH: 1.3–3.5; temperature: 95–70℃)
A new route of impurity rejection to remove ferric iron from a synthetic nickel leach solution was introduced, which simulated the chemical composition of a typical acid leach solution of nickel laterites under atmospheric pressure. The synthetic solution underwent a stepwise neutralization process, with each step adopting different pH value-temperature combinations. In a conventional nickel atmospheric leach (AL) process, the nickel loss could be as high as 10wt%, which was a longstanding issue and prevented this process from commercialization. The new impurity rejection route is the first step towards resolving this issue. The results show that, the best neutralization performance is achieved at the nickel loss of 3.4wt% in the neutralization scheme that employs ethylenediaminetetraacetic acid as a nickel stabilizer (pH: 1.3–3.5; temperature: 95–70℃)
2010, vol. 17, no. 3, pp.
262-266.
https://doi.org/10.1007/s12613-010-0303-y
Abstract:
The configuration of the tundish for a two-strand horizontal continuous caster was designed and optimized through water modeling. Three designs of the tundish were studied: the original tundish without any flow control devices, the tundish with a turbulence inhibitor at the bottom, and the tundish with an inlet launder and an inclined dam. The residence time, the location and size of the dead zone, and the fluid field pattern were investigated. At the same time, the asymmetry flow field and wavy inlet jet in the horizontal tundish were observed and the reasons for them were discussed. The results indicate that the tundish with an inlet launder and an inclined dam is the best of the three designs.
The configuration of the tundish for a two-strand horizontal continuous caster was designed and optimized through water modeling. Three designs of the tundish were studied: the original tundish without any flow control devices, the tundish with a turbulence inhibitor at the bottom, and the tundish with an inlet launder and an inclined dam. The residence time, the location and size of the dead zone, and the fluid field pattern were investigated. At the same time, the asymmetry flow field and wavy inlet jet in the horizontal tundish were observed and the reasons for them were discussed. The results indicate that the tundish with an inlet launder and an inclined dam is the best of the three designs.
2010, vol. 17, no. 3, pp.
267-275.
https://doi.org/10.1007/s12613-010-0304-x
Abstract:
The factors involved in simulating the continuous casting process of steel and the effects of the factors on the thermal behavior were investigated. The numerical methods and the influence of some assumptions were also analyzed, such as nodes used to discretize the steel in array size and computing time to obtain good approaches. The results show that some of these factors are related with the design of the continuous casting plant (CCP), such as geometrical configuration, and the operating conditions, such as water flow rate, heat removal coefficient in the mold, casting times, and casting speed in the strand, which affect the heat removal conditions over the temperature and solidification profiles.
The factors involved in simulating the continuous casting process of steel and the effects of the factors on the thermal behavior were investigated. The numerical methods and the influence of some assumptions were also analyzed, such as nodes used to discretize the steel in array size and computing time to obtain good approaches. The results show that some of these factors are related with the design of the continuous casting plant (CCP), such as geometrical configuration, and the operating conditions, such as water flow rate, heat removal coefficient in the mold, casting times, and casting speed in the strand, which affect the heat removal conditions over the temperature and solidification profiles.
2010, vol. 17, no. 3, pp.
276-281.
https://doi.org/10.1007/s12613-010-0305-9
Abstract:
The effect of titanium on the as-cast structure and the growth form of titanium precipitates, and the effect of cooling rate on the size and distribution of titanium precipitates were studied. It is shown that Ti-rich precipitates acting as heterogeneous nucleation sites play an important role in refining the grain size and increasing the equiaxed grain ratio. Cooling rate has a great effect on the size and distribution of precipitates. The number of precipitates increases and the size decreases with the increase of cooling rate. Ti-rich particles acting as heterogeneous nucleation sites at the onset of solidification are observed in the experiment. This result suggests that TiN nucleated on Ti2O3 is an effective inoculant for δ-ferrite during solidification in low carbon steel.
The effect of titanium on the as-cast structure and the growth form of titanium precipitates, and the effect of cooling rate on the size and distribution of titanium precipitates were studied. It is shown that Ti-rich precipitates acting as heterogeneous nucleation sites play an important role in refining the grain size and increasing the equiaxed grain ratio. Cooling rate has a great effect on the size and distribution of precipitates. The number of precipitates increases and the size decreases with the increase of cooling rate. Ti-rich particles acting as heterogeneous nucleation sites at the onset of solidification are observed in the experiment. This result suggests that TiN nucleated on Ti2O3 is an effective inoculant for δ-ferrite during solidification in low carbon steel.
2010, vol. 17, no. 3, pp.
282-289.
https://doi.org/10.1007/s12613-010-0306-8
Abstract:
The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.
The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.
2010, vol. 17, no. 3, pp.
290-296.
https://doi.org/10.1007/s12613-010-0307-7
Abstract:
The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 (θ phase) precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformation temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.
The microstructural evolution and element distribution of the Al-4Cu-Mg alloy during semi-solid compression were investigated, and the precipitate behavior and dislocation morphology were discussed. The experimental results show that the microstructure, the number of CuAl2 (θ phase) precipitates, and the dislocation density of the Al-4Cu-Mg alloy depend apparently on the process parameters. More segregation of Cu at the grain boundary happens with an increase of deformation temperature and a decrease of strain rate, leading to an increase in the number of θ phase. With an increase of height reduction, Cu segregation at the grain boundary decreases gradually. Moreover, unique dislocation morphologies including helical dislocations and dislocation loops appear at different process parameters and evolve to reduce the stored energy.
2010, vol. 17, no. 3, pp.
297-306.
https://doi.org/10.1007/s12613-010-0308-6
Abstract:
Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu (wt%, signed as 3C), fabricated by traditional cast (TC) and spray forming (SF) processes, were investigated by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that Al7Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802–813 K and 800–815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858–870 K and 876–890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.
Microstructural evolution and phase transformation induced by different heat treatments of the hypereutectic aluminium-silicon alloy, Al-25Si-5Fe-3Cu (wt%, signed as 3C), fabricated by traditional cast (TC) and spray forming (SF) processes, were investigated by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The results show that Al7Cu2Fe phase can be formed and transformed in TC- and SF-3C alloys between 802–813 K and 800–815 K, respectively. The transformation from β-Al5FeSi to δ-Al4FeSi2 phase via peritectic reaction can occur at around 858–870 K and 876–890 K in TC- and SF-3C alloys, respectively. The starting precipitation temperature of δ-Al4FeSi2 phase as the dominant Fe-bearing phase in the TC-3C alloy is 997 K and the exothermic peak about the peritectic transformation of δ-Al4FeSi2→β-Al5FeSi is not detected in the present DSC experiments. Also, the mechanisms of the microstructural evolution and phase transformation are discussed.
2010, vol. 17, no. 3, pp.
307-311.
https://doi.org/10.1007/s12613-010-0309-5
Abstract:
The primary crystallization of the Ti40Zr25Ni8Cu9Be18 amorphous alloy was studied by isochronal differential scanning calorimetry (DSC). The activation energy was determined by the Kissinger-Akahira-Sunose method. Trying to analyze the crystallization kinetics of the Ti40Zr25Ni8Cu9Be18 amorphous alloy by two different methods, it was found that the crystallization kinetics did not obey the Johnson-Mehl-Avrami equation. A modified method in consideration of the impingement effect was proposed to perform kinetic analysis of the isochronal crystallization of this alloy. The kinetic parameters were then obtained by the linear fitting method based on the modified kinetic equation. The results show that the isochronal crystallization kinetics of the amorphous Ti40Zr25Ni8Cu9Be18 alloy is heating rate dependent, and the discrepancy between the Johnson-Mehl-Avrami method and the modified method increases with the increase of heating rate.
The primary crystallization of the Ti40Zr25Ni8Cu9Be18 amorphous alloy was studied by isochronal differential scanning calorimetry (DSC). The activation energy was determined by the Kissinger-Akahira-Sunose method. Trying to analyze the crystallization kinetics of the Ti40Zr25Ni8Cu9Be18 amorphous alloy by two different methods, it was found that the crystallization kinetics did not obey the Johnson-Mehl-Avrami equation. A modified method in consideration of the impingement effect was proposed to perform kinetic analysis of the isochronal crystallization of this alloy. The kinetic parameters were then obtained by the linear fitting method based on the modified kinetic equation. The results show that the isochronal crystallization kinetics of the amorphous Ti40Zr25Ni8Cu9Be18 alloy is heating rate dependent, and the discrepancy between the Johnson-Mehl-Avrami method and the modified method increases with the increase of heating rate.
2010, vol. 17, no. 3, pp.
312-317.
https://doi.org/10.1007/s12613-010-0310-z
Abstract:
To study the precipitation mechanism of α-Cr phase in Inconel 718 alloy, the samples after long-time aging at 650 and 677℃ were examined by microstructural observations and chemical phase analysis methods. Combining the thermodynamics and kinetics calculation results, α-Cr always precipitates in the vicinity of δ phase, because δ phase rejects Cr into the γ-matrix when growing. The selected area diffraction patterns confirm that the crystallographic relationships of α-Cr with δ phase are (010)δ//(1 10)α-Cr and [100]δ//[111]α-Cr. A graphic model is also presented to show the crystallographic relation between α-Cr and δ phases.
To study the precipitation mechanism of α-Cr phase in Inconel 718 alloy, the samples after long-time aging at 650 and 677℃ were examined by microstructural observations and chemical phase analysis methods. Combining the thermodynamics and kinetics calculation results, α-Cr always precipitates in the vicinity of δ phase, because δ phase rejects Cr into the γ-matrix when growing. The selected area diffraction patterns confirm that the crystallographic relationships of α-Cr with δ phase are (010)δ//(1 10)α-Cr and [100]δ//[111]α-Cr. A graphic model is also presented to show the crystallographic relation between α-Cr and δ phases.
2010, vol. 17, no. 3, pp.
318-322.
https://doi.org/10.1007/s12613-010-0311-y
Abstract:
Starting from the quaternary Cu47Ti34Zr11Ni8 alloy, the compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni alloys was systematically investigated. Quaternary Cu-Ti-Zr-Ni alloys can be cast directly from the melt into copper molds to form fully amorphous strips or rods with the thickness of 3–6 mm. The evidence of the amorphous nature of the cast rods was provided by X-ray spectra. The measured glass transition temperature (Tg) and crystallization temperature (Tx) were obtained for the alloys using differential scanning calorimetry (DSC) at the heating rate of 20 K/s. In the results, the differences between the glass temperature and the crystallization temperature (ΔTx=Tx-Tg) are measured with values ranging up to 33–55 K. The reduced glass transition temperature (Trg), which is the ratio of the glass temperature to the liquidus temperature (Tl), is often used as an indication of the glass-forming ability of metallic alloys. For the present Cu-Ti-Zr-Ni alloys, this ratio is typically in the range of 0.5838–0.5959, characteristic of metallic alloys with good glass-forming ability. The elastic constants for several selected alloys were measured using ultrasonic methods. The values of the elastic shear modulus, bulk modulus, and Poisson’s ratio were also given.
Starting from the quaternary Cu47Ti34Zr11Ni8 alloy, the compositional dependence of thermal and elastic properties of Cu-Ti-Zr-Ni alloys was systematically investigated. Quaternary Cu-Ti-Zr-Ni alloys can be cast directly from the melt into copper molds to form fully amorphous strips or rods with the thickness of 3–6 mm. The evidence of the amorphous nature of the cast rods was provided by X-ray spectra. The measured glass transition temperature (Tg) and crystallization temperature (Tx) were obtained for the alloys using differential scanning calorimetry (DSC) at the heating rate of 20 K/s. In the results, the differences between the glass temperature and the crystallization temperature (ΔTx=Tx-Tg) are measured with values ranging up to 33–55 K. The reduced glass transition temperature (Trg), which is the ratio of the glass temperature to the liquidus temperature (Tl), is often used as an indication of the glass-forming ability of metallic alloys. For the present Cu-Ti-Zr-Ni alloys, this ratio is typically in the range of 0.5838–0.5959, characteristic of metallic alloys with good glass-forming ability. The elastic constants for several selected alloys were measured using ultrasonic methods. The values of the elastic shear modulus, bulk modulus, and Poisson’s ratio were also given.
2010, vol. 17, no. 3, pp.
323-326.
https://doi.org/10.1007/s12613-010-0312-x
Abstract:
Bulk metallic glass (BMG) formation was explored in the Fe-B-Si-Nb alloy system though combined use of the atomic cluster line approach and the minor alloying strategy. The basic ternary compositions in the Fe-B-Si system were determined by the intersection points of two cluster lines, namely, Fe-B cluster to Si and Fe-Si cluster to B. 3at%–4at% Nb was added to the quaternary Fe-B-Si-Nb alloy. The casting experiments revealed that good glass-forming ability (GFA) occurred at the (Fe73.4Si8.2B18.4)96Nb4 composition, and 3-mm diameter BMG samples were made. The glass transition temperature (Tg), crystallization temperature (Tx), and supercooled liquid region (ΔTx=Tx-Tg) of this BMG were measured to be 866, 889, and 23 K, respectively. The BMG shows a high Vickers hardness of about Hv 1164, a Young’s modulus of 180 GPa, and a good corrosion resistance in the solutions of 1 mol/L HCl and 3wt% NaCl.
Bulk metallic glass (BMG) formation was explored in the Fe-B-Si-Nb alloy system though combined use of the atomic cluster line approach and the minor alloying strategy. The basic ternary compositions in the Fe-B-Si system were determined by the intersection points of two cluster lines, namely, Fe-B cluster to Si and Fe-Si cluster to B. 3at%–4at% Nb was added to the quaternary Fe-B-Si-Nb alloy. The casting experiments revealed that good glass-forming ability (GFA) occurred at the (Fe73.4Si8.2B18.4)96Nb4 composition, and 3-mm diameter BMG samples were made. The glass transition temperature (Tg), crystallization temperature (Tx), and supercooled liquid region (ΔTx=Tx-Tg) of this BMG were measured to be 866, 889, and 23 K, respectively. The BMG shows a high Vickers hardness of about Hv 1164, a Young’s modulus of 180 GPa, and a good corrosion resistance in the solutions of 1 mol/L HCl and 3wt% NaCl.
2010, vol. 17, no. 3, pp.
327-330.
https://doi.org/10.1007/s12613-010-0313-9
Abstract:
The Zr62.55Cu17.55Ni9.9Al10 bulk metallic glass (BMG) was prepared by using copper-mold suction-casting. X-ray diffraction and differential scanning calorimetry were utilized to determine its structure and thermal stability. Uniaxial compression and Rockwell indentation tests were adopted to study the plastic deformation behavior at room temperature. The results show that the glass transition temperature and the onset temperature of exothermic reaction of the BMG are 651.5 and 748 K, respectively. During the compression test, the BMGs undergo an engineering strain of about 2.5%, i.e., true strain of 2.8%, and then fracture. The BMGs deform via the formation and propagation of shear bands. Under indentation loading, the BMGs deform through the formation of radiation-like and circular shear bands. The circular shear bands form earlier than the radiation-like ones. The formation mechanism of shear bands in the BMGs was analyzed and discussed.
The Zr62.55Cu17.55Ni9.9Al10 bulk metallic glass (BMG) was prepared by using copper-mold suction-casting. X-ray diffraction and differential scanning calorimetry were utilized to determine its structure and thermal stability. Uniaxial compression and Rockwell indentation tests were adopted to study the plastic deformation behavior at room temperature. The results show that the glass transition temperature and the onset temperature of exothermic reaction of the BMG are 651.5 and 748 K, respectively. During the compression test, the BMGs undergo an engineering strain of about 2.5%, i.e., true strain of 2.8%, and then fracture. The BMGs deform via the formation and propagation of shear bands. Under indentation loading, the BMGs deform through the formation of radiation-like and circular shear bands. The circular shear bands form earlier than the radiation-like ones. The formation mechanism of shear bands in the BMGs was analyzed and discussed.
2010, vol. 17, no. 3, pp.
331-334.
https://doi.org/10.1007/s12613-010-0314-8
Abstract:
The bulk metallic glassy (BMG) rods of [(Fe0.5Co0.5)0.72B0.192Si0.048Nb0.04]100-xYx (x=0-6) and [(FexCo1-x)0.72B0.192Si0.048Nb0.04]96Y4 (x=0.5-0.8) were prepared by copper mold casting. The structure, thermal stability, and magnetic properties of the samples were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometer (VSM). Adding 1at% to 6at% of yttrium, the bulk glassy alloy rods of [(Fe0.5Co0.5)0.72B0.192Si0.048Nb0.04]100-xYx(x=0-6) with the diameter of 3 mm were not formed, and the sample with 4at% of yttrium showed less crystalline phase than others. When the Fe/Co atomic ratio was between 5:5 and 7:3, the bulk glassy alloy rods of [(Fe1-xCox)0.72B0.192Si0.048Nb0.04]96Y4 (x=0.5-0.8) with the diameter of 2 mm were fabricated. In the (Fe, Co)-B-Si-Nb-Y BMGs, when the Fe content increased, the thermal stability, the supercooled liquid region, and the glass-forming ability (GFA) decreased, but the saturation magnetization (Ms) increased.
The bulk metallic glassy (BMG) rods of [(Fe0.5Co0.5)0.72B0.192Si0.048Nb0.04]100-xYx (x=0-6) and [(FexCo1-x)0.72B0.192Si0.048Nb0.04]96Y4 (x=0.5-0.8) were prepared by copper mold casting. The structure, thermal stability, and magnetic properties of the samples were studied by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and vibrating sample magnetometer (VSM). Adding 1at% to 6at% of yttrium, the bulk glassy alloy rods of [(Fe0.5Co0.5)0.72B0.192Si0.048Nb0.04]100-xYx(x=0-6) with the diameter of 3 mm were not formed, and the sample with 4at% of yttrium showed less crystalline phase than others. When the Fe/Co atomic ratio was between 5:5 and 7:3, the bulk glassy alloy rods of [(Fe1-xCox)0.72B0.192Si0.048Nb0.04]96Y4 (x=0.5-0.8) with the diameter of 2 mm were fabricated. In the (Fe, Co)-B-Si-Nb-Y BMGs, when the Fe content increased, the thermal stability, the supercooled liquid region, and the glass-forming ability (GFA) decreased, but the saturation magnetization (Ms) increased.
2010, vol. 17, no. 3, pp.
335-339.
https://doi.org/10.1007/s12613-010-0315-7
Abstract:
Nanocrystalline single-phase alloys with the nominal compositions (at%) of Nd12.3-xDyxFe79.7Zr0.8Nb0.8Cu0.4B6.0 (x=0, 0.5, 1.5, and 2.5) were prepared by melt-spinning and subsequent annealing. X-ray diffraction analysis shows that the as-spun ribbons were mainly composed of the amorphous phase. A slight content of Dy stabilizes the amorphous phase during annealing treatment. The grain size becomes smaller and the coercivity of the annealed ribbon is gradually improved with the increase of Dy content. Excessive Dy is harmful to the remanence. It is found that no intergranular phase exists between the grains by high-resolution transmission electron microscopy, and the grain boundaries are crystallographically coherent in the optimally annealed sample. The optimum magnetic properties of remanence (Jr=1.09 T), coercivity (Hci=1048 kA/m), and maximum magnetic energy product ((BH)m=169.5 kJ/m3) are obtained from the x=0.5 ribbon in a post heat-treated state (700℃, 10 min).
Nanocrystalline single-phase alloys with the nominal compositions (at%) of Nd12.3-xDyxFe79.7Zr0.8Nb0.8Cu0.4B6.0 (x=0, 0.5, 1.5, and 2.5) were prepared by melt-spinning and subsequent annealing. X-ray diffraction analysis shows that the as-spun ribbons were mainly composed of the amorphous phase. A slight content of Dy stabilizes the amorphous phase during annealing treatment. The grain size becomes smaller and the coercivity of the annealed ribbon is gradually improved with the increase of Dy content. Excessive Dy is harmful to the remanence. It is found that no intergranular phase exists between the grains by high-resolution transmission electron microscopy, and the grain boundaries are crystallographically coherent in the optimally annealed sample. The optimum magnetic properties of remanence (Jr=1.09 T), coercivity (Hci=1048 kA/m), and maximum magnetic energy product ((BH)m=169.5 kJ/m3) are obtained from the x=0.5 ribbon in a post heat-treated state (700℃, 10 min).
2010, vol. 17, no. 3, pp.
340-346.
https://doi.org/10.1007/s12613-010-0316-6
Abstract:
MgO-modified Li0.06(Na0.5K0.5)0.94NbO3 (L6NKN) lead-free piezoelectric ceramics were synthesized by normal sintering at a relatively low temperature of 1000℃. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sinterability of the L6NKN ceramics. X-ray diffraction analysis indicates that the morphotropic phase boundary (MPB) separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content (x) from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant (d33=238 pC/N), planar electromechanical coupling coefficient (kp=41.5%), relative dielectric constant (εr=905), and remanent polarization (Pr=38.3 μC/cm2) are obtained from the specimen with x=0.5at%, which suggests that the Li0.06(Na0.5K0.5)0.94Nb(1-2x/5)MgxO3 (x=0.5at%) ceramic is a promising lead-free piezoelectric material.
MgO-modified Li0.06(Na0.5K0.5)0.94NbO3 (L6NKN) lead-free piezoelectric ceramics were synthesized by normal sintering at a relatively low temperature of 1000℃. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sinterability of the L6NKN ceramics. X-ray diffraction analysis indicates that the morphotropic phase boundary (MPB) separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content (x) from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant (d33=238 pC/N), planar electromechanical coupling coefficient (kp=41.5%), relative dielectric constant (εr=905), and remanent polarization (Pr=38.3 μC/cm2) are obtained from the specimen with x=0.5at%, which suggests that the Li0.06(Na0.5K0.5)0.94Nb(1-2x/5)MgxO3 (x=0.5at%) ceramic is a promising lead-free piezoelectric material.
2010, vol. 17, no. 3, pp.
347-352.
https://doi.org/10.1007/s12613-010-0317-5
Abstract:
A novel red long-lasting phosphor, (Y1-xGdx)2O3:Eu3+, Sm3+, Si4+, Mg2+, was synthesized by the co-precipitation method using oxalate precipitation as the precursor. X-ray diffraction (XRD), scanning electronic microscopy (SEM), integrated thermal analyzer (TG), and photoluminescence spectra (PL) as well as the ST-900PM weak light photometer were used to study the synthesis conditions, morphology, luminescence properties, and the decay time of the phosphor. The XRD results show that the products synthesized at 1400℃ for 4 h have good crystallization without any detectable impurity phases. Based on the PL spectra, the optimal conditions are as the following. The molar ratios of Y3+ to Gd3+ and Eu3+ to Sm3+ are 2:8 and 3:1, respectively, and the contents of Mg2+ and SiO2 are 5mol% and 3mol%, respectively. The decay time monitored by the ST-900PM weak light photometer is 7200 s, increasing 44% and 100%, respectively, compared with the Eu3+ and Sm3+ single-doped phosphors. The results indicate that the energy transfer is from Sm3+ to Eu3+ ion, and Sm3+ is a good sensitizer to Eu3+.
A novel red long-lasting phosphor, (Y1-xGdx)2O3:Eu3+, Sm3+, Si4+, Mg2+, was synthesized by the co-precipitation method using oxalate precipitation as the precursor. X-ray diffraction (XRD), scanning electronic microscopy (SEM), integrated thermal analyzer (TG), and photoluminescence spectra (PL) as well as the ST-900PM weak light photometer were used to study the synthesis conditions, morphology, luminescence properties, and the decay time of the phosphor. The XRD results show that the products synthesized at 1400℃ for 4 h have good crystallization without any detectable impurity phases. Based on the PL spectra, the optimal conditions are as the following. The molar ratios of Y3+ to Gd3+ and Eu3+ to Sm3+ are 2:8 and 3:1, respectively, and the contents of Mg2+ and SiO2 are 5mol% and 3mol%, respectively. The decay time monitored by the ST-900PM weak light photometer is 7200 s, increasing 44% and 100%, respectively, compared with the Eu3+ and Sm3+ single-doped phosphors. The results indicate that the energy transfer is from Sm3+ to Eu3+ ion, and Sm3+ is a good sensitizer to Eu3+.
2010, vol. 17, no. 3, pp.
353-362.
https://doi.org/10.1007/s12613-010-0318-4
Abstract:
The wear of cutting tools in the machining of 2024Al alloy composites reinforced with Al2O3 particles using varying sizes and volume fractions of particles up to 23.3vol% was investigated by a turning process using coated carbide tools K10 and TP30 at different cutting speeds. Machining tests were performed with a plan of experiments based on the Taguchi method. The tool life model was developed in terms of cutting speed, size, and volume fraction of particles by multiple linear regressions. The analysis of variance (ANOVA) was also employed to carry out the effects of these parameters on the cutting tool life. The test results show that the tool life decreases with the increase of cutting speed for both cutting tools K10 and TP30, and the tool life of the K10 tool is significantly longer than that of the TP30 tool. For the tool life, cutting speed is found to be the most effective factor followed by particle content and particle size, respectively. The predicted tool life of cutting tools is found to be in very good agreement with the experimentally observed ones.
The wear of cutting tools in the machining of 2024Al alloy composites reinforced with Al2O3 particles using varying sizes and volume fractions of particles up to 23.3vol% was investigated by a turning process using coated carbide tools K10 and TP30 at different cutting speeds. Machining tests were performed with a plan of experiments based on the Taguchi method. The tool life model was developed in terms of cutting speed, size, and volume fraction of particles by multiple linear regressions. The analysis of variance (ANOVA) was also employed to carry out the effects of these parameters on the cutting tool life. The test results show that the tool life decreases with the increase of cutting speed for both cutting tools K10 and TP30, and the tool life of the K10 tool is significantly longer than that of the TP30 tool. For the tool life, cutting speed is found to be the most effective factor followed by particle content and particle size, respectively. The predicted tool life of cutting tools is found to be in very good agreement with the experimentally observed ones.
2010, vol. 17, no. 3, pp.
363-370.
https://doi.org/10.1007/s12613-010-0319-3
Abstract:
The mechanical and physical properties of concrete specimens obtained from replacing natural coarse aggregate with waste vehicle rubber tires at levels of 2vol%, 5vol%, 7vol%, and 10vol% were studied, and the corrosion behavior of reinforcing steels was investigated in these specimens. Corrosion rates were determined by measuring the galvanic current between steel-reinforced concrete specimens both with and without chloride addition. The change in electrode potential of reinforcing steels in these concrete specimens was measured daily for a period of 60 d in accordance with the testing method in ASTM C876. The results show that the use of waste vehicle tires in concrete instead of coarse aggregate decreases the mechanical strength of the specimens, and increases the corrosion rates of the reinforcing steels embedded in the concretes.
The mechanical and physical properties of concrete specimens obtained from replacing natural coarse aggregate with waste vehicle rubber tires at levels of 2vol%, 5vol%, 7vol%, and 10vol% were studied, and the corrosion behavior of reinforcing steels was investigated in these specimens. Corrosion rates were determined by measuring the galvanic current between steel-reinforced concrete specimens both with and without chloride addition. The change in electrode potential of reinforcing steels in these concrete specimens was measured daily for a period of 60 d in accordance with the testing method in ASTM C876. The results show that the use of waste vehicle tires in concrete instead of coarse aggregate decreases the mechanical strength of the specimens, and increases the corrosion rates of the reinforcing steels embedded in the concretes.
2010, vol. 17, no. 3, pp.
371-375.
https://doi.org/10.1007/s12613-010-0320-x
Abstract:
A simple process to fabricate chain-like carbon nanotube (CNT) films by microwave plasma-enhanced chemical vapor deposition (MPCVD) was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were ground with Fe-doped SiO2 powder. The nano-structure of the deposited films was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The field electron emission characteristics of the chain-like carbon nanotube films were measured under the vacuum of 10-5 Pa. The low turn-on field of 0.80 V/μm and the emission current density of 8.5 mA/cm2 at the electric field of 3.0 V/μm are obtained. Based on the above results, chain-like carbon nanotube films probably have important applications in cold cathode materials and electrode materials.
A simple process to fabricate chain-like carbon nanotube (CNT) films by microwave plasma-enhanced chemical vapor deposition (MPCVD) was developed successfully. Prior to deposition, the Ti/Al2O3 substrates were ground with Fe-doped SiO2 powder. The nano-structure of the deposited films was analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman spectroscopy. The field electron emission characteristics of the chain-like carbon nanotube films were measured under the vacuum of 10-5 Pa. The low turn-on field of 0.80 V/μm and the emission current density of 8.5 mA/cm2 at the electric field of 3.0 V/μm are obtained. Based on the above results, chain-like carbon nanotube films probably have important applications in cold cathode materials and electrode materials.
2010, vol. 17, no. 3, pp.
376-379.
https://doi.org/10.1007/s12613-010-0321-9
Abstract:
Nano-scale γ-AlOOH with various morphologies, such as whisker, bar, ball, and sheet, was synthesized successfully and controllably through a facile hydrothermal method just by adjusting the pH value of the solvent. Based on the analysis of the experimental data, the growth mechanism of nano-scale γ-AlOOH in the hydrothermal process was established. It is proposed that the growth unit and the growth direction are determined by the pH value of the solution and the growth unit, respectively. One-dimensional γ-AlOOH, such as whisker and bar, is formed in lower pH ranges, while two-dimensional γ-AlOOH such as sheet is formed only in high pH environment following the plane expansion crystallization mechanism.
Nano-scale γ-AlOOH with various morphologies, such as whisker, bar, ball, and sheet, was synthesized successfully and controllably through a facile hydrothermal method just by adjusting the pH value of the solvent. Based on the analysis of the experimental data, the growth mechanism of nano-scale γ-AlOOH in the hydrothermal process was established. It is proposed that the growth unit and the growth direction are determined by the pH value of the solution and the growth unit, respectively. One-dimensional γ-AlOOH, such as whisker and bar, is formed in lower pH ranges, while two-dimensional γ-AlOOH such as sheet is formed only in high pH environment following the plane expansion crystallization mechanism.
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