Search2016 Vol. 23, No. 8
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2016, vol. 23, no. 8, pp.
859-867.
https://doi.org/10.1007/s12613-016-1301-5
Abstract:
The possibility of using a centrifugal-gravity concentrator to reject Mg-bearing minerals and minimize metal losses in the flotation of base metals was evaluated. Sample characterization, batch scoping tests, pilot-scale tests, and regrind-flotation tests were conducted on a Ni flotation tailings stream. Batch tests revealed that the Mg grade decreased dramatically in the concentrate products. Pilot-scale testing of a continuous centrifugal concentrator (Knelson CVD6) on the flotation tailings revealed that a concentrate with a low mass yield, low Mg content, and high Ni upgrade ratio could be achieved. Under optimum conditions, a concentrate at 6.7% mass yield was obtained with 0.85% Ni grade at 12.9% Ni recovery and with a low Mg distribution (1.7%). Size partition curves demonstrated that the CVD also operated as a size classifier, enhancing the rejection of talc fines. Overall, the CVD was capable of rejecting Mg-bearing minerals. Moreover, an opportunity exists for the novel use of centrifugal-gravity concentration for scavenging flotation tailings and/or after comminution to minimize amount of Mg-bearing minerals reporting to flotation.
The possibility of using a centrifugal-gravity concentrator to reject Mg-bearing minerals and minimize metal losses in the flotation of base metals was evaluated. Sample characterization, batch scoping tests, pilot-scale tests, and regrind-flotation tests were conducted on a Ni flotation tailings stream. Batch tests revealed that the Mg grade decreased dramatically in the concentrate products. Pilot-scale testing of a continuous centrifugal concentrator (Knelson CVD6) on the flotation tailings revealed that a concentrate with a low mass yield, low Mg content, and high Ni upgrade ratio could be achieved. Under optimum conditions, a concentrate at 6.7% mass yield was obtained with 0.85% Ni grade at 12.9% Ni recovery and with a low Mg distribution (1.7%). Size partition curves demonstrated that the CVD also operated as a size classifier, enhancing the rejection of talc fines. Overall, the CVD was capable of rejecting Mg-bearing minerals. Moreover, an opportunity exists for the novel use of centrifugal-gravity concentration for scavenging flotation tailings and/or after comminution to minimize amount of Mg-bearing minerals reporting to flotation.
2016, vol. 23, no. 8, pp.
868-880.
https://doi.org/10.1007/s12613-016-1302-4
Abstract:
The effects of MgO and TiO2 on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared (FTIR) spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO2 content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO2 contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia–alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO2 content.
The effects of MgO and TiO2 on the viscosity, activation energy for viscous flow, and break-point temperature of titanium-bearing slag were studied. The correlation between viscosity and slag structure was analyzed by Fourier transform infrared (FTIR) spectroscopy. Subsequently, main phases in the slag and their content changes were investigated by X-ray diffraction and Factsage 6.4 software package. The results show that the viscosity decreases when the MgO content increases from 10.00wt% to 14.00wt%. Moreover, the break-point temperature increases, and the activation energy for viscous flow initially increases and subsequently decreases. In addition, with increasing TiO2 content from 5.00wt% to 9.00wt%, the viscosity decreases, and the break-point temperature and activation energy for viscous flow initially decrease and subsequently increase. FTIR analyses reveal that the polymerization degree of complex viscous units in titanium-bearing slag decreases with increasing MgO and TiO2 contents. The mechanism of viscosity variation was elucidated. The basic phase in experimental slags is melilite. Besides, as the MgO content increases, the amount of magnesia–alumina spinel in the slag increases. Similarly, the sum of pyroxene and perovskite phases in the slag increases with increasing TiO2 content.
2016, vol. 23, no. 8, pp.
881-890.
https://doi.org/10.1007/s12613-016-1303-3
Abstract:
A high-temperature reduction and smelting process was used to recover iron and calcium aluminate slag from high-ferrous bauxite. The effects of w(CaO)/w(SiO2) ratio, anthracite ratio, and reduction temperature and time on the recovery and size of iron nuggets and on the Al2O3 grade of the calcium aluminate slag were investigated through thermodynamic calculations and experiments. The optimized process conditions were the bauxite/anthracite/slaked lime weight ratio of 100:16.17:59.37, reduction temperature of 1450°C and reduction time of 20 min. Under these conditions, high-quality iron nuggets and calcium aluminate slag were obtained. The largest size and the highest recovery rate of iron nuggets were 11.42 mm and 92.79wt%, respectively. The calcium aluminate slag mainly comprised Ca2SiO4 and Ca12Al14O33, with small amounts of FeAl2O4, CaAl2O4, and Ca2Al2SiO7.
A high-temperature reduction and smelting process was used to recover iron and calcium aluminate slag from high-ferrous bauxite. The effects of w(CaO)/w(SiO2) ratio, anthracite ratio, and reduction temperature and time on the recovery and size of iron nuggets and on the Al2O3 grade of the calcium aluminate slag were investigated through thermodynamic calculations and experiments. The optimized process conditions were the bauxite/anthracite/slaked lime weight ratio of 100:16.17:59.37, reduction temperature of 1450°C and reduction time of 20 min. Under these conditions, high-quality iron nuggets and calcium aluminate slag were obtained. The largest size and the highest recovery rate of iron nuggets were 11.42 mm and 92.79wt%, respectively. The calcium aluminate slag mainly comprised Ca2SiO4 and Ca12Al14O33, with small amounts of FeAl2O4, CaAl2O4, and Ca2Al2SiO7.
2016, vol. 23, no. 8, pp.
891-897.
https://doi.org/10.1007/s12613-016-1304-2
Abstract:
The present study was conducted to elucidate the influence of impurities in waste ferrous sulfate on its recovery of magnetite. Ferrous sulfate solution was purified by the addition of NaOH solution to precipitate impurities, and magnetite was recovered from ferrous sulfate solution without and with purification pretreatment. Calcium hydroxide was added to the solution of ferrous sulfate as a precipitator. A mixed product of magnetite and gypsum was subsequently obtained by air oxidation and heating. Wet-milling was performed prior to magnetic separation to recover magnetite from the mixed products. The results show that with the purification pretreatment, the grade of iron in magnetite concentrate increased from 62.05% to 65.58% and the recovery rate of iron decreased from 85.35% to 80.35%. The purification pretreatment reduced the conglutination between magnetite and gypsum, which favors their subsequent magnetic separation. In summary, a higher-grade magnetite with a better crystallinity and a larger particle size of 2.35 μm was obtained with the purification pretreatment.
The present study was conducted to elucidate the influence of impurities in waste ferrous sulfate on its recovery of magnetite. Ferrous sulfate solution was purified by the addition of NaOH solution to precipitate impurities, and magnetite was recovered from ferrous sulfate solution without and with purification pretreatment. Calcium hydroxide was added to the solution of ferrous sulfate as a precipitator. A mixed product of magnetite and gypsum was subsequently obtained by air oxidation and heating. Wet-milling was performed prior to magnetic separation to recover magnetite from the mixed products. The results show that with the purification pretreatment, the grade of iron in magnetite concentrate increased from 62.05% to 65.58% and the recovery rate of iron decreased from 85.35% to 80.35%. The purification pretreatment reduced the conglutination between magnetite and gypsum, which favors their subsequent magnetic separation. In summary, a higher-grade magnetite with a better crystallinity and a larger particle size of 2.35 μm was obtained with the purification pretreatment.
2016, vol. 23, no. 8, pp.
898-905.
https://doi.org/10.1007/s12613-016-1305-1
Abstract:
The water leaching process of vanadium, sodium, and silicon from molten vanadium-titanium-bearing (V-Ti-bearing) slag obtained from low-grade vanadium-bearing titanomagnetite was investigated systematically. The results show that calcium titanate, sodium aluminosilicate, sodium oxide, silicon dioxide and sodium vanadate are the major components of the molten V-Ti-bearing slag. The experimental results indicate that the liquid-solid (L/S) mass ratio significantly affects the leaching process because of the respective solubilities and diffusion rates of the components. A total of 83.8% of vanadium, 72.8% of sodium, and 16.1% of silicon can be leached out via a triple counter-current leaching process under the optimal conditions of a particle size below 0.074 mm, a temperature of 90°C, a leaching time of 20 min, an L/S mass ratio of 4:1, and a stirring speed of 300 r/min. The kinetics of vanadium leaching is well described by an internal diffusion-controlled model and the apparent activation energy is 11.1 kJ/mol. The leaching mechanism of vanadium was also analyzed.
The water leaching process of vanadium, sodium, and silicon from molten vanadium-titanium-bearing (V-Ti-bearing) slag obtained from low-grade vanadium-bearing titanomagnetite was investigated systematically. The results show that calcium titanate, sodium aluminosilicate, sodium oxide, silicon dioxide and sodium vanadate are the major components of the molten V-Ti-bearing slag. The experimental results indicate that the liquid-solid (L/S) mass ratio significantly affects the leaching process because of the respective solubilities and diffusion rates of the components. A total of 83.8% of vanadium, 72.8% of sodium, and 16.1% of silicon can be leached out via a triple counter-current leaching process under the optimal conditions of a particle size below 0.074 mm, a temperature of 90°C, a leaching time of 20 min, an L/S mass ratio of 4:1, and a stirring speed of 300 r/min. The kinetics of vanadium leaching is well described by an internal diffusion-controlled model and the apparent activation energy is 11.1 kJ/mol. The leaching mechanism of vanadium was also analyzed.
2016, vol. 23, no. 8, pp.
906-919.
https://doi.org/10.1007/s12613-016-1306-0
Abstract:
In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.
In this work, low-carbon steel specimens were subjected to the quenching and partitioning process after being partially or fully austenitized to investigate their microstructural evolution and mechanical properties. According to the results of scanning electron microscopy and transmission electron microscopy observations, X-ray diffraction analysis, and tensile tests, upper bainite or tempered martensite appears successively in the microstructure with increasing austenitization temperature or increasing partitioning time. In the partially austenitized specimens, the retained austenite grains are carbon-enriched twice during the heat treatment, which can significantly stabilize the phases at room temperature. Furthermore, after partial austenitization, the specimen exhibits excellent elongation, with a maximum elongation of 37.1%. By contrast, after full austenitization, the specimens exhibit good ultimate tensile strength and high yield strength. In the case of a specimen with a yield strength of 969 MPa, the maximum value of the ultimate tensile strength reaches 1222 MPa. During the partitioning process, carbon partitioning and carbon homogenization within austenite affect interface migration. In addition, the volume fraction and grain size of retained austenite observed in the final microstructure will also be affected.
2016, vol. 23, no. 8, pp.
920-927.
https://doi.org/10.1007/s12613-016-1307-z
Abstract:
In the present study, pure iron/copper composite metal cladding was deposited onto carbon steel by tungsten inert gas welding. The study focused on interfacial morphological, microstructural, and mechanical analyses of the composite cladding layers. Iron liquid–solid-phase zones were formed at copper/steel and iron interfaces because of the melting of the steel substrate and iron. Iron concentrated in the copper cladding layer was observed to exhibit belt, globule, and dendrite morphologies. The appearance of iron-rich globules indicated the occurrence of liquid phase separation (LPS) prior to solidification, and iron-rich dendrites crystallized without the occurrence of LPS. The maximum microhardness of the iron/steel interface was lower than that of the copper/steel interface because of the diffusion of elemental carbon. All samples fractured in the cladding layers. Because of a relatively lower strength of the copper layer, a short plateau region appeared when shear movement was from copper to iron.
In the present study, pure iron/copper composite metal cladding was deposited onto carbon steel by tungsten inert gas welding. The study focused on interfacial morphological, microstructural, and mechanical analyses of the composite cladding layers. Iron liquid–solid-phase zones were formed at copper/steel and iron interfaces because of the melting of the steel substrate and iron. Iron concentrated in the copper cladding layer was observed to exhibit belt, globule, and dendrite morphologies. The appearance of iron-rich globules indicated the occurrence of liquid phase separation (LPS) prior to solidification, and iron-rich dendrites crystallized without the occurrence of LPS. The maximum microhardness of the iron/steel interface was lower than that of the copper/steel interface because of the diffusion of elemental carbon. All samples fractured in the cladding layers. Because of a relatively lower strength of the copper layer, a short plateau region appeared when shear movement was from copper to iron.
2016, vol. 23, no. 8, pp.
928-933.
https://doi.org/10.1007/s12613-016-1308-y
Abstract:
In the paper, a melt extraction method was used to fabricate Cu–4Ni–14Al (wt%) fiber materials with diameters between 50 and 200 μm. The fibers exhibited superelasticity and temperature-induced martensitic transformation. The microstructures and superelasticity behavior of the fibers were studied via scanning electron microscopy (SEM) and a dynamic mechanical analyzer (DMA), respectively. Appropriate heat treatment further improves the plasticity of Cu-based alloys. The serration behavior observed during the loading process is due to the multiple martensite phase transformation.
In the paper, a melt extraction method was used to fabricate Cu–4Ni–14Al (wt%) fiber materials with diameters between 50 and 200 μm. The fibers exhibited superelasticity and temperature-induced martensitic transformation. The microstructures and superelasticity behavior of the fibers were studied via scanning electron microscopy (SEM) and a dynamic mechanical analyzer (DMA), respectively. Appropriate heat treatment further improves the plasticity of Cu-based alloys. The serration behavior observed during the loading process is due to the multiple martensite phase transformation.
2016, vol. 23, no. 8, pp.
934-942.
https://doi.org/10.1007/s12613-016-1309-x
Abstract:
In the present study, bond-coats for thermal barrier coatings were deposited via air plasma spraying (APS) techniques onto Inconel 800 and Hastelloy C-276 alloy substrates. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to investigate the phases and microstructure of the as-sprayed, APS-deposited CoNiCrAlY bond-coatings. The aim of this work was to study the suitability of the bond-coat materials for high temperature applications. Confirmation of nanoscale grains of the γ/γ′-phase was obtained by TEM, high-resolution TEM, and AFM. We concluded that these changes result from the plastic deformation of the bond-coat during the deposition, resulting in CoNiCrAlY bond-coatings with excellent thermal cyclic resistance suitable for use in high-temperature applications. Cyclic oxidative stability was observed to also depend on the underlying metallic alloy substrate.
In the present study, bond-coats for thermal barrier coatings were deposited via air plasma spraying (APS) techniques onto Inconel 800 and Hastelloy C-276 alloy substrates. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and atomic force microscopy (AFM) were used to investigate the phases and microstructure of the as-sprayed, APS-deposited CoNiCrAlY bond-coatings. The aim of this work was to study the suitability of the bond-coat materials for high temperature applications. Confirmation of nanoscale grains of the γ/γ′-phase was obtained by TEM, high-resolution TEM, and AFM. We concluded that these changes result from the plastic deformation of the bond-coat during the deposition, resulting in CoNiCrAlY bond-coatings with excellent thermal cyclic resistance suitable for use in high-temperature applications. Cyclic oxidative stability was observed to also depend on the underlying metallic alloy substrate.
2016, vol. 23, no. 8, pp.
943-948.
https://doi.org/10.1007/s12613-016-1310-4
Abstract:
C–Mn steels prepared by annealing at 800°C for 120 s and overaging at 250–400°C were subjected to pre-straining (2%) and baking treatments (170°C for 20 min) to measure their bake-hardening (BH2) values. The effects of overaging temperature on the microstructure, mechanical properties, and BH2 behavior of 600 MPa cold-rolled dual-phase (DP) steel were investigated by optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that the martensite morphology exhibited less variation when the DP steel was overaged at 250–350°C. However, when the DP steel was overaged at 400°C, numerous non-martensite and carbide particles formed and yield-point elongation was observed in the tensile curve. When the overaging temperature was increased from 250 to 400°C, the yield strength increased from 272 to 317 MPa, the tensile strength decreased from 643 to 574 MPa, and the elongation increased from 27.8% to 30.6%. Furthermore, with an increase in overaging temperature from 250 to 400°C, the BH2 value initially increases and then decreases. The maximum BH2 value of 83 MPa was observed for the specimen overaged at 350°C.
C–Mn steels prepared by annealing at 800°C for 120 s and overaging at 250–400°C were subjected to pre-straining (2%) and baking treatments (170°C for 20 min) to measure their bake-hardening (BH2) values. The effects of overaging temperature on the microstructure, mechanical properties, and BH2 behavior of 600 MPa cold-rolled dual-phase (DP) steel were investigated by optical microscopy, scanning electron microscopy, and tensile tests. The results indicated that the martensite morphology exhibited less variation when the DP steel was overaged at 250–350°C. However, when the DP steel was overaged at 400°C, numerous non-martensite and carbide particles formed and yield-point elongation was observed in the tensile curve. When the overaging temperature was increased from 250 to 400°C, the yield strength increased from 272 to 317 MPa, the tensile strength decreased from 643 to 574 MPa, and the elongation increased from 27.8% to 30.6%. Furthermore, with an increase in overaging temperature from 250 to 400°C, the BH2 value initially increases and then decreases. The maximum BH2 value of 83 MPa was observed for the specimen overaged at 350°C.
2016, vol. 23, no. 8, pp.
949-958.
https://doi.org/10.1007/s12613-016-1311-3
Abstract:
The mechanical properties and constitutive behaviors of as-cast AA7050 in both the solid and semi-solid states were determined using the on-cooling and in situ solidification approaches, respectively. The results show that the strength in the solid state tends to increase with decreasing temperature. The strain rate plays an important role in the stress–strain behaviors at higher temperatures, whereas the influence becomes less pronounced and irregular when the temperature is less than 250°C. The experimental data were fitted to the extended Ludwik equation, which is suitable to describe the mechanical behavior of the materials in the as-cast state. In the semi-solid state, both the strength and ductility of the alloy are high near the solidus temperature and decrease drastically with decreasing solid fraction. As the solid fraction is less than 0.97, the maximum strength only slightly decreases, whereas the post-peak ductility begins to increase. The experimental data were fitted to the modified creep law, which is used to describe the mechanical behavior of semi-solid materials, to determine the equivalent parameter fGBWL, i.e., the fraction of grain boundaries covered by liquid phase.
The mechanical properties and constitutive behaviors of as-cast AA7050 in both the solid and semi-solid states were determined using the on-cooling and in situ solidification approaches, respectively. The results show that the strength in the solid state tends to increase with decreasing temperature. The strain rate plays an important role in the stress–strain behaviors at higher temperatures, whereas the influence becomes less pronounced and irregular when the temperature is less than 250°C. The experimental data were fitted to the extended Ludwik equation, which is suitable to describe the mechanical behavior of the materials in the as-cast state. In the semi-solid state, both the strength and ductility of the alloy are high near the solidus temperature and decrease drastically with decreasing solid fraction. As the solid fraction is less than 0.97, the maximum strength only slightly decreases, whereas the post-peak ductility begins to increase. The experimental data were fitted to the modified creep law, which is used to describe the mechanical behavior of semi-solid materials, to determine the equivalent parameter fGBWL, i.e., the fraction of grain boundaries covered by liquid phase.
2016, vol. 23, no. 8, pp.
959-965.
https://doi.org/10.1007/s12613-016-1312-2
Abstract:
To explore the reaction behavior of trace oxygen during the flash combustion process of falling FeSi75 powder in a nitrogen flow, a flash-combustion-synthesized Fe-Si3N4 sample was heat-treated to remove SiO2. The samples before and after the treatment were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, and the formation mechanism of SiO2 was investigated. The results show that SiO2 in the Fe-Si3N4 is mainly located on the surface or around the Si3N4 particles in dense areas, existing in both crystalline and amorphous states; when the FeSi75 particles, which are less than 0.074 mm in size, fell in up-flowing hot N2 stream, trace oxygen in the N2 stream did not significantly hinder the nitridation of FeSi75 particles as it was consumed by the surface oxidation of the generated Si3N4 particles to form SiO2. At the reaction zone, the oxidation of Si3N4 particles decreased the oxygen partial pressure in the N2 stream and greatly reduced the opportunity for FeSi75 particles to be oxidized into SiO2; by virtue of the SiO2 film developed on the surface, the Si3N4 particles adhered to each other and formed dense areas in the material.
To explore the reaction behavior of trace oxygen during the flash combustion process of falling FeSi75 powder in a nitrogen flow, a flash-combustion-synthesized Fe-Si3N4 sample was heat-treated to remove SiO2. The samples before and after the treatment were investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, and the formation mechanism of SiO2 was investigated. The results show that SiO2 in the Fe-Si3N4 is mainly located on the surface or around the Si3N4 particles in dense areas, existing in both crystalline and amorphous states; when the FeSi75 particles, which are less than 0.074 mm in size, fell in up-flowing hot N2 stream, trace oxygen in the N2 stream did not significantly hinder the nitridation of FeSi75 particles as it was consumed by the surface oxidation of the generated Si3N4 particles to form SiO2. At the reaction zone, the oxidation of Si3N4 particles decreased the oxygen partial pressure in the N2 stream and greatly reduced the opportunity for FeSi75 particles to be oxidized into SiO2; by virtue of the SiO2 film developed on the surface, the Si3N4 particles adhered to each other and formed dense areas in the material.
2016, vol. 23, no. 8, pp.
966-975.
https://doi.org/10.1007/s12613-016-1313-1
Abstract:
A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na2CO3 and was followed by leaching using NaOH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows: an Na2CO3-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO2 was 98.13%. The optimized carbonation conditions included a final solution pH value of 9.0, a temperature of 40°C, a CO2 flow rate of 6 mL/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1:9. The precipitation rate and granularity of the SiO2 particles were 99.63% and 200 nm, respectively. We confirmed the quality of the obtained ultrafine silica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.
A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na2CO3 and was followed by leaching using NaOH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows: an Na2CO3-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO2 was 98.13%. The optimized carbonation conditions included a final solution pH value of 9.0, a temperature of 40°C, a CO2 flow rate of 6 mL/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1:9. The precipitation rate and granularity of the SiO2 particles were 99.63% and 200 nm, respectively. We confirmed the quality of the obtained ultrafine silica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.
2016, vol. 23, no. 8, pp.
976-980.
https://doi.org/10.1007/s12613-016-1314-0
Abstract:
Moolooite particles with flaky morphology were synthesized by mixing dilute solutions of copper nitrate and sodium oxalate in the presence of citric acid. Solution pH value, citric acid concentration, and stirring were found to have large effect on the shape of the precipitated particles. Under the stirring, the radial area of flaky moolooite particles was enlarged and extended to become a thinner and larger flake. This is ascribed to growth promotion caused by the selective absorption of citric ligands onto a particular crystalline surface of the moolooite particles. Flaky shape of the moolooite particles tended to become spherical and disappeared completely when decomposed under an Ar atmosphere, leading to the formation of large porous aggregated particles composed of many tiny nanosized copper crystals.
Moolooite particles with flaky morphology were synthesized by mixing dilute solutions of copper nitrate and sodium oxalate in the presence of citric acid. Solution pH value, citric acid concentration, and stirring were found to have large effect on the shape of the precipitated particles. Under the stirring, the radial area of flaky moolooite particles was enlarged and extended to become a thinner and larger flake. This is ascribed to growth promotion caused by the selective absorption of citric ligands onto a particular crystalline surface of the moolooite particles. Flaky shape of the moolooite particles tended to become spherical and disappeared completely when decomposed under an Ar atmosphere, leading to the formation of large porous aggregated particles composed of many tiny nanosized copper crystals.
2016, vol. 23, no. 8, pp.
981-990.
https://doi.org/10.1007/s12613-016-1315-z
Abstract:
A new method was applied to produce an Al-0.5wt%Ti-0.3wt%Zr/5vol%B4C composite via stir casting with the aim of characterizing the microstructure of the resulting composite. For the production of the composite, large B4C particles (larger than 75 μm) with no pre-heating were added to the stirred melt. Reflected-light microscopy, X-ray diffraction, scanning electron microscopy, field-emission scanning electron microscopy, laser particle size analysis, and image analysis using the Clemex software were performed on the cast samples for microstructural analysis and phase detection. The results revealed that as a consequence of thermal shock, B4C particle breakage occurred in the melt. The mechanism proposed for this phenomenon is that the exerted thermal shock in combination with the low thermal shock resistance of B4C and large size of the added B4C particles were the three key parameters responsible for B4C particle breakage. This breakage introduced small particles with sizes less than 10 μm and with no contamination on their surfaces into the melt. The mean particle distance measured via image analysis was approximately 60 μm. The coefficient of variation index, which was used as a measure of particle distribution homogeneity, showed some variations, indicating a relatively homogeneous distribution.
A new method was applied to produce an Al-0.5wt%Ti-0.3wt%Zr/5vol%B4C composite via stir casting with the aim of characterizing the microstructure of the resulting composite. For the production of the composite, large B4C particles (larger than 75 μm) with no pre-heating were added to the stirred melt. Reflected-light microscopy, X-ray diffraction, scanning electron microscopy, field-emission scanning electron microscopy, laser particle size analysis, and image analysis using the Clemex software were performed on the cast samples for microstructural analysis and phase detection. The results revealed that as a consequence of thermal shock, B4C particle breakage occurred in the melt. The mechanism proposed for this phenomenon is that the exerted thermal shock in combination with the low thermal shock resistance of B4C and large size of the added B4C particles were the three key parameters responsible for B4C particle breakage. This breakage introduced small particles with sizes less than 10 μm and with no contamination on their surfaces into the melt. The mean particle distance measured via image analysis was approximately 60 μm. The coefficient of variation index, which was used as a measure of particle distribution homogeneity, showed some variations, indicating a relatively homogeneous distribution.
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