Search2022 Vol. 29, No. 12
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2022, vol. 29, no. 12, pp.
2087-2105.
https://doi.org/10.1007/s12613-021-2408-x
Abstract:
The application of coal-based reduction in the efficient recovery of iron from refractory iron-bearing resources is comprehensively reviewed. Currently, the development and beneficiation of refractory iron-bearing resources have attracted increasing attention. However, the effect of iron recovery by traditional beneficiation methods is unacceptable. Coal-based reduction followed by magnetic separation is proposed, which adopts coal as the reductant to reduce iron oxides to metallic iron below the melting temperature. The metallic iron particles aggregate and grow, and the particle size continuously increases to be suitable for magnetic separation. The optimization and application of coal-based reduction have been abundantly researched. A detailed literature study on coal-based reduction is performed from the perspectives of thermodynamics, reduction kinetics, growth of metallic iron particles, additives, and application. The coal-based reduction industrial equipment can be developed based on the existing pyrometallurgical equipments, rotary hearth furnace and rotary kiln, which are introduced briefly. However, coal-based reduction currently mainly adopts coal as a reductant and fuel, which may result in high levels of carbon dioxide emissions, energy consumption, and pollution. Technological innovation aiming at decreasing carbon dioxide emissions is a new trend of green and sustainable development of the steel industry. Therefore, the substitution of coal with clean energy (hydrogen, biomass, etc.) for iron oxide reduction shows promise in the future.
The application of coal-based reduction in the efficient recovery of iron from refractory iron-bearing resources is comprehensively reviewed. Currently, the development and beneficiation of refractory iron-bearing resources have attracted increasing attention. However, the effect of iron recovery by traditional beneficiation methods is unacceptable. Coal-based reduction followed by magnetic separation is proposed, which adopts coal as the reductant to reduce iron oxides to metallic iron below the melting temperature. The metallic iron particles aggregate and grow, and the particle size continuously increases to be suitable for magnetic separation. The optimization and application of coal-based reduction have been abundantly researched. A detailed literature study on coal-based reduction is performed from the perspectives of thermodynamics, reduction kinetics, growth of metallic iron particles, additives, and application. The coal-based reduction industrial equipment can be developed based on the existing pyrometallurgical equipments, rotary hearth furnace and rotary kiln, which are introduced briefly. However, coal-based reduction currently mainly adopts coal as a reductant and fuel, which may result in high levels of carbon dioxide emissions, energy consumption, and pollution. Technological innovation aiming at decreasing carbon dioxide emissions is a new trend of green and sustainable development of the steel industry. Therefore, the substitution of coal with clean energy (hydrogen, biomass, etc.) for iron oxide reduction shows promise in the future.
2022, vol. 29, no. 12, pp.
2106-2116.
https://doi.org/10.1007/s12613-022-2538-9
Abstract:
Industrial solid waste (ISW)–cement blends have the advantages of low carbon, low energy consumption, and low pollution, but their clinker replacement level in low carbon cement is generally low. To address this challenge, this study considers the latest progress and development trends in the ISW–cement blend research, focusing on the activation of ISWs, the formation of ISW–cement blends, and their associated hydration mechanisms. After the mechanical activation of ISWs, the D50 (average size) typically drops below 10 µm, and the specific surface area increases above 350 m2/kg. Thermal activation can increase the glassy-phase content and reactivity of ISWs, where the coal gangue activation temperature is usually set at 400–1000°C. Furthermore, the roles of ISWs in the hydration of ISW–cement blends are divided into physical and chemical roles. The physical action of ISWs usually acts in the early stage of the hydration of ISW–cement blends. Subsequently, ISWs participate in the hydration reaction of ISW–cement blends to generate products, such as C–(A)–S–H gels. Moreover, alkali activation affects the hydration kinetics of ISW–cement blends and modifies the proportion of gels. Environmental impacts and costs of ISW–cement blends have also been discussed to guide stakeholders in selecting sustainable ISWs.
Industrial solid waste (ISW)–cement blends have the advantages of low carbon, low energy consumption, and low pollution, but their clinker replacement level in low carbon cement is generally low. To address this challenge, this study considers the latest progress and development trends in the ISW–cement blend research, focusing on the activation of ISWs, the formation of ISW–cement blends, and their associated hydration mechanisms. After the mechanical activation of ISWs, the D50 (average size) typically drops below 10 µm, and the specific surface area increases above 350 m2/kg. Thermal activation can increase the glassy-phase content and reactivity of ISWs, where the coal gangue activation temperature is usually set at 400–1000°C. Furthermore, the roles of ISWs in the hydration of ISW–cement blends are divided into physical and chemical roles. The physical action of ISWs usually acts in the early stage of the hydration of ISW–cement blends. Subsequently, ISWs participate in the hydration reaction of ISW–cement blends to generate products, such as C–(A)–S–H gels. Moreover, alkali activation affects the hydration kinetics of ISW–cement blends and modifies the proportion of gels. Environmental impacts and costs of ISW–cement blends have also been discussed to guide stakeholders in selecting sustainable ISWs.
2022, vol. 29, no. 12, pp.
2117-2125.
https://doi.org/10.1007/s12613-021-2381-4
Abstract:
For deep rock mechanics and subsurface engineering, accurately characterizing and evaluating rock heterogeneity as well as analyzing the correlation between the heterogeneity and physical and mechanical properties of rocks are critical. This study investigated the characteristics of acoustic emission signals produced in the process of strong and weak phase damage to rocks. The failure mechanisms of the strong and weak phases were analyzed by performing Brazilian splitting tests on different metagabbros and granites. The strong–weak phase ratio of the rocks and the uniformity of their spatial distribution were characterized. Test results show that as the feldspar develops, the strong-phase ratio of the metagabbro increases. However, the spatial distribution of feldspar minerals in the metagabbro becomes less uniform. The mineral spatial distribution uniformity in the altered granite is good; however, its strong-phase ratio is low. Furthermore, the strong-phase ratio of the typical granite is high; however, its mineral spatial distribution uniformity is poor. Moreover, uniaxial and triaxial test results show that the peak strength and elastic modulus of the rocks are related to the strong–weak phase ratio and mineral spatial distribution uniformity of the rocks. This study provides a new analytical method for the mechanical evaluation of deep rocks.
For deep rock mechanics and subsurface engineering, accurately characterizing and evaluating rock heterogeneity as well as analyzing the correlation between the heterogeneity and physical and mechanical properties of rocks are critical. This study investigated the characteristics of acoustic emission signals produced in the process of strong and weak phase damage to rocks. The failure mechanisms of the strong and weak phases were analyzed by performing Brazilian splitting tests on different metagabbros and granites. The strong–weak phase ratio of the rocks and the uniformity of their spatial distribution were characterized. Test results show that as the feldspar develops, the strong-phase ratio of the metagabbro increases. However, the spatial distribution of feldspar minerals in the metagabbro becomes less uniform. The mineral spatial distribution uniformity in the altered granite is good; however, its strong-phase ratio is low. Furthermore, the strong-phase ratio of the typical granite is high; however, its mineral spatial distribution uniformity is poor. Moreover, uniaxial and triaxial test results show that the peak strength and elastic modulus of the rocks are related to the strong–weak phase ratio and mineral spatial distribution uniformity of the rocks. This study provides a new analytical method for the mechanical evaluation of deep rocks.
2022, vol. 29, no. 12, pp.
2126-2135.
https://doi.org/10.1007/s12613-021-2402-3
Abstract:
Efficient thickening of tailings is a prerequisite for the metal mine tailings backfill and surface disposal operation. The effective collision of ultrafine tailings particles in suspension with flocculant molecules is essential for flocs aggregates formation and settling. Unreasonable feeding speed and flocculant adding method will lead to the failure of effective dispersion of flocculant and high particle content in thickener overflow. In this work, the effect of turbulence intensity and flocculant adding method on floc size, strength, and movement characteristics are analysed. Aiming to solve the turbidity increased, a pilot-scale continuous thickening test was carried out. Taking a single particle and multiple flocs of full tailings as the research object, the particle iterative settlement model of flocs was established. The influence of turbulence intensity on collision effect is studied by tracking and simulating particle trajectory. The results show that in the process of single particle settlement, chaos appears in the iterative process owing to particle adhesion which caused by micro action. When the turbulence intensity is 25.99%, the maximum particle size of tailings floc is 6.21 mm and the maximum sedimentation rate is 5.284 cm·s−1. The tailings floc presents a multi-scale structure of particle-force chain system when hindered settling, and the interweaving of strong and weak force chains constitutes the topological structure of particles. The results are applied to a thicker in plant, the flocculant addition mode and feed rate are optimized, and the flocs settling speed and overflow clarity are improved.
Efficient thickening of tailings is a prerequisite for the metal mine tailings backfill and surface disposal operation. The effective collision of ultrafine tailings particles in suspension with flocculant molecules is essential for flocs aggregates formation and settling. Unreasonable feeding speed and flocculant adding method will lead to the failure of effective dispersion of flocculant and high particle content in thickener overflow. In this work, the effect of turbulence intensity and flocculant adding method on floc size, strength, and movement characteristics are analysed. Aiming to solve the turbidity increased, a pilot-scale continuous thickening test was carried out. Taking a single particle and multiple flocs of full tailings as the research object, the particle iterative settlement model of flocs was established. The influence of turbulence intensity on collision effect is studied by tracking and simulating particle trajectory. The results show that in the process of single particle settlement, chaos appears in the iterative process owing to particle adhesion which caused by micro action. When the turbulence intensity is 25.99%, the maximum particle size of tailings floc is 6.21 mm and the maximum sedimentation rate is 5.284 cm·s−1. The tailings floc presents a multi-scale structure of particle-force chain system when hindered settling, and the interweaving of strong and weak force chains constitutes the topological structure of particles. The results are applied to a thicker in plant, the flocculant addition mode and feed rate are optimized, and the flocs settling speed and overflow clarity are improved.
2022, vol. 29, no. 12, pp.
2136-2143.
https://doi.org/10.1007/s12613-021-2392-1
Abstract:
Effects of residues produced by agricultural wastes fermentation (AWF) on low grade copper sulfide ores bioleaching, copper recovery, and microbial community were investigated. The results indicated that adding appropriate bulk of AWF made contributions to low grade copper sulfide ores bioleaching, which may be mainly realized through reducing the passivation layer formed by Fe3+ hydrolysis. Improved copper recovery (78.35%) and bacteria concentration (9.56 × 107 cells·mL−1) were yielded in the presence of 5 g·L−1 AWF. The result of 16S rDNA analysis demonstrated that microbial community was differentiated by adding AWF. Bacteria proportion, such as Acidithiobacillus ferrooxidans, Moraxella osloensis, and Lactobacillus acetotolerans changed distinctly. Great difference between samples was showed according to beta diversity index, and the maximum value reached 0.375. Acidithiobacillus ferrooxidans accounted for the highest proportion throughout the bioleaching process, and that of sample in the presence of 5 g·L−1 AWF reached 28.63%. The results should show reference to application of agricultural wastes and low grade copper sulfide ores.
Effects of residues produced by agricultural wastes fermentation (AWF) on low grade copper sulfide ores bioleaching, copper recovery, and microbial community were investigated. The results indicated that adding appropriate bulk of AWF made contributions to low grade copper sulfide ores bioleaching, which may be mainly realized through reducing the passivation layer formed by Fe3+ hydrolysis. Improved copper recovery (78.35%) and bacteria concentration (9.56 × 107 cells·mL−1) were yielded in the presence of 5 g·L−1 AWF. The result of 16S rDNA analysis demonstrated that microbial community was differentiated by adding AWF. Bacteria proportion, such as Acidithiobacillus ferrooxidans, Moraxella osloensis, and Lactobacillus acetotolerans changed distinctly. Great difference between samples was showed according to beta diversity index, and the maximum value reached 0.375. Acidithiobacillus ferrooxidans accounted for the highest proportion throughout the bioleaching process, and that of sample in the presence of 5 g·L−1 AWF reached 28.63%. The results should show reference to application of agricultural wastes and low grade copper sulfide ores.
2022, vol. 29, no. 12, pp.
2144-2151.
https://doi.org/10.1007/s12613-021-2334-y
Abstract:
The chemical composition of vanadium slag significantly affects its element distribution and phase composition, which affect the subsequent calcification roasting process and vanadium recovery. In this work, seven kinds of vanadium slags derived from different regions in China were used as the raw materials to study the effects of different components on the vanadium slag’s elements distribution, phase composition, calcification roasting, and leaching rate of major elements using scanning electron microscope, X-ray diffraction analysis, and inductively coupled plasma-optical emission spectroscopy. The results show that the spinel phase is wrapped with silicate phase in all vanadium slag samples. The main elements in the spinel phase are Cr, V, and Ti from the interior to the exterior. The size of spinel phase in low chromium vanadium slag is larger than the other vanadium slags with higher chromium contents. The spinel phase of high-calcium and high-phosphorus vanadium slag is more dispersed. The strongest diffraction peak of vanadium spinel phase in the vanadium slag migrates to a higher diffraction angle, and (Fe0.6Cr0.4)2O3 is formed after calcification roasting as the chromium content increased. A large amount of Ca2SiO4 is produced because excess Ca reacts with Si in high-calcium and high-phosphorus vanadium slag. The vanadium leaching rate reaches 88% in some vanadium slags. The chromium leaching rate is less than 5% in all vanadium slags. The silicon leaching rate of high-calcium and high-phosphorus vanadium slag is much higher than that of the other slags. The leaching rate of manganese is higher than 10%, and the leaching rates of iron and titanium are negligible.
The chemical composition of vanadium slag significantly affects its element distribution and phase composition, which affect the subsequent calcification roasting process and vanadium recovery. In this work, seven kinds of vanadium slags derived from different regions in China were used as the raw materials to study the effects of different components on the vanadium slag’s elements distribution, phase composition, calcification roasting, and leaching rate of major elements using scanning electron microscope, X-ray diffraction analysis, and inductively coupled plasma-optical emission spectroscopy. The results show that the spinel phase is wrapped with silicate phase in all vanadium slag samples. The main elements in the spinel phase are Cr, V, and Ti from the interior to the exterior. The size of spinel phase in low chromium vanadium slag is larger than the other vanadium slags with higher chromium contents. The spinel phase of high-calcium and high-phosphorus vanadium slag is more dispersed. The strongest diffraction peak of vanadium spinel phase in the vanadium slag migrates to a higher diffraction angle, and (Fe0.6Cr0.4)2O3 is formed after calcification roasting as the chromium content increased. A large amount of Ca2SiO4 is produced because excess Ca reacts with Si in high-calcium and high-phosphorus vanadium slag. The vanadium leaching rate reaches 88% in some vanadium slags. The chromium leaching rate is less than 5% in all vanadium slags. The silicon leaching rate of high-calcium and high-phosphorus vanadium slag is much higher than that of the other slags. The leaching rate of manganese is higher than 10%, and the leaching rates of iron and titanium are negligible.
2022, vol. 29, no. 12, pp.
2152-2161.
https://doi.org/10.1007/s12613-021-2407-y
Abstract:
This work proposes a novel horizontal high-shear granulator for iron ore granulation before sintering process. The granulation behavior such as growth process and structure of granules were firstly analyzed, followed by the effects of operation conditions such as water content, initial particle size distribution, and the concentrate ratio. The results show that the granule size increased significantly with increasing the granulation time, and the structure of granule can be divided into three types: non-nuclei, single-nuclei, and multi-nuclei. Water promotes the coalescence and growth of particles, and a better granulation performance was obtained at the water content of 8.8wt% under the current raw material conditions. Increasing the nuclei particle ratio led to an increase in average size of granules and permeability of the granules bed, but a decrease in growth index. Besides, with increasing of concentrate ratio, granulation performance such as granule size, bed permeability, and uniformity became worse.
This work proposes a novel horizontal high-shear granulator for iron ore granulation before sintering process. The granulation behavior such as growth process and structure of granules were firstly analyzed, followed by the effects of operation conditions such as water content, initial particle size distribution, and the concentrate ratio. The results show that the granule size increased significantly with increasing the granulation time, and the structure of granule can be divided into three types: non-nuclei, single-nuclei, and multi-nuclei. Water promotes the coalescence and growth of particles, and a better granulation performance was obtained at the water content of 8.8wt% under the current raw material conditions. Increasing the nuclei particle ratio led to an increase in average size of granules and permeability of the granules bed, but a decrease in growth index. Besides, with increasing of concentrate ratio, granulation performance such as granule size, bed permeability, and uniformity became worse.
2022, vol. 29, no. 12, pp.
2162-2171.
https://doi.org/10.1007/s12613-021-2376-1
Abstract:
The phase equilibrium information of slag plays an important role in pyrometallurgical processes to obtain optimum fluxing conditions and operating temperatures. The smelting reduction of titanomagnetite and ilmenite ores in an iron blast furnace (BF) can form Ti(C,N) particles, causing the increased viscosities of slag and hot metal. HIsmelt has been developed in recent years for ironmaking and does not need coke and sinter. The formation of Ti(C,N) in the HIsmelt process is avoided because the oxygen partial pressure in the process is higher than that in the BF. The smelting of TiO2-containing ores in the HIsmelt process results in Al2O3–MgO–SiO2–CaO–TiO2 slag. Phase equilibrium in this slag system has been investigated using equilibration, quenching, and electron probe microanalysis techniques. The experimental results were presented in two pseudo-binary sections, which represent the process of HIsmelt for the treatment of 100% titanomagnetite ore and mixed titanomagnetite+ilmenite ore (mass ratio of 2:1), respectively. The primary phases observed in the composition range investigated include pseudo-brookite M3O5 (MgO·2TiO2–Al2O3·TiO2), spinel (MgO·Al2O3), perovskite CaTiO3, and rutile TiO2. The results show that the liquidus temperatures decrease in the TiO2 and M3O5 primary phase fields and increase in the spinel and CaTiO3 primary phase fields with the increase in CaO concentration. The calculation of solid-phase fractions from the experimental data has been demonstrated. The effect of basicity on the liquidus temperatures of the slag has been discussed. The smelting of titanomagnetite plus ilmenite ores has significant advantages to obtain low-sulfur hot metal and high-TiO2 slag. Experimentally determined liquidus temperatures were compared with the FactSage predictions to evaluate the existing thermodynamic databases.
The phase equilibrium information of slag plays an important role in pyrometallurgical processes to obtain optimum fluxing conditions and operating temperatures. The smelting reduction of titanomagnetite and ilmenite ores in an iron blast furnace (BF) can form Ti(C,N) particles, causing the increased viscosities of slag and hot metal. HIsmelt has been developed in recent years for ironmaking and does not need coke and sinter. The formation of Ti(C,N) in the HIsmelt process is avoided because the oxygen partial pressure in the process is higher than that in the BF. The smelting of TiO2-containing ores in the HIsmelt process results in Al2O3–MgO–SiO2–CaO–TiO2 slag. Phase equilibrium in this slag system has been investigated using equilibration, quenching, and electron probe microanalysis techniques. The experimental results were presented in two pseudo-binary sections, which represent the process of HIsmelt for the treatment of 100% titanomagnetite ore and mixed titanomagnetite+ilmenite ore (mass ratio of 2:1), respectively. The primary phases observed in the composition range investigated include pseudo-brookite M3O5 (MgO·2TiO2–Al2O3·TiO2), spinel (MgO·Al2O3), perovskite CaTiO3, and rutile TiO2. The results show that the liquidus temperatures decrease in the TiO2 and M3O5 primary phase fields and increase in the spinel and CaTiO3 primary phase fields with the increase in CaO concentration. The calculation of solid-phase fractions from the experimental data has been demonstrated. The effect of basicity on the liquidus temperatures of the slag has been discussed. The smelting of titanomagnetite plus ilmenite ores has significant advantages to obtain low-sulfur hot metal and high-TiO2 slag. Experimentally determined liquidus temperatures were compared with the FactSage predictions to evaluate the existing thermodynamic databases.
2022, vol. 29, no. 12, pp.
2172-2180.
https://doi.org/10.1007/s12613-021-2375-2
Abstract:
The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs. Transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to analyze the size and distribution of Ti(C,N) precipitates during solidification. Based on these results, the pinning pressure of Ti(C,N) precipitates on the growth of coarse columnar grains (CCGs) was studied. The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains (FCGs). Increasing the content of titanium reduces the region and the short axis of the CCGs. When the content of titanium is 0.09wt%, there is no CCG region. Dispersed microscale particles will firstly form in the liquid, which will decrease the transition temperature from FCGs to CCGs. The chain-like nanoscale Ti(C,N) will precipitate with the decrease of the transition temperature. Furthermore, calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N) precipitates.
The effect of titanium content on the refinement of austenite grain size in as-cast peritectic carbon steel was investigated by fast directional solidification experiments with simulating the solidification and growth of surface and subsurface austenite in continuously cast slabs. Transmission electron microscope (TEM) and scanning electron microscope (SEM) were used to analyze the size and distribution of Ti(C,N) precipitates during solidification. Based on these results, the pinning pressure of Ti(C,N) precipitates on the growth of coarse columnar grains (CCGs) was studied. The results show that the austenite microstructure of as-cast peritectic carbon steel is mainly composed of the regions of CCGs and fine columnar grains (FCGs). Increasing the content of titanium reduces the region and the short axis of the CCGs. When the content of titanium is 0.09wt%, there is no CCG region. Dispersed microscale particles will firstly form in the liquid, which will decrease the transition temperature from FCGs to CCGs. The chain-like nanoscale Ti(C,N) will precipitate with the decrease of the transition temperature. Furthermore, calculations shows that the refinement of the CCGs is caused by the pinning effect of Ti(C,N) precipitates.
2022, vol. 29, no. 12, pp.
2181-2188.
https://doi.org/10.1007/s12613-021-2326-y
Abstract:
The low cell voltage during electrolytic Mn from the MnCl2 system can effectively reduce the power consumption. In this work, the Ti/Sn−Ru−Co−Zr modified anodes were obtained by using thermal decomposition oxidation. The physical parameters of coatings were observed by SEM (scanning electron microscope). Based on the electrochemical performance and SEM/XRD (X-ray diffraction) of the coatings, the influence of Zr on electrode performance was studied and analyzed. When the mole ratio of Sn−Ru−Co−Zr is 6:1:0.8:0.3, the cracks on the surface of coatings were the smallest, and the compactness was the best due to the excellent filling effect of ZrO2 nanoparticles. Moreover, the electrode prepared under this condition had the lowest mass transfer resistance and high chloride evolution activity in the 1mol% NH4Cl and 1.5mol% HCl system. The service life of 3102 h was achieved according to the empirical formula of accelerated-life-test of the new type anode.
The low cell voltage during electrolytic Mn from the MnCl2 system can effectively reduce the power consumption. In this work, the Ti/Sn−Ru−Co−Zr modified anodes were obtained by using thermal decomposition oxidation. The physical parameters of coatings were observed by SEM (scanning electron microscope). Based on the electrochemical performance and SEM/XRD (X-ray diffraction) of the coatings, the influence of Zr on electrode performance was studied and analyzed. When the mole ratio of Sn−Ru−Co−Zr is 6:1:0.8:0.3, the cracks on the surface of coatings were the smallest, and the compactness was the best due to the excellent filling effect of ZrO2 nanoparticles. Moreover, the electrode prepared under this condition had the lowest mass transfer resistance and high chloride evolution activity in the 1mol% NH4Cl and 1.5mol% HCl system. The service life of 3102 h was achieved according to the empirical formula of accelerated-life-test of the new type anode.
2022, vol. 29, no. 12, pp.
2189-2200.
https://doi.org/10.1007/s12613-021-2394-z
Abstract:
ZrO2–YO1.5–TaO2.5 (ZYTO) is a promising top-coat material for thermal barrier coatings (TBCs). The bulk properties of ZYTO have been reported by several studies, but its performances as TBCs are less-well understood. In this work, ZYTO TBCs were prepared by air plasma spraying (APS) and their thermal cycling performances were investigated at 1150°C. Despite of the good bulk properties, APS ZYTO TBCs present an extremely short thermal fatigue life. This is attributed to the non-equilibrium grain-boundary segregation of TaO2.5 induced by limited solubility and rapid quenching during APS process, resulting in a tetragonal (t) to cubic (c) and metastable-tetragonal (tm) phase transformation in ZYTO TBCs. The volume shrinkage (~0.74vol%) of phase transformation leads to many cracks at the c/tm phase boundaries after deposition. On the other hand, the formation of cubic phase with massive grain-boundary Ta segregation induces a large intergranular embrittlement and a weak bonding strength (~5.3 MPa), resulting in the premature failure of the ZYTO TBCs.
ZrO2–YO1.5–TaO2.5 (ZYTO) is a promising top-coat material for thermal barrier coatings (TBCs). The bulk properties of ZYTO have been reported by several studies, but its performances as TBCs are less-well understood. In this work, ZYTO TBCs were prepared by air plasma spraying (APS) and their thermal cycling performances were investigated at 1150°C. Despite of the good bulk properties, APS ZYTO TBCs present an extremely short thermal fatigue life. This is attributed to the non-equilibrium grain-boundary segregation of TaO2.5 induced by limited solubility and rapid quenching during APS process, resulting in a tetragonal (t) to cubic (c) and metastable-tetragonal (tm) phase transformation in ZYTO TBCs. The volume shrinkage (~0.74vol%) of phase transformation leads to many cracks at the c/tm phase boundaries after deposition. On the other hand, the formation of cubic phase with massive grain-boundary Ta segregation induces a large intergranular embrittlement and a weak bonding strength (~5.3 MPa), resulting in the premature failure of the ZYTO TBCs.
2022, vol. 29, no. 12, pp.
2201-2211.
https://doi.org/10.1007/s12613-021-2362-7
Abstract:
Lithium-rich materials possess the ultra-high specific capacity, but the redox of oxygen is not completely reversible, resulting in voltage attenuation and structural instability. A stepwise co-precipitation method is used for the first time in this paper to achieve the control of the two-phase distribution through controlling the distribution of transition metal elements and realize the modification of particle surface structure without the aid of heterologous ions. The results of characterization tests show that the content of LiMO2 phase inside the particles and the content of Li2MnO3 phase on the surface of the particles are successfully increased, and the surface induced formation of Li4Mn5O12 spinel phase or some disorderly ternary. The electrochemical performance of the modified sample is as follows: LR (pristine) shows specific discharge capacity of 72.7 mA·h·g−1 after 500 cycles at 1 C, while GR (modified sample) shows specific discharge capacity of 137.5 mA·h·g−1 at 1 C, and the discharge mid-voltage of GR still remains above 3 V when cycling to 220 cycles at 1 C (mid-voltage of LR remains above 3 V when cycling to 160 cycles at 1 C). Therefore, deliberately regulating the local state of the two phases is a successful way to reinforced the material structure and inhibition the voltage attenuation.
Lithium-rich materials possess the ultra-high specific capacity, but the redox of oxygen is not completely reversible, resulting in voltage attenuation and structural instability. A stepwise co-precipitation method is used for the first time in this paper to achieve the control of the two-phase distribution through controlling the distribution of transition metal elements and realize the modification of particle surface structure without the aid of heterologous ions. The results of characterization tests show that the content of LiMO2 phase inside the particles and the content of Li2MnO3 phase on the surface of the particles are successfully increased, and the surface induced formation of Li4Mn5O12 spinel phase or some disorderly ternary. The electrochemical performance of the modified sample is as follows: LR (pristine) shows specific discharge capacity of 72.7 mA·h·g−1 after 500 cycles at 1 C, while GR (modified sample) shows specific discharge capacity of 137.5 mA·h·g−1 at 1 C, and the discharge mid-voltage of GR still remains above 3 V when cycling to 220 cycles at 1 C (mid-voltage of LR remains above 3 V when cycling to 160 cycles at 1 C). Therefore, deliberately regulating the local state of the two phases is a successful way to reinforced the material structure and inhibition the voltage attenuation.
2022, vol. 29, no. 12, pp.
2212-2220.
https://doi.org/10.1007/s12613-022-2498-0
Abstract:
To improve the efficiency of cathodic oxygen reduction reaction (ORR) in zinc–air batteries (ZABs), an adsorption–complexation–calcination method was proposed to generate cobalt-based multicomponent nanoparticles comprising Co, Co3O4 and CoN, as well as numerous N heteroatoms, on graphene nanosheets (Co/Co3O4/CoN/NG). The Co/Co3O4/CoN nanoparticles with the size of less than 50 nm are homogeneously dispersed on N-doped graphene (NG) substrate, which greatly improve the catalytic behaviors for ORR. The results show that the half-wave potential is as high as 0.80 V vs. RHE and the limiting current density is 4.60 mA∙cm−2, which are close to those of commercially available platinum/carbon (Pt/C) catalysts. Applying as cathodic catalyst for ZABs, the battery shows large specific capacity and open circuit voltage of 843.0 mAh∙g−1 and 1.41 V, respectively. The excellent performance is attributed to the efficient two-dimensional structure with high accessible surface area and the numerous multiple active sites provided by highly scattered Co/Co3O4/CoN particles and doped nitrogen on the carbon matrix.
To improve the efficiency of cathodic oxygen reduction reaction (ORR) in zinc–air batteries (ZABs), an adsorption–complexation–calcination method was proposed to generate cobalt-based multicomponent nanoparticles comprising Co, Co3O4 and CoN, as well as numerous N heteroatoms, on graphene nanosheets (Co/Co3O4/CoN/NG). The Co/Co3O4/CoN nanoparticles with the size of less than 50 nm are homogeneously dispersed on N-doped graphene (NG) substrate, which greatly improve the catalytic behaviors for ORR. The results show that the half-wave potential is as high as 0.80 V vs. RHE and the limiting current density is 4.60 mA∙cm−2, which are close to those of commercially available platinum/carbon (Pt/C) catalysts. Applying as cathodic catalyst for ZABs, the battery shows large specific capacity and open circuit voltage of 843.0 mAh∙g−1 and 1.41 V, respectively. The excellent performance is attributed to the efficient two-dimensional structure with high accessible surface area and the numerous multiple active sites provided by highly scattered Co/Co3O4/CoN particles and doped nitrogen on the carbon matrix.
2022, vol. 29, no. 12, pp.
2221-2231.
https://doi.org/10.1007/s12613-021-2332-0
Abstract:
Nanomaterials have been widely applied to many fields because of their excellent photocatalytic performance. The performance is closely related to the catalytic kinetics, but it is not completely clear about the influencing regularities of shape and particle size on the photocatalytic kinetics of nanomaterials and the photocatalytic kinetic mechanism. In this paper, nano-CeO2 with different shapes and particle sizes were prepared, the kinetic parameters of adsorption and photocatalytic degradation were determined, and the effects of shape and particle size on the kinetics of adsorption and photocatalysis and photocatalytic mechanism were discussed. The results show that the shape and particle size have significant influences. With the decreases of diameter, the performances of adsorption and photocatalysis of nano-CeO2 are improved; and these performances of spherical nano-CeO2 are greater than those of linear nano-CeO2. The shape and particle size have no effects on the kinetic order and mechanism of the whole photocatalytic process. Then a generalized mechanism of photocatalytic kinetics of nanomaterials was proposed and the mechanism rate equation was derived. Finally, the conclusion can be drawn: the desorption of photodegradation products is the control step of photocatalytic kinetics, and the kinetic order of photocatalytic degradation reaction is 1. The mechanism is universal and all nanomaterials have the same photocatalytic kinetic mechanism and order.
Nanomaterials have been widely applied to many fields because of their excellent photocatalytic performance. The performance is closely related to the catalytic kinetics, but it is not completely clear about the influencing regularities of shape and particle size on the photocatalytic kinetics of nanomaterials and the photocatalytic kinetic mechanism. In this paper, nano-CeO2 with different shapes and particle sizes were prepared, the kinetic parameters of adsorption and photocatalytic degradation were determined, and the effects of shape and particle size on the kinetics of adsorption and photocatalysis and photocatalytic mechanism were discussed. The results show that the shape and particle size have significant influences. With the decreases of diameter, the performances of adsorption and photocatalysis of nano-CeO2 are improved; and these performances of spherical nano-CeO2 are greater than those of linear nano-CeO2. The shape and particle size have no effects on the kinetic order and mechanism of the whole photocatalytic process. Then a generalized mechanism of photocatalytic kinetics of nanomaterials was proposed and the mechanism rate equation was derived. Finally, the conclusion can be drawn: the desorption of photodegradation products is the control step of photocatalytic kinetics, and the kinetic order of photocatalytic degradation reaction is 1. The mechanism is universal and all nanomaterials have the same photocatalytic kinetic mechanism and order.
2022, vol. 29, no. 12, pp.
2232-2240.
https://doi.org/10.1007/s12613-021-2320-4
Abstract:
TiAl alloy with high Nb content, nominally Ti–45Al–10Nb, was prepared by powder metallurgy, and the oxidation resistance at 850, 900, and 950°C was investigated. The high-temperature oxidation-resistance mechanism and oxidation dynamics were discussed following the oxide skin morphology and microstructural evolution analysis. The oxide skin structures were similar for 850 and 900°C, with TiO2+Al2O3 mixture covering TiO2 with dispersed Nb2O5. At 950°C, the oxide skin was divided into four sublayers, from the outside to the parent metal: loose TiO2+Al2O3, dense Al2O3, dense TiO2+Nb2O5, and TiO2 matrix with dispersed Nb2O5. The Nb layer suppressed the outward diffusion of Ti atoms, hindering the growth of TiO2, and simultaneously promote the formation of a continuous Al2O3 protective layer, providing the alloy with long-term high-temperature oxidation resistance.
TiAl alloy with high Nb content, nominally Ti–45Al–10Nb, was prepared by powder metallurgy, and the oxidation resistance at 850, 900, and 950°C was investigated. The high-temperature oxidation-resistance mechanism and oxidation dynamics were discussed following the oxide skin morphology and microstructural evolution analysis. The oxide skin structures were similar for 850 and 900°C, with TiO2+Al2O3 mixture covering TiO2 with dispersed Nb2O5. At 950°C, the oxide skin was divided into four sublayers, from the outside to the parent metal: loose TiO2+Al2O3, dense Al2O3, dense TiO2+Nb2O5, and TiO2 matrix with dispersed Nb2O5. The Nb layer suppressed the outward diffusion of Ti atoms, hindering the growth of TiO2, and simultaneously promote the formation of a continuous Al2O3 protective layer, providing the alloy with long-term high-temperature oxidation resistance.
2022, vol. 29, no. 12, pp.
2241-2251.
https://doi.org/10.1007/s12613-022-2514-4
Abstract:
Texture evolution and mechanical anisotropic behavior of an ultrafine-grained (UFG) pure copper tube processed by recently introduced method of hydrostatic tube cyclic expansion extrusion (HTCEE) was investigated. For the UFG tube, different deformation behavior and a significant anisotropy in tensile properties were recorded along the longitudinal and peripheral directions. The HTCEE process increased the yield strength and the ultimate strength in the axial direction by 3.6 and 1.67 times, respectively. Also, this process increased the yield strength and the ultimate strength in the peripheral direction by 1.15 and 1.12 times, respectively. The ratio of ultimate tensile strength in the peripheral direction to that in the axial direction, as a criterion for mechanical anisotropy, are 1.7 and 1.16 for the as-annealed coarse-grained and the HTCEE processed UFG tube, respectively. The results are indicative of a reducing effect of the HTCEE process on the mechanical anisotropy. Besides, after HTCEE process, a low loss of ductility was observed in both directions, which is another advantage of HTCEE process. Hardness measurements revealed a slight increment of hardness values in the peripheral direction, which is in agreement with the trend of tensile tests. Texture analysis was conducted in order to determine the oriental distribution of the grains. The obtained {111} pole figures demonstrate the texture evolution and reaffirm the anisotropy observed in mechanical properties. Scanning electron microscopy micrographs showed that different modes of fracture occurred after tensile testing in the two orthogonal directions.
Texture evolution and mechanical anisotropic behavior of an ultrafine-grained (UFG) pure copper tube processed by recently introduced method of hydrostatic tube cyclic expansion extrusion (HTCEE) was investigated. For the UFG tube, different deformation behavior and a significant anisotropy in tensile properties were recorded along the longitudinal and peripheral directions. The HTCEE process increased the yield strength and the ultimate strength in the axial direction by 3.6 and 1.67 times, respectively. Also, this process increased the yield strength and the ultimate strength in the peripheral direction by 1.15 and 1.12 times, respectively. The ratio of ultimate tensile strength in the peripheral direction to that in the axial direction, as a criterion for mechanical anisotropy, are 1.7 and 1.16 for the as-annealed coarse-grained and the HTCEE processed UFG tube, respectively. The results are indicative of a reducing effect of the HTCEE process on the mechanical anisotropy. Besides, after HTCEE process, a low loss of ductility was observed in both directions, which is another advantage of HTCEE process. Hardness measurements revealed a slight increment of hardness values in the peripheral direction, which is in agreement with the trend of tensile tests. Texture analysis was conducted in order to determine the oriental distribution of the grains. The obtained {111} pole figures demonstrate the texture evolution and reaffirm the anisotropy observed in mechanical properties. Scanning electron microscopy micrographs showed that different modes of fracture occurred after tensile testing in the two orthogonal directions.
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