A stable δ- and β-bismuth trioxide was prepared at room temperature by vacuum vapor-phase oxidation. The average crystal size of products was 14.6 nm (by XRD), the d(0.5) value was in the range from 62 nm to 69 nm, ...A stable δ- and β-bismuth trioxide was prepared at room temperature by vacuum vapor-phase oxidation. The average crystal size of products was 14.6 nm (by XRD), the d(0.5) value was in the range from 62 nm to 69 nm, and geometric standard deviation(GSD) was from 1.42 to 1.64. The results show that δ-Bi2O3 is formed when quenching rates is rapid and β-Bi2O3 is formed when it is slow. The size of grains increases with rising reaction temperature, flow rate of carrier gas, residual pressure of system and longer growing time of grains.展开更多
A bond coat for thermal barrier coating (TBC), NiCrAlY coating, is subjected to vac-uum heat treatment in order to remove internal stress before ceramic top coat is de-posited. The effect of vacuum heat treatment on t...A bond coat for thermal barrier coating (TBC), NiCrAlY coating, is subjected to vac-uum heat treatment in order to remove internal stress before ceramic top coat is de-posited. The effect of vacuum heat treatment on the oxidation behavior of the sputtered NiCrAlY coating has been investigated. The as-sputtered NiCrAlY coating consists of γ-Ni and b-NiAl phases. After vacuum heat treatment, the sputtered NiCrAlY coating mainly consists of γ'-Ni3Al, β-NiAl, γ-Ni, and trace of α-Al2O3 phases. The isothermal oxidation of sputtered NiCrAlY coating with and without vacuum heat treatment has been performed at 1000℃. It is shown that a-Al2O3 formed during vacuum heat treatment acts as nuclei for the formation of a-Al2O3, and the protective a-Al2O3 scale is formed more rapidly on the vacuum heat treated NiCrAlY coating than that formed on the untreated coating. Also the a-Al2O3 scale has a better adherence to the vacuum heat treated NiCrAlY coating. Therefore the vacuum heat treatment improves the oxidation resistance of sputtered NiCrAlY coating.展开更多
The electrodeposited Y2O3-dispersedγ-Ni+γ′-Ni3Al coatings on Ni substrates were developed by the conversion of electrodeposited Ni-Al-Y2O3 films with dispersed Al microparticles in Ni matrix into Ni3Al by vacuum an...The electrodeposited Y2O3-dispersedγ-Ni+γ′-Ni3Al coatings on Ni substrates were developed by the conversion of electrodeposited Ni-Al-Y2O3 films with dispersed Al microparticles in Ni matrix into Ni3Al by vacuum annealing at 800℃for 3 h. For comparison,Y2O3-freeγ-Ni+γ′-Ni3Al coatings with a similar Al content were also prepared by vacuum annealing the electrodeposited microparticle-dispersed composite coatings of Ni-Al under the same condition.SEM and TEM characterizations show that the electrodeposited Y2O3-dispersedγ+γ′coatings exhibit finer grains,a more homogeneous distribution ofγ′,and a narrowedγ′phase spacing compared with the electrodeposited Y 2 O3-freeγ+γ′coatings.The oxidation at 1 000℃shows that the addition of Y2O3 significantly improves the oxidation resistance of the electrodepositedγ+γ′coatings.The effect of Y2O3 particles on the microstructure and oxidation behavior of the electrodepositedγ+γ′coatings was discussed in detail.展开更多
A green and effective electrolytic process was developed to produce high-purity Mg metal using primary and secondary resources containing Mg O as a feedstock. The electrolysis of various Mg O resources was conducted u...A green and effective electrolytic process was developed to produce high-purity Mg metal using primary and secondary resources containing Mg O as a feedstock. The electrolysis of various Mg O resources was conducted using a Cu cathode in MgF2– LiF – KCl molten salt at 1043 K by applying an average current of 1.44 A for 12.5 h. The electrolysis of calcined North Korean magnesite and seawater Mg O clinker yielded Mg alloys of MgCu2and(Cu) phases with current efficiencies of 89.6–92.4%. The electrolysis of oxidized Mg O-C refractory brick, aged ferronickel slag, and ferronickel slag yielded Mg alloys of MgCu2and(Cu) phases with current efficiencies of 59.3–92.3%. The vacuum distillation of Mg alloys obtained was conducted at 1300 K for 10 h to produce high-purity Mg metal. After vacuum distillation, Mg metal with a purity of above 99.994% was obtained. Therefore, this study demonstrates the feasibility of the production of high-purity Mg metal from various Mg O resources using a novel electrolytic process with a Cu cathode, followed by vacuum distillation.展开更多
The TBC system is examined with regards to its response to thermal exposure at high temperature. It has been established before that the thermally grown oxide (TGO) layer that forms upon bond coat oxidation is the key...The TBC system is examined with regards to its response to thermal exposure at high temperature. It has been established before that the thermally grown oxide (TGO) layer that forms upon bond coat oxidation is the key factor determining the performance of the TBC system and/or its failure. However, characteristics of TGO growth, bond coat rumpling, principles governing failure of TBC systems and the various failure mechanisms have been studied extensively in case of just super alloy with bond coat or with thick top coating. In this study super alloy/bond coat system with single splats of YSZ instead of thick topcoat is analyzed in order to scrutinize the effect on the first layer of splats during thermal exposure. The splats with microcracks are the building blocks of the top coat. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. The interactions between the YSZ splats and the evolving TGO is directly linked to the presence or absence of bond coat oxidation. Therefore the high temperature behavior of this system is analyzed with variations in heat treatment involving, temperature, duration and environment of thermal exposure.展开更多
The TBC system’s response to thermal exposure at high temperature is discussed here. The relevance of the microstructural aspects of each component of the TBC system is emphasized. The top coat is a YSZ ceramic coati...The TBC system’s response to thermal exposure at high temperature is discussed here. The relevance of the microstructural aspects of each component of the TBC system is emphasized. The top coat is a YSZ ceramic coating consisting of a collection of splats on top of one another. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. This study investigates the effect of thermal exposure on the microstructure and sintering behavior in single splats produced using different starting powders since this has been shown to influence the basic microstructure of YSZ topcoat. The bond coat is an MCrAlY metallic coating which serves as an Al reservoir and allows the formation of a protective alumina, Thermally Grown Oxide (TGO) layer between the bond coat (BC) and the top coat (TC) layers. This oxide scale formed upon thermal exposure prevents further oxidation of the underlying component (substrate) and thus provides protection. As such, the content of free Al in the bond coat layer is of significance and makes it crucial to understand the influence of bond coat microstructure evolution and oxidation involved during its formation. The interaction between the bond coat, the TGO and the top coat layers is examined in this study to understand the high temperature behavior of the TBC system with regards to variations in the top coat and bond coat material systems used.展开更多
In this study,a novel Mg production process for producing high-purity Mg metal from dolomite was developed.When the electrolysis of calcined dolomite was conducted using Cu cathode and C anode in MgF_(2)–LiF molten s...In this study,a novel Mg production process for producing high-purity Mg metal from dolomite was developed.When the electrolysis of calcined dolomite was conducted using Cu cathode and C anode in MgF_(2)–LiF molten salt at 1083–1173 K by applying an average current of 1.42–1.46 A for 9.50–21.0 h,the current efficiency of 66.4–88.6%was obtained.The produced Mg alloys consisted of MgCu_(2)and Cu(Mg)or MgCu_(2)and CuMg_(2)phases,depending on the Mg concentration in the Mg alloy.When the electrolysis of calcined dolomite was conducted in MgF_(2)–LiF–CaF_(2)molten salt at 1083 K,the current efficiency was 40.9–71.4%,owing to undesired reactions such as electroreduction of Ca^(2+)or/and CO_(3)^(2−)ions.Meanwhile,the current efficiency increased from 40.9%to 63.2%by utilizing a Pt anode,because the occurrence of CO_(3)^(2−)ions in the molten salt was prevented.After vacuum distillation of the obtained Mg alloys at 1300 K for 10 h,Mg metal with a purity of 99.9996–99.9998%was produced.Therefore,the feasibility of this novel process for the production of high-purity Mg metal from dolomite was demonstrated.展开更多
The green synthesis of nitrate(NO_(3)^(−))via electrocatalytic nitrogen oxidation reaction(NOR)is a promising strategy for artificial nitrogen fixation,which shows great advantages than traditional nitrate synthesis b...The green synthesis of nitrate(NO_(3)^(−))via electrocatalytic nitrogen oxidation reaction(NOR)is a promising strategy for artificial nitrogen fixation,which shows great advantages than traditional nitrate synthesis based on Haber–Bosch and Ostwald processes.But the poor N_(2)absorption,high bond energy of N≡N(941 kJ·mol^(−1)),and competing multi-electron-transfer oxygen evolution reaction(OER)limit the activity and selectivity.Herein,we fabricated MXene-derived irregular TiO_(2)−x nanoparticles anchored Cu nanowires(Cu-NWs)electrode for efficient electrocatalytic nitrogen oxidation,which exhibits a NO_(3)−yield of 62.50μg·h^(−1)·mgcat^(−1)and a Faradaic efficiency(FE)of 22.04%,and a significantly enhanced NO_(3)−yield of 92.63μg·h^(−1)·mgcat^(−1),and a FE of 40.58%under vacuum assistance.The TiO_(2)−x/Cu-NWs electrode also shows excellent reproducibility and stability under optimal experimental conditions.Moreover,a Zn-N_(2)reaction device was assembled with TiO_(2−x)/Cu-NWs as an anode and Zn plate as a cathode,obtaining an extremely high NO_(3)−yield of 156.25μg·h^(−1)·mgcat^(−1).The Zn-nitrate battery shows an open circuit voltage(OCV)of 1.35 V.This work provides novel strategies for enhancing the performance of ambient N_(2)oxidation to obtain higher NO_(3)^(−)yield.展开更多
Highly ordered mesoporous NiMoO4 material was successfully synthesized using mesoporous silica KIT-6 as hard template via vacuum nanocasting method. The structure was characterized by means of XRD, TEM, N2 adsorption-...Highly ordered mesoporous NiMoO4 material was successfully synthesized using mesoporous silica KIT-6 as hard template via vacuum nanocasting method. The structure was characterized by means of XRD, TEM, N2 adsorption-desorption, Raman and FT-IR. The mesoporous NiMoO4 with the coexistence of a-NiMoO4 and fl-NiMoO4 showed well-ordered mesoporous structure, a bimodal pore size distribution and crystalline framework. The catalytic performance of NiMoOa was investigated for oxidative dehydrogenation of propane. It is demonstrated that the mesoporous NiMoO4 catalyst with more surface active oxygen species showed better catalytic performance in oxidative dehydrogena- tion of propane in comparison with bulk NiMoO4.展开更多
Organic polymer materials were used as a layer of adhesive into the graphene sheet between the layers to enhance the interaction force between the nano-structure to achieve excellent mechanical properties and barrier ...Organic polymer materials were used as a layer of adhesive into the graphene sheet between the layers to enhance the interaction force between the nano-structure to achieve excellent mechanical properties and barrier properties. PLA with good flowability and easy processing was selected. The mechanical properties and barrier properties of the graphene-based composites were improved by the use of PLA for good flowability, making it easy to enter the GO layer as a binder. Three methods of preparation of GO/PLA homogeneous composite membranes were designed by vacuum filtration. The experimental results show that the injection of PLA as a molecular binder into the GO layer can effectively mimic the nano-structure, and enhance the intergranular force of the graphene molecules and the compatibility with the polymer matrix.展开更多
The current electrolytic processes for magnesium(Mg)metal have several disadvantages,such as anhydrous magnesium chloride(MgCl_(2))preparation and generation of harmful chlorine(Cl_(2))gas.To overcome these drawbacks,...The current electrolytic processes for magnesium(Mg)metal have several disadvantages,such as anhydrous magnesium chloride(MgCl_(2))preparation and generation of harmful chlorine(Cl_(2))gas.To overcome these drawbacks,a novel Mg production process to produce high-purity Mg metal directly from magnesium oxide(MgO)was investigated in this study.The electrolysis of MgO was conducted using a liquid tin(Sn)cathode and a carbon(C)anode in the eutectic composition of a magnesium fluoride(MgF_(2))-lithium fluoride(LiF)molten salt under an applied voltage of 2.5 V at 1053-1113 K.Under certain conditions,the Mg-Sn alloys with Mg_(2)Sn and Mg(Sn)phases were obtained with a current efficiency of 86.6%at 1053 K.To produce high-purity Mg metal from the Mg-Sn alloy,vacuum distillation was conducted at 1200-1300 K for a duration of 5-10 h.Following the vacuum distillation,the concentration of Mg in the Mg-Sn alloy feed decreased from 34.1 to 0.17 mass%,and Mg metal with a purity of 99.999%was obtained at 1200 K.Therefore,the electrolytic process developed here is feasible for the production of high-purity Mg metal from MgO using an efficient method.展开更多
A new class of defects has been recently discovered,which are regarded double oxide film defects.In this study, a number of Ni-based vacuum-cast test bars were investigated. The fractures in the broken test barswere o...A new class of defects has been recently discovered,which are regarded double oxide film defects.In this study, a number of Ni-based vacuum-cast test bars were investigated. The fractures in the broken test barswere observed by Scanning Electron Microscopy (SEM). Energy Dispersive Spectroscopy (EDS), as well asWavelength Dispersive Spectroscopy (WDS) were used to characterize the chemical elements of the fracture'ssurface. Observation by SEM revealed the presence of inclusions identified as films that appeared to have initiatedthe growth of carbides. This study has added to the evidence that oxide film defects do exist in Ni-based super-alloyin certain vacuum casting conditions. It provides a reference for researchers' further study on the defects, andprovides a possible direction for researchers to improve casting technology so as to remove these defects.展开更多
基金Project(03SSY4056) supported by the Bureau of Science and Technology of Hunan Province, China Project(04C034) supported by the Bureau of Education of Hunan Province, China
文摘A stable δ- and β-bismuth trioxide was prepared at room temperature by vacuum vapor-phase oxidation. The average crystal size of products was 14.6 nm (by XRD), the d(0.5) value was in the range from 62 nm to 69 nm, and geometric standard deviation(GSD) was from 1.42 to 1.64. The results show that δ-Bi2O3 is formed when quenching rates is rapid and β-Bi2O3 is formed when it is slow. The size of grains increases with rising reaction temperature, flow rate of carrier gas, residual pressure of system and longer growing time of grains.
基金The authors thank Prof.H. Y. Lou for sputtering NiCrAlY coating.
文摘A bond coat for thermal barrier coating (TBC), NiCrAlY coating, is subjected to vac-uum heat treatment in order to remove internal stress before ceramic top coat is de-posited. The effect of vacuum heat treatment on the oxidation behavior of the sputtered NiCrAlY coating has been investigated. The as-sputtered NiCrAlY coating consists of γ-Ni and b-NiAl phases. After vacuum heat treatment, the sputtered NiCrAlY coating mainly consists of γ'-Ni3Al, β-NiAl, γ-Ni, and trace of α-Al2O3 phases. The isothermal oxidation of sputtered NiCrAlY coating with and without vacuum heat treatment has been performed at 1000℃. It is shown that a-Al2O3 formed during vacuum heat treatment acts as nuclei for the formation of a-Al2O3, and the protective a-Al2O3 scale is formed more rapidly on the vacuum heat treated NiCrAlY coating than that formed on the untreated coating. Also the a-Al2O3 scale has a better adherence to the vacuum heat treated NiCrAlY coating. Therefore the vacuum heat treatment improves the oxidation resistance of sputtered NiCrAlY coating.
基金Project(06-13)supported by the Scientific Research Startup Foundation of Heilongjiang University of Science and Technology,China
文摘The electrodeposited Y2O3-dispersedγ-Ni+γ′-Ni3Al coatings on Ni substrates were developed by the conversion of electrodeposited Ni-Al-Y2O3 films with dispersed Al microparticles in Ni matrix into Ni3Al by vacuum annealing at 800℃for 3 h. For comparison,Y2O3-freeγ-Ni+γ′-Ni3Al coatings with a similar Al content were also prepared by vacuum annealing the electrodeposited microparticle-dispersed composite coatings of Ni-Al under the same condition.SEM and TEM characterizations show that the electrodeposited Y2O3-dispersedγ+γ′coatings exhibit finer grains,a more homogeneous distribution ofγ′,and a narrowedγ′phase spacing compared with the electrodeposited Y 2 O3-freeγ+γ′coatings.The oxidation at 1 000℃shows that the addition of Y2O3 significantly improves the oxidation resistance of the electrodepositedγ+γ′coatings.The effect of Y2O3 particles on the microstructure and oxidation behavior of the electrodepositedγ+γ′coatings was discussed in detail.
基金supported by the Korea Evaluation Institute of Industrial Technology funded by the Korean Ministry of Industry in Korea (Project No.:20000970, 20–9805)Basic Research Project (22–3803) of the Korea Institute of Geoscience and Mineral Resources (KIGAM) funded by the Ministry of Science and ICT of Korea。
文摘A green and effective electrolytic process was developed to produce high-purity Mg metal using primary and secondary resources containing Mg O as a feedstock. The electrolysis of various Mg O resources was conducted using a Cu cathode in MgF2– LiF – KCl molten salt at 1043 K by applying an average current of 1.44 A for 12.5 h. The electrolysis of calcined North Korean magnesite and seawater Mg O clinker yielded Mg alloys of MgCu2and(Cu) phases with current efficiencies of 89.6–92.4%. The electrolysis of oxidized Mg O-C refractory brick, aged ferronickel slag, and ferronickel slag yielded Mg alloys of MgCu2and(Cu) phases with current efficiencies of 59.3–92.3%. The vacuum distillation of Mg alloys obtained was conducted at 1300 K for 10 h to produce high-purity Mg metal. After vacuum distillation, Mg metal with a purity of above 99.994% was obtained. Therefore, this study demonstrates the feasibility of the production of high-purity Mg metal from various Mg O resources using a novel electrolytic process with a Cu cathode, followed by vacuum distillation.
文摘The TBC system is examined with regards to its response to thermal exposure at high temperature. It has been established before that the thermally grown oxide (TGO) layer that forms upon bond coat oxidation is the key factor determining the performance of the TBC system and/or its failure. However, characteristics of TGO growth, bond coat rumpling, principles governing failure of TBC systems and the various failure mechanisms have been studied extensively in case of just super alloy with bond coat or with thick top coating. In this study super alloy/bond coat system with single splats of YSZ instead of thick topcoat is analyzed in order to scrutinize the effect on the first layer of splats during thermal exposure. The splats with microcracks are the building blocks of the top coat. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. The interactions between the YSZ splats and the evolving TGO is directly linked to the presence or absence of bond coat oxidation. Therefore the high temperature behavior of this system is analyzed with variations in heat treatment involving, temperature, duration and environment of thermal exposure.
文摘The TBC system’s response to thermal exposure at high temperature is discussed here. The relevance of the microstructural aspects of each component of the TBC system is emphasized. The top coat is a YSZ ceramic coating consisting of a collection of splats on top of one another. The most important aspect of this layer is the inherent inter-splat and intra-splat porosity which undergoes sintering during thermal exposure. This study investigates the effect of thermal exposure on the microstructure and sintering behavior in single splats produced using different starting powders since this has been shown to influence the basic microstructure of YSZ topcoat. The bond coat is an MCrAlY metallic coating which serves as an Al reservoir and allows the formation of a protective alumina, Thermally Grown Oxide (TGO) layer between the bond coat (BC) and the top coat (TC) layers. This oxide scale formed upon thermal exposure prevents further oxidation of the underlying component (substrate) and thus provides protection. As such, the content of free Al in the bond coat layer is of significance and makes it crucial to understand the influence of bond coat microstructure evolution and oxidation involved during its formation. The interaction between the bond coat, the TGO and the top coat layers is examined in this study to understand the high temperature behavior of the TBC system with regards to variations in the top coat and bond coat material systems used.
基金supported by the National Research Councile of Science and Technology funded by the Korean Ministry of Industry in Korea(Project Nos.:1711173260,22-3803)the Korea Evaluation Institute of Industrial Technology funded by the Korean Ministry of Industry in Korea(Project Nos.:1415179713,20011157).
文摘In this study,a novel Mg production process for producing high-purity Mg metal from dolomite was developed.When the electrolysis of calcined dolomite was conducted using Cu cathode and C anode in MgF_(2)–LiF molten salt at 1083–1173 K by applying an average current of 1.42–1.46 A for 9.50–21.0 h,the current efficiency of 66.4–88.6%was obtained.The produced Mg alloys consisted of MgCu_(2)and Cu(Mg)or MgCu_(2)and CuMg_(2)phases,depending on the Mg concentration in the Mg alloy.When the electrolysis of calcined dolomite was conducted in MgF_(2)–LiF–CaF_(2)molten salt at 1083 K,the current efficiency was 40.9–71.4%,owing to undesired reactions such as electroreduction of Ca^(2+)or/and CO_(3)^(2−)ions.Meanwhile,the current efficiency increased from 40.9%to 63.2%by utilizing a Pt anode,because the occurrence of CO_(3)^(2−)ions in the molten salt was prevented.After vacuum distillation of the obtained Mg alloys at 1300 K for 10 h,Mg metal with a purity of 99.9996–99.9998%was produced.Therefore,the feasibility of this novel process for the production of high-purity Mg metal from dolomite was demonstrated.
基金the Natural Science Foundation of Shandong Province(No.ZR2021MB075)the National Natural Science Foundation of China(No.51602297).
文摘The green synthesis of nitrate(NO_(3)^(−))via electrocatalytic nitrogen oxidation reaction(NOR)is a promising strategy for artificial nitrogen fixation,which shows great advantages than traditional nitrate synthesis based on Haber–Bosch and Ostwald processes.But the poor N_(2)absorption,high bond energy of N≡N(941 kJ·mol^(−1)),and competing multi-electron-transfer oxygen evolution reaction(OER)limit the activity and selectivity.Herein,we fabricated MXene-derived irregular TiO_(2)−x nanoparticles anchored Cu nanowires(Cu-NWs)electrode for efficient electrocatalytic nitrogen oxidation,which exhibits a NO_(3)−yield of 62.50μg·h^(−1)·mgcat^(−1)and a Faradaic efficiency(FE)of 22.04%,and a significantly enhanced NO_(3)−yield of 92.63μg·h^(−1)·mgcat^(−1),and a FE of 40.58%under vacuum assistance.The TiO_(2)−x/Cu-NWs electrode also shows excellent reproducibility and stability under optimal experimental conditions.Moreover,a Zn-N_(2)reaction device was assembled with TiO_(2−x)/Cu-NWs as an anode and Zn plate as a cathode,obtaining an extremely high NO_(3)−yield of 156.25μg·h^(−1)·mgcat^(−1).The Zn-nitrate battery shows an open circuit voltage(OCV)of 1.35 V.This work provides novel strategies for enhancing the performance of ambient N_(2)oxidation to obtain higher NO_(3)^(−)yield.
基金supported by NSFC(21073235,21173270,21177160,21376261)863 Program(2013AA065302)PetroChina Innovation Foundation(2011D-5006-0403)
文摘Highly ordered mesoporous NiMoO4 material was successfully synthesized using mesoporous silica KIT-6 as hard template via vacuum nanocasting method. The structure was characterized by means of XRD, TEM, N2 adsorption-desorption, Raman and FT-IR. The mesoporous NiMoO4 with the coexistence of a-NiMoO4 and fl-NiMoO4 showed well-ordered mesoporous structure, a bimodal pore size distribution and crystalline framework. The catalytic performance of NiMoOa was investigated for oxidative dehydrogenation of propane. It is demonstrated that the mesoporous NiMoO4 catalyst with more surface active oxygen species showed better catalytic performance in oxidative dehydrogena- tion of propane in comparison with bulk NiMoO4.
基金the National Natural Science Foundation of China(No.51675491)
文摘Organic polymer materials were used as a layer of adhesive into the graphene sheet between the layers to enhance the interaction force between the nano-structure to achieve excellent mechanical properties and barrier properties. PLA with good flowability and easy processing was selected. The mechanical properties and barrier properties of the graphene-based composites were improved by the use of PLA for good flowability, making it easy to enter the GO layer as a binder. Three methods of preparation of GO/PLA homogeneous composite membranes were designed by vacuum filtration. The experimental results show that the injection of PLA as a molecular binder into the GO layer can effectively mimic the nano-structure, and enhance the intergranular force of the graphene molecules and the compatibility with the polymer matrix.
基金supported by the National Research Council of Science and Technology(NST)grant by the Korea government(MSIT)(No.CRC-1506-KIGAM)。
文摘The current electrolytic processes for magnesium(Mg)metal have several disadvantages,such as anhydrous magnesium chloride(MgCl_(2))preparation and generation of harmful chlorine(Cl_(2))gas.To overcome these drawbacks,a novel Mg production process to produce high-purity Mg metal directly from magnesium oxide(MgO)was investigated in this study.The electrolysis of MgO was conducted using a liquid tin(Sn)cathode and a carbon(C)anode in the eutectic composition of a magnesium fluoride(MgF_(2))-lithium fluoride(LiF)molten salt under an applied voltage of 2.5 V at 1053-1113 K.Under certain conditions,the Mg-Sn alloys with Mg_(2)Sn and Mg(Sn)phases were obtained with a current efficiency of 86.6%at 1053 K.To produce high-purity Mg metal from the Mg-Sn alloy,vacuum distillation was conducted at 1200-1300 K for a duration of 5-10 h.Following the vacuum distillation,the concentration of Mg in the Mg-Sn alloy feed decreased from 34.1 to 0.17 mass%,and Mg metal with a purity of 99.999%was obtained at 1200 K.Therefore,the electrolytic process developed here is feasible for the production of high-purity Mg metal from MgO using an efficient method.
文摘A new class of defects has been recently discovered,which are regarded double oxide film defects.In this study, a number of Ni-based vacuum-cast test bars were investigated. The fractures in the broken test barswere observed by Scanning Electron Microscopy (SEM). Energy Dispersive Spectroscopy (EDS), as well asWavelength Dispersive Spectroscopy (WDS) were used to characterize the chemical elements of the fracture'ssurface. Observation by SEM revealed the presence of inclusions identified as films that appeared to have initiatedthe growth of carbides. This study has added to the evidence that oxide film defects do exist in Ni-based super-alloyin certain vacuum casting conditions. It provides a reference for researchers' further study on the defects, andprovides a possible direction for researchers to improve casting technology so as to remove these defects.