The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies pre...The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress–strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%–90% of the initial value with GH dissociation, and the modulus decreases by 50% –75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.展开更多
High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost ...High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost alloyed cast iron rolls is poor and the cost of high-quality PM hard alloy rolls is very high. By means of centrifugal casting, HSS rolls having excellent wear resistance have been manufactured. The hardness of the HSS roll is 6.5~67 HRC, the range of variation is smaller than 2 HRC and its impact toughness is 15 J/cm<sup>2</sup>. The wear rate of HSS rolls used in the pre-finishing stands of high-speed hot wire-rod rolling mill reaches 2.5×10<sup>-4</sup>mm per ton steel. Furthermore, the manufacturing cost of HSS rolls is significantly lower than that of PM hard alloy rolls; it is only 30 percent of that of PM hard alloy rolls.展开更多
To understand the forming behaviour of aluminum alloys, the upsetting test of aluminum alloys at evaluated temperature is conducted. Because in warm forging the flow stress decreases with increasing straining, which i...To understand the forming behaviour of aluminum alloys, the upsetting test of aluminum alloys at evaluated temperature is conducted. Because in warm forging the flow stress decreases with increasing straining, which is so-called work softening, no appropriate material formulation is available. For the evaluation of flow stress of aluminum alloys in warm forging processes, in this paper, a formula is derived by analyzing the stress data measured at various temperatures. It is demonstrated that the formula fits the flow stress obtained from experiment.展开更多
One-dimensional(1D) GaN nanomaterials exhibiting various morphologies and atomic structures were prepared via ammoniation of either Ga_2O_3 nanoribbons, Ga_2O_3 nanorods or Ga nanowires filled into carbon nanotubes(CN...One-dimensional(1D) GaN nanomaterials exhibiting various morphologies and atomic structures were prepared via ammoniation of either Ga_2O_3 nanoribbons, Ga_2O_3 nanorods or Ga nanowires filled into carbon nanotubes(CNTs). The 1D GaN nanomaterials transformed from Ga_2O_3 nanoribbons consisted of numerous GaN nanoplatelets having the close-packed plane, i.e.(0002)2H or(111)3C parallel to the axes of starting nanoribbons. The 1D GaN nanomaterials converted from Ga_2O_3 nanorods were polycrystalline rods covered with GaN nanoparticles along the axes. The 1D GaN nanomaterials prepared from Ga nanowires filled into CNTs displayed two dominant morphologies:(i) single crystalline Ga N nanocolumns coated by CNTs, and(ii) pure single crystalline Ga N nanowires. The cross-sectional shape of Ga N nanowires were analyzed through the transmission electron microscopy(TEM) images. Formation mechanism of all-mentioned 1D GaN nanomaterials is then thoroughly discussed.展开更多
To suppress the inner charge recombination and inject vast electrons,CdTe nanocrystals are embedded into ultrathin ZnIn_(2)S_(4) nanosheets to construct ZnIn_(2)S_(4)/CdTe heterostructures,where the nanocrystals are g...To suppress the inner charge recombination and inject vast electrons,CdTe nanocrystals are embedded into ultrathin ZnIn_(2)S_(4) nanosheets to construct ZnIn_(2)S_(4)/CdTe heterostructures,where the nanocrystals are generated by a laser irradiation method.The optimal ZnIn_(2)S_(4)/CdTe heterojunction exhibits an excellent catalytic activity of 24.3 mmol/h/g,which is relatively high among the ZnIn_(2)S_(4)-based photocatalysts with-out noble metals.This enhancement is ascribed to a win-win mechanism of nanoscale heterojunctions and sulfur vacancies.The strong electron coupling effect,which is verified by density functional the-ory(DFT)calculations,impels the photo-generated electrons transfer from CdTe to ZnIn_(2)S_(4),boosting the charge separation.Meanwhile,the sulfur vacancies existing in ZnIn_(2)S_(4) can capture photoelectrons and act as active sites,facilitating the H_(2) generation reaction.In addition,the ZnIn_(2)S_(4) base and the ZnIn_(2)S_(4)/CdTe heterojunction also possess an evident photothermal effect and renewable cycle phenomena,enhancing the photocatalytic performance.This research provides new insights into the regulation of charge transfer through embedding nanocrystals.展开更多
基金supported by the National Natural Science Foundation of China(Grants 41376078,51639008,and 51239010)the China Geological Survey(Grant DD20160216)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant 2017027)
文摘The changes in the mechanical properties of gas hydrate-bearing sediments(GHBS) induced by gas hydrate(GH) dissociation are essential to the evaluation of GH exploration and stratum instabilities. Previous studies present substantial mechanical data and constitutive models for GHBS at a given GH saturation under the non-dissociated condition. In this paper, GHBS was formed by the gas saturated method, GH was dissociated by depressurization until the GH saturation reached different dissociation degrees. The stress–strain curves were measured using triaxial tests at a same pore gas pressure and different confining pressures. The results show that the shear strength decreases progressively by 30%–90% of the initial value with GH dissociation, and the modulus decreases by 50% –75%. Simplified relationships for the modulus, cohesion, and internal friction angle with GH dissociated saturation were presented.
文摘High speed steel (HSS) rolls can replace traditional rolls such as alloyed cast iron rolls and powder metallurgical (PM) hard alloy rolls. The main reasons for the replacement are that the wear resistance of low-cost alloyed cast iron rolls is poor and the cost of high-quality PM hard alloy rolls is very high. By means of centrifugal casting, HSS rolls having excellent wear resistance have been manufactured. The hardness of the HSS roll is 6.5~67 HRC, the range of variation is smaller than 2 HRC and its impact toughness is 15 J/cm<sup>2</sup>. The wear rate of HSS rolls used in the pre-finishing stands of high-speed hot wire-rod rolling mill reaches 2.5×10<sup>-4</sup>mm per ton steel. Furthermore, the manufacturing cost of HSS rolls is significantly lower than that of PM hard alloy rolls; it is only 30 percent of that of PM hard alloy rolls.
文摘To understand the forming behaviour of aluminum alloys, the upsetting test of aluminum alloys at evaluated temperature is conducted. Because in warm forging the flow stress decreases with increasing straining, which is so-called work softening, no appropriate material formulation is available. For the evaluation of flow stress of aluminum alloys in warm forging processes, in this paper, a formula is derived by analyzing the stress data measured at various temperatures. It is demonstrated that the formula fits the flow stress obtained from experiment.
基金National Natural Science Foundation of China(No.10774053)Hubei Province Nature Science Foundation of China(No.2007ABB008)Programs Foundation of Ministry of Education of China(No.20070487038)
文摘One-dimensional(1D) GaN nanomaterials exhibiting various morphologies and atomic structures were prepared via ammoniation of either Ga_2O_3 nanoribbons, Ga_2O_3 nanorods or Ga nanowires filled into carbon nanotubes(CNTs). The 1D GaN nanomaterials transformed from Ga_2O_3 nanoribbons consisted of numerous GaN nanoplatelets having the close-packed plane, i.e.(0002)2H or(111)3C parallel to the axes of starting nanoribbons. The 1D GaN nanomaterials converted from Ga_2O_3 nanorods were polycrystalline rods covered with GaN nanoparticles along the axes. The 1D GaN nanomaterials prepared from Ga nanowires filled into CNTs displayed two dominant morphologies:(i) single crystalline Ga N nanocolumns coated by CNTs, and(ii) pure single crystalline Ga N nanowires. The cross-sectional shape of Ga N nanowires were analyzed through the transmission electron microscopy(TEM) images. Formation mechanism of all-mentioned 1D GaN nanomaterials is then thoroughly discussed.
基金The research was sponsored by the National Natural Science Foundation of China(Nos.52172101 and 51872240)the National Key R&D Program for International Cooperation(No.2021YFE0115100)+2 种基金Shaanxi Province Key Research and Develop-ment Program(No.2021ZDLGY14-08)the Fundamental Research Funds for the Central Universities(No.3102019JC005)the Guangdong Basic and Applied Basic Research Foundation(No.2022A1515110228).The authors thank the Analysis and Test Center of Northwestern Polytechnical University and Shaanxi Materials Analysis and Research Center for XPS,SEM,and TEM characterizations.
文摘To suppress the inner charge recombination and inject vast electrons,CdTe nanocrystals are embedded into ultrathin ZnIn_(2)S_(4) nanosheets to construct ZnIn_(2)S_(4)/CdTe heterostructures,where the nanocrystals are generated by a laser irradiation method.The optimal ZnIn_(2)S_(4)/CdTe heterojunction exhibits an excellent catalytic activity of 24.3 mmol/h/g,which is relatively high among the ZnIn_(2)S_(4)-based photocatalysts with-out noble metals.This enhancement is ascribed to a win-win mechanism of nanoscale heterojunctions and sulfur vacancies.The strong electron coupling effect,which is verified by density functional the-ory(DFT)calculations,impels the photo-generated electrons transfer from CdTe to ZnIn_(2)S_(4),boosting the charge separation.Meanwhile,the sulfur vacancies existing in ZnIn_(2)S_(4) can capture photoelectrons and act as active sites,facilitating the H_(2) generation reaction.In addition,the ZnIn_(2)S_(4) base and the ZnIn_(2)S_(4)/CdTe heterojunction also possess an evident photothermal effect and renewable cycle phenomena,enhancing the photocatalytic performance.This research provides new insights into the regulation of charge transfer through embedding nanocrystals.