随着冻结法立井建设在西部矿区富水地层的大规模运用,研究冻结壁在爆破、机械破岩等不同强度冲击荷载下的力学特性及损伤效应,对解决冻结壁开裂渗水及失稳透水问题具有重要意义。因此,该文章以甘肃省五举煤矿冻结凿井穿越的白垩系富水...随着冻结法立井建设在西部矿区富水地层的大规模运用,研究冻结壁在爆破、机械破岩等不同强度冲击荷载下的力学特性及损伤效应,对解决冻结壁开裂渗水及失稳透水问题具有重要意义。因此,该文章以甘肃省五举煤矿冻结凿井穿越的白垩系富水软岩为研究对象,分析不同冻结温度(25℃,-5℃,-10℃,-15℃和-20℃)红砂岩在正梯度冲击下(即冲击荷载逐渐加强)的动力学特性,同时采用核磁共振(nuclear magnetic resonance,NMR)技术对冲击过程中红砂岩孔隙数量、面积及孔隙度的变化进行检测,分析冻结红砂岩在正梯度冲击作用下的损伤演化规律。结果表明:相较于低、中速率冲击,在高速率冲击时,冻结红砂岩应变率随冻结温度的下降变化明显,温度效应显著;不同冻结温度红砂岩的峰值应力和弹性模量增幅随冲击荷载的升高而增加;峰值应变在-5℃时达到最大值,在-10℃~-20℃随冻结温度的降低其增长趋势逐渐放缓;由T谱曲线及谱面积可知,在正梯度冲击作用下,温度由25℃下降到-10℃,小孔隙孔径先减小后增大,数量先增加后降低,中、大孔隙孔径及数量则相反,谱面积先降低后升高,由-15℃下降到-20℃,小孔隙数量增加、孔径减小,中、大孔隙数量和孔径均呈小幅稳定增长,谱面积呈小幅增长;采用孔隙度的变化定义岩石损伤度,发现在正梯度冲击作用下,-10℃红砂岩的损伤趋势和损伤度最大,在-5℃~-10℃内出现损伤薄弱区。展开更多
Using ab initio molecular dynamics(AIMD)simulations,classical molecular dynamics(CMD)simulations,small-angle X-ray scattering(SAXS),and pulsed-field gradient nuclear magnetic resonance(PFG-NMR),the solvation structure...Using ab initio molecular dynamics(AIMD)simulations,classical molecular dynamics(CMD)simulations,small-angle X-ray scattering(SAXS),and pulsed-field gradient nuclear magnetic resonance(PFG-NMR),the solvation structure and ion dynamics of magnesium bis(trifluoromethanesulfonyl)imide(Mg(TFSI)_(2))aqueous electrolyte at 1,2,and 3 m concentrations are investigated.From AIMD and CMD simulations,the first solvation shell of an Mg;ion is found to be composed of six water molecules in an octahedral configuration and the solvation shell is rather rigid.The TFSI^(-)ions prefer to stay in the second solvation shell and beyond.Meanwhile,the comparable diffusion coefficients of positive and negative ions in Mg(TFSI)_(2)aqueous electrolytes have been observed,which is mainly due to the formation of the stable[Mg(H_(2)O_(6))_(2)]^(+)complex,and,as a result,the increased effective Mg ion size.Finally,the calculated correlated transference numbers are lower than the uncorrelated ones even at the low concentration of 2 and 3 m,suggesting the enhanced correlations between ions in the multivalent electrolytes.This work provides a molecular-level understanding of how the solvation structure and multivalency of the ion affect the dynamics and transport properties of the multivalent electrolyte,providing insight for rational designs of electrolytes for improved ion transport properties.展开更多
In situ NMR measurements of the diffusion coefficients,including an estimate of signal strength,of lithium ion conductor using diffusion-weighting pulse sequence are performed in this study.A cascade bilinear model is...In situ NMR measurements of the diffusion coefficients,including an estimate of signal strength,of lithium ion conductor using diffusion-weighting pulse sequence are performed in this study.A cascade bilinear model is proposed to estimate the diffusion sensitivity factors of pulsed-field gradient using prior information of the electrochemical performance and Arrhenius constraint.The model postulates that the active lithium nuclei participating electrochemical reaction are relevant to the NMR signal intensity,when discharge rate or temperature condition is varying.The electrochemical data and the NMR signal strength show a highly fit with the proposed model according our simulation and experiments.Furthermore,the diffusion time is constrained by temperature based on Arrhenius equation of reaction rates dependence.An experimental calculation of Li_4Ti_5O_（12）（LTO）/carbon nanotubes（CNTs） with the electrolyte evaluating at 20 ℃ is presented,which the b factor is estimated by the discharge rate.展开更多
文摘随着冻结法立井建设在西部矿区富水地层的大规模运用,研究冻结壁在爆破、机械破岩等不同强度冲击荷载下的力学特性及损伤效应,对解决冻结壁开裂渗水及失稳透水问题具有重要意义。因此,该文章以甘肃省五举煤矿冻结凿井穿越的白垩系富水软岩为研究对象,分析不同冻结温度(25℃,-5℃,-10℃,-15℃和-20℃)红砂岩在正梯度冲击下(即冲击荷载逐渐加强)的动力学特性,同时采用核磁共振(nuclear magnetic resonance,NMR)技术对冲击过程中红砂岩孔隙数量、面积及孔隙度的变化进行检测,分析冻结红砂岩在正梯度冲击作用下的损伤演化规律。结果表明:相较于低、中速率冲击,在高速率冲击时,冻结红砂岩应变率随冻结温度的下降变化明显,温度效应显著;不同冻结温度红砂岩的峰值应力和弹性模量增幅随冲击荷载的升高而增加;峰值应变在-5℃时达到最大值,在-10℃~-20℃随冻结温度的降低其增长趋势逐渐放缓;由T谱曲线及谱面积可知,在正梯度冲击作用下,温度由25℃下降到-10℃,小孔隙孔径先减小后增大,数量先增加后降低,中、大孔隙孔径及数量则相反,谱面积先降低后升高,由-15℃下降到-20℃,小孔隙数量增加、孔径减小,中、大孔隙数量和孔径均呈小幅稳定增长,谱面积呈小幅增长;采用孔隙度的变化定义岩石损伤度,发现在正梯度冲击作用下,-10℃红砂岩的损伤趋势和损伤度最大,在-5℃~-10℃内出现损伤薄弱区。
基金supported by the Joint Center for Energy Storage Research(JCESR),a U.S.Department of Energy,Energy Innovation Hub。
文摘Using ab initio molecular dynamics(AIMD)simulations,classical molecular dynamics(CMD)simulations,small-angle X-ray scattering(SAXS),and pulsed-field gradient nuclear magnetic resonance(PFG-NMR),the solvation structure and ion dynamics of magnesium bis(trifluoromethanesulfonyl)imide(Mg(TFSI)_(2))aqueous electrolyte at 1,2,and 3 m concentrations are investigated.From AIMD and CMD simulations,the first solvation shell of an Mg;ion is found to be composed of six water molecules in an octahedral configuration and the solvation shell is rather rigid.The TFSI^(-)ions prefer to stay in the second solvation shell and beyond.Meanwhile,the comparable diffusion coefficients of positive and negative ions in Mg(TFSI)_(2)aqueous electrolytes have been observed,which is mainly due to the formation of the stable[Mg(H_(2)O_(6))_(2)]^(+)complex,and,as a result,the increased effective Mg ion size.Finally,the calculated correlated transference numbers are lower than the uncorrelated ones even at the low concentration of 2 and 3 m,suggesting the enhanced correlations between ions in the multivalent electrolytes.This work provides a molecular-level understanding of how the solvation structure and multivalency of the ion affect the dynamics and transport properties of the multivalent electrolyte,providing insight for rational designs of electrolytes for improved ion transport properties.
基金supported by the National Major Scientific Equipment R&D Project (No. ZDYZ2010-2)the National Natural Science Foundation of China (No. 51307165)
文摘In situ NMR measurements of the diffusion coefficients,including an estimate of signal strength,of lithium ion conductor using diffusion-weighting pulse sequence are performed in this study.A cascade bilinear model is proposed to estimate the diffusion sensitivity factors of pulsed-field gradient using prior information of the electrochemical performance and Arrhenius constraint.The model postulates that the active lithium nuclei participating electrochemical reaction are relevant to the NMR signal intensity,when discharge rate or temperature condition is varying.The electrochemical data and the NMR signal strength show a highly fit with the proposed model according our simulation and experiments.Furthermore,the diffusion time is constrained by temperature based on Arrhenius equation of reaction rates dependence.An experimental calculation of Li_4Ti_5O_（12）（LTO）/carbon nanotubes（CNTs） with the electrolyte evaluating at 20 ℃ is presented,which the b factor is estimated by the discharge rate.
