The phase evolution,microstructure and magnetic properties of Nd9-xYxFe72Ti2Zr2B15(x=0,0.5,1,2) nanocomposite ribbons were investigated.It was found that substitution of Y enhanced glass forming ability of the over-qu...The phase evolution,microstructure and magnetic properties of Nd9-xYxFe72Ti2Zr2B15(x=0,0.5,1,2) nanocomposite ribbons were investigated.It was found that substitution of Y enhanced glass forming ability of the over-quenched ribbons and stabilized the amorphous phase during post annealing treatment.Appropriate content of Y substitution effectively refined the microstructure and enhanced the remanence of the annealed samples.The residual amorphous intergranular phase in the annealed sample improved the square...展开更多
In order to improve electrochemical properties,especially cycling stability,Co was partially substituted by Fe in A2B7-type La-Mg-Ni-based alloys.The La0.74Mg0.26Ni2.55Co0.65-xFex(x=0,0.10,0.20,0.30) alloys were prepa...In order to improve electrochemical properties,especially cycling stability,Co was partially substituted by Fe in A2B7-type La-Mg-Ni-based alloys.The La0.74Mg0.26Ni2.55Co0.65-xFex(x=0,0.10,0.20,0.30) alloys were prepared by inductive melting,and their phase structure and electrochemical properties were studied.The XRD and SEM results showed that the alloys consisted mainly of(La,Mg)2Ni7 phase,(La,Mg)5Ni19 phase and LaNi5 phase,except for absence of LaNi5 phase in the non-substituted alloy.The(La,Mg)5Ni19 ph...展开更多
To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were stud...To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml0.80Mg0.20（Ni2.90Co0.50-Mn0.30Al0.30）x （x=0.68, 0.70, 0.72, 0.74, 0.76） alloys and Cu-substituted Ml0.80Mg0.20（Ni2.90Co0.50-yCuyMn0.30Al0.30）0.70 （y=0, 0.10, 0.30, 0.50） alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi5 phase, a LaNi3 phase, and a minor La2Ni7 phase;in addition, in the case of Cu-substitution, the Nd2Ni7 phase appears and the LaNi3 phase vanishes. Ther-modynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with in-creasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ame-liorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.展开更多
The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La0.35Ce0.65Ni3.54Co0.80-xMn0.35Al0.32Mox （x=0.00, 0.10, 0.15, 0.20, 0.25） hydrogen storage alloy...The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La0.35Ce0.65Ni3.54Co0.80-xMn0.35Al0.32Mox （x=0.00, 0.10, 0.15, 0.20, 0.25） hydrogen storage alloys prepared by arc-melting method were sys-tematically studied in this paper. The X-ray diffraction （XRD） showed that after partial substitution of Mo for Co, the alloys remained a single LaNi5 phase with a hexagonal CaCu5-type structure. The P-C isotherms indicated that the equilibrium pressure gradually decreased with in-creasing of Mo content. Electrochemical studies showed that the substitution of Mo for Co could greatly increase discharge capacity, improve activation ability and reduce self-discharge of alloy electrodes. The alloy with x=0.25 exhibited a higher rate dischargeability （HRD1200= 50.9%）. Moreover, Mo is a vital element in favor of kinetic properties of AB5-type hydrogen storage alloys. As Mo content increased, the ex-change current density I0, the hydrogen diffusion rate gradually increased.展开更多
Yttrium （Y） has been used as the partial substitution element for lanthanum （La） to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. Lao.80-xYxMg0.20Ni2.85Mn0.10Coo.55Al0...Yttrium （Y） has been used as the partial substitution element for lanthanum （La） to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. Lao.80-xYxMg0.20Ni2.85Mn0.10Coo.55Al0.10 （x=0.00, 0.05 and 0.10） alloys were prepared by the inductive melting technique. The alloys were composed of LaNi5 and （La,Mg）2Ni7 phases, the introduction of Y promoted the formation of （La,Mg）2Ni7 phase, and thus the Y-substituted alloy electrodes exhibited higher discharge capacities. Y substitution was also found to be effective to improve the discharge kinetics of the alloy electrodes. When the Y content x increased from 0.00 to 0.10, the high-rate dischargeability of the alloy electrodes at a discharge current density of 1800 mA/g （HRDl800） in- creased from 23.6% to 39.7% at room temperature. In addition, the measured HRD1800 showed a linear dependence on both the ex- change current density and the hydrogen diffusion coefficient at different temperatures, respectively.展开更多
Ni-rich layered oxide LiNi_(x)Co_(y)Mn_(1-x-y)O_(2)(x≥0.8)is the most promising cathodes for future high energy automotive lithium-ion batteries.However,its application is hindered by the undesirable cycle stability,...Ni-rich layered oxide LiNi_(x)Co_(y)Mn_(1-x-y)O_(2)(x≥0.8)is the most promising cathodes for future high energy automotive lithium-ion batteries.However,its application is hindered by the undesirable cycle stability,mainly due to the irreversible structure change at high voltage.Herein,we demonstrate that F substitution with the appropriate amount(1 at%)is capable for improve the electrochemical performance of LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2) cathode significantly.It is revealed that F substitution can reduce cation mixing,stabilize the crystal structure and improve Li transport kinetics.The resulted LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(1.99)F_(0.01)cathode can deliver a high capacity of 194.4 mAh g^(-1) with capacity retention of 95.5%after 100 cycles at 2 C and 165.2 mAh g^(-1) at 5 C.In-situ synchrotron X-ray technique proves that F ions in the cathode materials can suppress the irreversible phase transition from H2 phase to H3 phase in high voltage region by preventing oxygen gliding in a-b planes,ensuring a long-term cycle stability.展开更多
The development of Ni-based single crystal superalloys relies heavily on the composition design with the addition of critical alloying elements,e.g.,Re and Ru.Understanding the role of alloying effects require to know...The development of Ni-based single crystal superalloys relies heavily on the composition design with the addition of critical alloying elements,e.g.,Re and Ru.Understanding the role of alloying effects require to know the configurations of the alloying element distribution betweenγ-Ni andγ′-Ni3Al phases and among various non-equivalent sites.This work employed firstprinciples density functional theory calculations to study the preference of phase and site occupancy of 11 alloying elements including Al and transition metal elements:3d (Ti,Cr,Co,Ni),4d (Mo,Ru),and 5d (Hf,Ta,W,Re) in Ni and Ni3Al.We calculated the substitution energies of 1298 triple-site doping configurations including 286 Ni Ni Ni site doping of Ni,726 Al Ni Ni site doping,and 286 Ni Ni Ni site doping of Ni3Al with alloying elements Ni,Co,Ru,Cr,Re,Mo,W,Al,Ti,Ta,and Hf.In the dual-site and triple-site doping of Ni and Ni3Al,all studied alloying elements preferred to occupy Ni phase rather than Ni3Al phase.We found that the most stable defect complexes often contained the favorable substitutions of Al,Ti,Ta,and Hf for the Ni sites that stabilized the alloying elements doping at the other one or two nearest neighbor sites.The co-substitutions of various alloying elements at multiple sites are critical to understanding the strengthening mechanism of alloying elements in Ni-based single crystal superalloys.展开更多
Hydrogen storage alloys(LaGdMg)Ni3.35-xCoxAl0.15(x=0,0.1,0.3,0.5,1.0,1.5,2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere.The effects of partly replacing Ni by Co element in(...Hydrogen storage alloys(LaGdMg)Ni3.35-xCoxAl0.15(x=0,0.1,0.3,0.5,1.0,1.5,2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere.The effects of partly replacing Ni by Co element in(LaGdMg)Ni3.35Al0.15 on the phase structure and electrochemical properties of(LaGdMg)Ni3.35-xCoxAl0.15 alloys were investigated.Structure analysis showed that the alloys consisted of Ce2Ni7-type(Gd2Co7-type),CaCu5-type,Pr5Co19-type,PuNi3-type phase structure.The addition of Co element obviously reduced the contents of CaCu5-type phase and increased the contents of Ce2Ni7-type phase.However,Pr5Co19-type and CaCu5-type phase obviously increased with the high content of Co.Rietveld analysis showed that the c-axis lattice parameters and cell volumes of the component phases increased with increasing Co content.The electrochemical measurements showed that as the Co content increased,the maximum discharge capacity and the cyclic stability of the annealed alloys both first increased then decreased.The(LaGdMg)Ni3.05Co0.3Al0.15 alloy electrode exhibited the maximum discharge capacity(392.92 mAh/g),and the(LaGdMg)Ni1.85Co1.0Al0.15 alloy electrode showed the best cyclic stability(S100=96.1%).展开更多
Ⅰ. INTRODUCTIONAfter H. Maeda et al. discovered a high T_c superconductor in the Bi-Sr-Ca-Cu-O system, which does not contain any notable rare-earth element, Z. Z. Sheng et al. discovered subsequently another high T_...Ⅰ. INTRODUCTIONAfter H. Maeda et al. discovered a high T_c superconductor in the Bi-Sr-Ca-Cu-O system, which does not contain any notable rare-earth element, Z. Z. Sheng et al. discovered subsequently another high T_c superconductor in T1-Ba-Ca-Cu-O system. Its T_c seems higher than Bi-system. The crystal structure and superconductivity of both oxides were stated to be either identical or isomorphous. There are two or three superconductive phases with T_c～85 K and ～105 K or even higher. These phases are of 2212 and 2223, or even of more different in chemical composition, usually called as the lower and the higher superconductive phases. A number of studies were carried out to explore a pure single superconductive phase with different treatments and to find out their structure relation for these phases.展开更多
Dicyandiamide (cyanoguanidine) is widely used in the syntheses of melamine and medicines such as barbiturates and guanidine derivatives. However, the substitution reaction of dicyandiamide, particularly the tetra subs...Dicyandiamide (cyanoguanidine) is widely used in the syntheses of melamine and medicines such as barbiturates and guanidine derivatives. However, the substitution reaction of dicyandiamide, particularly the tetra substitution reaction, has not been reported so far. We report here the substitution reaction of dicyandiamide in the presence of phase transfer catalyst.展开更多
Benefiting from the unique"Phonon-Glass,Electron-Crystal"(PGEC)characteristic,Zintl phases have been considered as a kind of promising thermoelectric materials.For the typical AM2X2 compounds with the CaAl2S...Benefiting from the unique"Phonon-Glass,Electron-Crystal"(PGEC)characteristic,Zintl phases have been considered as a kind of promising thermoelectric materials.For the typical AM2X2 compounds with the CaAl2Si2-type structure,YbMg_(2)Bi2 has shown competitive thermoelectric performance recently.Nevertheless,the optimization of YbMg_(2)Bi2 compounds is primarily focused on the substitution on Yb or Mg site.Herein,the Bi site is substituted by isoelectric Sb and the effect on the thermoelectric transport behavior is investigated.The partial substitution reduces the carrier concentration and induces the lattice deformation caused by the different atomic radius and mass between Bi and Sb,further leading to the decreased power factor and thermal conductivity.Fortunately,the reduction extent of the thermal conductivity outperforms that of power factor.Finally,the Sb substitution successfully results in a better thermoelectric performance compared with that of the pristine YbMg_(2)Bi1.98.Especially,the calculated energy conversion efficiency(a)of YbMg_(2)Bi1.88Sb0.1 which also possesses a relatively high output power density reaches the maximum value of 9.8% when Th=873 K,and Tc=300 K,respectively.This work demonstrates that the idea of substitution on anionic site should be a new strategy to achieve better ZT values for AM2X2 compounds.展开更多
The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr i...The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr is affected by Cr and Al contents and limits of occupation probabilities of Cr atom in L12 phase are present. The precipitate is single L12 phase when the component is less than the limit, Cr atoms substitute the Al sublattices in Ll2 phase, and both of atoms Al and Cr occupy the β-sites and complex phases Ni3（Al1-xCrx） are formed; Cr atoms enter Ni sites when Al and Cr contents exceed the limit, and substitute β-sites or both of α- and β-sites. The DO22 phase is formed at the boundary of Ll2 phase.展开更多
Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance ...Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance is challenging.Here,the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass m*d,weighted mobility mw and quality factor B is discussed in ZnO system.The results show that the secondary spinel phase Ga2O_(3)(ZnO)9 not only impacts on k but also on s and S at high temperature,while the effect of carrier concentration seem to be dominant at low temperature.For the high-spinel-segregation sample,a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperaturedependent m*d.The compensation process also induces a band sharpening,a small mw reduction,and a large B enhancement.As a result,In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%,owing to enhanced Seebeck coefficient by 110%as compared to the good Zn-substitution sample.展开更多
Dechlorination of crude oil is an effective way to alleviate corrosion in refinery units,and the critical process is the removal of organochlorine which can be efficiently removed through nucleophilic substitution rea...Dechlorination of crude oil is an effective way to alleviate corrosion in refinery units,and the critical process is the removal of organochlorine which can be efficiently removed through nucleophilic substitution reaction catalyzed by phase transfer.Herein,seven typical chlorinated alkanes were selected as model compounds to study the mechanism of dechlorination of crude oil by phase transfer catalyst in the nucleophilic substitution method,and a new dechlorination reagent using hexamethyl quaternary ammonium hydroxide(HMQAH)with two quaternary ammonium groups as phase transfer catalyst,ethylenediamine as nucleophile and ethanol as solvent was developed.The results show that the dechlorinating performance of the dechlorination reagent on the model compounds decreases in the following order:epichlorohydrin>1,2-dichlorobutane>1,2-dichloroethane>1,3-dichloropropane>2-chloropropane>1-chlorobutane>chloroisobutane.Meanwhile the results of the reaction kinetics show that epichlorohydrin with epoxy structure has the lowest activation energy in the process of nucleophilic substitution reaction by the phase transfer catalyst which makes it easier to be removed by the dechlorination reagent.The removal rate of epichlorohydrin can reach up to 99.4%.The optimal dechlorination reagent used ethylenediamine as nucleophile,ethanol as solvent and HMQAH as phase transfer catalyst.The dechlorinating rate of the Iranian crude oil reached 71.6%under conditions covering a reaction temperature of 95℃,a reaction time of 90 minutes,a dechlorination reagent dosage of 1000μg/g,and a phase transfer reagent/nucleophile molar ratio of 6:1.In addition,the mechanism of phase transfer in nucleophilic substitution reaction of chloroalkanes was investigated in the paper.展开更多
文摘The phase evolution,microstructure and magnetic properties of Nd9-xYxFe72Ti2Zr2B15(x=0,0.5,1,2) nanocomposite ribbons were investigated.It was found that substitution of Y enhanced glass forming ability of the over-quenched ribbons and stabilized the amorphous phase during post annealing treatment.Appropriate content of Y substitution effectively refined the microstructure and enhanced the remanence of the annealed samples.The residual amorphous intergranular phase in the annealed sample improved the square...
基金supported by the National Natural Science Foundation of China (20673093)the Natural Science Foundation of Hebei Province (B2007000303)Support Program for Hundred Excellent Innovation Talents from the Universities and Colleges of Hebei Province
文摘In order to improve electrochemical properties,especially cycling stability,Co was partially substituted by Fe in A2B7-type La-Mg-Ni-based alloys.The La0.74Mg0.26Ni2.55Co0.65-xFex(x=0,0.10,0.20,0.30) alloys were prepared by inductive melting,and their phase structure and electrochemical properties were studied.The XRD and SEM results showed that the alloys consisted mainly of(La,Mg)2Ni7 phase,(La,Mg)5Ni19 phase and LaNi5 phase,except for absence of LaNi5 phase in the non-substituted alloy.The(La,Mg)5Ni19 ph...
基金supported by the National Natural Science Foundation of China(Nos.21303157 and 21106123)the Natural Science Foundation of Hebei Province,China(No.B2012203104)+1 种基金the China Postdoctoral Science Foundation Project(2013M541201)the Research Fund for the Doctoral Program of Higher Education of China(20131333120008)
文摘To improve the electrochemical properties of rare-earth-Mg-Ni-based hydrogen storage alloys, the effects of stoichiometry and Cu-substitution on the phase structure and thermodynamic properties of the alloys were studied. Nonsubstituted Ml0.80Mg0.20（Ni2.90Co0.50-Mn0.30Al0.30）x （x=0.68, 0.70, 0.72, 0.74, 0.76） alloys and Cu-substituted Ml0.80Mg0.20（Ni2.90Co0.50-yCuyMn0.30Al0.30）0.70 （y=0, 0.10, 0.30, 0.50） alloys were prepared by induction melting. Phase structure analysis shows that the nonsubstituted alloys consist of a LaNi5 phase, a LaNi3 phase, and a minor La2Ni7 phase;in addition, in the case of Cu-substitution, the Nd2Ni7 phase appears and the LaNi3 phase vanishes. Ther-modynamic tests show that the enthalpy change in the dehydriding process decreases, indicating that hydride stability decreases with in-creasing stoichiometry and increasing Cu content. The maximum discharge capacity, kinetic properties, and cycling stability of the alloy electrodes all increase and then decrease with increasing stoichiometry or increasing Cu content. Furthermore, Cu substitution for Co ame-liorates the discharge capacity, kinetics, and cycling stability of the alloy electrodes.
基金supported by the National Natural Science Foundation of China (20673093)
文摘The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La0.35Ce0.65Ni3.54Co0.80-xMn0.35Al0.32Mox （x=0.00, 0.10, 0.15, 0.20, 0.25） hydrogen storage alloys prepared by arc-melting method were sys-tematically studied in this paper. The X-ray diffraction （XRD） showed that after partial substitution of Mo for Co, the alloys remained a single LaNi5 phase with a hexagonal CaCu5-type structure. The P-C isotherms indicated that the equilibrium pressure gradually decreased with in-creasing of Mo content. Electrochemical studies showed that the substitution of Mo for Co could greatly increase discharge capacity, improve activation ability and reduce self-discharge of alloy electrodes. The alloy with x=0.25 exhibited a higher rate dischargeability （HRD1200= 50.9%）. Moreover, Mo is a vital element in favor of kinetic properties of AB5-type hydrogen storage alloys. As Mo content increased, the ex-change current density I0, the hydrogen diffusion rate gradually increased.
基金Project supported by the National Natural Science Foundation of China(51171165,21303157)the Natural Science Foundation of Hebei Province(B2012203027,B2012203104 and B2014203114)
文摘Yttrium （Y） has been used as the partial substitution element for lanthanum （La） to improve the electrochemical kinetic performances of La-Mg-Ni-based hydrogen storage alloys. Lao.80-xYxMg0.20Ni2.85Mn0.10Coo.55Al0.10 （x=0.00, 0.05 and 0.10） alloys were prepared by the inductive melting technique. The alloys were composed of LaNi5 and （La,Mg）2Ni7 phases, the introduction of Y promoted the formation of （La,Mg）2Ni7 phase, and thus the Y-substituted alloy electrodes exhibited higher discharge capacities. Y substitution was also found to be effective to improve the discharge kinetics of the alloy electrodes. When the Y content x increased from 0.00 to 0.10, the high-rate dischargeability of the alloy electrodes at a discharge current density of 1800 mA/g （HRDl800） in- creased from 23.6% to 39.7% at room temperature. In addition, the measured HRD1800 showed a linear dependence on both the ex- change current density and the hydrogen diffusion coefficient at different temperatures, respectively.
基金financially supported by the National Natural Science Foundation of China(No.52071085,51671058)the Science and Technology Commission of Shanghai Municipality(No.19ZR1404200)。
文摘Ni-rich layered oxide LiNi_(x)Co_(y)Mn_(1-x-y)O_(2)(x≥0.8)is the most promising cathodes for future high energy automotive lithium-ion batteries.However,its application is hindered by the undesirable cycle stability,mainly due to the irreversible structure change at high voltage.Herein,we demonstrate that F substitution with the appropriate amount(1 at%)is capable for improve the electrochemical performance of LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2) cathode significantly.It is revealed that F substitution can reduce cation mixing,stabilize the crystal structure and improve Li transport kinetics.The resulted LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(1.99)F_(0.01)cathode can deliver a high capacity of 194.4 mAh g^(-1) with capacity retention of 95.5%after 100 cycles at 2 C and 165.2 mAh g^(-1) at 5 C.In-situ synchrotron X-ray technique proves that F ions in the cathode materials can suppress the irreversible phase transition from H2 phase to H3 phase in high voltage region by preventing oxygen gliding in a-b planes,ensuring a long-term cycle stability.
基金the Independent Research and Development Project of State Key Laboratory of Advanced Special Steelthe Shanghai Key Laboratory of Advanced Ferrometallurgy+2 种基金Shanghai University(Grant No.SKLASS 2019-Z024)the Science and Technology Commission of Shanghai Municipality(Grant No.19DZ2270200)the National Key Research and Development Program of China(Grant Nos.2017YFB0701502 and 2017YFB0702901)。
文摘The development of Ni-based single crystal superalloys relies heavily on the composition design with the addition of critical alloying elements,e.g.,Re and Ru.Understanding the role of alloying effects require to know the configurations of the alloying element distribution betweenγ-Ni andγ′-Ni3Al phases and among various non-equivalent sites.This work employed firstprinciples density functional theory calculations to study the preference of phase and site occupancy of 11 alloying elements including Al and transition metal elements:3d (Ti,Cr,Co,Ni),4d (Mo,Ru),and 5d (Hf,Ta,W,Re) in Ni and Ni3Al.We calculated the substitution energies of 1298 triple-site doping configurations including 286 Ni Ni Ni site doping of Ni,726 Al Ni Ni site doping,and 286 Ni Ni Ni site doping of Ni3Al with alloying elements Ni,Co,Ru,Cr,Re,Mo,W,Al,Ti,Ta,and Hf.In the dual-site and triple-site doping of Ni and Ni3Al,all studied alloying elements preferred to occupy Ni phase rather than Ni3Al phase.We found that the most stable defect complexes often contained the favorable substitutions of Al,Ti,Ta,and Hf for the Ni sites that stabilized the alloying elements doping at the other one or two nearest neighbor sites.The co-substitutions of various alloying elements at multiple sites are critical to understanding the strengthening mechanism of alloying elements in Ni-based single crystal superalloys.
基金Project supported by the National Natural Science Foundation of China (50941019)
文摘Hydrogen storage alloys(LaGdMg)Ni3.35-xCoxAl0.15(x=0,0.1,0.3,0.5,1.0,1.5,2.0) were prepared by induction melting followed by annealing treatment in argon atmosphere.The effects of partly replacing Ni by Co element in(LaGdMg)Ni3.35Al0.15 on the phase structure and electrochemical properties of(LaGdMg)Ni3.35-xCoxAl0.15 alloys were investigated.Structure analysis showed that the alloys consisted of Ce2Ni7-type(Gd2Co7-type),CaCu5-type,Pr5Co19-type,PuNi3-type phase structure.The addition of Co element obviously reduced the contents of CaCu5-type phase and increased the contents of Ce2Ni7-type phase.However,Pr5Co19-type and CaCu5-type phase obviously increased with the high content of Co.Rietveld analysis showed that the c-axis lattice parameters and cell volumes of the component phases increased with increasing Co content.The electrochemical measurements showed that as the Co content increased,the maximum discharge capacity and the cyclic stability of the annealed alloys both first increased then decreased.The(LaGdMg)Ni3.05Co0.3Al0.15 alloy electrode exhibited the maximum discharge capacity(392.92 mAh/g),and the(LaGdMg)Ni1.85Co1.0Al0.15 alloy electrode showed the best cyclic stability(S100=96.1%).
文摘Ⅰ. INTRODUCTIONAfter H. Maeda et al. discovered a high T_c superconductor in the Bi-Sr-Ca-Cu-O system, which does not contain any notable rare-earth element, Z. Z. Sheng et al. discovered subsequently another high T_c superconductor in T1-Ba-Ca-Cu-O system. Its T_c seems higher than Bi-system. The crystal structure and superconductivity of both oxides were stated to be either identical or isomorphous. There are two or three superconductive phases with T_c～85 K and ～105 K or even higher. These phases are of 2212 and 2223, or even of more different in chemical composition, usually called as the lower and the higher superconductive phases. A number of studies were carried out to explore a pure single superconductive phase with different treatments and to find out their structure relation for these phases.
文摘Dicyandiamide (cyanoguanidine) is widely used in the syntheses of melamine and medicines such as barbiturates and guanidine derivatives. However, the substitution reaction of dicyandiamide, particularly the tetra substitution reaction, has not been reported so far. We report here the substitution reaction of dicyandiamide in the presence of phase transfer catalyst.
基金supported financially by the National Natural Science Foundation of China(Nos.51771065 and 51871082)。
文摘Benefiting from the unique"Phonon-Glass,Electron-Crystal"(PGEC)characteristic,Zintl phases have been considered as a kind of promising thermoelectric materials.For the typical AM2X2 compounds with the CaAl2Si2-type structure,YbMg_(2)Bi2 has shown competitive thermoelectric performance recently.Nevertheless,the optimization of YbMg_(2)Bi2 compounds is primarily focused on the substitution on Yb or Mg site.Herein,the Bi site is substituted by isoelectric Sb and the effect on the thermoelectric transport behavior is investigated.The partial substitution reduces the carrier concentration and induces the lattice deformation caused by the different atomic radius and mass between Bi and Sb,further leading to the decreased power factor and thermal conductivity.Fortunately,the reduction extent of the thermal conductivity outperforms that of power factor.Finally,the Sb substitution successfully results in a better thermoelectric performance compared with that of the pristine YbMg_(2)Bi1.98.Especially,the calculated energy conversion efficiency(a)of YbMg_(2)Bi1.88Sb0.1 which also possesses a relatively high output power density reaches the maximum value of 9.8% when Th=873 K,and Tc=300 K,respectively.This work demonstrates that the idea of substitution on anionic site should be a new strategy to achieve better ZT values for AM2X2 compounds.
基金Project(50071046) supported by the National Natural Science Foundation of China
文摘The simulations of Cr atom substitution character during the formation of L12 and DO22 phases in Ni-Cr-Al alloy were performed at 873 K based on microscopic phase-field model. It is found that the substitution of Cr is affected by Cr and Al contents and limits of occupation probabilities of Cr atom in L12 phase are present. The precipitate is single L12 phase when the component is less than the limit, Cr atoms substitute the Al sublattices in Ll2 phase, and both of atoms Al and Cr occupy the β-sites and complex phases Ni3（Al1-xCrx） are formed; Cr atoms enter Ni sites when Al and Cr contents exceed the limit, and substitute β-sites or both of α- and β-sites. The DO22 phase is formed at the boundary of Ll2 phase.
基金supported by the Vietnam Ministry of Science and Technology under grant numberÐTÐL.CN-23/18.
文摘Conductivity s and thermal conductivity k are directly related to carrier concentration while Seebeck coefficient S is inversely proportional to carrier concentration.Therefore,improving thermoelectric(TE)performance is challenging.Here,the first-time analysis of secondary phase-controlled TE performance in terms of density-of-state effective mass m*d,weighted mobility mw and quality factor B is discussed in ZnO system.The results show that the secondary spinel phase Ga2O_(3)(ZnO)9 not only impacts on k but also on s and S at high temperature,while the effect of carrier concentration seem to be dominant at low temperature.For the high-spinel-segregation sample,a compensation of dopant atoms from the spinel to substitutional sites in the ZnO matrix at high temperature leads to a low decreased rate of temperaturedependent m*d.The compensation process also induces a band sharpening,a small mw reduction,and a large B enhancement.As a result,In and Ga co-doped ZnO bulk with the highest spinel segregation achieves the greatest PF improvement by 112.8%,owing to enhanced Seebeck coefficient by 110%as compared to the good Zn-substitution sample.
基金We acknowledge the financial support from the Joint Fund by the National Natural Science Foundation of China and PetroChina(Project U1862204).
文摘Dechlorination of crude oil is an effective way to alleviate corrosion in refinery units,and the critical process is the removal of organochlorine which can be efficiently removed through nucleophilic substitution reaction catalyzed by phase transfer.Herein,seven typical chlorinated alkanes were selected as model compounds to study the mechanism of dechlorination of crude oil by phase transfer catalyst in the nucleophilic substitution method,and a new dechlorination reagent using hexamethyl quaternary ammonium hydroxide(HMQAH)with two quaternary ammonium groups as phase transfer catalyst,ethylenediamine as nucleophile and ethanol as solvent was developed.The results show that the dechlorinating performance of the dechlorination reagent on the model compounds decreases in the following order:epichlorohydrin>1,2-dichlorobutane>1,2-dichloroethane>1,3-dichloropropane>2-chloropropane>1-chlorobutane>chloroisobutane.Meanwhile the results of the reaction kinetics show that epichlorohydrin with epoxy structure has the lowest activation energy in the process of nucleophilic substitution reaction by the phase transfer catalyst which makes it easier to be removed by the dechlorination reagent.The removal rate of epichlorohydrin can reach up to 99.4%.The optimal dechlorination reagent used ethylenediamine as nucleophile,ethanol as solvent and HMQAH as phase transfer catalyst.The dechlorinating rate of the Iranian crude oil reached 71.6%under conditions covering a reaction temperature of 95℃,a reaction time of 90 minutes,a dechlorination reagent dosage of 1000μg/g,and a phase transfer reagent/nucleophile molar ratio of 6:1.In addition,the mechanism of phase transfer in nucleophilic substitution reaction of chloroalkanes was investigated in the paper.
