Kinetics and mechanism of oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction were researched in air using vertical high temperature thermal dilatometer from 25℃to 1...Kinetics and mechanism of oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction were researched in air using vertical high temperature thermal dilatometer from 25℃to 1400℃.It is shown that oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced Al4C3 in situ reaction is the common logarithm of oxidation time t and the oxygen partial pressure P inside MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction in air at 1400℃is as follows:P=F(-2.75×10^-4A+2.13×10^-3)lnt.The nonsteady diffusion kinetic equation of O2 at 1400℃inside the composites is as follows:J=De lnt.Acceleration of the total diffusional?flux of oxygen inside the composites at 1400℃is in inverse proportion to the oxidation time.The nonsteady state effective diffusion coefficient De of O2(g)inside the composites decreases in direct proportional to the increase of the amount of metallic aluminium.The method of preventing the oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction is to increase the amount of Al.The slag erosion index of MgO-Al2O3 spinel carbon composite reinforced by Al4C3 in situ reaction is 0.47 times that of MgO-CaO brick used in the lining above slag line area of a VOD stainless steel-making vessel.HMOR of MgO-Al2O3 spinel carbon composite reinforced by Al4C3 in situ reaction is 26.7 MPa,HMOR of the composite is 3.6 times the same as that of MgO-CaO brick used in the lining above slag line area of a VOD vessel.Its service life is two times as many as that of MgO-CaO brick.展开更多
The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are f...The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl 2 O 4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5.10 eV for MgAl 2 O 4 and 4.81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point ( band), the coherent tunneling effect might be expected to appear in MgAl 2 O 4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2.9 J m 2 ) and MgAl 2 O 4 (2.27 J m 2 ) on the {100} orientation, and the smaller lattice mismatch between MgAl 2 O 4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl 2 O 4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.展开更多
One of the central tasks in the field of heterogeneous catalysis is to establish structure‐function relationships for these catalysts,especially for precious metals dispersed on the sub‐nanometer scale.Here,we repor...One of the central tasks in the field of heterogeneous catalysis is to establish structure‐function relationships for these catalysts,especially for precious metals dispersed on the sub‐nanometer scale.Here,we report the preparation of MgAl2O4‐supported Pt nanoparticles,amorphous aggregates and single atoms,and evaluate their ability to catalyze the hydrogenation of benzaldehyde.The Pt species were characterized by N2adsorption,X‐ray diffraction(XRD),aberration‐corrected transmission electron microscopy(ACTEM),CO chemisorption and in situ Fourier transform infrared spectroscopy of the chemisorbed CO,as well as by inductively coupled plasma atomic emission spectroscopy.They existed as isolated or neighboring single atoms on the MgAl2O4support,and formed amorphous Pt aggregates and then nanocrystallites with increased Pt loading.On the MgAl2O4support,single Pt atoms were highly active in the selective catalytic hydrogenation of benzaldehyde to benzyl alcohol.The terrace atoms of the Pt particles were more active but less selective;this was presumably due to their ability to form bridged carbonyl adsorbates.The MgAl2O4‐supported single‐atom Pt catalyst is a novel catalyst with a high precious atom efficiency and excellent catalytic hydrogenation ability and selectivity.展开更多
本文利用1.7 M eV电子辐照MgA l2O4尖晶石后,通过吸收谱测量表明,被电子辐照的尖晶石可产生大量的F型色心缺陷,而且电子的辐照剂量明显地影响尖晶石的光谱特性。随着电子辐照剂量增加,F型色心缺陷的浓度增大;椭偏光谱分析得到的光学常...本文利用1.7 M eV电子辐照MgA l2O4尖晶石后,通过吸收谱测量表明,被电子辐照的尖晶石可产生大量的F型色心缺陷,而且电子的辐照剂量明显地影响尖晶石的光谱特性。随着电子辐照剂量增加,F型色心缺陷的浓度增大;椭偏光谱分析得到的光学常数谱随电子辐照剂量的变化而改变。我们对上述现象进行了合理的分析。展开更多
基金Funded by the National Torch Plan of China(No.2005EB031110)the National Scientific and Technique Program of Ninth-five Year Plan(96-22-01-19)。
文摘Kinetics and mechanism of oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction were researched in air using vertical high temperature thermal dilatometer from 25℃to 1400℃.It is shown that oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced Al4C3 in situ reaction is the common logarithm of oxidation time t and the oxygen partial pressure P inside MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction in air at 1400℃is as follows:P=F(-2.75×10^-4A+2.13×10^-3)lnt.The nonsteady diffusion kinetic equation of O2 at 1400℃inside the composites is as follows:J=De lnt.Acceleration of the total diffusional?flux of oxygen inside the composites at 1400℃is in inverse proportion to the oxidation time.The nonsteady state effective diffusion coefficient De of O2(g)inside the composites decreases in direct proportional to the increase of the amount of metallic aluminium.The method of preventing the oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction is to increase the amount of Al.The slag erosion index of MgO-Al2O3 spinel carbon composite reinforced by Al4C3 in situ reaction is 0.47 times that of MgO-CaO brick used in the lining above slag line area of a VOD stainless steel-making vessel.HMOR of MgO-Al2O3 spinel carbon composite reinforced by Al4C3 in situ reaction is 26.7 MPa,HMOR of the composite is 3.6 times the same as that of MgO-CaO brick used in the lining above slag line area of a VOD vessel.Its service life is two times as many as that of MgO-CaO brick.
基金supported by the National Natural Science Foundation of China (Nos. 50831002, 50971025, 11174031,51071022)Program for Changjiang Scholars and Innovative Research Team in University, Beijing Nova Program (No.2011031)+1 种基金Beijing Natural Science Foundation (No.2102032)the National Basic Research Program of China(No. 2012CB932702)
文摘The electronic structures of spinel MgAl 2 O 4 and MgOtunnel barrier materials were investigated using first-principles density functional theory calculations. Our results show that similar electronic structures are found for the MgAl 2 O 4 and MgO tunneling barriers. The calculated direct energy gaps at the Γ-point are about 5.10 eV for MgAl 2 O 4 and 4.81 eV for MgO, respectively. Because of the similar feature in band structures from Γ high-symmetry point to F point ( band), the coherent tunneling effect might be expected to appear in MgAl 2 O 4-based MTJs like in MgO-based MTJs. The small difference of the surface free energies of Fe (2.9 J m 2 ) and MgAl 2 O 4 (2.27 J m 2 ) on the {100} orientation, and the smaller lattice mismatch between MgAl 2 O 4 and ferromagnetic electrodes than that between MgO and ferromagnetic electrodes, the spinel MgAl 2 O 4 can substitute MgO to fabricate the coherent tunneling and chemically stable magnetic tunnel junction structures, which will be applied in the next generation read heads or spintronic devices.
基金supported by the National Natural Science Foundation of China(21403213,21673226,21376236,U1462121)the"Hundred Talents Programme"of the Chinese Academy of Sciences+3 种基金the"Strategic Priority Research Program"of the Chinese Academy of Sciences(XDB17020100)National Key R&D Program of China(2016YFA0202801)Department of Science and Technology of Liaoning province under contract of 2015020086-101the Natural Science Foundation of Hunan Province(2016JJ2128)~~
文摘One of the central tasks in the field of heterogeneous catalysis is to establish structure‐function relationships for these catalysts,especially for precious metals dispersed on the sub‐nanometer scale.Here,we report the preparation of MgAl2O4‐supported Pt nanoparticles,amorphous aggregates and single atoms,and evaluate their ability to catalyze the hydrogenation of benzaldehyde.The Pt species were characterized by N2adsorption,X‐ray diffraction(XRD),aberration‐corrected transmission electron microscopy(ACTEM),CO chemisorption and in situ Fourier transform infrared spectroscopy of the chemisorbed CO,as well as by inductively coupled plasma atomic emission spectroscopy.They existed as isolated or neighboring single atoms on the MgAl2O4support,and formed amorphous Pt aggregates and then nanocrystallites with increased Pt loading.On the MgAl2O4support,single Pt atoms were highly active in the selective catalytic hydrogenation of benzaldehyde to benzyl alcohol.The terrace atoms of the Pt particles were more active but less selective;this was presumably due to their ability to form bridged carbonyl adsorbates.The MgAl2O4‐supported single‐atom Pt catalyst is a novel catalyst with a high precious atom efficiency and excellent catalytic hydrogenation ability and selectivity.
文摘本文利用1.7 M eV电子辐照MgA l2O4尖晶石后,通过吸收谱测量表明,被电子辐照的尖晶石可产生大量的F型色心缺陷,而且电子的辐照剂量明显地影响尖晶石的光谱特性。随着电子辐照剂量增加,F型色心缺陷的浓度增大;椭偏光谱分析得到的光学常数谱随电子辐照剂量的变化而改变。我们对上述现象进行了合理的分析。
