镁基储氢合金氢化物Mg2NiH4的制备及性能研究

以不经压制的Mg、Ni混合粉末为原料,利用氢化燃烧合成法在合成温度850 K和1.8 MPa初始合成氢压下制备了镁基储氢合金氢化物Mg2NiH4,并利用XRD及PCT仪分析了其物相组成和储氢性能.研究表明,产物由单一物相Mg2NiH4组成,无未反应的Ni和不完全氢化的Mg2NiH0.3;相对于传统熔炼法制备的Mg2Ni,氢化燃烧合成产物具有更高的氢化活性,在没有任何活化处理的前提下,第一次吸氢就能以很快的速度达到饱和吸氢量,同时在任何吸氢温度下均具有较好的吸氢动力学性能,且随温度的降低,最大吸氢量降低幅度较小,平台压和吸放氢温度的关系为:lgP(0.1 MPa)=-3 187.6/ T 6.362 4(吸氢),lgP(0.1 MPa)=-3 468.4/T 6.694 3(放氢).     

Thermal desorption of hydrogen from Mg2Ni hydrogen storage materials

In order to investigate the influence of HCS on the hydrogen occupation site of Mg2Ni alloy, the thermal desorption technique has been applied to Mg2Ni hydride made by hydriding combustion synthesis (HCS). Mg2Ni was made under low temperature in a short time by the HCS compared to conventional melting process. At various initial hydride wt% from 0.91 to 3.52, the sample was heated to 623 K at a rate of 1.0 K/min. The starting temperature of the evolution of hydrogen goes higher as the initial hydride wt% increases. Only one peak is shown in the case of the small initial hydride wt%. But two peaks appeared with increasing initial hydride wt%. The activation energies obtained by the first and second peaks are 113.0 and 99.5 kJ/mol respectively. The two site occupation model by Darriet et al. was proved. The influence of HCS on the hydrogen occupation site of Mg2Ni alloy is nonexistent.     

A study on the hydriding-dehydriding kinetics of Mg1.9Al0.1Ni

The hydrogen absorption/desorption (A/D) kinetics of hydrogen storage alloys Mg_1.9Al_0.1Ni prepared by hydriding combustion synthesis in two-phase (-) region in the temperature range from 523 to 573 K have been investigated. The hydriding/dehydriding (H/D) reaction rate constants were extracted from the time-dependent A/D curves. The obtained hydrogen A/D kinetic curves were fitted using various rate equations to reveal the mechanism of the H/D processes. The relationships of rate constant with temperature were established. It was found that the three-dimensional diffusion process dominated the hydrogen A/D. The activation energies of Mg_1.9Al_0.1Ni are 52 ± 2 and 48 ± 1 kJ/mol H₂ for the H/D processes smaller than that of Mg₂Ni, which can be explained that the improvement of H/D reaction kinetics in Mg₂Ni by using additive Al.     

Cu的添加对Mg2Ni合金储氢性能的影响

采用机械合金化法,制备了Mg2Ni1-xCux(x=0、0.1、0. 3)合金,研究了Cu对Mg2Ni储氢合金储氢性能的影响.XRD和SEM研究表明Cu的加入使合金中产生了Cu11Mg10Ni9新相.利用PCT测试仪测定了合金的储氢性能,结果表明,添加Cu元素会降低合金的吸氢量,但能有效地提高放电容量和循环稳定性.制备出的Mg2Ni0.9Cu0.1与Mg2Ni0.7Cu0.3相比,前者具有较大的吸氢量,后者的放电容量较大,循环稳定性较好.     

机械合金化制备Mg76-xTi12Ni12Mnx（x=2,4,6,8）合金及其贮氢性能研究

利用机械合金化法制备了Mg76-xTi12Ni12Mnx(x=2,4,6,8)合金,并研究了Mn添加量对合金贮氢性能的影响。结果表明,在Mg76-xTi12Ni12Mnx(x=2,4,6,8)合金中合金相主要由Mg2Ni和Ti2Ni相组成,合金最大贮氢量分别为3.47%、3.32%、3.60%和3.11%(质量分数,下同),合金氢化物的分解热依次为-79.2kJ/mol、-78.0kJ/mol、-73.7kJ/mol和-73.6kJ/mol,添加Mn可降低合金氢化物的稳定性,改善其热力学性能,非晶化不利于提高合金的贮氢性能。     

The explosive oxidation of hydrocarbons in a supercritical water

The kinetics of oxidation of naphthalene and a heavy oil residue (upon vacuum distillation) by oxygen dissolved in supercritical water is studied in a wide range of temperatures (663 K≤T≤1075 K) and pressures (31MPa≤P≤67MPa). It is established that the oxidation process exhibits an explosive (blow-up) character. The kinetic constants characterizing the thermal explosion are determined. For naphthalene, the heat evolution rate during the explosive oxidation obeys the law W _N=10^13.10±0.30exp((170.4±1.0 kJ/mol)/RT)×[C₁₀H₈]^0.46±0.01[O₂]^0.63±0.01[H₂O]^1.66±0.03kJ/(l s).     

NbCl5 and CrCl3 catalysts effect on synthesis and hydrogen storage performance of Mg–Ni–NiO composites

Two kinds of novel materials, Mg–1·6 mol%Ni–0·4 mol%NiO–2 mol%MCl (MCl = NbCl ₅ , CrCl ₃ ), along with Mg–1·6 mol%Ni–0·4 mol%NiO for comparison, were examined for their potential use in hydrogen storage applications, having been fabricated via cryomilling. The effects of NbCl ₅ and CrCl ₃ on hydrogen storage performance were investigated. A microstructure analysis showed that besides the main Mg and Ni phases, NiO and Mg ₂ Ni phases were present in all samples. MgCl ₂ was only found in halide-doped samples and NbO was only found in NbCl ₅ -doped samples after ball milling. The particle size decreased significantly after 7 h of cryomilling. MgH ₂ , Mg ₂ NiH ₄ and Mg ₂ NiH_0·3 were present in all the samples, while NbH ₂ was only observed in the NbCl ₅ -doped sample afterabsorption. The NbCl ₅ -containing composite exhibited a low onset absorption temperature of 323 K, which was 10 K lower than that of the no-halide doped catalyst. It absorbed 5·32 wt% of hydrogen in 370 s at 623 K under 4 MPa hydrogen pressure and can absorb 90% of its full hydrogen capacity in 50 s. Having an onset desorption temperature of 483 K in vacuum, the NbCl ₅ -containing composite desorbed hydrogen faster than the no-halide doped sample. The hydriding–dehydriding kinetics performance of the CrCl ₃ -doped sample did not improve, but it did exhibit a lower onset desorption temperature of 543 K under 0·1 MPa, which was 20 K lower than that of the no-halide doped sample. NbO, NiO and NbH ₂ played important roles in improving absorption and desorption performances.     

机械合金化(Mg+Mg2 Ni)+TiO2合金的储氢性能

用机械合金化法合成了(Mg Mg2Ni) TiO2储氢合金,借助XRD分析了TiO2的加入对合金的物相结构的影响,SEM考察了合金的形貌.TiO2在合金的吸放氢过程中起到很好的催化作用,降低合金放氢温度并且提高合金储氢量,(Mg Mg2Ni) 10wt%TiO2合金在573K下的储氢量是5.84wt%.     

Hydrogen sorption characteristics of the composites 90 wt.% Mg (MgH2)–10 wt.% V0.855Ti0.095Fe0.05

The hydrogen absorption–desorption characteristics of composites containing 90 wt.% Mg or MgH₂ and 10 wt.% of the intermetallic compound V_0.855Ti_0.095Fe_0.05 obtained by mechanical alloying for 1 and 5 h in an inert medium were investigated. Absorption measurements were performed under a hydrogen pressure P = 1 MPa at temperatures of 623, 573, 523, and 473 K. Dehydriding was studied at 623 and 573 K and a pressure of 0.15 MPa. It was established that the presence of the additive improved significantly the hydriding kinetics of magnesium while the effect of the duration of mechanical alloying was less pronounced. Due to the small difference in specific surface areas and crystallite sizes, both composites investigated showed no substantial difference in behavior during absorption and desorption of hydrogen. The best absorption–desorption properties were found with the composite 90 wt.% Mg–10 wt.% V_0.855Ti_0.095Fe_0.05 mechanically activated for 5 h.     

Thermodynamics and kinetics of MgH<Subscript>2</Subscript>–nfTa<Subscript>2</Subscript>O<Subscript>5</Subscript> composite for reversible hydrogen storage application

The thermodynamics and kinetics of hydrogen absorption–desorption of nfTa₂O₅–Mg–MgH₂—composite (nf stands for nano-flakes) have been studied. The nfTa₂O₅–Mg composite could absorb hydrogen at room temperature (17 °C). The hydrogen desorption of nfTa₂O₅–MgH₂ composite starts at 200 °C. The remarkably improved hydrogen absorption–desorption of catalyzed Mg–MgH₂ could be attributed to the nano-engineered surface by nfTa₂O₅. The enthalpies of hydrogen absorption–desorption were found to be 80 ± 2, and 76 ± 3 kJ/mol respectively. The activation energy of hydrogen absorption was evaluated as 49 ± 5 kJ/mol which is same as the energy barrier for diffusion of hydrogen in Mg matrix. The apparent activation of hydrogen desorption of nfTa₂O₅–MgH₂ was found to be 74 ± 7 kJ/mol. The nfTa₂O₅–MgH₂ composite has shown cyclic stability up to fifty hydrogen absorption–desorption without significant changes in the kinetics and hydrogen storage capacity.     

Effect of grain size and indium addition on tensile characteristics of Al–1Si alloy

Abstract

The effect of grain size and indium addition on the workhardening characteristics of Al–1Si (wt-%) alloy has been investigated at room temperature (RT). The samples were preaged at different temperatures in the range 523–623 K. The yield stress, the fracture stress, the fracture time and the linear workhardening coefficient generally decreased with increasing temperature and/or grain size, while the fracture strain and dislocation slip distance increased. The yield and fracture stresses for different grain sizes at different temperatures were found to be linearly related to grain diameters. Indium addition caused general increase for all the measured strength parameters. As concluded from transmission electron microscope (TEM) investigations, In addition to Al–Si alloy may retard the coarsening of Si particles. The energies activating the operating fracture mechanisms were found to be 79·6±0·4 and 32·4±0·4 kJ mol^?1 for alloys Al–1Si and Al–1Si–0·2In respectively. This suggests a value of 47·2 kJ mol^?1 as a binding energy between Si and In atoms in Al matrix.     

Ca3-xMg2+xNi13合金的储氢性能

为了弄清Mg含量对Ca3Mg2Ni13型化合物结构参数和储氢性能的影响,利用X射线衍射研究了Ca3-xMg2+x,Ni13(x=0.5,1.0和1.5)合金的相结构,并采用Sieverts型设备测量了其P-C-T曲线.研究表明,Mg在Ca3Mg2Ni13型化合物中的最大固溶度接近于Ca1.5Mg<,3.5>Ni13合金中的Mg含量.固溶的Mg含量增加导致化合物点阵常数减小,这可以有效地改善吸放氢热力学性能,其中Ca2Mg3Ni13吸、放氢的焓变分别为-28,30 kJ/mol H2.此外,Ca2Mg3Ni13在吸放氢循环过程中不发生氢致非晶化和氢致分解,因而具有良好的循环稳定性.     

Binary System MnO-Nb_2O_5

The phase diagram of the binary systemMnO-Nb_2O_5 was studied by means of the differentialthermal analysis(DTA),X-ray diffraction analysis andscanning electron microscopy(SEM).Thermodynamic da-ta of the new compounds 4MnO·Nb_2O_5 andMnO·Nb_2O_5were found as follows:4MnO·Nb_2O_5:t_m=1398±2℃△H_m=129000(J/mol)△S_m=77(J/mol,K)△G_m~o=129000-77T(J/mol)MnO·Nb_2O_5:t_m=1499±2℃△H_m=86940(J/mol)△S_m=49.6(J/mol,K)△G_m~o=86940-49.6T(J/mol)The eutectic parameters for the system are given below:t_(E1)=1383±3℃ N_(E1(MnO))=0.896t_(E2)=1312±2℃ N_(E2(MoO))=0.713t_(E3)=1400±4℃ N_(E3(MnO))=0.231     

Thermodynamic functions of ScVO<Subscript>4</Subscript> at temperatures from 0 to 350 K

The heat capacity of ScVO₄ has been determined by adiabatic calorimetry at temperatures from 14.52 to 347.13 K, and smoothed heat capacity data have been used to evaluate its thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy). At 298.15 K, the thermodynamic functions of scandium orthovanadate are C _p ⁰(298.15 K) = 110.5 ± 0.1 J/(mol K), S ⁰(298.15 K) = 110.9 ± 0.1 J/(mol K), H ⁰(298.15 K) − H ⁰(0) = 18.53 ± 0.01 kJ/mol, and Φ⁰(298.15 K) = −[G ⁰(298.15 K)/298.15] = 48.75 ± 0.12 J/(mol K). The calculated Gibbs energy of formation of scandium orthovanadate from its constituent elements is Δ_f G ⁰(ScVO₄, 298.15 K) = −1644.0 ± 2.2 kJ/mol.     

Interaction of intermetallic compounds of rare-earth metals, nickel, and aluminum with hydrogen

AtT=293 K andp _H2≤10 MPa. we synthesized hydridesR _3Ni8Al-H_7.2–15.2 (R=Nd. Sm. Gd. Tb. Dy, Ho, Er, Tm, and Lu). The X-ray analysis revealed an isotropic deformation of the original crystal lattice due to hydrogen penetration. For the hydrides obtained, the lattice constanta exceeds that of the original intermetallide by 3.9–6.0% and the constantc and the cell volumeV are increased by 6.0–12.6% and 15.6–26.4%, respectively. The volume expansion per absorbed hydrogen atom is (2.4–3.6)·10⁻³ nm⁻³. By construction of the isotherms of hydrogen desorption for the systemsR _3Ni>8Al-H, we established the existence of the α-solid hydrogen solution and the region of its coexistence with β-hydride, the region of coexistence of β- and γ-hydrides, and the β- and γ-hydride phases. Heats of the phase transitions were determined as follows: ΔH=31.4±0.8 kJ/(mole H₂) in the system Gd₃Ni₈Al-H for the transition γ→β, ΔH=39.8±1.1 kJ/(mole H₂) in the system Tb₃Ni₈Al−H for the transition β→α. and ΔH=37.1±5.1 kJ/(mole H₂) in the system Tm₃Ni₈Al−H for the transition γ→β. Among the products of hydrogenation, intermetallic compounds Lu₃Ni8Al and Tm₃Ni₈Al. we revealed the β′- and γ-phases. We also found that, atp _H2≤10 MPa andT=400–430 K, the phases of Sm₃Ni₈Al and Gd₃Ni₈Al decay into two hydridesRH_2–3 andR(Ni.Al)₅H _x . Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 36, No. 1, pp. 76–82, January–February, 2000.     

The influence of tetrahydrofuran treatment on hydrogen storage properties of the magnesium

The hydriding and dehydriding properties of the tetrahydrofuran (THF) treated magnesium, along with its electronic energy states, crystalline structure and micro morphology have been investigated. The THF treated magnesium absorbs 6.3 wt% hydrogen at 723 K and 3.5 MPa. After hydrogenation, in addition to the expected hydride MgH₂, a new less-stable hydride phase appears at 673 K, but not at a lower temperature. Desorption produces 5.5 wt% hydrogen at 723 K against a back-pressure of 1.3 Pa after 20 cycles of hydriding–dehydriding. The THF treatment improves the kinetics of hydrogen absorption and desorption. The THF treated Mg exhibited reasonable reaction rates with hydrogen at 623 K. XPS (X-ray Photo-electron Spectroscopy) studies show that THF treatment causes the electronic energy state of the magnesium atoms to shift, but the XRD (X-Ray Diffractometer) studies show the crystal structure remains unchanged. It is believed that the chemical state of magnesium surface is activated by THF treatment in favor of hydrogen absorption and desorption. Metallographic observation of the magnesium hydrides reveals some interesting features during hydrogenation.     

Heat Capacity and Thermodynamic Functions of Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript> from 14 to 320 K

The heat capacity of Ga₂Se₃ is measured from 14 to 320 K by adiabatic calorimetry. The smoothed heat capacity data are used to evaluate temperature-dependent thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) of gallium selenide. Under standard conditions, the thermodynamic properties of Ga₂Se₃ are C _p ⁰ (298.15 K) = 120.8 ± 0.2 J/(K mol), S⁰(298.15 K) = 180.4 ± 0.4 J/(K mol), H⁰(298.15 K) - H⁰(0) = 25.32 ± 0.05 kJ/mol, and Φ⁰(298.15 K) = 95.52 ± 0.19 J/(K mol). The Debye characteristic temperature of Ga₂Se₃ evaluated from heat capacity data is 340 ± 10 K.     

Influence ofF centers on the optical and adsorptive properties of doped ZrO2 crystals

The optical and adsorptive properties of Y₂O₃-stabilized (10 mol %) cubic ZrO₂ crystals reduced in a hydrogen atmosphere at 1473 K for 3 and 5 h were studied by ellipsometry. The optical constantsn, k, ε _l , andε ₂ were determined from the ellipsometric parameters measured in the temperature range 297 to 623 K in vacuum. The optical constants were found to depend on the reduction time, obviously due to changes in oxygen stoichiometry. CO₂ adsorption on the surface of the crystal reduced for 3 h was studied in the range 523–623 K. At CO₂ pressures of ≤2 kPa, the amount of adsorption was found to rise with temperature. The thickness of the surface layer disturbed by CO₂ adsorption attained 260 Å at 623 K.F ⁺ centers are assumed to act as active surface sites.     

添加Co对AB3.5型储氢合金结构及性能影响的理论与实验研究

基于密度泛函理论,采用总能量平面波赝势方法,设计了La0.75Mg0.25Ni3.5-xCox(x=0、0.25、0.5、0.75)系列合金,并研究了其晶体及电子结构.计算结果显示随着Co含量的增加,La原子上的电荷转移先增大后保持不变,在Co含量为0.5时达到最大;费米能级处的态密度值先增加后稍减小,Co含量在0.5时达到最大.利用悬浮感应熔炼法制备了该系列合金La0.75Mg0.25Ni3.5-xCox(x=0、0.3、0.5、0.7).对熔炼所得合金进行了结构和性能表征,XRD结果显示,随着Co含量的增加,合金的主相均为Ce2Ni7型AB3.5相;电化学测试显示,x=0.5时,合金的放电容量和循环性能均较好,为398.5 mAh/g,容量保持率S250为62%;PCT结果表明,在室温条件下合金的吸氢平台在0.04~0.09 MPa之间,当x=0.5时,吸氢平台压最低,为0.04 MPa,同时吸氢量最大,为1.587wt%.综合分析计算和实验的结果,AB3.5合金性能随Co添加量的变化趋势符合第一性原理计算的预测.     

Thermodynamics of calcium uranosilicate

The standard enthalpy of formation at 298.15 K of crystalline α-Ca(HSiUO₆)₂ · 5H₂O (?6781.0 ± 9.5 kJ mol^?1) was determined by reaction calorimetry. The heat capacity in the range of 80–300 K was measured by adiabatic vacuum calorimetry, and the thermodynamic functions of this compound were evaluated. The standard entropy of formation (?1978.6±1.2 J mol^?1 K^?1) and the Gibbs free energy of formation (6191.0±10.0 kJ mol^?1) at 298.15 K were calculated. The standard thermodynamic functions of reactions of calcium uranosilicate synthesis were analyzed.