低钴稀土系贮氢合金的研究

通过在稀土系贮氢合金中添加不同含量的Fe或Cu元素,部分替代合金中Co的方法,研究低钴贮氢合金电化学性能上的差异.结果表明:由于合金组成和化学计量比的不同,同样是添加了Fe或Cu的合金在电化学性能上表现不同,但总体说,含Cu低钴贮氢合金容量和倍率放电性能较好,含Fe低钴贮氢合金有较好的循环稳定性,过化学计量比的合金循环稳定性要好于欠化学计量比的合金.     

Structure and electrochemical hydrogen storage characteristics of the as-cast and annealed La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 （x=0-0.4） alloys

In order to ameliorate the electrochemical cycle stability of the RE-Mg-Ni based A2B7-type electrode alloys, the Mg content in the alloy was reduced and La in the alloy was partially substituted by Sm. The La0.8-xSmxMg0.2Ni3.15Co0.2Al0.1Si0.05 (x=0, 0.1, 0.2, 0.3, 0.4) elec-trode alloys were fabricated by casting and annealing. The microstructures of the as-cast and annealed alloys were characterized by XRD and SEM. The electrochemical hydrogen storage characteristics of the as-cast and annealed alloys were measured. The results revealed that all of the experimental alloys mainly consisted of two phases: (La,Mg)2Ni7 phase with the hexagonal Ce2Ni7-type structure and LaNi5 phase with the hexagonal CaCu5-type structure. As Sm content grew from 0 to 0.4, the discharge capacity and the high rate discharge ability (HRD) first in-creased and then decreased for the as-cast and annealed alloys, whereas the capacity retaining rate (S100) after 100 cycles increased continuously.     

High-Temperature oxidation of cathodically hydrogen-charged two-phase (Ti3Al,TiAl) titanium aluminides

Ti-42A1, Ti-45A1, and Ti-5OA1 (at. pct) titanium aluminides, which were cathodically hydrogen charged in a 5 pct H₂SO₄ solution for charging times between 1.8 ks (0.5 hours) and 14.4 ks (4 hours), were oxidized in a static air under atmospheric pressure at temperatures between 1170 K (897 °C) and 1350 K (1077 °C). All the hydrogen-charged alloys, as well as alloys without hydrogen charging, followed parabolic oxidation kinetics. The weight gains of the alloys after hydrogen charging for normally less than 3.6 ks (1 hour) were 20 to 30 pct less than those without hydrogen charging. In the alloys charged with hydrogen for more than 7.2 ks (2 hours), the weight gains increased with increasing the charging time. The activation energies of oxidation indicated that the oxidation-controlling factor would change after a charging time of 7.2 ks (2 hours) in all the alloys. The decrease in the activation energies with charging time was more drastic in the Ti-5OA1 alloy, which suggested that hydrogen damage, such as cracking, was more severe in the Ti-50Al alloy than in the Ti-42A1 or Ti-45A1 alloys. The formation of cracks during hydrogen charging provides titanium-diffusion paths and accelerates formation of rutile (TiO₂) scale on the surface of the alloys. The TiO₂ on the alloys after hydrogen charging formed at a comparatively lower temperature than that on the alloys without charging.     

The prediction of the hydriding thermodynamics of Pd-Rh-Co ternary alloys

A dilute solution model (with respect to the substitutional alloying elements) has been utilized to accurately predict the hydride formation and decomposition thermodynamics and hydrogen storage capacities of dilute Pd-Rh-Co alloys. The effect of varying the rhodium and cobalt compositions on the thermodynamics of hydride formation and decomposition and hydrogen capacity of several palladiumrhodium-cobalt ternary alloys has been investigated using pressure-composition (PC) isotherms. Alloying in the dilute regime (<10 at. pct) causes the enthalpy for hydride formation to linearly decrease with increasing alloying content. Cobalt has a stronger effect on the reduction in enthalpy than rhodium for equivalent alloying amounts. Also, an increasing alloying content of cobalt reduces the hydrogen storage capacity. The plateau thermodynamics are strongly linked to the lattice parameters of the alloys. A near-linear dependence of the enthalpy of hydride formation on the lattice parameter was observed for both the binary Pd-Rh and Pd-Co alloys, as well as for the ternary Pd-Rh-Co alloys. The Pd-5Rh-3Co (at. pct) alloy was found to have similar plateau thermodynamics to a Pd-10Rh alloy; however, this ternary alloy had a diminshed hydrogen storage capacity relative to Pd-10Rh. This article is based on a presentation made at “The Milton Blander Symposium on Thermodynamic Predictions and Applications” at the TMS Annual Meeting in San Diego, California, on March 1–2, 1999, under the auspices of the TMS Extraction and Processing Division and the ASM Thermodynamics and Phase Equilibrium Committee.     

Electrochemical Properties of Sn Doped AB_5 Non-Stoichiometric Hydrogen Absorbing Alloys-Ⅱ

Ｒａｒｅｅａｒｔｈｈｙｄｒｏｇｅｎａｂｓｏｒｂｉｎｇａｌｌｏｙｓａｒｅｗｉｄｅｌｙｕｓｅｄｉｎｎｉｃｋｅｌ ｍｅｔａｌｌｉｃｈｙｄｒｉｄｅｂａｔｔｅｒｉｅｓ(Ｎｉ ＭＨ )ｂｅｃａｕｓｅｏｆｔｈｅｈｉｇｈｐｅｒｆｏｒｍａｎｃｅｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｔｈｅｓｅｍａｔｅｒｉａｌｓｉｎｒｅｓｐｅｃｔｔｏｅｎｅｒｇｙｄｅｎｓｉｔｙ ,ａｃｔｉｖａｔｉｏｎａｎｄｃｙｃｌｉｎｇｌｉｆｅ .ＴｈｅｒａｔｅｃａｐａｂｉｌｉｔｙｏｆＮｉ ＭＨｂａｔｔｅｒｉｅｓｍｕｓｔｂｅｉｍｐｒｏｖｅｄｇｒｅａｔｌｙｂｅｃａｕ…     

Hydrogen diffusion coefficients in the titanium alloys IMI 834, Ti 10-2-3, Ti 21 S, and alloy C

The diffusion coefficients of hydrogen were determined for three beta titanium alloys, which differ in the stability of the beta phase, and, for comparison, for one near-alpha titanium alloy in the temperature range from 40 °C to 500 °C. For this purpose, a step hydrogen concentration profile was produced by charging one side of rods of these materials with hydrogen by means of an electrochemical technique. After subsequent diffusion annealing, the hydrogen concentration profiles were determined analyzing small discs cut from these rods. The corresponding diffusion coefficient was calculated by adapting its value in such a way that a numerical diffusion simulation yields the experimentally determined profile. In all cases studied, the hydrogen diffusion coefficient was found to be independent of the hydrogen concentration and showed an Arrhenius-type temperature dependence. Hydrogen diffusion in alpha titanium was slower as compared to the beta titanium alloys under investigation. Furthermore, the diffusion coefficient of the metastable beta titianium alloys is only slightly affected by the prior heat treatment that determines the morphology and volume fraction of the precipitated alpha phase.     

Comparative Study of Hydrogen Embrittlement of Three Heat-resistant Cr-Mo Steels Subjected to Electrochemical and Gaseous Hydrogen Charging

Hydrogen embrittlement (HE) behaviors of low carbon steel and three heat-resistant Cr-Mo steels having different Cr contents were compared through tensile testing, silver decoration, and blistering observation after electrochemical hydrogen charging and hardness testing after gaseous hydrogen charging. It was observed that higher Cr content caused a longer suppression in charging hydrogen into the steels. However, under hydrogen supersaturation conditions, the higher the strength of the heat-resistant steels, the poorer the HE resistance after electrochemical charging. In contrast, the higher the Cr content, the better the HE resistance under high-temperature gaseous charging conditions.

     

不同纯铅对铅钙锡铝板栅合金性能的影响

利用线性电位扫描(LSV)、交流阻抗(EIS)、循环伏安(CV)和金相组织分析(MSA)等研究方法对四种不同纯铅铸造的铅钙板栅合金的性能进行了研究。研究表明采用不同原料、不同方法冶炼的纯铅铸造的铅钙合金在性能上存在较大的差异,特别是用电解精炼矿生铅铸造的铅钙合金具有最高的析氢、析氧过电位,能有效地抑制氢气、氧气的析出,其表面腐蚀产物PbO2和钝化膜Pb(Ⅱ)氧化物的生成量最少,电化学性能最优。     

烧结温度对LiNi0.8Co0.15Al0.05O2结构和电化学性能的影响

采用共沉淀法+高温固相法,首次在740~820℃制备了一系列LiNi_0.8Co_0.15Al_0.05O₂正极材料,探讨温度变化对材料结构性能的影响.通过X射线分析仪、扫描电镜、电化学工作站、电池充放电测试系统表征材料性能.结果显示在780℃烧结出的材料有纯的六方晶相、层状结构优异,在2.75~4.2 V、0.1 C倍率获得188.11 mAh/g,0.5 C循环100次后容量稳定率为88.55 %,高于其他温度制备的材料; 经过不同倍率放电后,780℃烧结出的材料不可逆容量损失远低于其他温度制备的材料.      

镍氢电池负极用低成本储氢合金的研究

研究了ABS型储氢合金在低Co含量条件下，随B组元替代元素Co，Al，Si等含量的变化对合金电化学性能的影响规律，同时研究了A组元中不同La／Ce比对合金电化学性能的影响情况。结果表明，随合金中Co含量的降低，合金的活化性能和放电容量得以改善，但合金的循环寿命下降也比较明显；在试验范围内，随Al元素的加入，合金的循环寿命得以改善，但材料的放电容量和活化性能均有所下降；随合金La／Ce比的降低，合金的放电容量略有下降，但其循环寿命和放电电压平台有较大提高。     

A study of the hydrogen-induced degradation of two steels differing in sulfur content

Two steels with different sulfur contents: 0.003 and 0.024 wt pct, were cathodically charged under three different conditions and brought to fracture in tension immediately after charging or after aging at room temperature. All hydrogen charged specimens showed embrittlement, with a little higher loss of ductility in the high sulfur steel. The hydrogen embrittlement was reversible in both steels when specimens were charged in arsenic-free sulfuric acid solution at room temperature but was irreversible when charged in arsenic-containing acid at the same temperature. After charging in molten salts at 200 °C, some of the low sulfur steel specimens exhibited irreversible hydrogen damage with the appearance of quasicleavage fractures, while all high sulfur steel specimens were restored to the uncharged ductility by aging at room temperature. These results are interpreted by assuming that an increased sulfur content in steel increases the density of trapping sites for hydrogen at the sulfide/matrix interfaces. These traps are inactive above 150 °C and become operative after cooling. Therefore, at the same hydrogen content in steel after cooling, the greater content of sulfur results in a decreased activity of the lattice dissolved hydrogen, hence in reduced embrittlement.     

碳含量对Mn-B钢氢致延迟断裂行为的影响

采用电化学阴极充氢、氢热分析(TDS)和慢应变速率拉伸等试验方法,研究了4种不同碳含量Mn-B钢经不同热处理制度处理后的氢致延迟断裂行为。结果表明,在低于400℃回火时,随着碳含量的增加,试验钢的氢脆敏感性升高,当碳的质量分数高于0.3%后,试验钢的氢脆敏感性几乎不再增加;碳含量一定时,试验钢的氢脆敏感性随回火温度的升高而降低,且以20MnB试验钢的降低趋势最为明显;当回火温度达到600℃时,各试验钢对氢几乎不再敏感;TDS分析表明,试验钢充氢后的氢含量明显增加,其中以可扩散性氢量的增加为主;随碳含量的增加,试验钢充入的氢量增加;当碳含量一定时,随回火温度的升高,试验钢充入的氢量减少;SEM断口观察表明,试验钢充氢后的脆性断裂倾向性增加;随着碳含量的升高,试验钢的断裂方式由韧性断裂向脆性断裂转变;碳含量一定时,随回火温度的升高,试验钢由淬火态的脆性断裂向高温回火态的韧性断裂转变。     

Structure and properties of WC-Co alloys in solid-phase sintering. I. Geometrical evolution

The paper examines the geometrical evolution and particulate interaction in WC-Co alloys produced by solid-phase sintering. It is shown that solid-phase sintering actively modifies the geometric structure: carbide particles grow, become facetted and grow together, and the cobalt phase is redistributed. The WC particles grow irregularly over different temperature ranges. The low rate of growth is characteristic of temperature ranges between 1050 and 1200°C. When alloys are sintered at 1200°C and higher temperatures, the growth of tungsten carbide particles intensifies substantially (by four times). Hence, the temperature 1200°C separates two structurization areas in solid-phase sintering. At this temperature, there is a bend on the specific resistivity curve, which is evidence of higher-quality grain and phase boundaries.     

正极浆料黏度对汽车动力电池的影响

为了研究LiNi_0.5Co_0.3Mn_0.2O₂正极材料浆料的黏度对锂离子汽车动力电池的影响.首先通过研究不同NMP含量对浆料黏度的影响，由此产生的对电池一致性和电化学性能的影响，再选取最优NMP含量的配方研究不同搅拌时间对正极浆料黏度的影响.利用黏度计、内阻测试仪、加速绝热量热仪、电池测试系统表征浆料的黏度、电池内阻、电池热稳定性和电化学性能，实验结果表明, NMP含量为880 g及搅拌6 h的浆料，平均黏度为6.348 pa·s，做出的电池容量差和内阻差比较小，电池在25 ℃, 2.75～4.2 V, 0.5 C倍率下首次放电比容量为163.5 mAh/g，循环100次后容量保持率为98.6 %，电池在绝热环境下充放电过程中温度最高为47.3 ℃，电池表现出良好的一致性、较好的电化学性能和热稳定性能.      

The effects of cathodically charged hydrogen on the flow stress of nickel and nickel-carbon alloys

Effects caused by the introduction of hydrogen by electrochemical cathodic charging have been studied in nickel and nickel-carbon alloys. Cathodic charging can cause both softening and hardening of nickel depending on the charging current density, temperature and strain rate. The degree to which the flow stress is altered depends on the purity of the nickel. The mechanisms of the softening and hardening caused by the cathodic charging of nickel with hydrogen are discussed on the basis of these studies.     

Effects of Strip Casting and Annealing on Electrochemical Properties of LPCNi3.55Co0.75Mn0.4Al0.3 Hydrogen Storage Alloys

The effect of thickness (1～10 mm) of the ingots on the electrochemical properties of as-cast and annealed strip cast LPCNi3.55Co0.75Mn0.4Al0.3 hydrogen storage alloys was investigated. It is found that the 0.2 C discharge capacity of as-cast LPCNi3.55Co0.75Mn0.4Al0.3 alloy increases with the increase of the thickness of the ingots. As-cast alloy with the thickness of 10 nun shows better activation property, higher 1C discharge capacity and better cyclic stability than others.It is mainly contributed to its larger unit cell volume and less internal stress. Annealed LPCNi3.55Co0.75Mn0.4Al0.3 alloywith the thickness of 3 mm shows much better comprehensive electrochemical properties than as-cast one; The cyclic stability of the alloy with the thickness of 6 mm and the activation properties of the alloys with the thickness of 3～6 mm are improved after annealing. It is mainly owing to the great release of intemal stress and the decrease fo the segregation of Mn in the alloys.     

快淬纳米晶/非晶Mg2-xLaxNi (x=0～0.6)合金的贮氢动力学

为了改善Mg2Ni型合金气态及电化学贮氢动力学性能,用La部分替代合金中的Mg,用快淬技术制备了Mg2-xLaxNi(x=0,0.2,0.4,0.6)合金,用XRD,SEM,HRTEM分析了铸态及快淬态合金的微观结构;用自动控制的Sieverts设备测试了合金的气态贮氢动力学性能,用程控电池测试仪测试了合金的电化学贮氢动力学.结果发现,快淬无La合金具有典型的纳米晶结构,而快淬含La合金显示了以非晶相为主的结构,表明La替代Mg提高Mg2Ni型合金的非晶形成能力.La替代Mg明显地改变Mg2Ni型合金的相组成.当La替代量x=0.4时,合金的主相改变为(La,Mg) Ni3+ LaMg3.合金的气态及电化学吸放氢动力学对La含量及快淬工艺敏感,La替代使合金的吸氢动力学降低,但适量的La替代可以明显改善合金的放氢动力学及高倍率放电能力.适当的快淬处理可以提高合金的气态及电化学贮氢动力学,但获得最佳贮氢动力学的快淬工艺与合金的成分密切相关.     

Solubility of hydrogen in solid Ni−Co and Ni−Cu alloys

The solubility of hydrogen was measured in solid Ni, Co, and Cu, and in the Ni?Co and Ni?Cu systems. A unique sampling technique was used in which equilibrated specimens were quenched by dropping into mercury. The measurements were made as a function of temperature in the range from 700° to 1225°C and of hydrogen pressure, up to 1 atm. Dissolved hydrogen in all metals and alloys obeyed Sieverts' Law. An attempt was made to correlate the hydrogen solubility with solution models based on the electronic structure of the alloys. A nonlinear correlation was found with the electronic specific heat coefficient which relates to the density of states at the Fermi surface.     

LaMg11Zr+200%Ni+x%La(x=O,5,10)储氢合金结构及电化学性能

采用机械合金化法(MA)制备了非晶态LaMg11Zr+200%(质量分数,下同)Ni+x%La(x=0,5,10)系列储氢合金,并详细研究了La添加对该系列合金的相结构及电化学性能的影响.结构分析表明,球磨20h该系列合金都呈非晶态,La添加后合金颗粒得到明显细化;电化学研究表明,La添加后,合金电极充电阻力减小,放电容量随La含量的增加而增大,适量v的添加一定程度上改善了合金电极的循环稳定性和动力学性能,LaMg11Zr+200%Ni+5%La合金电极达到最大放电容量597.2mAh·g-1,循环30次后的容量保持率仍为53.5%.     

Co含量对La0.55Pr0.05Nd0.15Mg0.25Ni3.5-xCoxAl0.25（x=0～0.4）储氢合金电极性能的影响

采用电磁感应悬浮炉制备La0.55Pr0.05Nd0.15Mg0.25Ni3.5-xCoxAl0.25(x=0,0.1,0.2,0.3,0.4)系列合金,研究Co含量对合金的相结构、吸放氢性能和电化学性能的影响。研究结果表明,该系列合金主要由LaNi5、Nd2Ni7相组成。当Co含量大于0.2时,合金中出现La2Ni7相。压强-吸氢量-温度(Pressure-Content-Temprature)测试显示在303 K温度下,合金具有良好的吸氢性能,当x=0.4时合金的最大吸氢量为1.29(质量分数,%)。电化学测试表明:随x值变化,合金电极的最大放电容量分别为340.0(x=0.0)、346.6(x=0.1)、370.0(x=0.2)、320.0(x=0.3)和346.6(mA.h)/g(x=0.4);随Co含量增加,合金电极容量保持率不断增加,高倍率放电性能先增加后减小,循环伏安曲线、氢在合金体中的扩散系数D共同反映了合金电极的动力学特性。