含稀土镁铝系合金耐腐蚀性能的研究现状

镁铝系合金是目前最常用的商业材料之一,但由于合金的耐蚀性能较差,因此对合金的耐蚀性研究具有重要意义。本文综述了稀土在镁铝系合金中的存在形式以及含稀土镁铝系合金在国内外的研究现状,讨论了稀土对合金耐蚀性的影响机理。     

非化学计量比混合稀土—镍系贮氢合金的研究

本文研究了非化学计量比混合稀土－镍系贮氢合金ＭｍＢｘ的配比数ｘ对合金结构、热力学性能和金属氢化物（ＭＨ）电极充放电发性能的影响。随着配比数ｘ的减小,合金晶胞体积和金属氢化物生成焓（－ΔＨ）增加,平台压力降低且与配比ｘ有ｌｎｐｅｑ＝１．９９ｘ－１１．１３的关系。当ｘ〈５．０时,合金在ＣａＣｕ５型主相之外析出Ｃｅ２Ｎｉ７第二相,该第二相具有较高的电催化活性。ｘ〈５．０时,合金电极具有较高的初容量和活化     

NiCoCrAlYSi涂层对镍基单晶合金高温氧化特性的影响

通过对有/无NiCoCrAlYSi涂层镍基单晶合金高温氧化后的组织结构观察与分析、及等温循环氧化质量变化动力学曲线测定,研究了有/无涂层合金的高温氧化特性.结果表明:在高温氧化期间,无涂层合金表层发生明显的氧化和内氧化,在异形大颗粒内氧化物附近出现贫Al区,使区内y'相消失;元素贫化区尺寸随时间的变化服从抛物线规律;无涂层合金经不同温度循环氧化具有不同的动力学特征,1040℃循环氧化表现的较大增减重波动幅度的原因是元素Al和Cr的交替选择性氧化:涂层合金经不同温度循环氧化后无明显失重特征,该涂层可有效改善合金的抗氧化性能.     

掺杂镧系金属对氢化燃烧合成镁镍储氢合金的影响

借助于XRD，TG-DSC等技术研究了掺杂镧系金属对氢化燃烧合成镁镍储氢合金合成条件及合金性能的影响。结果表明：掺杂镧系金属的试样在氢气压力为2．0MPa，600℃下保温2h可大量形成Mg2NiH4；氢气压力越大，形成Mg2NiH4越多；过高的合成温度和过长的保温时间极不利于Mg2NiH4的形成；镧系金属的掺入使Mg2NiH4晶胞发生了一定的畸变；掺杂镧系金属的Mg2NiH4放氢温度为271．7℃左右，比未掺杂的降低了110℃左右；掺杂镧系金属试样的总放氢量可达3．21％（质量分数，下同）；掺杂镧系金属的试样在300℃，0．1MPa下的放氢时间为7min～8min；活化可适当提高吸放氢量。     

镍-铜高温合金主蒸汽滤网开裂失效分析

对某电厂镍基高温合金制造的主蒸汽滤网的开裂失效进行了分析.结果表明,造成主蒸汽滤网开裂的主要原因是晶界高温氧化,断口呈典型的沿晶开裂特征.主蒸汽滤网内孔涂层的成分与主蒸汽滤网基体接近,主要是多出了氧元素,其组织为Ni(Cu)＋Ni(Cu)O双相组织.内孔涂层上局部有开裂,进一步促进了基材的氧化与开裂.     

PtAl_2单相涂层的高温抗氧化性能及失效机制研究

在镍基铸造高温合金K38G上采用脉冲电镀的方法沉积Pt镀层,通过分步加热粉末包埋渗Al处理后,获得表层为单相PtAl2,内层为β-NiAl的Pt-Al涂层.分别对单相PtAl2涂层进行1100℃静态氧化及循环氧化测试,并分析涂层在2种氧化条件下的氧化行为及失效机制.结果表明,单相PtAl2涂层表现出良好的抗静态氧化能力,初期快速增重主要来自于θ-Al2O3的生成,很快θ-Al2O3转变为α-Al2O3且增重趋于平缓.但是,单相PtAl2涂层的抗循环氧化能力较差,循环氧化过程中产生的热应力会导致部分区域PtAl2层剥离或脱落,继而引发涂层过早失效.因此,单相PtAl2涂层不适用于高温负载服役环境,其在循环氧化过程中的失效和退化主要来自于PtAl2层剥落以及剥落区附近β-NiAl层Al元素的快速消耗.     

几种Ni—Cr—Al基低偏析高温合金的抗氧性能研究

在１０００－１１００℃之间，对三种Ｃｒ，Ａｌ含量及微量元素，Ｓ，Ｚｒ含量不同的Ｎｉ－Ｃｒ－Ａｌ基合金进行了恒温和循环氧化实验。结果表明，高Ｃｒ，低Ａｌ，Ｓ含量，且不含Ｚｒ的合金其氧化膜层主要由连续致密的Ｃｒ２Ｏ３外氧化层和树根状Ａｌ２Ｏ３内氧化层构成，氧化膜的粘附性较好。     

镁系合金的贮氢性能

近年来，镁系合金作为下一代基础结构材料受到关注，正在作为笔记本电脑、移动电话等的壳体材料在许多领域得到实际应用。它作为金属结构材料具有轻量，耐久、振动吸收、电导、热导性能好以及良好的再生利用特性。镁还具有贮氢特性，可吸收7.6wt%(质量分数)的氢，与氢的可逆反应可探索用于贮氢及氢的输送。 镁是密排六方晶体结构，与氢结合形成稳定的氢化物相，是金红石型正方晶结构的β- MgH2。氢化物生成焓为－74.6kJ/molH2，脱氢反应要在300℃以上进行，这一温度在实用上显然过高，而且镁对氢分子离解为氢原子的触媒作用极弱，因此，Mg…     

含铼镍基单晶高温合金在900℃的循环氧化行为

采用X射线衍射(XRD),扫描电镜(SEM)及能谱(EDAX)等手段,研究了一种含铼镍基单晶高温合金在900℃的高温循环氧化行为.结果表明,在氧化初期合金的氧化质量增加较快,随着氧化时间延长氧化增重和失重交替进行,氧化动力学曲线不符合抛物线规律.高温氧化期间,合金发生明显的外氧化和内氧化,900℃氧化形成的氧化膜由三层组成,外层氧化膜由NiO、A12O3和(Ni,Co)Cr2O4组成;中间层为平直的CrTaO4及AlTaO4层;内层氧化物为Al2O3.在合金的氧化期间,分布在中间层的富Re、Ta和W相可抑制基体中Al向外扩散,并抑制氧化膜的生长,使氧化速度降低.     

Influences of heat treatment on electrochemical characteristics of La0.75Mg0.25Ni2.8Co0.5 hydrogen storage electrode alloy

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稀土元素对La0.8 Mg0.2 Ni2.8 Co0.6 储氢合金性能的影响

以La0.8Mg0.2Ni2.8Co0.6合金为基材,采用感应熔炼法制得以Ce,Pr,Nd部分替代La的系列储氢合金。3种稀土元素的加入对合金的组织没有本质的影响。与La0.8Mg0.2Ni2.8Co0.6的相组成相似,新合金也是在主相LaNi5中含有LaNi3第二相,且随着Ce,Pr,Nd替换量的增多,LaNi3相所占比例升高。在La0.8-xRExMg0.2Ni2.8Co0.6合金中,当Pr替换至x=0.2时,新合金基本保持La0.8Mg0.2Ni2.8Co0.6的放电容量375mA·h/g;其他添加比例及添加元素都在一定程度上降低了新合金的放电容量。加入Ce和Pr普遍提高放电电位,而Nd对放电电位的影响不大。La0.8Mg0.2Ni2.8Co0.6的容量衰减速率为1.07mA·h/(g·cycle),当Ce,Pr,Nd分别替换至x=0.3,0.6,0.6时,新合金的容量衰减速率依次降低到0.566,0.625,0.453mA·h/(g·cycle),循环稳定性有了很大提高。     

退火对La0.75Mg0.25Ni3.5 Co0.4贮氢合金电化学性能的影响

为了改善La-Mg-Ni-Co系合金电极的循环稳定性,对铸态合金La0.75Mg0.25Ni3.5 Co0.4在0.3MPa压力氩气保护下进行不同温度的退火(1123,1223和1323K),保温时间均为10h.研究了退火温度对合金的电化学性能的影响.X射线衍射(XRD)分析结果表明,铸态及1123K温度退火后合金主要由LaNi5,(La,Mg)2(Ni,Co)7相以及少量LaNi2相组成;退火温度为1223和1323K时,合金中LaNi2相消失,合金主要由LaNi5,(La,Mg)2(Ni,Co)7及(La,Mg)(Ni,Co)3相组成.随退火温度升高,最大放电容量从341.2mAh/g增加365.8mAh/g;循环稳定性得到改善,100次充放电循环后容量保持率从铸态合金的58.63%提高到1323K时的72.91%.     

Effect of Ni on Mg based hydrogen storage alloy Mg3Nd

Magnesium-neodymium based alloys were prepared by induction melting in an alumina crucible under protection of pure argon atmosphere. XRD patterns show that the as-melted Mg-Nd and Mg3NdNi 0.1 diffraction peaks can be excellently indexed with D03 structure (BiF3 type, space group Fm3m ). The lattice constant of Mg3Nd phase is 0.7390 nm, which is determined by XRD analysis using Cohen's extrapolation method. The reversible hydrogen storage capacity reaches 1.95wt.% for Mg3Nd and 2.68wt.% for Mg3NdNi0.1 . The desorption of hydrogen takes place at 291 ℃ for Mg3Nd and at 250 ℃ for Mg3NdNi 0.1 . The alloys could absorb hydrogen at room temperature with rapid hydriding and dehydriding kinetics after only one cycle. The enthalpy (ΔH ) and entropy (ΔS ) of Mg3Nd-H dehydriding reaction were -68.2 kJ·mol-1 H2 and -0.121 kJ·(K·mol)-1 H2 determined by using van't Hoff plot according to the pressure-composition-isotherms (P-C-I) curve measured at different temperatures. Hydrogen absorption kinetic property of Mg3NdNi 0.1 alloy was also measured at room temperature.     

Effects of amorphous Co–C on the structural and electrochemical characteristics of La0.8Mg0.2Ni0.8Mn0.1Co0.5Al0.1 hydrogen storage alloy

Amorphous Co–C powder prepared by ball milling was introduced to improve the performance of La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 hydrogen storage alloy. The structural and electrochemical properties of the as-prepared La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1–x wt.% Co–C composites were investigated systematically. Scanning electron microscopic images show La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 alloy was coated by Co–C particles. X-ray diffraction patterns suggest that the composite almost remained original phase structures of La_0.8Mg_0.2Ni_0.8Mn_0.1Co_0.5Al_0.1 and Co–C in both charge and discharge processes. The maximum discharge capacity of the composites reached 414 mAh g^?1 at a current density of 50 mA g^?1 at 298 K. The cyclic stability and the discharge capacities of the composite electrodes were noticeably improved in comparison with single La–Mg–Ni-based alloy due to increased corrosion resistance and the catalysis of the Co–C powder. Cyclic voltammogram and potentiodynamic polarization studies on the composite indicate that the electrochemical kinetics was improved and the corrosion resistance was increased. The cycling performance of the composite electrode at high current density is good as well.     

La0.8-χREχMg0.2Ni3.2CO0.6储氢合金的结构及电化学性能

通过感应容炼制备了La0.8-xREMg0.2Ni3.2Co0.6(RE=Sm,Dy,0≤x≤0.3)合金.采用X射线衍射分析了该合金的晶体结构,并研究了其电化学性能.结果表明该合金是由LaNi5主相和LaNi3第二相构成;随着Sm(Dy)取代La量的增加,合金主相单胞体积线性收缩,合金储氢量和放电容量减小,当Sm(Dy)取代量分别为0.1、0.2、0.3时,合金容量由380 mA·h/g分别减小到370(362)、355(334)、329(295)mA·h/g,但高倍率放电能力和循环稳定性得到改善,100次循环后的容量损失率由20%分别降低到18%(17%)、16%(14%)、13%(11%).     

球磨法制备Mg_2Ni-xMLNi_(3.8)Co_(0.75)Mn_(0.4)Al_(0.2)储氢合金的电化学性能研究

研究了球磨方法制备的Mg_2Ni-xMLNi_(3.8)Co_(0.75)Mn_(0.4)Al_(0.2)(x=0,10,20,30)复合型镁基储氢合金的电化学性能。结果表明,相比原始Mg_2Ni合金,添加球磨制备的MLNi_(3.8)Co_(0.75)Mn_(0.4)Al_(0.2)复合型镁基储氢合金的循环放电性能和电化学催化活性都得到改善,其中以Mg_2Ni-30wt%MLNi_(3.8)Co_(0.75)Mn_(0.4)Al_(0.2)复合型镁基储氢合金的电化学性能改善效果最佳。     

Structure and electrochemical properties of low-cobalt La1- xLixNi3.2Co0.3Al0.3(0≤x≤0.2) hydrogen storage electrode alloys

The structure and electrochemical properties of a new low cobalt hydrogen storage electrode alloys La1-xLixNi3.2Co0.3Al0.3(0≤ x ≤0.2) were investigated with a different additions of Li in replacement of La. With the increase of Li contents the maximum discharge capacity increases from 240 mAh·g -1 ( x =0) to 328.4 mAh·g -1(x=0.1) and the cycle stability is improved correspondingly. The capacity decay can remaiN28.6% ( x =0.2) after 230 charge/discharge cycles. The high rate discharge(HRD) ability of the alloys( x≤0.1) is improved and the best HRD is 34.1%( x =0.1) under the discharge current density 1200 mA·g -1 . It is found that the prepared alloys are basically composed of LaNi5 as matrix phase and LaNi3 as second phase( x ≤0.1). But the abundance of LaNi3 phase dramatically decreases with increasing x . When x =0.2, a new phase Al(NiCo)3 is formed.     

Electrochemical hydrogen storage characteristics of La0.75-xMxMg0.25Ni3.2Co0.2Al0.1 (M =Zr, Pr; x =0, 0.1) alloys prepared by melt spinning

In order to ameliorate the electrochemical hydrogen storage performances of La-Mg Ni system A2B7-type electrode alloys,the partial substitution ofM (M =Zr,Pr) for La was performed.The melt spinning technology was used to fabricate the La0.75-xMxMg0.25Ni3.2Co0.2Al0.1 (M =Zr,Pr; x =0,0.1) electrode alloys.The influences of the melt spinning and substituting La with M (M =Zr,Pr) on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated.The analysis of XRD,SEM,and TEM reveals that the as-cast and spun alloys have a multiphase structure composed of two main phases (La,Mg)2Ni7 and LaNi5 as well as a residual phase LaNi2.The as-spun (M =Pr) alloy displays an entire nanocrystalline structure,while an amorphous-like structure is detected in the as-spun (M =Zr) alloy,implying that the substitution of Zr for La facilitates the amorphous formation.The electrochemical measurements exhibit that the substitution of Pr for La clearly increases the discharge capacity of the alloys; however,the Zr substitution brings on an adverse impact.Meanwhile,the M (M =Zr,Pr) substitution significantly enhances its cycle stability.The melt spinning exerts an evident effect on the electrochemical performances of the alloys,whose discharge capacity and high rate discharge ability (HRD) first mount up and then fall with the growing spinning rate,whereas their cycle stabilities monotonously augment as the spinning rate increases.     

银和铝对Mg2Ni合金储氢性能的影响

用氢化燃烧法合成Mg2-xAgxNi(x=0．05，0．1，0．2，0．5)和Mg1-xAlxNi(x=0，0．1，0．2，0.5)。PCT结果说明合成的Mg-Ni—Ag和Mg—Ni—Al储氢合金材料具有很高的活性和理想的储氢性能。对两个体系的PCT结果分别进行计算，得出温度和氢平衡压的关系式。在423K时Mg1.8Ag0.2Ni在5min之内的放氢量为2．14％／min(质量分数)；Mg1.5Al0.5Ni在α β相区的吸氢速率为4．88％／min(质量分数)，放氢速率为1．26％／min(质量分数)。用XRD方法进行物相分析表明：添加少量银没有改变Mg2Ni的结构；添加铝却改变了Mg2Ni的结构，使储氢合金材料的储放氢动力学性能均得到改善。