多晶Ni-Mn-Ga磁性记忆合金的相变行为及稀土元素铽的作用

研究了Ni50Mn25 xGa25-x 和Ni50Mn29Ga21-xTbx 2种成分系列磁性记忆合金的相变行为. 保持Ni含量不变, 增加Mn, 降低Ga含量会使马氏体相变温度明显提高, 同时相变滞后温区减小, 居里温度基本不变. 如果添加稀土元素铽, 相变温度继续升高, 居里温度仍然不变, 材料继续保持强的铁磁性及热弹性马氏体相变的特征.     

Ba1－xSrxTiO3的Sol-gel法制备与结构相变研究

采用sol-gel法制备了钛酸锶钡(Ba1－xSrxTiO3)．用XRD、DSC、Raman等表征技术研究了Ba1－xSrxTiO3的晶体结构和相变行为.结果表明,随着锶含量的增加,晶胞体积逐渐减小,c/a趋近于1,相变温度降低,相变热减少,相变弥散性增强,且存在热滞现象.Raman光谱发生有趣变化,当x=0.30时,室温下发生结构相变, Ba1－xSrxTiO3以立方相为主要存在相,相变具有有序-无序特征.     

La0.6Pr0.05Fe11.5-xCoxSi1.5合金的磁性和磁热效应

使用电弧炉熔炼法制备La0.6Pr0.05Fe11.5-xCoxSi1.5(x=0,0.1,0.2,0.3,0.4,0.5和0.6)系列合金.XRD分析与SEM成分分析表明该系列合金中除含有少量富镧相(P4/nmm)和α-Fe相外.均由NaZh13型立方结构单相组成.品格常数随着Co含量的增加基本保持不变.磁性测量表明该系列合金的Tc随着Co含母的增加旱线性增加,当x=0.6时,Tc达264 K.合金的升、降温磁化曲线随着Co含量的增加逐渐重合,即表明该系列合金的热滞随着Co含量的增加而减小;利用Maxwell方程计算得出在x=0时,合金在△B=1.5 T的外磁场下-△Sm达到38.4 J·kg-1·K-1.这种磁熵变来源于外磁场引起的一级相变,随着Co含量的增加-△Sm线性减小,这是由于Co含量的增加使合金的磁相变出现由一级相变向二级相变转变.     

Gd0．6DY0．4Co2-xAlx系合金磁热性能的研究

用量子磁强仪对Cd0.6Dy0.4Co2-xAlx(x=0,0.1)系合金的居里温度、磁相变、磁熵变等磁性质进行了研究.结果表明:该系合金居里温度随着X量的引入而增加;热处理后,X=0,0.1合金由双相晶体结构基本变为单相晶体结构,磁熵变比铸态合金分别提高53.2%和33.1%,居里温度基本不变.铝元素的加入并没有改变合金的相变类型,合金仍保持二级相变.     

La2-xMgNi9-5x (x=0～1.0)贮氢合金的晶体结构与电化学性能研究

系统研究了La2-xMgNi9-5x (x=0～1.0)合金的晶体结构与电化学性能. XRD及Rietveld全谱拟合方法分析表明, x=1.0时合金由单一相的LaMgNi4相组成, 其余合金均由LaMgNi4与 (La, Mg)Ni3相组成. 随x的减小, 合金中LaMgNi4相丰度递减, x=0.5时合金中主相变为PuNi3型 (La,Mg)Ni3. 在LaMgNi4相中, Mg占据4c位置, 而在(La, Mg)Ni3相中Mg占据6c位置. 电化学实验表明, 合金氢化物电极放电容量随x的减小而增加, 由x=1.0时的170 mAh*g-1增加至x=0.0时的392 mAh*g-1.     

一级相变磁制冷材料LaFe_(11.6)Si_(1.4)合金的磁相变特性系统分析

以La Fe11.6Si1.4合金为研究对象,系统分析了该一级相变材料的居里温度(TC)、磁场诱导磁相变的临界磁场(HC)、磁化率(χ)、磁滞、磁熵变(ΔS)、制冷能力(RCP)等磁性特性。结果表明:温度诱导磁相变的居里温度和磁场诱导磁相变的临界磁场均随磁场呈线性增加,ΔTC和ΔH随磁场和温度的变化率的值分别为4.1 K·T-1和0.2 T·K-1。当合金处于纯铁磁态和顺磁态时熵变磁熵变几乎为零,但磁场诱导的磁相变,会导致某一定温度下合金磁熵变有一个突变。但合金最大熵变并不是随磁场的增加而线性增加,当磁场达到一定值后随磁场增加其值基本没有变化。不同模型计算的制冷能力均随磁场的增加而呈线性增加。在两相共存态中,同一温度下两种不同铁磁的磁化率存在差异,即因磁场诱导的铁磁态相与合金中本身的铁磁态相的磁化率存在差异,且前者小于后者,这种物理现象对深入研究温度诱导和磁场诱导磁相变的差异有一定的参考价值。     

Tb(Co_(1-x)Sn_x)_2合金的结构和磁热效应

通过X射线衍射和磁性测量研究了Tb(Co1-xSnx)2(x=0,0.025,0.050,0.075,0.100)合金的相结构和磁热性能。经分析可知Sn在TbCo2中的替代是有限的,X粉末衍射分析确定TbCo2具有MgCu2结构,其他样品由TbCo2,TbCo3和Tb5Sn3三相组成,TbCo2为主要相。随着Sn成分的增加,杂质相TbCo3和Tb5Sn3的含量增加,所有样品保持第二序磁相变。Sn的替代使磁相变的温度稍微有所提高,样品TbCo2的TC值为230 K,样品Tb(Co0.950Sn0.050)2的TC值为233 K,但Sn的成分继续增加,样品的TC值有所下降。在外加磁场2 T的作用下,样品Tb(Co1-xSnx)2(x=0,0.025,0.050,0.075)最大磁熵变值分别为3.44,2.29,1.64,1.16 J.kg-1.K-1。     

稀土合金Gd5(SixGe1-x)4(0.24＜x≤0.5)的场诱导相变

基于对室温磁致冷材料稀土合金Gd5(SixGe1-x)4(0．24＜x≤0．5)主要实验结果的分析与研究，提出了该系合金场诱导相变的一个理论描述。按照Landau-Devonshire理论和次晶格假设，合理地解释了该系合金的磁行为，并且其数值结果与实验数据较为一致。     

Dy_3NiSi_2合金磁相变与磁热性能研究

通过对Dy_3NiSi_2合金样品的X射线粉末衍射谱、等温变磁磁化曲线、等磁场变温磁化曲线分析,主要研究了合金的相结构和晶格参数、磁相变属性和磁热性能。X射线衍射谱表明Dy_3NiSi_2样品几乎为Gd_3NiSi_2型正交结构(空间群:Pnma, No.62)的单相合金,其晶格常数分别为a=1.1242(3) nm,b=0.41073(3) nm,c=1.1223(9) nm。在45～300 K温度范围内, Dy_3NiSi_2合金仅展现出铁磁-顺磁相变, 0.01 T磁场下的dM/dT和0～2 T磁场下的Arrott图表明, Dy_3NiSi_2合金的磁相变为居里温度T_c=54 K的铁磁-顺磁二级磁相变。在0～2 T磁场范围内, Dy_3NiSi_2合金居里温度处的最大磁熵变为3.65 J·(kg·K)~(-1),相对制冷量为167.9 J·kg~(-1)。     

La-Mg-Ni系A2B7型贮氢合金的结构与电化学性能

合金结构研究表明,La2-xMgxNi7(x=0.3～0.8)主要由Ce2Ni7,Gd2Co7,PuNi3型物相组成.合金中Mg含量对合金相结构有着重要影响,主相的晶胞参数随Mg含量(x)的增加呈线性减小,合金的吸放氢平台也随之升高.电化学测试表明,随合金中Mg含量的增加,合金电极的放电容量先增大后减小,合金电极的循环稳定性呈恶化趋势,La1.4Mg0.6Ni7合金电极具有最高的电化学放电容量(378 mAh·g-1),La1.6Mg0.4Ni7合金电极具有最佳的循环稳定性(S270=81%).合金电极的高倍率放电性能(HRD)随Mg含量的增加而增大.当合金中Mg含量较低时(x≤0.5),合金电极反应速度控制步骤为氢在合金体相中的扩散;当Mg含量较高时(x≥0.5),合金电极反应速度控制步骤转变为电极表面的电荷转移.     

Ni-Mn-Ga-RE(RE=Tb,Sm)合金的马氏体相变和磁感生应变

研究了Ni48Mn33Ga19合金添加微量稀土元素Tb和Sm后，对合金的马氏体相变、磁感生应变及机械抗弯性能的影响。结果发现，微量稀土元素Tb和Sm的掺人，降低了合金的马氏体相变温度和居里温度，但晶粒显著细化，使合金的抗弯强度显著提高，具有良好的塑韧性；同时，使合金的磁感生应变值有一定下降。     

钙钛矿型LaxSr1－xNi1－yCoyO3光电催化活性研究

用甘氨酸-硝酸盐燃烧合成法, 制备La_xSr_1－xNi_1－yCo_yO₃复合氧化物的陶瓷粉末, 对钙钛矿氧化物进行了XRD结构分析. 在通氧或不通氧下测试氧还原和氧析出的循环伏安曲线. 结果表明: 该氧电极具有双功能催化特性, 但不完全可逆. 利用汞灯作为激发光源, 进行几种水溶性染料和五种混合染料光解实验, 利用紫外-可见、红外以及人工神经网络光度法研究La_xSr_1－xNi_1－yCo_yO₃的催化性能. 结果表明: La_xSr_1－xNi_1－yCo_yO₃ (x＝0.7, 0.9, 1; y＝0.3, 0.75)复合氧化物都具有较强光催化特性; La_xSr_1－xNi_1－yCo_yO₃的光催化活性高于La_xSr_1－xNiO₃, 这与B位离子(Ni^2—, Co^2－)的电子构型有关; Co^2＋的加入可使La_xSr_1－xNiO₃的光催化活性有所提高.     

Efficient overall water splitting under visible-light irradiation on (Ga(1-x)Zn(x))(N(1-x)O(x)) dispersed with Rh-Cr mixed-oxide nanoparticles: Effect of reaction conditions on photocatalytic activity

The photocatalytic activity of (Ga(1-x)Zn(x))(N(1-x)O(x)) loaded with Rh-Cr mixed-oxide (Rh(2-y)Cr(y)O3) nanoparticles for overall water splitting under visible-light irradiation (lambda > 400 nm) is investigated with respect to reaction pH and gas pressure. The photocatalytic performance of the catalyst is found to be strongly dependent on the pH of the reactant solution but largely independent of gas pressure. The present photocatalyst exhibits stable and high photocatalytic activity in an aqueous solution of pH 4.5 for 72 h. The photocatalytic performance is much lower at pH 3.0 and pH 6.2, attributable to corrosion of the cocatalyst and hydrolysis of the catalyst. The dispersion of Rh(2-y)Cr(y)O3 as a cocatalyst on the (Ga(1-x)Zn(x))(N(1-x)O(x)) surface promotes hydrogen evolution, which is considered to be the rate-determining step for overall water splitting on this catalyst.     

Large thermal conductivity reduction induced by La/O vacancies in the thermoelectric LaCoO3 system

A series of compact La/O-vacant La(1-x)CoO(3-y) compounds were prepared by a cold high-pressure procedure, and their thermoelectric (TE) properties were investigated. Compared with the ion-substituted hole-type LaCoO(3) systems (e.g., La(1-x)Sr(x)CoO(3)), the thermal conduction of La(1-x)CoO(3-y) is noticeably reduced by the La/O vacancies, whereas the electric transport is less influenced, which results in an efficient ZT enhancement. We demonstrate that the large thermal conductivity reduction originates from the strong point-defect scattering, and La(1-x)CoO(3-y) can be rationalized as a partially filled solid solution: La(1-x)?(x)CoO(3-y)?(y), where ? denotes a vacancy. Such intrinsic thermal conductivity suppression provides an effective pathway for the design of better TE materials.     

Evaluation of multi-cycle performance of chemical looping dry reforming using CO_2 as an oxidant with Fe–Ni bimetallic oxides

Chemical looping dry reforming(CLDR) is an innovative technology for CO_2 utilization using the chemical looping principle.The CLDR process consists of three stages,i.e.CH4 reduction,CO_2 reforming,and air oxidation.Spinel nickel ferrite(NiFe_2O_4) was prepared and its multi-cycle performance as an oxygen carrier for CLDR was experimentally investigated.X-ray diffraction(XRD) and Laser Raman spectroscopy showed that a pure spinel crystalline phase(NiFe_2O_4) was obtained by a parallel flow co-precipitating method.NiFe_2O_4was reduced into Fe-Ni alloy and wustite(Fe_xO) during the CH_4 reduction process.Subsequent oxidation of the reduced oxygen carrier was performed with CO_2 as an oxidant to form an intermediate state:a mixture of spinel Ni_(1-x)Fe_(2+x)O_4,Fe_(2+y)O_4 and metallic Ni.And CO was generated in parallel during this stage.Approximate 185 mL of CO was generated for 1 g spinel NiFe_2O_4 in a single cycle.The intermediate oxygen carrier was fully oxidized in the air oxidation stage to form a mixture of Ni_(1+x)Fe_(2-x)O_4 and Fe_2O_3.Although the original state of oxygen carrier(NiFe_2O_4) was not fully regenerated and agglomeration was observed,a good recyclability was shown in 10 successive redox cycles.     

Phase relations and crystal structures in the system Ta-V-Ge

Phase equilibria have been derived for the isothermal section of the Ta-V-Ge system at 1500 °C (for concentrations <45 at% Ge) on the basis of X-ray powder diffraction, EPMA and TEM analyses of argon arc melted alloys annealed in high vacuum at 1500 °C up to 200 hours. Four ternary phases have been identified within the isothermal section, out of which three were characterized by Rietveld refinement of X-ray powder diffraction data. τ(1)-(Ta(1-x)V(x))(5)Ge(3) (0.21 ≤ x ≤ 0.63) adopts the Mn(5)Si(3)-type and τ(2)-Ta(Ta(x)V(1-x-y)Ge(y))(2), x = 0.02, y = 0.12 was found to be a MgZn(2)-type Laves phase. Detailed transmission electron microscopy (TEM) in several crystallographic directions confirmed lattice parameters and crystal symmetry of this phase and rejected the presence of any superstructure. τ(3)-Ta(9-x+y)V(4+x-y-z)Ge(1+z), x = 0.32, y = 0.51, z = 0.98 crystallizes with the Nb(9)Co(4)Ge-type, whereas the structure of τ(4) is not yet known. Although a MgCu(2)-type cubic Laves phase is not present in the Ta-V binary at this temperature, additions of Ge stabilize this phase in the ternary system: C15-Ta(Ta(x)V(1-x-y)Ge(y))(2), x = 0.04, y = 0.05. V(11)Ge(8) (Cr(11)Ge(8) type) shows a large solubility up to (Ta(x)V(1-x))(11)Ge(8), x = 0.64 at 1500 °C.     

O2结构Liy[Mn1—xMx]O2（M＝Cr，Mg）的合成及结构研究

由高温焙烧法制备层状前驱体Na_(2/3)[Mn_(1-x)M_x]O_2（M＝Cr, Mg），再 经离子交换反应得到层状O2结构产物Li_y-[Mn_(1-x)M_x]。XRD表明Li_y[Mn_(1-x) M_x]O_2属六方晶系，P3ml空间群。Cr的添加量对前驱体的晶体结构有很大影响： 随着x值的增大，前驱体逐渐由层状P2结构Na_(2/3)[Mn_(1-x)Cr_x]O_2向正交结构 Na_4Mn_90_(18)转变。由SEM可以看到样品Li_y[Mn_(1-x)Cr_x]-O_2(x≤0.05)具有 六方层状结构。XPS分析结果表明样品Li_y[Mn_(0.95)Cr_(0.05)]O_2表面上的Mn和 Cr分别以Mn~(4+)存在，并且表面中Cr相对含量高于体相，而样品Li_y[Mn_(0.90) Mg_(0.10)]O_2的表面Mn和Mg分别以Mn~(4+)和Mg~(2+)存在，Mg/Mn比在表面与体相 基要一致。     

Ce1-xNixO2/Al2O3/FeCrAl催化剂的制备及其甲烷催化燃烧性能

以FeCrA l合金薄片为基体,A l2O3为过渡载体,Ce1-xN ixO2(x=0.1-0.3)、CeO2和N iO为活性组分,制备了Ce1-xN ixO2/A l2O3/FeCrA l、CeO2/A l2O3/FeCrA l和N iO/A l2O3/FeCrA l金属基整体式催化剂,在固定床微型反应器中评价了催化剂的甲烷催化燃烧性能,用SEM、XRD、TPR等方法对催化剂的物相、表面形貌和氧化还原性进行了表征.结果表明,Ce1-xN ixO2在催化剂表面的分散性比CeO2和N iO要好;Ce1-xN ixO2/A l2O3/FeCrA l(x=0.1-0.3)催化剂具有好的催化活性和高温稳定性,CeO2/A l2O3/FeCrA l和N iO/A l2O3/FeCrA l催化剂有好的初活性但高温稳定性较差;活性组分与A l2O3和FeCrA l金属基体之间存在较强的相互作用.     

锂离子电池爆炸机理分析

研究L iCoO2(或L1.05Co1/3N i1/3Mn3O2)/L ixC6锂离子电池材料的热分解特性以及锂离子电池在加热、过充、短路等情况下的爆炸机理.实验表明,50~350℃之间负极表面存在SEI膜的分解、L ixC6与电解液乃至L ixC6与PVDF等3种放热反应,电解液于178℃时开始放热,L i1-xCo1/3N i1/3Mn1/3O2的热分解反应起始于230℃.锂离子电池在150℃加热时爆炸,1.5 C过充至15 m in时爆炸,短路情况下不发生爆炸.