Fe-V合金中~(57)Fe的超精细参数

本文用穆斯堡尔效应研究了Fe-V合金系中~(57)Fe的超精细相互作用。当x≤0.1时,Fe_(1-x)V_x合金中超精细场和同质异能移位可表为:     

ε-Fe_xN合金(2

陈冠冕 《核技术》1984,(4)

FeBSi非晶态合金系列的穆斯堡尔谱学和四端电位法研究

本文应用穆斯堡尔谱学方法研究了Fe_(80)B_(20)和Fe_(82)B_(18-x)Si_x(x=2,4,6,8,10)非晶态合金的超精细场分布,得出在各种不同B、Si浓度下平均超精细场的变化曲线。研究结果表明:在x=2至10范围内,Fe_(82)B_(18-x)Si_x的平均超精细场(?)随着Si含量的增大而略有增大。这是因为Si原子数目增加时,体积较大的Si原子取代了,Fe_(82)B_(18-x)Si_x非晶合金中处于间隙位置的B原子,从而使形变和平均超精细场都有所增加。     

镁固溶对钙钛锆石陶瓷固化体的影响北大核心CSCD

以CaTiO_(3)、ZrO_(2)、TiO_(2)和MgO为原料,经固相烧结法在1350℃下制备镁固溶钙钛锆石陶瓷固化体(Ca_(1-x)Zr_(1+x)Ti_(2-x)Mg_(x)O_(7),0≤x(固溶度)≤0.20),并研究Mg^(2+)固溶度对固化体物相组成、微观形貌和晶体结构的影响。X射线衍射结果表明:Ca_(1-x)Zr_(1+x)Ti_(2-x)Mg_(x)O_(7)结构中的Ti位可容纳固溶度x=0.05~0.15的Mg^(2+);并通过选区电子衍射实验进一步验证,固化体的主要晶体结构为单斜相钙钛锆石(2M,空间群C2/c)。当固溶度x=0.05~0.15时,钙钛锆石产物的相对质量分数高于97%,仅有微量的钙钛矿杂质相生成;随着Mg^(2+)固溶度的进一步增加(x=0.20时),Mg^(2+)浓度超过固溶度极限,使杂质相含量大幅增加。同时,扫描电子显微镜观察结果表明,固化体抛光面结构致密;在Mg^(2+)固溶度x≤0.15时,阳离子浓度符合所设计的化学计量比。     

UO_(2-x)燃料芯块的晶粒生长动力学

本文采用恒速升温和等温烧结实验方法研究了亚化学计量UO_(2-x)燃料芯块的晶粒生长动力学。结果表明,以UO_(2+x)+5%U为原料,可得到密度为94.91%TD～96.23%TD(TD为理论密度)、O与U的原子个数比为1.975～1.990的合格的亚化学计量UO_(2-x)燃料芯块;在烧结温度≤1 650℃时晶粒生长速率较低,在烧结温度≥1 750℃时晶粒生长速率较高;初始晶粒尺寸G_0不能忽略不计,亚化学计量UO_(2-x)燃料芯块的晶粒生长动力学符合4次方模型G~4-G■=k_0texp(-1 000Q/RT),晶粒生长速率常数k_0=78.76μm~4/h,激活能Q=433.35 kJ/mol。     

铈基镧系氧化物的制备与晶体结构变化

通过制备和表征镧系元素的氧化物来模拟研究次锕系元素的混合氧化物固溶体的晶体结构。采用草酸盐共沉淀法和程序煅烧,得到了阳离子分布均匀的以CeO_2为本底的混合氧化物Ce_(1-x)Ln_xO_(2-x/2)(其中x∈[0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.9,1];Ln=Nd、Sm)。利用红外光谱、拉曼光谱、热重分析和X射线衍射,表征了草酸盐前驱体(Ce_(1-x)Ln_x)_2(C_2O_4)_3·10H_2O的结构和特殊官能团,并使用X射线衍射法研究了Ce_(1-x)Ln_xO_(2-x/2)系列混合氧化物的晶体结构。结果表明,当固体氧化物中镧系元素含量较低时(对于Nd,x≤0.4;对于Sm,x≤0.3),可观察到典型的Fm-3 m萤石结构;当x较高(对于Nd,x≥0.5;对于Sm,x≥0.4)时,可观察到Ia-3立方结构。通过Rietveld方法计算晶格常数,表明其与平均阳离子半径遵从一种二次关系,这种二次关系是逐渐增长的平均阳离子半径和由于氧空位造成的O-O斥力减少综合作用的结果。     

非晶态合金（Fe1—xYx）84B16的穆斯堡尔谱学和磁学研究

用穆斯堡尔效应和磁测量方法对非晶态薄带(Fe_(1-x)Y_x)_(84)B_(16)(0≤x≤0.21)进行了研究。实验结果证实在所研究的样品中存在短程有序相互作用和由于钇替代而产生的不均匀区域。     

模拟核素固化体SrZr_xTi_(1-x)O_3的化学稳定性

为研究90Sr衰变子体对90Sr Ti O3固化体结构稳定性的影响,以C4H6O4Sr·0.5H2O、Ti O2及Zr OCl2·8H2O粉体作为原料,按照化学计量比Sr ZrxTi1-xO3(0≤x1)设计配方,采用高温固相法制备一系列固化体。利用X射线衍射光谱(X-ray Diffraction,XRD)、扫描电镜(Scanning Electron Microscope,SEM)及红外(Fourier Transform Infrared,FT-IR)谱仪对制备固化体的物相、结构和微观形貌进行分析表征,并对其抗浸出性能和辐照性能进行了研究。结果表明,当x0.5时,固化体为单一物相;当x≥0.5时,固化体中出现第二相。固化体中的Sr2+、Zr4+的浸出浓度随浸泡时间而增大,在浸泡42 d时,Sr2+的最大浸出浓度为0.006 5μg?m L-1,Zr4+的最大浸出浓度为0.01μg?m L-1。     

中子散射研究HoFe_(1-x)Cr_xO_3(x=0.0,0.2,…,1.0)固溶体磁性

正利用固相反应法制备了HoFe_(1-x)Cr_xO_3(x=0.0,0.2,…,1.0)系列固溶体化合物,利用磁性测量和变温中子衍射对样品进行了研究,建立了体系的磁相图。发现随着Cr从0.0到1.0,体系的Neel温度大约从650K下降到140K。在x=0.0～0.7的范围之内,在Neel温度以下体系呈现Γ4反铁磁结构,在某一温度T_(sr)下,体系磁结构转变为Γ_2结构。随着x从0.0增加到0.7,T_(sr)逐渐从56 K增加到大于200 K并接近T_N。当x处于0.8～1.0之间的时候,在T_N以下系统     

金属钒及其氢化物的第一原理研究(英文)

用Castep程序的局域密度泛函近似方法(LDA)对金属钒及不同原子比的钒氢化物进行了结构优化和总能计算。获得了VH_x(0≤x≤2)体系的各种氢化物的晶体结构的计算结果;判断了钒氢化物的稳定性;说明了氢含量对V-H体系相组成的影响。与现有的实验结果相比较,二者是基本相符的。     

Spectroscopic and microscopic study of the corrosion of iron–silicon steel by lead–bismuth eutectic (LBE) at elevated temperatures

The performance of iron–silica alloys with different silicon composition was evaluated after exposure to an isothermal bath of lead–bismuth eutectic (LBE). Four alloys were evaluated: pure iron, Fe–1.24%Si, Fe–2.55%Si and Fe–3.82%Si. The samples were exposed to LBE in a dynamic corrosion cell for periods from 700 to 1000 h at a temperature of 550 °C. After exposure, the thickness and composition of the oxide layer were examined using optical microscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS), including sputter depth profiling. Particular attention was paid to the role, spatial distribution, and chemical speciation of silicon. Low-binding-energy silicon (probably silicates or ) was found in the oxide; while elemental silicon (Si) was found in the metal as expected, and silica (SiO₂) was found at the bottom of the oxide layer, consistent with the formation of a layer between the oxide and the metal. Alloys with low concentrations of Si contained only silicate in the oxide. Alloys with higher concentrations of Si contained a layer of silica at the boundary between the oxide and the bulk metal. All of the alloys examined showed signs of oxide failure. This study has implications for the role of silicon in the stability of the oxide layer in the corrosion of steel by LBE.     

Investigation of thermodynamic properties of BCC solid solutions of uranium (II). The uranium-niobium system

The physical basis is presented of the model on which calculations of solid solution thermodynamic functions are based, and the relevant physical characteristics of γ-uranium-niobium solid solutions. The excess entropy and enthalpy of mixing at 1100 K are calculated for these alloys. Results are presented of an experimental study of the thermodynamic properties of U-Nb solid solutions in the temperature range from 1048 to 1173 K, by measuring EMF in a molten-salt electrolyte. For entropy of mixing the experimental data are closely consistent with the calculated curve, but there is no such agreement for the enthalpy of mixing. The reasons for this are considered. The possibility of the formation of an intermediate phase in the U-Nb system is briefly discussed.     

Mass spectrometric studies of alloys proposed for high temperature reactor systems: II. Inconel alloy 617 and nimonic alloy PE 13

The vaporization of the alloys inconel 617 and nimonic PE 13 was studied by high-temperature mass spcctromctry. This is of particular interest for the use of these alloys in advanced gas-cooled high temperature reactors and thermonuclear fusion devices. Therefore, the partial pressures of nickel, chromium (1355–1527 K) and cobalt (1214–1517 K) over inconel 617 as well as of nickel, chromium, iron (1349 to 1493 K) and cobalt (1279 to 1500 K) over nimonic PE 13 were determined in the given temperature ranges. Chemical activities, partial free energies of mixing and excess partial free energies of the alloy components were computed from the partial pressures. The thermodynamic functions obtained are discussed.     

The dissolution of oxide on α-Zr(1%Nb) and β-Zr(20%Nb) alloys

The oxide dissolution rates on β-Zr(20%Nb) and α-Zr(1%Nb) alloys have been measured by AES at various temperatures. The results indicated that oxide films on the β-Zr(20%Nb) alloy dissolve much more rapidly into the bulk alloy than is the case for the α-Zr(1%Nb) alloy. The oxygen diffusion coefficients in both the β-Zr(20%Nb) and α-Zr(1%Nb) alloys were deduced from the oxide dissolution kinetics, which are 0.172 exp(−187.47 kJ/RT) and 0.69 exp(−149.45 kJ/RT) for the α-Zr(1%Nb) alloy and β-Zr(20%Nb) alloy, respectively.     

基于核定位序列-DNA四面体复合纳米结构的细胞核成像研究

基因治疗的关键是如何高效转运基因进入细胞核并发挥作用,实时观察脱氧核糖核酸(Deoxyribonucleic acid,DNA)在细胞核中的分布对于了解基因治疗的效果非常重要。其中,载体的安全性、运输效率等是基因治疗的关键影响因素。本工作构建了核定位序列(Nuclear Localization Signal,NLS)与DNA四面体的复合结构,提高了细胞核摄取DNA四面体的效率。利用"点击"化学反应将NLS与DNA四面体进行共价连接,解决了简单混合带来的稳定性差等问题。进一步研究了不同长度和等电点的NLS序列在与DNA四面体连接时的效率,发现与经典的NLS_(12)相比,等电点为4.84的NLS29与DNA的非特异性结合显著降低,连接反应的效率从37.3%提高到72.3%。经高效液相色谱(High Performance Liquid Chromatography,HPLC)分离纯化后的NLS12-DNA和NLS29-DNA均可以靶向细胞核,说明改变NLS的长度和等电点后仍保持了很好的活性。该研究改善了正电NLS与负电DNA之间由于非特异性结合容易形成沉淀的问题,为临床基因治疗奠定了基础。     

EDXRF and micro-EDXRF studies of Late Bronze Age metallurgical productions from Canedotes (Portugal)

Metallurgical production in Central Portugal during the Late Bronze Age was primarily based on copper-tin alloys, despite influences from the Atlantic area where copper-tin-lead alloys are common. Metallic artefacts from archaeological site of Canedotes (Central Portugal) were analysed by EDXRF to establish the type of alloys present. Polished spots in selected artefacts were also analysed by micro-EDXRF to determine the major and minor elemental composition of the original alloys. The collection constitutes 18 copper-tin artefacts and one unalloyed copper artefact with tin and arsenic as minor constituents. Artefacts that require a thermomechanical finishing process, such as tools and weapons, seem to have improved control over the tin content. The composition of two buttons, one cramp and one metallic droplet suggest that some of the copper sources were rich in arsenic. Finally, the low iron content of the artefacts seems to agree well with the smelting of copper ores in crucible furnaces, a smelting process used in certain areas of the Iberian Peninsula until pre-Roman times.     

Roman bronze artefacts from Thamusida (Morocco): Chemical and phase analyses

Twenty-six objects (1st to the 3rd century AD) found at the archaeological site of Thamusida (Morocco), which is a military settlement between the 1st and the 3rd century AD, have been investigated by means of portable X-ray fluorescence and time of flight-neutron diffraction. The combination of element-sensitive X-ray fluorescence and structure-sensitive neutron diffraction yields, in a totally non-destructive way, the necessary information to discriminate the copper alloy from corrosion and alteration layers. Results allowed dividing the repertory into five groups: (a) unalloyed copper, (b) binary alloys made of Cu and Sn, frequently leaded; (c) unleaded binary alloys made of Cu and Zn; (d) ternary alloys made of Cu, Sn and Zn, both leaded and unleaded; (e) quaternary alloys made of Cu, Sn, Zn and As. The choice of alloy is heterogeneous, mainly depending on availability and costs of raw and/or scrap materials and on technological constraints. Interestingly, the reconstruction obtained for Thamusida could either anticipate the important change in the Roman use of copper alloys generally referred as ‘zinc decline’, or more likely, indicate that brass never conspicuously entered the local metal-working activities of this military site.     

AN INVESTIGATION OF THE PERMANENT MAGNETS Nd_(15)(Fe, Co)_(77)B_8 WITH Dy AND Al ADDITIVES

Nd-(Fe,Co)-B alloys with Dy and Dy-Al additives have been studied by the Mossbauer effect and X- ray diffraction. The results indicate that the alloys consist of a tetragonal phase, a B-rich phase and a Nd-rich phase. The average magnetic moment of Fe atoms in the tetragonal phase has been determined. The variation of remanence due to Dy and Dy- Al additives has been derived from the Mossbauer data and found to agree with the results of magnetic measurements. The site substitutions of Dy and Al in the alloys are also discussed.     

MOSSBAUER STUDIES OF MAGNETIC ANISOTROPY OF AMORPHOUS Fe-(Co, Cr)-Zr ALLOYS

Magnetic anisotropies and hyperfine fields of amorphous a-Fe-(Co, Cr)-Zr alloys, their temperature and thermal stress effects were studied by using a Mossbauer spectroscopy. The results are in the following: A tensile stress field is easily created during the material production process, having the plane anisotropy to be increased for the alloys containing strong ferromagnetic coupling such as Fe-Co and Fe-Ni; a pressure stress field is easily produced, making the perpendicular anisotropy increase for the alloys containing antiferromagnetic coupling such as Fe-Cr and Fe-Mn. Introducing the new idea of attractive and repulsive forces, the fact was explained well that the dependence of anisotropies on the average outer electron concentration of 3d transition metal is similar to that of the average hyperfine field.     

Ion-beam induced compositional changes in alloys at elevated temperatures

Near-surface compositional changes in alloys during ion bombardment have been studied theoretically. The scheme employed ensures pressure relaxation of the target, and the effects of preferential sputtering, collisional mixing, radiation-enhanced diffusion, and Gibbsian and radiation-induced segregation are allowed for. High-fluence composition profiles were determined directly from a nonlinear integro-differential equation by means of an efficient iteration procedure developed recently. The dependence of the composition profile on input parameters such as target temperature and defect mobility was examined for Ni---Cu and Ni---Pd alloys.