Magnetic and electrical properties of the UCu2T3Al7 alloys

The UCu₂T₃Al₇-type compounds with T = Cr, Mn and Fe crystallize in the tetragonal ThMn₁₂-type structure (I4/mmm space group). Magnetic properties have been examined in magnetic fields up to 50 kOe in the temperature range 1.9–400 K using a SQUID magnetometer. The Cr based pseudoternary alloy is paramagnetic with the linear field dependence of the magnetization at 1.9 K. The temperature dependence of the magnetic susceptibility is described by a modified Curie–Weiss (MCW) law. The Mn containing compound is ferrimagnetic and the field dependence of the magnetization does not reach saturation while the magnetic susceptibility follows the MCW law at high temperature. The Fe alloy is ferromagnetic and at higher temperature the MCW law is fulfilled. The temperature dependence of the electrical resistivity of all materials was examined between 4.2 and 300 K showing metallic character. The Mn and Fe based compounds demonstrate some anomalies in the ρ(T) plot at low temperature. The results are discussed in relation to the anomalies observed in magnetic measurements.     

High pressure electrical resistivity studies on Ni-doped TiO2 nanoparticles

Electrical resistivity measurement of Ni-doped TiO₂ nanoparticles were performed under high pressure using a Bridgman opposed anvil setup. It is observed that, anatase phase nanoparticles shows a sudden increase in resistivity below the pressure limit of 4 GPa and is attributed to the transition from anatase to rutile phase. In addition, the transition limit is shifted towards lower pressure region with increase in dopant concentration. But, Ni-doped TiO₂ nanoparticles with rutile phase shows a rapid decrease in resistivity up to 5 GPa and thereafter it becomes constant. Samples with constant resistivity behavior are mainly ascribed to the semiconductor-metallic transformation.     

High pressure study of β-UH3 crystallographic and electronic structure

The crystallographic and electronic structure of β-UH₃ were studied as a function of pressure by combining X-ray diffraction results with the full potential linearized augmented plane wave (LAPW) calculations. No phase transition was observed up to a pressure of 29 GPa, with a total volume contraction of V/V₀=0.87, and a bulk modulus value of B₀=33±5 GPa. The calculated value of the electric field gradient main component at the uranium 6(c) site was found to be linear dependent in the pressure induced volume reduction. This linear dependence is attributed to the increase in the positive p–p contribution to the efg as a function of volume, while the negative s–d, d–d and the lattice contributions to the efg are almost pressure independent.     

High pressure behaviour of TmTe and EuO

The high pressure behaviour of TmTe and of EuO have been investigated up to pressures of 49 and 63 GPa respectively, using the energy dispersive X-ray diffraction technique and synchrotron radiation. TmTe shows a phase transformation at 8 GPa to a possible tetragonal structure. Above 35 GPa this structure undergoes a further distortion. EuO shows a normal compressibility curve leading up to an NaCl to CsCl type phase transition beginning at 47 GPa.     

The ternary system: silicon–titanium–uranium

Phase equilibria in the system Si–Ti–U were established at 1000 °C by optical microscopy, EMPA and X-ray diffraction. Two ternary compounds were observed and were characterised by X-ray powder data refinement: (1) stoichiometric U₂Ti₃Si₄ (U₂Mo₃Si₄-type) with a small homogeneity region of about 3 at.% exchange U/Ti and (2) U_2−xTi_3+xSi₄ (Zr₅Si₄-type) extending at 1000 °C for 0.7<x<1.3. Mutual solubility of U-silicides and Ti-silicides was found to be below about 1 at.%. The Ti,U-rich part of the diagram was also investigated at 850 °C establishing the tie-lines to the low temperature compounds U₂Ti and U₃Si. U₂Ti₃Si₄ is weakly paramagnetic following a Curie–Weiss law above 50 K with μ_eff.=2.67 μ_B/U, Θ_P=−150 K and χ₀=1.45×10⁻³ emu/mol (18.2×10⁻⁹ m³/mol).     

Recent studies of uranium and plutonium chemistry in alkaline radioactive waste solutions

Solubility studies of uranium and plutonium in a caustic, radioactive Savannah River Site tank waste solution revealed the existence of uranium supersaturation in the as-received sample. Comparison of the results to predictions generated from previously published models for solubility in these waste types revealed that the U model poorly predicts solubility while Pu model predictions are quite consistent with experimental observations. Separate studies using simulated Savannah River Site evaporator feed solution revealed that the known formation of sodium aluminosilicate solids in waste evaporators can promote rapid precipitation of uranium from supersaturated solutions.     

Transformation behaviour with thermal cycling in NiTi alloys

The transformation behaviour of NiTi alloys were investigated by differential scanning calorimetry in order to reveal the effects of thermal cycles with the repetition of the transformation. The thermal cycles tend to lower the transformation temperature between the high and low temperature phases and to stabilize the intermediate phase during cooling to result in a two-stage transformation, while the reverse transformation during heating remains a one-stage transformation. Because these effects of the thermal cycles depend on the composition and the deformation, it is thought that defects play an intrinsic role in the complicated behaviour of NiTi alloys.     

Low-temperature thermoelectric properties of α- and β-Zn4Sb3 bulk crystals prepared by a gradient freeze method and a spark plasma sintering method

The low temperature thermoelectric properties of Zn₄Sb₃ samples prepared by the gradient freeze (GF) method and sintering have been characterized. With decreasing temperature a dramatic rise in the thermal expansion is observed associated with the structural transition from β- to α-phase; Δl/l=2.8×10⁻⁴ at T_s^GF=257.4 K for GF and Δl/l=1.6×10⁻⁴ at T_s^S=236.5 K for sintered samples. Enhancement is observed in electrical conductivity and p-type thermopower at T_s^GF and T_s^S, while a reduction is observed in the magnetic susceptibility. The GF sample exhibits higher thermoelectric performance than the sintered sample. The power factor of the α-phase in the GF sample is twice as large as that of the β-phase; it exceeds 20 μW/cm·K² between 120 and 240 K, indicating that the α-phase Zn₄Sb₃ is one of the prime candidates for thermoelectric materials for cryogenic use.     

高压柱塞泵气蚀现象及其控制

为减小配流冲击、降低噪声,高压柱塞泵的柱塞腔在吸排油转换的过程中必须通过机械闭死压缩、膨胀和减振槽引油共同作用来实现预升压和预卸压.这一过程中,减振槽的两端均作用较大的变化的压差,槽中的油液产生较大速度的压差流,导致低压区的出现,形成气穴,气泡再破裂时产生气蚀,破坏配流盘和缸体表面.通过优化减振槽的参数和结构,减小气穴...     

高压内啮合齿轮泵的测试与分析

基于所构建的液压泵综合试验台,对高压内啮合齿轮泵的排量、功率、流量、效率等性能进行了测试与分析,特别对内啮合齿轮泵在高压下的工作特性进行了测试,分析了其高压下的压力脉动特性,为内啮合齿轮泵的研究提供了依据。     

Experimental measurement of pre-melting and melting of thorium dioxide

Thorium dioxide samples have been submitted to homogeneous four-beam laser pulses in an autoclave filled with different gases. Phase transitions were analysed through the produced thermal arrest stages, which were detected by a precise multichannel pyrometer. The spectral emissivity of the samples, measured on line during heating up to 4000 K, is also reported in the paper. Thoria exhibits a melting point at 3651 K, and a pre-melting transition at 3090 K. These temperatures are weakly influenced by chemical reduction of the sample. Whilst virtually stoichiometric thoria melts congruently, in the hypostoichiometric oxide, the liquids and solidus temperatures could be clearly observed at O/Th = 1.98. The analysis of the measured data and, in particular, of the heat capacity shows that the features of the pre-melting transition can be described by a Debye-Hückel oxygen defect model, where co-operative effects lead, in the oxygen sublattice, to a critical order-disorder transition, whose thermodynamic nature depends on the parameters of the defect mean-field coulomb interaction. A comparison of the high temperature phase diagrams of thoria and urania indicates close analogies in the pre-melting behaviour of these two compounds.     

Specific heat of the antiferro/ferro-magnet NpGa3

The specific heat of NpGa₃ has been measured for the first time. The magnetic transitions and more generally the full magnetic phase diagram have been re-established precisely. The Sommerfeld coefficient and the magnetic entropy point to a rather localized system, in agreement with previous studies, in particular high pressure Mössbauer and resistivity. The comparison with other NpX₃ suggests that NpGa₃ is the most localized member of the series.     

全自动高压吹料清洗机的研制

为某金属零件加工生产线研制了一种全自动高压吹料清洗机,可以快速去除金属零件腔体内部和表面残留的金属屑。根据生产线的结构和企业清洗要求,给出设备总体设计方案,并进行了机械结构设计和基于PLC与触摸屏的电气控制系统设计。设备投入使用后,性能稳定,清洗效果好,提高了生产线的自动化程度,降低了工人的劳动强度。     

Magnetic and electrical properties of NdNiSn

Magnetization and resistivity measurements have been carried out on the equiatomic ternary compound NdNiSn in the temperature range 2–200 K. The compound crystallizes in the orthorhombic CeNiSn-type structure with space group Pna2₁. Magnetic susceptibility shows a distinct feature at T_N=3 K (Néel temperature), typical of a phase transition from an antiferromagnetic to paramagnetic state. In the paramagnetic regime, the magnetic susceptibility obeys Curie–Weiss behavior yielding an effective magnetic moment μ_eff=3.32μ_B at lower temperatures, and 3.88 μ_B at higher temperatures. The reduction in the magnetic moment at lower temperatures is attributed to a crystalline electric field (CEF) effect, while the slight excess of magnetic moment at high temperatures compared to that of the free Nd³⁺ ion (3.62 μ_B) indicates that only a very small magnetic moment, at most 0.3 μ_B, is induced at the Ni sites. The electrical resistivity exhibits metallic behavior and no anomaly is observed at the respective Néel temperature. Analysis of the resistivity data in terms of crystalline electric fields including s–d electron scattering reveals that the ground magnetic state for the Nd³⁺ ions is a doublet of J=±5/2 states, with a first exited doublet of J=±7/2 states having an energy splitting of 56 K, with the next exited multiplet 139 K above the ground levels. These results are in fairly good agreement with those reported in the literature based on magnetic susceptibility and heat capacity measurements.     

高压泵结构参数对喷油性能的影响分析

对柴油机高压共轨燃油喷射系统中的高压泵进行研究,介绍了共轨系统的组成结构和工作原理,利用GT-Fuel分析软件建立高压泵仿真模型。分析高压泵弹簧刚度、预压力及柱塞直径对共轨管内燃油喷射特性的影响。仿真结果表明:弹簧刚度和预压力对燃油喷射压力、喷油率和喷油量几乎无影响;柱塞直径在不同喷射期间对喷油压力有不同的影响。仿真数据为高压泵的设计和模拟提供了理论依据和实践价值。     

高压共轨系统台架试验与仿真分析

在高压共轨试验台架搭建的基础上,进行了喷油泵台架试验。试验结果表明:电控单元能够完成信号采集、驱动控制、串行通信的基本控制、共轨压力的闭环控制以及高精度喷油量的检测。在不同的工况下,压力测量精度达到±2%;在轨压波动实验中,PID控制结果基本符合控制要求;在变工况条件下,轨压能够在0.1 s内完成切换;在发动机变工况工作时,ECU首先采集转速信号和油门信号做出判断,并通过查MAP,得到新的目标轨压,然后进行PID调节。     

High-temperature electrical conductivity of Li–Ge ferrites

Electrical conductivity of germanium-substituted lithium ferrites of different compositions have been investigated as a function of composition and temperature. Plots of log(σT) versus 10³/T are almost linear and have shown a transition near the Curie temperature. The activation energy in the ferromagnetic region is in general less than that in the paramagnetic region. An attempt is made to explain the conduction mechanism in Li–Ge ferrites.     

Long-term amorphisation of C and N2 implanted layers on a uranium surface

Ion implantation of C⁺ or N₂⁺ on uranium surfaces produces crystalline compounds (uranium carbides or nitrides, respectively), which have been shown to provide excellent protection against ambient corrosion. Some long-term changes of these implanted layers were detected that even though not affecting the protection ability, still are of fundamental interest. The most prominent change is the amorphisation of the carbide or nitride layers, which takes place after a few years of air exposure. This amorphisation did not result from the oxidation of the layer (the formed oxides are much thinner than the thickness of the implanted layers), but is still assisted by air exposure (i.e., the amorphisation rates of samples kept under vacuum are much lower than those exposed to the ambient atmosphere). Some additional long-term changes in the layer compositions (transitions of UN₂ to U₂N₃) and distributions (inward diffusion of the implanted ions) were also apparent. It is suggested that the presence of hydrogen in the implanted layer, originating from the dissociation of water molecules on the surface, may accelerate the amorphisation and the UN₂ to U₂N₃ transition due to the possible increase in the diffusion constant.