Effect of annealing on the characteristics of Au layers grown on the high-temperature deposited Ni50Fe50 layers

80 nm-thick Ni₅₀Fe₅₀ layers were sputter-deposited on glass substrates at 400 °C and then Au layers were sputter-deposited on the Ni₅₀Fe₅₀ layers. The Au/Ni₅₀Fe₅₀ bilayer films were annealed in a vacuum of 5×10⁻⁴ Pa from 250 to 450 °C for 30 min or 90 min. The characteristics of the Au layers were studied by Auger electron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and a four-point probe technique. When the annealing temperature reaches 450 °C, Fe and Ni atoms diffuse markedly into the Au layer and the Fe content is more than the Ni content. When the annealing temperature is lower than 450 °C, the grain size of the Au layers does not change markedly with annealing temperature. However, as the annealing temperature reaches 450 °C, the annealing promotes the grain growth of the Au layer. As the annealing temperature exceeds 300 °C, the resistivity of the bilayer films increases with increasing annealing temperature. The diffusion of Fe and Ni atoms into the Au layer results in an increase in the resistivity of the annealed bilayer film. Large numbers of Fe and Ni atoms diffusing into the Au layer of the annealed Au/Ni₅₀Fe₅₀ bilayer film lead to a significant decrease in the lattice constant of the Au layer.     

Rapid Small-Scale Column Tests for Arsenate Removal in Iron Oxide Packed Bed Columns

Arsenate breakthrough in column studies with a porous granular ferric hydroxide (GFH) was investigated in model waters and groundwaters. In this study, the use of rapid small-scale column tests (RSSCTs) initially designed for simulating the removal of organic compounds by granular activated carbon was extended for arsenate adsorption onto GFH. Adsorption kinetic studies and a comparison of laboratory RSSCT performance versus pilot-scale performance suggests that proportional diffusivity (PD) RSSCT scaling approaches are more valid than constant diffusivity (CD) approaches for arsenate onto GFH. Adsorption densities from column tests (qcolumn) were calculated at the point in the breakthrough curve when arsenate equaled 10 μg/L in the column effluent. For a simulated 2.5 min empty-bed contact time (EBCT), a model water (pH=8.6) had qcolumn values of 0.99 to 1.5 mgAs/gGFH versus 0.02 to 0.28 mgAs/gGFH with a comparable pH and EBCT in a natural groundwater. The differences were attributed to the silica, phosphate, vanadium, and other adsorbable inorganics in the groundwater. At pH 7.6 to 7.8, qcolumn values from PD-RSSCTs in the three natural waters were comparable (1.5±0.3 mgAs/gGFH) and higher than CD-RSSCT qcolumn values (0.57±0.26 mgAs/gGFH) in the three natural waters. All the RSSCTs captured changes in water quality (source water and pH) and operational regimes (e.g., EBCTs) and could be used to aid in the selection and design of arsenic removal media for full-scale treatment facilities.     

Diffusive Behavior of Bedform-Induced Hyporheic Exchange in Rivers

Solute transport in natural streams is a complex phenomenon that involves both in-stream dispersion and mass exchange with the porous zones surrounding the water body. Due to the complex nature of the riverine systems several models may be used to simulate and analyze the transport of solutes with different degrees of complexity. The bedform-induced hyporheic transport is a stream-subsurface exchange mechanism that can be reproduced in controlled systems, such as laboratory flumes. Application of a simple Fickian diffusion model to laboratory data obtained with passive solutes and stationary bedforms proves successful within a range of durations of the contamination process. A dimensionless form of the diffusion coefficient, scaled with dynamic, physical, and geometric properties of the system is derived by comparison with another physically based model. A prediction of the dimensionless diffusion coefficient is obtained as a function of the timescale of the exchange process and is validated with a few sets of results from laboratory tests.     

Kinetics of reactive diffusion between Au and Sn during annealing at solid-state temperatures

The reactive diffusion between Au and Sn was experimentally studied at solid-state temperatures using Sn/Au/Sn diffusion couples prepared by a diffusion bonding technique. The diffusion couples were annealed at temperatures of T = 393 and 473 K for various times in an oil bath with silicone oil. After annealing, compound layers composed of AuSn₄, AuSn₂ and AuSn were recognized to form at the Au/Sn interface. The thickness of the AuSn₄ layer is about six and four times greater than those of the AuSn₂ and AuSn layers at T = 393 and 473 K, respectively. The ratio of the thicknesses of the compound layers is kept constant independently of the annealing time. The total thickness l of the compound layers is described as a function of the annealing time t by the equation l = k(t/t₀)ⁿ, where t₀ is unit time, 1 s. The exponent n is nearly equal to 1/2 at T = 393 K but takes a value between 1/4 and 1/2 at T = 473 K. Such an intermediate value of n at T = 473 K indicates that the grain boundary diffusion contributes to the reactive diffusion and the grain growth occurs at certain rates. As the annealing temperature decreases, the contribution of the grain boundary diffusion should become more remarkable, but the grain growth will slow down. Consequently, n becomes close to 1/2 at T = 393 K. According to the constancy of the ratio of the thicknesses, it is concluded that the same rate-controlling process works in the AuSn₄, AuSn₂ and AuSn layers at a constant annealing temperature.     

核事故条件下的大气扩散模式及应用

本文介绍一个适用于核事故条件的大气扩散模式(粒子-烟团模式)的建立与调试。模式在模拟大气扩散的粒子随机游走方法中引入类似于扩散烟团的核函数概念，用以反映单个随机游走粒子所代表的污染物质的空间影响范围。模式解决了随机游走粒子与核函数“烟团”耦合后反映扩散物理真实过程的一致性问题，在约200km的范围内模拟结果与理论结果相一致。与代表实际大气典型扩散状况的高斯烟羽模式的结果进行定量比较，表明本模式结果在10km的范围内总体合理，但在近源处有系统偏小。模式瞬时浓度的涨落相对于平均轴线浓度大体控制在20％～30％的范围内。将模式应用于秦山地区的实际地形和气象条件进行实例测试表明，其结果可以反映当地复杂的大气扩散过程和特性。     

Kinetics of titanium nitride coatings deposited by thermo-reactive deposition technique

In this study, the growth kinetics of titanium nitride layer deposited on pre-nitrided AISI 1020 steel samples by thermo-reactive diffusion (TRD) techniques in a solid medium was reported. Steel was at first tufftrided and then titanium nitride coating treatment was performed in a powder mixture consisting of ferro-titanium, ammonium chloride and alumina at 1173, 1223 and 1273 K for 1-4 h. Titanium nitride layer thickness on the titanium nitride coated AISI 1020 steel ranged from 5.5 to 19.2 μm depending on treatment time and temperature. Layer growth kinetics was analyzed by measuring the depth of titanium nitride layer as a function of time and temperature. The kinetics equation of the reaction has also been determined with Arhenius equation K=K_oexp(−Q/(RT). The result showed that the diffusion coefficient (K) of the process increased with treatment temperature. Activation energy (Q) for TRD process was calculated as 187.09 kJ/mol. The diffusion coefficients (K) changed between 6.637×10⁻¹¹ and 2.097×10⁻¹⁰ cm²/s depending on the process temperature.     

镍氢电池在放电过程中的电极极化

利用暂态技术－电流阶跃法对镍氢电池的正负极在放电过程中的电化学极化、浓差极化及欧姆极化进行了研究。镍氢电池放电电压的衰减主要是由正极衰减引起的,浓差极化又是正极衰减的主要原因。负极的电化学极化和浓差极化随放电深度的增加而变化,但电化学极化增加的幅度较小。     

强流脉冲电子束轰击作用下的扩散模型及其数值计算

在温度场和应力场计算的基础上建立了强流脉冲电子束轰击作用下的扩散模型,并给出了数值方法及其数值解。该模型与方法同样适用于其它高能束流作用下的扩散过程。计算表明,浓度扩散流仍然是影响扩散的主要因素;而轰击超过一定次数后,扩散的作用将减弱;当边界条件为表面扩散时,扩散进行较快,这是表面涂覆加脉冲电子束后处理快速表面合金化工艺的理论基础。对实验结果和理论结果的对比分析表明,在脉冲轰击下,扩散激活能随空位浓度的增加而下降,从而加速扩散过程;在表面有熔化的情况下,则液态时的对流混合作用是主导因素。     

PE－AA辐射接枝共聚合的反应历程研究

研究了聚乙烯（ＰＥ）与丙烯酸（ＡＡ）、甲基丙烯酸（ＭＡＡ）的接枝共聚反应，探讨了接枝反应过程及特征：单体首先在ＰＥ表面接枝，然后进入内部进行本体接枝。研究表明：表面接枝为动力学控制，本体接技系扩散控制，单体在膜内的扩散与单体极性及聚合物的结晶度等有关     

Radionuclides in primary coolant of a fluoride salt-cooled high-temperature reactor during normal operation

The release of fission products from coated particle fuel to primary coolant,as well as the activation of coolant and impurities,were analysed for a fluoride salt-cooled high-temperature reactor (FHR) system,and the activity of radionuclides accumulated in the coolant during normal operation was calculated.The release rate (release fraction per unit time) of fission products was calculated with STACY code,which is modelled mainly based on the Fick's law,while the activation of coolant and impurities was calculated with SCALE code.The accumulation of radionuclides in the coolant has been calculated with a simplified model,which is generally a time integration considering the generation and decay of radionuclides.The results show that activation products are the dominant gamma source in the primary coolant system during normal operation of the FHR while fission products become the dominant source after shutdown.In operation condition,health-impacts related nuclides such as 3H,and 14C originate from the activation of lithium and coolant impurities including carbon,nitrogen,and oxygen.According to the calculated effective cross sections of neutron activation,6Li and 14N are the dominant 3H production source and 14C production source,respectively.Considering the high production rate,3H and 14C should be treated before being released to the environment.