The Effect of Adsorbed Atomic Hydrogen on the Electrochemical Dissolution Kinetics of Iron

A functional dependence of the potentiostatic dissolution rate of iron on the metal surface coverage with hydrogen () is found. An increase in the anodic current with time after the potential jump is related to the decrease in . A potential dependence of the dissolution rate of iron at = const is obtained. The high Tafel slope of this polarization curve shows that the first one-electron stage of iron ionization is substantially irreversible.     

A Kinetic Model for the Boriding Kinetics of AISI D2 Steel During the Diffusion Annealing Process

In this work, a diffusion model was proposed to estimate the boron activation energies for FeB and Fe₂B layers during the pack-boriding of AISI D2 steel at temperatures of 1223, 1253 and 1273 K for a treatment time varying between 2 and 10 h. This model considers the effect of boride incubation times during the formation of the FeB and Fe₂B phases. To study the influence of diffusion annealing process on the boriding kinetics of AISI D2 steel, the mass balance equations were modified in order to follow the evolution of boride layers as a function of annealing time for the specified boriding parameters. Finally, the kinetic model was validated by a comparison of the experimental thicknesses of boride layers with the predicted ones at a temperature of 1243 K for 2, 4 and 6 h. A simple equation was then obtained for estimating the total time necessary to get a single boride layer (Fe₂B) that depends on the boriding parameters and on the thickness of each boride layer prior to the diffusion annealing process.     

The Kinetics of the Titanium Dissolution in a Domain of Cathodic Evolution of Hydrogen

The existence of a linear dependence of the titanium dissolution current on potential in a domain of cathodic evolution of hydrogen is experimentally shown. The principle of independence of concurrent electrochemical reactions is discussed.     

2D double-layered metal–radical complexes: Crystal structures and magnetic properties

Two new complexes [Mn(NIT4Py)(2,4-PDA)(H₂O)₂] (1) and [Co(NIT4Py)(2,4-PDA)(H₂O)₂] (2) (where NIT4Py stands for 2-(4′-pyridinyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, 2,4-PDA stands for pyridine-2,4-dicarboxylate) have been synthesized and characterized. The single-crystal X-ray diffraction demonstrates that complex 1 present dimeric structure with two 2,4-PDA anions function as bridging ligands, connecting two Mn(II) centers. The dimeric units form an infinite 2D double-layered network via hydrogen bonds. Complex 2 consists of infinite 1D chain, in which each 2,4-PDA anion bridges two adjacent Co(II) ions in monodentate–bidentate mode. These 1D chains are further connected together by hydrogen bonds, generating a 2D double-layered structure, too. The variable temperature magnetic susceptibility measurements reveal that the magnetic couplings between Mn(II) and NIT4Py, Co(II) and NIT4Py are weak ferromagnetic and antiferromagnetic interactions for complexes 1 and 2, respectively.     

Kinetics of 2D electrons in a magnetic field in the presence of microwave radiation: Response of a nonequilibrium system to a weak measuring field

Kinetics of spatially uniform distributions of two-dimensional (2D) electrons in crossed electrical and magnetic fields has been studied in the presence of microwave radiation. In the model presented, the contribution from radiation and quantization is taken into account exactly, whereas the effects of scattering are treated in terms of a perturbation theory. In this case, the Landau-Floquet states interact with the field of impurities, leading to transitions between these levels. It has been shown that the method of a nonequilibrium statistical matrix in combination with the method of a canonical transformation makes it possible to construct a theory of the linear response of a nonequilibrium 2D electron gas to a weak measuring electric field. The theory constructed describes the dependence of the magnetoresistance of a 2D electron gas on the electron mobility, strength of the magnetic field, and frequency of the microwave radiation observed in experiments. It has been shown that the photoconductivity of the 2D electron gas is an oscillating function of the ratio of the radiation frequency to the cyclotron frequency and, depending on this ratio, can be both positive and negative. The theory predicts the possibility of observation of magnetoresistance oscillations in samples with a lower mobility of the 2D electron gas when using an enhanced frequency of microwave radiation.     

Justifying the Model of Spatial Separation of Metal Dissolution and Passivation Processes

Results of studying the dissolution of fresh-formed iron surface and voltammetry of liquid and solid gallium are used to justify the concept of the direct participation of surface charge-transfer complexes, resulting from water adsorption, in the anodic dissolution of hydrophilic metals. The concept also implies both the effect of steady-state surface morphology on the kinetic parameters of the anodic dissolution and the effect of potential on the surface morphology. This concept underlies a model of spatial separation of processes of metal dissolution and passivation. Using this model, anodic voltammograms for iron in solutions with different concentration of chloride ion and pH were calculated. The calculated curves are in close agreement with experimental ones.     

3D Visualization of the Dissolution Products of a Metal in the Near-Electrode Layer at the Metal-Solution Interface

A 3D profile of the layer of the metal dissolution products precipitated from a solution is reconstructed by means of reflectometry. Its nano-scale resolution in thickness enables one to investigate in situ the formation of micro- and nano-size adsorption islets, new phase nuclei, and steady-state localized superficial domains (with different rates of the metal dissolution and complex formation processes). In this way, the originally unseen structure of the metal surface defects is visualized. The digital optical images obtained with a scanner for a small probed surface spot were processed in order to clarify the pitting nature of the metal dissolution in distilled water and visualize the latent defective metal structure. Local dissolution centers (pits) appear mainly in the first 10 to 20 min and determine the corrosion rate. The technique is highly sensitive to thin layers and, consequently, to the ions in solution. All these peculiarities make the measurements of the tangential non-uniformity of the layer at the studied spot of the electrode surface highly informative. The secondary precipitated layer of dissolution products can be considered as a distributed sensor layer immobilized at defects of the metal surface. Minor changes in the solution chemistry (pH, oxygen content, etc.) lead to the change in the dissolution rate and, hence, in the thickness, structure, and composition of the secondary precipitated sensor layer. __________ Translated from Zashchita Metallov, Vol. 41, No. 6, 2005, pp. 547–561. Original Russian Text Copyright ? 2005 by Kotenev, Petrunin, Maksaeva, Tsivadze.     

Simplified Topographic Model of Metal Dissolution: Comparison of Metals with Ideal and Real Lattices

A system of equations is formulated and solved for the dissolution model of a defect-free crystal with a simple cubic packing, which describes self-consistence of the atomic structure of a dissolving surface (including the edge concentration) and the dissolution rate. The enhanced corrosion resistance is shown to be associated with a small (edge concentration compared with that typical of a real defective crystal.     

Kinetics of gadolinium extraction with D2EHPA and Cyanex301 using single drop column

The extraction kinetics of Gd(III) from the nitric acid medium using bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex301) and 2-ethylhexyl phosphoric acid (D2EHPA) in kerosene solution were measured by the single drop technique. The influences of hydrogen ion concentration, gadolinium ion concentration, extractant concentration, column height, and nozzle diameter on the extraction rate were investigated. The forward rate equations for the gadolinium extraction with D2EHPA and Cyanex301 were obtained. Based on the experimental results, the forward extraction rate constant was calculated. With the increase of D2EHPA or Cyanex301 concentration, the drop rising diameter and the value of interfacial tension decrease in the studied system, which shows that D2EHPA or Cyanex301 has interfacial activity as a kind of surfactant. Also, the droplet diameter and interfacial tension decrease with the increase of aqueous solution acidity. The experimental results show that the D2EHPA extractant provides faster extraction rate in comparison with Cyanex301 extractant, and it would be useful in industrial continuous extraction process.     

金属材料CO_2腐蚀数据库的设计和实现

在Microsoft Win XP中文专业版环境下,使用Microsoft SQL Server 2000数据库管理系统,设计和开发了一个全中文环境下的金属材料CO2腐蚀数据库。用Origin制图工具生成存储图像,以SQL Server的二维表存储数据,采用C#编程。采用C/S三层架构完成开发。系统包括了数据编辑、检索浏览、数据维护以及图像显示等多种功能实现。     

Thermodynamic Theory of “Irregular” Solutions and Kinetic Model of the Passive Alloy Dissolution

Thermodynamic model of an irregular solution developed earlier for small mixing parameter values (nearly regular solution) is generalized for arbitrary (real) values of the parameter. In this case, an interaction between components results in a chemically nonuniform solution, i.e., in the formation of micrograins of diverse composition, which increase in the size with an increase in the mixing parameter and a decrease in the concentration of one of the components. The passivating film on the alloy surface is modeled as a solid solution of oxide “molecules” of the components, which enables us to proceed from thermodynamics to the reaction rates theory and bring the theory in agreement with the data on the passive alloy dissolution. The chemical non-uniformity forces us to interpret the values referred to in the theory (component concentrations and dissolution rates) as statistically average, i.e., averaged over the surface of the specimen dissolved and over the time of experiment. However, this approach may be insufficient (when it is necessary to take into account fluctuations or deviations from the mean values) for example, under conditions when the surface nonuniformity may result in pit nucleation. __________ Translated from Zashchita Metallov, Vol. 41, No. 6, 2005, pp. 562–572. Original Russian Text Copyright ? 2005 by Alekseev.     

基于团簇和胶粘原子模型的(Fe-Ni)-B-Y-Nb块体非晶合金

应用团簇+胶粘原子模型在三元Fe-B-Y合金系中设计三元合金成分,选择最密堆的CN10 Archimedes八面体反棱柱Fe8B3作为基本团簇,Y为胶粘原子。在此基础上添加3at%Nb作为微合金化元素形成四元合金。以适量的Ni替换Fe,形成五元合金[(Fe100-xNix)8B3-Y]97-Nb3。结果表明,当Ni的含量小于30at%时,均可形成直径为2 mm的块体非晶合金,其中,合金[(Fe94Ni6)8B3-Y]97-Nb 3具有最大的Tg、Tx和Trg值,分别为：884 K、972 K和0.634。     

基于团簇和胶粘原子模型的(Fe-Ni)-B-Y-Nb块体非晶合金

应用团簇+胶粘原子模型在三元Fe-B-Y合金系中设计三元合金成分,选择最密堆的CN10Archimedes八面体反棱柱Fe8B3作为基本团簇,Y为胶粘原子。在此基础上添加3at%Nb作为微合金化元素形成四元合金。以适量的Ni替换Fe,形成五元合金[(Fe100-xNix)8B3-Y]97-Nb3。结果表明,当Ni的含量小于30at%时,均可形成直径为2mm的块体非晶合金,其中,合金[(Fe94Ni6)8B3-Y]97-Nb3具有最大的Tg、Tx和Trg值,分别为:884K、972K和0.634。     

Application of a Simple Statistical Spalling Model for the Analysis of High-Temperature,Cyclic-Oxidation Kinetics Data

A statistical cyclic-oxidation model is presented. This model gives analytical formulas to assess stabilized metal consumption in cyclic-oxidation experiments. The model is first detailed, then applied to se eral Ni-base superalloys, which form an -alumina scale during oxidation above 1000C. A new map is introduced in order to compare the cyclic-oxidation beha ior of these alloys.     

Growth and Characterizations of ZnGeP2 Crystal by a Vertical Bridgman Method

采用改进的垂直布里奇曼法在自制的三温区炉内生长出尺寸达Ф24 mm ′ 70 mm的磷锗锌（ZnGeP2,ZGP）单晶体,将晶体在600 ℃下于同成分粉末包裹中进行了500 h退火热处理。采用X射线衍射仪（XRD）、X射线荧光仪（XRF）以及傅里叶红外光谱仪(FTIR)对ZGP晶体结构、成分和光学性能进行了测试和分析表征。加工制作出ZGP光参量振荡器（ZGP-OPO）,采用2.1 mm、7 kHz激光泵浦ZGP-OPO,实现了3~5 mm中红外调谐激光输出,功率达0.48 W。上述结果表明所研制的ZGP晶体结构完整,品质高,能够用于制作非线性光学元器件应用     

振动条件下晶体游离模型探讨及实验验证

通过对晶核发生器表面晶粒初生相的受力分析，建立了振动条件下晶体游离的力学模型。发现决定晶体是否游离的主I-N素包括振动频率、振幅及晶核发生器激冷温度等。采用NH4Cl-70％wtH2O溶液，实验考察了上述3种主要参数对振动晶核发生器表面晶粒游离难易程度的影响，实验结果与理论分析获得了较好的吻合。