Optical and microstructural properties of anodically oxidized aluminum

Scanning electron microscopy, Auger electron spectroscopy, emissometer and reflectometer measurements have been made on anodic oxide coatings on aluminum prepared from solutions of phosphoric, chromic and sulfuric acid. The anodic oxide films are very porous, with the porosity greatest in films which were produced in phosphoric acid. A structural model for the oxide coatings has been generated from the data, and microstructural parameters for the model were defined. The IR emittance as well as the spectral hemispherical reflectance of the oxides have been measured as a function of film parameters, with specific emphasis on optimization of optical properties for use of the coatings as the matrix material for solar absorber coatings.     

Electrochemical passivation behaviour of nanocrystalline Fe80Si20 coating in borate buffer solution

Passivation behaviour of nanocrystalline coating (Fe₈₀Si₂₀) obtained by in situ mechanical alloying route is studied and compared with that of the commercial pure iron and cast Fe₈₀Si₂₀ in sodium borate buffer solution at two different pH values (7·7 and 8·4). The coating reveals single passivation at a pH of 7·7 and double stage passivity at a pH of 8·4. The first passive layer is due to the dissolution mechanism and second passivity is related to stable passivation. The cast sample shows single stage passivity in the solution of pH 8·4. The difference in the passivation behaviour for the cast alloy (Fe₈₀Si₂₀) and the coating is related to the presence of highly iron-enriched localized regions, formed during the processing stage of coating.     

块体纳米晶工业纯铁在盐酸溶液中的电化学腐蚀行为

通过静态失重试验,动电位极化曲线,电化学阻抗谱(EIS)实验,研究了块体纳米工业纯铁(BNIPI)和粗晶工业纯铁棒(CGPIR)在室温1mol/l盐酸溶液中的腐蚀行为.结果表明,BNIPI与CGPIR相比,开路腐蚀电位Ecorr正向移动114mV,平均腐蚀速度和腐蚀电流Icorr变小,极化电阻Rp增大为1.58倍.BNIPI抗盐酸的腐蚀能力与CGPIR相比,不但没有下降,相反有所增强.使用扫描电子显微镜(SEM)对静态腐蚀失重试样的形貌进行了观察,显示BNIPI上几乎没有点蚀坑出现.     

Formation of through-holes in Si wafers by using anodically polarized needle electrodes in HF solution

Electrochemical pore formation in Si using an anodized needle electrode was studied. In the electrochemical process, a Pt, Ir or Pd needle with a diameter of 50-200 μm was brought into contact at its tip with a Si wafer, which was not connected to an external circuit, in HF solution. By applying an anodic potential to the needle electrode against a Pt counter electrode, a pore with a diameter slightly larger than the diameter of the needle electrode was formed in both p-type and n-type Si, of which current efficiency was higher for n-type Si. Through-holes were electrochemically formed in p-type and n-type Si wafers at speeds higher than 30 μm min(-1) using a sharpened Ir needle electrode. A model was proposed to explain the results, in which the pore formation was attributed to successive dissolution of Si atoms near the 3-phase (Si/metal/HF solution) boundary by positive holes injected from the needle electrode to the surface of Si.     

Nanostructure and radiation resistance of carbon stripper foils

Raman light scattering has been used to analyze the short-range order structure of carbon stripper foils. It has been shown that the radiation resistance of the foils depends strongly on their nanostructure. It was observed that under the action of a 2 MeV hydrogen ion beam, soot-like foils have a considerably longer life than foils with a graphite-like nanostructure. Pis’ma Zh. Tekh. Fiz. 24, 79–84 (August 12, 1998)     

Nanostructure characterization of mechanical alloyed and consolidated iron alloys

High-energy ball milling (which is readily adoptable to commercial application) was used to develop sufficient quantities of nanostructured material to produce compacts capable of being measured for macroscopic properties. Characterization of the ball-milled powders show that grain boundary properties play a significant role in the overall properties of the milled powder. Nearly full-dense compacts were produced by hot-pressing. Characterization of the strength properties of these compacts show that there was little influence of hardness, density, or alloy composition on the failure properties. The range of failure stress was large and when fitted to a Weibull distribution suggest that failure was the result of flaws or cracks resulting from the hot-pressing. Hardness data, commonly used to evaluate the strength of nanostructured materials, showed no correlation to tensile strength, but correlated highly to compression maximum stress.     

Grain-size dependence of coercive force in sputtered and annealed iron films

Magnetic properties such as coercive force, initial susceptibility, etc., are structure sensitive parameters. Especially, the coercive force depends on the existence of crystal defects such as dislocations and grain boundaries. In this study, the grain-size dependence of coercive force was investigated in an iron film, 150 nm in thickness, deposited by sputtering method on a (001) KCl substrate at room temperature. The grain size of the film was changed from 15 to 120 nm by annealing in a vacuum. The coercive force increased with the increase of grain size and was proportional to the square of grain size. The magnetic domain had a ripple structure when the grain size was smaller than 50 nm. A grain size larger than 50 nm led to an irregular domain wall configuration and the formation of domain walls in the grain.     

Ultrasonic investigation and infrared absorption of some sodium borate glasses

Ultrasonic velocities and absorption measurements in sodium borate glasses containing Na₂O have been made using the pulse echo technique at 4, 5 and 6 MHz. Results showed an increase in velocity as the sodium oxide content (mol%) increased. The ultrasonic absorption results showed the presence of very high and well-defined peak which shifts its position to lower temperatures with increasing frequency. This suggests some sort of relaxation process and the activation energy of this process increased with increasing Na₂O concentration (mol%). The infrared absorption spectra of sodium borate glasses confirmed the results obtained by ultrasonic investigations.     

Electrical and magnetic properties of lithium borate glass containing iron

Journal of Materials Science Letters -     

Molar volume and magnetic susceptibility of borate glasses containing iron

A glass system was prepared from reagent grade chemicals having the formula 58 mol % B₂O₃ - 22 mol % CaO - (20 - ) mol % Al₂O₃ - mol % Fe₂O₃, where has different values between 2 and 20 mol %.The molar volume () and magnetic susceptibility () of these glasses has been measured as a function of Fe₂O₃ content. The values of and were found to increase as the Fe₂O₃ content in the glass increases in the region between 2 and 8 mol % and in the region where the content is greater than 10 to 16 mol %, while a decrease was found for samples having an Fe₂O₃ content of 10 mol % and more than 16 mol %. These results could be explained by the change in coordination of iron from FeO₆ to FeO₄, and also the change of Fe³⁺ to Fe²⁺ and change of Fe²⁺ from six coordination to four coordination.     

Adiabatic Shear in annealed and shock-hardened iron and in quenched and tempered 4340 steel

Adiabatic shear localization is a catastrophic failure mechanism which can occur in ductile metals under high strain rate loading. This mechanism is driven by a thermal instability process in which rapid temperature rise due to plastic work couples with thermal softening to cause uniform deformation to collapse into narrow bands of intense shear within which material ductility is exhausted. Adiabatic shear localization is studied in three ferrous metals: annealed Armco and as-received Remco iron, both of which are high purity alpha iron; shock-hardened Remco iron; and 4340 steel quenched and tempered to a range of hardness levels. Using a compressive split-Hopkinson bar, punching-shear experiments were performed at room and elevated initial temperatures at shear strain rates of up to 45000 s^–1. Optical and scanning electron microscopy was performed on the deformed shear specimens to determine the extent of shear localization and mode of failure. Experimental evidence showed that the tempered 4340 steels were susceptible to localization through adiabatic shear banding; however, as-received and shock-hardened Remco iron and annealed Armco iron were not. Finite element simulations of the experiments were performed utilizing a user material subroutine developed as part of this research. This constitutive routine incorporates two adiabatic shear failure criteria, namely (i) maximum shear stress with a minimum critical shear strain rate and (ii) flow localization. These criteria proved to be capable of predicting the onset of an instability; however, the deformation which follows the instability was not predicted well.     

Significant acceleration of nitriding kinetics in pure iron by pressurized gas treatment

The effect of nitriding pressure on the formation of nitrides and the nitriding kinetics in pure iron were investigated by applying pressurized gas nitriding at 500 °C for 5 h. Increasing the nitriding pressure from 1 atm (conventional nitriding condition) to 5 atm significantly increased the nitrided layer thickness from about 210 μm to 1100 μm. Furthermore, it was found that the constituents of the compound layer can be controlled by changing the nitriding pressure. These improvements are related to the fast reaction rates and high inward diffusive flux of nitrogen during the pressurized gas nitriding.     

Detection of crack nucleation in sheet metalforming by monitoring infrared radiation

In the present work a method is described for the early detection of large plastic strains localisation and subsequent crack nucleation in sheet metalforming. The method is based on the monitoring of the infrared radiation emitted from the material during stretching. It is concluded that the point of the final crack nucleation can be located in the very early stages of stretching, when overall mean strains are insignificant (less than 20% of the yielding strain of the material).     

膜电解法制备纯氯化镍溶液的研究

介绍了以金属镍板为原料采用膜电解法制备纯氯化镍溶液的工艺.研究了电流密度、温度、极距、膜支撑方式等对电解制备氯化镍溶液过程的影响,并进行了长时间连续运行扩大试验.在电流密度为400A/m2,极距为18mm,膜靠向阴极的条件下电解,电流效率大于96%,平均槽电压小于2.3V,电溶1t镍的能耗小于2170kW.h,得到的纯氯化镍溶液pH约为5,Ni2 浓度大于80g/L;膜对镍的截留率大于99.5%.     

Kinetics of abnormal grain growth in pure iron

Grain growth after primary recrystallization in unstrained and strained specimens of pure iron is examined during isothermal anneals at three different temperatures (664, 680, 690° C). Undeformed specimens undergo continuous grain growth, while the deformed ones show a stage of rapid discontinuous growth. The peculiar characteristics of the abnormal growth kinetics, and in particular the presence of three well-defined stages of growth, are brought out by plotting, versus annealing time, the ratio between the mean grain diameters of deformed and undeformed samples. The parametersn (exponent of the kinetic equation) andQ (apparent activation energy) are determined.     

Dechlorination of trichloroethylene in aqueous solution by noble metal-modified iron

Bimetallic particles are extremely interesting in accelerating the dechlorination of chlorinated organics. Four noble metals (Pd, Pt, Ru and Au), separately deposited onto the iron surface through a spontaneous redox process, promoted the TCE dechlorination rate, and the catalytic activity of the noble metal followed the order of Pd>Ru>Pt>Au. This order was found to be dependent on the concentrations of adsorbed atomic hydrogen, indicating that the initial reaction was cathodically controlled. Little difference in the distribution of the chlorinated products for the four catalysts (cis-DCE: 51%; 1,1-DCE: 27%; trans-DCE: 15% and VC: 7%) was observed. The chlorinated by-products accumulated in both Pt/Fe and Au/Fe (10.3% and 2.5% of the transformed TCE, respectively), but did not accumulate in Pd/Fe and Ru/Fe. Ru/Fe was further examined as an economical alternative to Pd/Fe. The 1.5% Ru/Fe was found to completely degrade TCE within 80 min. Considering the expense, the yield of chlorinated products and the lifetime of a reductive material, Ru provides a potential alternative to Pd as a catalyst in practical applications.     

Removal of chromium from aqueous solution by using oxidized multiwalled carbon nanotubes

The batch removal of hexavalent chromium (Cr(VI)) from aqueous solution by using oxidized multiwalled carbon nanotubes (MWCNTs) was studied under ambient conditions. The effect of pH, initial concentration of Cr(VI), MWCNT content, contact time and ionic strength on the removal of Cr(VI) was also investigated. The removal was favored at low pH with maximum removal at pH <2. The adsorption kinetics was modeled by first-order reversible kinetics, pseudo-first-order kinetics, pseudo-second-order kinetics, and intraparticle diffusion models, respectively. The rate constants for all these kinetic models were calculated, and the results indicate that pseudo-second-order kinetics model was well suitable to model the kinetic adsorption of Cr(VI). The removal of chromium mainly depends on the occurrence of redox reaction of adsorbed Cr(VI) on the surface of oxidized MWCNTs to the formation of Cr(III), and subsequent the sorption of Cr(III) on MWCNTs appears as the leading mechanism for chromium uptake to MWCNTs. The presence of Cr(III) and Cr(VI) on oxidized MWCNTs was confirmed by the X-ray photoelectron spectroscopic analysis. The application of Langmuir and Freundlich isotherms are applied to fit the adsorption data of Cr(VI). Equilibrium data were well described by the typical Langmuir adsorption isotherm. Overall, the study demonstrated that MWCNTs can effectively remove Cr(VI) from aqueous solution under a wide range of experimental conditions, without significant Cr(III) release.     

Scattering matrix of infrared radiation by ice finite circular cylinders

Scattering matrix characteristics of polydisperse, randomly oriented, small ice crystals modeled by finite circular cylinders with various ratios of the length to diameter (L/D) ratio are calculated by use of the exact T-matrix approach, with emphasis on the thermal infrared spectral region that extends from the atmospheric short-wave IR window to the far-IR wavelengths to as large as 30 microm. The observed ice crystal size distribution and the well-known power-law distribution are considered. The results of the extensive calculations show that the characteristics of scattering matrix elements of small ice circular cylinders depend strongly on wavelengths and refractive indices, particle size distributions, and the L/D ratios. The applicability of the power-law distribution and particle shapes for light scattering calculations for small ice crystals is discussed. The effects of the effective variance of size distribution on light scattering characteristics are addressed. It seems from the behavior of scattering matrix elements of small ice crystals that the combination of 25 and 3.979 microm has some advantages and potential applications for remote sensing of cirrus and other ice clouds.