Recovery of low temperature electron irradiation-induced damage in n-type gaas

Undoped n-type GaAa was irradiated near 5 and 77 °K with electrons having incident energies between 0.46 and 1.30 MeV. The recovery of the electrical resistivity and the Hall coefficient upon annealing from 4 to 520 °K was monitored. Changes which occurred upon annealing below 200 °K could be reversed by ionizing radiation. A small amount of irreversible ionization-induced recovery was observed after irradiation near 5 °K. Major irreversible recovery stages were centered near 235 (stage I), 280 (stage II) and 520 °K (stage III). Recovery in stage I and II obeyed first order kinetics. The activation energies of stages I and II were determined as 0.72 and 0.83 eV, respectively. The carrier concentration changes per unit irradiation dose corresponding to the three recovery stages differed in their energy dependence indicating that the defects which are removed in stage III have the lowest threshold energy. The carrier concentration changes per unit irradiation dose corresponding to stages I and III were higher for irradiation near 5 °K than for irradiation near 77 °K.     

Strain-induced interaction of interstitials in IVA group hcp metals

Strain-induced (elastic) interactions of oxygen, nitrogen and carbon atoms in IVA group metals, α-Ti, Zr, and -Hf, are calculated in the framework of the microscopic Krivoglaz-Kanzaki-Khachaturyan theory. The experimental elastic constants, lattice spacing of the host metal, and concentration expansion coefficients are used as the input numerical parameters. The resulting interactions are stronger in α-Ti than in α-Zr and α-Hf. A comparative analysis of interactions in the hcp IVA group metals with those in bcc and fcc solid solutions reveals the crystal structure effect. In general, the strain-induced interactions of O, N, and C in hcp IVA group metals are weaker than in bcc solid solutions and are stronger than in fcc solid solutions.     

Adsorption of Pb on NiAl(1 1 0): energetics and structure

The adsorption of Pb onto a NiAl(1 1 0) single crystal surface at 300 K has been studied by Auger electron spectroscopy (AES), Low energy electron diffraction (LEED), molecular beam/surface scattering and single crystal adsorption calorimetry (SCAC). AES indicates a Stranski-Krastanov growth mode, i.e., Pb initially grows on NiAl(1 1 0) two-dimensionally until the first layer completes at 0.89 ML, where a superstructure is observed by LEED, followed by 3D islanding. Measurements of the Pb gas that does not stick indicate that Pb sticks on NiAl(1 1 0) with an initial probability of 0.99. The initial heat of adsorption of Pb on NiAl(1 1 0) is 249 ± 10 kJ/mol. Due to the repulsive interactions between Pb adatoms, the heat of adsorption decreases within the first layer to a value identical to the heat of sublimation of bulk Pb (195 kJ/mol), where it remains at higher coverages. This first application of adsorption calorimetry on such a thick sample (75 μm versus 0.2-8 μm previously) demonstrates that adsorption calorimetry can be extended to a wider range of surfaces, since this thickness can be achieved with nearly any single crystal material by simple mechanical thinning.     

Effective synthesis of carbon nanotubes via catalytic decomposition of methane: Influence of calcination temperature on metal–support interaction of Co–Mo/MgO catalyst

The present work investigated the influence of calcination temperature for bimetallic Co–Mo/MgO catalyst on the synthesis of carbon nanotubes (CNTs) via catalytic chemical vapor deposition (CCVD) of methane. The experimental results showed that variation in the catalyst calcination temperature affected carbon yield, diameter distribution and quality of the CNTs. Increasing the catalyst calcination temperature enabled Co–Mo/MgO catalysts in growing CNTs at higher yield, narrower diameter distribution and better degree of graphitization, credited to the strong metal–support interaction (MSI) formed between CoO species and MgO support. We also discovered that the catalysts of weak MSI were beneficial to the nucleation and growth of CNTs, meanwhile the catalysts with strong MSI provoked the growth of CNTs with narrow diameter distribution. The catalyst calcined at 700 °C, possessing moderate MSI, was found to be the most suitable catalyst for the growth of high quality CNTs with the diameter of 7.70±0.77 nm and the carbon yield of as high as 647.4%.     

高频红外吸收法测定钛合金中的碳

应用高频红外碳硫仪测定钛合金中碳的含量。对助熔剂、称样量、比较水平等测定条件进行了优化研究。方法快速、简便 ,具有良好的精密度和准确度 ,结果满意     

Vanadium carbide coatings on die steel deposited by the thermo-reactive diffusion technique

Thermal reactive diffusion coating of vanadium carbide on DIN 1.2367 die steel substrate was performed in a powder mixture consisting of ferro-vanadium, ammonium chloride, alumina and naphthalene at 950, 1050 and 1150 °C for 1-5 h. The carbide layers were characterized by means of microstructure, microhardness, X-ray diffraction and chemical analysis. Depending on the coating process time and temperature, the thickness of the vanadium carbide layer formed on the substrate ranged from 2.3 to 23.2 μm. The hardness of vanadium carbide layers was about 2487 HV. Dry wear tests for uncoated and coated DIN 1.2367 die steel were carried out on pin-on-disk configuration and at a sliding speed of 0.13 m/s. The results showed superior wear properties of the coated samples. The kinetics of vanadium carbide coating by the pack method was also studied and the activation energy for the thermo-reactive diffusion process was estimated to be 173.2 kJ/mol.     

Reversed phase partition chromatographic separation of divalent copper with N-n-octylaniline on silica gel

A novel separation method was developed for the extraction and chromatographic separation of copper(II). The quantative extraction of 25.0–125.0 μg copper(II) has been observed from 0.05 to 0.25 mol/L of ascorbic acid at pH 9.0–12.0 with 0.087 mol/L N-n-octylaniline (liquid anion exchanger) coated on silica gel at a flow rate of 1.0 ml/min. The extracted metal ion has been recovered by eluting with 25.0 ml of 1.0 mol/L hydrochloric acid and determined spectrophotometrically by rubeanic acid method. The various influencing parameters viz. acid concentrations, reagent concentration, eluates effect of pH, and effect of flow rate on extraction were studied. The method is free from large number of interferences from cations and anions. A scheme for mutual separation of copper(II), gold(III) and bismuth(III) has been developed. Copper(II) has been separated from ayurvedic (Herbal) medicine and synthetic mixtures corresponding to alloy. The log–log plot of N-n-octylaniline concentration versus the distribution coefficient indicates that the probable extracted species is [.     

GHz microwave properties of melt spun Fe-Si alloys

The structural and microwave properties of melt spun Fe_100−xSi_x (x = 10, 20, 30) nanocomposites were investigated. The phases varied with Si content in FeSi alloys. It is found that the Fe₃Si and FeSi phases could be obtained with Si content up to 20 at.%. The X-ray absorption fine structure (XAFS) spectra of Fe K-edges show that the local structures around Fe atoms in melt spun Fe-Si alloys become more disordered with increasing Si content when compared with that of α-Fe. The complex permittivity-frequency and permeability-frequency properties were determined in the microwave frequency regime of 2-18 GHz by vector network analysis. It is found that flake-like FeSi powder composite has the largest values of μ′ and μ″ at 2 GHz. The reflection loss shifts to the higher frequency with the Si content increasing for melt spun FeSi alloys. A minimum reflection loss of −16.5 dB is obtained at 13.9 GHz for composition Fe₇₀Si₃₀ with the thickness of 1.5 mm. However, for composition Fe₇₀Si₃₀, the minimum reflection loss shifts to lower frequency and larger value with the thickness increasing. The results suggest a new design for microwave absorbers based on electromagnetic wave-absorbing materials.