Key Engineering Materials Vols. 510-511

Abstract: Austenitic stainless steel with submicron gain size has been attracted due to fine structural control of mechanical properties. In order to achieve a submicron grain size, meta-stable austenitic steel AISI 304 is severely cold deformed and then annealed to different heat treatment cycles. The heat treated samples were then tested for metallurgical phase change, texture components and hardness. It was observed that at 750°C, all the martensite transformed completely into austenite. Further, at the same temperature, it was observed that the texture component {221}<232> was the dominant texture component.

Abstract: Non toxicity, bio compatibility and nanometer sizes regime which is comparable to the size of a cell, makes nanocrystalline Co ferrites particles very proficient. In the present research Zn doped cobalt ferrites were prepared by the chemical co-precipitation method and characterized by X-ray diffraction (XRD) at room temperature for structural analysis. X-ray diffraction patterns confirmed the FCC spinel structure of synthesized particles. Crystallite sizes were calculated from the most intense peak (311) using the Debye-Scherrer formula. The obtained crystallite sizes were in nanometer range for all the samples synthesized at reaction temperature of 70°C. Then samples were sintered at 550°C for 2 hours, characterized again by X-ray diffraction at room temperature. The crystallite sizes and lattice constants for all the samples were calculated again from the data obtained by XRD. DC electrical resistivity and AC electrical transport properties were analyzed. The magnetic properties such as coercivity (H_c) and remanence (M_r) of Co_1-xZn_xFe₂O₄ for x = 0.0, 0.2, 0.4 were measured at room temperature by vibrating sample magnetometer. Coercivity and remanence were found maximum with minimum value of Zn in Co_1-xZn_xFe₂O_4. Observed structural and conduction properties of synthesized nanomaterials were correlated.

Abstract: In this study, we have investigated the source of the n-type conductivity in bulk ZnO. Four samples with Zn concentrations 52%, 53%, 54% and 55 % were prepared by molecular beam epitaxy (MBE). ZnO layers exhibited reamarkable increase in carrier concentration (5.0×10¹⁶ cm^-3 to 2.2×10¹⁹ cm^-3) and decrease in resistivity (14.4 Ω cm to 0.009 Ω cm) as a function of Zn contents (52% to 55%) in the layers, respectively. We observed that with increasing thickness, the microstructure of films was improved. The thick films have less Zn-interstitials defects and consequently have lower carrier concentration and higher resistivity. The shifting of Raman E₂^high mode of ZnO towards higher frequency with increasing Zn contents in the samples also confirmed the presence of excessive Zn-interstitials in the layer.

Abstract: Advantage of alloys on the basis of system Al-Be,Al-Be-REM is raised technological, physical, chemical and corrosion resistance properties in damp and excessively aggressive atmospheres [. According to literary reviews, this alloys basically are foundry-hypoeuthectic and hypereuthectic, and the technology of moulding of these alloys very difficult and demands application of operations modifying. Difficultly deleted impurity basically (Fe), specifically influence phase structure, naturally influencing on physical and chemical properties industrial silumines with the maintenance not less than 0.4-0.5 %. Many additives as Fe, Mg, Ti, Be, especially in hypoeuthectic silumines increasing strength and foundry properties, can reduce them corrosion-resistance. In connection with the above-stated is of interest researches of influence of impurity such elements as, Be and REM on corrosion resistance industrial alumines. Studies corrosion-resistance spent samples potentiostatic a method on device " Potentiostate P-50" with a registering recorder in the environment of the muriatic solutions in a mode "Potential". he analysis of experimental data have shown, that addition Be, positively modifying structure of foundry alloys, reduces influences containing in it Fe, increases strength and corrosion resistance, which calculations testify experimental data of electrochemical indicators [2,3].

Abstract: Aluminum and its alloys are the second most commonly used metal for a variety of industrial applications. They normally solidify in coarse grain columnar structure which tends to reduce their mechanical behavior and surface quality. It was found that this large grain size structure can be refined by using titanium, Ti, or titanium plus boron, Ti+B, and using the latter resulted in reducing the amount of Ti to fifth its values although boron itself is not a grain refiner. This is why it is becoming customary in the aluminum foundry to add Ti or Ti+B to their melt before solidification. The available literature reveals that most of the work is directed towards the metallurgical aspects and little was directed on the mechanical aspects. To the best of the authors knowledge, no work was directed on the aspects of grain refiners on the formability of metals. In this paper, the effect of addition of Zr on the mechanical properties of commercially pure aluminum grain refined by Ti+B in the as cast and extruded conditions is investigated. Comparison between the addition of Zr alone or Zr+Ti+B is also investigated. It was found that addition of Ti+B either alone or in the presence of Zr resulted in grain refinement of aluminum both in the as cast and in the cold extruded conditions. The maximum reduction in grain size was 53.22% and 76.92%, respectively. Similarly, it was found that addition of Ti+B either alone or in the presence of Zr to Al resulted in improvement of its Vickers's hardness, However addition of Zr alone to Al resulted in decrease of its hardness in the as cast conditions but increase in the extruded condition .The maximum increase was in the case of adding both of them in the extruded condition being 94.59 %, (from Hv 37 to Hv72). Similarly the ultimate tensile strength, UTS, was improved at all additions except when Ti+B or Zr is added alone. On the whole it may be concluded that addition of Zr to Al grain refined by Ti+B resulted in enhancement of its grain size and improvement of its hardness, mechanical strength and ductility in the cold extruded conditions and resulted in slight decrease of its ductility when added in the as cast condition.

Abstract: The present study describes the preparation, structural and electrical characterization of nanosized Zr-Mn cobalt-ferrites. The nominal compositions CoFe_2-2xZr_xMn_xO₄ (0.10.4) have been synthesized by the co-precipitation method. These nanopowder products were sintered in furnace at temperature of 800 °C for 8 hour with a heating rate of 10^οC/min to obtain these ferrites. The nanopowder was evaluated using XRD, FT-IR and SEM. The XRD data showed that all the samples are of single phase and the crystallite size is found in the range of 2630 nm. The lattice constant (a), X-ray density (dx), porosity (P) and bulk density (dm) are also calculated from XRD data. FT-IR study confirms the presence of ferrite functional groups. The IR spectra of Zr-Mn ferrite system have been analyzed in the frequency range 400650 cm^-1. It revealed two prominent bands υ₁ and υ₂ which are assigned to tetrahedral and octahedral metal complexes, respectively. The position of the highest frequency band is around 550 cm^-1 while the lower frequency band is around 425 cm^-1. The structural properties are also analyzed on scanning electron microscopy (SEM) at room temperature. Additionally, the dc electrical resistivity decreased with the rise in temperature for all the samples, showing a semiconductor like behavior. From the dc electrical resistivity the activation energy and drift mobility are determined. Both the drift mobility and activation energy increase with a rise in x.

Abstract: The first measurement of thermal transport properties on the polycrystalline D-Er₂Si₂O₇ have been made in the temperature range 77-300K. Both the thermal conductivity and the thermal diffusivity follow modified Euckens law in this temperature region. The Transient Plane Source technique (TPS) has been used to measure thermal conductivity and thermal diffusivity simultaneously.

Abstract: Laser Induced Plasma Assisted Ablation (LIPAA) has been used to carry out back side dry etching/ablation of different optical glasses under vacuum. It is observed that etching depth increases with decrease in target-substrate gap and becomes maximum (50 μm) at zero gap size for steel-quartz pair. The maximum ablation depth for brass-quartz pair was 25 μm. The effects of laser power on etching depth and laser scan speed has also been reported.

Abstract: In this study, the effect of polar face on Schottky barrier diodes has been investigated. Two samples of ZnO were grown hydrothermally under similar growth conditions. The Palladium (Pd) metal contacts of area 0.78 mm² were fabricated on both faces and were studied comprehensively using DLS-83 Deep Level Spectrometer over temperature range of 160K330K. The current-voltage (IV) measurements revealed that the ideality factor n and barrier height ϕ_B were strongly temperature dependent for both faces (Zn and O-face) of ZnO, indicating that the thermionic emission is not the dominant process, which showed the inhomogenity in the barrier heights of grown samples. This barrier height inhomogenity was explained by applying Gaussian distribution model. The extrapolation of the linear ϕ_ap verses n plot to n = 1 has given a homogeneous barrier height of approximately 0.88±0.01 eV and 0.76±0.01 eV for Zn and O-faces respectively. ϕ_ap versus 1/T plot was drawn to obtain the values of mean barrier height for Zn and O-face (0.88±0.01 eV, 0.76±0.01 eV) and standard deviation (δ_s) (0.015±0.001 V, 0.014±0.001 V) at zero bais respectively. The value of δ_s for the Zn-face is larger than O-face, showing that inhomogenity in the barrier heights is more in the sample grown along Zn-face as compared to the sample grown along O-face.

Abstract: Nickel deposited on carbon has been used as adsorbent to recover Zn (II) from aqueous system. The adsorbent was synthesized by depositing nickel nitrate on carbon under inert conditions and decomposing it to nickel by raising the temperature, washing and vacuum drying. Various techniques including XRD, FTIR, and SEM were employed for its characterization. FTIR showed that the nickel deposition enhanced the carbon functionalization due to presence of OH, C=O and C-O groups.Average crystallite size ofabout 9 nm was determined from XRD. Nickel deposition resulted in further division particles as indicated from the morphological study. Zn (II) was subjected to adsorptionon the synthesized adsorbent. It was observed that the rate of adsorption increased significantly on the nickel deposited carbon than the carbon alone. Morris-Weber, Lagergren and Reichenberg models were applied to find out the type and rate of adsorption employingfirst and second order rate equations.The adsorption data were applied toLangmuir, Freundlich and D-R isotherms and values of isotherm constants were calculated and were higher for Ni/C than carbon alone. The mean free energy of zinc sorption on carbon and Ni/C are 16.67 and 18.26 kJmol^-1 which shows chemisorption. Thermodynamic studies were done to find out the effect of temperature on sorption. Positive values of ΔH and negative values of ΔG show endothermic and spontaneous type of sorption.