Advanced Materials Research Vol. 117

Abstract: The ages used by humankind can be divided in the Stone Age, the Bronze Age, and the Iron Age. In twentieth century instead of one material, a number of diversified materials dominated, and all are diversified. “Right materials in right purposes” was the motto in the last century. In the twenty-first century, the limitation of natural resources and balance of earth have to be considered. Global warming is one of the most important problems in the present world. Materials development and utilization should be done as shown in the model of double helices. Use of comparatively clean nuclear energies is important. Here we discuss the education about the materials from Japanese viewpoint.

Abstract: An electrochemical sensor based on the silver sulphide precipitate was fabricated in the laboratory and characterized by x-ray diffraction, SEM equipped with EDAX, and electrochemical techniques. Ion selective electrode (ISE) was found to be sensitive enough to sense the sulphide ion concentration from 10-1 to 10-5 M in alkaline medium. The change in electrode potential per decade change in sulphide ion concentration was found to be 31.5 mV at laboratory temperature indicating adherence of the ion selective electrode to Nernst’s equation. The sensor have been successfully used for the quantitative determination of thiamine in pharmaceutical preparations, hydrogen sulphide in cigarette smoke and determination of solubility products of sparingly soluble silver salts. A trace amount of hydrogen sulphide, a toxic gas, is present in the cigarette smoke. The quantitative estimation of hydrogen sulphide in cigarette smoke is a challenging task to analytical chemist. Hydrogen sulphide in cigarette smoke had been determined by absorbing the cigarette smoke in 0.1 M sodium hydroxide and the resulting solution was analyzed using silver sulphide based ion sensor by standard addition technique using modified Gran plot. The average amounts of hydrogen sulphide produced by a stick of cigarette in 8 different brands of Nepalese cigarette ware found to range from 0.0332 mg to 0.0766 mg. The sensitivity and reliability of these home made ion sensors were excellent and in par with commercial electrodes. For developing countries like Nepal, who can not afford to procure high cost commercial ion selective electrodes, these home made ion sensors are especially appealing since the sensor can be fabricated with ease from the materials that are readily available in the chemistry laboratory and the sensor is quite sensitive and gives reproducible results which are sufficiently accurate for the analysis with ion selective electrodes.

Abstract: Electrochemical studies on nickel hydroxide have shown that three reduction reactions take place simultaneously at the cathode to reduce nitrate to nitrite, nitrite to ammonium ion and nitrate to ammonium ion. All the three reactions produce hydroxyl ion which raise pH to a level favorable to precipitate Ni(OH)2. Current density, which regulates flow of OH- supply, has prominent effect on the process and products. It determines whether α- or β-Ni(OH)2 would be precipitated and has a direct relationship with size and structure of the product and also with the associated water molecules. Replacement of Ti anode with consumable Ni sheet remarkably improves current efficiency (production rate) and decreases power consumption.

Abstract: A possibility to reduce core loss in non-oriented (NO) electrical steel by applying magnetic coating has been investigated. This technique involves electroless plating of magnetic coating onto the surface of electrical steel. The material system was NiCoP coatings with different thicknesses (1, 5, and 10 􀁐m) deposited onto the surface of commercially available Fe-3%Si NO electrical steel. Characterization of deposited NiCoP coating was carried out using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectrometer. The deposited Ni-Co-P coatings were amorphous/nanocrystalline and composed of 56-59% Ni, 32-35% Co and 8-10% P by mass. Effect of coatings on core loss of the electrical steel was determined using a single sheet test. A core loss reduction was achieved with the NiCoP coating with a thickness of 1 􀁐m magnetized at a magnetic flux density of 0.3T.

Abstract: Titanium dioxide (Titania, TiO2) nanoparticles have been deposited on the surface of acid treated multi-walled carbon nanotubes (MWCNTs) by simple chemical route. The resultant TiO2/MWCNTs composites were characterized by different techniques. The oxidation of MWCNTs and presence of titania nanoparticles on the surface of MWCNTs is confirmed by transmission electron microscopy, energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. TEM image shows the size of titania nanoparticles are around 5 nm. Raman spectroscopy showed the oxidation and functionalization of nanotubes. The TGA curve showed decrease in thermal decomposition temperature of MWCNTs after oxidation and attachment with titania nanoparticles.

Abstract: Arrays of ZnO nanowires were synthesized within the well distributed pores of AAO template by employing an easy wet chemical method. Nanoporous AAO template was fabricated by electrochemical anodization of aluminium, controlling the anodization parameters. ZnO nanowires were characterized by SEM, XRD and EDS. It was found that the ZnO nanowires/AAO exhibits intense photoluminescence (PL) in the UV and visible regions. The blue emission band (432 nm) of the AAO template was originated from the singly ionized oxygen vacancies. The ZnO nanowires exhibit luminescence in the UV (379 nm) and in visible regions (460 and 510 nm), which can be attributed to the band to band electronic transition and oxygen vacancy related defect centers, respectively.

Abstract: In this work, it was intended to improve the corrosion resistance of welds of A356 and AA6061 by adopting mainly a special welding techniques, viz., pulsed current gas tungsten arc welding (PCGTAW), electron beam welding (EBW) and friction stir welding (FSW). It was found that the corrosion resistance of A356 and AA6061 welds could be improved by PCGTAW technique rather than continuous current gas tungsten arc welding (CCGTAW). It can be further improved by using electron beam welding. Improved corrosion resistance in A356 welds could be obtained by selecting T6 temper rather than as cast condition. In the case of AA6061, improved corrosion resistance was achieved by selecting T4 temper rather than T6 temper. As for as the welding techniques, friction stir welding (FSW) is useful than fusion welding techniques like CCGTAW,PCGTAW and EBW for improving the corrosion resistance of both the welds.

Abstract: Pitting corrosion of two tempers (T6 and T73) of 7075 Aluminium alloy were quantified by digital image processing. The effect of pitting corrosion on fatigue life in 7075 Aluminium alloy in two aging conditions was studied. Pitting was found to be slightly more severe for T6 tempers compared to T73 tempers for different time of exposures. The fatigue lives of two tempers of 7075 Aluminium alloy at high peak stresses were compared in the uncorroded and pre-corroded (pitted) states. Absolute fatigue lives of T73 samples were much higher than that of T6 in the uncorroded as well as pre-corroded condition. The various crack initiation methodologies observed through fractographic analysis is discussed.

Abstract: This study aims to reveal the underlying mechanism associated with the enhancement of wear resistance of tool steels by deep cryogenic treatment and to resolve the issue of reported varied degree of improvement in wear resistance through structure-property correlation of cryotreated vis-à-vis conventionally treated AISI D2 steel. Microstructures of heat treated specimens have been characterized employing various techniques with specific emphasis on quantitative estimation of the characteristics of secondary carbides. Evaluations of properties include measurements of bulk hardness, apparent strength of the matrix, fracture toughness and dry sliding wear resistance under wide rage of normal loads supplemented by in-depth characterizations of worn surfaces, wear debris and subsurfaces of worn specimens in order to identify the operative mode and mechanism of wear. It has been demonstrated that the favorable modifications of the precipitation behavior of secondary carbides in addition to removal of retained austenite are the governing mechanisms for the enhancement of wear resistance of tool steels by deep cryogenic treatment. The cause of the reported varied degree of improvement in wear resistance by deep cryogenic treatment has been explained by disparity of the operative modes and mechanisms of wear.