Papers by Keyword: Molybdenum

Abstract: This study focuses on the role of Mo addition on the mechanical properties of an Al-Si-Cu-Mg alloy in as-cast and heat-treated condition at ambient and elevated temperature. Addition of 0.4 to 0.6 wt.% Mo forms Mo-bearing dispersoid particles which have a relatively high melting point and improve high temperature tensile strength. Ductility suffered in the presence of Mo-bearing particles. Trace addition of Mo up to 0.6 wt.% has a negligible influence on the yield strength and hardness of Al-Si-Cu-Mg alloy in as-cast and heat-treated conditions at ambient temperature and 250 °C.

Abstract: The present study describes the preparation of catalyst MoO₃ supported on smectite clay by the solution impregnation method and its evaluation as a heterogeneous catalyst in the production of biodiesel from soybean oil. The individual effects of catalyst (hard green clay and MoO₃/hard green clay) on kinematic viscosity of produced biodiesel and conversion were investigated. The samples were characterized by X-ray diffraction, X-ray fluorescence spectroscopy and N₂ adsorption-desorption. Conditions of soybean oil transesterification were: 5% catalyst by weight, 1:12 oil to methanol molar ratio, at 200 oC for 60 minutes. Patterns of X-ray diffraction showed the characteristic peaks of the structure of smectite. The results of X-ray diffraction suggests that MoO₃ species exist as highly dispersed surface species. Molybdenum metal identified as effective catalysts for the transesterification reaction of soybean oil with methanol. A preliminary design assessment show that this catalysts (MoO₃/HGC) is sufficiently active achieving conversion in excess of 62,07% at temperature below 200 oC.

Abstract: Introduction of refractory elements into alumina ceramics to improve its properties, is usually carried out by mixing the alumina with oxides of refractory metals. In this work this problem has been solved by pre-alloying refractory element with aluminum and subsequent dispersion of alloy in aqueous alkaline solutions. Characteristics of microstructure, phase composition and rheological properties of powders obtained by chemical dispersion of alloys Al-Mo, Al-V and Al-Zr with 10 wt.% refractory element in 20% aqueous sodium hydroxide solution, as well as the impact of heat treatment at 1250 oC on these properties, have been discussed. On the basis of X-Ray analysis (XRA) and electron microscopy the conclusion was adopted that heat treatment of powder leads to significant phase and structural transformations of such powders and is a necessary stage of preparation for sintering.

Abstract: The effects of destabilisation and tempering heat treatments on hardness and corrosion behavior in 28 wt.%Cr-2.6 wt.%C cast irons with up to 6 wt.%Mo addition were studied. The irons were destabilised at 1025 °C for 4 h and air cooled. Tempering was carried out at 450 °C for 4 h. Phase identification and microstructure were investigated by X-ray diffraction (XRD), light microscope (LM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Vickers macro-hardness was measured. A potentiodynamic technique was used to indicate aqueous corrosion resistance. The results revealed that the as-cast microstructure of 28 wt.%Cr iron consisted of primary austenite dendrites with eutectic M₇C₃ carbides. In the irons with 6 wt.%Mo addition, eutectic carbides including M₇C₃, M₂₃C₆ and M₆C were found. After destabilisation, the microstructure contained secondary carbide precipitates within an essentially martensitic matrix. Vickers macro-hardness of the as-cast and destabilised irons increased from 500 HV30 and 736 HV30 in the 28 wt.%Cr iron up to 570 HV30 and 870 HV30 in the iron with 6 wt.%Mo addition. Tempering slightly increased the macro-hardness. The as-cast 28 wt.%Cr iron had the lowest values for critical current density and passive current density. The destabilised + tempered treatment gave the lowest corrosion resistance.

Abstract: Austempered Ductile Iron (ADI) is characterized by high tensile strength with acceptable ductility. Steel, as a large competitor to ADI, also meets the tensile and yield strength. Nevertheless, the main advantages of ADI compared to steel are the lower density (7.2 g/cm3 to 7.85 7.87 g/cm3) for weight reduction and lower manufacturing costs because of less energy consumption during the production. One of the main problems of producing ADI is the quenching process during heat treatment of thick-walled castings. The inner part of a massive casting – in contrast to the outer part – cools down more slowly, resulting in a heterogeneous microstructure with parts of pearlite and ferrite embedded in austenite before reaching the isothermal transformation temperature. Molybdenum is, besides nickel, copper and manganese, one of the possible alloying elements that postpone the transition point of ferrite and/or pearlite. To investigate the influence of molybdenum in thick-walled castings experiments with different molybdenum contents were performed. In dependence on the molybdenum content, different austenisation and ausferritisation temperatures and times are examined in order to investigate the transformation points, fraction and morphology of different phases. The mechanism of molybdenum in ADI has been investigated by means of dilatometer tests, microstructure analysis and mechanical tests.

Abstract: We report on the development of a new generation of SiC Schottky rectifier devices employing a Molybdenum based barrier metal system and a new stripe cell design for field shielding and optimized area utilization. The Schottky barrier height is reduced and thus the conduction losses are decreased significantly. The balance between forward conduction and reverse leakage losses as well as the homogeneity and stability of the new barrier system are investigated carefully.

Abstract: Monolithic fuel plates have been developed utilizing low enriched U alloyed with 10 wt.% Mo to replace highly enriched fuels in research and test reactors, in accordance with the goals of the Materials Management and Minimization Reactor Conversion Program. The fuel plates consist of U10Mo fuel, Zr diffusion barrier, and AA6061 cladding. They are fabricated by co-rolling the U10Mo and Zr, which are then encapsulated via hot isostatic pressing of the entire U10Mo/Zr/AA6061 assembly. During fabrication, the metal constituents of the fuel plates undergo phase transformations as well as interdiffusion and reactions at interfaces. The areas of interest are the U10Mo fuel, U10Mo/Zr interface, U10Mo/AA6061 interface, Zr/AA6061 interface, and AA6061-AA6061 bond line. Knowledge of the transformations and growth in the plates is necessary to optimize fabrication parameters and predict behavior as they relate to irradiation performance. Numerous studies have been conducted to analyze these reactions in monolithic fuel plates, and a summary of their observations is provided in this paper.

Abstract: The depletion of rare metals is an issue of major concern since rare metals are limited in the abundance but essential for high technology industry. However, the present rare metal recovery technical by chemical methods has high environmental impact, poor selectivity, and is too expensive to be practical. To resolve these problems, this study aimed to create a rare metal recover system using yeast, and molybdenum was selected as the first target. A molybdenum binding protein, ModE, which was derived from Escherichia coli was selected. A fusion gene was generated by linking partial modE with a secretion signal and a domain of α-agglutinin to display the ModE on the surface of yeast cells. The expression of fusion protein on the cell surface was detected by immunofluorescence labeling. As for the recovery experiment, the engineered yeast cells were incubated in 10 mM of sodium molybdate solution for 2 h, and the recovery of molybdenum ion was measured by ICP-AES. The results of fluorescence micrographs showed that the designed fusion protein was successfully expressed on yeast cell surface. According to the results of ICP-AES, the cell surface engineered yeast adsorbed molybdenum and the cells after 72~84 h incubation gave the best adsorption. Besides, the results suggested that the optimization of each functional domain in the fusion protein was important. The selectivity and the lower limit of recoverable concentration are under investigation, while this study provides a preliminary result of bio-extraction technology using cell surface engineered yeast.

Abstract: Bioremediation is the process of detoxification or elimination of pollutants using microorganisms with different metabolic capabilities. Biodegradation by natural populations of microorganisms is one of the primary mechanisms by which oil and other pollutants of hydrocarbon origin can be removed from the environment and it is also much cheaper than the other remediation technologies.In this study, we analyzed the samples of historical waste from the oil industry, which contained sand, organic materials, heavy fuel oil and catalysts used during the process of hydrodesulfurization (HDS) of oil. The aim was to examine the fate of cobalt and molybdenum, toxic heavy metals present in those catalysts. A consortium of microorganisms isolated from the complex pollutants from the oil industry was added to the samples. During the study, beside the transformation of cobalt and molybdenum forms, we also monitored the biodegradation process of the total petroleum hydrocarbons (TPH).

Abstract: The mineral surface chemistry characterization is essential to describe the dissolution kinetics in leaching and bioleaching. Five different methods, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy, have been applied to study the surface chemistry changes during pyrite, sphalerite and molybdenite bioleaching. The surface characterizations have been done for samples before and after biological and chemical leaching. The SEM images illustrated that the minerals surfaces were smooth before processing, while they covered with an ash layer after biological treatment. Although EDS analysis and Raman spectrum demonstrated the potassium jarosite formation on the pyrite surface during bioleaching, the formation of jarosite layer did not occur on the sphalerite surfaces during bioleaching. On the other hand, a sulfur layer formation on the sphalerite surface was confirmed by mentioned characterization methods. Finally, according to the XRD and EDS spectrum the molybdenite surface had been covered both with sulfur and jarosite.