Adaptive coatings are an important development in tribology. These coatings widen the range at which solid lubricants are useful in various environments. In this paper, coatings founded on molybdenum nitride are studied, with a focus on thermal cycling. These coatings were fabricated by unbalanced magnetron sputtering and characterized with techniques including x-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, energy dispersive x-ray spectroscopy (EDS), and pin-on-disk tribometer. The results of two sets of coatings are reported. The first set of coatings is a nanocomposite of Mo2N/MoS2/Me (Me = Ag, Au, Cu). The second is a complex multi-layer system of Mo2N/Ag and a diffusion barrier of TiN which has been etched, then filled and coated with a layer of MoS2. After heating, these compounds produced silver molybdates. The Mo2N/MoS2/Ag nanocomposite shows promise with a 0.02 coefficient of friction at room temperature, while the multi-layer system eventually equilibrated at approximately 0.6. At high temperatures, again the nanocomposite was better, producing a 0.25 frictional coefficient compared to a 0.3 from the multilayer system. These results provide insight into what is needed to achieve thermal cycling.

Binuclear mixed biscarbene complexes of bithiophene were synthesized via the classical Fischer method of synthesis. The metal carbonyls, Mo(CO)6, Cr(CO)6, W(CO)6 and Mn(MeCp)(CO)3 were reacted with dilithiated bithiophene to afford complexes of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(OEt})M'(CO)5] (in case of manganese, M(CO)5 is replaced with MMeCp(CO)2), where [M] and [M'] are the metal carbonyls in different combinations. Quenching was achieved with triethyl oxonium tetrafluoroborate. In all the reactions the products included monocarbene complexes, biscarbene complexes and the decomposition products. C-C coupling reactions produced unexpected biscarbene complexes of Cr, W, and Mo having extended bithiophene spacers. The complexes were of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(R)-C(R)C4H2S-C4H2SC(OEt})M'(CO)5] (R = O, OH or OEt). These complexes were characterized with NMR, infrared spectroscopy and some with mass spectrometry. Furthermore, three biscarbene complexes of the metal combinations Mo(CO)6 and Cr(CO)6, W(CO)6 and Cr(CO)6, and Mn(MeCp)(CO)3 and Cr(CO)6 were all reacted with 3-hexyne. The result was the benzannulation or the Dötz products. / Chemistry / M. Sc. (Chemistry)

Orientador: Silvio José Bicudo / Banca: Dirceu Maximino Fernandes / Banca: Helio Grassi Filho / Banca: José Roberto Santos / Banca: Hideaki Wilson Takahashi / Resumo: Considerando a hipótese de que a eficácia da utilização do molibdênio é dependente do ajuste em etapas importantes da determinação de sua concentração no solo, bem como da dose e forma de aplicação, realizou-se a presente pesquisa com o objetivo de aprimorar a etapa de retirada do molibdênio da resina trocadora de íons, durante o procedimento analítico de determinação de molibdênio na solução do solo; e avaliar a eficácia de doses e formas de aplicação de molibdênio na cultura do milho. Para o aprimoramento da etapa de retirada do molibdênio da resina trocadora de íons, durante o procedimento analítico de determinação de molibdênio, foram realizados estudos no laboratório para avaliar qual a solução que retira o molibdênio retido na resina melhor representava o molibdênio adicionado ao solo, sendo aplicados nesses estudos o delineamento inteiramente casualizado, com quatro repetições. Para avaliar a eficácia de doses e formas de aplicação de molibdênio na cultura do milho, foram instalados três experimentos em casa de vegetação pertencente à FCA/UNESP, Campus de Botucatu, em dois anos. No primeiro ano foram realizados dois experimentos, um com calagem: Experimento I; e outro sem calagem: Experimento II; no segundo ano foi realizado mais um experimento com calagem: Experimento III. O delineamento experimental, para os três experimentos foi o de blocos casualizados, com quatro repetições. Os experimentos I e II obedeceram a um arranjo fatorial de 2x3x4+1, sendo seus tratamentos compostos por dois tipos solos com texturas diferentes: Neossolo Litólico (RL) e Latossolo Roxo álico (LRa); três formas de aplicação: via folha, via semente e via solo; e quatro doses de molibdênio: 25, 100, 400 e 1600 g ha-1 (para a aplicação via folha e via solo) e 5,625; 11,25; 22,5 e 45,0 g ha-1 (para a aplicação via semente), mais uma testemunha absoluta... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Assuming that the effective use of molybdenum is dependent on accurate determination of its concentration in soil as well as the dose and method of application, put into practice this research with the objective of improving the determination of the concentration of molybdenum in soil and evaluate the effectiveness of application methods and doses in maize. To improve the determination of molybdenum in soil, studies were carried in the laboratory to evaluate which solution mixed extraction of molybdenum contained in the resin that best represented the molybdenum added to soil, being applied in these studies the entirely randomized design, with four replications. To evaluate the effectiveness of doses and methods of application of molybdenum in maize, essays were carried in a greenhouse belonging to the FCA/UNESP, Botucatu, in two years. In the first year two experiments had been carried through, one with lime: Experiment I; another without lime: Experiment II; in the second year it was carried through an experiment with lime: Experiment III. The experimental design, in the three experiments, was a randomized block with four replications. In the experiments I and II used a factorial arrangement of 2x3x4+1, being their treatments made of two soils with different textures: soil Neossolo Litólico (LR) and soil Latassolo Roxo álico (LRa), three application forms (leaf, seeds, and soil aplications) and four levels of molybdenum: 25, 100, 400 and 1600 g ha-1 (for leaf and soil applications) and 5.625, 11.25, 22.5 and 45.0 g ha-1 (for seeds application) and a control without molybdenum fertilization. The Experiment III was installed in only kind of soil, the Nitossolo Litólico (RL), in factorial arrangement of 3x4+1, being their treatments made of by same application forms and levels of molybdenum used in Experiments I and II. The essays were conducted on experimental plots... (Complete abstract click electronic access below) / Doutor

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Made available in DSpace on 2014-06-11T19:30:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-17Bitstream added on 2014-06-13T19:19:11Z : No. of bitstreams: 1 pereira_frs_dr_botfca.pdf: 1161993 bytes, checksum: 12e776fae4e5259fe0e366a10986b5ed (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Considerando a hipótese de que a eficácia da utilização do molibdênio é dependente do ajuste em etapas importantes da determinação de sua concentração no solo, bem como da dose e forma de aplicação, realizou-se a presente pesquisa com o objetivo de aprimorar a etapa de retirada do molibdênio da resina trocadora de íons, durante o procedimento analítico de determinação de molibdênio na solução do solo; e avaliar a eficácia de doses e formas de aplicação de molibdênio na cultura do milho. Para o aprimoramento da etapa de retirada do molibdênio da resina trocadora de íons, durante o procedimento analítico de determinação de molibdênio, foram realizados estudos no laboratório para avaliar qual a solução que retira o molibdênio retido na resina melhor representava o molibdênio adicionado ao solo, sendo aplicados nesses estudos o delineamento inteiramente casualizado, com quatro repetições. Para avaliar a eficácia de doses e formas de aplicação de molibdênio na cultura do milho, foram instalados três experimentos em casa de vegetação pertencente à FCA/UNESP, Campus de Botucatu, em dois anos. No primeiro ano foram realizados dois experimentos, um com calagem: Experimento I; e outro sem calagem: Experimento II; no segundo ano foi realizado mais um experimento com calagem: Experimento III. O delineamento experimental, para os três experimentos foi o de blocos casualizados, com quatro repetições. Os experimentos I e II obedeceram a um arranjo fatorial de 2x3x4+1, sendo seus tratamentos compostos por dois tipos solos com texturas diferentes: Neossolo Litólico (RL) e Latossolo Roxo álico (LRa); três formas de aplicação: via folha, via semente e via solo; e quatro doses de molibdênio: 25, 100, 400 e 1600 g ha-1 (para a aplicação via folha e via solo) e 5,625; 11,25; 22,5 e 45,0 g ha-1 (para a aplicação via semente), mais uma testemunha absoluta... / Assuming that the effective use of molybdenum is dependent on accurate determination of its concentration in soil as well as the dose and method of application, put into practice this research with the objective of improving the determination of the concentration of molybdenum in soil and evaluate the effectiveness of application methods and doses in maize. To improve the determination of molybdenum in soil, studies were carried in the laboratory to evaluate which solution mixed extraction of molybdenum contained in the resin that best represented the molybdenum added to soil, being applied in these studies the entirely randomized design, with four replications. To evaluate the effectiveness of doses and methods of application of molybdenum in maize, essays were carried in a greenhouse belonging to the FCA/UNESP, Botucatu, in two years. In the first year two experiments had been carried through, one with lime: Experiment I; another without lime: Experiment II; in the second year it was carried through an experiment with lime: Experiment III. The experimental design, in the three experiments, was a randomized block with four replications. In the experiments I and II used a factorial arrangement of 2x3x4+1, being their treatments made of two soils with different textures: soil Neossolo Litólico (LR) and soil Latassolo Roxo álico (LRa), three application forms (leaf, seeds, and soil aplications) and four levels of molybdenum: 25, 100, 400 and 1600 g ha-1 (for leaf and soil applications) and 5.625, 11.25, 22.5 and 45.0 g ha-1 (for seeds application) and a control without molybdenum fertilization. The Experiment III was installed in only kind of soil, the Nitossolo Litólico (RL), in factorial arrangement of 3x4+1, being their treatments made of by same application forms and levels of molybdenum used in Experiments I and II. The essays were conducted on experimental plots... (Complete abstract click electronic access below)

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Molybdenum is a versatile alloying and refractory metal of strategic importance. In India almost all molybdenite is obtained currently as st byproduct from copper and uranium deposits. The present Indian production is only about 66 tonnes while the demand is over 1000 tomes. It thus becomes important to explore newer deposits of molybdenum and develop efficient beneficiation strategies to recover the metal. A potential source of primary rnolybdenite has been found in the Ham area of Dharmapuri district in Tamil Nadu. In the present investigation, taking into consideration the importance of the problem beneficiation studies have been undertaken on core - drill molybdenite ore samples from the Hanu area. Initially, detailed characterization of the molybdenite ore has been carried out with respect to its mineralogy and chemical composition. The X-ray diffkactogam of the ore has also been recorded These studies have indicated that quartz and sericite are the major minerals followed by carbonates and feldspar. Among the sulphide minerals, pyrite is dominant with trace amounts of galena, sphalerite, chalcopyrite and molybdenite. The molybdenum content in the ore sample has been determined to be about 0.1%. Liberation studies have revealed that molybdenum is more or less uniformly distributed in the different size fractions from 1.7 mm down below to 75 microns. However, mineralogical analysis of the different size fractions has indicated that about 85% of the molybdenite is liberated. from associated silicate and carbonates below 2 12 microns. The results of the flotation kinetic tests have shown that percentage recovery and grade of molybdenum foLZow an inverse relationship with time. Studies carried out to evaluate different reagent - combinations, reveal that optimum values of grade and recovery could be achieved using kerosene and M1IBC. Further, these studies have shown that flotation time of 4 minutes is adequate, as beyond this time the grade of molybdenum is found to deteriorate. Detailed mesh-of-grind studies have indicated that 20 minutes of grinding yields optimum values of molybdenum and lead in the float product and this time was fixed for all subsequent experiments. Preliminary experiments conducted to evaluate djfferent depressants for galena have shown that satisfactory results are obtained only with sodium dichromate. Optimisation studies performed to arrive at the dosage of sodium dichromate have shown that the addition of 0.25kg/t of sodium dichromate gives optimum results with respect to overall recovery and grade of molybdenum, copper and lead in the float and tailing fractions. In a similar manner, the optimum dosage of kerosene (collector for molybdenite) has been arrived at to be 0.8kg/t taking a holistic view of the grades and recoveries of the different metal values of interest. Based on the studies carried out with respect to optimization of the mesh-of-grind, depressant and collector concentrations, it became apparent that a grade of about 0.8% Mo only could be achieved with over 80% recovery. The redeeming feature however was that over 90% of the feed could be rejected at the rougher flotation stage itself with a negligence loss of about 0.02% Mo in the tailings. It was thus considered logical to further upgrade the Mo content by regrinding. An extensive flotation campaign was therefore mounted, adopting the following strategies: (1) Ist stage regrinding and one cleaning (2) IInd stage regrinding and three cleanings (3) IIIrd stage regrinding and two cleanings Based on the first stage regrinding tests it was found that by regrinding to 100% passing 106 microns, the Mo assay could be enhanced to over 32% from a initial value of about 0.1% in the feed. The enrichment ratio at this stage corresponds to about 340.After the second stage regrinding followed by three stages of cleaning, close to 75% recovery of Mo with an assay value of about 52% could be achieved, further enhancing the enrichment ratio to about 540. A few experiments were conducted using sodium cyanide during second stage regrinding tests and it was found that copper assay could be brought down to 0.3% from about 0.8%, without affecting the grade of lead and molybdenum. The results of the third stage regrinding tests have highlighted that a final concentrate assaying about 55% molybdenum with over 70% recovery could be obtained. It is worthy to mention that the concentrate so produced meets the specification of metallurgical grade molybdenite. The overall enrichment ratio obtained, commencing from a feed assaying 0.1% Mo, corresponds to about 580. In order to explore the efficacy of organic depressants, which are more acceptable on environmental grounds, detailed flotation studies were carried out using dextrin with particular emphasis on galena depression. A series of experiments was carried out in an identical manner to those conducted using sodium dichromate. Here again, three stages of regrinding/cleanings test where carried out, akin to those performed using sodium dichromate. A dextrin concentration of 0.01 kg/t was found to be an optimum value from the point of grade, wt. % recovery and distribution of molybdenum, lead and copper in the cleaner concentrate. It is noteworthy that after second stage regrinding followed by four stages of cleaning, the molybdenum assay value has significantly improved from 16% to about 53% with over 70% recovery. Another notable feature is that copper content in the concentrate is only about 0.2% even without the addition of sodium cyanide. The results of the third stage regrinding/cleaning tests have shown marginal improvement in the molybdenum assay values without affecting the grade of copper and lead. On a comparative basis, it can be inferred that dextrin holds promise to be used as a potential substitute for the inorganic depressants such as sodium dichromate and sodium cyanide. On the basis of the extensive investigations carried out on the beneficiation of molybdenite ore, a comprehensive flowsheet has been developed.

<p>Low enriched uranium (LEU, < 20 % 235U)-molybdenum (U-Mo) alloy is the primary nuclear fuel candidate for research and test reactors, and it is also considered one of the fuel candidates for fast reactors. Furthermore, U-Mo monolithic fuel is currently undergoing a qualification process to replace highly-enriched uranium (≥ 20 % 235U) fuel for high-performance research and test reactors. As part of the fuel qualification process, it is critical to examine the microstructural evolution in the final form of U-Mo fuel under irradiation. However, there is a lack of knowledge on the microstructural evolution of the rolled U-Mo alloy foil, which is a proposed geometry for research and test reactors/high-performance research and test reactors, as well as the U-Mo alloy fuel that is cast into a slug form without rolling, which is a more suitable geometry for other advanced reactor fuel types. The effects of the fabrication methods, specifically arc-casting and cold-rolling, on the phase decomposition in U-10Mo alloy subjected to low neutron fluence (0.01 displacements per atom (dpa) and 0.1 dpa) in the temperature range of 150–350oC are evaluated using synchrotron X-ray techniques and scanning electron microscopy (SEM). The as-cast U-10Mo alloys demonstrated better irradiation performance than the U-10Mo alloy foils in research reactor conditions for the investigated regimes. This study will help optimize fuel fabrication techniques to tune phase decomposition under irradiation. </p> <p>Additionally, irradiation behavior in Mo, a critical element in U-Mo fuel, as well as a candidate for cladding material for the next generation of nuclear power plants, is investigated at the atomistic scale following low neutron fluence regimes (0.01 dpa and 0.1 dpa) in the temperature range of 150–800oC using synchrotron X-ray techniques. Lattice contraction was observed in irradiated Mo by synchrotron XRD, indicating that interstitial diffusion is faster than vacancy diffusion in Mo. More interstitials diffuse into the sinks, such as grain boundaries, while fewer vacancies diffuse into the sinks due to slow diffusion, resulting in a higher steady-state concentration of vacancies than that of interstitials under irradiation. The synchrotron PDF also supported the synchrotron XRD results by demonstrating a decrease in the atomic distances under irradiation. </p>

Recently, refractory materials have been proposed as a strong alternative to poly-silicon and aluminum alloys as metallization systems for Very Large Scale Integrated (VLSI) circuits because of their improved performance at smaller Integrated Circuit (IC) feature size and higher interconnect current densities. However, processing and reliability problems associated with the use of refractory materials have limited their widespread acceptance. The hot-wall low pressure chemical vapor deposition (LPCVD) of Molybdenum and Tungsten from their respective hexacarbonyl sources has been studied as a potential remedy to such problems, in addition to providing the potential for higher throughput and better step coverage. Using deposition chemistries based on carbonyl sources, Mo and W deposits have been characterized with respect to their electrical, mechanical, structural, and chemical properties as well as their compatibility with conventional IC processing. Excellent film step coverage and uniformity were obtained by low temperature (300-350 C) deposition at pressures of 400-600 mTorr. As-deposited films were observed to be amorphous, with a resistivity of 250 and 350 microohm-cm for Mo and W respectively. On annealing at high temperatures in a reducing or inert atmosphere, the films crystallize with attendant reduction in resistivity to 9.3 and 12 microohm-cm for Mo and W, respectively. The average grain size also increases as a function of time and temperature to a maximum of 2500-3000 A. The metals and their silicides that are deposited, using silane as silicon source, are integratable to form desired metal-silicide gate contact structures. Thus, use of the low resistivity of the elemental metal coupled with the oxidation resistance of its silicide manifests the quality and economy of the process. MOS capacitors with Mo and W as the gate material have been fabricated on n-type (100) silicon. A work function of 4.7 +/- 0.1 eV was measured by means of MOS capacitance-voltage techniques. The experimental results further indicate that the characteristics of W-gate MOS devices related to the charges in SiO₂ are comparable to those of poly-silicon; while, the resistivity is about two orders of magnitude lower than poly-silicon. It is therefore concluded that hot-wall low pressure chemical vapor deposition of Mo and W from their respective carbonyl sources is a viable technique for the deposition of reliable, high performance refractory metal/silicide contact and interconnect structures on very large scale integrated circuits.

A new powder processing approach to produce oxidation resistant molybdenum alloys for high temperature use has been developed. Oxidation protection is provided by fine dispersion of silica glass particles within a molybdenum matrix. As the molybdenum oxidizes, the glass is exposed and melts to form a self-healing protective oxide coating. Additionally, homogeneously dispersed Mo5SiB2 and/or Mo2B provide boria upon oxidation which reduces glass viscosity and allows flowing glass to coat the surface while remaining solid internally. This is similar to the oxidation protection used in Mo-3Si-1B (wt%) systems; however embedding the glass directly into the Mo matrix and eliminating the Mo3Si (A15) phase provides the same volume of glass at lower volume fractions of brittle phases and also without embrittling Si impurities in solution in Mo. Additionally the glass composition can be tailored for different applications and different temperatures beyond that achievable in Mo-Si-B based systems. A variety of microstructures, compositions and additional components for improved oxidation protection are also explored, and mechanisms of the oxidation protection are discussed.