Thesis (Ph. D.)--Cornell University, 1918. / "Reprinted from the Physical review, vol. XII, no. 5, November, 1918."

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 84-85). Also available on the World Wide Web.

Made available in DSpace on 2014-06-11T19:35:05Z (GMT). No. of bitstreams: 0 Previous issue date: 2000-02-21Bitstream added on 2014-06-13T19:44:56Z : No. of bitstreams: 1 zacharias_ma_dr_araiq.pdf: 3695623 bytes, checksum: f2762446db235d48a685f25509e7eeb2 (MD5) / O presente trabalho tem como objetivo a obtenção de óxidos de molibdênio e de tungstênio com propriedades texturais controladas, particularmente com elevadas áreas específicas. Tais óxidos serão posteriormente empregados como precursores nas sínteses de nitretos e carbetos de molibdênio e de tungstênio, materiais potencialmente promissores na decomposição catalítica da hidrazina em sistemas micropopulsivos de satélites. Sabe-se da literatura que uma rede inorgânica de óxidos pode ser proveniente de vários precursores. Visando alcançar o objetivo do trabalho proposto, procurou-se primeiramente obter os óxidos, via processo sol-gel, a partir da decomposição térmica dos alcóxidos de molibdênio e de tungstênio. No decorrer do desenvolvimento do projeto de pesquisa achou-se também conveniente testar a decomposição térmica de outros precursores. Estas novas rotas exigem as sínteses de complexos de molibdênio (VI) e de tungstênio (VI) com ácidos a-hidroxicarboxílicos, de ácidos molíbdico e túngstico e dos saia de amônio dos referidos metais. Os materiais sintetizados foram, sempre que possível, analisados por espectroscopia na região infravermelho, difração de raios X e medidas de adsorção de nitrogênio na sua temperatura de condensação. Algumas amostras foram submetidas à análise elementar para a determinação dos teores de C, N e H. Efetuou-se a decomposição térmica de todos os precursores, sendo os óxidos obtidos analisados pelas mesmas técnicas utilizadas anteriormente. Os óxidos de molibdênio apresentaram uma fase cristalina ortorrômbica, exceto em algumas amostras onde se observou além desta fase, a presença de uma pequena quantidade de material amorfo.Com relação ao óxido de molibdênio, o maior valor de área específica de um foi de 8m2/g para uma amostra proveniente da hidrólise controlada de um alcóxido metálico... / The present work hás a objective the obtaining of molibdenum and tungsten oxides with texturais controlled properties, particularly with high specific areas. Such oxides will be used later on as precursors in the nitrides and carbides synthesis of molibdenium and tungsten, materials potentially promissing in the catalytic decomposition of the hydrazine in micropopulsives system of satellites. It's known about the literature that an inorganic net of oxide can come from several precursors. Seeking to reach the objective of the proposed work, it was firstly tried to obtain the oxides through sol-gel process, starting from the thermal decomposition of the molybdenum and tungsten alcoxides. In elapsing of the development in the research project it was also convenient to test the thermal decomposition of others precursors. These new routes demand the syntheses of molibdenium(VI) and tungsten(VI) complexes with the a-hidroxycarboxylic acids, of molybdic and tungstic acids and of the ammonium salts of the referred metals.The synthesized materials were, whenever possible, analysed by spectroscopy in the infrared region, of X-rays diffraction and measures of adsorption of nitrogen in its condensation temperature. Some samples were submitted the elementary analysis for the determination of texts of C, N and H. The thermal decomposition of all precursors was made, being the obtained oxides analysed same techniques previously used. The molibdenium oxides presented crystalline orthorhombic phase, except in some samples where it was observed besides this phase, the presence of a small amount of amorphous material. With relationship to molibdenium oxide, the largest value of specific area went of 8m2/g to a coming sample of the controlled hydrolysis of a metallic alcoxide. It was also obtained of area around 8m2/g for the ocide, coming from a of molybdic acid sample... (Complete abstract, click electronic address below)

Thermolysis of Cp*W(NO)(CH ₂CMe₃) ₂,CpW(NO)(CH ₂CMe₃)₂, Cp*W(NO)(CH₂SiMe₃)(η²-CPhCH₂), or Cp*W(NO)[CH(Ph)CH₂CH(nPr)CH₂]in cyclic olefins results in the formation of ring-retaining oligomers having lengths up to dodecamers. The main cyclohexene dimer is 3-cyclohexylcyclohexene. A small percentage of oligomers contain neopentyl or CH=CHPh end groups. Turnover frequencies for the Cp*-tungsten precatalysts range from 5.5 to 6.5 mol/h at 100 °C. In room temperature solutions, Cp*Mo(NO)(CH₂CMe₃)₂ generates the alkylidene intermediate [Cp*Mo(NO)(=CHCMe₃)], which couples with cyclic olefins to form cismetallacycles. The isolable cyclopentene-derived cis-metallacycle, Cp*Mo(NO)[cis-η² CH(CH₂)₃CHCHCMe₃], converts in the solid state to the allyl-hydride complex Cp*Mo(NO)(H)(η³-CH(CH₂)3CCHCMe₃). With larger cyclic olefins (cyclohexene through cyclooctene) the initial cis-metallacycles isomerize to trans-metallacycles of the form Cp*Mo(NO)[trans-η²-CH(CH₂)nCHCHCMe₃] (n = 4, 5, 6), and these subsequently convert with loss of dihydrogen to η⁴-diene complexes, Cp*Mo(NO)[η⁴-CHCH(CH₂)n-₁CCHCMe₃]. Thermolysis of the η⁴-diene complexes in cyclohexene results in decomposition of the organometallic complex with small amounts of oligomer formation. Thermolysis of Cp*W(NO)CH₂CMe₃)₂ in cyclic-olefm substrates generates the alkylidene intermediate [Cp*W(N0)(=CHCMe₃)], which couples with cyclic olefins in a manner analogous to the Cp*Mo-system. Tungsten trans-metallacycles are observed by ¹H NMR spectroscopy, but the organometallic subsequently reacts further with loss of the coupled neopentyl-cyclic olefin and coordination of two substrate molecules to form the putative Cp*W(NO)(cyclic olefm)₂ complex. Two additional cyclooctene products are isolated, the 1,4- diene Cp*W(N0)[η⁴-CHCH(CH₂)₅CHCCH(CH₂)₆] and the allyl hydride Cp*W(NO)(H)[η³- CH(CH₂)₆CCCHCH(CH₂)₅], both containing two coupled cyclooctene molecules. A tungsten cis-metallacycle forms with 2,5-dihydrofiiran, but a ring-opened alkoxy-allyl complex forms with 3,4-dihydro-2H-pyran, and 1,2,3,6-tetrahydro-pyridine undergoes N -H bond activation to afford an amido product. CpW(NO)(CH₂CMe₃)₂ produces some oligomers of cyclohexene, but in all other reactions bimetallic decomposition pathways predominate. / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

A description of the geochemistry of tungsten is given. The geochemical properties of tungsten have a strong influence on its mineralogy, distribution and abundance in crustal rocks and rock-forming minerals , and its migration/deposition within the ore-forming and supergene environments. The behaviour of tungsten during migration, from source to site of deposition, within the crust is discussed in some detail and environments considered favourable to the concentration of tungsten ore minerals are suggested. All major types of tungsten ore deposit are described with emphasis placed on those of greater economic importance. Characteristic features of each type of deposit are particularly emphasized in order to provide clear guidelines to exploration. Hydrothermal, pyrometasomatic and stratabound tungsten deposits present themselves, economically, as the most important exploration targets. The recently developed concept of syngenetic stratabound tungsten mineralisation is outlined. Exploration for deposits of this type should be aimed predominantly, but not exclusively, at volcano-sedimentary sequences of Lower Palaeozoic age, particularly within regions known to contain occurrences of Sb and Hg. Tungsten deposits commonly contain concentrations of one or more of the following metals: Sn, Sb, Bi, Mo, Au and Ag. The presence and possible extractive value of these metals, together with commonly associated metal impurities such as As, must always be taken into account in a feasibility study / Adobe Acrobat 9.53 Paper Capture Plug-in

The reactions of (ɳ⁵-C₅R₅)M(NO)(CO)₂ (R = H, Me; M = Mo, W) with PCl₅ result in the formation of the corresponding (ɳ⁵-C₅R₅)M(NO)(Cl)₂ products in high isolated yields (85-95%). These products have been fully characterized by conventional analytical and spectroscopic techniques including an X-ray crystallographic study of [ɳ⁵-C₅Me₅)Mo(NO)(Cl)₂]₂. Alkylation of the (ɳ⁵-C₅R₅)W(NO)(Cl)₂ compounds with Grignard reagents results in the formation of the corresponding complexes, (ɳ⁵-C₅R₅)W(NO)(R')₂ (R = H, Me; R' = CH₂CM₃, CH₂CM₂Ph: R = Me; R' = p-C₆H₄Me, Ph). An electrochemical study of (ɳ⁵-C₅H₅)W(NO)(CH₂CMe₃)₂, (ɳ⁵-C₅H₅)W(NO)(CH₂CMe₂Ph)₂, and (ɳ⁵-C₅Me₅)W(NO)(p-C₆H₄Me)₂ shows 2 successive, chemically reversible, one electron reductions in THF for each complex. The complexes (ɳ⁵-C₅R₅)W(NO)(R')₂ (R = H; R' = CH₂CMe₃, CH₂CMe₂Ph: R = Me; R' = CH₂CMe₂Ph,p-C₆H₄Me) react with 1 atm of CO resulting in the formation of the singly inserted products (ɳ⁵-C₅R₅)W(NO){C(O)R'}(R') in good yields, presumably via initial CO coordination. These acyl complexes have been completely characterized by conventional techniques. The IR and NMR spectroscopic properties of these complexes are indicative of an ɳ²-acyl coordination mode for all of the acylalkyl and acylaryl products. Under 6 atm of CO the (ɳ⁵-C₅H₅)W(NO)(R')₂ (R' = CH₂CMe₃, CH₂CM₂Ph) complexes are doubly carbonylated to form the corresponding (ɳ⁵-C₅H₅)W(NO){C(O)R'}₂ products. Furthermore, (ɳ⁵-C₅Me₅)W(NO){C(O)p-C₆H₄Me}(p-C₆H₄Me) reacts to form (ɳ⁵-C₅Me₅)W(NO)(CO){C(O)p-C₆H₄Me}(p-C₆H₄Me) under 6 atm of CO, but there is no evidence for the formation of a bis(acyl) product. A preliminary X-ray crystallographic investigation of (ɳ⁵-C₅H₅)W(NO){C(O)CH₂CMe₂Ph}₂ reveals the presence of one ɳ²-acyl ligand and one ɳ¹acyl ligand. The ¹H and ¹³C{¹H} NMR spectra of the (ɳ⁵-C₅H₅)W(NO){C(O)R'}₂ compounds exhibit signals for only one type of acyl ligand, indicating that the complexes are stereochemically non-rigid in solution through a process which averages the signals for the ɳ¹and ɳ³- acyl ligands. The bis(benzyl) complexes, (ɳ⁵-C₅R₅)M(NO)(CH₂Ar)₂ (R = H, Me; M = Mo, W; Ar = Ph, p-Tol), react with HCl to form (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ar)(Cl) complexes. These complexes have been reacted with Grignard reagents, R'MgCl, to form the corresponding (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ar)(R') (R' = CH₂SiMe₃, CH₂CMe₃, p-Tol) products. The benzyl ligand in all of these complexes is coordinated in an ɳ²-fashion, similar to that seen in the solid-state molecular structures of the bis(benzyl) precursors. The coordination mode of the benzyl ligands has been confirmed by solid-state molecular structure determinations of the representative examples (ɳ⁵-C₅Me₅)Mo(NO)(CH₂Ph)(Cl) and (ɳ⁵-C₅Me₅)Mo(NO)(CH₂Ph)(CH₂SiMe₃). The ¹H and ¹³C{¹H} NMR spectroscopic data for all of the complexes are discussed, with focus on the diagnostic characteristics for the ɳ²-benzyl ligand. A possible qualitative interpretation for the symmetric ɳ²-bonding mode in these complexes is presented. The (ɳ⁵-C₅Me₅)M(NO)( ɳ²-CH₂Ph)(Cl) (M = Mo, W) complexes react with AgBF₄ in CH₃CN to form electrophilic complexes of the type [(ɳ⁵-C₅Me₅)M(NO)( ɳ²-CH₂Ph)(NCCH₃)]BF₄. The solid-state molecular structures of these complexes are discussed and contrasted with those found for the neutral ɳ²-benzyl complexes. The reaction of racemic AgO₂CCH(Et)(Ph) with the (ɳ⁵-C₅R₅)M(NO)( ɳ²-CH₂Ph)(Cl) (R = H, Me; M = Mo, W: R = H; M = Mo) compounds forms the corresponding diastereomeric (ɳ⁵-C₅R₅)M(NO)( ɳ¹-CH₂Ph)(O₂CCH(Et)(Ph)) products. The ɳ¹ coordination of the benzyl ligand and bidentate coordination of the carboxylate ligand are established by the IR, ¹H, and ¹³C{¹H} NMR spectroscopic data for these products. A mixture of two diasteromeric products is demonstrated by the ¹H and ¹³C{¹H} NMR spectroscopic data and initial attempts to separate these diastereomers by crystallization are described. / Science, Faculty of / Chemistry, Department of / Graduate

Studies were conducted into several aspects of the recovery of a spark gap consisting of 6 mm. diameter, flat tungsten electrodes, after an initial discharge of 32 kamp. maximum, and duration 11 sec. The controlling effect of electrode heat transport on the intermediate recovery of the spark gap was demonstrated using air at 760 mm. Hg as a discharge medium, and gap lengths of 3, 4, and 5 mm. In the intermediate stages of recovery, the increase in breakdown strength of the gap was found to be proportional to t½, and to be nearly independent of gap length. These results are explained on the basis of uniaxular heat flow, through the electrodes. A previously observed long-time or delayed recovery in a hydrogen spark gap between clean tungsten electrodes was investigated to establish the possible role of hydrogen-tungsten adsorption in this effect. The temperatures of the electrodes were varied by means of small heating coils, and the recovery characteristics for heated electrodes measured. By comparing these results to the normal recovery characteristic, the phenomana of delayed recovery was shown to be at least partially attributable to the adsorption of hydrogen onto the electrode surfaces. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

This dissertation describes the preparation and application of a novel class of hydroprocessing catalysts, transition metal phosphides. Concentration was placed on molybdenum and tungsten monophosphides because of the importance of these elements in standard sulfidic hydrotreating catalysts. Transition metal phosphides exist over a wide range of stoichiometry, and their properties have a great deal of variation, ranging from phosphorus poor compounds with metallic electrical properties to phosphorus rich compounds with semiconducting or insulating properties. The x-ray diffraction patterns of the phosphides studied here were unchanged under the conditions of catalytic hydroprocessing, demonstrating their stability toward the hydroprocessing conditions and allowing study of their intrinsic catalytic properties. Materials were prepared in bulk form, supported on alumina, and supported on silica. The mechanism of hydrodenitrogenation on MoP/SiO2 and WP/SiO2 catalysts was investigated by comparison of hydrodenitrogenation reactions of pyridine, piperidine, n-pentylamine, tert-pentylamine, and neo-pentylamine. / Ph. D.

No description available.