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Keen interest in additive manufacturing (AM) of refractory metals such as tungsten has been motivated by the demand for materials capable of enduring extreme temperatures in aerospace and nuclear applications. The aims of this work were to develop alloy compositions for high-temperature applications in the space propulsion and nuclear fusion sectors, and to establish processing windows for these compositions fabricated using laser powder bed fusion additive manufacturing (LPBF-AM). Tungsten (W)-based alloys are well-suited for high working temperatures because of their high melting points, excellent thermal conductivity, low corrosion resistance, and low coefficient of thermal expansion. The integrated computational materials engineering (ICME) approach was implemented to establish the connections among composition-printability-microstructure-properties-performance framework. ThermoCalc-CALPHAD software was used for Scheil-Gulliver solidification simulation (SGSS) of W-based compositions with various alloying element additions. Chromium, vanadium, and niobium were down-selected as suitable alloying elements based on SGSS results. Further, addition of carbon enhanced printability due to eutectic solidification by the formation of various carbides towards the end of solidification leading to crack-free microstructure as well as being vital for control of oxygen. This work demonstrates the successful manufacturing of multiple crack-free W-based alloy components using LPBF-AM, which had a wide range of working temperatures and enhanced mechanical properties.

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)

Evidence is reported for the formation of carbon-containing contamination products at the copper-tungsten (Cu-W) interface during the metal organic chemical vapor deposition (MOCVD) of copper on tungsten. Cu(II)bishexafluoroacetylacetonate [Cu(hfac)_2] was physisorbed onto lightly oxidized tungsten (WO_x) at 115K, under ultra-high vacuum conditions, and then annealed sequentially to higher temperatures. Copper reduction was observed by 320K. Carbonaceous and carbidic contamination of the WO_x surface was observed, even after sample warming to 625K in UHV. The results indicate that low temperature MOCVD of Cu may be possible, but interfacial contamination from the organic ligand fragmentation is a major concern.

<p>Thin films of refractory metals and carbides have been studied extensively over many years because of their wide range of application. The two major techniques used are Chemical Vapour Deposition (CVD) and Physical Vapour Deposition (PVD). These can result in the deposition of two-dimensional blanket or patterned thin films. Laser-assisted Chemical Vapour Deposition (LCVD) can provide a maskless alternative for localised deposition in two and three dimensions. This thesis describes LCVD of micrometer-sized tungsten, molybdenum and tungsten carbide rods. The kinetics, phase composition and microstructure have been studied as a function of in situ measured laser induced deposition temperature.</p><p>Tungsten and molybdenum rods were deposited by hydrogen reduction of their corresponding hexafluorides, WF6 and MoF6, respectively. Single crystal and polycrystalline tungsten rods were obtained, depending on the H2/WF6 molar ratio and deposition temperature. The molybdenum rods were either single crystals or dendritic in form depending on experimental conditions. The field emission characteristics of the tungsten single crystals were investigated. The results showed LCVD to be a potential fabrication technique for field emitting cathodes.</p><p>Nanocrystalline tungsten carbide rods were deposited from WF6, C2H4 and H2. TEM analysis showed that the carbide rods exhibited a layered structure in terms of phase composition and grain size as a result of the temperature gradient induced by the laser beam. With decreasing WF6/C2H4 molar ratio, the carbon content in the rods increased and the phase composition changed from W/W2C to WC/WC1-x and finally to WC1-x/C.</p>

Thin films of refractory metals and carbides have been studied extensively over many years because of their wide range of application. The two major techniques used are Chemical Vapour Deposition (CVD) and Physical Vapour Deposition (PVD). These can result in the deposition of two-dimensional blanket or patterned thin films. Laser-assisted Chemical Vapour Deposition (LCVD) can provide a maskless alternative for localised deposition in two and three dimensions. This thesis describes LCVD of micrometer-sized tungsten, molybdenum and tungsten carbide rods. The kinetics, phase composition and microstructure have been studied as a function of in situ measured laser induced deposition temperature. Tungsten and molybdenum rods were deposited by hydrogen reduction of their corresponding hexafluorides, WF6 and MoF6, respectively. Single crystal and polycrystalline tungsten rods were obtained, depending on the H2/WF6 molar ratio and deposition temperature. The molybdenum rods were either single crystals or dendritic in form depending on experimental conditions. The field emission characteristics of the tungsten single crystals were investigated. The results showed LCVD to be a potential fabrication technique for field emitting cathodes. Nanocrystalline tungsten carbide rods were deposited from WF6, C2H4 and H2. TEM analysis showed that the carbide rods exhibited a layered structure in terms of phase composition and grain size as a result of the temperature gradient induced by the laser beam. With decreasing WF6/C2H4 molar ratio, the carbon content in the rods increased and the phase composition changed from W/W2C to WC/WC1-x and finally to WC1-x/C.

In recent years, the conventional Flash memory with floating structure is expected to reach physical limits as devices scaling down in near future. In order to overcome this problem, alternative memory technologies have been widely investigated. And the resistance random access memory (RRAM) has attracted extensive attention for the application in next generation nonvolatile memory, due to the excellent memory property including lower consumption of energy, lower operating voltage, higher density, fast operating speed, simple structure, higher endurance, retention and process compatibility with CMOS. In this study, the tungsten-based oxide is chosen as RRAM switching layer because the tungsten is compatible with the present complementary metal oxide semiconductor (CMOS) process. The Pt/WOX/TiN structure device cells had the resistance switching property successfully. However, the experiment result revealed the inferior resistance switching property. The resistance switching characteristic of the WOX thin film is extremely unstable, it is impossible to become the products. Compared with WOX, the resistance switching property of WSiOX RRAM device is improved substantially such as stability of resistance states and reliability of device. In second parts, we purposed two methods to enhance the device switching characteristic, including controlling the filament formation/ interruption in the W doped SiOX layer and restricting oxygen movement in the WSiON layer. Finally, the transport mechanisms of carrier is analyzed and researched from the current-voltage (I-V) switching characteristic of the device. A designed circuit was used in this study to accurately observe the resistance switching process with a pulse generator and oscilloscope, which reveals that the switching process is related to both time and voltage. The oxygen movement will drift in the low temperature due to the electrical field and restricted the crystal lattice vibration. But, it will diffuse through thermal dynamics in the high temperature.

Silanethiolate salts of K(18-crown-6)+, N(CH3)4 +, Cs+, K+ were synthesized and characterized by vibrational and NMR spectroscopy. The [N(CH3)4][SSi(CH3)3] salt was used to prepare the new [N(CH3)4][WSF5] salt directly from WF6. Alternatively, [N(CH3)4][WSF5] was prepared by the reaction of WSF4 with [N(CH3)4][F]. Pure WSF4 was prepared via a facile new route and was fully characterized by Raman, infrared, and 19F NMR spectroscopy, and an improved crystal structure. The Lewis-acid properties of WSF4 were studied in reactions with pyridine, yielding the new WSF4·C5H5N adduct, which was studied by Raman and 19F NMR spectroscopy. A 2:1 stoichiometry of WSF4 and [N(CH3)4][F] yielded W2S2F9 - in solution. The novel W2SOF9 - anion was characterized in solution by 19F NMR spectroscopy. Molybdenum sulfide tetrafluoride was synthesized and unambiguously characterized by Raman, infrared, and 19F NMR spectroscopy and single-crystal X-ray diffraction. The experimental characterization of WSF4, MoSF4, WSF5 -, and SSi(CH3)3 - was supplemented by density functional theory calculations. / xv, 131 leaves : ill. ; 29 cm.

Access to abstract permanently restricted to Ball State community only / Construction of experimental setup -- Synthesis of MoS₂ and WS₂ fullerene like structures -- Synthesis of MoS₂ and WS₂ nanotube like structures -- Infrared spectroscopy of acetonitrile adsorption on synthesized MoS₂ materials. / Access to thesis permanently restricted to Ball State community only / Department of Chemistry

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)