Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 178-186). Also available on the Internet.

Thesis (Ph. D.)--University of Michigan, 1938. / Caption title. Thesis note on label attached to p. 437. "Reprinted from Economic Geology, vol. XXXIV, no.4, June-July, 1939." eContent provider-neutral record in process. Description based on print version record.

Thesis--Wisconsin. / Vita. Includes bibliographical references (leaves 270-278).

Thesis (Ph. D.)--University of Michigan, 1938. / Caption title. Thesis note on label attached to p. 437. "Reprinted from Economic Geology, vol. XXXIV, no.4, June-July, 1939."

Thesis (Ph. D.)--Oregon Graduate Center, 1984.

No description available.

Pool oscillations in tungsten inert gas welding pools have been used in a closed-loop control system for orbital welding of ultra high purity tubing, determining a target level of penetration by altering the welding current in real-time. The technique is ideally suited to this application since it is does not contravene the cleanliness requirements for the inner bore and can be implemented outside the small orbital heads that are commonly used. The results presented in this thesis show how clear pool oscillation signals in extremely small molten pools can be monitored by optimising the welding conditions and signal processing of the arc voltage signal. As an indicator of the likely variation in cast behaviour present particularly in austenitic stainless steels, a 'time-to-penetrate' characterisation was made of the materials, using the time of the transition from the Mode 1 to the Mode 3 oscillation behaviour as the measured variable. By applying the test across a range of welding currents, significant insight was obtained into the cast and associated penetration behaviour. Late transitions indicated casts that exhibited significantly different responses to the more usually applied welding procedures, especially at the lower levels of welding current (highlighting their potentially more problematic penetration behaviour). It was shown that the established theoretical models were difficult to apply with certainty to moving weld pools, and consequently a fuzzy logic model was used in the control strategy. The closed-loop system comprised a user-interface PC, a control rack and commercial welding power source - control signals were applied every 2 to 3 Hz. Mode 3 pool oscillations were found to offer a more than satisfactory sensitivity to the inner bead width created for the various casts of 1.65 mm wall thickness materials studied.

No description available.

<p> Chan and Riley (1967) developed a colorimetric method for the determination of tungsten in natural waters and silicate rocks. Applied to silicate rocks this method contains the following stages: evaporation of silica with hydrofluoric acid, co-precipitation of tungsten and some other elements, with hydrous manganese dioxide and cation-exchange separation of vanadium, molybdenum and tungsten. When applying this method on standard solutions and the new U.S.G.S. standard rocks, the results obtained are lower than those suggested by the authors. The results obtained recently with neutron activation analysis of the same standard rocks by Johansen and Steinnes (1970), although different from the results of the present work, also disagree with Chan and Riley. The method was abandoned since a tungsten loss is believed to occur throughout the procedure.</p> / Thesis / Master of Science (MSc)

The integration of copper (Cu) and dielectric materials has been outlined in the International Technology Roadmap for Semiconductors (ITRS) as a critical goal for future microelectronic devices. A necessity toward achieving this goal is the development of diffusion barriers that resolve the Cu and dielectric incompatibility. The focus of this research examines the potential use of tungsten nitride as a diffusion barrier by characterizing the interfacial properties with Cu and evaluating its process capability for industrial use. Tungsten nitride (β-W2N) development has been carried out using a plasma enhanced chemical vapor deposition (PECVD) technique that utilizes tungsten hexafluoride (WF6), nitrogen (N2), hydrogen (H2), and argon (Ar). Two design of experiments (DOE) were performed to optimize the process with respect to film stoichiometry, resistivity and uniformity across a 200 mm diameter Si wafer. Auger depth profiling showed a 2:1 W:N ratio. X-ray diffraction (XRD) showed a broad peak centered on the β-W2N phase. Film resistivity was 270 mohm-cm and film uniformity < 3 %. The step coverage (film thickness variance) across a structured etched dielectric (SiO2, 0.35 mm, 3:1 aspect ratio) was > 44 %. Secondary ion mass spectroscopy (SIMS) measurements showed good barrier performance for W2N between Cu and SiO2 with no intermixing of the Cu and silicon when annealed to 390o C for 3 hours. Cu nucleation behavior and thermal stability on clean and nitrided tungsten foil (WxN = δ-WN and β-W2N phases) have been characterized by Auger electron spectroscopy (AES) and thermal desorption spectroscopy (TDS) under controlled ultra high vacuum (UHV) conditions. At room temperature, the Auger intensity ratio vs. time plots demonstrates layer by layer Cu growth for the clean tungsten (W) surface and three-dimensional nucleation for the nitride overlayer. Auger intensity ratio vs. temperature measurements for the Cu/W system indicates a stable interface up to 1000 K. For the Cu /WxN/W system, initial Cu diffusion into the nitride overlayer is observed at 550 K.