In this study, a particle welding tester has been employed to weld the 500 £gm diamond particle coated copper on the aluminum workpiece surface. The DC power supply is used as the welding energy to weld. The resistance material is added into the interface between the electrode and the diamond particle. Hence the welding energy can transfer from the diamond particle to aluminum surface so that the aluminum softens and the diamond particle is embedded into the surface under the applied force. In this experiment, the effects of the applied force (2-20 N), power (13-35 W) on the welding pattern and the behavior of welding interface. When the silicon carbide is used as the resistance material, the weld able region map is established in terms of the applied force and power. The map is divided into the insufficient heat input, the normal welding and the excess heat input. In the insufficient heat input region the power is less than 20 W, and the diamond can not be embed into the workpiece surface because the power is not enough. In the normal welding region, the power is in the range between 20 to 30 W, where the welding quality is quite good. In the excess heat input region, the power is greater than 30 W, where the welding quality is poor because the blowhole and the gas hole are generated on the surface. In the normal welding region, the embedded depth can be controlled by the different force during welding process.

No description available.

Thesis (Ph. D.)--Ohio State University, 2001. / Title from first page of PDF file. Document formatted into pages; contains xiii, 165 p.; also contains graphics (some col.). Includes abstract and vita. Advisor: Jonathan P. Pelz, Dept. of Physics. Includes bibliographical references (p. 160-165).

In this research, silicon carbide (SiC) has been confirmed to be catalytically active for the formation of polycyclic aromatic hydrocarbons (PAHs) from acetylene (C2H2). Aromatization reactions of C2H2wasexamined by gas-phase experiments in vacuo using α-SiC and β-SiC respectively, characterized with in situ time-of-flight mass spectrometry (TOF-MS)in which abundant information of intermediates was record-ed. The significance of this catalytic reaction lies in the fact that the reagents –acety-lene, the catalyst –SiC, and the PAH products are all coexisting in interstellar environment and this reaction indicates one of the possible channels for the formation of PAHs. Reaction products obtained were further confirmed by gas chromatography mass spectrometry (GCMS). The SiC catalysts were analyzed before and after the re-action using high-resolution transmission electron microscopy (HRTEM), X-ray dif-fraction(XRD) and derivative thermogravimetry (DTG).Results of experiments indicate that SiC catalyzes aromatization of C2H2starting from 400℃with activities dependent on temperature and notable difference has been observed between α and β crystal forms. For a long-time reaction at a particular temperature, the changes in productions of the four major PAH products, i.e. naphthalene, anthracene, phenan-threne and pyrene showed the transition from small PAHs to larger PAHs. Carbon deposition on the catalyst depends on temperature, which explains the deactivation of SiC catalyst at high temperatures. Based on experimental results, two new mechanisms for activation of acetylene on SiC that are closely connected with SiC surface dangling bonds have been proposed: 1)breakage of C-H bond by interaction of H with dangling bonds; 2) radical addition of hydrocarbon to form a surface ring structure which is then desorbed from the surface. Subsequent ring-growth process is suggested to follow the H abstraction / C2H2addition (HACA) mechanism. The activation effect of SiC dangling bonds was then extended to aromatization of propylene (C3H6) and propane (C3H8) starting from 650℃ and 750 ℃respectively in similar conditions. Comparison among reactions of C2H2, C3H6and C3H8provides further evidence for the proposed mechanism. / published_or_final_version / Chemistry / Master / Master of Philosophy

The deformational and microstructural behaviour of the commercial Al-Li alloy 8090 and an 8090 based composite containing silicon carbide particulate has been investigated. The materials were deformed at elevated temperature by the test methods of plane strain compression (PSC) and torsion to provide stress-strain data for the formulation of constitutive relationships. Torsion testing also provided high temperature ductility data. Isothermal annealing of rolled samples was carried out at the solution temperature of 530°C to investigate the recrystallisation kinetics and microstructures produced, with particular emphasis on the effect of the inclusion of reinforcement particles on the behaviour of the matrix alloy. Hyperbolic sine forms of constitutive equation have been produced and are found to provide good agreement with the experimental data. High values of the activation energy are calculated for the deformation of both the alloy and composite from the PSC test data. The equations obtained from the two different test methods are found to be comparable for the composite material, but a discrepancy is found for the monolithic alloy, where apparently less hardening results from torsion testing. A distinct transition in microstructure from recrystallised equiaxed grains when deformed at low temperature to an elongated, sometimes partially recrystallised, structure for material rolled at high temperature is present in the monolithic material. This is attributed to the balance of recrystallisation driving force and the Zener pinning force exerted by the 13' (A1 3Zr) phase. The composite material exhibited greatly enhanced recrystallisation kinetics in agreement with the theory of particle stimulated nucleation (PSN) of recrystallisation.

Thesis (Ph. D.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains x, 119 p. : ill. Includes abstract. Includes bibliographical references (p. 108-114).

The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Title from PDF of title page (University of Missouri--Columbia, viewed September 10, 2009). Thesis advisor: William Nunnally. Includes bibliographical references.

The dissertation focuses on the analysis of the extended defects present in as-grown and proton bombarded β-SiC (annealed and unannealed) grown by chemical vapour deposition (CVD) on (001) Si. The proton irradiation was done to a dose of 2.8 × 1016 protons/cm2 and the annealing took place at 1300°C and 1600°C for 1hr. The main techniques used for the analysis were transmission electron microscopy (TEM) and high resolution TEM (HRTEM). From the diffraction study of the material the phase of the SiC was confirmed to be the cubic beta phase with the zinc-blende structure. The main defects found in the β- SiC were stacking faults (SFs) with their associated partial dislocations and microtwins. The SFs were uniformly distributed throughout the foil. The SFs were identified as having a fault vector of the type 1/3 <111> with bonding partial dislocations of the type 1/6 <121> by using image simulation. The SFs were also found to be predominantly extrinsic in nature by using HRTEM analysis of SFs viewed edge-on. Also both bright and dar-field images of SFs on inclined planes exhibited symmetrical and complementary fringe contrast images. This is a result of the anomalous absorption ratio of SiC lying between that of Si and diamond. The analysis of the annealed and unannealed irradiated β-SiC yielded no evidence of radiation damage or change in the crystal structure of the β-SiC. This confirmed that β-SiC is a radiation resistant material. The critical proton dose for the creation of small dislocation loops seems to be higher than for other compound semiconductors with the zinc-blende structure.

A point-of-load converter was designed for a distributed power architecture using a normally off silicon carbide (SiC) junction field effect transistor (JFET) as the enabling technology. The power supply accepts a 208-V single phase input and generates a +26 V and +10 V output for pulsed loads as well as a +5 V and -5 V auxiliary supplies for digital/control circuitry. This work focuses on the integration of the first normally off SiC JFET to allow for an efficient (≥ 93%), high power density (≥ 100 W/in3) power converter demonstrating higher switching frequency. A switching frequency of 500 kHz was achieved which more than doubles the operating frequency of a reference design with silicon MOSFETs. The power supply design described in this thesis integrates a power factor correction pre-regulator with multiple output Weinberg and flyback converters each utilizing normally off SiC JFETs. Experimental results are presented to validate the design.

Doping control is the most important technology for any semiconductor system. In spite of significant progress in the doping of SiC, advancements are needed in the growth techniques and dopant incorporation. During processes such as Chemical Vapor Deposition (CVD), hydrogen is known to be trapped at defects or impurities and to alter the electrical properties of the material. This effect is known as ?hydrogen passivation?. In addition to the observed hydrogen passivation of shallow impurities in SiC crystals, it is important to know whether, and how, hydrogen present in the epi ? reactor can passivate doping impurities during growth of the material. Variations in hydrogen incorporation can affect the net doping density and make process control difficult. This makes it essential for technologists to understand the process of hydrogen passivation and its effects on the doping concentration in the crystal. To understand this phenomenon, a process has been developed to intentionally hydrogenate SiC crystals by striking a hydrogen plasma using the Reactive Ion Etching (RIE) System in the Emerging Materials Research Laboratory at MSU. Photoluminescence (PL) and Capacitance ? Voltage (CV) were used to determine the effect of hydrogen incorporation on dopants in the SiC crystal lattice. Crystal annealing was performed at 1000 oC using the Thermco Oxidation Furnace to drive hydrogen out of the lattice (a process referred to as ?de-hydrogenation?). PL and CV measurements were taken to look for changes in the hydrogen concentration as well as free carrier concentration, respectively. Experiments conducted during this thesis research were successful in incorporating hydrogen and then driving it out of the lattice. CV profiling did not indicate a considerable change in free carrier concentration, probably because of the shallow diffusion depth of hydrogen in the SiC lattice. More reliable characterization techniques such as Secondary Ion Mass Spectrometry (SIMS) are required to get a clear picture of the doping densities of all chemical species present in the lattice at the end of each processing stage. However, resources did not permit this to be conducted during this preliminary work. As a result of this research, a process for hydrogenating and de-hydrogenating the SiC lattice has been developed to permit more extensive future studies.