Browsing by Subject "Carbon compounds"
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Item Carbon chemistry : the high temperature syntheses and applications of nanotubes and sp-hybridized compounds(2002-05) Mitchell, Daniel Robert, 1971-; Lagow, Richard J.Item Design and fabrication of sub-millimeter scale gas bearings with tungsten-containing diamond like carbon coatings(2004) Kim, Daejong; Bryant, Michael D.Micro gas bearings of sub millimeter size (diameter of 500µm and length of 300µm) with micron clearances were designed and fabricated through X-ray lithography and Ni electroplating. Details of the fabrication processes for the micro gas bearings are described. Procedures to make X-ray mask and technical issues are discussed. Static and dynamic hydrodynamic characteristics of the micro gas bearings were assessed using Molecular Gas Lubrication (MGL) theory. Fabricated micro gas bearings had lower stability than plain circular gas bearings due to lower load capacity and poor gas damping. Improved bearing designs having non-symmetrical step geometry with deep axial groove were suggested. These bearings were predicted to have much higher load capacities and dynamic stabilities than the fabricated micro gas bearings. Micro gas bearings were tested via an air jet-driven micro turbine made of SU-8, press-fitted onto the shaft. A self-aligning assembly technique for the micro gas bearings (using capillary action of photo resist) was developed and proved to be very effective. Successful operation of micro gas bearings at 60,000 rpm was demonstrated under limited operating conditions. Tribological characteristics of Ni micro bearings and amorphous tungsten hydrocarbon (W-C:H) coated micro bearings were investigated in dry friction mode, using a newly designed micro tribo tester. 900nm thick uniform conformal coatings were deposited onto the inner surface of micro bearings. Chemical and mechanical microstructures were studied via X-ray Photoelectron Spectroscopy (XPS), Raman micro spectroscopy. Wear rates, mechanical and material properties, and other tribological characteristics of W-C:H coated Ni micro bearings were investigated and compared to those of uncoated Ni micro bearings. Uncoated Ni micro bearings, as deposited and annealed at 800o C, experienced severe wear and appeared inadequate for tribological applications. Micro bearings with low tungsten-containing (5% wt) hydrocarbon had higher wear resistance than micro bearings with high tungsten-containing (11% wt) hydrocarbon. During the wear test of the W-C:H coated micro bearings, a transfer layer formed on the counter steel shaft even under very small contact pressure, leading to low steady state friction and high wear resistance.Item Elimination reactions forming carbon-nitrogen double bonds(Texas Tech University, 1980-05) Cho, Bong-raeNot availableItem Structural phases of disordered carbon materials(Texas Tech University, 1996-08) Dallas, Timothy E. J.The purpose of this study is to characterize the structural and optical properties of a number of disordered carbon materials using the non-destructive optical techniques of Raman and photoluminescence spectroscopies. The samples were produced with many different growth techniques and included microcrystalline graphites, amorphous carbons, and synthetic diamond films. A new CCD-based, multichannel Raman system was set up and used to measure spectra with very high signal-to-noise in a very short period of time. Micro-Raman spectroscopy was used to determine the bonding structure of a pulse-laser annealed graphite sample. The extent of crystalline structure was quantitatively determined in both the planar and stacking directions. A follow-up study on a series of graphitic amorphous carbon (GAC) samples confirmed models by showing evidence that GAC contained very small hexagonal clusters interconnected by odd-membered rings. Annealing the GAC increased the size of the hexagonal clusters and reduced the amount of disorder. A shift in the energy position of the main phonon band of graphite has been attributed to a finite-size effect. Disorder induced vibrational modes in carbons can vary in intensity and peak position depending upon the excitation wavelength used for Raman scattering. This resonance Raman phenomena was used to help detect difference in the Raman spectra of GAC, amorphous carbon, and disordered synthetic diamond. Continuous wave (CWPL) and time-resolved (TRPL) photoluminescence spectroscopies were used to study low level point defects and structures in synthetic polycrystalline diamond films. A series of sharp peaks observed in the CWPL spectrum of a film produced by Arc-Jet chemical vapor deposition have been attributed to tungsten atoms incorporated during growth. Broadband PL in the red wavelength region was determined to be a combination of emissions from vibronics and amorphous carbon structure.