Engineering topics
Yang, C. Y.
Publications and source records attributed to Yang, C. Y..
Zirconium carbide as an electrocatalyst for the chromous-chromic redox couple
Zirconium carbide is used as a catalyst in a REDOX cell for the oxidation of chromous ions to chromic ions and for the reduction of chromic ions to chromous ions. The zirconium carbide is coated on an inert electronically conductive electrode which is present in the anode fluid of the cell.
Carbon Fibers Conductivity Studies
In an attempt to understand the process of electrical conduction in polyacrylonitrile (PAN)-based carbon fibers, calculations were carried out on cluster models of the fiber consisting of carbon, nitrogen, and hydrogen atoms using the modified intermediate neglect of differential overlap (MINDO) molecular orbital (MO) method. The models were developed based on the assumption that PAN carbon fibers obtained with heat treatment temperatures (HTT) below 1000 C retain nitrogen in a graphite-like lattice. For clusters modeling an edge nitrogen site, analysis of the occupied MO's indicated an electron distribution similar to that of graphite. A similar analysis for the somewhat less stable interior nitrogen site revealed a partially localized II electron distribution around the nitrogen atom. The differences in bonding trends and structural stability between edge and interior nitrogen clusters led to a two-step process proposed for nitrogen evolution with increasing HTT.
Relativistic scattered wave calculations on UF6
Self-consistent Dirac-Slater multiple scattering calculations are presented for UF6. The results are compared critically to other relativistic calculations, showing that the results of all molecular orbital calculations are in qualitative agreement, as measured by energy levels, population analyses, and spin-orbit splittings. A detailed comparison is made to the relativistic X alpha(RX alpha) method of Wood and Boring, which also uses multiple scattering theory, but incorporates relativistic effects in a more approximate fashion. For the most part, the RX alpha results are in agreement with the present results.
Crystallography of decahedral and icosahedral particles. II - High symmetry orientations
Based on the exact crystal structure of decahedral and icosahedral particles, high energy electron diffraction patterns and image profiles have been derived for various high symmetry orientations of the particles with respect to the incident beam. These results form a basis for the identification of small metal particle structures with advanced methods of transmission electron microscopy.
Crystallography of decahedral and icosahedral particles. I - Geometry of twinning
The crystal structure of the tetrahedral twins in multiply-twinned particles with decahedral and icosahedral point group symmetries has been examined and correlated with the face-centered cubic structure. Details on the crystal structure as well as the geometrical relationships among twins in each particle are presented. These crystallographic facts serve as a basis for the interpretation of small particle images obtained with advanced methods of transmission electron microscopy.
The structure of small, vapor-deposited particles. II - Experimental study of particles with hexagonal profile
'Multiply-twinned' gold particles with hexagonal bright field TEM profile were determined to be icosahedra composed of 20 identical and twin-related tetrahedral building units that do not have an fcc structure. The crystal structure of these slightly deformed tetrahedra is rhombohedral. Experimental evidence supporting this particle model was obtained by selected-zone dark field and weak beam dark field electron microscopy. In conjunction with the results of part I, it has been concluded that multiply-twinned gold particles of pentagonal or hexagonal profile that are found during the early stages of the vapor deposition growth process on alkali halide surfaces do not have an fcc crystal structure, which is in obvious contrast to the structure of bulk gold.
A structural analysis of small vapor-deposited 'multiply twinned' gold particles
High resolution selected zone dark field, Bragg reflection imaging and weak beam dark field techniques of transmission electron microscopy were used to determine the structure of small gold particles vapor deposited on NaCl substrates. Attention was focused on the analysis of those particles in the 50-150 A range that have pentagonal or hexagonal bright field profiles. These particles have been previously described as multiply twinned crystallites composed of face-centered cubic tetrahedra. The experimental evidence of the present studies can be interpreted on the assumption that the particle structure is a regular icosahedron or decahedron for the hexagonal or the pentagonal particles respectively. The icosahedron is a multiply twinned rhombohedral crystal and the decahedron is a multiply twinned body-centered orthorhombic crystal, each of which constitutes a slight distortion from the face-centered cubic structure.
Relativistic scattered-wave theory. II - Normalization and symmetrization
Formalisms for normalization and symmetrization of one-electron Dirac scattered-wave wavefunctions are presented. The normalization integral consists of one-dimensional radial integrals for the spherical regions and an analytic expression for the intersphere region. Symmetrization drastically reduces the size of the secular matrix to be solved. Examples for planar Pb2Se2 and tetrahedral Pd4 are discussed.