No description available.

No description available.

Intermetallic composites of molybdenum disilicide reinforced with various amounts of silicon carbide particulate were produced by combustion synthesis from their elemental powders. Elemental powders were mixed stoichiometrically then ball-milled. The cold- pressed mixture was then chemically ignited at one end under vacuum at approximately 700°C. The combustion temperature of the process was approximately 1600°C which was lower than the melting point of molybdenum disilicide. This processing technique allowed the fabrication of the composites at 700°C within a few seconds, instead of sintering at temperatures greater than 1200°C for many hours. The end product was a porous composite, which was densified to >97% of the theoretical density by hot pressing. The grains of the matrix were 8-14 μm in size surrounded by SiC reinforcement of 1-5 μm. The morphology and structure of the products were studied by x-ray diffraction and scanning electron microscopy (SEM). Samples were prepared for hardness, fracture strength, and toughness testing at room temperature. There were improvements in the mechanical properties of the composites with increasing SiC reinforcement. The hardness of the materials increased from 10.1 ± 0.1 GPa (959 ± 13 kg/mm2) to 11.7 ± 0.6 GPa (1102 ± 52 kg/mm2) to 12.7 ± 0.4 GPa (1199 ± 36 kg/mm2) with the 10 vol% and 20 vol% SiC reinforcement, respectively. The strength increased from 195±39 MPa to 237±39 MPa with 10 vol% and to 299 ± 43.2 MPa with a 20 vol% SiC reinforcement. The fracture toughness increased from 2.79 ± 0.36 MPa.m1/2 to 3.31± 0.41 MPa.m1/2 with 10 vol% SiC and to 4.08± 0.30 MPa.m1/2 with 20 vol% SiC. The increase in hardness and flexural strength is due to the effective load transfer across the strong interface in the composites. The main toughening mechanism is crack deflection by the residual stress in the materials, induced by the differences in the thermal expansion coefficients and the elastic moduli of the matrix and reinforcement. / Thesis / Master of Engineering (ME)

No description available.

The research detailed herein has been conducted in two different areas. The first research goal was to develop and study a supramolecular system coupling two light absorber units to a central metal site capable of collecting two electrons; this has been accomplished. The complex {[(bpy)2Ru(dpp)]2RhCl2}(PF6)5 was synthesized and characterized using electrochemistry and electronic absorption spectroscopy. The electrochemical properties of {[(bpy)2Ru(dpp)]2RhCl₂}(PF6)5 were probed with cyclic voltammetry and bulk electrolysis studies to investigate the behavior of the system upon two-electron reduction of the rhodium metal center. Bulk electrolysis showed that the rhodium center underwent two-electron reduction. A water modulation of product distribution for the bulk electrolysis studies was found, and the nature of this process was studied. In the presence of water, two-electron reduction of the rhodium metal center afforded a RhI complex that had lost two chloride ligands: {[(bpy)2Ru(dpp)]2RhI}+5. In the absence of sufficient water, two-electron reduction yields a breakdown of the trimetallic resulting in [(bpy)2Ru(dpp)]+2 and {[(bpy)2Ru(dpp)]RhICl₂}+. The second research goal was to develop integrated molecular modeling, synthesis, and characterization laboratory experiments, to incorporate into the undergraduate inorganic laboratory curriculum, and to evaluate and modify this curricular approach. This was accomplished with organometallic [Mo(CO)4(N-N)] complexes, where N-N is a bidentate nitrogen donor ligand. [Mo(CO)4(N-N)] complexes were selected because they were amendable to molecular modeling and could be synthesized via two synthetic routes with reasonable yields, low reaction times, and were air stable. Many of these complexes are new, so a series of [Mo(CO)4(N-N)] complexes were synthesized by either thermal or photochemical substitution reactions. The systems were characterized using cyclic voltammetry, electronic absorption spectroscopy, and ¹H NMR spectroscopy. Molecular modeling was performed on the series of [Mo(CO)4(N-N)] complexes using the CAChe software from Oxford Molecular, Ltd. These calculations typically provided reasonable structures, orbital locations, and relative orbital energies for the [Mo(CO)4(N-N)] systems. Correlations between the computational and experimental data were established. The electronic absorption spectral MLCT frequency versus calculated HOMO-LUMO energy gap, Epa versus calculated HOMO energy, E1/2red versus calculated LUMO energy, and 1H NMR chemical shift for [Mo(CO)4(1,10-phen)] and the substituted [Mo(CO)4(1,10-phen)] complexes versus ZINDO calculated partial charge were compared, where 1,10-phen = 1,10-phenanthroline. From the analyses of physical versus computational data, it was concluded that molecular modeling results are useful in predicting physical data for these complexes. The integrated molecular modeling, synthesis, and characterization experiment was developed and incorporated into the undergraduate inorganic chemistry laboratory. In both 1998 and 1999, a qualitative evaluation of student response was completed. This was done using a recorded interview technique; interviews were subsequently transcribed and rendered to extract themes. This interview style was an effective evaluation technique for this project, providing the detailed comments and student feedback that were desired. These interviews showed that the majority of the students both enjoyed this experiment and felt that the exposure to molecular modeling was worthwhile within this type of integrated lab forum. The students felt this experiment aided in their understanding of the orbital properties of inorganic systems. Student comments and suggestions facilitated modifications for future offerings in 1999 and 2000. Continued evaluation and expansion of this curricular approach are in progress. / Ph. D.

The observations which have been noted and. discussed are consistent with the proposed hypothesis that molybdenum inhibits Some facet of protein Synthesis <u>in vivo</u>. The hypothesis warrants further investigation and with the rapid improvements in protein synthesis experimentation, definitive experiments should be possible. / Ph. D.

The feeding or 200 to 500 parts per million or molybdenum to rats resulted in a greater percentage of the total liver copper being found in the nuclei and debris and mitochondrial fractions at the expense of the supernatant fraction, while the molybdenum was found to be concentrated in the supernatant fraction. Dietary inorganic sulfate while lowering liver levels of copper and molybdenum appeared to have little or no effect upon their distribution. Dietary molybdenum also caused the relative amount of copper in the supernatant fraction and erythrocytes of blood to decrease, while the increase occurred in the albumin fraction. As with liver, the blood fraction which contained the most molybdenum was the supernatant. Statistical analysis indicated that a quantity whIch was relatively well correlated with molybdenum toxicity as measured by weight gain was a combination of liver molybdenum and copper concentrations divided by body weight. It appeared that the only beneficial effect of sulfate was to lower this quantity. Sulfate excretion or the manner in which rats handled a toxic amount of phenol was found to be unaffected by molybdenum feeding. Earlier reports that dietary molybdenum caused a decrease in cytochrome-c oxidase activity and an increase in erythrocyte fragility could not be substantiated. An injected dose of radioactive molybdenum was found not to be equilibrated with the already present dietary molybdenum in sixteen hours. / Ph. D.

Molybdenum-permalloy powder cores are manufactured to fall within required permeability limits. However, these limits are sufficiently broad to cause sizeable labor loss in adjusting the number of turns for required inductance values; for example, an Arnold Engineering Company A-930157-2 core with a 1000-turn winding may range from 135 to 179 millihenries. It is therefore highly desirable that large-scale users of these cores grade them into groups by some simple inductance test. This permits cores to be wound with a predetermined number of turns, thereby essentially eliminating the labor of adjusting the number of turns of the winding to meet required inductance values. The following work has been accomplished: (1) The design and construction of a multi-turn split jig suitable for rapid testing of cores to permit economical grading. (2) The construction of a modified Owen alternating-current bridge with component capacitor and resistor values such that the inductance of the unwound cores and the finished coils may be read directly from one decade resistance box in microhenries and millihenries, respectively. (3) The preparation of a family of curves each representing a group of graded cores showing the number of turns required to yield a given inductance. Sketches and photographs of a core, finished coil, multi-turn split jig, and the test circuit are included. / Master of Science

Empirically estimated potentials were used to study the defects in Ni₃Al. A computer program which uses the conjugate gradient technique to obtain the relaxed structures was used. Atoms in the vicinity of the planar defects on the (111) plane were found to relax in two different oscillation modes namely the acoustic and optical modes. While the former is similar to the relaxation observed in pure Aluminum or Nickel, the latter was found to be a result of micromoments within the unit cell. The presence of atoms that differ in size and charge are believed to create micro-moments within each unit cell. The energy of a surface seem to depend directly on the atomic density of the terminating plane. A vacancy prefers to be formed near the boundary rather than in the bulk. The formation of an Nickel vacancy is preferred, also a Nickel vacancy has more activation energy to migrate to the boundary. The effect of the Σ = 5 boundary seems to be felt only until a distance of approximately 5 Å away from the boundary. / M.S.

Thirty-six mature, nongestating, crossbred ewes were randomly allotted to three diets: basal (6 ewes); 50% basal and 50% broiler litter (24 ewes), and 50% basal and 50% broiler litter with the addition of 25 ppm molybdenum (Mo) and 5 g sulfate/kg feed. The 24 litter fed ewes were allotted to withdrawal times of 0-, 30-, 60- and 120-d. The control (basal) diet contained and the deepstacked broiler litter contained 8 and 257 ppm Cu, dry basis, respectively. The ewes were fed the diets for 140-d at which time the control, the six litter-fed ewes with 0-d withdrawal and the Mo and SO₄ supplemented ewes were slaughtered. Liver samples were obtained from these ewes by biopsy initially and at 40-, 80-, and 120-d of the trial. At slaughter liver, kidney, muscle and duodenum samples were taken. Liver Cu content was increased (P<.01) by feeding broiler litter (404 vs 1543 ppm, dry basis). Liver Cu (962 ppm) accumulation and serum Cu were depressed (P<.05) by supplementing litter containing diets with Mo and SO₄. Zinc levels of the liver and Zn and Cu levels of the kidney and muscle were not affected by additional Mo and SO₄. Duodenum Cu and Zn levels reflected the dietary metal content. During the withdrawal period liver and duodenum Cu levels were not lowered (P>.05). A linear increase (P<.001) in SGOT activity was observed with time throughout the withdrawal period, suggesting possible liver damage. Serum Cu decreased at 30-d and increased thereafter (quadratic effect, P<.05). This observation coupled with increases in muscle and kidney Cu (P<.05) indicated an apparent redistribution of Cu stores. Metallothionein (MT) increased 12-fold above control values in the litter-fed ewes (P<.05) and tended to decrease during the withdrawal period. Therefore, it appears that supplementing Mo and SO₄ to a diet containing high Cu broiler litter may reduce the accumulation of hepatic Cu. Liver Cu stores will not be dissipated upon withdrawal of the high Cu litter from the diet. / Master of Science