Engineering Commons^™

The Effect Of Porosity On Strength Degradation In Thermally Shocked Alumina, Russell David Smith

Masters Theses

"Strength degradation and crack propagation in Al₂O₃ are shown to depend on the initial strength and porosity of the material. Specimens were fabricated containing between 0 and 5% induced cylindrical, two dimensional, and spherical porosity. The strengths of the various porosity samples decreased discontinuously at a critical quenching temperature. No difference was observed in the critical temperature for the various aluminas; initial strength decrease occurred between 165°C and 175°C temperature differential. The strength retained after thermal shock decreased with increasing initial strength. The degree of damage sustained upon shocking was also characterized by crack density and crack …

Oxidation Of Tetragonal Pbo In Air, Charles A. Sorrell

Materials Science and Engineering Faculty Research & Creative Works

Isothermal oxidation of tetragonal PbO in air produced multiphase assemblages with apparent equilibrium compositions which varied linearly with temperature from PbO1.548 at 286°C to PbO1.333 at 351°C. Oxidation at each temperature was relatively rapid to PbO1.40 and very slow from PbO1.40 to apparent equilibrium values. Pseudocubic PbO1+x, with compositions between PbO1.41 and PbO1.57, was indexed on a cubic unit cell at the lower O/Pb ratios and on a tetragonal unit cell at the higher ratios. Linear changes in lattice parameters and deviation from cubic symmetry accompanied reversible oxidation and reduction of the phase. Pseudocubic PbO1+x was reduced irreversibly to Pb3O4 …

Formation And Densification Of Cadmium Manganese Ferrite, B. W. Jong, P. D. Ownby

Materials Science and Engineering Faculty Research & Creative Works

Formation of Ni-ferrite, Mn-ferrite, NiZn-ferrite, Zn-ferrite and Mg-ferrite have been investigated using X-ray diffraction analysis. Jander's diffusion equation described the data from these investigations over a portion of the temperature ranges studied. However, the reaction mechanisms and sequences involved in the formation of mixed ferrites have not been well defined in the literature. The purposes of this investigation were: ( 1) To further the understanding of the formation of CdMnferrite by studying first the kinetics of the formation of Cd-ferrite and Cd-manganite, which provides a basis for understanding the details of the mixed CdMn-ferrite reaction and to obtain the optimum …

Characterization Of A Mexican Halloysitic Clay And Behavior In Dry Pressing, Jesus L. Derat

Masters Theses

"A Mexican clay, intended to be used as refractory raw material, was identified. Problems encountered in the characterization of halloysitic clays are discussed and emphasis is made on the use of the electron microscope (scanning or transmission type) as a definite evidence of the existence of halloysite due to its unique morphology within the kaolinite group of clay minerals.

Beneficiation of this particular clay was carried out on a small scale hydrocyclone equipment and the results are discussed.

In an attempt to increase the green density in dry pressing of this halloysitic clay, mixtures with grog were prepared using different …

The Effect Of Gating On Soundness Of Al-Alloy Permanent Mold Castings, Dinesh Shantilal Patel

Masters Theses

"This thesis describes the step by step approach to the design of a gating system for the production of sound plate castings in permanent molds. Castings of different thicknesses were produced, utilizing various gating systems, and examined radiographically to evaluate the effectiveness of these gating systems in the production of sound castings. A gating system which allows metal to enter the mold cavity with no turbulence and which establishes proper temperature gradients in the casting will produce sound permanent mold castings"--Abstract, page ii.

Premartensitic Elasticity Of Fe-Ni Invars, Bryce Linn Shriver

Doctoral Dissertations

"The premartensitic temperature dependence of ultrasonic wave propagation in Fe-30 pct Ni polycrystals and Fe-32 pct Ni single crystals was measured by using a continuous wave technique. As the temperature was lowered to within 10°C of the M_s, a nonlinear decrease of the relative shear velocity was observed. This effect is related to dislocation stacking fault instabilities which may trigger the martensitic phase transformation. In addition, the single crystals show a frequency dependence of the shear elastic constant C' well above the M_s. The dispersion is believed to be caused by fluctuations in the anisotropic molecular …

Initial Surface Reactions And Nucleation Kinetics Of Boron On Atomically Clean Molybdenum Substrates, Richard Eugene Moore

Doctoral Dissertations

"A study of the chemical vapor deposition (CVD) of boron from boron triiodide (BI₃) on molybdenum has been done with field emission microscopy (FEM) and low energy electron diffraction (LEED).

A correlation of the efficiency by which BI₃ is effectively dissociated to form adsorbed boron, and the temperature of the substrate has been shown through work function measurements on the boron covered molybdenum field emitter surfaces. The boron-induced work function change of molybdenum has been shown to be in agreement with a theoretical model which predicts positive, as well as negative work functions for adsorbate-substrate systems. It …

Precipitation Of Carbon From Martensite In Ductile Iron, Devendra Ratilal Majmundar

Masters Theses

"Since metallographic studies of quenched and tempered cast iron have indicated that the carbon might precipitate directly as graphite rather than as carbides which are found in steels, this investigation used the Debye-Scherrer x-ray diffraction technique to examine electrolytically extracted residues from quenched and tempered ductile cast iron samples to determine if cementite was present. The precipitation of carbon in quenched samples of this ductile cast iron was found to be similar to the precipitation process in steels. Cementite was identified during the early stages of the tempering process when the tempering temperature was 800 degrees F, 900 degrees F, …

Sintering And Microstructure Control Of A Ferrimagnetic Mn-Zn Ferrite Spinel, Joel Keith Michel

Masters Theses

"The effect of minor additions of CaO dopant to a manganese zinc ferrite – Zn_.25Mn_.75 Fe_2.17 O_4.0 - on its grain growth and densification kinetics in air at 1250°C., 1300°C., and 1350°C. was studied. Grain growth was controlled over a range of dopant levels. At a sintering temperature of 1350°C. and time of six hours a ferrite with the smallest dopant addition was sintered to the highest density - 98% of theoretical. Under the same sintering conditions ferrites with higher dopant levels also sintered with normal growth but sintered to lower densities.

Due to discontinuous …

A New And Direct Process For The Reduction Of Lead Sulfide, Rolando Oscar Fernandez

Masters Theses

"The direct reduction of lead sulfide concentrates by iron was investigated. An oxygen-bearing flux was shown to be a necessary ingredient for complete reduction of the concentrate. The effects of time and temperature on lead recovery were studied. Only a trace amount of sulfur dioxide is evolved during reduction, which is in agreement with thermochemical calculations"--Abstract, page ii.

Prebainitic Phenomena In Aisi 86b80 And 0.8c-5.3ni Steels, Chung Lim

Doctoral Dissertations

"An ultrasonic investigation shows that the prebainitic kinetics of AISI 86B80 and 0.8C-5.3Ni steels follow t^2/3 and or t¹ time laws in the lower bainite temperature region. The data analysis indicates that these kinetics signal carbon segregation to dislocations. The simple time laws are interrupted at the bainite start time. It is shown that at this time the carbon depleted regions around dislocations transform martensitically. The lower bainite reaction is thus initiated by the formation of supersaturated ferrite through carbon segregation and the subsequent local martensitic transformation"--Abstract, page iii.

Oxidation State Control Of Volatile Species In Sintering, P. D. Ownby

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

Polynary Silicon Arsenic Chalcogenide Glasses With High Softening Temperatures, H. E. Anthonis, N. J. Kreidl, W. H. Ratzenboeck

Materials Science and Engineering Faculty Research & Creative Works

The introduction of Ag in SiAsTe glasses permits the incorporation of Se, otherwise volatile and/or degradable as a constituent in Si-containing chalcogenide glasses. SiAsAgTeSe glasses exhibit much higher softening ranges and glass transition temperatures than encountered in known chalgogenide systems. A glass Si35As15Ag10Te20Se20 had the viscosity log ν = 13 at about 500°C, as compared to 370°C for the base glass Si35As25Te40, the viscosity of log ν = 9.8 at about 560°C, as compared to 442°C for the base glass. Phase separation occurs in the system SiAsAgTeSe and becomes manifest in two glass transitions indicated by changes in the slopes …