Browsing by Subject "Metallurgy"
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Item Experiments Concerning the Mold Materials Used in the Production of the Copper Ingots from the Late Bronze Age Shipwreck Excavated at Uluburun, Turkey(2010-01-14) Larson, Thomas S.Underwater excavations of a Late Bronze Age shipwreck at Uluburun, Turkey recovered a combined 475 oxhide and plano-convex discoid copper ingots. While the hoard of ingots excavated at Uluburun brings the total number of copper ingots from the Late Bronze Age to over 1000, interestingly, only one ingot mold from the that period has been identified. Scholars have speculated over the means behind the creation of these ingots for decades, but with a relative absence of archaeological molds the most promising method of reaching any conclusions as to the types of molds used in antiquity seems to be experimentation. Experimental archaeology, has, in recent years been responsible for many breakthroughs in how the past is viewed. In the face of an overwhelming disparity of copper ingot molds from the Late Bronze Age, trials designed around testing different mold materials and casting techniques have the potential to determine, with relative certainty, how copper ingots were cast over 3000 years ago. This thesis examines the possible materials used to create copper ingot molds through a study of their prevalence in antiquity and also details experiments in which these materials were used, in concert with different casting techniques, to create copper ingots. The results of these experiments are combined with analyses of the Uluburun ingots in an effort to bring some closure to the debate surrounding copper ingot molds in the Late Bronze Age.Item Modeling of multipass grinding effect on residual stresses distribution and surface integrity of D2 thread rolling dies(Texas Tech University, 2004-08) Karabelchtchikova, OlgaThree questions were raised in this study: Can residual stresses after multipass grinding be predicted? What will be their superposition relationship between initial and final residual stresses distributions? Is there a method to predict and optimize surface integrity of the material after certain number of passes in order to improve the tools life? The procedure followed included a nested factorial experiment. The experimental protocol consisted of six steps, which included microstructural investigation, hardness, roughness, relative cold work, surface and subsurface residual stresses evaluation. All the main effects, including heat treatment, type of grinding operation, and multipass grinding technique and their interactions were found to be significant at a 0.05 level. Experimental significance was summarized with a second order model representing the grinding dynamics. The model was selected among four other candidates since it provided the least predicting errors and the most parsimonious structure with only one explanatory parameter, the damping ratio. The prediction of the complex nature of the residual stresses was achieved in two-folds. First, given the multipass grinding operation preceded by heat treatment, the damping ratio would change based on the experimental data. Then, this thesis provides the prediction on how the residual stresses pattern at different depth would change due to the damping ratio parameter. The contribution of this study was characterization of heat treatment and grinding effects on the surface integrity factor of D2 thread-rolling dies and development of a plausible methodology and potential theory in describing the memory relationship among multipasses during grinding operations.Item Synthesis and characterization of patterned surfaces and catalytically relevant binary nanocrystalline intermetallic compounds(2009-05-15) Cable, Robert E.As devices and new technologies continue to shrink, nanocrystalline multi-metal compounds are becoming increasingly important for high efficiency and multifunctionality. However, synthetic methods to make desirable nanocrystalline multi-metallics are not yet matured. In response to this deficiency, we have developed several solution-based methods to synthesize nanocrystalline binary alloy and intermetallic compounds. This dissertation describes the processes we have developed, as well as our investigations into the use of lithographically patterned surfaces for template-directed self-assembly of solution dispersible colloids. We used a modified polyol process to synthesize nanocrystalline intermetallics of late transition and main-group metals in the M-Sn, Pt-M?, and Co-Sb systems. These compounds are known to have interesting physical properties and as nanocrystalline materials they may be useful for magnetic, thermoelectric, and catalytic applications. While the polyol method is quite general, it is limited to metals that are somewhat easy to reduce. Accordingly, we focused our synthetic efforts on intermetallics comprised of highly electropositive metals. We find that we can react single-metal nanoparticles with zero-valent organometallic Zinc reagents in hot, coordinating amine solvents via a thermal decomposition process to form several intermetallics in the M??-Zn system. Characterization of the single-metal intermediates and final intermetallic products shows a general retention of morphology throughout the reaction, and changes in optical properties are also observed. Following this principle of conversion chemistry, we can employ the high reactivity of nanocrystals to reversibly convert between intermetallic phases within the Pt-Sn system, where PtSn2 ? PtSn ? Pt3Sn. Our conversion chemistry occurs in solution at temperatures below 300 ?C and within 1 hour, highlighting the high reactivity of our nanocrystalline materials compared to the bulk. Some evidence of the generality for this process is also presented. Our nanocrystalline powders are dispersible in solution, and as such are amenable to solution-based processing techniques developed for colloidal dispersions. Accordingly, we have investigated the use of lithographically patterned surfaces to control the self-assembly of colloidal particles. We find that we can rapidly crystallize 2-dimensional building blocks, as well as use epitaxial templates to direct the formation of interesting superlattice structures comprised of a bidisperse population of particles.