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The research is aimed to evaluate thermal spray coatings to address material issues in supercritical and ultra-supercritical Rankine cycles. The primary purpose of the research is to test, evaluate, and eventually implement a coating to improve corrosion resistance and increase efficiency of coal fired power plants. The research is performed as part of a comprehensive project to evaluate the ability of titanium, titanium carbide, or titanium diboride powders to provide fireside corrosion resistance in supercritical and ultra-supercritical steam boilers, specifically, coal driven boilers in Illinois that must utilize high sulfur and high chlorine content coal. [1] The powder coatings that were tested are nano-sized titanium carbide (TiC) and titanium di-boride (TiB2) powders that were synthesized by a patented process at Southern Illinois University. The powders were then sent to Gas Technology Institute in Chicago to coat steel coupons by HVOF (High Velocity Oxy-Fuel) thermal spray technique. The powders were coated on an austenitic 304H stainless steel substrate which is commonly found in high temperature boilers, pipelines, and heat exchangers. The samples then went through various tests for various lengths of time under subcritical, supercritical, and ultra-supercritical conditions. The samples were examined using a scanning electron microscope and x-ray diffraction techniques to study microstructural changes and then determined which coating performed best.

The possibility that iron and copper can ameliorate the effects of 2,4-dichlorophenoxy acetic acid (2,4-D) on the morphology and yield of plants has been investigated by Wort (64). A study of the literature indicates that although there is considerable variation among plant species and also parts of the same plant, 2,4-D concentrations below 50 p.p.m. promote or have no effect on respiration, while higher concentrations are generally inhibitory. Photosynthesis is generally inhibited. An experiment was planned and executed to determine whether iron and copper protect against the effects of 2,4-D on photosynthesis and respiration, and on fresh, dry and ash weights. Each treatment was replicated six times. Potato (Solanum tuberosum L.) plants were grown to the age required for treatment (4-7 weeks) in a hydroponic system. Treatment was applied either in the form of 'Attaclay' dust including growth substance and/or metal, or as aqueous spray in which the metal was applied two hours before the growth substance. At given intervals after treatment, photosynthesis and respiration in the leaflets were determined by the diethanolamine buffer method (60) on the Warburg apparatus. After the leaflets had been removed for the final determination of photosynthesis and respiration, the plants were harvested and their fresh, dry and ash weights were determined. A comparison was made of photosynthetic values based on both area and fresh weight. The results were analysed for statistical significance by the analysis of variance and Duncan's new multiple range test. Coefficients of variability (C.V.%) were calculated for the various measurements. In most cases the coefficients were shown to decrease by half during the course of the experiment. Results showed that 2,4-D was more inhibitory to gas exchange than its copper salt and also caused greater deformation of the plants. Further results indicated that application of iron with 2,4-D inhibited the effects measured for 2,4-D. Gas exchange values for the 2,4-D treated plants were frequently significantly different from those of plants treated two hours earlier with an iron spray. The iron spray when followed by 2,4-D application caused a significant height increase. This suggested that the effective concentration of 2,4-D had been lowered by the iron. These observations are discussed in the light of recent publications on the role of metal chelation in auxin action. / Science, Faculty of / Botany, Department of / Graduate

The corrosion rate of copper in deaerated aqueous, sulfuric-acid solutions, with regard to the effect of strain, temperature and electrolyte concentration was studied. Copper in the form of wire was subjected to applied stresses of 1728, 8640, and 17,280 pounds per square inch. Five temperatures in the range 15°C to 75°C. were investigated for electrolyte concentrations of 0.1, 0.5 and 1.0 molar sulfuric acid. The rate of corrosion was followed by noting the rate of copper uptake by the solution through a polarographic analysis run periodically for up to 30 hours. Reproducible results were obtained, it was found that: 1. The rate of reaction for the dissolution of copper in sulfuric acid was first order with respect to cupric ion concentration. 2. Experimentally, the reaction rate was pseudo-first order with respect to hydrogen ion activity. 3. Stress, in general, increased the reaction rate slightly, the effect becoming less at higher temperatures. 4. The activation energy for unstressed corrosion was 10.6 Kcal. for the temperature range 15-75 degrees. 5. For 1.0M and 0.5M acid solutions, stress decreased the activation energy and hence increased the reaction rate. 6. The average increase in reaction rate for 10 degree changes in temperature between 15 and 75 degrees was about 1.5. 7. A diffusion controlled mechanism could be proposed for the dissolution of copper in sulfuric acid solutions. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The influence of a liquid metal and a stress corrosion environment on the mechanical properties of α and β brasses was investigated under continuous tensile loading conditions: strain rate and grain size (α brass only) were systematic variables. Increasing strain rate or decreasing grain size was found to increase the ductility and fracture stress of the polycrystalline material in either environment. Single crystal studies revealed (1) that grain boundaries are not essential for embrittlement by either media and (2) that the surface films induced by the environment are mechanically very weak. The fractured surfaces of a brass were examined (1) for topographical features using both direct and indirect replica electron microscopy and (2) for evidence of thin films using a low angle electron diffraction technique. Crack path in both environments was invariably intergranular, and details of fractured surfaces were similar. Thin films were detected on the fractured surfaces, and the compositions determined. In general, both environments conferred the same general embrittling effects. It is possible to account for the current observations by a common cracking mechanism: the development of such a model based on the slip step displacement of a passive surface film is discussed. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

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The aim of this research was to identify the effect of alloying additions and heat treatment on the localized corrosion mechanisms of AA7xxx alloys that have been grain refined with an Al-5Ti-1B master alloy. The major alloying elements, Zn (3.5 – 6.5 wt. %), Mg (1.5 – 2.5 wt.%), Cu (0 – 3 wt. %), and Ti (0.04 – 0.25 wt.%), were varied and ten AA7xxx aluminum alloys were cast, heat treated to the T4, T6, T79, T76, and T73 tempers, and studied extensively. Casting high integrity near net shaped AA7xxx components by introducing Ti and B into the melt to facilitate a non-dendritic microstructure produced a unique microstructure due to the phenomena of athermal nucleation, unconstrained growth, and solute field impingement. The three phenomena listed above create three microstructural regimes; dendritic area rich in Ti, interdendritic region lean in Ti, and grain boundary area rich in eutectic phases. The breakdown potential, Eb, in a detreated 0.5 M NaCl(aq) was determined for each alloy and heat treatment after 1 h at the open circuit potential. The effect of alloying element composition and heat treatment on Eb was examined and an empirical expression was created. It was determined that a semi-logarithmic relationship exists between Eb and the Zn/Cu weight ratio. Zn and Cu have opposing effects on Eb, where, Zn-depletion from the solid solution into the strengthening precipitates increased the Eb while Cu-depletion decreased the same. Cu-lean alloys have a continually increasing Eb from T4 to T6 and T7x temper conditions, while, Cu-rich alloys have no significant change in Eb with temper condition. The critical Zn/Cu weight ratio was determined to be approximately 5. Corrosion initiation mechanisms of a Cu-lean and Cu-rich alloy were studied using the dual beam FIB-SEM platform after 5 min of potentiostatic polarization in detreated 0.5 M NaCl(aq) at potentials of interest. The initiation mechanism of the Cu-rich alloy (alloy 3) was determined to be dealloying of the S-phase (Al2CuMg) along the grain boundary leading to intergranular corrosion. The surface of the Cu-lean alloy (alloy 6) after potentiostatic polarization above Eb showed three mechanisms of corrosion; corrosion domes, corrosion rings, and interdendritic corrosion. Corrosion rings were identified as the initiation mechanism, corrosion domes were determined to be metastable sites and not a precursor to further corrosion, interdendritic corrosion was determined to be the propagation mechanism. Interdendritic corrosion is the selective dissolution of the interdendritic region leaving the dendritic regime intact after immersion in a corrosive solution which is unique to these alloys grain refined with the Ti-B master alloy. Corrosion domes were shown to cause an active-passive region in the potentiodynamic polarization curve. Modified EXCO experiments were used to study the propagation mechanism in each of the alloys at each temper. All alloys and tempers were susceptible to interdendritic corrosion, however Cu-lean alloys showed less surface damage after 96 h of immersion in the modified EXCO solution. Alloys with a Zn/Mg weight ratio < 2 were susceptible to intergranular corrosion in the T6 temper, however, in the T4 and T7x temper the primary mode of corrosion propagation is interdendritic corrosion. Due to the bimodal distribution of the grain size, intergranular corrosion was only observed in the small grain areas. The extent of attack was more severe in the small grain regions with intergranular corrosion present than areas without leading to the conclusion that intergranular corrosion is more detrimental than interdendritic corrosion. / Thesis / Master of Applied Science (MASc)

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No description available.