A novel concept has been developed for the direct carbon fuel cell (DCFC) based on molten carbonate recirculating electrolyte. In the cathode, co-current flow of electrolyte with entrained gases carbon dioxide and oxygen is sent in the upward direction through a porous bed grid. In the anode, co-current flow of a slurry of electrolyte entrained with carbon particles is sent in the downward direction through a porous bed grid. The gases carbon dioxide and oxygen in the cathode react on the grid surface to form carbonate ions. The carbonate ions are then transported via conduction to the anode for reaction with carbon to produce carbon dioxide for temperatures under 750 deg C. A mathematical model based on this novel DCFC concept has been developed. The model includes governing equations that describe the transport and electrochemical processes taking place in both the anode and cathode and a methodology for solving these equations. Literature correlations from multi-phase packed-bed chemical reactors were used to estimate phase hold-up and mass transfer coefficients. CO production and axial diffusion were neglected. The results demonstrated that activation and ohmic polarization were important to the cell output. The impact of concentration polarization to the cell output was comparatively small. The bed depths realized were of the order of 10cm which is not large enough to accommodate the economies of scale for a large scale plant, however thousands of smaller cells (10 m^2 area) in series could be built to scale up to a 10 MW industrial plant. Limiting current densities of the order of 1000-1500 A/m^2 were achieved for various operating conditions. Maximum power densities of 200-350 W/m^2 with current densities of 500-750 A/m^2, and cell voltages of 0.4-0.5 V have been achieved at a temperature of 700 deg C. Over temperatures ranging from 700 to 800 deg C, results from the modeled cell are comparable with results seen in the literature for direct carbon fuel cells that are similar in design and construction. / Ph. D.

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This study focused on molten salt purification processes to effectively reduce or eliminate the corrosive contaminants without altering the salt's chemistry and properties. The impurity-driven corrosion behavior of HAYNES® 230® alloy in the molten KCl-MgCl2-NaCl salt was studied at 800 ºC for 100 hours with different salt purity conditions. The H230 alloy exhibited better corrosion resistance in the salt with lower concentration of impurities. Furthermore, it was also found that the contaminants along with salt's own vaporization at high temperatures severely corroded even the non-wetted surface of the alloy. The presence of Mg in its metal form in the salt resulted in an even higher mass-loss possibly due to Mg-Ni interaction. The study also investigated the corrosion characteristics of several nickel and ferrous-based alloys in the molten KCl-MgCl2-NaCl salt. The average mass-loss was in the increasing order of C276 < SS316L < 709-RBB* < IN718 < H230 < 709-RBB < 709-4B2. The corrosion process was driven by the outward diffusion of chromium. However, other factors such as the microstructure of the alloy i.e. its manufacturing, refining, and heat-treatment processes have also shown to influence the corrosion process. Lowering the Cr content and introducing W and Mo in the alloy increased its resistance to corrosion but their non-uniform distribution in the alloy restricted its usefulness. To slow-down the corrosion process, and enhance the material properties, selected alloys were boronized and tested for their compatibility in the molten KCl-MgCl2-NaCl salt. The borided alloys exhibited better resistance to molten salt attack, where the boride layer in the exposed alloy was still intact, non-porous, and strongly adhered to the substrate. The alloys also did not show any compensation in their properties (hardness). It was also found that the boride layer always composed of an outermost silicide composite layer, which is also the weakest and undesired layer as it easily cracks, breaks, or depletes under mechanical and thermal stresses. Various different grades of "virgin" nuclear graphites were also tested in the molten KF-UF4-NaF salt to assist in the selection of tolerable or impermeable graphites for the MSR operational purposes. It was found that molten salt wettability with graphite was poor but it still infiltrated at higher pressure. Additionally, the infiltration also depended on the pore-size and porosity of the graphite. The graphite also showed severe degradation or disintegration of its structure because of induced stresses. / Doctor of Philosophy / Molten salts are considered as potential fuel and coolant candidates in MSRs because of their desirable thermophysical properties and heat-transfer capabilities. However, they pose grave challenges in material selection due to their corrosive nature, which is attributed to the impurities and their concentration (mostly moisture and oxygen-based) in the salt. This study focused on purifying the salt to reduce these contaminants without compromising its composition and properties. The influence of purification processes on the corrosion behavior of HAYNES® 230® alloy was studied in the molten chloride salt with different purity conditions. Various nickel and ferrous-based alloys were also studied for their compatibility in the molten chloride salt. This will assist in expediting the material selection process for various molten salt applications. It was observed that several factors such as alloy composition, its microstructure, impurities in the salt attribute to molten salt corrosion. It was also quite evident that corrosion in molten salts is inevitable and hence, the focus was shifted on slowing down this process by providing protective barriers in the form of coatings (i.e. boronization). The borided (coated) alloys not only improved the corrosion resistance but also enhanced and retained their properties like hardness after exposure to molten salts. Since these studies were conducted under static conditions, a more detailed investigation is needed for the selected alloys by subjecting them to extreme flow-conditions and for longer a duration of time. To achieve this objective, a forced circulation molten salt loop was designed and fabricated to conduct flow corrosion studies for alloys in molten chloride salt. Graphite is another critical component of the MSR where it is used as a moderator or reflector. Generally, molten salts exhibit poor wettability with graphite, but they can still infiltrate (graphites) at higher applied pressures, and result in the degradation or disintegration of graphite's structure, and eventually its failure in the reactor. This study provides infiltration data, and understanding of the degradation of various 'virgin' nuclear graphite grades by the molten fluoride salt. This should assist in the selection of tolerable or impermeable graphite grades for MSR operational purposes.

<p>  </p> <p>Concentrated solar power (CSP) is a technology that utilizes focused sunlight to heat a high-temperature medium (such as a molten salt). Heat from this medium can be transferred to a working fluid (such as supercritical CO2) that is then used to drive a turbine to generate electricity. Alternatively, the hot medium/fluid can be pumped into tanks for thermal energy storage (TES), for heat extraction later to generate dispatchable electricity and/or for electricity production at night or on cloudy days. By increasing the fluid temperature to <u>></u>750oC and utilizing TES, CSP can become more cost competitive with fossil-based electricity production. Current CSP systems utilize molten nitrate salts for heat transfer and TES that are known to thermally degrade at temperatures >600oC. To achieve temperatures <u>></u>750oC, molten chloride salts, such as ternary MgCl2-KCl-NaCl compositions, are being considered as heat transfer and thermal energy fluids for next generation CSP plants due to their higher temperature stability, low cost, and availability. </p> <p>In this work, it was demonstrated that MgCl2-containing molten salts are prone to oxidation in ambient air at 750oC, which can enhance corrosion of the containment materials and alter the thermophysical properties of the fluid. An alternative, low-cost, earth-abundant, MgCl2-free, oxidation-resistant molten salt, a eutectic CaCl2-NaCl composition, was developed, along with a corrosion mitigation strategy, to enable the slow growth of protective oxide layers on metals that are resistant to dissolution by such MgCl2-free molten chloride salts. </p> <p>This strategy was expanded to other low-cost, oxidation resistant compositions, such as eutectic BaCl2-CaCl2-KCl-NaCl with tailored chemical and thermophysical properties for CSP and TES. The melting temperature, heat capacity, oxidation resistance, and crystallization behavior were measured for eutectic a BaCl2-CaCl2-KCl-NaCl(17.5-47.8-3.3-31.4 mol%) (BCKN) salt and a MgCl2-KCl-NaCl (40-40-20 mol%) salt. BCKN salt was shown to have a similar melting temperature while having a higher heat capacity and far better oxidation resistance. </p> <p>The corrosion of the nickel-based superalloy Haynes 214 was studied in molten MgCl2-KCl-NaCl (40-40-20 mol%) salt at 750oC under inert atmosphere conditions using a custom-built rotating-disc corrosion testing apparatus that maintained laminar fluid flow on the sample. Non-protective external Cr-, Al-, and Mg- oxide layers were formed on Haynes 214 that were prone to spallation. Internal oxidation of Al was also observed along with Cr depletion zones within Haynes 214.  Corrosion kinetics were evaluated to quantify the role of fluid flow for application of this alloy for use in containment and transportation of this molten chloride salt. </p>

The original purpose of this investigation was to attempt to apply the coulostatic method directly to a molten salt system. The inability to duplicate the reported capacity data for this system resulted in an investigation of the probable cause of this discrepancy between the data obtained by these different methods (14, 15).

Manufacturers of cast metal parts are interested in the development of a feedback control system for use with the Precision Sand-Casting (PSC) process. As industry demands the ability to cast more complex geometries, there are a variety of challenges that engineers have to address. Certain characteristics of the mold, such as thick-to-thin transitions, extensive horizontal or flat surfaces, and sharp corners increase the likelihood of generating defective casts due to the turbulent metal-flow during fills. Consequently, it is critical that turbulent flow behavior within the mold be minimized as much as possible. One way to enhance the quality of the fill process is to adjust the flow rate of the molten metal as it fills these critical regions of the mold. Existing systems attempt to predict the position of the metal level based on elapsed time from the beginning of the fill stage. Unfortunately, variability in several aspects of the fill process makes it very difficult to consistently predict the position of the metal front. A better approach would be to embed a sensor that can detect the melt through a lift-off distance and determine the position of the metal-front. The information from this sensor can then be used to adjust the flow rate of the aluminum as the mold is filled. This thesis presents the design of a novel non-invasive sensor monitoring system. When deployed on the factory floor, the sensing system will provide all necessary information to allow process engineers to adjust the metal flow-rate within the mold and thereby reduce the amount of scrap being produced. Moreover, the system will exhibit additional value in the research and development of future mold designs.

A novel process for single-pot conversion of biomass to biofuels was developed called the molten salt catalytic pyrolysis (MSCP) method. The proposed single-pot MSCP process proved to be an inherently more efficient and cost-effective methodology for converting lignocellulosic biomass. In this study, several parameters that affect yield of bio-oil were investigated including carrier gas flow rate; pyrolysis temperature; feed particle size; varying types of molten salt and catalysts. Use of molten salt as the reaction medium offered higher liquid yield and experiments containing ZnCl2 showed higher yield than other chloride salts. The highest yield of bio-oil was up to 66% obtained in a ZnCl2-KCl-LiCl ternary molten salt system compared with 32.2% at the same condition without molten salts. In addition, the effect of molten salt on the composition of bio-oil was also studied. It was observed that molten salt narrowed the product distribution of bio-oil with furfural and acetic acid as the only two main components in the liquid with the exception of water. Finally, a thermogravimetric kinetic study on the pyrolysis of biomass in MSCP was conducted.

In recognition of the shortcomings inherent to the operating temperature ranges of current fuel cell systems, namely the“temperature gap" between 200C and 600C, an effort to develop an intermediate-temperature molten-salt electrolyte fuel cell (IT-MSFC) was undertaken. In this type of fuel cell, the molten salt electrolyte is supported on a porous support, in a planar or other geometry similar to that used in existing fuel cell technologies, such as phosphoric acid fuel cell (PAFC) and molten carbonate fuel cells (MCFC). Such a fuel cell using a molten hydroxide electrolyte and Pt/C catalyst was constructed and tested using hydrogen and oxygen as fuel. The performance was comparable to that which has been obtained from PEM fuel cells at the low end of the voltage range, reaching 950ma/cm2 at 0.4 V in the highest performing test. Performance was superior to PEM fuel cells at the high end of the voltage range, due to the more favorable kinetics at the higher temperatures, with an open circuit voltage (OCV) of 1.0 V with a linear performance curve between 1.0 V and 0.6 V, which is characteristic of fuel cells with low kinetic overpotentials. Longevity of the fuel cell was very poor, however a number of experiments were undertaken to improve it, enabling extension of operating life from 5 minutes to 30 minutes, which is still far too low for practical use. The key problem was identified as electrolyte retention by the support matrix and possible degradation of the gas diffusion layer and catalyst. Experiments were also conducted using methanol vapor as fuel, and it was found to provide performance close to that recorded with pure hydrogen. Experiments were also conducted using several alternative molten salts, including nitrate and chloride eutectics. Combinations of nitrates with hydroxides added to act as a charge carrier produced a working fuel cell, however performance was greatly reduced. Though preliminary, the work described herein demonstrates the great potential of IT-MSFC, and outlines the work needed to make this type of fuel cell practical.