Silicon is conventionally extracted by the carbothermic reduction process, which is energetically very inefficient, besides being harmful to the environment. The proposed Solid Oxide Membrane (SOM) process to manufacture Silicon and other metals is energy-efficient and environmentally friendly. The process and its set-up are similar to those of a conventional Solid Oxide Fuel Cell (SOFC). However, the operating temperature is much higher, and therefore, the Nickel-Zirconia cermet that is used for anode in conventional SOFCs cannot be used in this process. The present work reports the development of a suitable anode cermet coating for the purpose. Based on known physical properties of various materials and the requirements of the application, it was decided to pursue the development of an anode based on Molybdenum-Yttria Stabilized Zirconia (YSZ) cermet. Research was conducted to develop with a process to make a Molybdenum-Yttria Stabilized Zirconia cermet coating that would adhere well to the SOM substrate, which is made from YSZ and would have good electronic conductivity and porosity. The molybdenum oxide and Yttria Stabilized Zirconia mixtures were milled together and slip-cast into pellets. The variation of the cermet characteristics was studied with respect to various milling times and sintering/reduction temperatures. YSZ substrate tubes were dip-coated with slurries of made from milled mixtures of Molybdenum Oxide and Yttria Stabilized Zirconia with methanol. They were sintered and reduced in an atmosphere of Argon with five percent Hydrogen, with the intention of getting Molybdenum-Yttria Stabilized Zirconia cermet coatings. These produced flaky coatings that did not adhere to the substrate. Thus, the experiments with Molybdenum Oxide and Yttria Stabilized Zirconia mixtures demonstrated the difficulty in making the cermets by that technique. Cermet coatings were made using a slurry of Molybdenum metal and Yttria Stabilized Zirconia powder. Molybdenum powder was milled with Yttria Stabilized Zirconia and the resulting powders were made into sluITY with methanol and dip-coated onto the substrate tubes. It was seen in the cermet coatings produced that the electrical conductivity and porosity increased, whereas adherence to the substrate decreased with increasing Mo-content in the cermets. In order to make a cem1et coating that had good electrical conductivity and porosity as well as adherence to the YSZ substrate, a double-layered Molybdenum-YSZ cermet coating was made with a zirconia-rich lower layer and a molybdenum-rich upper layer. This coating had good electrical conductivity and porosity, as well as adherence. This double-layer coating was recommended as the cermet coating for use as the anode for the SOM cell.

The traditional aluminum production process (Hall-Héroult process) involves electrolyzing the alumina dissolved in the molten cryolite salt. This process is energy intensive and emits massive amounts of CO2 and other greenhouse gases. The market demand of aluminum and the environmental impact of the current aluminum production process justify research and development of alternative electrolytic processes for aluminum production that can both reduce the cost and eliminate adverse environment impacts. Solid oxide membrane (SOM) based electrolysis process is an innovative technology that has been demonstrated to successfully produce many energy-intensive metals directly from their oxides in an efficient, economical and environmentally sound way. During the SOM electrolysis process, an oxygen-ion-conducting SOM tube made of ytteria-stabilized zirconia (YSZ) separates the pre-selected molten flux with dissolved metal oxide from the inert anode assembly inside the YSZ tube. When the applied DC potential between the cathode and the anode exceeds the dissociation potential of desired metal oxide, the metal is reduced at the cathode while oxygen ions migrate through the YSZ membrane and are oxidized at the anode. Employing the inert anode allows the oxygen to be collected at the anode as a value added byproduct. In this work, a zero-direct-carbon-emission aluminum production process utilizing SOM electrolysis is presented. The molten flux used in the electrolysis process is optimized through careful measurements of its physio-chemical properties. The liquidus temperature, volatilization rate, alumina solubility, aluminum solubility, YSZ membrane degradation rate and electrical conductivity of various flux compositions were measured, and the flux chosen for SOM electrolysis was a eutectic MgF2-CaF2 system containing optimized amounts of YF3, CaO and Al2O3. Laboratory scale SOM electrolysis employing the inert anode were performed at 1100 ~ 1200oC to demonstrate the feasibility of producing and collecting aluminum while producing pure oxygen as a byproduct. The aluminum product was characterized by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). An equivalent circuit model for the electrolysis process was developed in order to identify the polarization losses in the SOM electrolysis cell. / 2016-12-21T00:00:00Z

The Solid oxide membrane (SOM) electrolysis is an innovative green technology that produces technologically important metals directly from their respective oxides. A yttria-stabilized zirconia (YSZ) tube, closed at one end is employed to separate the molten salt containing dissolved metal oxides from the anode inside the YSZ tube. When the applied electric potential between the cathode in the molten salt and the anode exceeds the dissociation potential of the desired metal oxides, oxygen ions in the molten salt migrate through the YSZ membrane and are oxidized at the anode while the dissolved metal cations in the flux are reduced to the desired metal at the cathode. Compared with existing metal production processes, the SOM process has many advantages such as one unit operation, less energy consumption, lower capital costs and zero carbon emission. Successful implementation of the SOM electrolysis process would provide a way to mitigate the negative environmental impact of the metal industry. Successful demonstration of producing ytterbium (Yb) and silicon (Si) directly from their respective oxides utilizing the SOM electrolysis process is presented in this dissertation. During the SOM electrolysis process, Yb2O3 was reduced to Yb metal on an inert cathode. The melting point of the supporting electrolyte (LiF-YbF3-Yb2O3) was determined by differential thermal analysis (DTA). Static stability testing confirmed that the YSZ tube was stable with the flux at operating temperature. Yb metal deposit on the cathode was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). During the SOM electrolysis process for silicon production, a fluoride based flux based on BaF2, MgF2, and YF3 was engineered to serve as the liquid electrolyte for dissolving silicon dioxide. YSZ tube was used to separate the molten salt from an anode current collector in the liquid silver. Liquid tin was chosen as cathode to dissolve the reduced silicon during SOM electrolysis. After electrolysis, upon cooling, silicon crystals precipitated out from the Si-Sn liquid alloy. The presence of high-purity silicon crystals in the liquid tin cathode was confirmed by SEM/EDS. The fluoride based flux was also optimized to improve YSZ membrane stability for long-term use.

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