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.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/49071 |
| Date | January 2002 |
| Creators | Joshi, Salil Mohan |
| Publisher | Boston University |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | This work is being made available in OpenBU by permission of its author, and is available for research purposes only. All rights are reserved to the author. |
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