Graphite Fugitive Layer Assists Formation of Nonporous Zirconia Layer on Fuel-Cell Tubes
- PDF / 2,692,715 Bytes
- 2 Pages / 612 x 792 pts (letter) Page_size
- 56 Downloads / 176 Views
crystal structure of lanthanum iron oxide (perovskite structure) has a long axis that lay in the plane of the thin-film sample along two directions at right angles. Both the size and orientation of the sample’s crystal domains coincided with its magnetic domains, showing that they are closely correlated. Lanthanum iron oxide is an antiferromagnetic material whose domain structure is large enough to be resolved by the PEEM2, but it is not the material used in technological devices. Eric Fullerton of IBM Almaden Research Center said that “in current read-head devices, more common antiferromagnets like nickel oxide and iron manganese are used.” He said that the study of those materials will require higher resolution.
Graphite Fugitive Layer Assists Formation of Nonporous Zirconia Layer on Fuel-Cell Tubes Solid-oxide fuel cells convert gaseous, hydrogen-rich fuels like natural gas, biogas, alcohols, and coal-derived gas directly into electrical energy. They do this in a reaction that eventually breaks the fuel down into water and carbon dioxide. The
MRS BULLETIN/APRIL 2000
tubular solid-oxide fuel cells, consisting of bundles of tubes with oxygen flowing inside and gaseous hydrocarbon flowing over the tubes, operates at about 1800°F. Working with Merrilea J. Mayo and Clive A. Randall, both associate professors of materials science and engineering at The Pennsylvania State University, postdoctoral associate Rajendra N. Basu developed a method to apply a gas-tight layer of zirconia on the tubes. Along with separating the fuel from the air in order to avoid an explosion, zirconia serves as a conductor of oxygen ions. Mayo said, “Electricity is produced by the oxygen gas-to-oxygen ion interconversion, which occurs at the surfaces of the zirconia film: On the air-exposed surface, oxygen gas separates into oxygen ions. The ions travel through the film, then give up their electrons on the other side when they react with hydrogen to form water. The electrons thus generated are captured in an external circuit, to provide an electricity source.” Basu, who is a scientist at Central Glass and Ceramic Research Institute, a national laboratory in Calcutta, India, said that other researchers have tried using electrophoretic deposition to make zirconia coating, “but with limited success.” While
electrochemical vapor deposition is used to make these coatings, the existing method is very expensive, driving up the costs of manufacturing solid oxide fuel cells. In electrophoretic deposition, a suspension of yttrium-doped zirconium oxide powder is made in very high concentration acetic acid. The application of an electrical potential allows the charged powder to move toward and deposit on the electrode with the opposite charge. The object with its powder coating is then fired at a very high temperature so that the coating forms into a continuous film on the underlying material. However, depositing zirconium oxide on the bare, porous-ceramic cathode-tube surfaces of the tubular solid-oxide fuel cells leads to an inhomogeneous coating th
Data Loading...
