Title
Investigation of rare-earth alumino-silicate refractories for molten aluminum alloy containment
Degree Type
Dissertation
Date of Award
1988
Degree Name
Doctor of Philosophy
Department
Materials Science and Engineering
First Advisor
Mufit Akinc
Second Advisor
D. R. Wilder
Abstract
Several commercial alumino-silicate minerals doped with small amounts of light rare-earth oxides were tested for resistance to molten aluminum alloy attack. Although undoped compositions were severely attacked by aluminum alloy 7075, the addition of rare-earth oxides up to 15 percent by weight virtually eliminated the alloy attack. These rare-earth containing compositions were also resistant to the attack of Na[subscript]2CO[subscript]3 containing alloy. The dopants CeO[subscript]2, La[subscript]2O[subscript]3 and bastnasite, a rare-earth concentrate, were all effective in rendering the alumino-silicate minerals resistant to alloy attack;The addition of rare-earth oxide to bauxite was shown to alter its microstructure, forming a network of uniformly shaped corundum crystals interlinked with cerium containing strands. This unique microstructure was found to be primarily responsible for the enhanced attack resistance of the doped alumino-silicates. Several other possible mechanisms of protection were not supported by the experimental findings. Among these were enhanced sintering, the excess oxygen content of CeO[subscript]2 dopant and higher thermodynamic stability of the doped refractory compositions;The lattice energies of crystals were calculated from a computer summation of the Coulombic interaction energies. After evaluating this technique using several simple crystal systems, the lattice energies of the light rare-earth (La through Eu) pyrosilicates, RE[subscript]2Si[subscript]2O[subscript]7, were calculated. The lattice energies calculated for simple crystal systems were within 10% of the experimentally measured values. The enthalpies of formation for the rare-earth pyrosilicate were estimated from the calculated lattice energies by applying the Born-Haber cycle.
DOI
https://doi.org/10.31274/rtd-180813-11316
Publisher
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Copyright Owner
Michael Hughes O'Brien
Copyright Date
1988
Language
en
Proquest ID
AAI8825428
File Format
application/pdf
File Size
143 pages
Recommended Citation
O'Brien, Michael Hughes, "Investigation of rare-earth alumino-silicate refractories for molten aluminum alloy containment " (1988). Retrospective Theses and Dissertations. 9707.
https://lib.dr.iastate.edu/rtd/9707
