7 September 2001 Compressive strengthening of sapphire by neutron irradiation
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Abstract
Neutron irradiation of sapphire with 1 x 1022 neutrons(<EQ MeV)/m2 increases the c-axis compressive strength by a factor of 3 at 600 degree(s)C. The mechanism of strength enhancement is the retardation of r-plane twin propagation by radiation-induced defects. 1-B and Cd shielding was employed during irradiation to filter our thermal neutrons (<EQ1 eV), thereby reducing residual radioactivity in the sapphire to background levels in a month. Yellow-brown irradiated sapphire is nearly decolorized to pale yellow by annealing at 600 degree(s)C with no loss of mechanical strength. Annealing at sufficiently high temperature (such as 1200 degree(s)C for 24 h) reduces the compressive strength back to its baseline value. Neutron irradiation decreases the flexure strength of sapphire at 600 degree(s)C by 0-20% in some experiments. However, the c- plane ring-on-ring flexure strength at 600 degree(s)C is doubled by irradiation. Elastic constants of irradiated sapphire are only slightly changed by irradiation. Infrared absorption and emission and thermal conductivity of sapphire are not affected by irradiation at the neutron fluence used in this study. Defects that might be correlated with strengthening were characterized by electron paramagnetic resonance spectroscopy. Color centers observed in the ultraviolet absorption spectrum were not clearly correlated with mechanical response. No radiation-induced changes could be detected by x-ray topography or x-ray diffraction.
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Thomas M. Regan, Daniel C. Harris, Rhonda M. Stroud, John R. White, David W. Blodgett, Kevin C. Baldwin, Joseph A. Miragliotta, Michael E. Thomas, Milton J. Linevsky, John W. Giles, Thomas A. Kennedy, Mohammad Fatemi, David R. Black, K. Peter D. Lagerloef, "Compressive strengthening of sapphire by neutron irradiation", Proc. SPIE 4375, Window and Dome Technologies and Materials VII, (7 September 2001); doi: 10.1117/12.439191; https://doi.org/10.1117/12.439191
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