Accession Number:

AD0248935

Title:

INTERNAL FRICTION IN ALUMINUM OXIDE SINGLE CRYSTALS

Descriptive Note:

Corporate Author:

UTAH UNIV SALT LAKE CITY INST FOR THE STUDY OF RATE PROCESSES

Personal Author(s):

Report Date:

1960-11-01

Pagination or Media Count:

1.0

Abstract:

INTERNAL FRICTION MEASUREMENTS WERE MADE ON Al2O3 single crystals in longitudinal oscillation at a frequency of 50 kc and at strain amplitudes up to 10 to the -5th power, by the composite oscillator technique as a function of temperature between 25 and 1850 degrees C, and as a function of plastic deformation of the samples. Dislocation densities over range from about 5 x 10 to the 6th power dislocations sq cm. in the undeformed crystals to near 5 x 10 to the 7th power dislocations sq cm. in the heavily deformed samples. Undeformed crystals showed no observable change in internal friction below 1800 degrees C. Samples deformed near 1300 C showed a thermally activated change in internal friction which was observable above a background logarithmic decrement of 4 x 10 to the -5th power at temperatures greater than 1450 C. The logarithmic decrement at the maximum temperature of 1850 was 4 x 10 the -3rd power. Activation energies ranged between 80 and 140 kilocaloriesmole. A few minutes exposure of these samples to temperatures above 1900 C resulted in a decrease of a factor of 5 in the internal friction vs. temperature curve. Crystals deformed in tension in an oxygen-natural gas flame near 1900 C showed a similar form, but smaller increase in internal friction than the samples deformed at the lower temperature. No amplitude dependence was observed at strains of 10 to the -5th power or less. Author

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Distribution Statement:

APPROVED FOR PUBLIC RELEASE