Surface and Environmental Effects on Ceramic Materials

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Report Number: ASD TR 61-182
Author(s): Gibbs, P., Baker, G. S., Dick, B. Gale, Beauchamp, E. K., Miles, M. H., Rogers, W. G.
Corporate Author(s): University of Utah
Laboratory: Directorate of Materials and Processes
Date of Publication: 1961-08
Pages: 27
Contract: AF 33(616)-6832
DoD Project: 7350
DoD Task: 73500
Identifier: AD0267247

Abstract:
Polycrystalline sintered compacts of doped Alucer MC alumina have been deformed in three point beam loading from 1000° to 1350°C. The steady state creep rate of specimens doped with MgO or Mn(CO3)2 from 50ppm to 5000ppm by weight were fit to the expression A exp (-E/kT). The activation energy E was found to be 130 Kcal/Mole independent of added impurity. The constant A was independent of Mn(CO3)2, but decreased by a factor of 3-5 on the addition of MgO. It is suggested that polycrystalline creep is controlled by diffusion of vacancies in the steady state.Creep behavior of Linde corundum 0.1 inch diameter rods (1000°-1250°C) is described. At the lowest temperatures and stresses studied, measureable creep ( .1μ per hour beam deflection) began after about an hour's time delay, and increased at an accelerating rate. One run was successfully continued to reach a "steady state" (7500μ deflection). Activation energies increased as creep proceeded (71-135 Kcal/Mole). No mechanical effect could be attributed to flam polishing the samples.A study is described of the dispersal of impurities from a metal contact over the free surface of corundum at 10-4 mm Hg, by measuring the current flowing between two vacuum deposited films as a function of time, temperature (20-640°C), and applied field (0-12v.). At a given temperature, the current increases linearly with time. Heating to 640°C may increase the room temperature current by 4 orders of magnitude, although the current decreases with decreasing temperature. It is suggested that detaching Ag from the deposited film controls the rate of formation of a "semiconducting bridge" on or just beneath the corundum "free surface."

Provenance: Lockheed Martin Missiles & Fire Control

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