Heat resistance of alumina ceramics

Heat resistance of alumina ceramics A method for evaluating the heat resistance of structural ceramics according to which the thermally stressed state is created by blowing a directed air flow into the tip of a notch in a heated prismatic specimen is presented. For this purpose a special complexly shaped notch is formed in order to provide free inflow of the air to its tip. The radius of curvature of the notch in alumina ceramics is 5 Μm. In blowing, the heat is removed predominantly from a local volume at the tip of the notch, thus providing a “local” thermal shock. The heat resistance of alumina ceramics obtained by sintering and reaction bonding is studied. The mechanical properties of Al2O3 tend to improve after a local thermal shock. The tendency is proved by testing a statistically reliable sample of unnotched specimens by the conventional method for determining the heat resistance. This tendency can be explained by “curing” of some of the defects (commensurable with the elements of the substructure) in densely sintered ceramics under the effect of thermal stresses. This was established due to the low scattering of the values of the mechanical properties measured in testing a sample of specimens with a special notch. It cannot be detected in tests of unnotched specimens within the same sample. A heat cycle of “850‡C-water” worsens the mechanical properties of notched and unnotched specimens due to the initiated microfracture. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Refractories and Industrial Ceramics Springer Journals

Heat resistance of alumina ceramics

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Publisher
Springer US
Copyright
Copyright © 1999 by Kluwer Academic/Plenum Publishers
Subject
Chemistry; Characterization and Evaluation of Materials; Materials Science; Ceramics, Glass, Composites, Natural Methods
ISSN
1083-4877
eISSN
1573-9139
D.O.I.
10.1007/BF02762437
Publisher site
See Article on Publisher Site

Abstract

A method for evaluating the heat resistance of structural ceramics according to which the thermally stressed state is created by blowing a directed air flow into the tip of a notch in a heated prismatic specimen is presented. For this purpose a special complexly shaped notch is formed in order to provide free inflow of the air to its tip. The radius of curvature of the notch in alumina ceramics is 5 Μm. In blowing, the heat is removed predominantly from a local volume at the tip of the notch, thus providing a “local” thermal shock. The heat resistance of alumina ceramics obtained by sintering and reaction bonding is studied. The mechanical properties of Al2O3 tend to improve after a local thermal shock. The tendency is proved by testing a statistically reliable sample of unnotched specimens by the conventional method for determining the heat resistance. This tendency can be explained by “curing” of some of the defects (commensurable with the elements of the substructure) in densely sintered ceramics under the effect of thermal stresses. This was established due to the low scattering of the values of the mechanical properties measured in testing a sample of specimens with a special notch. It cannot be detected in tests of unnotched specimens within the same sample. A heat cycle of “850‡C-water” worsens the mechanical properties of notched and unnotched specimens due to the initiated microfracture.

Journal

Refractories and Industrial CeramicsSpringer Journals

Published: Nov 21, 2007

References

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