ASTM C554 Test for Crazing Resistance of Fired Glazed Ceramic Whitewares by a Thermal Shock Method

Scope:

The glaze is an impervious layer of a vitreous substance that has been fused to a ceramic body through firing. Firing introduces residual stresses in the ceramic. In addition, ceramic whiteware also faces thermal stresses in service. Therefore, glazed whiteware should be resistant to repeated abrupt thermal changes. Inadequate resistance to thermal shock leads to the appearance of a crazed pattern in the glaze. This ASTM C554 test provides useful information for the development and quality control of ceramic whiteware resistant to abrupt thermal changes. For whitewares with negligible moisture expansion, such as vitreous and impervious ware, the thermal shock method described here is preferred.

Test Procedure:

For ASTM C554 testing, the oven is adjusted to 250°F. When the oven temperature has reached equilibrium, the specimens are placed in the oven to allow ample heat penetration of all specimens. The specimens are placed on the edge of a custom metal rack. A custom metal rack permits surrounding air circulation so that the specimens are separated to allow at least 1⁄2 inches of air space on all sides. The specimens are heated in the oven for at least 45 min.  Water containers are placed near the oven. After the specimens have been heated, they are transferred from the oven to the water for quenching. When the specimens have cooled, they are removed and dried. The glazed surface is examined for craze patterns using dye and oblique lighting. Specimens that exhibit crazing are omitted from further testing, but undamaged specimens are subjected to another heating and quenching cycle. As long as the specimens do not show crazing, they are heated and quenched repeatedly for three cycles at oven temperatures which are increased by increments of 25°F until a temperature of 450°F is achieved.

Video 01: Ceramic crazing resistance test

Specimen size:

For ASTM C554 testing the specimens should preferably be whole pieces of ware. Cut or broken specimens are used only when whole pieces are impractical or impossible to test. If the specimens are cut from whole ware, they should be representative of the item to be tested. While cutting specimens, cracks can be induced; therefore, broken or cut specimens are inspected for cracks by using dye under oblique lighting before the test. Only broken or cut specimens free from cracks should be used. Minimum of five samples are required.

Data:

In ASTM C554, the oven temperature and cycle number together with the number of specimens failing at each quenching are reported. Separate listings are made of failures caused by crazing and failures caused by body cracking.

Conclusion:

This ASTM C554 test provides useful information for the development and quality control of ceramic whiteware resistant to abrupt thermal changes.