ASTM C370 Test for Moisture Expansion of Fired Whiteware Products

Scope:

ASTM C370 test method helps to determine the increases in the physical dimension of fired whiteware materials called moisture expansion. Moisture expansion is the tendency of matter to change in volume in response to a change in moisture content. The macroscopic effect is similar to that of thermal expansion but the microscopic causes are very different. Moisture expansion is caused by hygroscopy. Changes in physical dimensions from water can influence the integrity and stability of a material. In the case of glazed ware, moisture expansion can lead to crazing. Crazing is the phenomenon that produces a network of fine cracks on the surface of a material.

Test Procedure:

In ASTM C370, the specimen is measured and marked. It is placed in an autoclave where it is subjected to steam pressure. After a 5-h treatment, the steam pressure is relieved by opening the blow-off valve. The specimen is removed from the autoclave and dried to constant weight at a temperature not exceeding 110°C and the specimen is then cooled to room temperature. The specimen is measured again. 

Video 01: How to use an autoclave?

Specimen size:

For ASTM C370, the specimens should be unglazed. It should be rod-like in shape, 3 to 4 inches long. It should be cut from the center of production pieces of ware. The specimen’s thickness must not exceed 0.75 inches, and the least dimension should be not less than 0.10 inches. At least five specimens are required.

Data:

The percent of moisture expansion is reported. 

Conclusion:

ASTM C370 test method helps to determine the increases in the physical dimension of fired whiteware materials called moisture expansion.