ASTM C424 Test for Crazing Resistance of Fired Glazed Whitewares by Autoclave Treatment

Scope:

Crazing is the phenomenon that produces a network of fine cracks on the surface of glazed whiteware. ASTM C424 test method determines how resistant a ceramic specimen is to crazing by using an autoclave. This method is particularly useful for porous materials that can exhibit moisture expansion. This test is used in specifications, quality control, and research and development. It is also used as a referee test method in purchasing contracts or agreements.

Test Procedure:

ASTM C424 test is carried out using an autoclave. An autoclave is a machine used to carry out scientific processes requiring elevated temperature and pressure. The specimen is placed in the autoclave. The autoclave is gradually heated until it reaches the desired temperature and pressure. The autoclave is allowed to cool for 30 min. The specimen is removed from the autoclave and allowed to cool for 30 min before the examination. To detect crazing failures, ink is applied on the glazed surface, and oblique lighting is used. Only failures visible to the naked eye are considered. 

Video 01: Ceramic crazing resistance tester

Specimen size:

This ASTM C424 test requires at least ten identical uncut specimens with facial dimensions up to and including 6 by 6 inches. For larger specimens, specifically tile products, five samples will suffice. Larger specimens may be cut to fit into the autoclave. However, all cut pieces should be as large as possible, and all cut pieces are to be tested.

Data:

The following information is reported in ASTM C424:

1. Table listing each steam pressure with the number of specimens failing at each pressure.  

2. Average failure pressure, calculated by multiplying each pressure by the number of specimens failing at that pressure and dividing the sum of these products by the total number of pieces tested, and 
3. Time consumed for steam release, if the pressure was not released immediately after each test.

Conclusion:

 ASTM C424 test method determines how resistant a ceramic specimen is to crazing by using an autoclave. This method is particularly useful for porous materials that can exhibit moisture expansion.