Low‐Expansion Cordierite Porcelains

The crystalline nature and expansion characteristics of compositions in the region surrounding the cordierite area of the system MgO–Al 2 O 3 –SO 2 were investigated. The selected compositions were fired to temperatures of 1250°, 1300°, 1350°, and 1400°C., and the thermal expansion characteristics were determined with the interferometer. Coefficients of linear thermal expansion were determined in the temperature range of 20° to 300°C. and were found to lie between 9.8 ± 10 –7 and 50.5 ± 10 –7 . The qualitative, as well as the quantitative, determination of crystalline constituents was made utilizing strontium fluoride as an internal standard in the X‐ray spectrometer. In the compositions studied crystalline cordierite ranged from 38 to 97%. There was a close correlation between the linear thermal expansion coefficient and the crystalline cordierite content of the bodies.