The correlation between temperature transforming into bloating of a formed sample and nominal temperature equivalent to its refractoriness in the JIS method was positive. This result suggested that refractoriness of Amakusa pottery stone is determined by thermal expansion curves. The various thermal expansion curves were measured under different conditions of milling time of samples, pellet thickress, forming pressure, heating rate and loading. Anomalous expansion due to bloating was observed, and the temperature (T
5) giving a linear expansion coefficient of 5×10
-4cm/cm/°C was independent of the pellet thickness, forming pressure and loading. The rectification method of T
5 under the different condition of particle size distribution and heating rate was discussed. The thermal expansion curves of 58 samples were measured under the fixed conditions: milling time: 0.5min, pellet thickness: 3mm, forming pressure: 2500kg/cm
2, heating rate: 10°C/min and loading: 10g. Hence values of T
5 from the above mentioned thermal expansion curves were calculated. The nominal temperature (T
sk) equivalent to its refractoriness of the same samples was measured by the JIS method. A correlative equation between the rectified temperature (T
5′(°C)) from T
5 using the contents of particles larger than 10μm, and T
sk (°C) was calculated by the method of least squares as follows,
T
sk=-1.931×10
-3T
5′
2+6.288T
5′-3464.
The correlation coefficient between T
sk calculated by this equation and T
sk measured by JIS method was 0.980. The result showed that refractoriness for Amakusa pottery stone can be determined by thermal expansion.
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