On the Sintering Phenomenon of Barium Titanate Ceramics
Especially the expansion and shrinkage characteristics at high temperature
1957 Volume 65 Issue 738 Pages 137-143
Details
1957 Volume 65 Issue 738 Pages 137-143
In order to find out the best firing condition of Barium Titanate ceramics for use as electro-acoustic transducer, we measured at first the thermal expansion and shrinkage characteristics of Barium Titanate at high temperature. Our method of measurement was to observe the variation in length of the test piece continuously as a function of both temperature and time, over the temperature range from room temperature to 1400°C, by means of telescope. The results obtained are summarized as follows.
(1) When the temperature was raised from room temperature to 1400°C at the constant rate of 275°C/hr., we found there was an abnormal expansion at 1000°C amounting maximal to 7.5%. This phenomenon seems to be caused by the decomposition of Barium Carbonate.
(2) Considering that the sintering phenomenon is the result of the completion of diffusion reaction among particles of solids, we calculated inversely, the reacted quantity of Barium Titanate by the rate of shrinkage and found that Jander's diffusion formula can be applied here. Applying this result, the activation energy of reaction was calculated to be 98kcal/mol.
(3) The calculated results with respect to the shrinkage characteristics of Barium Titanate in the firing process nearly coincided with experimental results.
(4) By the above mentioned results, we found that when Barium Titanate ceramics are to be fired, sufficient attention must be paid not only for the highest firing temperature and it's duration but also for the raising rate of temperature, especially over the temperature range of abnormal expansion and rapid shrinkage.
On applying the obtained results, we made next some further experiments with regard to the difference between the calcined and not calcined material in electrical and acoustic properties of Barium Titanate. We found by the experimental results that the materials which were not calcined had approximately the same quality as those which were calcined, though the former showed slightly higher value than the latter with respect to frequency constant of radial mode vibration.
