Detection of Pressure-Induced Transformations by measuring the Change of Inductance

Abstract

The pressure in a simple piston-cylinder type apparatus was calibrated by detecting volume change associated with polymorphic transformation of the specimen as the change of inductance of high frequency coil wound on the specimen. The flow of pressure transmittor of pyrophyllite during compression was also studied by means of the same method. Specimens used were KNO₃ and AgI, which were known to have the transformation at a pressure of 3.6 and 3.0 kbar at room temperature, respectively. Results are summarized as follows:
(1) The transformtion points of the specimens were measured with good accuracy and reproducibility in spite of a small volume of specimen, about 8.7% of the total volume of pressure cell. (2) Loss of pressure in the present high pressure apparatus and arrangement of pressure cell was as small as about 3%. This fact seemed to be caused from the reduction of friction between pistons and cylinder by using a Myler and asbestos composite paper and from pressure multiplication by the steel disks used. (3) At the moment pressure was reached 3 kbar, the flow of pyrophyllite was found to be completed. At 1 kbar, however, it required about 5 min. to complete the flow of pyrophyllite. The flow of pyrophyllite was greatly affected by the arrangement of pressure cell.
The present method is expected to be used for detecting the transformation associated with the change in dielectric constant or magnetic susceptibility.