Phase Transition Evaluation of a Medium Using Acoustic Reverberation Time

Non-destructive monitoring of a material's state during its physico-chemical transformation is of interest for several industrial fields including food processing and industrial manufacturing. Recent research trends have focused on the monitoring of elastic properties (Young's modulus, shear modulus) of sol-gel products. The use of ultrasound to provide reliable information about physico-chemical properties is becoming increasingly popular. In fact, ultrasonic techniques have the main advantage of being rapid and non-invasive methods that allow parameters such as product composition, structure and physical state to be obtained. Yet, classical techniques are limited to the characterization of the medium along the propagation path using first wave packets. In this paper, an alternative technique based on studying the reverberated signals is used, by analogy with those classically used in room acoustics. These complex signals contain useful quantitative and qualitative information about medium properties and are sensitive to structural changes. In previous works, this method has shown its capability to characterize materials. Compared to classical techniques, it has the advantage of studying a medium as its whole structure. Using this method, the determination of sol-gel phase transition of Salol is presented. Measurements were performed using an aluminum mould and nine piezoelectric (PZT) patches randomly distributed on the mould rear face. One of them is used as a source and the others are connected to an eight-channel oscilloscope and are used as receivers. The mean reverberation time over four receivers has been studied and its evolution can be linked to a sol-gel phase transition.