Ultrasonic self-calibrated method applied to monitoring of sol–gel transition

• Published in: Ultrasonics 2012-07, Vol.52 (5), p.622-627
• Main Authors: Robin, Guillaume, Vander Meulen, François, Wilkie-Chancellier, Nicolas, Martinez, Loïc, Haumesser, Lionel, Fortineau, Jérôme, Griesmar, Pascal, Lethiecq, Marc, Feuillard, Guy
• Format: Article
• Language: English
• Subjects: Acoustics; Algorithms; Attenuation; Calibration; Cross-disciplinary physics: materials science; rheology; Elasticity; Electric potential; Electronics; Engineering Sciences; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Gels - chemistry; Monitoring; Phase Transition; Phase velocity; Physics; Quality Control; Real time; Rheology; Rheology - methods; Self-calibrated; Silica gel; Silicon Dioxide - chemistry; Sol gel process; Techniques and apparatus; Transducers; Transduction; acoustical devices for the generation and reproduction of sound; Ultrasonic testing; Ultrasonics; Ultrasound; Vibration; Viscosity
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2011.12.008

In many industrial processes where online control is necessary such as in the food industry, the real time monitoring of visco-elastic properties is essential to ensure the quantity of production. Acoustic methods have shown that reliable properties could be obtained from measurements of velocity and attenuation. This paper proposes a simple, real time ultrasound method for monitoring linear medium properties (phase velocity and attenuation) that vary in time. The method is based on a pulse echo measurement and is self-calibrated. Results on a silica gel are reported and the importance of taking into account the changes of the mechanical loading on the front face of the transducer will be shown. This is done through a modification of the emission and reception transfer parameters. The simultaneous measurement of the input and output currents and voltages enables these parameters to be calculated during the reaction. The variations of the transfer parameters are in the order of 6% and predominate other effects. The evolution of the ultrasonic longitudinal wave phase velocity and attenuation as a function of time allows the characteristic times of the chemical reaction to be determined. The results are well correlated with the gelation time measured by rheological method at low frequency.