Monitoring of the nonlinear coefficient during silica gel formation using an ultrasonic self-calibrated method

The sol-gel process is currently used to develop new materials with a wide range of applications in chemical and food industries. An ultrasonic self-calibrated method is used to evaluate the behavior of the nonlinear coefficient during the sol to gel reaction. The method uses a single piezoelectric transducer in burst echo-mode. Assuming a classical non linearity, the propagation of ultrasonic waves in the sol-gel material can be modeled in a quasi-linear regime using the KZK equation. The temporal evolution of the nonlinear coefficient of silica gel is analyzed. A variation of around 6% of the nonlinear coefficient is observed during the formation of a sol-gel with an initial hydrolysis ratio of 4 and a surrounding temperature at 30°C. Nonlinear results are compared to linear measurements and to literature data, showing a good sensitivity of the nonlinear coefficient with the conventional linear approach of gelation process monitoring.