Sound propagation in magnetic fluids based on mineral oils near the glass transition temperature of the dispersion medium

Aim. The paper establishes the dependence of the influence of the concentration of the solid phase on the acoustic parameters of a magnetic fluid based on transformer oil in a wide temperature range, including the temperature close to the glass transition point of the dispersion medium. Methodology. The research is based on methods of physical acoustics and the pulse method of variable distance under external temperature influence in particular. Results. The temperature and concentration dependences of the density, velocity and absorption coefficient of ultrasonic waves are investigated. A comparison is performed with the main theoretical models and approaches. In the temperature range near the glass transition point of the dispersion medium, additional effects are observed that are not described in the literature and are inconsistent with the currently existing theories of sound propagation in dispersed systems with a large density difference between the liquid and solid phase. Research implications. Scientific and practical interest is due to the fact that the study of non-magnetized ferromagnetic colloids with a high contrast of densities between phases near the glass transition point of the dispersion medium is relevant, since there is a lack of research in this temperature range and, moreover, additional effects associated with the displacement of the phase transition at high concentrations of the solid phase are possible.