The Application of Piezo-Magnetic Alloys to Ultrasonic Viscometers operating at High Temperatures and Pressures

The paper describes development work at the National Physical Laboratory on torsional ultrasonic viscometers for temperatures up to 250°C, which can probably be extended to 650°C, and for high pressures up to 12500 atm. The present frequency range extends from 10 to 250 kc/s, with a possible further extension to 700 kc/s. Measurements of Newtonian liquids present no difficulties and most liquids possessing a simple shear compliance can be examined to determine this and the viscosity. The instrument described will provide useful, though not necessarily complete, information about the behaviour of multiple-component Maxwellian liquids. The device consists essentially of a tubular piezo-magnetic torsional resonator compactly encapsulated so as to be used in a small highpressure vessel under hydrostatic pressure. The preferred active material is ordered or semi-ordered cobalt-iron-vanadium (49: 49: 2) alloy heat-treated at 675°C; this has a Curie temperature of around 930°C, permitting operation at very high temperatures.