Active control devices based on metal-hydrogen systems

Abstract

Abstract Experiments are reported which demonstrate that structural phase transitions occurring in metal-hydrogen alloys can be used in sensing and controlling devices. The first example is the thermostatic valve where the temperature-sensing capsule is filled with a metal-hydrogen alloy containing two solid phases. Thus the hydrogen equilibrium pressure which is needed to drive a membrane or bellows depends only on temperature. A similar experiment with two fillings (a conventional volatile organic liquid and an LaNi 5 -H alloy) shows the major advantage of the LaNi 5 -H alloy, i.e. the absence of recondensation phenomena in the cooler membrane chamber. The second example is an electrothermal resistor made from a sealed NbH 0.49 alloy wire. It exploits the large increase in resistivity at the triple-point line at 360 K. The resistor is removed from thermal equilibrium with the surrounding medium by applying an electric current. This leads to nonlinear S-shaped voltage-current characteristics. The application of this device as a level and flow monitor in liquids is shown. Finally the use of such systems as models for studying dissipative structures occurring far from equilibrium is mentioned.