A novel capacitive device for the study of volumetric expansion of hydride powders

• A capacitive device was manufactured to study volumetric changes of hydride beds.
• Electrical a.c. measurements are performed in parallel with hydrogen concentration.
• Physical parameters are obtained through a simple equivalent circuit model.
• The device was successfully calibrated for the hydride of the metallic alloy LaNi5.
• Porosity and agglomeration effects are also observable with the device.

A new experimental device was developed to assist in the study of materials with potential for hydrogen storage with energy applications. Through measurements of electrical resistance and capacitance in AC, we can evaluate the alterations in porosity and volumetric expansion of very small amounts of material (∼ 0.1 g) as functions of hydrogen concentration. Observations of global sample resistivity permit the qualitative evaluation of changes of powder packing and grain mobility. To obtain the physical parameters of the materials, we propose an equivalent circuit with a complex impedance function developed from the internal geometry of the device. The circuit has been calibrated with three different conductive metallic alloys and tested successfully in the hydride of LaNi5 on samples free of stresses. We measured an increase of the volume expansion of the hydride bed on hydrogen cycling, evolving from below to above the crystallographic volume expansion.