PADOVA UNIVERSITY AND CNISM  

HYDROGEN GROUP

Settore Materiali-Dipartimento di Ingegneria Meccanica (DIM)
Dipartimento di Fisica (DF)

The Hydrogen Group of Padova University has been studying since some years materials for solid state hydrogen storage. Our laboratory has facilities for the synthesis of materials (high energy ball milling) and for their morphological and structural analysis (X-ray diffraction and BET porosimetry). A Sievert's volumetric type Gas Reaction Controller (supplied by Advanced Materials Co., USA) is currently used to study absorption/desorption (a/d) kinetics and thermodynamics of the materials of interest. The GRC allows:

- fully automatic and manual data acquisition of a/d kinetics and a/d pressure-composition isotherms (PCI));

- programming of operations in sequence (up to 12) even in cyclic form;

- thermoregulation: both constant temperature and temperature ramps.

The working values for temperature and hydrogen pressure (up to 500 °C and up to 200 bar, respectively) allow to study materials even in extreme conditions .

The Sievert's type Gas Reaction Controller used in the laboratory	The Gas Reaction Controller control panel from which it is possible to follow the measurements in real time

In the following are shown examples of hydrogen desorption kinetics, figure (a), and of pressure-composition isotherms, figure (b), measurements carried out at different temperatures on Mg88Ni11Fe1 powder samples prepared by high energy milling. From figure (a) it is evident the improvement of desorption kinetics by increasing the temperature. The effect of temperature on the equilibrium pressure of hydrogen a/d processes is evidenced in figure (b). The two plateaux are due to the formation of two different types of hydrides, MgH2 and Mg2NiH4. The physical meaning of the plateau is explained at Section metallic hydrides.

figure (a)		figure (b)