An empirical dependence of frequency in the oscillatory sorption of H2 and D2 in Pd on the first ionization potential of noble gases

TL;DR

This study investigates how inert gases influence the oscillatory sorption of H2 and D2 in palladium, revealing a dependence of oscillation frequency on the inert gas’s ionization potential and atomic mass, with implications for calorimetric analysis.

Contribution

It introduces an empirical relationship linking oscillation frequency to inert gas properties and presents a novel calibration method for calorimetric measurements in sorption studies.

Findings

Oscillation frequency decreases from He to Kr.

Frequency depends on ionization potential and atomic mass of inert gases.

Thermal effects of sorption remain consistent across different inert gases.

Abstract

Oscillatory heat evolution in sorption of H2 and D2 in Pd can be induced by admixture of ca. 10 % vol. of inert gases He, Ne, Ar, Kr or N2 to either isotope prior to its contact with palladium powder. The oscillations are represented in a form of calorimetric time series, recorded using gas flow-through microcalorimeter at the temperatures of 75 {\deg}C for D2 and 106 {\deg}C for H2. For both D2 and H2, the oscillation parameters changes as a function of the kind of inert gas used: the amplitude increases and the frequency decreases in passing from He to Kr. An empirical dependence of the oscillation frequencies observed for various admixtures and normalized with respect to Kr has been found. Accordingly, the frequency is a function of a product of the first ionization potential and the square root of atomic mass of the inert gas (He, Ne, Ar, Kr or N2). On the other hand, invariance of the thermal effects of sorption is evident from the integrated areas under the calorimetric time series yielding the molar heats of sorption conserved, irrespective of the inert gas admixture. A novel calibration procedure has been devised in order to deal with an instability of calibration factor arising in desorption of H2 and D2 from Pd. A concept of dynamic calibration factor made it possible to obtain a good agreement between the heats of sorption and desorption of both H2 and D2 within individual sorption-desorption cycles for all inert gas admixtures.