In-situ monitoring of room temperature reactions of lanthanides with nitrogen and hydrogen at low pressures

TL;DR

This study investigates the low-pressure, room-temperature reactions of lanthanides with nitrogen and hydrogen, using in-situ conductance to monitor nitridation and ammonia formation, revealing the effects of oxygen presence and reaction rates.

Contribution

It provides the first in-situ measurements of lanthanide nitridation rates at low pressures and explores the impact of oxygen and hydrogen on these reactions.

Findings

Oxygen inhibits lanthanide nitridation at low pressures.

Nitridation rates vary among different lanthanides.

Ammonia formation occurs when lanthanides react with both N₂ and H₂.

Abstract

The dissociative chemisorption of molecular nitrogen on clean lanthanide surfaces at ambient temperature and low pressure is explored. In-situ conductance measurements track the conversion from the lanthanide metals to the insulating lanthanide nitrides. A small partial pressure of oxygen ($\sim 10^{-8}$ mbar) is shown to inhibit the nitridation of lanthanides at $10^{-4}$ mbar of N$_2$. The rate of nitridation as a function of nitrogen pressure is measured at low pressure for a series of lanthanide elements, gadolinium, terbium, dysprosium, ytterbium and praseodymium. Exposure of the lanthanide surfaces to both N$_2$ and H$_2$ results in the formation of NH$_3$.