Diagnostic and modeling of N₂-H₂ discharges for iron nitriding^*

¹ CPAT, Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse, France
² Centro de Fisica de Plasmas, Instituto Superior Tecnico, 1096 Lisboa, Portugal
³ LPGP-Université Paris-Sud, 91405 Orsay, France
⁴ Departamento de Fisica, Instituto Tecnologico de Aeronautica, Centro Tecnico Aeroespacial, 12228-900 - Sao Jose de Campos, Brazil
⁵ LSGS, École des Mines, Parc de Saurupt, 54042 Nancy, France

Corresponding author: ricard.a@cpa22.ups-tlse.fr

Received: 26 December 1997
Revised: 25 May 1998
Accepted: 26 June 1998
Published online: 15 October 1998

Abstract

The production of N and H atoms has been studied in DC and HF N₂-H₂ flowing discharges and post-discharges in connection with nitriding of iron substrates. Experimentally, the N and H atoms have been detected by emission spectroscopy and Laser Induced Fluorescence (LIF). A strong increase of the Mayn gas atom density (N or H) was found when a small amount of a second gas (H₂ or N₂) was added. This increase in N or H atom densities is interpreted by a model describing the kinetics in the reactive gas volume and on the surface of the reactor walls (pyrex tube). In particular, it is shown that the destruction probabilities of N and H atoms on the tube wall are reduced by a factor of about 2 as a few % of H₂ or N₂ is introduced into N₂ or H₂. Correlations are established between the density of N and H atoms and the thickness and quality of iron nitride layers growing on iron substrates located within a reactor and placed in the post-discharge of a N₂−H₂ HF flowing discharge. Under the conditions of maximum N and H atom density, thick ϵ−Fe₂N_1−x layers without iron oxide superficial sublayer have been found on the iron surface.