A Film-Thickness Determination of Nitrogen Diffusion in Zirconium Nitride

Abstract

Calculations of the diffusion coefficient for nitrogen in zirconium nitride are given in terms of a unidirectional, two-phase, volume-diffusion model. These calculations require the knowledge of both the thicknesses of nitride films and of nitrogen diffusion coefficients in the underlying zirconium metal 9 The values obtained can be represented by D ----7 9 • 10 -5 exp N---~ ZrN (--35,900/RT) cm2/sec for the temperature range of 650~176 Zirconium nitriding kinetics for extended exposures up to 900 hr are also reported 9 The portion of nitrogen confined to the s-zirconium phase amounts to about 80 w/o of the total nitrogen consumed during the over-all nitriding process 9The zirconium-nitrogen reaction has not attracted the interest of many investigators 9 Gulbransen and Andrew (1) described this metal-gas reaction in the temperature range of 400~176and Dravnieks (2) studied the kinetics at 862~176 Mallett et al. (3) measured the rate of surface reaction of zirconium with nitrogen in the range of 975~176 at 1 arm pressure. All these investigators report that the reaction conformed strictly to a parabolic relationship and that the reaction rate was much slower than with oxygen. These experiments were carried out for short time exposures, up to 7 hr.More recently, Rosa and Smeltzer (4) investigated nitriding kinetics in terms of models based on the growth of the reaction product layer and simultaneous dissolution of the reactant in the metal substrate. They found that over the temperature range 750 ~ 1000~and for exposures up to 170 hr, the reaction obeys the parabolic rate law. Using microhardness measurements, they determined the diffusion coefficient of nitrogen in s-zirconium as DN a-zr ~ 0 9 exp (--54,100/RT) cm2/sec, which to the best knowledge of the present authors is the only relationship available at this time.The purpose of this investigation is to evaluate the diffusion coefficients of nitrogen in hypostoichiometric zirconium nitride for the temperature range of 650 ~ 850~ in terms of data from nitriding kinetics and from the growth rates of the nitride layer. A comprehensive model relevant to the forthcoming calculations is presented. ExperimentalThe commonly used gravimetric method has been employed for measuring nitriding kinetics of 2 • 1 • 0.2 cm, 99.93 w/o (weight per cent) pure, zirconium samples 9 High-purity, better than 99.9 v/o (volume per cent) pure, nitrogen was passed through a cold trap and glass columns containing silica gel and phosphorous pentoxide to remove residual water vapor. Before exposing to nitrogen at a pressure of 400 Torr, specimens were treated by wet abrasion on 200 through 600-grit silicon carbide papers followed by final polishing on 8 and 1# diamond-dust impregnated laps, acetone washing, and careful drying to avoid water stains 9To prevent formation of a gap between the metal and mounting material, whenever microscopic measurements of nitride thicknesses had to be taken, all samples are cold mounted in "Hysol" self-setting epoxy resin and prepared for metallography by us...

Interfacial Reactions between Cu-Zr filler metal and alumina and kinetics of reaction layer growth

“…The activation energy for the growth was 126 kJ/mol. This value agreed well with the activation energy for the diffusion of oxygen in ZrO2 determined in other works [7][8][9].…”

Oxidation kinetics and oxygen diffusion in low-tin Zircaloy-4 up to 1523K

“…Rosa and Haget [6] got oxygen diffusivity in hypostoichiometric zirconia in the temperature range of 1048-1323 K, using oxygen diffusivity in a Zr and b Zr phases. Meanwhile, Debuigne [7] studied the oxygen diffusion in pure zirconium and got the oxygen diffusivity in a Zr , b Zr and zirconia phases.…”

Marker Techniques for Studying the Mechanism of Scaling of Metals Based on the Use of the O[sup 18](p,n)F[sup 18] Nuclear Reaction

“…This raises some question regarding the interpretation to be placed on the values for the diffusion coefficient of oxygen which have been derived from an analysis of the diffusion-controlled oxidation kinetics of Zr at temperatures between 400 ~ and 1050~ (65)(66)(67). Along with Cox and Roy (46), we believe that these derived or calculated values do not represent bulk diffusion coefficients; instead, they probably correspond to the product of the grain boundary diffusion coefficient and the effective cross-sectional area of highdiffusivity paths in the scale.…”