Kinetics and Mechanism of Nickel-Sulfur Reaction

Abstract

Kinetics and mechanism of the reaction between nickel and sulfur vapors were investigated in the temperature range 480~176 under atmospheric pressure. The sulfurization of nickel has been found to follow, under these conditions, the parabolic rate law. The activation energy of this process amounts to 22 kcal/mole. The examination of x-ray patterns of the scale formed on the surface of the metal has demonstrated that this scale layer is composed almost entirely of NiS. Morphologic investigations show that the scale is composed of two distinct layers. The outer layer, constituting the main part of the whole scale, is compact, polycrystalline, and exhibits an ordered growth texture. The inner layer is porous and does not exhibit any growth texture. The investigations carried out with the aid of the radioactive sulfur isotope *~S have demonstrated that the sulfide scale on nickel is formed exclusively by the outward diffusion of the metal.The confrontation of experimental data with the results obtained by Dravnieks (1) leads to the assumption that the mechanism of the sulfide scale formation on nickel does not depend on the state of aggregation of the oxidizing medium. (2) have demonstrated that the sulfurization of nickel in molten sulfur in the temperature range 205o-445 ~ follows the parabolic rate law. On the other hand Hauffe and Rahmel (3), as well as Pfeiffer (4), stated that if the reaction was carried out in sulfur vapor at 630 ~ under a pressure not exceeding 1 mm Hg the course of the reaction could be described with a linear rate law. Dravnieks (1) and Wagner and Lichter

The sulphidation of metals and alloys

“…19 ,20 Although kinetics that at first sight appears to be parabolic may be observed, subsequent analysis in some cases shows that the rate law in fact is only approximately parabolic, and the overall kinetics could be better described as 'protective'. This situation has for example been reported by Rickert,49 by Rickert and 0'Brianin,50 and by Czerski et al 51 during the interaction between silver or copper and sulphur. These authors observed that in the early stages of sulphidation a time law prevails (linear) which is independent of the thickness of the Ag 2S (or Cu 2S) layer.…”

“…This result for NiS appears at first sight to be anomalous, at least in view of the evidence of cation vacancies in the lattice obtained from many sulphidation studies. [36][37][38][39] Bearing in mind the electrical-conductivity data both for pure nickel sulphide and for material doped with silver sulphide, reported earlier in this section, which again did not fit in with the other evidence regarding the defect ionic species in NiS, it must be concluded that the electrondefect equilibria in NiS are not as yet satisfactorily explained. Thermoe1ectric-power measurements have also been carried out on chromium sulphides of variable stoichiometry.…”

Comparison of the Isothermal Oxidation Behavior of As-Cast Cu–17%Cr and Cu–17%Cr–5%Al Part I: Oxidation Kinetics

“…The oxidation of pure copper has been extensively studied by several investigators since the 1930s [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. These studies have elucidated the oxidation rate kinetics for copper [6-8, 10, 14-16, 19, 22] while largely confirming the applicability of the Wagner's parabolic oxidation rate theory for this metal above 473 K [14,15].…”

Brief review of oxidation kinetics of copper at 350 °C to 1050 °C

“…[6][7][8][9][10] The activation energies (Q a ) for the copper oxidation reported in the literature are shown in Table I. [6][7][8][9][10][11][12][13] On the basis of their change in slope, the Arrhenius plots in Figure 1 are roughly divisible into three regions: a high temperature region (900 °C to 1050 °C), an intermediate temperature region (600 °C to 850 °C), and a low temperature region (350 °C to 550 °C).…”