A Preliminary Study of the Oxidation and Vapor Pressure of Chromium

Abstract

The high vacuum behavior of chromium at temperatures between 600 ~ and 1015~ was studied. Using decarburized specimens, chromium acts as a getter to oxygen, while above 825~ chromium vaporizes at an appreciable rate. The vapor pressure of chromium was determined between 885 ~ and 1015~ and a value of 93.9 -4-0.2 kcal per mole was found for /xH~. Oxide and nitride films have no appreciable effect on the vapor pressure curve in this temperature and thickness range. The reaction of carbon with the surface oxide occurs at temperatures of 800~ and higher with the carbon being removed as carbon monoxide.The oxidation reaction was studied over the temperature range 700 ~ to 900~ Except for the initial period of the reaction the data may be fitted by the parabolic rate 1 law. A plot' of log K/T vs. ~ gives a heat of activation of 66,300 cal/mole. Application of the transition state reaction rate theory to the rate data gives positive values of 10.7 to 13.5 entropy units for the entropy of activation.A comparison of the rate data with that of other metals shows that chromium has a good oxidation resistance although inferior to beryllium and the Ni-Cr series of alloys.

Paralinear Oxidation of Chromium in O2 + H2O Environment at 600–700 °C

“…1a), with k p values of 8.61 9 10 -15 g 2 /cm -4 s -1 at 600°C and 6.44 9 10 -14 g 2 /cm -4 s -1 at 700°C. Gulbransen et al [16], report mass gain curves up to 2 h at 700°C which are in good agreement with the present results. (Note that the parabolic rate constants in [16] are given in erroneous units).…”

“…Equation 21b implies that indeed, the early differential mass change between oxidation under wet and dry conditions is dominated by a term linear in time, for which from (21b) the slope k' s (compare (16)) is approximatelyqðCr 2 O 3 Þ Á k s . Finally, k s may be determined from (20) and (21a).…”

Oxidation or Nitridation Behavior of Pure Chromium and Chromium Alloys Containing 10 mass%Ni or Fe in Atmospheric Heating

“…The past studies of the oxidation kinetics of pure chromium were mostly conducted in pure oxygen atmosphere under the control of partial pressure, 12,14,17,19,20) and the parabolic rate growth of Cr 2 O 3 was realized in the temperature range of 1023 to 1373 K, while the effect of partial pressure of oxygen on the parabolic rate constant value was relatively small. The growth of the Cr 2 O 3 layer seems to be controlled by diffusion of the Cr cation through the Cr 2 O 3 layer because the voids were observed beneath the outer Cr 2 O 3 layer.…”

“…Early oxidation studies of chromium had been performed from the 1950s to the beginning of the 1970s, and several studies on high temperature oxidation or nitridation behavior of chromium under a pure oxygen or nitrogen gas atmosphere had been reported. [12][13][14][15][16][17][18][19] Lillerud and Kofstad summarized the past oxidation kinetics studies of pure chromium, and discussed in detail the causes for the large variation in parabolic rate constant values reported in numerous past studies. 20,21) However, very few studies of oxidation and nitridation of chromium-based alloys in atmospheric heating have been carried out, 16,22) and no detailed analyses of scale and subsurface regions have yet been reported.…”

Thermodynamic Modelling of Oxide Conversion Processes for Metals of Life

“…As should be noted here, the constructed installation for conversion of oxides allows creating a gaseous environment in two different ways: 1-using an oxygen pump [2], or 2-via injection of ethyl alcohol in the closed contour of the reactor [5]. In spite of the nearly, the same evacuation rate of oxygen in the reactor, the deoxidizing abilities of these methods are completely different (see Tables 1 and 2).…”