Untitled

Abstract

A method is proposed to allow a more accurate evaluation of thermogravimetric data to identify diffusion or partial diffusion control of scaling kinetics. This method is based on the ® tting of mass-gain data to a parabola over a short time interval. The translation of the time interval over the entire test time period provides an actual instantaneous parabolic rate constant independently of any transient stage or simultaneous reaction steps. The usefulness and limitations of this procedure are illustrated from oxidation tests performed on several metallic materials (pure nickel, single-crystal superalloys, and Nb± Ti± Al alloy).

Effects of crystallographic orientation on the early stages of oxidation in nickel and chromium

“…Given that the grain size was the only microstructural variable that differed among the three, changes in oxidation rate can be attributed to a grain size effect. An increase in the total grain boundary length at the surface corresponds to an increase in the available high diffusivity paths for ion transport; this microstructural effect on oxidation rate has been suggested previously [5,6,9,16,[26][27][28]. The effect of grain size (or total grain boundary length) on oxidation rate may also be evident in the studies of orientation effects in polycrystals.…”

Oxidation of Stainless Steel Powder

“…1) has been applied to the experimental data, the mass gain is normalized by the surface area of the powder (Fig. 8) [7]. The fitted value of k p is equal to 2.5 9 10 -12 g 2 cm -4 s -1 in agreement with the literature data for Cr 2 O 3 growth (at 800°C: k p = 8 9 10…”

Corrosion behavior of Fe₃Al intermetallics with addition of lithium, cerium and nickel in 2.5 % SO₂+N₂ at 900 °C

“…This morphology was observed between 800 °C and 950 °C, and generally contains high concentration of vacancies, which can lead to cavities nucleation [32] . The EDS analysis carried out on the external surface on this intermetallic indicated that mainly is Al 2 O 3 , whereas the iron detected indicates that the formation of an iron oxide would be possible.…”