The Influence of Yttrium on High Temperature Oxidation of Valve Steels

Abstract

The influence of small amounts of yttrium, electrochemically deposited on the surface of four steels utilized in the production of valves in car engines, on the protective properties of the oxide scale and its adherence to the surface of the oxidized materials has been studied under isothermal and thermal cycle conditions. Oxidation measurements have been carried out at 1173 K. It has been found that yttrium addition improves considerably the scale adherence to the substrate surface, increasing thereby corrosion resistance of the studied materials.

Concentration of Point Defects in Metal Deficient Zn1-yO

“…Consequently, the discussed indirect method [8] cannot be used in its proposed form to determine the point defect concentration in p-type ZnO, because oxidation of zinc would take place at temperatures much lower than Tammann's temperature for ZnO. Therefore, it would not be possible to draw any rational conclusions concerning defect concentration in the investigated material.…”

“…Recently, a novel method has been demonstrated, which enables an indirect way of determining very low defect concentration in transition metal oxides by studying the influence of aliovalent metallic additions on the oxidation kinetics of given metals, in the reaction product of which the nonstoichiometry is to be calculated (i. e. from doping effect) [8]. The validity of the proposed method was illustrated on the example of nonstoichiometric nickel oxide, Ni 1-y O, in which defect concentration and the mobility of defects have been calculated.…”

“…Therefore, it would not be possible to draw any rational conclusions concerning defect concentration in the investigated material. Thus, the previously proposed indirect method [8] was modified so that it could be possible to determine native point defect concentration in metal-deficit Zn 1-y O.…”

Chromium-based oxidation-resistant coatings for the protection of engine valves in automotive vehicles

“…This apparatus is equipped with an electronic microbalance enabling the determination of weight gains of the oxidizing steel samples with an accuracy of the order of 10 -6 g. 17 On the other hand, the corrosion tests under the thermal-shock conditions were carried out in the experimental set, described elsewhere. 19 These experiments consisted of determining the mass changes of corroded samples as a function of the number of thermal shocks. Thus, a given sample was rapidly heated from room temperature up to 900°C and after the heat treatment at this temperature for two hours, it was cooled down rapidly (quenching) to room temperature.…”

The Interpretation of Marker Experiment Conducted during Formation of Higher Oxide on the Surface of Lower Oxide

“…The application of marker method in studies of the type of the predominant disorder in oxides growing not on the metal surface but on the surface of lower oxides, need some modification of either the experimental procedure and interpretation of the obtained results [10,15]. In this case, the markers are deposited not on the metal surface, but on the surface of lower oxide (Me a X b ).…”