Corrosion of alloy 800H and the effect of surface-applied CeO2 in a sulphidizing/oxidizing/carburizing environment at 700°C

The corrosion behavior of a wrought austenitic Fe-20Cr-32Ni steel, Alloy 800H, was studied in a simulated coal-gasification atmosphere at 700°C for exposure times up to 2500 hr. The influence of preoxidation and CeO2-surface application followed by preoxidation on the corrosion resistance of this material was assessed. The improvement in the corrosion resistance due to preoxidation of the blank material was small, whereas the effect of the CeO2-treatment was significant. This difference is thought to be due to better scale adherence in the case of CeO2-surface application

The properties of protective oxide scales containing cerium on alloy 800H in oxidizing and oxidizing/sulphidizing environments

The corrosion protection of oxide scales formed by electrophoretic deposition in a cerium-containing sol on Alloy 800H, a 32Ni-20Cr steel, followed by firing in air at 1123 K was studied in oxidizing and mixed oxidizing/sulphidizing environments at elevated temperatures. In particular, the influence of type of sol solvent, sol concentration, and thickness of deposited layer on the protection were studied. An optimized treatment was deduced which led to a significant improvement in corrosion behavior in oxidizing/sulphidizing environments.\u

Gedrag en modificatie van een warmtebestendig staal in kolenvergassings-atmosferen: corrosie, kruip en hun interactie

Mechanical Maritime and Materials Engineerin

Studies of the Oxidation Mechanism of Yttrium Implanted Chromium Using XAFS and GAXRD

The first stages of the oxidation of yttrium implanted chromium have been examined using EXAFS at the yttrium and chromium K-edges. Initially a thin chromia layer forms on the surface, and the implanted yttrium rapidly oxidises to form nanocrystallites of yttria. Upon further oxidation some yttrium is incorporated into the chromia scale, probably at the grain boundaries. The local atomic structure around these yttrium ions resembles that of YCrO4

Various X-ray diffraction investigations to study the oxidation mechanism of yttrium implanted chromium at elevate temperatures

Attention is paid on the role played by yttrium implantation on the isothermal oxidation behaviour of pure chromium at high temperature. Chromium specimens were oxidized in synthetic air at 800, 900 and 1000 $^{\circ}$C. Many techniques such as Thermogravimetry, Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD) and in situ XRD were used to characterise the oxide scale formed on chromium-implanted specimens. We have shown that the presence of yttrium limits the nitrogen diffusion through the scale into the metallic matrix. Thus the formation of chromium nitrides is reduced and a better scale adherence is observed. Implanted yttrium has a beneficial effect on the chromium oxidation up to 900$^{\circ}$C. We have shown, by in situ XRD, that it is related to the presence of the yttrium mixed oxide YCrO$_3$ in the scale at high temperature.Cette étude porte sur l'oxydation du chrome pur dans l'air synthétique à 800, 900 et 1000 $^{\circ}$C. Plusieurs techniques, telles que l'analyse thermogravimétrique (ATG), la microscopie électronique à balayage (MEB) et la diffraction des rayons X (DRX) in situ, ont été employées pour caractériser les couches d'oxyde formées sur le chrome implanté à l'yttrium. Nous avons pu montrer que la présence de l'yttrium limite la diffusion de l'azote au travers de la couche d'oxyde et dans la matrice métallique sous-jacente. Ainsi, la formation des nitrures de chrome est plus faible et une meilleure adhérence de la couche d'oxyde est observée. L'yttrium implanté montre un effet bénéfique sur l'oxydation du chrome jusqu'à une temperature de 900$^{\circ}$C. Nous avons pu montrer par diffraction des rayons X in situ que ce phénomène est lié à la présence de l'oxyde mixte YCrO$_3$ dans la couche formée à haute température

Cyclotron production of “very high specific activity” platinum radiotracers in No Carrier Added form

Prodn. and quality assurance methods for short-lived and high specific activity radionuclides were developed. Irradiations were performed with the Scanditronix MC40 cyclotron (K = 38; p, d, He-4 and He-3). In order to optimize the irradn. conditions for Pt radiotracer prodn., both thin-and thick-target excitation functions of natOs(\u3b1,xn) nuclear reactions were measured. A selective radiochem. sepn. to obtain Pt radiotracers in no-carrier-added form, was developed. Specific activity and chem. purity of the radiotracers were detd. by n activation anal. and at. absorption spectrometry. An isotopic diln. factor of 4850 was achieved