Papers by Author: Renaud Podor

Abstract: The determination of the corrosion processes of metallic materials in glass melts is of great interest for glass makers. Our attention has been specifically focussed on Cr-bearing alloys that form Cr2O3 layers when they are immersed in a silicate melt and offer a good resistance to melt corrosion. The comprehension of the corrosion processes has been extensively studied in the last 10 years using stationary electrochemical techniques. Results relative to the thermodynamic state were described. Complex impedance spectroscopy offers the possibility to determine the reaction kinetics in terms of limiting processes. Three chromium rods were directly immersed in molten glass at T=1050°C, maintained respectively in the active, passive and transpassive state and studied using electrochemical techniques. The results that are reported in this paper show a good agreement between complex impedance spectroscopy data, scanning electron microphotographies of the glass/metal interface and previous results obtained using stationary electrochemical techniques.

Abstract: Most of equipments used in glass industry are superalloys containing up to 30 wt% chromium. The ability of these alloys to resist against silicate melt corrosion is directly linked to the formation of a chromia (Cr2O3) layer at the alloy/melt interface which can be protective under particular conditions. These conditions have been previously identified and are the temperature, melt composition and redox conditions. The aim of the present study is to establish the relationship between the protective (or non protective) behaviour of the chromia layer with the solubility of chromia in silicate melts under given conditions. The combination between results from the electrochemical study of pure chromium corrosion and total Cr solubility in Na2O-xSiO2 melts clearly indicates that both parameters are linked: the lower the total Cr solubility, the better the Cr is corrosion resistant.

Abstract: The knowledge of the quinary Pb–Bi–O–Fe–Hg is necessary for understanding the degradation mechanisms of the T91 steel used as structural material in future ADS nuclear reactors. In this device, the steel will be in direct contact with the liquid spallation target (which is constituted by lead or lead-bismuth eutectic) surrounded by a reduced oxygen pressure atmosphere. In the present work, the characterization of the pseudo-binary PbO–Fe2O3 cut has been performed. In order to complete the available data in the literature, some experimental investigations by DTA, isothermal annealing, SEM and EPMA have been done. These results have allowed proposing a thermodynamic assessment using the Calphad method by the ThermoCalc software.

Abstract: The efficiency of Waste-to-Energy (W-t-E) boilers is affected by fireside corrosion of the heat exchangers that involve unexpected shutdown of facilities for repairs and limit the increase of steam conditions used to produce electricity. The parameters governing fireside corrosion are various and mechanisms are very complex, nevertheless, they are relatively well documented in the literature. In this paper, a laboratory-scale corrosion pilot, which reproduces MSWI boilers conditions, is described. The specificity of our approach includes simultaneous simulation of the temperature gradient at flue-gas/tube interface, the velocity of flue-gas and ashes. Corrosion rates obtained on Tu37C carbon steel at a metal temperature equal to 400°C and a flue gas temperatures of 650°C and 850°C (1100 ppm HCl, 110 ppm SO2 and synthetic ashes free of heavy metals) are respectively around 1.6 2m/hour and 5.6 2m/hour. Preferential metal loss, attributed to erosion-corrosion phenomena, is also observed at low flue-gas temperature (T=650°C) on the face exposed at 90° to the flue-gas. The analysis of corrosion scales demonstrates the reproducibility of results and the reliability of corrosion mechanisms determined from experiments, with degradation observed similar to superheater tubes from EfW facilities. Thus, the corrosion pilot developed can be used as an accurate simulator of the environment encountered in MSWI.