Papers by Author: Zbigniew Grzesik

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Authors: Zbigniew Grzesik, Krzysztof Adamaszek, Zbigniew Jurasz, S. Mrowec
Abstract: The corrosion behavior of four valve steels (X33CrNiMn23-8, X50CrMnNiNbN21-9, X53CrMnNiN20-8 and X55CrMnNiN20-8) in combustion gases of fuel oil, containing different bio-component concentrations of (5 and 10 wt. %) has been studied under thermal shock conditions. It has been found that the addition of bio-components to the fuel oil decreases the corrosion resistance of all steels under investigation, this effect being the stronger, the higher was the concentration of bio-component addition. It has been shown, that in spite of bio-component addition, the X33CrNiMn23-8 steel containing the highest chromium concentration, behaved much better than three remaining steels due to the formation of the highly protective chromia scale.
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Authors: Zbigniew Jurasz, Krzysztof Adamaszek, Romuald Janik, Zbigniew Grzesik, Stanisław Mrowec
Abstract: Detailed investigations of nonstoichiometry as well as chemical and self-diffusion in nickel oxide have shown that doubly ionised cation vacancies and electron holes are the predominant defects in this material. The present work is an attempt to demonstrate that aliovalent impurities (Cr, Al, Na and Li) may considerably influence the concentration of these defects and, consequently, the oxidation rate of nickel at high temperatures. It has been shown that small amounts of tri-valent impurities (Cr, Al) bring about an increase of the oxidation rate, while mono-valent ones (Li, Na) decrease the rate of oxidation. These phenomena may satisfactorily be explained in terms of a doping effect. All experiments have been carried out as a function of temperature (1373-1673 K) and oxygen pressure (1-105 Pa) and consequently, it was possible to determine the influence of impurities not only on the oxidation rate but also on the activation energy of reaction and its pressure dependence. The results of these investigations could again be elucidated in terms of doping effect.
775
Authors: Zbigniew Grzesik, Marek Danielewski, Stanisław Mrowec
Abstract: The kinetics and mechanism of metal dusting corrosion of 9Cr-1Mo steel, commonly used in CCR platforming units, have been studied as a function of temperature (773 – 1173 K) in propane-butane atmosphere, being the mixture of 70 vol. % of propane and 30 vol. % of butane with the total pressure equal 105 Pa. The kinetics of corrosion have been studied thermogravimetrically in the apparatus enabling the mass changes of corroded sample to be followed continuously with the accuracy of the order of 10-6 g. It has been found that metal dusting corrosion in this atmosphere, modeling in some way industrial environments in petrochemical industry, is complex and two-stages of linear kinetics may be distinguished. In the first stage, which may be considered as an incubation period, the reaction proceeds with rather low rate, which increases dramatically in the second stage, the beginning of which depends strongly on temperature. Linear course of reaction indicates that chemical reactions and not diffusion processes determine the rate of corrosion. This conclusion is confirmed by the fact, that the layer of corrosion products is not compact but considerably porous.
477
Authors: Zbigniew Grzesik, Anna Kaczmarska, Stanisław Mrowec
Abstract: Nonstoichiometry and chemical diffusion in Co3O4 oxide have been studied as a function of temperature (973-1173 K) and oxygen pressure (30-105 Pa), using thermogravimetric techniques. It has been found that at very low oxygen pressures, close to the dissociation pressure of the oxide, interstitial cations and quasi-free electrons are the predominant point defects, while at high pressures cation vacancies and electron holes predominate. This behaviour is reflected in complex dependence of the deviation from stoichiometry, y, in the Co3±yO4 oxide on oxygen pressure. At low pressures, namely, deviation from stoichiometry decreases with increasing oxygen pressure, reaching virtually constant value in intermediate pressures and increases at highest pressure range. Finally, these data as well as the results of kinetic rate measurements of Co3±yO4 formation have been utilized in calculating the chemical diffusion coefficient as a function of temperature.
421
Authors: Stanisław Mrowec, Zbigniew Grzesik
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Authors: Zbigniew Grzesik
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Authors: Zbigniew Grzesik, Stanisław Mrowec, J. Dąbek
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Authors: Zbigniew Grzesik, A. Poczekajło, S. Mrowec
Abstract: Because of considerable experimental difficulties, the defect structure of NiS2 has not been elucidated so far. The first step in these investigations was to explain which sublattice of this compound is predominantly disordered. In order to solve this problem, the mechanism of sulphidation of NiS to NiS2 has been studied using marker technique. These experiments have been carried out at temperatures 823-923 K in sulphur vapors under pressure 103 105 Pa. It has been found that the predominant defects in NiS2 occur in cation sublattice. The problem then arised whether these defects are cation vacancies or interstitial cations. This phenomenon could have been explained in studying the kinetics of NiS sulphidation as a function of sulphur activity. It has been found that the parabolic rate constant of this reaction increases with sulphur activity, strongly suggesting that cation vacancies, and not cation interstitials, are the prevailing defects. If, namely, interstitial cations would prevail, the sulphidation rate would be virtually pressure independent.
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