Nils-Gösta Vannerberg

The influence of silicon on the oxidation properties of iron

Abstract Five Fe—Si alloys containing between 0·06 and 5·3 w/o have been oxidized in a gaseous mixture of 20 w/o oxygen in argon. The oxidation temperatures were 500°, 625°, 800°, 900° and 1000°C. The reaction kinetics have been studied gravimetrically and the oxidized samples examined microscopically, with an electron microprobe and with X-ray methods. The detrimental effect of silicon on the oxidation rate of iron is most pronounced at high temperatures and silicon contents. For comparative purposes, the oxidation of two chromium-nickel alloyed steels has been studied at 800° and 1000°C.

The influence of the relative humidity and corrosion products on the adsorption of sulfur dioxide on metal surfaces

The adsorption of sulfur dioxide on metal surfaces has been followed using an S-35 isotope. Experiments have been performed with 1·0 · 10−5 per cent SO2 (0·10 ppm) at r.h. between 50 and 98 per cent. The adsorption properties of polished iron, zinc, copper and aluminium samples have been compared with those of pre-exposed samples of these metals. Measurements have shown a pronounced dependence of the adsorption rate on the humidity. Almost quantitative adsorption of sulfur dioxide has been obtained on pre-exposed iron samples at r.h. ⩾ 80 per cent. Remarkably low adsorption capacities at humidities <90 per cent have been found for the corrosion products of copper and aluminium. Changes in the adsorption rate with time have been used to study the corrosion initiation on polished iron surfaces.

NUCLEATION AND FORMATION OF ZINC PHOSPHATE CONVERSION COATING ON COLD-ROLLED STEEL

Abstract The basic reactions in the nucleation and formation of zinc phosphate coatings on cold-rolled steel have been studied. The iron oxides on the steel surface were found to be crucial for the formation of a fine-grained phosphate coating. The best result was obtained if the oxide layer consisted mainly of γ-Fe2O3. The temperature of the steel also influences the nucleation of zinc phosphate crystals, whereas accelerators, such as nitrate and nitrite, have little effect on the number of nuclei formed on an oxidized surface. The accelerators increase the growth rate of the phosphate crystals and thereby shorten the time needed for the formation of a covering phosphate coating.

Reaction between SO2 and wet metal surfaces

The drastic corrosion of Fe in an atmosphere containing SO2 has been shown to be dueto the catalytic effect of Fe oxides and hydroxides on the formation of H2SO4 from SO2, H2O and O2. Measurements performed on samples of Fe and rust in an atmosphere containing water vapour, O2 and SO2 at 95 ± 1°C indicate an almost quantitative oxidation of adsorbed SO2 to H2SO4. The protons thus formed accelerate the corrosion attack on materials containing Fe. The rate of production of protons from samples of Cu and Al is low and these metals also show a relatively good resistance to SO2. Despite a low proton production rate, however, samples of Zn are severely corroded in atmospheres containing sulphur dioxide, which indicates a corrosion mechanism differing from that proposed for Fe.

SOx adsorption/desorption processes on γ-alumina for SOx transfer catalyst

Abstract The SOx (SO2 and SO3) adsorption/desorption for the different conditions simulating the Fluid Ctalytic Cracking (FCC) operation has been studied thermo-gravimetrically for γ-alumina. The presence of O2 and the absence of CO are necessary in order to obtain sufficient adsorption at 700 °C. This is in accordance with the fact that the use of γ-alumina as an SOx transfer catalyst requires the regenerator to be operated in the total CO-combustion mode. The desorption in different reducing atmospheres at 500 °C shows that H2 does not react with adsorbed SOx. H2S and LPG (propane) do react with adsorbed SOx but the desorption rates are low. Therefore the desorption in the riser will be negligible and most of the desorption will take place in the stripper. Changing the operating conditions towards longer solid residence time in the stripper and higher concentrations of H2S and hydrocarbons in the stripper steam, e.g. by adding small amounts of H2S and hydrocarbons to the stripper steam, should improve the performance of γ-alumina as an SOx-transfer catalyst. The thermal stability of γ-alumina does not seem to be a critical factor at the simulated FCC conditions which have been used.

The effect of the oxygen pressure and the growth of whiskers on the oxidation of pure Fe

The weight increase curves of pure iron specimens cold-worked by abrasion with SiC and 7-μ diamond paste have been registered as a function of pressure and temperature. The oxidation rate increases with temperature and pressure when the pressure is raised from 0.02 to 0.2 bar. When the pressure is further increased to 1.02 bar at 500 and 625°C the oxidation rate decreases. This decrease is attributed to an orientation of the oxide grains in the α-Fe2O3 surface.

A microscopic study of steel surfaces exposed to a humid SO2-containing atmosphere

Abstract Electropolished and etched steel samples have been exposed to a humid, sulphur dioxide-containing atmosphere under controlled conditions. The surface structure of the samples and the distribution of the points of attack after exposure have been studied with a scanning electron microscope.

An X-ray photo-emission spectroscopy study of iron-oxide, iron-benzoic acid inhibitor films

Abstract Surface oxide and benzoic acid films on pure iron have been examined by X-ray photo-emission spectroscopy (XPS). The passivation and inhibitor properties of these films is correlated with chemical features arising in the spectra. Surface hydroxyl groups are observed on surfaces having good passivation properties. Benzoic acid forms an oriented salt film.

The corrosion of unprotected steel in an inert-gas atmosphere containing water vapour, oxygen, nitrogen and different amounts of sulphur dioxide and carbon dioxide

Abstract The atmospheric corrosion of a commercial steel has been studied in a nominal inert gas. This gas exists inside the cargo tanks of some crude-oil tankers. The gas contained 3.0–21%O 2 , 0–12%CO 2 , 0–300 ppm SO 2 ; the balance was N 2 . Relative humidity was 90% at 295 K (22.0°C). In contrast to the behaviour at moderate concentrations of SO 2 at high concentrations protective films were formed on the surface of the steel. A mechanism for the process is given. Corrosion products were studied using X-ray, i.r. and ESCA techniques. The following phases were identified: FeS, α-FeSO 3 ·3H 2 O, γ-FeSO 2 ·3H 2 O, FeSO 3 ·2H 2 O and FeSO 4 ·7H 2 O. Crystallographic data of the previously unknown phases γ-FeSO 3 ·3H 2 O and FeSO 3 ·2H 2 O are given.

The Structure of Cesium Hydrogensulfite

The structure of the hydrogensulfite ion has been determined for the first time in CsHSO 3 which crystallizes in space group R3m with a = 4.6721 (7) ,/k, a = 85.31 (1) °, Z = 1. The absolute configuration of the structure was refined to R = 0-014 for 506 independent reflections. The S atom has tetrahedral coordination, with three pyramidal S-O bonds and an S-H bond in the fourth direction. The S-O distance is 1.454 (2),~, and the O-S-O angle 113.1 (2) °. The bond distance is similar to that in the SO ]- ion, while it differs markedly from that in the SO]- ion. The Cs + ion is nine-coordinated with Cs-O distances of 3.231 (4)3.249 (4) A.