Ppm O2 Research Articles

Stratified oxide scale growth on two Cr-Ni steels oxidized in high-pressure steam at 800�C

A commercial 18% Cr-11% Ni steel and a laboratory-made 21% Cr-11% Ni alloy have been oxidized in steam at 50 atm pressure and with approximately 0.2 ppm O2 at 800°C for 50–1000 hr. The oxide scales have been studied by optical microscopy, replica electron microscopy, x-ray, and selected-area-electron diffraction and microprobe analysis. The diffusion processes have been studied by gold markers and autoradiography by means of the reaction18O (p, n)18F. On both materials internal oxidation in combination with external scale formation is observed. The interface between the external scale and the inner internally oxidized scale coincides very closely with the original metal surface. The oxide phases present have been identified. The scale is of fairly even thickness on the 21% Cr-11% Ni alloy and grows by a cubic rate law. The scale on the commercial steel is of very irregular thickness; areas with protective Cr-oxide alternate with areas of the above-mentioned structure, so-called nodules. The zones of internal oxidation in the nodules are frequently intersected by bands of compact oxide. The growth mechanism of the nodules is discussed in terms of the theory for internal oxidation. The reason for the beneficial effect of increased Ni content with constant Cr content is discussed briefly.

Technique for Studying the Kinetics of Intergranular Crack Nucleation on AISI Type 304 Stainless Steel in Oxygenated Water at 289 C

Abstract The design of a system with which to study the kinetics of intergranular crack nucleation on Type 304 stainless steel in water containing 100 ppm O2 at 289 C (554 F) is described. A bellows loading system capable of holding samples in simple uniaxial tension is discussed, and the results of constant load experiments on sensitized Type 304 stainless steel are presented. The elongation-time behavior of the above material is characterized by a distinct “stair-step” type of curve which is taken to indicate the presence of a mechanical event in the cracking mechanism. The nucleation or induction time, Tn, is shown to increase markedly as the applied stress was decreased from 30 to 20 kpsi. Cathodic protection inhibits crack initiation indefinitely, thereby indicating the presence of an electrochemical event in the cracking mechanism. Crack nuclei are shown to be associated with regions of plastic deformation, and can in certain instances initiate and propagate transgranularly down carbide decorated sl...

The Influence of Hydrogen, Oxygen, and Ammonia on the Corrosion Behavior of Plain Carbon Steel in High Temperature Water

Abstract The corrosion behavior of plain carbon steel in high temperature water has been studied using electrochemical polarization techniques. The influence of oxygen, hydrogen, and ammonia on the corrosion behavior has been studied over the range < 0.1–100 ppm. Potentiostatic anodic polarization data indicate that only oxygen has any effect on the anodic dissolution kinetics of carbon steel at 289 C (552 F). Controlled potential corrosion experiments at highly noble potentials in oxygenated water did not produce any form of localized corrosion. Cathodic Tafel polarization data indicate that the primary cathodic partial process during corrosion on ammonia and hydrogenated solutions is the reduction of hydrogen ions. Reduced steady-state corrosion rates observed in ammoniated solutions are due to the severe reduction in the limiting diffusion rate of hydrogen ions because of a simple pH effect. In oxygenated solutions, over the range 0.1–50 ppm O2, the major reduction process is the reduction of H+. At 50–100 ppm O2 levels, however, the reduction process changes to O2 + 2H2O + 4e → 4OH−, with the formation of a protective oxide film and a reduction of the steady-state corrosion rate to 0.2 mdd. Linear polarization studies indicated that the steady-state corrosion rate of carbon steel on hydrogenated solutions is relatively independent of H2 content. The corrosion rate on ammoniated solutions decreased with NH3 content over the range 1–100 ppm NH3. Corrosion rates in oxygenated water over the range < 0.08–100 ppm increase through a maximum at approximately 50 ppm then decreases to a low value at 100 ppm. This behavior is interpreted by the formation of a protective oxide film which is dependent on oxygen content. X-ray diffraction studies indicate the presence of a duplex oxide film in high oxygen solutions consisting of γFe2O3 and Fe3O4. At lower oxygen levels, only αFe2O3 was observed and also in ammoniated solutions. In hydrogenated solutions, with the highers corrosion rates, only αFe2O3 was observed on the surface.

高圧処理による自由転位の増殖

Observations by transmission electron microscopy on the pressurized iron thin foils have confirmed that the density of dislocations increases in the region near the particles of second phase upon hydrostatic pressure exposure at 10 or 14 kb. These pressure-induced dislocations are observed around FeO particles of several microns in diameter but not around the small carbides (size effect). These observations are in agreement with the following experimental results. (1) The most significant pressure effect, i.e. the lowering of yield stress and the decrease of the Lüders elongation are found for iron containing 600 ppm O2 but no effects are found for a zone refined iron the oxygen content of which is 68 ppm. (2) The pressure effect on iron containing 200 ppm O2 is not prominent, although the iron contains a great number of fine carbide particles.The shear stress arising from the surface of inclusions by the volume indentation effect under a pressure of several thousand atmospheres is about one hundredth of the stress to nucleate dislocations, which leads to the conclusion that pressurization unpins old dislocations and multiplicates them around large inclusions.

Low-octane gasoline raffinates as raw material for the production of lower olefins

Climate change is one of the most pressing matters of modern society. The current models for assessing CO2 emissions do not consider the oxygen drainage from the atmosphere. Oxygen depletion is happening at rates much higher than the natural capacity of the planet to regenerate the oxygen back to the atmosphere through photosynthesis. On average, each 1.0 ppm increase of CO2 brings a corresponding loss of 2.15 ppm of O2 in the atmosphere. The present work provides a new methodology for emissions assessment that includes oxygen usage called Atmospheric Profit and Loss Score. Simple examples are provided to demonstrate that, once oxygen is included in the assessment, renewable and photosynthesis-based processes that follow the sustainability criteria become much more attractive to society.