High-temperature Oxidation In Air Research Articles

鉄の高温酸化に対する酸化鉛の影響

鉄の高温酸化に対する酸化鉛の影響

Oxidation Behavior of SiC‐Whisker‐Reinforced Alumina‐Zirconia Composites

During high‐temperature oxidation in air, SiC‐whisker‐reinforced Al2O3—ZrO2 composites degrade by the formation of a whisker‐depleted mullite‐zirconia scale. The reaction kinetics have been studied as a function of time and temperature for composites with whiskers preoxidized for different times. The evolution of the microstructure has been investigated by optical, scanning and transmission electron microscopy. Possible reaction mechanisms have been discussed. A model compatible with our observations on Al2O3—ZrO2—SiC and the results reported in the literature for Al2O3—SiC whisker composites is proposed: The oxidation occurs at an internal reaction front. Oxygen diffuses along dislocations and grain boundaries through the mullite scale to react at this front with silicon carbide, thereby forming amorphous silica and graphite. Silica penetrates grain boundaries and further reacts with alumina and zirconia to form mullite and zircon, while the second reaction product, graphite, is oxidized into carbon monoxide when the reaction front moves deeper into the sample.

Behavior of aluminum nitride ceramic surfaces under hydrothermal oxidation treatments

Aluminum nitride (AlN) ceramics were subjected to various hydrothermal oxidation treatments, such as high-temperature oxidation in air at 1000 degrees C, water and high-pressure steam treatments, and copper sulfate plating solution at 70 degrees C for 8 h. The resulting physical and chemical changes of these surfaces were characterized using various analytical techniques, such as surface profilometry, scanning electron microscopy (SEM), thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS). These studies indicate that the AlN ceramic surfaces are altered significantly by the surface treatments. The interaction of water as well as steam with the AlN ceramic surfaces resulted in the formation of AlOOH and Al(OH)/sub 3/. The thermally grown oxide layer (Al/sub 2/O/sub 3/) on AlN is more stable and offers protection from subsequent wet treatments. Surface treatment using a copper sulfate additive plating solution revealed significant alteration in the surface roughness value, from an initial value of 0.5 mu m to a final value of 25.0 mu m during 8 h of treatment at 70 degrees C. SEM studies revealed the alteration of AlN surface morphology. The chemical change occurring on the AlN was analyzed using the XPS method, and results are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The effect of carbide and nitride additives on the oxidation resistance of silicon nitride ceramics

AbstractThe mechanism of high temperature oxidation in air (up to 1500°C) for silicon nitride materials containing SiC, TiN, TiC0.5N0.5, ZrN and EN was investigated. The effect of non-oxide refract...

Corrosion behaviour of boronized low carbon steel

In this paper we present the results of corrosion resistance of boronized 1020 steel in naphthenic acid and during high temperature oxidation. The boride layer, consisting of FeB in the outer region and Fe 2B in the inner zone, was found to be extremely resistant to naphthenic acid containing media, both in the liquid and vapour phase. During high temperature oxidation in air at 650°C a very thin, 10 M protective oxide layer was formed on the boronized steel, indicating that the boride layer acts as a barrier to oxygen and/or Fe diffusion. Finally both the morphology and distribution of FeB/Fe 2B layers changed during high temperature oxidation.

Surface enrichment of rhodium in Pd-Rh alloys after high temperature air oxidation

Foils of Pd-Rh alloys of two different compositions (85% Pd and 95% Pd) were heated in air in the temperature range 600–1100 °C, and their surface composition was determined by Auger electron spectroscopy and argon ion sputtering-depth profiling. Apparent surface enrichment of palladium as an oxide was observed for foils heated at or below 800 °C, whereas rhodium enrichment was found for foils heated between 850 and 950 °C. When the foils were heated at 1000 and 1100 °C, a slight (monolayer) enrichment of rhodium was observed. These changes in the surface composition can be attributed to the thermodynamic differences in the formation and decomposition of palladium and rhodium oxides and to diffusional processes in thick surface oxides formed on palladium-rich alloys.

Surface composition of polycrystalline Pd15Rh following high temperature oxidation in air

The composition of the near-surface region of Pd15Rh polycrystalline foil heated in air was investigated by sputter depth profiling using Auger electron spectroscopy. Profiles obtained from a series of samples heated for various times (0.25–8 h) at fixed temperature in the range of 875–1125 K confirm results of a previous investigation which found that a Rh-free oxide forms on the surface below approximately 1000 K. Secondary effects of ion sputtering were identified, and in particular, the preferential sputtering of palladium with respect to rhodium was correlated with oxygen concentration. The rate at which the Rh-free oxide layer forms on the surface was observed to increase with temperature up to 1000 K. The transition from a Rh-free to a Rh-enriched oxide layer at temperatures above 1000 K appears to involve the transport of Rh toward the surface in addition to the decomposition of palladium oxide. Depth-profile data are shown to provide useful input to further detailed study of the oxide by means of optical spectroscopy.

Application of DTA-DTG-TG complex thermal analysis to study diamond oxidation processes

The process of synthetic diamond high temperature oxidation in air has been studied by DTA-DTG-TG complex method of thermal analysis. The studies have been carried out on MTB 10-8 thermal microanalyser (SETARAM, France). Mechanism of diamond oxidation is found to be a multistage process dependent on reaction medium composition, crystals quality and their impurity content.

An X-ray Study of Strain Generation Behavior of a Steel-scale System during High Temperature Oxidation in Air

Stress generation behavior in a steel-scale system and its relations to the structural and compositional changes of the oxide scale and the steel during high temperature oxidation were investigated by an X-ray method. A high temperature furnace capable of in situ measurement of elastic strains by X-ray diffraction up to 900°C under controlled atmosphere was newly designed. With the furnace, mild steel SS 41A(1.19% Mn, 0.2% C) was oxidized in air over a temperature range of 250-500°C, the stresses and lattice constants of the steel and oxide were measured by using the sine ψ method with Kα1 radiations of Cr and Co. The stresses in the steel measured by Cr-Kα1 X-ray during oxidation at 500°C were found to become compressive after 100h oxidation, while those of pure iron, and of the steel measured by Co-Kα1 X-ray remained tensile under the same oxidation condition. A gradual decrease of lattice constant was observed in the steel after prolonged time of oxidation at 500°C, while those of the pure iron, and of the steel measured by Co-Kα1 X-ray were nearly constant. Those differences were attributed to the compositional changes of some constituents in the steel near the steel-scale interface.

Oxygen-18 study of high-temperature air oxidation of SO 2

The oxygen-18 enrichment in sulfates formed at high temperatures (475–500°C) by platinum-catalyzed air oxidation of SO 2 to SO 3 in humidified air, was found to be several parts per thousand higher than in the air oxygen, SO 2, or water vapor from which the sulfates were formed. Variation of the δ 18O in the sulfates showed little dependence on variation of the δ 18O in the water vapor. The mechanism of sulfate formation involved isotopic exchange between the air oxygen and water vapor, isotopic exchange between the water vapor and SO 2, and formation of the hydrate, H 2SO 4· 3H 2O. When Fe 2O 3 or V 2O 5 was heated in mixtures of air, water vapor, and SO 2, some of the SO 2 was analytically oxidized (via SO 3 formation) to sulfate of relatively high δ 18O and the remainder to chemisorbed sulfate of relatively low δ 18O. Charcoal and fly ash (containing unburned carbon and basic oxides) reacted with the SO 2 to yield chemisorbed sulfates of relatively low δ 18O.

High temperature air oxidation behaviour of “poor man” high manganese‐aluminum steels

AbstractThe behaviour of austenitic high manganese (19.8%–32.5%)aluminum (7.1%–10.2%) steels in high temperature air has been examined. Tests have been carried out in the 600–900°C temperature range for durations up to 200 h. The steels form a high manganese scale at high oxidation rates; aluminum does not contribute to the formation of this scale. Only a 1.5% silicon bearing steel shows a good oxidation resistance up to 700°C, the oxidation rate being lower because as shown by XPS analyses a silicon‐containing scale is formed. The oxidation resistance of these steels is always lower than that of conventional grades of austenitic stainless steels.

The formation of chlorodibenzo-p-dioxins by air oxidation and chlorination of bituminous coal

A well characterized bituminous coal was subjected to high temperature air oxidation and chlorination. After an extensive cleanup procedure, the reaction products were analyzed for chlorinated dibenzo-p-dioxins by gas chromatography-mass spectrometry. Substantial quantities of chlorodibenzo-p-dioxins, some of which are known to be highly toxic, were observed with chlorination by hydrogen chloride and chlorine gas.

Effect of heat treatment on the reactivity of polyarylene alkylenes

After high temperature oxidation in air, polyarylene methylenes are able to inhibit liquid phase processes of radical polymerization and oxidation of cumene. Polyarylene ethylenes oxidized in air do not have a similar effect. This behaviour is based on various products of thermal of oxidizing breakdown of polyarylene alkylenes. Heat treatment of polyphenoxy phenylene alkylenes in vacuum, in contrast to other polyarylene alkylenes, also results in an ability to inhibit liquid phase processes, which is evidently due to processes of regrouping.

High temperature oxidation of Fe13Cr xAl alloys in [formula omitted] vapour mixtures

High-temperature oxidation in air of Fe13Cr xAl alloys containing up to 4.5 Al has been studied in the temperature range 680–980°C. A primary aim was to study the oxidation as a function of the Al concentration in the alloys and the water vapour content (from 0.03 to 2.3 vol. % H 2O) in the oxidizing gas. The Fe13Cr alloy exhibits an initial protective behaviour due to formation of protective Cr 2O 3 and Cr 2O 3 Fe 2O 3 films. This protective stage is succeeded by breakaway oxidation due to depletion of chromium in the alloy beneath the oxide scale; double-layered, porous scales develop and chromium is internally oxidized. Under these conditions the oxidation rate increases significantly with increased water vapour content. Additions of aluminium modify the oxidation behaviour. At sufficiently high Al concentrations protective scales of AL 2O 3 (α-AL 2O 3) are found. The critical Al concentration necessary for selective Al oxidation increases as the temperature increases. Thus at 980°C 4Al is necessary while at 680°C 1Al provides excellent oxidation resistance. When continuous Al 2O 3 scales are formed the oxidation is not significantly dependent on the water vapour content in the air. At Al contents below the critical Al concentration, porous, multilayered scales are formed enriched with Al 2O 3 in the innermost layer. Under these conditions the oxidation rate increases significantly with water vapour content. The results strongly suggest that the increased rate of oxidation with water vapour content is due to gaseous transport across voids and pores with H 2O, H 2, and O 2 as carrier gases.