The properties of protective oxide scales containing cerium on alloy 800H in oxidizing and oxidizing/sulphidizing environments

The corrosion protection of oxide scales formed by electrophoretic deposition in a cerium-containing sol on Alloy 800H, a 32Ni-20Cr steel, followed by firing in air at 1123 K was studied in oxidizing and mixed oxidizing/sulphidizing environments at elevated temperatures. In particular, the influence of type of sol solvent, sol concentration, and thickness of deposited layer on the protection were studied. An optimized treatment was deduced which led to a significant improvement in corrosion behavior in oxidizing/sulphidizing environments.\u

The effect of thermal annealing on the properties of thin alumina films prepared by low pressure MOCVD

Thin amorphous alumina films were prepared on stainless steel, type AISI 304, by low pressure metal-organic chemical vapour deposition. The effect of thermal annealing in nitrogen (for 2, 4 and 17 h at 600, 700 and 800 °C) on the film properties, including the protection of the underlying substrate against high temperature corrosion and the chemical composition of the film, were investigated.\ud \ud Corrosion experiments performed at 450 °C in a hydrogen sulphide-containing gas, showed that the thermal annealing process had a detrimental effect on the protective properties of the alumina films. From FTIR and Auger measurements, it was found that the amorphous alumina, containing boehmite, converted to ¿-alumina during the annealing process

The mechanical properties of thin alumina film deposited by metal-organic chemical vapour deposition

Amorphous alumina films were deposited by metal-organic chemical vapour deposition (MOCVD) on stainless steel, type AISI 304. The MOCVD experiments were performed in nitrogen at low and atmospheric pressures. The effects of deposition temperature, growth rate and film thickness on the mechanical properties have been studied.\ud \ud The experiments were performed with the dynamic ultra-micro-hardness tester, DUH-200, and the scanning scratch tester, SST-101, both developed by Shimadzu. The DUH-200 is associated with crack formation during indentation. This technique involves a qualitative method to study the crack behaviour of the thin alumina films as well as a method to estimate the fracture toughness of the film and the film/substrate interface. The experiments performed with the SST-101 are based on the estimation of the film adhesion to the substrate by determining a critical load; the load where the film starts to spall or to delaminate.\ud \ud The best mechanical properties were obtained using low deposition rates and high deposition temperatures. Therefore, low-pressure MOCVD is recommended in addition to the deposition of alumina films at high temperatures

The pyrolytic decomposition of metal alkoxides (di-acetoxy-di-t-butoxy-silane, DADBS) during chemical vapour deposition of thin oxide films

In this study the effects of the nature of metal alkoxides on their vapour pressures and thermal decomposition chemistry are reported. The vapour pressure and the volatility of a metal alkoxide strongly depends on the steric effect of its alkoxy group.\ud \ud The thermal decomposition chemistry of one metal alkoxide (di-acetoxy-di-t-butoxy-silane, DADBS) has been studied by mass spectrometry at temperatures between 423 and 923 K. The pyrolytic products were acetic acid anhydride and 2-methyl propene. The acetic acid anhydride is formed at temperatures above 473 K and 2-methyl propene is formed above 673 K by a ß -hydride elimination mechanism. In these steps, a 6-ring intermediate is supposed to be formed. The silicon acid finally remaining is proposed to react by poly-condensation to SiO2 coatings or powder

Properties of protective oxide scales containing cerium on Incoloy 800H in oxidizing and sulfidizing environments. I. Constant-extension-rate study of mechanical properties

The mechanical properties of ceramic coatings containing cerium oxide, prepared by the sol-gel method and used to protect Incoloy 800H against aggressive environments, are reported. Deformation and cracking behavior in oxidizing and sulfidizing environments has been investigated by constant-extension-rate tests. Extension rates were between 9.3×10−6 and 3.7×10−7 sec−1 at 823 <T<973 K. Under these conditions, cerium oxide sol-gel-coated specimens do not show any failure at extensions of 1.0% or more, but in hydrogen, sulfide failure is found at lower extensions than in air

The effect of thermal annealing on the properties of alumina films prepared by metal organic chemical vapour deposition at atmospheric pressure

Thin films deposited at 330°C by metal organic chemical vapour deposition on stainless steel, type AISI 304, were annealed in a nitrogen atmosphere for 1, 2 and 4 h at 600, 700 and 800°C. The film properties, including the protection of the underlying substrate against high temperature corrosion, the chemical composition of the film and the microstructure, were investigated.\ud \ud Corrosion experiments performed at 450°C in a hydrogen sulphide containing gas, showed that the cracks in the alumina films almost completely disappeared after a post-deposition heat treatment, probably as a result of stress relaxation. The porosity of the alumina films was not affected by this heat treatment. X-ray diffraction measurements of these films, deposited at 330°C, revealed an amorphous structure. Owing to the thermal annealing process, the amorphous alumina films were converted to λ-alumina, and OH-groups disappeared.\u

Corrosion resistant coatings (Al2O3) produced by metal organic chemical vapour deposition using aluminium-tri-sec-butoxide

The metal organic chemical vapour deposition (MOCVD) of amorphous alumina films on steel was performed in nitrogen at atmospheric pressure. This MOCVD process is based on the thermal decomposition of aluminium-tri-sec-butoxide (ATSB). The effect of the deposition temperature (within the range 290–420 °C), the precursor vapour pressure (5.33×10-3−2.67×10-2 kPa), and the gas flow (6.5−12.5 1 min-1) of the MOCVD process have been studied in relation to corrosion properties at high temperatures. The corrosion experiments were performed at 450 °C in a gas atmosphere containing 1% H2S, 1% H2O, 19% H2, and balanced Ar.\ud \ud It was found that the amount of corrosion products on an alumina film (0.20±0.05 mg cm-2)-AISI 304 combination decreased with increasing deposition temperature of the coating. This was more pronounced for the products formed through the coating owing to a certain porosity. The crack density, where products were also formed, was almost unaffected.\u

Gas chromatographic-mass spectrometric analysis of tar compounds formed during pyrolysis of rice husks

Pyrolysis of agricultural waste to produce fuel gas involves formation of tars as noxious by-products. In this paper the qualitative analysis of tars formed during pyrolysis of rice husks is presented, based on identification by gas chromatography—mass spectrometry and interpolation of retention times on a polyaromatic hydrocarbon index scale. The influence of some reaction parameters on product formation is briefly discussed

Exploring the trade-off between quality and fairness in human partner choice

Partner choice is an important force underpinning cooperation in humans and other animals. Nevertheless, the mechanisms individuals use to evaluate and discriminate among partners who vary across different dimensions are poorly understood. Generally, individuals are expected to prefer partners who are both able and willing to invest in cooperation but how do individuals prioritize the ability over willingness to invest when these characteristics are opposed to one another? We used a modified Dictator Game to tackle this question. Choosers evaluated partners varying in quality (proxied by wealth) and fairness, in conditions when wealth was relatively stable or liable to change. When both partners were equally fair (or unfair), choosers typically preferred the richer partner. Nevertheless, when asked to choose between a rich-stingy and a poor-fair partner, choosers prioritized fairness over wealth—with this preference being particularly pronounced when wealth was unstable. The implications of these findings for real-world partner choice are discussed