Papers by Keyword: High Temperature Oxidation

Abstract: One candidate material for boiler components in supercritical water gasification (SCWG) processes is oxide dispersion-strengthened steels (ODS), which can resist aggressive humidified atmospheres under high pressures and temperatures. The high-temperature oxidation resistance of ODS steel can be improved by adding nanooxide particles such as Al₂O₃. In this study, the corrosion resistance of Fe-18Cr ferritic ODS steel reinforced with different nanoAl₂O₃ between 0.5-3.0 wt% in a humidified atmosphere containing 80% H₂O at 800 °C was investigated. The lump phase of chromium and nanoAl₂O₃ particles were dispersed on iron matrixes after sintering. Several pores occurred in the Fe-18Cr ODS matrix due to air entrainment during forming processes, but they decreased after reinforcing with the nanoAl₂O₃. Adding 0.5 wt% nanoAl₂O₃ decreased the porosity of the ODS steel by around 1.8 times. After the oxidation test for 10 hours, the mass gain of the ferritic ODS steel decreased by about 9 % when the nanooxide was added. Fe-Al-rich oxides were found with hematite and Fe-Cr spinel oxide layers, which increased the oxidation resistance of the ODS steel.

Abstract: This study examines the application of depositing Ni5Al and Fe13Cr alloy coatings onto AISI 321 stainless steel substrates and evaluates their mechanical and oxidative resistance qualities. The Ni5Al coating was found to have a hardness value that is 38% greater than the Fe13Cr coating, as determined by Micro-Vickers hardness testing. Additionally, the Ni5Al coating displayed a more homogenous microstructure. The cyclic oxidation measurements provide evidence of the better performance of the Ni5Al coating in elevated temperatures. The better performance can be attributed mainly to the presence of Al₂O₃ as the predominant oxide, which is well-known for its exceptional heat resistance and protective properties. However, the overall performance of the Fe13Cr coating is negatively impacted by the presence of Fe₂O₃, even though there are other favorable oxides such as Cr₂O₃, NiCr₂O, NiO, and Mn₂Co₃. The Fe₂O₃ presence greatly diminishes the oxidative stability of the Fe13Cr coating. The results emphasize the capability of Ni5Al as a highly efficient coating material for applications that require exceptional hardness and strong resistance to oxidation. This indicates that it is suitable for high-temperature industrial applications where durability and performance are crucial.

Abstract: Owing to its fairly higher melting point (2468°C) and superior thermal conductivity, Niobium alloys are rendered as candidate material for high temperature applications, where state of the art Nickel base super alloys cannot be used. Its applications possess wide range of aerospace components mainly encompassing aircraft exhaust chambers, thrust augmenters, rocket engines and other industries such as chemical and petrochemical. The only limitation with niobium alloys is their inferior oxidation resistance, which can be tackled by developing a high temperature oxidation resistant coating. In this regard, Nickel Aluminide (NiAl) having a melting point of 1638°C embraces a paramount importance amongst the coating categories. In this study, NiAl was synthesized using vacuum melting and strip casting followed by ball milling. The powder was coated on C-103 Niobium alloy specimens using air plasma technique and evaluated for high temperature stability. It was deduced that the coating was exceptionally stable up to 1234 °C in ambient conditions.

Abstract: The addition effect of Mn alloying element on the oxide growth behavior of 800H nickel-based alloy has been study in this paper. The alloy was experienced a cyclic oxidation at 900 °C. The cyclic oxidation test was carried out at oxidizing temperature for one hour followed by cooling at about 200 °C for 20 minutes for each cycle. The test samples were exposed to the cyclic condition up to 150 cycles. The oxidized samples of selected cycles were characterized in term of oxidation kinetic, phase analysis using x-ray diffraction (XRD) spectrometer and oxide scale morphology in plan and cross-sectional view by using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) spectrometer. As a results, the oxidation kinetic exhibited a weight gain pattern as the exposure cycle increase. Several protective oxide phases which are Cr₂O₃ and MnCr₂O₄ oxides were formed. In addition, continuous oxides scale was formed on the sample surface with evidence of Cr-Mn and Cr-rich oxide as detected by EDX analysis.

Abstract: In this research, a 800H Ni-based alloy was experienced a solution treatment procedure at two different temperatures. The solution-treated alloys were undergo a high-temperature oxidation under isothermal conditions at 500°C for 500 hours in laboratory air. The alloy was characterized using OES, XRD, SEM and FESEM equipped with an EDX spectrometer. It was found that the solution-treated alloy at 950°C produced a small grain size, and alloy treated at 1100°C produced a large grain size. The XRD results show that various oxides phases were detected. The oxidation kinetics followed the parabolic rate law indicating the oxide was formed based on diffusion-controlled oxide growth rate. The alloys with small grain sizes exhibited a lower oxidation rate, hence have excellent oxidation resistance. This is due to the accessibility of the high ion diffusion route through the grain boundaries of small-grained alloy and thus permits the speedy establishment of the initial oxide layer. Uniform oxide scale formed on a small-grained oxidized sample with visible overgrow discrete oxide particle comprised of Ti-rich oxide. The large-grained oxidized sample indicates evidence of oxide exfoliation indicating poor oxidation protection.

Abstract: The evaporation of volatile chromium species from ferritic stainless steels (FSSs) used as interconnect is well-known as degradation source for planar solid oxide fuel cell (SOFC) stacks. This work presents a feasibility study to quantify chromium evaporation from FSSs. It is based on measuring carbon dioxide produced by an intermediate reaction. Cr evaporated is collected by sodium carbonate forming sodium chromate and carbon dioxide. Measuring the resulting carbon dioxide allowed to quantify online the amount of reacted chromium with the carbonates. The post-experiment quantification of sodium chromate confirmed the applicability of the proposed method.

Abstract: This paper investigates the performance of Fe-33Ni-18Cr alloy at high temperature oxidation. The samples were isothermally oxidized at three different oxidation temperatures, namely, 600 °C, 800 °C and 1000 °C for 150 hours. This alloy was ground by using several grits of SiC paper as well as weighed by using analytical balance and measured by using Vernier caliper before oxidation test. The characterization was carried out using scanning electron microscope (SEM) equipped with energy dispersive x-ray (EDX) and x-ray diffraction (XRD). The results show that, the higher oxidation temperatures, the weight gain of the samples were increase. Sample of 1000 °C indicate more weight gain compared to samples oxidized at 600 °C and 800 °C. The kinetic of oxidation of all samples followed the parabolic rate law. The surface morphology of oxide scale at lower temperature is thin and form a continuous layer, while at high temperature, the oxide scale develops thick layer with angular oxide particles.

Abstract: This chapter primarily reviews the nature of water vapour when it presents in bulk gas. The change in a ratio between water vapour and corresponding dissociated hydrogen, which determine the thermodynamic stability of the oxide formation, is analysed when the oxidation kinetics are linear and parabolic. When water vapour reaches the solid/gas interface, chromium species volatilisation and oxidation controlled by surface reaction can occur. The adsorbed water vapour can be further incorporated into the oxide possibly in the form of hydrogen defects. The role of these defects on altering the defect structure of the oxide is discussed. Finally, characteristics of the oxide scale on stainless steels formed in the atmosphere containing water vapour are reviewed.

Abstract: This chapter introduces stainless steels and their classification for the high temperature applications. The enabling theories for the high temperature corrosion i.e. thermodynamics and kinetics are further addressed. The basic concept of thermodynamics is given and the stability of the formation of thermal oxide on stainless steel is exemplified. Types of defect in the oxide and Fick’s first law for the diffusion of defect though the oxide are introduced. Oxidation kinetics is explained with the emphasis on the derivation of the parabolic rate law.

Abstract: This chapter is dedicated to the description of high temperature oxidation of both chromia and alumina forming alloys. The defect structures of iron and chromium are firstly reviewed. The effects of elements on stainless steel oxidation behaviour are further addressed. For the chromia-forming stainless steel, the oxidation rate is reduced with the increased silicon content but not in a monotonic manner. Titanium and niobium can reduce breakaway oxidation of Fe–18Cr–10Ni austenitic stainless steel. Titanium can enhance the adhesion of scale to the Fe–18Cr by mechanical keying effect of TiO₂ formed at the steel/scale interface. For the alumina-forming stainless steel, the formation of alumina and its transformation during oxidation are reviewed. Chromium can be added to reduce the critical aluminium content in the steels in order to form alumina at high temperatures. The addition of reactive elements with appropriate level can improve scale adhesion and reduce the steel oxidation rate. Refractory element like molybdenum can increase strength of material but also accelerate the oxidation rate of the steels containing reactive elements. The development of new alumina-forming austenitic alloy grades is finally described.