High-temperature Oxide Films Research Articles

Oxidation resistance of Mg-Y alloys at elevated temperatures and the protection performance of the oxide films

Oxidation behaviours of Mg-xY (x = 0.5, 1.0, 1.7, 3.7 and 5.5 wt%) alloys were investigated below melting temperature (550–625 °C) in dry air. The corrosion protection properties of the high-temperature oxide films on Mg-xY alloy matrix in 3.5 wt% NaCl solution were explored. The results showed that oxidation resistance of the Mg-Y alloys increased as a function of addition of Y. Mg-5.5Y alloy exhibited the highest oxidation resistance. The oxidation behaviours of the Mg-Y alloys depended on Y content and the oxidation temperature. Importantly, the oxide films of the Mg-Y alloys were transformed from a loose MgO-rich film to a compact Y2O3-rich counterpart that suppressed inward diffusion of oxygen and thus prevented further oxidation. Owing to the higher diffusion rate of Mg2+ ions compared to that of Y3+ ions in the oxide film, Y2O3 was primarily forming at metal/oxide interface, and MgO was formed at oxide/air interface. Hydrogen evolution tests indicated that the formation of such compact Y2O3-rich film was beneficial for improving the corrosion resistance of Mg-Y alloys in 3.5 wt% NaCl solutions. However, due to the existence of a large fraction of Mg24Y5, the protective role of Y2O3-rich films was deteriorated in oxidized Mg-5.5Y alloy.

Influence of Oxidation Temperature on the High-Temperature Oxide Film Forming Behavior of T22 Heat-Exchange Tubes

In this study, without changing the whole manufacturing process of T22 coiled tubes, high-temperature oxide films are formed through atmosphere adjustment by taking advantages of the cooling process after stress elimination heat treatment. The corrosion resistance of T22 heat-exchange tubes is improved, which are used in the steam generators (SG) of high-temperature gas cooled reactors (HTR). The surface microscopic morphology of the oxide films is observed using a scanning electron microscope, and the structure of these films is characterized using an X-ray diffractometer. The stability of the high-temperature oxide film forming process is investigated using TG-DTG, as well as the thermal expansion coefficient of the films. The results prove that: (1) The oxide film generated at 550 °C is uniform and dense; (2) The oxide films formed at various holding temperatures are mainly consisted by Fe2O3 and Fe3O4. When the holding temperature is 550 °C, the content of Fe3O4 is the highest as 70.1%; (3) The films are stable when placed in inert atmosphere (N2) below 900 °C, and there is not any change in the composition and structure of the films even after reacting with steam at 550 °C for 24 h; (4) The expansion coefficient of high-temperature oxide films is very close to that of the matrix of the heat exchange tube, and the difference between these two thermal expansion coefficients is 5.3×10-9 mm/°C.

XPS and UPS characterization for Cr and Mn in high-temperature oxide films of bulk nanocrystalline 304 stainless steel

The authors studied the binding energies of valence electrons of two oxide scales, the atomic percentages of Cr and Mn elements in two oxide films, the work function of two oxide films on bulk nanocrystalline 304 stainless steel (BN-SS304) and conventional polycrystalline 304 stainless steel (CP-SS304). BN-SS304 was prepared by severe rolling technique, and the two oxide films were formed in atmosphere at 900 degrees C for 24 hours oxidation on BN-SS304 and CP-SS304 surfaces. In the two oxide films, Cr and Mn elements exist in the forms of Cr3+, Cr0, Mn4+ and Mn0. The atomic percentage ratios of Cr+ / (Cr3+ + Cr0) and Mn4+ / (Mn4+ + Mn0) in the oxide film on BN-SS304 are lower than those in the oxide film on CP-SS304. The interactions of the two oxides and the valence electrons of elements are Mn-O, Cr-O,3d and 4s of Mn0 and Cr0. The binding energies of the valence electrons in the oxide film on BN-SS304 are larger than those in the oxide film on CP-SS304, the work function of the oxide film on BN-SS304 is 0.07 eV larger than that on CP-SS304.

Characterization of high-temperature oxide films on dysprosium-doped Fe-20Cr alloys by electrochemical techniques

The oxidation properties of Fe-20Cr, Fe-20Cr-0.2Dy and Fe-20Cr-1Dy alloys were studied using gravimetric and electrochemical techniques. The high-temperature oxide films of Dy-doped Fe-20Cr alloys were prepared in air at 900 °C for 24, 48 and 100 h, respectively. The electrochemical experiment was performed by a three-electrode electrochemical cell and in 0.1 mol/L Na2SO4 aqueous solution. Proper models were built for describing electrochemical impedance spectroscopy of the different oxide layers and the spectra were interpreted in terms of a two-layer model of the films. The results revealed that the oxide films of Dy-doped Fe-20Cr alloys became compacter than that of undoped alloys and retained their good protective ability for a relatively long time. With increasing content of Dy, the protection of the oxide films slightly decreased. Mott-Schottky curves indicated that all the oxides were n-type semi-conductors, and the Nd value of oxide film on Fe-20Cr was much larger than that of Dy-doped Fe-20Cr alloys. The results of kinetic curves and SEM were in agreement with electrochemical impedance spectroscopy and Mott-Schottky data.

Oxide-Nitride-Oxide막을 게이트 절연막으로 사용하여 제조한 다결정실리콘 박막트랜지스티의 특성

HTO(High Temperature Oxide) films are mainly used as a gate insulator for polysilicon thin film transistors(Poly-Si TFT's). The HTO films, however, show the demerits of a high leakage current and a low electric breakdown voltage comparing with conventional thermal oxides even though they have a better surface in roughness than the thermal oxides. In this paper, we propose an ONO(Oxide-Nitride-Oxide) multilayer as the gate insulator for poly-Si TFT's. The leakage current and electric breakdown voltage of the ONO and HTO were measured. The drain current variation of poly-Si TFT's with a variety of gate insulators was observed. The thickness optimization in ONO films was carried out by studying I<TEX>$\_$</TEX>on/I<TEX>$\_$</TEX>off/ ratio of the poly-Si TFT's as a function of the thickness of ONO film adopted as gate insulator.

A mixed-conduction model for oxide films on Fe, Cr and Fe–Cr alloys in high-temperature aqueous electrolytes––I. Comparison of the electrochemical behaviour at room temperature and at 200 °C

The aim of this two-part work is to propose a model for the corrosion mechanism of ferrous alloys in high-temperature aqueous environments. In the first part of the work, experimental results of the electrochemical behaviour of pure Fe, pure Cr, Fe–12%Cr alloy and Fe–25%Cr alloy during the initial stage of oxide film formation at 200 °C are compared to those obtained at room temperature. The results have been obtained by using voltammetry, electrochemical impedance spectroscopy (EIS), contact electric resistance (CER) and contact electric impedance (CEI) techniques. An increase of temperature from room temperature up to 200 °C has been found to result in higher currents in the passive region for all the materials. The CER, EIS and CEI results indicate that the film especially on Fe is considerably thicker at the higher temperature. In addition, the EIS and CEI results give information of an ionic transport process at 200 °C, which has not been observed in the EIS response at room temperature. The dependence of the electrical and transport properties of the film on potential suggests that the films at 200 °C can also be described by a mixed-conduction model (MCM) introduced recently for room temperature. However, the faster rate of ionic defect transport has to be emphasised at the higher temperature. The adaptation of the MCM to high-temperature oxide films is discussed in more detail in the second part of this work.

XPS and SIMS depth profiling of chlorine in high-temperature oxynitrides

Thin oxides deposited by low-pressure chemical vapour deposition (LPCVD) at high temperature are being widely investigated in VLSI technology to be used as possible substitutes for the usual thermal oxides. High-temperature oxide deposition involves reactions between N 2 O and dichlorosilane or silane. Considering possible active dielectric applications, the effect of further nitridation and annealing of deposited films has to be considered. Evaluation of the nitrogen content and the distribution profile of these dielectrics then becomes a relevant analytical issue. Moreover, it is also crucial to monitor the amount of possible contaminant species, such as chlorine, introduced by the precursor gases during the deposition. In this work we present the development of an analytical methodology for quantitative depth profiling of chlorine in thin oxides using SIMS and XPS. In addition, the evolution of chlorine distribution in an appropriate set of high-temperature oxide films submitted to nitridation and further thermal processes will be shown.

EIS Study of High-Temperature Oxide Films on a Stainless Steel (253MA)- Influence of Alloying Elements

Alloying elements such as chromium, silicon and cerium in stainless steels are important for the oxidation behavior of the material at high temperatures. In this work, the oxide films formed on a stainless steel (253MA) with a small variation in the content of chromium, silicon and cerium, were characterized by electrochemical impedance spectroscopy (EIS), after exposure up to 100 hours in air at 750 and 1100 °C. The EIS spectra suggest a two-layer feature of the oxide films, in agreement with complementary surface analysis. The influence of a small variation in alloying element content on the oxidation behavior was revealed by the difference in the electrical properties of the oxide films. At 750 °C, the influence becomes pronounced after 100 hours of oxidation, and the steel with a lower content of chromium, silicon and cerium exhibits a lower film resistance. At 1100 °C, the oxide film formed on the steel with a lower content of chromium, silicon and cerium starts to degrade earlier than that on the steel with a higher content of chromium, silicon and cerium.

Characterization of High-Temperature Oxide Films on Stainless Steels by Electrochemical-Impedance Spectroscopy

Oxide films formed on three stainless steels(UNS S30403; S44600; S30815) in air at 800°C werecharacterized by electrochemical-impedance spectroscopy(EIS). The film evolution vs. oxidation time wasinvestigated from 1 to 1000 hr. A three-electrodeelectrochemical cell and 0.1 MNa2SO4 solution were employed forEIS measurements. The spectra were interpreted in termsof a two-layer model of the films, where the capacitance and resistance obtained can berelated to the thickness (or roughness) anddefectiveness of the films. The results reveal that theoxide on S30403 grows and becomes defective, the oxideon S44600 thickens rapidly and retains its protectiveability for a relatively long time, and the oxide onS30815 remains thin and resistive. The two-layer modelis supported by surface characterization with SEM/EDS and in-depth profile of the oxide filmsobtained through glow discharge optical emissionspectroscopy (GDOES).

High Temperature Oxide Films and Scales of Fe-Si-Cr System Alloys

High Temperature Oxide Films and Scales of Fe-Si-Cr System Alloys

Effects of Si upon High Temperature Oxide Films of Heat Resisting Alloys

Effects of Si upon High Temperature Oxide Films of Heat Resisting Alloys

シヨットピーニング加工したFe-Al合金の高温酸化膜

シヨットピーニング加工したFe-Al合金の高温酸化膜