Oxidation Behavior In Air Research Articles

The influence of CeO2 on the oxidation resistance of TaC/Ni composites

The in-situ TaC/Ni composites with different CeO2 content (0 wt%, 1 wt%, 2 wt%) were prepared by reactive sintering method, and their oxidation behavior in air at 1073 K was analyzed by static cyclic oxidation method to investigate the influence mechanism of CeO2 on the oxidation resistance of composites. The results show that the CeO2 particles are distributed around the TaC particles in the Ni matrix, and the oxidation behavior of composites with different CeO2 content conforms to the linear kinetic law. The oxide film is mainly composed of NiTa2O6 and a small amount of NiO. The generation reactions of Ta2O5 and NiTa2O6 induce a high expansion and compressive stress in oxide scale, leading to the formation of nonprotective oxide film with pores and cracks on the surface. As the addition of CeO2 increases from 0 wt% to 2 wt%, the thickness of oxide scale on composites obviously reduces from 505 μm to 122 μm, and the Ni and Ta oxides content decreases, leading to the reduction of pores and cracks in oxide scale. The Ce ion generated from the dissolution of CeO2 particles mainly distributes in the Ta oxides during the oxidation process, which hinders the outward diffusion of Ni and Ta ions, resulted in the improved oxidation resistance of TaC/Ni composites.

Air Oxidation Behavior of Sanicro-25 with Different Surface Finishes

AbstractSanicro-25 is a high-temperature material used as the structural material for steam superheaters and reheaters in advanced ultra-supercritical power plants. The air oxidation behavior of Sanicro-25 with various surface roughnesses is being assessed at 650 °C for about 1000 h. Different surface-roughened samples were studied, namely polishing the sample up to diamond finish, grinding up to (80-grit finish and 600-grit finish) and grit blasted. The diamond finish sample showed more weight gain than others, and higher weight gain was observed in the initial oxidation stage. Attributed to different surface preparations leads to defects at different levels, which further alters the diffusion of various elements. The diamond finish sample showed the presence of Cr-rich oxides, and other samples showed the presence of Fe-rich oxides. Smooth surfaces promoted the formation of thick protective oxide scales.

Microstructure evolution and high temperature air oxidation behaviour of thick Cr coatings at 1200 °C

Microstructure evolution and high temperature air oxidation behaviour of thick Cr coatings at 1200 °C

Influence of Alloy 625 Manufacturing Process on 950 °C Oxidation Behavior in Air and Post-oxidation High-Cycle Fatigue Performance

Influence of Alloy 625 Manufacturing Process on 950 °C Oxidation Behavior in Air and Post-oxidation High-Cycle Fatigue Performance

High Temperature Air and Steam Oxidation and Fireside Corrosion Behavior of 304HCu Stainless Steel: Dichotomous Role of Grain Boundary Engineering

High Temperature Air and Steam Oxidation and Fireside Corrosion Behavior of 304HCu Stainless Steel: Dichotomous Role of Grain Boundary Engineering

Preparation of Cr2AlC powder and its isothermal oxidation behavior in dry air and pure steam

As a promising candidate ceramic for using in harsh environments, Cr2AlC ternary carbide possesses numerous unique properties at elevated temperatures. Herein, high-purity Cr2AlC powders had been synthesized by using a facile method with a mixture of Cr7C3, Cr3C2 and Al powders at 1200 °C for 3 h. Subsequently, the oxidation behaviors of Cr2AlC powders were investigated in dry air and pure steam at temperatures ranging from 900 to 1100 °C, respectively. In addition, the oxidation products were characterized and the mass gain curves were analyzed via the real physical picture (RPP) kinetic model. As a result, thicker Al2O3-rich oxide scale and porous Cr7C3 subscale were generated during dry air oxidation compared to pure steam oxidation. Notably, the oxidative active energy of Cr2AlC was 446.5 kJ/mol in pure steam, while in dry air it was decreased by 14.4%. Theoretical calculations further verified that Cr2AlC oxidizes more sluggishly in steam than in dry air.

Water vapor effects on the oxidation resistance of modified potassium silicate coating at high temperature

An inorganic potassium silicate coating with pigments of alumina, aluminum phosphate, NiCrAlY and copper chromite black was prepared on CB2 stainless steel. Oxidation behavior in either ambient air or O2+H2O mixture at 630 °C for 2000 h was comparatively studied, and the coating exhibited excellent resistance under both test conditions. The water vapor considerably accelerated the oxidation of the uncoated CB2 steel, as the hydroxide, the main constituent of the coating, had a negligible evaporation rate at test temperature, while it had a limited effect on the coated sample. Meanwhile, the existence of coating may prolong or eliminate the incubation period in the O2+H2O mixture at 630 °C. After oxidation, the coating matrix is in an amorphous state and fillers as alumina and copper chromite black are stable in the coating. Leucite (KAlSi2O6) formed by Al from NiCrAlY and potassium silicate in the coatings was detected after tests either in O2 or O2+H2O mixture.

Thermophysical properties and oxidation behaviour of the U0.8Zr0.2N solid solution

Thermophysical properties and oxidation behaviour of the composite pellet UN–20 vol%ZrN were investigated experimentally and compared with the behaviour of the pure UN pellet. A compound of a single phase, a solid solution of the average composition U0.8Zr0.2N, was obtained by Spark Plasma Sintering (SPS) of the powders UN and ZrN. Crystallographic and microstructural characterisation of the composite was performed using Scanning Electron Microscopy (SEM), standardised Energy Dispersive Spectroscopy (EDS) and Electron Backscatter Diffraction (EBSD). Nano hardness and Young’s modulus were also measured by the nanoindentation method. High-Temperature X-ray diffraction (XRD) was applied to obtain the lattice expansion as a function of temperature (room temperature to 673 K). Thermogravimetric Analysis (TGA) was applied to evaluate oxidation behaviour in air. Results demonstrate that the fabrication method results in a matrix of solid solution with homogeneous composition averaged to U0.8Zr0.2N. The mechanical properties of such solution are uniform, with variation only due to the crystallographic orientation of the grains of the solution phase, similar to pure UN. The obtained value for the average linear thermal expansion coefficient is α¯ = 7.94 × 10-6/K, which compares well to UN (α¯ = 7.95 × 10-6/K) for the same temperature range. The degradation behaviour of the composite pellet UN-20 vol%ZrN in air shows a lower oxidation onset temperature, compared to pure UN, with the final product of oxidation being mainly U3O8. Smaller crystallites in the product of corrosion of the composite pellet indicate that the mechanism of degradation of the solid solution phase U0.8Zr0.2N is accompanied by the formation of two distinct oxides and their interaction.

The oxidation of uranium diboride in flowing air atmospheres

The air oxidation behaviour of UB2 synthesized via the carbo/borothermic reaction has been investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), through heating ramp and isothermal studies. Heating ramps from room temperature up to 1173 K showed an on-set of rapid oxidation occurred at a temperature of 807 ± 6 K for samples in fragment form and 799 ± 5 K for finely powdered material. The ramp tests yielded UB2O6 as the ultimate oxidation product. A thermodynamic model for the U-B-O system was used to propose a reaction pathway for the oxidation process in excess oxidiser condition and to predict the amount of heat released. The predictions of the model agreed with the observed phenomena and with the values measured via DSC.

Raman structural transition studies and optical band calculation on the multiphase of tin selenides

A comprehensive investigation of tin selenide's oxidation behaviour in air and the subsequent phase transition is necessary in order to employ it in realistic temperature thermoelectric applications. The surface induced oxidation caused by annealing influences the physical properties that govern all other properties of synthesized SnSe. Understanding the temperature range where SnSe may be employed effectively for commercial applications is important. The paper reports a simple and environmentally sustainable method for synthesizing SnSe and the temperature dependence on phase change of the synthesized samples is investigated. The synthesized SnSe were annealed at 450 °C, 500 °C, 550 °C, and 600 °C in air, and phase transitions are studied using structural, morphological, optical, and thermal analysis. The structural studies confirmed the phase purity of the synthesized samples and the phase change of SnSe to SnSe2 and SnO2 as the annealing temperature increases. TGA confirms the thermal stability of SnSe, and the phase is found to be stable up to 420 °C. The sheet-like morphology of the as-synthesized SnSe changed to a rod-like structure for the samples that were annealed at 450 °C and become agglomerated and uneven as the annealing temperature increased. In addition, a theoretical modeling tool based on density functional theory (DFT) was utilized to gain a better understanding of these materials' semiconducting nature. The band gaps and bandstructure of SnSe and SnSe2 estimated using the LDA approximation are shown to be in good agreement with the observed experimental values. This study gives a way for assessing the structural stability of SnSe and aids in understanding the mechanisms that lead to SnSe oxidation which could be employed for developing realistic device architectures and sealing technologies for energy harvesting applications.

Steam and air oxidation behaviour of thermal spray chromium carbide-based composite coatings

Thermal spray chromium carbide-based composites have been widely used industrially because of their superior oxidation resistance at elevated temperatures compared to other metal matrix composite coatings. In this work, the serviceability of HVOF sprayed coatings from an atomized chromium carbide-based feedstock (Cr23C6-40NiCr) was compared with those from a conventional Cr3C2-25NiCr agglomerated and sintered feedstock. Coatings were exposed to 540 °C and 610 °C for 168 h in both air and steam environments. These conditions are indicative of industrial power plant working conditions to assess their real-time performance. Quantitative Rietveld analysis of the Cr23C6-40NiCr coating XRD patterns indicated a comparable concentration of Cr23C6 in both the powder and coating, implying minimal carbide dissolution. However, the Cr3C2 content in the conventional Cr3C2-25NiCr coating was markedly reduced compared to the initial powder composition, indicating that carbide dissolution occurred to a greater extent. Air oxidation led to the formation of coarse surface oxide, due to the initial formation of Ni-based oxides before a continuous Cr2O3 layer could develop underneath. A notably finer and more uniform oxidized surface composed only of Cr2O3 was formed during steam treatment across both coating types. More importantly, the oxide scale was intact and crack-free in Cr23C6-40NiCr compared to Cr3C2-25NiCr. Moreover, despite Cr23C6 being the main carbide phase and the high binder content (40%NiCr), the microhardness of the Cr23C6-40NiCr coating was comparable to that of the conventional Cr3C2-25NiCr coating, both in the as-sprayed and heat exposed states.

The oxidation behavior of Tix(AlCrNb)100−x light-weight medium-entropy alloys in dry air at 600–800 °C

Air-oxidation behavior of three Tix(AlCrNb)100−x light-weight medium-entropy alloys, where x = 70, 65, and 40, was investigated at 600–800 °C. The oxidation kinetics of all alloys obeyed the parabolic-rate law, having the oxidation rates steadily increasing with temperature and Ti content. Intermixed scales of TiO2 and Al2O3 formed on all alloys, and an exclusive TiO2 layer formed in the inner layer and an internal nitrogen attack to form TiN was noted at 800 °C. The oxidation mechanism was due mainly to inward oxygen diffusion.

Oxidation behavior in static air and its effect on tensile properties of a powder metallurgy EP962NP nickel-based superalloy

Oxidation behavior and its effect on tensile properties of a powder metallurgy EP962NP superalloy have been investigated. Results show that the oxidation resistance of studied alloy has been improved by hot isostatic pressing as compared to the as-cast one. Oxidation process of the alloy powder metallurgy EP962NP is limited by diffusion of Cr3+ due to oxidation activation energy of 244.1 kJ·mol−1. In addition, the main reason for cracking and spalling during steady-state oxidation can be inferred as the rapid increase in growth stress caused by spinel. Interestingly, the tensile samples oxidized at 900 °C exhibit improved plasticity due to the refinement of γ′ caused by octet splitting.

Oxidation of typical Zr-1 Nb alloy in high-temperature air under 700–900 °C

In order to promote the understanding of Zirconium alloy cladding failure under loss of coolant accidents (LOCA), air oxidation behavior of Zr-1 Nb-0.12 O (M5) alloy at 700–900 °C for 1–2 h was investigated. At different temperatures and times, m-ZrO2 was always the dominant phase of surface oxides, whereas oxide shapes, the integrity and roughness of oxide films differed noticeably. At 900 °C, M5 alloy exhibited accelerated kinetics and breakaway oxidation after approximately 80 min air exposure. The presence of ZrO and ZrO0.35 sub-oxides accounts for the high reaction activation energy (149.6 kJ/mol). During the kinetics acceleration, some intergranular cracks turned transgranular. The oxide/metal (O/M) interface became wavy, massive long transverse cracks and small radial cracks appeared in the oxide film, and pores distributed on the oxide layer and O/M interface. Air ingress through the oxide layer to initiate the matrix oxidation is jointly affected by air transport and ion diffusion.

Oxidation behavior and mechanism of Ag-9.8Sn-1.3Bi-0.4Cu alloy powders in different oxidant

The oxidation behavior of Ag-9.8Sn-1.3Bi-0.4Cu alloy powders is investigated used by XRD, SEM, EPMA and TEM. The results show that the oxidation behavior in air and air+Ag2O is different for Ag-9.8Sn-1.3Bi-0.4Cu microparticles, but that is similar for Ag-9.8Sn-1.3Bi-0.4Cu nanoparticles. The size of oxides formed in air is larger than that in air+Ag2O and the size of CuO is larger than that of SnO2 and Bi2Sn2O7. The oxides mainly distribute on powder surface in air oxidation, while those mainly distribute on grain boundaries in air+Ag2O oxidation. The nucleation priority order of oxides is SnO2 >Bi2O3 >Bi2Sn2O7 >CuO during oxidation both in air and air+Ag2O.

Effect of Surface Preparation on the Air Oxidation Behaviour of Modified 9Cr–1Mo Steel

Effect of Surface Preparation on the Air Oxidation Behaviour of Modified 9Cr–1Mo Steel

Hot corrosion and air oxidation behavior of pulsed current gas tungsten arc welded and CO2 laser beam welded SMO 254 at 800 °C

This research aims to investigate the hot corrosion behaviour of SMO 254 steel samples after PCGTA and CO2 laser beam welding, as well as air oxidation. A salt mixture simulated the waste incinerator environment involving 40 wt. % Na2SO4 + 40 wt. % K2SO4 + 10 wt. % NaCl + 10 wt. % KCl are employed. The hot corrosion tests were carried out for 103.33 h at 800 °C, with a thermogravimetric investigation availed to calculate the impact of corrosion. The weight gain rate for PCGTAW molten salt corroded specimens is greater (33.45 mg/cm2) than the weight gain rate for CO2 Laser molten salt corroded specimens, which is 67.55% higher. The weight of the hot corroded sample rises in the molten salt surroundings due to the creation of compounds including CrS, FeMo2S4, Na2S, Fe2O3, K2S3, Cl4CrNa2. CO2 LBW air oxidation has the lowest rate of corrosion due to the synthesis of beneficial oxides, such as NiCr2O4, NiO, and Cr2O3. Optical microscopy and SEM/EDS were employed on both surface and cross-sectional surfaces to get microstructure at the interface of the fusion region, parent metal, and fusion region using point mapping, line mapping, and X-ray mapping techniques. The corrosion products produced during corrosion were studied using XRD.

Oxidation Behavior of the Si-B-X (X = Mo, Cr, or Ti) Alloys in the Temperature Range of 1000-1400 °C.

Low-melting-point silicon–boron system alloys are promising for low-temperature reactive melt infiltration to reduce high-temperature damage to silicon carbide fibers during the densification of SiC/SiC composites. Meanwhile, the oxidation resistance of the alloys will have a large impact on the intrinsic oxidation resistance of the composite. Herein, three alloys, Si-14.88B-7Mo, Si-14.88B-7Ti, and Si-14.88B-7Cr, were fabricated to investigate the oxidation behavior in air at 1000–1400 °C. The results showed that the oxidation weight gains of the Si-B-Mo alloy after oxidation at 1400 °C for 100 h were 0.9 mg/cm–2, which were only 50 and 1.5% of those of Si-B-Ti and Si-B-Cr alloys, respectively. The excellent oxidation resistance of Si-B-Mo alloys at 1000–1400 °C was attributed to the formation of glassy-surface layers and the dense internal oxide layer. The dense oxide layer and the low solubility of Mo ions in SiO2 inhibit the volatilization of MoO3 and the oxidation reaction, reducing the oxidation rate of the Si-B-Mo alloy. The difference in the coefficients of thermal expansion for SiO2 and TiO2 led to penetrating cracks in the oxide layer of the Si-B-Ti alloy during cooling, thereby reducing the oxidation resistance. In addition, the rate of volatilization of Cr2O3 as CrO3 in an oxidation atmosphere above 1200 °C increased significantly in the Si-B-Cr alloy. The simultaneous volatilization of B2O3 and CrO3 resulted in the formation of loose oxide layers in the CrB2 region of the Si-B-Cr alloy, leading to severe oxidation.

Oxidation Behavior in Static Air and its Effect on Tensile Properties of a Powder Metallurgy Ep962np Nickel-Based Superalloy

Oxidation Behavior in Static Air and its Effect on Tensile Properties of a Powder Metallurgy Ep962np Nickel-Based Superalloy

Uranium nitride advanced fuel: an evaluation of the oxidation resistance of coated and doped grains

The oxidation behaviour of the composite UN-AlN, UN-Cr 2 N/CrN and UN-AlN-Cr 2 N/CrN pellets in air and anoxic steam under thermal transient conditions was investigated and compared with the pure UN pellet. The composite pellets were manufactured to contain the engineered microstructure of coated (the addition of matrix-insoluble AlN) and doped (the addition of matrix-soluble Cr 2 N/CrN) grains. The composite powders were produced by powder metallurgy and sintered into pellets using the SPS method. Sintered composite pellets were subjected to a thermal transient up to 1273 K in an STA-EGA (TGA-DSC-Gas-MS) system, followed by crystallographic characterization by XRD and morphological and elemental analysis by FEG-SEM. Improved oxidation behaviour in air compared to pure UN was demonstrated by the UN-Cr 2 N/CrN composite pellet. The formation of the ternary oxide UCrO 4 from the ternary (U 2 Cr)N 3 phase (doped grain) was observed, consistent with the delayed oxidation onset and slower reaction rates. In an anoxic steam environment UN-Cr 2 N/CrN exhibited a higher onset oxidation temperature relative to UN, although the reaction progressed faster than for UN sample. Composite UN-AlN pellet oxidised at a lower temperature in both air and steam, compared to pure UN, due to internal stresses in the fuel matrix. A mechanism for degradation of the composite materials is proposed and the influence of the individual phases on the oxidation behaviour of the composites is discussed.