Isothermal Oxidation Kinetics Research Articles

Oxidation kinetics of typical high FeO ferrous spinels

In this study, the isothermal oxidation kinetics of magnetite (OM), high-Mg magnetite (MM), titanomagnetite (TM), and chromite (CM) were investigated by applying thermogravimetry (TG) analysis at temperatures ranging from 1073 K to 1223 K. The results show that different high-FeO spinels possess distinct oxidizability. The oxidation process of OM in the temperature range from 1073 K to 1223 K is faster than others, followed by MM and TM. While CM exhibits the poorest oxidizability, and generally undergoes complex phase transitions. In the initial stage of oxidation, high FeO spinels have a higher oxidation rate due to the surface oxidation of spinel particles. However, the oxidation rate gradually declines in the later stages of oxidation due to increased internal diffusion resistance. The results of oxidation kinetics indicate that the initial oxidation stage of four spinels can be described as random nucleation and subsequent growth mechanism. The average apparent activation energies of the initial oxidation stage of OM, MM, TM, and CM are 25.09 kJ/mol, 32.39 kJ/mol, 58.10 kJ/mol, and 82.42 kJ/mol, respectively.

Role of TiC and WC Addition on the Mechanism and Kinetics of Isothermal Oxidation and High-Temperature Stability of ZrB2–SiC Composites

Role of TiC and WC Addition on the Mechanism and Kinetics of Isothermal Oxidation and High-Temperature Stability of ZrB2–SiC Composites

Isothermal low-temperature oxidation behavior and kinetics of heavy oil

In this study, the isothermal low-temperature oxidation (LTO) behavior of heavy oil was investigated by thermogravimetry combined with Fourier transform infrared spectroscopy. Furthermore, the kinetics analysis was conducted using general reaction rate models. The findings revealed that the LTO process of heavy oil could be divided into three distinct phases. The first phase, occurring between 50 and 100 °C, exhibited minimal mass loss and low absorbance of gas-phase products. In the second phase (100–250 °C) the produced gas predominantly consisted of saturated hydrocarbons and substances containing C=O groups. Lastly, in the third phase (250–300 °C), the signals of CO2 and CO in the produced gas were significantly higher compared to the 50–250 °C range, indicating a shift in the oxidation mode of heavy oil from oxygenation to bond cleavage for temperatures higher than 250 °C. Kinetics analysis demonstrated an initial increase in reaction order and reaction rate from 50 to 100 °C, followed by a decrease from 100 to 250 °C, and a final increase from 250 to 300 °C. The negative activation energy observed in the second temperature interval was attributed to the negative temperature coefficient effect. This study provided valuable insights into the isothermal LTO reactions of heavy oil.

Oxidation behaviour of Zr added hypereutectic Nb-19Si-5Mo-20Ti alloy

The influence of Zr (3 at%) addition on non-isothermal and isothermal oxidation behaviour of the Nb-19Si-5Mo-20Ti (base alloy) has been investigated. During heating in a thermogravimetric analyser to 1300 °C in air, the mass-gain begins at ∼600 °C, and shows a more gradual rise as well as a lower peak value for the Zr-containing alloy compared to the base alloy. Furthermore, the Zr-containing alloy exhibits superior oxidation resistance in isothermal test for 24 h at 1100 °C, but not at 900 °C and 1200 °C, probably due to the differences in oxide scale growth kinetics and defect density. The oxidation products have been identified as Nb2O5, SiO2, TiO2, MoO2, TiNb2O7, Ti2Nb10O29 for both the alloys, with ZrO2 being additionally observed in the Zr-containing alloy. Analysis of the isothermal oxidation kinetics suggests an initial stage of interface-reaction controlled rapid mass increase followed by parabolic behaviour, where oxygen diffusion through the oxide scale is apparently rate-controlling. Slow down to parabolic kinetics is ascribed to the formation of a SiO2-rich compact oxide scale. The oxide scale becomes protective due to reduced oxygen anion diffusivity in Nb2O5 having Mo, Ti and Zr as substitutional solute, along with the formation of ZrO2 and TiO2 with Pilling-Bedworth ratio less than 2.

Long-term effects of soft-chromising Ni-electroplated AISI 441 commodity steel for SOC stack interconnects

Using commodity steel AISI 441 with Ni-based oxide coatings can facilitate large-scale interconnect manufacturing for solid oxide cell stacks, but adverse Ni-diffusion limits the high-temperature suitability. As a remedy, chromium is here added to the steel by a soft-chromising treatment. The (cyclic) oxidation resistance of virgin and soft-chromised AISI 441 is evaluated up to 8300 h at 780 °C, and further benchmarked against more commonly used Crofer 22 APU, with a Co(Mn)-spinel coating. Results revealed lowest isothermal oxidation kinetics for the soft-chromised, Ni-coated AISI 441, further preventing oxide spallation otherwise observed during thermal cycling of the virgin AISI 441 counterpart.

Isothermal oxidation kinetics of industrial South African chromite concentrates in air

The oxidation of chromite pellets prior to smelting in a submerged arc furnace is key to ensuring that maximum benefit can be derived in the subsequent smelting step. Oxidized pellet feed material reduces operating costs by increasing energy and reductant efficiency, as well as increasing chrome recoveries.There is significant compositional variance in chromites used in South African chromite smelting operations due to the different seams from which the materials are mined. The impact of these variances on the extent and rate of oxidation of chromite ores has not been studied before, and it was the impetus for this study.A detailed kinetic study was carried out on three different types of chromite ores, originating from different commercially mined seams in South Africa, specifically the UG2, LG6 and MG seams. Thermogravimetric analysis was performed on these samples in air at temperatures ranging from 873 to 1473 K, which was used as input to the kinetic analysis. The proposed mechanism of chromite oxidation was found to occur in two stages: initially by random nucleation and growth of a sesquioxide phase, followed by a three-dimensional diffusion-controlled mechanism. The activation energy for oxidation was found to be similar for UG2 and LG6 ore, but higher for MG at all tested temperatures.The effect of chromite composition, temperature, and time on the extent of oxidation (α) was further quantified and captured in a single regression equation, confirming that time and temperature increase the extent and rate of oxidation. The Ti content was found to be directly correlated with higher values of α for a given time and temperature. The regression equation partially resembles the functional form of the diffusivity equation for cations in chromite found in the literature. It was also found that the distribution between Cr and Al impedes oxidation, with higher Cr content resulting in lower values of α for a given time and temperature.

Oxidation behavior and mechanism of Al4O4C powders at 1000–1300 °C

The high temperature non–isothermal and isothermal oxidation behavior of Al4O4C powders were investigated in the temperature range of 1000 to 1300 °C. The phase composition, micro–structure evolution, and the thickness of the oxide scale were characterized. The Al4O4C powders showed a good oxidation resistance at 1000 and 1100 °C, owing to the generation of the dense nanoscale rod–like and worm–like α–Al2O3 layer. Density functional theory (DFT) calculation illustrated that Al4O4C performed a high–temperature stability due to the strong covalent bond. The grain sizes of α–Al2O3 increased evidently at 1200 °C, and the staggered growth of α–Al2O3 particles and their corresponding volume shrinkage dominated the generation of the porous surface structure of oxidized Al4O4C powders. Subsequently, the gas phase diffused quickly through these porous structures, and thus resulted in rapid and complete oxidation of Al4O4C powders at 1300 °C. The isothermal oxidation kinetics of Al4O4C powders can be accurately described by the Carter model, and their corresponding apparent activation energy was calculated to be 350.93 kJ/mol at 1000–1300 °C.

Oxidation and Electrical Property Studies on Ferritic Steels as Potential Interconnects in Electrochemical Devices for Energy Conversion

This work presents the results of oxidation studies on commercially available Nirosta 4016/1.4016 ferritic steel, which contains 16.3 wt.% chromium, as well as the electrical properties of steel/scale layer systems in order to determine the usefulness of this steel for constructing metallic interconnects in solid oxide fuel cell (SOFC) and solid oxide electrolyzer cell (SOEC) stacks. The E-Brite ferritic steel, consisting of up to 26 wt.% chromium, was chosen as a reference material. High-temperature isothermal oxidation kinetics studies were carried out on both steels at 1073 K for 255, 505, 760 and 1010 h in air atmosphere. These conditions are representative of those present in the cathode compartment of a SOFC and the anode compartment of a SOEC. Area specific resistance (ASR) measurements were performed on steel/scale layer systems, obtained after the previous oxidation of both steels in the above-mentioned conditions, in the air in the temperature range of 573–1073 K using the pseudo-DC four-probe method. On the basis of these studies, complemented by morphology observations, as well as chemical and phase composition analysis of the oxidation products, the usefulness of Nirosta 4016/1.4016 ferritic steel for manufacturing interconnects in energy conversion electrochemical devices operating at 1073 K was confirmed.

Oxidation Property of a Fourth-Generation Powder Metallurgy FGH4108 Nickel-Based Superalloy

Isothermal oxidation kinetics of a fourth-generation powder metallurgy FGH4108 nickel-based superalloy is investigated at 800 °C to 1100 °C by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). At 800 °C and 900 °C, the oxidation kinetic curves of the FGH4108 superalloy follow parabolic law. At 1000 °C, the oxidation kinetic curve follows cubic law. At 1100 °C, the oxidation kinetic curve has two distinct parts: the first part follows a parabolic law, and the second one obeys a linear law. Cross-sectional morphologies and elemental distributions show that the oxide film consists of two parts at 800 °C: the outer layer is a continuous dense protective Cr2O3 oxide film, and the inner layer is a discontinuous Al2O3 oxide layer. At 900–1100 °C, the oxides consist of three layers: the outermost is the oxides of Cr2O3 and TiO2, the middle is a continuous oxide of Al2O3, and the innermost is dotted oxides of TiO2. The thickness of the inner TiO2 oxide layer increases with the increase of oxidation temperature. On this basis, the oxidation behavior of the FGH4108 superalloy at high temperatures is confirmed to be controlled by the diffusion of Cr, Al, Ti, and O. From the aspect of oxidation resistance, the long-term service temperature of the FGH4108 superalloy should not exceed 1000 °C.

Study on oxidation kinetics of three kinds of candidate superalloys for VHTR under air ingress accident

Inconel 617 alloy, Incoloy 800H alloy and Hastelloy X alloy are three alternative superalloys for heat transfer tubes used in the steam generator (SG) in the very high temperature gas cooled reactors (VHTR). In this paper, the oxidation kinetics of isothermal oxidation of three superalloys in the circulating air at 950 ℃ during the air ingress accident is investigated. Oxidation kinetic parameters of superalloys, such as the oxidation rate indexes (np and nt), mass parabola rate constant (kp) and oxide layer thickness parabola rate constant (kt) are calculated by the experimental data. In addition, tested samples of superalloys were analyzed by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS) and X-ray diffraction (XRD). The results show that these three superalloys exhibit parabolic oxidation behavior in air atmosphere. The oxidation behavior of Incoloy 800H alloy is closer to the cubic oxidation law as time increases. The mass gain of three alloys does not fully match with the growth law of the oxide layer, which should be attributed to the internal oxidation degree of the alloy. The arithmetic square root of kp and kt, L, are proposed to quantify the internal oxidation degree. And the L of Inconel 617 alloy is the largest compared to Inconel 800H alloy and Hastelloy X alloy. This work is helpful to explain the behavior of oxidation of superalloys.

Isothermal low-temperature oxidation kinetics of heavy crude oil and its oxidized oils

A large amount of heavy oil inevitably encountered different degrees of isothermal low-temperature oxidation (LTO) reactions in the processes of in-situ combustion, storage, and transportation, so it was of vital importance to study the isothermal LTO kinetics of heavy oil that was still less well-understood. In this study, a thermogravimetry was used to study the isothermal LTO characteristics of heavy crude oil and its oils oxidized at 120, 160, and 200 °C, and four LTO temperatures of 125, 200, 275, and 350 °C with 1 h heating treatment were taken into account. The isothermal kinetic models were then established based on the n-order reactions. Subsequently, the comparisons of conversion degree between experiments and predictions were conducted to ensure the reliability of the established kinetics. The results showed that the mass losses for all the oil samples were almost linearly proportional to the LTO duration at 125 °C, indicating that the LTO time generated a significant effect on the thermal deposition. The shift rightward of the LTO peak with the elevated LTO temperature verified that the structures of all the oil samples were affected by LTO to a certain extent. After thermal degradation at 350 °C, 49.5% of LTO residue remained for the oxidized at 200 °C, obviously more than that for the other three oil samples. This gave a hint that the oils oxidized at higher LTO temperatures could be transformed into more fuel serving for combustion reactions. The appropriate values of reaction order of crude oil and its oils oxidized at 120, 160, and 200 °C were determined to be 4, 5, 5, and 7, respectively. There was no apparent difference in the values of activation energy, indicating that all the oil samples had close mass loss rates that determined the entire mass loss during isothermal LTO. The oil oxidized at 200 °C had fairly higher frequency factor than the other three oil samples, due primarily to its stronger polar molecular structure that resulted in higher molecular collision frequency. The prediction lines matched well with the experimental ones for all the oil samples, demonstrating that the developed isothermal kinetics was a useful tool to predict the LTO behavior of heavy oils.

Thermal analysis of the effects of cobalt additions on the high temperature expansion, melting and oxidation behaviors of nickel-based superalloys

ABSTRACT Cobalt is rarely present in nickel-based superalloys. When present, Co may produce a solid solution hardening effect on matrix or a stabilising effect for tantalum carbides if present. Co may also influence the general behaviour of Ni alloys at high temperature. In this work, the effects of Co on several high-temperature properties of a chromium-rich nickel-based alloy designed to be reinforced by TaC carbides are investigated. Different thermal analysis techniques are used: differential scanning calorimetry (DSC), thermo-mechanical analysis (TMA), and thermogravimetry (TG). Results show that the progressive addition of cobalt influences significantly the as–cast microstructure and the isothermal oxidation kinetics, but much less the refractoriness of the alloy and the thermal expansion behaviour. By adding Co, the interdendritic carbide population is made of more and more tantalum carbides, at the expense of chromium carbides. At the same time, the rate of mass gain due to oxidation increases.

Isothermal Low-Temperature Oxidation Kinetics of Heavy Crude Oil and its Oxidized Oils

Isothermal Low-Temperature Oxidation Kinetics of Heavy Crude Oil and its Oxidized Oils

High temperature isothermal oxidation behavior of electron beam melted multi-phase γ-TiAl alloy

The γ-TiAl alloys fabricated by additive manufacturing have gathered significant attention in recent years due to their unique microstructural features and properties. However, the oxidation kinetics of additively manufactured γ-TiAl alloys have not been studied thoroughly. Herein, the TNM-B1 alloy was fabricated with the help of electron beam melting (EBM) for the first time and tested for 100 h over a temperature range of 800 °C-1000 °C; this was aimed at investigating its isothermal oxidation kinetics. Subsequently, the exposed samples were systematically analyzed to study the oxide scales, which was achieved with the help of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Spallation was observed at 900 °C and 1000 °C after an exposure of 30 h and 5 h, respectively. The results showed that the oxide comprises alternative layers of Al2O3, TiO2, and mixture phases. The oxidation resistance of the EBM-processed TNM-B1 alloy was observed to be superior to those of the conventionally processed TNM-B1 and other γ-TiAl alloys. Finally, the significance of a fine fully lamellar microstructure on the oxidation kinetics of TNM-B1 alloy was explained.

Isothermal oxidation kinetics of laser cladded NiCoCrAl/WC + La2O3 hybrid composite coatings at 700 °C

Isothermal oxidation kinetics of laser cladded NiCoCrAl/WC + La2O3 hybrid composite coatings at 700 °C

High Temperature Oxidation Study of Nano-Y2O3 Dispersed Ferritic Alloys Synthesized by Mechanical Alloying and Sintering

This study concerns mechanism and kinetics of isothermal oxidation of four Fe-Cr-Al-Ti ferritic alloys in the range 700 °C to 900 °C for up to 50 hours in air. These four alloys with nominal compositions of 83.0Fe-13.5Cr-2.0Al-0.5Ti (alloy A), 79.0Fe-17.5Cr-2.0Al-0.5Ti (alloy B), 75.0Fe-21.5Cr-2.0Al-0.5Ti (alloy C), and 71.0Fe-25.5Cr-2.0Al-0.5Ti (alloy D) each with 1.0 wt pct nano-Y2O3 dispersion were synthesized by mechanical alloying and sintering at 1000 °C by hot isostatic pressing, high pressure sintering, hydrostatic extrusion and pulse plasma sintering techniques. A detailed characterization of the phase aggregate, microstructure and micro-composition of the oxide scale was carried out by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy, respectively. Oxidation kinetics appear to follow a parabolic rate with an activation energy of 135 to 234 kJ/mol, which depend on alloy composition (i.e., Cr content). Oxidation mostly occurred by counter-ionic diffusion of oxygen from air to the interior and cations (Cr+3 or Fe+3) from the bulk toward the surface. Alloy D sintered by hot isostatic pressing offered the highest resistance to oxidation.

Isothermal oxidation kinetics of nitrided Ti-6Al-4V studied by infrared emissivity

The oxidation kinetics of Ti-6Al-4V samples nitrided in forming gas (N2+5%H2) between 520 and 805 °C is investigated using infrared emissivity measurements. Several kinetic exponents have been observed depending on temperature and time. The activation energy corresponding to the main parabolic rutile growth stage is 223 ± 10 kJ/mol. This value is significantly higher than that corresponding to TiN oxidation, which suggests that it is not the rate-limiting step. The protective role of the nitridation is attributed to the internal Ti2N layer. The microstructural characterization reveals a reduction in the oxygen-diffusion depth compared to non-nitrided Ti-6Al-4V, and a multi-layered Al2O3-TiO2 oxide.

NiCoCrAlYTa coatings on nickel-base superalloy substrate: Deposition by high velocity oxy-fuel spraying as well as investigation of mechanical properties and wear resistance in relation to heat-treatment duration

NiCoCrAlYTa coating, a metal-based coating, was prepared on Inconel 718 Ni-base superalloy substrate by high velocity oxy-fuel (HVOF) spraying. The as-polished NiCoCrAlYTa coating was heated at 1000 °C for different durations to afford coatings C1, C2, C3, and C4. The microstructure, element distribution, phase composition and crystalline structure of the as-deposited coating and heat-treated ones were analyzed by transmission electron microscopy, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction and electron back-scattered diffraction. Moreover, the oxidation behavior of the NiCoCrAlYTa coatings was evaluated based on isothermal oxidation kinetics as well as weight loss measurements; and the effects of surface oxide layers on the microstructure, mechanical properties as well as friction and wear behavior of the NiCoCrAlYTa coatings were investigated. Results show that the as-sprayed coating exhibits dense and uniform microstructure as well as excellent oxidation resistance. Oxide layers, mainly composed of Al2O3, Cr2O3, NiO, Y2O3, Ta2O5, NiCr2O4, and CoCr2O4, are formed on the surface of the coating upon heat-treatment in air; and the microstructure and mechanical properties of the NiCoCrAlYTa coatings as well as oxide layers are governed by heat-treatment time. Particularly, coating C3, obtained after heat-treatment of the as-polished NiCoCrAlYTa coating at 1000 °C for 50 h, exhibits greatly increased indentation hardness, elastic modulus, and wear resistance. This is because the joint functions of a compact and continuous surface oxide layer with gradient nanostructure formed after heat-treatment, and the amorphous protective layer generated on the rubbed surface of coating C3.

Factors affecting isothermal oxidation of pure chromium in air

Isothermal oxidation kinetics of pure chromium at 950–1200°C in purely oxidizing (Ar-20%O2), purely nitriding (N2-5%H2), and oxidizing-nitriding (synthetic air, N2-20%O2) atmospheres were studied. Effects of factors such as oxide volatilization, multiple mass-gains, and nitridation on oxidation kinetics of chromium were investigated using thermal analysis, acoustic emission analysis, and electron microscopy. Results obtained in single oxidant atmospheres compared to those obtained in air clearly showed the transparency of chromia against nitrogen in air. The abrupt mass gain steps observed during isothermal oxidation were appeared due to the local oxide scale failure resulting from growth stresses in the thermally grown chromia scale.

Isothermal oxidation kinetics of ilmenite concentrate powder from Panzhihua in air

The objective of this study was to establish the kinetics of oxidation of ilmenite concentrate powders, which promotes reduction via the oxidation process. In this paper, the kinetics of the oxidation of ilmenite concentrate powders from low temperature to high temperature was studied comprehensively using the thermal gravity method. The reaction mechanism and model function were studied using two different classical methods, and then the results were compared. The results showed that, when the oxidation temperature was below 973K (700°C), the reaction mechanism is the three-dimensional diffusion, and the model function was Gα=1−23α−1−α2/3 (α, reaction degree). When the temperature was above 1273K (1000°C), the reaction mechanism is random nucleation and subsequent growth, and the model function was G(α)=[−ln(1−α)]1/3. No single model function can fit well the oxidation process at 1023K (750°C), 1073K (800°C), 1123K (850°C), and 1173K (900°C); thus, a multistage mechanism was proposed to explain the reaction process; this mechanism includes three-dimensional diffusion, random nucleation and subsequent growth in the order of increasing reaction degree. The apparent activation energies for the oxidation were also studied using two different methods: 199.43 and 194.01kJ/mol at 873K (600°C), 923K (650°C), and 973K (700°C); 4.11 and 3.96kJ/mol at 1273K (1000°C), 1373K (1100°C), and 1473K (1200°C). The relationship of oxidation degree with time and temperature is also discussed, which is helpful for the selection of the parameters of the oxidation process.