Parabolic Oxidation Behavior Research Articles

Oxidation behavior of ZrB 2–MoSi 2–SiC composites in air at 1500 °C

We investigated the oxidation behavior and the effect of the amount of SiC added on oxidation resistance in both hot-pressed ZrB 2–MoSi 2–SiC composites, 55ZrB 2–40MoSi 2–5SiC and 40ZrB 2–40MoSi 2–20SiC (vol.%), exposed to dry air at 1500 °C for up to 10 h. Quantitative electron microprobe analysis characterizations of the chemical compounds of post-oxidized composites were carried out. Parabolic oxidation behavior was observed for both composites. The addition of SiC improved the oxidation resistance of ZrB 2–MoSi 2–SiC composites, and the improvement enhanced with amount of SiC added. The microstructure of the post-oxidized composites consisted of two characteristic regions: oxidized reactive region and unreactive bulk material region. The oxidized reactive region divided into an outermost dense silica-rich scale layer and oxidized reactive mixture layer. The improvement of oxidation resistance with SiC addition is associated with the presence of a thicker dense outermost scale layer which inhibited inward diffusion of oxygen through it.

Comparison of the High-Temperature Steam Oxidation Kinetics of Advanced Cladding Materials

Isothermal and transient steam oxidation kinetics of the fuel rod cladding materials Duplex, M5™, E110, and Zircaloy-4 (Zry-4) were determined in separate-effect tests at various temperatures between 1073 and 1673K. All materials show parabolic time dependence at all temperatures, at least at the beginning of the oxidation. The temperature dependence of the oxidation rate is Arrhenius-like. All materials investigated show changes in the activation energy of the steam oxidation connected with the tetragonal-monoclinic phase transformation in the oxide. The temperatures of these changes differ between the Zr-Sn (Zry-4, Duplex: 1223 to 1273 K) and the Zr-Nb alloys (M5™, E110: 1273 to 1323 K). At temperatures below this phase transition, parts of the oxide layer can spall after longer oxidation times. It is known as the so-called “breakaway effect.” This effect occurs in Zry-4 and E110, whereas it was not detected in Duplex and M5™. The breakaway effect results in nearly linear oxidation kinetics. The width of the temperature range and the morphology of the spalled oxide parts differ significantly between Zry-4 and E110. For Zry-4, the breakaway effect was found only at temperatures between 1233 and 1313 K. The spalling of the oxide layer at E110 was detected between 1073 and 1313 K. This wide temperature range also affects the transient steam oxidation behavior. For heating rates below 0.1 K/s, a stronger oxidation was found than expected for parabolic oxidation behavior. The oxide parts spalled from E110 specimens are much finer than the particles after breakaway from Zry-4.

Quantitative Electron Microprobe Characterizations of Oxidized ZrB2 Containing MoSi2 Additives

This study reports the oxidation behavior of hot-pressed ZrB2 ceramics, with 10, 20 and 40 vol.% MoSi2 additives, exposed to dry air at 1500 °C for up to 10 h. The effect of the amount added MoSi2 on oxidation resistance was assessed. Quantitative electron microprobe characterizations of the oxidized ZrB2 with MoSi2 additives were carried out with electron probe micro analysis. Parabolic oxidation behavior was observed for the three compositions. The oxidation resistance was significantly improved with MoSi2 additives. Reaction-product phase compositions and phase distribution were thoroughly characterized from the oxidized surface through to the unreactive bulk material. It was found that the oxidation products consisted of nonstoichiometric amorphous SiO2, stoichiometric crystalline ZrO2, and MoB. The amounts of these phases in the oxidized reactive region were qualitatively determined.

Quantitative interpretation of parabolic oxidation behaviour of nitride powders

The oxidation behaviour of nitride powder under the condition of diffusion controlled has been investigated from both experimental and theoretical aspects. The effects of factors, such as oxidation time t, temperature T, oxygen partial pressure Po2, temperature increasing rate η and particle size R0, on the reacted fraction of oxidation have been studied, in which many factors have never been studied quantitatively before. The applications of the authors' model to both experimental data of AlN, BN and β-SiAlON powder provided by the authors' lab as well as the data of SiAlON and MgAlON powders offered by literature show that this model works well. Finally, after the calculation error comparison, it is clear to show that the authors' new model would lead to a more accurate calculation result against the model used in literatures currently.

High-temperature strength and oxidation behavior of Sc 3+/Lu 3+ co-doped α-sialon

The high-temperature strength and oxidation behavior of hot-pressed ScLu–α-sialon were investigated. The flexural strength at 1400 °C could reach 611 MPa, which was ∼94% of the room-temperature strength. A thin, dense oxidation scale was formed after exposure to air at 1300 °C. It exhibits parabolic oxidation behavior, with a maximum specific weight gain of 0.686 mg cm −2 and a rate constant of 4.21 × 10 −6 mg 2 cm −4 s −1 at 1300 °C. The excellent performance is attributed to the elimination of amorphous grain-boundary phase and formation of refractory secondary phases.

Quantitative interpretation of the parabolic and nonparabolic oxidation behavior of nitride ceramic

The oxidation behavior of nitride ceramic under the conditions of different rate-controlling steps existing has been investigated from theoretical aspect. A series of formulae have been introduced to express the oxidation weight gain and oxide layer thickness as a function of temperature, time and the size of materials explicitly. They give an analytic solution, which simplifies the calculation and is convenient for theoretical analysis and discussion. Available experimental data in literature for oxidation of nitride ceramic were used to evaluate the model. Good agreement was obtained between theory and experimental data.

Oxidation of single crystal PWA 1483 at 950°C in flowing air

Abstract The oxidation behaviour of single crystal PWA 1483 at 950 °C was investigated by means of XRD, SEM and EDS. The parabolic oxidation behaviour, as defined by mass gain and the respective oxide layer thicknesses, is characterized by a parabolic rate constant of about 4 × 10−6 mg2/(cm4 × s) and the formation of a multi-layered oxide scale. An outer scale contains a Ti-bearing thin film composed of TiO2 and NiTiO3 but mostly Cr in Cr2O3 and (Ni/Co)Cr2O4 besides NiTaO4. This outer scale is connected to a discontinuous layer of Al2O3 and an area of γ′-depletion within the base material.

Oxidation behaviour of an Alloy 617 in very high-temperature air and helium environments

The oxidation characteristics of Alloy 617, a candidate structural material for the key components in the very high-temperature gas-cooled reactor (VHTR), were investigated. High-temperature oxidation tests were conducted at 900 and 1100 °C in air and helium environments and the results were analysed. Alloy 617 showed parabolic oxidation behaviour at 900 °C, but unstable oxidation behaviour at 1100 °C, even in a low oxygen-containing helium environment. The SEM micrographs also revealed that the surface oxides became unstable and non-continuous as the temperature or the exposure time increased. According to the elemental analysis, Cr-rich oxides were formed on the surface and Al-rich discrete internal oxides were formed below the surface oxide layer. After 100 h in 1100 °C air, the Cr-rich surface oxide became unstable and non-continuous, and the matrix elements like Ni and Co were exposed and oxidized. Depletion of grain boundary carbides as well as matrix carbides was observed during the oxidation in both environments. When tensile loading was applied during high-temperature oxidation, the thickness of the surface oxide layer, the internal oxidation, and decarburization were enhanced because of the increase in diffusion of oxidizing agent and gaseous reaction products. Such enhancement would have detrimental effects on the high-temperature mechanical properties, especially the creep resistance of Alloy 617 for the VHTR application.

Oxidation behavior of HVOF sprayed Ni–5Al coatings deposited on Ni- and Fe-based superalloys under cyclic condition

Ni–5Al coating was obtained on three superalloy substrates viz. Superni 76, Superni 750 and Superfer 800 using high velocity oxy-fuel (HVOF) spray process. Oxidation studies were carried out on both bare and coated superalloy substrates in air at 900 °C for 100 cycles. The weight change was measured at the end of each cycle and observed that the weight gain was high in Superni 750 alloy when compared to Superni 76 and Superfer 800. A nearly parabolic oxidation behavior was observed for Ni–5Al coated Superni 750 and Superfer 800 alloys but a Ni–5Al coated Superni 76 substrate showed a slight deviation. The scale was analysed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) and electron probe microanalysis (EPMA). The coating increased the oxidation resistance for all the alloy substrates at 900 °C. Among the three-coated superalloys, Superfer 800 substrate has shown the best resistance to oxidation. The protective nature of the Ni–5Al coated superalloys was due to the formation of protective oxide scales such as NiO, Al 2O 3 and Cr 2O 3.

A new high-temperature, oxidation-resistant in situ TiB and TiC reinforced Ti6242 alloy

This study concerns an attempt to investigate the oxidation behavior of an in situ TiB and TiC reinforced titanium matrix composites (TMCs) in air over the temperature range 823–923 K. TMCs exhibited a parabolic oxidation behavior with the activation energy of 312.3 kJ mol −1. The results of oxidation kinetics and oxide scales formed in the test temperature for 1–300 h indicate that TMCs imparts excellent oxidation resistance. A detailed characterization of the microstructure and distribution of the phases within the scale following oxidation studies has been undertaken to suggest the possible mechanism for the oxidation of TMCs.

Hot‐Pressed Silicon Nitride with Lu2O3 Additives: Oxidation and Its Effect on Strength

The oxidation behavior and effect of oxidation on room‐temperature flexural strength were investigated for hot‐pressed Si3N4 ceramics, with 3.33 and 12.51 wt% Lu2O3 additives, exposed to air at 1400° and 1500°C for up to 200 h. Parabolic oxidation behavior was observed for both compositions. The oxidation products consisted of Lu2Si2O7 and SiO2. The Lu2Si2O7 grew out of the surface silicate in preferred orientations. The morphology of oxidized surfaces was dependent on the amount of additive; Lu2Si2O7 grains in the 3.33 wt% composition appeared partially in a needlelike type, compared with a more equiaxed type exhibited in the 12.51 wt% case. The high resistance to oxidation shown for both compositions was attributed to the extensive amounts of crystalline, refractory secondary phases formed during the sintering process. Moreover, after 200 h of oxidation at 1400° and 1500°C, the strength retention displayed by the two compositions was 93%–95% and 85%–87%, respectively. The strength decrease was associated with the formation of new defects at the interface between the oxide layer and the Si3N4 bulk.

Periodic oxide breakdown during oxidation of AlN/Sapphire(0001) films

We present an in situ synchrotron x-ray scattering study on the thermal oxidation of epitaxial AlN/Sapphire(0001) films. During annealing to 700 °C, an epitaxial AlN film transforms progressively into a planar epitaxial γ-Al2O3 layer. The oxidation proceeds through the γ-Al2O3/AlN interfacial motion that is observed directly from the intensity fringes near the AlN(0002) Bragg reflection. The oxidation rate, deduced from the interfacial motion, exhibits repeating transitions from a linear to a parabolic oxidation behavior. This suggests that the oxide break down periodically. During the oxidation the strain in the remaining AlN reverts to the value measured at the same thickness during the growth of the AlN film.

Oxidation behavior of in situ TiB short fibre reinforced Ti-6Al-1.2B alloy in air

The oxidation behavior of an in situ TiB short fibre reinforced Ti-6Al-1.2B alloy was investigated in a flowing air over the temperature range 873–1223 K. The alloy exhibited a parabolic oxidation behavior with the activation energy of 250 kJ/mol, which was supposed to be mainly controlled by the inward diffusion of oxygen. The oxide scales consisted mainly of TiO2, a small amount of Al2O3 and amorphous B2O3. The morphology of TiO2 changed from fine needle-shape at 1023 K to fine sphere at 1073 K and then well-developed block at a higher temperature. The microstructure of the subsurface showed that B2O3 pores and crack appear at the Ti/TiB interface above 1023 K as a result of the oxidation of TiB and evaporation B2O3. Combined with the thermodynamic analysis, it was suggested that the presence of TiB and formation of B2O3 could not act as an oxidation resistance. Finally, the diffusion coefficient of oxygen in Ti-6Al-1.2B exposure to 1073 K in air was determined to be 4.22 × 10−11 cm2/s.

Oxidation Behaviors of Two Phase NiAl+Ni3Al Intermetallic Compounds

Improvement of toughness of the brittle intermetallics was reported by controlling the morphologies of the Ni 3 Al phase through the solution and aging treatment in two phase NiAl+Ni 3 Al alloy. In this work, oxidation behaviors of two phase NiAl+Ni 3 Al intermetallic compounds were studied while paying special attention to the early stage oxidation behaviors as well as to the effect of boron addition. Experimental results from oxidation testing at 1100 °C in air flowing at the rate of 70cc/min showed that both types of intermetallic compounds with and without boron addition showed general parabolic oxidation behavior, but addition of boron to the two phase NiAl+Ni 3 Al intermetallic compounds deteriorated the oxidation resistance. The differences in the oxidation resistance between the intermetallic compounds with and without boron addition could be attributed to the microstructural difference, in that an accelerated oxidation along the thin layer of Ni 3 Al at the grain boundary observed in the Ni-32at.%Al-0.5at.%B intermetallic compound was responsible for the poor oxidation resistance, compared with the Ni-32at.%Al intermetallic compound showing no grain boundary Ni 3 Al phase. In the early stage, quite complex oxidation behaviors involving several types of oxide such as NiO, NiAl 2 O 4 , θ-Al 2 O 3 , α-Al 2 O 3 phases were observed, depending upon the location at the grain boundary regions in the Ni-32at.%Al-0.5at.%B intermetallic compound.

Microstructural aspect and oxidation resistance of an aluminide coating on 310 stainless steel

Surface alloying of Al into AISI 310 austenitic stainless steel to increase its high temperature oxidation resistance was attempted by employing pack cementaion process. After aluminization, the surface microstructure mainly consisted of an outer high aluminum-containing layer, an intermediate intermetallic compound layer and a ferritic stainless steel layer followed by the austenitic substrate. Oxidation resistances of AISI 310 stainless steel with or without aluminization treatment were evaluated by conducting thermal gravimetric analysis (TGA) in air at 700 and 1000°C. At these temperatures, parabolic oxidation behavior was observed for all the specimens investigated. Enhanced oxidation resistances (increased with increasing Al content) were found for the aluminized layers as compared with 310 stainless steel substrate. After TGA, the oxides formed on the specimen surfaces were identified by X-ray diffraction analyses. The results showed that the oxides formed on 310 stainless steel were composed of an outer spinel of Fe/Mn oxide and an inner layer of chromium oxide. For aluminized stainless steel specimens tested, the main constituent of the oxide layer was Al 2O 3.

Mechanisms of Ni 3Al oxidation between 500°C and 700°C

Oxidation of single- and polycrystalline Ni 3Al in air and at low (≤5.3 × 10 −3Pa) and high (2 × 10 4Pa) oxygen pressures in the temperature range from 500–700°C was studied by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). To study the influence of the initial condition, the surface composition was changed by annealing the samples at low pressures before oxidation in pure oxygen at high pressures. Preannealing at low pressures results in γ-Al 2O 3 layers with some metallic nickel. NiO particles grow on the Al 2O 3 scale after increasing the oxygen pressure. The initial stages of oxidation in air are characterized by the formation of NiO and Al 2O 3. Both oxides grow by outward diffusion of the metal cations until the faster growing NiO covers Al 2O 3. Subsequent oxidation occurs by outward diffusion of nickel and internal oxidation of aluminium to γ-Al 2O 3. Single crystalline Ni 3Al samples show a parabolic oxidation behaviour, but a variation by a factor of up to 5 of the oxide layer thickness after oxidation treatments at the same temperatures and times is observed. This is attributed to differences in the native oxide layers which consist of NiO and amorphous Al 2O 3. In some cases small amounts of γ-Al 2O 3 are found leading to a thicker oxide scale during the following oxidation.

High-temperature oxidation behavior of pure Ni3Al

The high-temperature oxidation behaviour of pure Ni3Al alloys in air was studied above 1000°C. In isothermal oxidation tests between 1000 and 1200°C, Ni3Al showed parabolic oxidation behavior and displayed excellent oxidation resistance. In cyclic oxidation tests between 1000 and 1300°C, Ni3Al exhibited excellent oxidation resistance between 1000 and 1200°C, but drastic spalling of oxide scales was observed at 1300°C. When Ni3Al was oxidized at 1000°C, Al2O3 was present as θ-Al2O3 in a whisker form. But, at 1100°C the gradual transformation of initially formed metastable θ-Al2O3 to stable α-Al2O3 was observed after oxidation for about 20 hr. After oxidation at 1200°C for long times, the formation of a thick columnar-grain layer of α-Al2O3 was observed beneath a thin and fine-grain outer layer of α-Al3O3. The oxidation mechanism of pure Ni3Al is described.

High-temperature oxidation behavior of iridium-based alumina-forming ternary intermetallics

The oxidation behavior of iridium-based intermetallics in the ternary iridium-aluminum-silicon system has been investigated. Additions of up to 20 at. % silicon to iridium-aluminum binary alloys reduce the aluminum concentration necessary for the formation of a protective alumina scale from greater than 55 at.% in the absence of silicon to as low as 20 at.% when 20 at.% silicon is present. Ternary iridium-aluminum-silicon alloys with 30–50 at.% aluminum and 8–10 at.% silicon exhibit parabolic oxidation behavior, and the rate constants are in good agreement with those previously determined for binary iridium-aluminum alloys. The oxidation rate of ternary iridium-aluminum-silicon alloys with 10 at.% silicon and 30–40 at.% aluminum deviates from the parabolic-oxidation behavior for alumina scale growth in the later oxidation stage, presumably due to the formation of a silica inner layer. Thermal cycling of the Ir-50 Al-8Si and Ir-60-Al samples does not result in scale spallation due to the coefficient of thermal expansion match between the alumina scale and intermetallic substrate.

Interpretation of the Parabolic and Nonparabolic Oxidation Behavior of Silicon Oxynitride

The oxidation process of Si2N2O, prepared by a hot isostatic pressing technique, has been studied by the thermogravimetric method. The oxidation has been performed in oxygen for 20 h in the temperature range 1300° to 1600°C, producing oxide scales of amorphous SiO2 and α‐cristobalite. The weight gain for T 1350°C does not begin to follow a parabolic rate law, until a certain time, t0. The A0 parameter in the parabolic rate law, (Δw/A0)2=Kpt+B, represents the cross section area, A, through which the oxygen diffuses; in the derivation of this law A is assumed to be constant during the experiment. If crystallization occurs during the oxidation process, A will decrease with time. A function, A(t), describing the time dependence, has been developed and incorporated into the parabolic rate law, yielding a new rate law, which reads ΔW/A0=a arctan √bt+c√t. This new rate law is valid in the time interval t < t0, whereas, for t > t0, the oxidation process follows the equation (Δw/A0)2=K°pt+B0. The relation of the latter equation to the common parabolic rate law is described. All of the oxidation curves are described by these equations. The activation energy of the oxygen diffusion (and of the oxidation (Kp)) is found to be 245 ± 25 kJ/mol, which is consistent with literature values reported for oxygen diffusion.

Correlation of acoustic emission events with parabolic oxidation behaviour of 2.25Cr-1Mo steel

In this work AE events and cumulative AE events have been measured during oxidation of 2.25 Cr-1 Mo steel at 773, 873, 973 and 1073 K and the results are compared with a corresponding thermogravimetric study