Papers by Keyword: Oxidation Kinetics

Abstract: The oxidation behaviors and kinetics of in-situ β-Sialon bonded Al₂O₃-C refractories were investigated by TGA techniques via isothermal oxidation experiments at different temperatures. The results show that the oxidation process of in-situ β-Sialon bonded Al₂O₃-C refractories can be divided into three stages: oxidation reaction rate controlling stage, reaction and diffusion controlling stage, and diffusion controlling stage. The oxidation rate controlled by the reaction rate has no obvious changes as the temperature increases. The oxidation rate controlled by the reaction rate and the diffusion rate together has a trend of decline, so is the oxidation rate controlled by the diffusion rate.

Abstract: Thermogravimetric analyzer (TGA) was used to simulate isothermal 60-min oxidation process of Fe-1.5Si alloy under air condition at 700°C-1150°C. Cross-sectional scale morphology and elemental distribution of the oxide layer were investigated by electron probe microanalysis (EPMA). At 700°C-1150°C the oxide scale is composed of external scale and internal Si precipitates zone. And Si-rich oxides can be detected in the inner parts of the outer oxide scale. It was found at 700-1000°C that oxidation mass gain curve obeys the parabolic law but at 1100-1150°C the relationship of mass gain and oxidation time is complex. The parabolic rate constant is lowered at 900-1000°C that should be related with thicker internal oxidation zone at 900°C and formation of the obvious Si-rich layer in external oxide scale at 1000°C.

Abstract: The specific heat capacity was calculated by DSC and the kinetics of oxidation was determined for alloys from the NiAl, FeAl and TiAl phase equilibrium system. The Ti48Al alloy contained an addition of 2 at.% of chromium and niobium. The highest value of heat capacity had the Ti-Al and Fe-Al alloys. At temperatures above 673K, the Ti48Al alloy showed an anomaly, that is, a lower value of the heat capacity. The change in heat capacity was related with an exothermic reaction. The oxidation of alloys was running according to either parabolic or cubic law. Alloys characterised by high thermal capacity showed a higher gain in weight. The slowest to oxidise was the Ni₃Al intermetallic phase.

Abstract: SiC whisker reinforced Si3N4 composite was used for studying crack healing behavior. Surface crack and straight-through crack were introduced on the tensile surface of specimens by Vickers hardness indenter and single edge pre-crack beam method. The cracked specimens were heat-treated at 1000 , 1100 , 1200 and 1300 for 1 hour in air. Bending strength was measured at room temperature by three point bending tests system. It was investigated that the best heat treatment temperature of Si3N4/SiC whisker composite is 1200 -1300 . The relationship between bending strength and logarithm of crack area was near linear and parabola in original and heat-treated specimens, respectively. Crack healing behavior was analyzed by oxidation filling model according to oxidation kinetics.

Abstract: The oxidation behaviour of AlCuTiFeNiCr high-entropy alloy with was studied at 850 oC in atmosphere. The oxide layer of long-term oxidation behavior were examined using optical, X-ray powder diffraction (XRD) with the aid of scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis (EDX). The oxidation kinetics follows a parabolic rate law. The oxidation rate decreases gradually as the oxidation proceeds.

Abstract: Superplastic forming provides significant industrial application for forming complicated, lightweight components of aerospace propulsion application. Since superplastic forming process is a function of temperature, time, applied pressure and contact condition of the matched surfaces, the oxidation is one of the concerned subjects. In the present work, the oxidation behavior of UNS31803 was studied in superplastic forming atmosphere. It is shown that the Pieraggi model is successfully applied to the high temperature oxidation of this alloy. The effective activation energy of the oxidation is 399 KJ/mol at this condition.

Abstract: The oxidation kinetics of copper or aluminum added with magnesium was investigated by a modified Chou model. The effect of the addition of magnesium in copper or aluminum was discussed. The calculation results showed that the activation energy of CuMg0.34 was the highest among Cu-Mg alloys at 600-900 °C, which indicated that it had the best oxidation resistance in all of the samples. The aluminum alloy AA3004 containing 1.0 wt.% Mg showed the better anti-oxide behavior than AA5182 with 4.0 wt.% Mg, and the relation between oxidation rate and oxygen partial pressure could be expressed as 0.71 times power law.

Abstract: The high temperature oxidation and microstructure evolution of 55%Al-Zn-Si coated sheets were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD). After oxidation, the coatings consisted of three phases including ZnO, Fe₂Al₅, and FeAl from topcoat to the substrate. The different diffusion rate of Fe and Al result in forming voids at the interface of intermetallic layer and the substrate. A good agreement has been reached between the experimental data and the calculation from Chou diffusion model, which has a good predicted function. Moreover, the characteristic oxidation time and the apparent activation energy were obtained.

Abstract: The Oxidation kinetics of Ti-48Al-2Nb-2Cr composites (TANC) with addition of different weight contents of CaF2 solid lubricant was evaluated. It is indicated that oxidation dynamic curve follow quasi-parabolic rate law under 800 °C. Once the temperature exceed 1100 °C, the oxidation dynamic curve seems to do not follow quasi-parabolic rate law. The contents of solid lubricant in TANC matrix occur an important influence for oxidation resistance

Abstract: Isothermal oxidation of two g-TiAl-based intermetallic alloys: Ti48Al and Ti46Al8Nb alloys was studied in synthetic air at 1073-1223 K for up to 240 hrs. Mass change per unit area for the oxidized samples followed approximately the parabolic rate law. The k_p values for the studied temperature interval were in the range from 7.2×10^-13 to 1.8×10^-11 g²cm^-4s^-1. The activation energy for oxidation of Ti48Al alloy in air at 1073-1223 K was E_a = 165±12 kJ/mol. Niobium addition to Ti48Al alloy in the amount of 8% increased its oxidation resistance. Structure and chemical composition of the oxidation products, and morphology of the oxidized samples were investigated using XRD, SEM-EDS, and TEM. The oxide scales formed on Ti48Al and Ti46Al8Nb alloys were well adherent to the metallic substrates and exhibited a multilayer structure. Depending on the oxidation temperature and the alloy composition, the scale consisted of variable amounts of TiO₂ and Al₂O₃. Additionally TiN, and niobium rich particles were also identified in the appropriate oxide scale. To understand the growth mechanism of oxide scale formed on Ti46Al8Nb alloy, two stage oxidation experiment was performed using ¹⁶O₂/¹⁸O₂, followed by SNMS and TEM-EDS. Particular attention was paid to the use of TEM in order to precisely characterize the reaction products on the Ti46Al8Nb alloy.