Papers by Keyword: Oxidation

Abstract: Hot corrosion behavior of a powder metallurgy superalloy (Alloy 1) in molten 95% Na₂SO₄+5%NaCl salts at 800 °C are investigated with average corrosion rate calculation, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy spectrum analyzer (EDS). Meanwhile, the hot corrosion tests of Alloy 2 at 800°C were also carried out for comparison. Experimental results show that the corrosion layers obtained after 100h of hot corrosion were mainly composed of Cr₂O₃, Al₂O₃ , NiO , Ni₃S₂ , NiCr₂O₄ and Cr₂S₃ at 800 °C. The cross-sectional morphologies and corresponding elemental maps indicate that a large amount of sulfides and oxides appeared in internal substrate. According to these results, the cooperating mechanism of oxidation and sulfuration in Na₂SO₄-NaCl salts for Alloy 1 is confirmed. Compared with Alloy 2, the increased Co and Al content in Alloy 1 with better hot corrosion resistance at 800 °C promoted the rapid formation of continuous Cr₂O₃ and Al₂O₃ protective films on the alloy surface in which Co inhibited internal oxidation of Al and reduced internal diffusion of S through the third element effect. Key words: powder metallurgy superalloy; hot corrosion; oxidation; molten Na₂SO₄-NaCl salts; sulfuration

Abstract: Bitumen is a hydrocarbon product prone to oxidative aging. For this reason, the aim of this study is to evaluate physical and rheological properties of modified bitumen with pruning residues from blueberry bushes powder (RPA), anti-aging natural compound, to reduce the oxidative damage of bitumen. Rolling thin film oven test (RTFOT) was performed to simulate short term aging of modified bitumen with 2, 6 and 10% RPA by weight. The results of conventional tests (penetration, softening point, ductility and rotational viscosity) indicated that the addition of RPA increases the stiffness of bitumen and decreases its temperature susceptibility. In addition, dynamic shear rheometer test (DSR) shows that modified binders improve their resistance against deformation and enhance their elastic response. The 6% RPA binder demonstrated better oxidative aging resistance without compromising its performance at low temperature.

Abstract: In this study, the effect of oxidation on the transformation temperatures and microstructure of Ti-Ta₂₀-Al₅ high temperature shape memory alloys (Ti-Ta₂₀-Al₅ HTSMAs) is studied. The alloy was studied under two conditions, as cast and after cold rolling and recrystallizing (CR +RE). The microstructure, phase composition, and phase transformation temperature of Ti-Ta₂₀-Al₅ HTSMAs before oxidation were studied. Thermogravimetric analysis (TGA) combination with microstructural investigations were performed after oxidation at temperatures range from 25°C up to 1000°C. For both conditions, the alloy consisted mostly of β – BCC and martensite ʺα – orthorhombic phase before oxidation. Ti-Ta₂₀-Al₅HTSMAs as (CR +RE) shows martensitic transformation temperature higher than 400°C. The oxidation behaviour was linear until 650°C, while parabolic at elevated temperatures. For both conditions, the alloy consisted of β – BCC phase (Ta – rich) and α-hexagonal phase (Ti – rich) with not strong precipitation of ω – phase after oxidation. The results show that the formation of multi – layer oxide, which consists of Al₂O₃, TiO₂, and Ta₂O₅. For both conditions, oxidation can suppress martensitic phase transformation by precipitation of α-hexagonal phase (Ti – rich), Al₂O₃, TiO₂, and Ta₂O₅, and ω phase, would result in degradation of the martensitic phase transformation.

Abstract: The MCrAlY overlay coatings are widely used for high-temperature protection of hot section part of gas turbines and jet engines. This type of coatings are usually thermally sprayed using APS (Atmospheric Plasma Spraying), LPPS (Low Pressure Plasma Spraying) as well as HVOF (High Velocity Oxygen Fuel) methods. In present article the newly developed ethanol based HVOF gun was used for production of this type of coatings. The stainless steel 18-8 type was used as a base material. The AMDRY 386 (Oerlikon-Metco) NiCrAlY powder was used for coatings production. In the research different oxygen (400, 500, 600 NLPM) and ethanol (16.5, 18.3, 21.3, 23.6 and 26.6 dm³/h) flow ratio were selected for experimental processes. The powder feed ratio was also changed during process. After deposition the microstructural assessment using Scanning Electron Microscopy and chemical composition analysis using EDS method were conducted. The obtained results showed that coating was above 100 μm thick depending on the process parameters. The low concentration of pores and oxides was also observed on coatings cross-section. Using of ethanol HVOF gun enables to form good quality MCrAlY coatings with 50% reduction of oxygen consumption in comparison with conventional HP/HVOF torch using kerosene such as JP 5000. The other benefit of its using is lower CO₂ emission and lower concentration of carbon in coating in comparison with classic JP 5000 HVOF gun. The ethanol HVOF is a promising technology and might be considered as an replacement of LPPS and HVOF process for production of MCrAlY type of coatings.

Abstract: Supported 3wt%Pd/α-Al₂O₃ catalyst was tested in selective oxidation of 1,2-propanediol by molecular oxygen. It was found that the catalyst is active in an alkaline water solution. Lactic acid was obtained as the main product of the reaction. Influence of different reaction conditions on 1,2-PDO conversion and oxidation process selectivity was studied. Partial kinetic orders of the reaction with respect to 1,2-propanediol, c₀(NaOH), p(O₂), n(1,2-PDO)/n(Pd)) were determined and an experimental kinetic model of the catalytic oxidation reaction was obtained. Activation energy of the process was calculated and was found to be about 53 ± 5 kJ/mol.

Abstract: The process of oxidation of hydrocarbon with oxygen proceeds with formation of the corresponding hydroperoxide as the primary product [1,2]. A catalyst is the most important factor that influences on the direction of flow of the oxidation reaction. Catalysts based on metals of variable valency, and their derivatives are the most active in reactions of oxidation of hydrocarbon [3].

Abstract: : In this paper, activation procedures under size effects of some gold nanoparticles (Au₁₀₁, Au_naked and Au_citrate) and nanoclusters (Au₈ and Au₉) immobilized on powder Norit^® activated carbon (abbreviated to AC) and/or Vulcan carbon (abbreviated to VC) on the catalytic activity of gold nanocatalysts were studied. The gold nanostructures were activated through the washing procedure with a base in MilliQ water or hot toluene and then followed by heating in static air (abbreviated to W+S) or under vacuum (abbreviated to W+V) at 100 °C for 3 h. The highest activity of gold nanocatalysts for benzyl alcohol oxidation was obtained for activated (W+V) ‘naked’ gold nanoparticles immobilized on Norit^® activated carbon when the gold nanoparticle diameters was ~4.4 nm.

Abstract: MCrAlY can be used as bond coats for thermal barrier coatings (TBCs) with good ductility and excellent resistance against high temperature oxidation and hot corrosion. The behavior of the microstructure development in the MCrAlY coatings plays a key role on the oxidation resistance. In this paper, the microstructure in the coatings oxidized at 750~1100 °C was analyzed. The formation of the phases and their fraction were studied by comparing thermodynamic simulation results with the experimental observations. At higher temperatures (>1000 °C) β-to-γ’-to-γ phase transformation took place while at lower temperatures (<1000 °C) β phase would transfer to γ directly. The results show that the simulation can semi-quantitatively predict the microstructure formed in the coating.

Abstract: MCrAlY can be used as bond coats for thermal barrier coatings (TBCs) with good ductility and excellent resistance against high temperature oxidation and hot corrosion. The behavior of the thermally grown oxide (TGO) scale formed at the MCrAlY coatings plays a key role on the oxidation resistance. In this paper, the oxidation kinetic curves of a MCrAlY coating at 900~1000 °C were obtained by measuring the thickness of the TGO scales. The curves basically conveyed parabolic laws, indicating a diffusion-controlled mechanism of the TGO growth. The thickness of TGO was positively correlated with the consumption of β phase during the early stage of the oxidation processes. After about the half-life of the β phase consumption, the depletion of the β phase significantly accelerated, which was caused by coating-substrate interdiffusion. In addition, the microstructure of the TGO was analyzed

Abstract: This article discusses the ways of intensification of the oxidation process with the formation of surface properties necessary to increase the service life of one of the parts of an internal combustion engine - a cylinder made of cast aluminum alloy. A brief overview of existing technologies for hardening the aluminum surface is presented. Environmentally friendly options are proposed for using the potential of processes that have accumulated energy within an electrolytic cell by activating the interelectrode gap and forming an oxide with desired properties. The main difference from the existing model approaches of oxide formation lies in the parallel excitation of the main participant in the process, oxygen, in order to dominate it over other, oxygen-containing donors. Ways of using the energy of cavitation phenomena due to acoustic resonance in an electrolytic solution are proposed. Redistribution of the field potential by replacing a flat cathode with a pointed one changed the conductivity conditions in the interelectrode gap as a result of the electroconvective action. The structure of the oxide layer, phase changes, and physical properties confirming the originality of oxide coatings have been investigated.