Papers by Keyword: FeCrAl

Abstract: FeCrAl alloy powder is used to mix with an additive to prepare a powder mixed paste. FeCrAl alloy honeycombs are fabricated by extruding the powder mixed paste, then dried and sintered. While sintering at 1200°C, with sintering time increase, the volume of sintered honeycombs increase and density decrease. The structure parameters and properties of sintered honeycombs were obtained by measuring and calculating. Results show that wall thickness 0.18~0.23mm, cell number (1/in²) 316~339, clear cross section (%) 69~74, specific surface Sv (sq m/cu dm)2.35~2.52; specific heat capacity C_p(J/g.K) 0.60~0.70, heat conductivity κ (W/m.K) 6.52~6.78. SEM/XRD analysis shows that a large number of oxides formed on the surface of sintered honeycombs during sintering, such as Fe₂Cr₂0₄, Fe₂Si0₄, Al₂O₃.These oxides connect together to form film on surface of sintered honeycombs. By impregnating and baking test, the surface of sintered honeycomb can firmly adhere γ-Al₂O₃ catalytic washcoat. The oxide film formed on the surface sintered honeycombs is benefit for adhering and supporting the catalytic active components.

Abstract: Metal supported catalysts in hydrogen production reactor has a very broad application prospect. However, the film adhesion of active coating with the metal support is the key problem which needed to be solved urgently. In this paper, FeCrAl alloy was chosen as the metallic substrate. The effects of oxidation temperature and time on the morphology, crystal phase and element composition of the metal surface were investigated by XRD, SEM and EDAX. The results show that after pre-treatment of FeCrAl Metallic Substrate,a dense transition layer of α-Al₂O₃ formed on the surface of the metallic support. Thus the oxidized α-Al₂O₃ layer and the γ-Al₂O₃ coating could combine together better. The optimum pre-treatment condition is at 950°C for 10h in air atmosphere.

Abstract: Scale surface and scale/alloy interface for alumina-forming (Fe-20Cr-4Al) alloys with noble metal (palladium, platinum) and yttrium were studied in oxidizing atmospheres (oxygen, oxygen-water vapor) for 18ks at 1473, 1573 and 1673K, by mass gain measurements, amount of spalled oxide, X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission-transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS). After oxidation at 1473K for 18ks in oxygen, the mass gains of the FeCrAl, FeCrAlPd and FeCrAlPt alloys showed almost the same values. Those of the FeCrAlY alloys decreased with increasing yttrium of up to 0.1% followed by an increase with the yttrium content. The mass gain of the FeCrAlPtY alloys with appropriate additions of platinum and yttrium were lower than that of the FeCrAlY alloy with 0.1mass% yttrium, and alumina/alloy interface of the alloy showed good coherency by TEM. The scale surface of the FeCrAl, FeCrAlPd and FeCrAlPt alloys were rough, however, those of the FeCrAlY and FeCrAlPtY alloys were smooth. After oxidation at 1673K for 18ks in water-vapor (47vol%), FeCrAlPt alloy with 0.5mass% platinum showed good oxide adherence. Platinum concentration was observed at alloy side of the alumina/alloy interface by FE TEM/EDS.

Abstract: The long term oxidation test of FeCrAl substrate treated by ultrasonic and electroplating methods was performed at 9000C in air environment for 100 hours. The purpose of this paper is to show the nickel layer evolution of that substrate. Oxide scale and layer evolution were assessed on specimens using scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). The nickel layer disappeared and fully converted to be nickel oxide on FeCrAl treated using ultrasonic and nickel electroplating after oxidation exposure at 9000 C in air for 100 hours. In this condition, the nickel oxide still existed. Not only nickel oxide and Al2O3 were occurred when oxidation exposure at this condition but also Cr2O3 and Fe2O3. The lowest parabolic rate constant was obtained from FeCrAl ultrasonic treatment with SiC for 50 minutes at 1.21 x 10-4 mg2mm4h-1, and FeCrAl ultrasonic treatment with Al2O3 for 30 minutes at 1.15 x 10-4 mg2mm4h-1. The lower parabolic rate constant indicated the higher long time to failure of the FeCrAl substrate.

Abstract: The palladium based combustion catalysts on FeCrAl alloy substrate (Pd/FeCrAl) were prepared by electroless plating method. By means of scanning electron microscopy (SEM), X-ray diffraction and BET specific surface area, it was found that the prepared catalyst after calcination treatment at 800°C could obtain utmost PdO phases, which were well dispersed on substrate with small and uniform particles. The EDX analysis and the adherence tests further indicated that a synergistic interaction was formed between palladium components and substrate on catalyst calcined above 600°C, which might be caused by α-alumina whiskers packaging palladium particles on the surface of substrate. Moreover, the results of activity tests for toluene combustion showed that the 0.1%Pd/FeCrAl catalyst had good low temperature catalytic activity and temperature-resistance property. The total combustion temperature (T90) for toluene over catalyst calcined at 600, 800 and 1000°C was at 218, 207 and 217°C respectively. And the toluene conversion could keep up above 99% during the stability test of Pd/FeCrAl catalyst at 210°Cfor 50 h, indicating the good catalytic stability of Pd/FeCrAl catalyst.

Abstract: The irregular surface roughness morphology due to ultrasonic method was used approach for increasing the high surface area of substrate and catalyst. The purpose of this paper is to show the ultrasonic and nickel electroplating methods for NiO automotive catalyst development on FeCrAl substrate. The process began with pretreatment of FeCrAl using SiC and/or Al2O3 solution agitating by ultrasonic and followed with nickel electroplating. The oxidation test was conducted for developing the NiO. The physical morphology structure of the presence NiO on the FeCrAl substrate was analyzed using scanning electron microscope (SEM) in combination with energy dispersive X-ray spectroscopy (EDS). The cross sectional observation show the NiO catalyst completely existed on the FeCrAl. The ultrasonic method increases the irregular surface roughness morphology on FeCrAl substrate that influenced the homogeneous and stability of nickel electroplating and NiO surface area development.

Abstract: Long-term cyclic oxidation behavior was compared for commercial FeCrAl alloys and model Fe-Al and FeCrAl alloys, and their coefficients of thermal expansion (CTE) were measured. For single-phase disordered (ferritic) Fe(Al) alloys, the CTE increased only slightly with Al content and was similar to that of FeCrAl alloys. More significant CTE increases were observed at ≥20%Al, as intermetallic phases, Fe3Al and FeAl, formed. As expected, the intermetallic compositions showed increased oxide spallation rates during cyclic oxidation at 1100° and 1200°C. However, after extensive spallation and loss of Al from the substrate, the compositions of Fe3Al and FeAl specimens entered the ferritic phase field, and the amount of scale spallation decreased. Among commercial oxide dispersion strengthened (ODS) FeCrAl alloys, a composition containing Mo (ODM751) exhibited the lowest thermal expansion and showed the slowest degradation rate in long-term testing at 1100°C. The concept of minimizing CTE as a route for alloy development was investigated.

Abstract: The effect of reactive element additions (external doping as an yttrium-oxide coating on the metal) on the oxidation behaviour of a commercial FeCrAl alloy (Kanthal A1) has been investigated during isothermal exposures in air at 1373K. The scale growth kinetics of the bare alloy obey a parabolic rate law during the whole oxidation test whereas the kinetic curves of the yttrium-bearing specimen exhibit an initial transient stage during the first hours, followed by a parabolic regime. The yttrium addition to the bare alloy does not give the beneficial effect usually ascribed to the reactive elements. No significant oxidation rate improvement of the alloy is observed, the parabolic rate constants values obtained are roughly similar for the both specimens. In situ X-ray diffraction reveals a marked influence of the reactive element on the composition of the oxide scale. The oxide layer formed on the yttrium-bearing specimen revealed, in addition to α- alumina which is the main oxide also identified on the bare specimen, the presence of yttrium aluminates (YAlO3, Y3Al5O12) located in the outermost part of the layer.

Abstract: Two FeCrAlRE alloys, a commercial, 0C404, and a model alloy in the form of thin foils, with different Mn, Nb, Mo and Ti concentrations were subjected to cyclic oxidation in lab air at 1100°C. The oxidized samples were studied by gravimetry, Grazing-Incidence X-ray Diffraction (GI-XRD), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive X-ray (EDX) analysis. The two FeCrAl alloys exhibit different oxidation kinetics; however, both alloys have the same weight gain after 500 hours exposure. During the early stages the scale consists mainly of α-Al2O3 together with some oxide particles containing Mn, Al, Fe and Cr formed on the alloys. After 500 hours the 0C404 scale locally also consists of larger polycrystalline regions of Mn-Cr-Al spinel. In addition, Si-rich oxide, chromia and Al-Cr oxide could be observed at the metal/oxide interface.

Abstract: The effect of the addition of 5 and 10 at.% Cr on the oxidation of a binary Fe-10 at.% Al alloy (Fe-10Al) was studied in 1 atm O2 at 1000°C. Fe-10Al underwent a very slow initial nearly-parabolic stage followed by a breakaway composed of two subsequent parabolic stages with a smaller rate constant for the final period. The two ternary alloys (Fe-5Cr-10Al and Fe-10Cr-10Al) presented two parabolic stages with final rate constants similar to each other and much lower than that for Fe-10Al. The alumina scale developed initially on Fe-10Al was replaced later by a layered scale containing mixtures of Fe and Al oxides plus many Fe-rich oxide nodules. Fe-5Cr-10Al was mostly covered by a thin alumina layer just above the alloy surface with some Fe-rich nodules formed in the beginning of oxidation, which later on were healed by alumina with a large decrease of the oxidation rate. A continuous alumina layer formed on the whole sample surface without any Fe-rich nodule for Fe-10Cr-10Al. Therefore, the addition of chromium is obviously beneficial for the oxidation resistance of Fe-10Al by inhibiting the formation of fast-growing Fe-containing oxides and promoting the development of an exclusive alumina layer. However, the effect of chromium is different from the classical third-element effect.