Pudji Untoro

Time dependence of Mg-incorporation in alumina scales on FeCrAl alloys studied by FIB-prepared TEM cross sections

AbstractMinor alloying additions and alloy impurities can be of crucial importance for the protective properties of oxide scales on high temperature alloys. An example of an impurity is magnesium. In the present study, the effect of Mg impurity (concentration 80 ppm) on the oxidation behaviour of a commercial FeCrAl alloy at 1200°C was investigated. By a combination of various analysis techniques, such as optical metallography, SEM/EDX/WDX, X-ray diffraction and TEM, it was found that Mg appeared to become easily incorporated in the surface oxide already after relatively short exposure times.Comparison of the oxidation products showed a change in the scale growth mechanism to occur in course of the oxidation treatment. Magnesium was found to migrate through the alumina scale and it became enriched in the outer part of the oxide scale forming a layer of a (Mg,Mn)Al2O4 spinel. An important effect associated with the Mg-enrichment and spinel formation was the development of porosity within the scale which ma...

Effect of Nanocrystalline and Ti Implantation on the Oxidation Behaviour of Fe80Cr20 Alloy and Commercial Ferritic Steel

The oxidation behaviour of developed Fe80Cr20 alloy and commercial ferritic steel at 1173 - 1373 K in air is studied. Effects of crystallite size and titanium implantation on the oxidation behaviour of specimens were analyzed based on oxide morphologies and microstructures. Oxide scales characterisations of specimen after oxidized were identified by X-ray diffraction (XRD). The surface morphology of oxide scales were examined with scanning electronic microscope (SEM) and energy dispersive X-ray analysis (EDX). The rate constant of oxidation were determined using Wagner method. The results show that crystallite size and titanium implantation has remarkably enhanced the oxidation resistance. The oxidation kinetics indicate that the developed Fe80Cr20 as the finer crystallite size both unimplanted and implanted specimens show better performance.

Determination of Nanocrystalline Fe80Cr20 Powder Based Alloys Using Williamson-Hall Method

The aim of this study is to determine the nanocrystalline size by using Williamson-Hall method of Fe80Cr20 powder which prepared by mechanical alloying process. X-rays diffraction line profile analysis was adopted to analyze the crystallite size and microstrains of Fe80Cr20 alloys powder. Transmission Electron Microscopy (TEM) was used to examine the microstructure morphology of the nanosized of Fe80Cr20 alloys. The crystallite size, microstrain, and lattice parameters were estimated by Williamson–Hall plot. The results showed that the mechanical alloying processes resulted the final product in nanocrystalline size range (below 12 nm) which confirmed by TEM observation and XRD line profile analysis.

Microstructure Study on Fe/Cr Based Alloys Added with Yttrium Oxide (Y2O3) Prepared via Ultrasonic Technique for Solid Oxide Fuel Cell (SOFC) Application

Solid oxide fuel cells (SOFC) are the current research having several potential to obtain high efficiency, high energy–density power generation which operated at relatively higher temperature. Yttrium oxide (Y2O3)contributions at high temperature are accelerating to the development oxide layer of FeCr alloy. The aim of this research is to investigate the microstructure of Fe/Cr added with Y2O3 acting as a reactive element. The purpose is to improve macrostructure of Fe/Cr powders which can be applied at steel industry. In this study the mixing process of Fe/Cr and Y2O3 powder was conducted via ultrasonic treatment at a frequency of 22 kHz, and at two different holding time of 2.5 h and 3.5 h. The particle size of chromium (Cr) can be reduced by ultrasonic treatment at from 60µm to 30µm through threshing the cluster of Cr particle. It shows that the ultrasonic vibration effectively removes oxides and other contaminates on a surface coating. Therefore, homogeneity of the parent material, segregation, and uniform distribution of second phase were increased.

Microstructure and Mechanical Properties of Nanocrystalline FeCr Alloy Prepared by Spark Plasma Sintering

This paper investigates the efficiency of two consolidation processing techniques prepared by spark plasma sintering (SPS) and hot pressing (HP) which allow obtaining fully dense nanostructured materials. FeCr powders were sintered by using spark plasma sintering (SPS) and hot pressing (HP) sintering techniques over sintering temperature up to 1000oC. The microstructures of the sintered end-products were characterized by Scanning Electron Microscopy (SEM). X-rays diffraction line profile analysis was adopted to analyze the crystallite size of starting and sintered FeCr using Williamson–Hall method. The density of the sintered specimens was measured by using the Archimedes method. The result indicated that the dense specimen with relative similar density and approaching the equilibrium state obtained in shorter time and lower sintering temperature by spark plasma sintering compared to conventional hot pressing. The FeCr specimen prepared by SPS showed more effective to retain nanocrystalline and better mechanical properties than those prepared by HP. The diffraction investigation revealed that the grain growth was not significant in SPS process compared to HP, which would enhance the mechanical properties of the SPS sintered FeCr.

NiO Development on FeCrAl Substrate for Catalytic Converter Using Ultrasonic and Nickel Electroplating Methods

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.

Preparation of NiO Catalyst on FeCrAl Substrate Using Various Techniques at Higher Oxidation Process

The cheap nickel oxide (NiO) is a potential catalyst candidate to replace the expensive available platinum group metals (PGM). However, the current methods to adhere the NiO powder on the metallic substrates are complicated. Therefore, this work explored the development of nickel oxide using nickel (Ni) on FeCrAl substrate through the combination of nickel electroplating and oxidation process for catalytic converter application. The approach was started with assessment of various nickel electroplating process based on the weight gain during oxidation. Then, the next experiment used the best process in which the pre-treatment using the solution of SiC and/or Al2O3 in methanol. The specimens then were carried out to short term oxidation process using thermo gravimetric analysis (TGA) at 1000 oC. Meanwhile, the long term oxidation process was conducted using an automatic furnace at 900, 1000 and 1100 oC. The atomic force microscopy (AFM) was used for surface analysis in nanometer range scale. Meanwhile, roughness test was used for roughness measurement analysis in micrometer range scale. The scanning electron microscope (SEM) attached with energy dispersive X-ray (EDX) were used for surface and cross section morphology analysis. The specimen of FeCrAl treated using ultrasonic prior to nickel electroplating showed the lowest weight gain during oxidation. The surface area of specimens increased after ultrasonic treatment. The electroplating process improved the high temperature oxidation resistance. In short term oxidation process indicated that the ultrasonic with SiC provided the lower parabolic rate constant (kp) and the Al2O3 and NiO layers were also occurred. The Ni layer was totally disappeared and converted to NiO layer on FeCrAl surface after long term oxidation process. From this work, the ultrasonic treatment prior to nickel electroplating was the best method to adhere NiO on FeCrAl substrate.

Ni Layer Evolution of FeCrAl Substrate Treated by Ultrasonic and Electroplating Methods in Long Term Oxidation at 900°C

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.

Preparation of Nanocrystalline γ-Alumina Using Ultrasonic Technique

The γ-alumina powder is a potential material for washcoat application. This paper shows the preparation of γ-alumina using ultrasonic technique in order to obtain nanocrystalline of γ-alumina powder. The 50 gr of the γ-alumina powders was treated in the 250 gr ethanol solution using ultrasonic technique within 10, 20, 30, and 60 minutes, respectively. The process of sonication was set at the fixed frequency (18.520 kHz) and current of 2 A. Crystallite size was evaluated by using X-ray diffraction (XRD) data based with Scherrer analysis and Williamson-Hall method. The microstructural characterization of the γ-alumina powders was observed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX) analysis. The result shows that the optimum of nanocrystalline size of γ-alumina at ultrasonic process for 30 minutes are approximately 4.80 nm and 29.50 nm with Scherrer and Williamson-Hall calculation, respectively.