Magnetic nanoparticles of cobalt ferrite (CoFe2O4) have been synthesized by co-precipitation method with various synthesis temperatures, concentration of NaOH and stirring duration. The results showed that nanoparticles have well crystallized structure with various grain sizes which depend on synthesis parameters. The grain size increased with increasing synthesis temperature, decreasing concentration of NaOH and decreasing stirring duration. Magnetic characterization of CoFe2O4 nanoparticles measured by Vibrating Sample Magnetometer (VSM) showed that coercive field was decrease with the decreasing of particle size. The saturation and remnant magnetization showed increasing when crystallinity increased. However, it also depends on presence of α-Fe2O3 phases and their grain size. Based on magnetic characterization analysis, sample with parameter of synthesis temperature 80°C, concentration of NaOH 5 M and stirring duration 120 minutes have been selected to be modified using polyethylene glycol (PEG)-4000. XRD and TEM analysis showed that surface modification with PEG-4000 could increase the crystallinity of nanoparticles, decrease agglomeration and control the shape to more spherical. VSM analysis showed that modification PEG-4000 could decrease the saturation magnetization which is due to the existence of α-FeO(OH) and γ-FeO(OH) phases from bonds at interface of CoFe2O4 as confirmed by XRD and Furrier Transform Infra Red (FTIR) analysis. Keywords: magnetic nanoparticles, CoFe2O4, copresipitation, PEG-4000
<span>Magnetic nanoparticles of cobalt ferrite (CoFe<span>2<span>O<span>4<span>) have been synthesized by co-precipitation <span>method with various synthesis temperature and concentration of NaOH. The structural <span>characteristics and particle size of CoFe<span>2<span>O<span>4 <span>were determined by X-ray diffraction (XRD) and <span>Transmission Electron Microscopy (TEM), its showed that nanoparticles well crystallized with <span>various grain size which depend on synthesis parameters. The grain sizes estimated using the <span>Scherrer formula were found that the grain size increased with increasing temperature <span>synthesis and decreasing concentration of NaOH. Magnetic characterization of CoFe<span>2<span>O<span>4 <span>nanoparticles was investigated by using a Vibrating Sample Magnetometer (VSM). Sample <span>with various concentration of NaOH showed that coercivity was decrease with the decrease of <span>particle size. In other hand, samples with various synthesis temperature found that sample with<br /><span>smallest grain size have high coersivity. The saturation magnetization increase when <span>crystallinity increase. Based on the results, it can be concluded that magnetic characterization <span>of CoFe<span>2<span>O<span>4 <span>was influenced by grain size and crystallinity.</span></span></span></span></span></span></span></span></span></span></span></span><br /></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
Austenitic ODS (Oxide Dispersion Strengthened) 316L steel was fabricated using 316L SS (Stainless Steel) pre-alloyed powder and yttria powders by mechanical milling with APS (Arc Plasma Sintering) method. The powders were milled in High Milling Shaker at 1000 rpm in rotational speed for 10 hours at 10 BPR (Ball Powder Ratio). As milled powders were pressed at 20 Ton and sintered with APS for 0 to 12 minutes at 70 A. The samples were analysed using X-Ray Diffraction (XRD), Microscope Optic (MO) with micro-hardness tester and Scanning Electron Microscope – Energy Dispersive X-Ray Spectroscope (SEM-EDS). The results of phase and microstructure showed the austenitic grade of the samples. The sintering time contributed to the microstructure of the samples. At room temperature, the mechanical properties of ODS 316L SS was higher than conventional 316L SS.
An Austenitic ODS steel was developed for reactor structural material by dispersed 0.5 wt % of nano powder zirconia (ZrO2) to the AISI 316L steel. The synthesis was carried out by the powder metallurgy process with high energy milling and cooled compacting process. A new apparatus of APS (Arc Plasma Sintering) was used for consolidation the sample in the sintering process. Characterizations of the microstructure and elemental composition distribution were performed using the Scanning Electron Microscope (SEM) with X-ray Diffraction Spectroscopy (EDX) and area mapping. Identification for the change of phasesand hardness were analyzed using the XRD-test and Vickers Hardness measurement. Austenitic phase with relatively equiaxed grain and homogeny distribution of the ZrO2 dispersoid were identified after the sintering process followed by the improvement of hardness due to the pinning effect of the grain boundaries.
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