Authors:Monika Furko, Zsolt Fogarassy, Katalin Balázsi and Csaba Balázsi
A new method for preparing multi-layered graphene oxide powder was developed. In this method, the raw material was commercially available micro-sized graphite powder. The graphite powder was milled using a high speed attritor mill to reduce the particle size of the graphite to nanometer and to exfoliate the graphite into multi-layered graphene particles. The graphene particles were then oxidized into graphene oxide (GO) using the combination of strong oxidizing agents, thermal oxidizing, and sonication. Thorough morphological characterizations have been carried out to reveal the structure and the size of GO particles. The results confirmed that the oxidation process was successful.
Authors:Haroune Rachid Ben Zine, Filiz Cinar Sahin, Zsolt E. Horváth, Zsolt Czigány, Ákos Horváth, Katalin Balázsi and Csaba Balázsi
The effect of the submicrometer-sized Si3N4 addition on the morphological and structural properties of the ceramic dispersion strengthened (CDS) 316L stainless steels prepared by powder technology has been studied. Two composites were prepared: 316L/0.33 wt. % Si3N4 and 316L/1 wt. % Si3N4. In order to assure a good dispersion of the ceramic particles in the stainless steel powders and a grain size reduction at the same time, the high efficient attrition milling has been used. Spark plasma sintering (SPS) was used for fast compacting of milled composites. Structural and morphological changes were studied after milling and sintering process. It was found that the amount of Si3N4 addition influenced the efficiency of milling process resulting in powder mixtures with different 316L stainless steel grain size and shapes. In the case of 0.33 wt. % Si3N4 addition, the flat 316L stainless steel grains with submicrometer size in thickness have been resulted after milling compared to 1 wt. % Si3N4 added powder mixtures which consisted of almost globular 316L stainless steel grains with 50–100 μm in diameter. The intensive milling assured an optimal coverage of 316L stainless grains with Si3N4 submicrometer-sized particles in both cases as demonstrated by energy dispersive spectroscopy (EDS) and TEM. On the other hand, the 316L phase has been maintained during and after the milling and sintering. The partial phase transformation of α-Si3N4 to SiOx was observed by EDS.