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:Nikolett Oláh, Mónika Furkó, Zoltán May, Attila Sulyok and Katalin Balázsi
The aim of this article is to study the influence of TiC/a:C protective thin film on the corrosion and mechanical properties of sandblasted/polished Ti and TiAl6V4 substrates. The electrochemical corrosion behaviors of the samples were investigated in simulated body fluid (SBF) by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques at 7.4 pH and 37 °C. The metal ion release has been quantified by inductively coupled plasma optical emission spectroscopy (ICP-OES). The experimental results obtained from different electrochemical methods, ICP-OES, and scanning electron microscopy (SEM) showed that the TiC/a:C protective coating on sandblasted implant device improves the corrosion properties of the implant material and it is able to control the metal ion release. It was also shown that the hardness of the bare implant materials is improving by four orders of magnitude with the TiC/a:C nanocomposite coating beside a moderate elastic modulus value. The highest hardness (H) of ~28 GPa ± 3 was observed in the case of the film prepared at ~38 at% Ti content. Overall, the TiC/a:C thin film has suitable electrochemical characteristics for further consideration and assessment as a protective coating.
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.
Authors:I. Szilágyi, Judit Pfeifer, C. Balázsi, A. Tóth, Katalin Varga-Josepovits, J. Madarász and G. Pokol
We studied the thermal stability of different hexagonal tungsten trioxide, h-WO3 samples, which were prepared either by annealing hexagonal ammonium tungsten bronze, (NH4)0.33−xWO3−y, or by soft chemical synthesis from Na2WO4. The structure and composition of the samples were studied by powder XRD, SEM-EDX, XPS and 1H-MAS NMR. The thermal properties were investigated by simultaneous TG/DTA, on-line evolved gas analysis (TG/DAT-MS), SEM
and in situ powder XRD. The preparative routes influenced the thermal properties of h-WO3 samples, i.e. the course of water release, the exothermic collapse of the hexagonal framework and the phase transformations
were all affected.