Éva Fazakas

Characterization of luminescent silicon carbide nanocrystals prepared by reactive bonding and subsequent wet chemical etching

Fabrication of nanosized silicon carbide crystals is a crucial aspect for many biomedical applications. Here, we report an effective fabrication method of silicon carbide nanocrystals based on the reactive bonding method followed by electroless wet chemical etching. Our samples show strong violet-blue emission in the 410–450 nm region depending on the used solvents. Raman and infrared measurements unraveled the surface bonding structure of the fabricated nanoparticles being different from silicon carbide microcrystals. This might give an opportunity to use standard chemistry methods for biological functionalization of such nanoparticles.

Spark plasma sintering of Mn–Al–C hard magnets

Structural and magnetic characterization of isotropic Mn-Al-C bulk samples obtained by spark plasma sintering (SPS) is reported. This technique, to the best of our knowledge, has not been used for preparation of Mn-Al-based permanent magnets previously. Transformation from the parent -phase to the ferromagnetic τ-phase occurred on heating in the process of sintering. The phase constitution of the melt-spun precursors and consolidated samples was determined by x-ray diffraction. Magnetic hysteresis loops were recorded using a vibrating sample magnetometer. The compositional dependence of the coercivity, magnetization and density of the sintered materials is analysed. To combine good magnetic properties with proper densification, further optimization of the production parameters is necessary.

Corrosion Resistance of TIG Welded Joints of Stainless Steels

The aim of this work was to analyze the performance of joints made by TIG (Tungsten Inert Gas) welding process in austenitic and duplex stainless steels with special regards to their corrosion resistance. Three different types of stainless steel were butt welded with TIG method. Ferric-chloride test and electrochemical treatments revealed how does the TIG process affects the corrosion resistance depending upon the alloy used for welding the joint. This work focuses on the weldability of the 2304, 2404 and 304 type stainless steel heterogeneous welds.

Formation of amorphous state by ball milling and mechanical crystallization in Al-Ti-Ni alloy system

Formation of Al50Ti50, Al50Ti45Ni5 and Al50Ti40Ni10 amorphous alloys by ball milling and their mechanical crystallization upon further milling have been investigated. Ni addition improves the thermal stability and increases the strength of the powder compacts obtained by hot pressing.

Electrochemical and Morphological Characterization of Silver Doped Bioceramic Layer on Metallic Implant Materials for Orthopaedic Application

This study presents the production of silver doped bioactive calcium-phosphate (CaP) coatings on commonly used orthopaedic implant materials (Ti6Al4V). The deposition process was performed by pulse current technique from electrolyte containing the appropriate amount of Ca(NO3)2 and NH4H2PO4 components at 70 °C. In order to modify the CaP layer, Ag+ ions were added to the base electrolyte. The electrochemical behaviour of the coatings was investigated by potentiodynamic polarization method in conventional Ringer’s solution in a three-electrode open cell. The corrosion properties of samples prepared with different parameters were compared. During immersion, the coating comes into contact with the electrolyte and corrosion occurs. Due to the potential difference between layer and the metallic substrate, discrete anodic and cathodic areas can be formed, which result in the release of silver and calcium ions. For antimicrobial applications of the modified CaP coated implant alloys, it is important to maintain a continuous release of silver ions, while the bioactive CaP layer enhance the biocompatibility properties of the layer by fostering the bone cell growth. The morphology and grain size of coatings as deposited have been investigated and confirmed by different methods such as Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray (EDX) analysis.

Deposition of nanostructure ZnO with variable morphology by electrochemical and hydrothermal methods onto nonwoven materials

ZnO nanostructures were synthesized by two wet-chemical methods (hydrothermal and electrochemical) featuring low temperature (95°C) and atmospheric pressure onto nonwoven substrates. We investigated a hydrothermal method using reagents Zn (NO3)2.6H2O and hexamethylenetetramine (HMTA) as well as an electrochemical method using ZnCl2, and KCl containing electrolyte with H2O2 and/or O2 bubbling. The surface condition of substrate material and the experimental conditions played a key role in the nanowire formation. The morphologies observed by scanning electron microscopy (SEM) include wurtzit or cabbage-like. These morphologies were found to vary with the method applied.

Characterization of the Solidifying Microstructure in Ti60(NixCu40-x)40 Alloys

Ti60(NixCu40-x)40 x = 5 - 40 at% ternary alloys were prepared by arc-melting followed by a centrifugal casting into a wedge-shaped copper mould in order to examine glass forming of these compositions. Microstructure of the master alloys and wedge-shaped samples were studied. Among the master alloys, which solidified under non-equilibrium conditions, the sample with 15 at% Ni content displayed clear eutectic structure and its wedge-shaped sample had the finest structure but still crystalline. Microstructure of the other compositions was far from amorphous state.

Dilatometer Study of Aluminium-Silicon Based Alloys with Metastabile Structures

Aluminum-Silicon alloys are sought in a large number of automotive and aerospace applications due to their low coefficient of thermal expansion and high wear resistance. The fine structure of Si precipitates is controlled by forced solid solution structure obtainable by rapidly solidification techniques [1, 2, 3]. Present study focuses on precipitation of silicon in Al88Si12 as a function of temperature by dilatometer analysis. Different structures out of equilibrium have been obtained after casting in sand, black-lead and steel mould and by melt spinning. The average value of the activation energy for the precipitation of Si in steel mould casting of eutectic composition was found to be 47 kJ/mol. Our dilatometer studies were complemented by metallographic microscopy and XRD measurements.