Ferenc Wéber

Nano-hydroxyapatite preparation from biogenic raw materials

Hydroxyapatite (HAp) was successfully produced from recycled eggshell, seashell and phosphoric acid. The phases obtained depended on the ratio of calcined eggshell/ seashell to phosphoric acid, the calcination temperature and the mechanochemical activation method (ball milling or attrition milling). The HAp structures were characterized by X-ray diffraction, scanning electron microsopy and infrared spectroscopy. Attrition milling was more effective than ball milling, yielding nanosize, homogenous and pure Hap.

Preparation and examination of multilayer graphene nanosheets by exfoliation of graphite in high efficient attritor mill

AbstractGraphene multilayers have been prepared by mechanical method based on milling graphite in high efficient attritor mill. The results showed that the best dispersion media is ethanol, and 10 hours of intensive milling proved to be the most efficient way to separate the graphite layers as it was shown by scanning electron microscopy and X-ray diffraction measurements.

Tribology Study of Silicon Nitride-Based Nanocomposites with Carbon Additions

Tribology tests were conducted on silicon nitride-based nanocomposites with various carbon additions to explore the effects of microstructure, the type and quantity of carbon additives and the preparation routes on the behavior. The nanocomposites consisted of Si3N4 and C in the proportions of 1 – 10 wt % carbon nanotube (CNT), or carbon black (CB), or graphite, or graphene. Specimens were produced by hot isostatic pressing. X-ray diffraction and scanning electron microscopy were used to reveal phase composition and microstructure. Unlubricated ball-on-disk tribology tests with silicon nitride counter face were carried out at room temperature in ambient atmosphere. Contact profilometer was used to profile the wear tracks. The friction coefficients of the pure Si3N4 and Si3N4 samples with 3% CNT varied between 0,77-0,81. Addition of 10% graphite and 3% CB to Si3N4 resulted in friction coefficients of 0,83 and 0,72 respectively. Si3N4 samples with 3% graphene showed distinctly lower friction levels of 0,52 and smaller scatter of the measured values. The wear track study revealed that high graphene content in the Si3N4 matrix caused relatively big wear particles and an uneven wear track.

Biopolymer-Hydroxyapatite Scaffolds for Advanced Prosthetics

Biocompatibility in research and development of advanced prosthetics is a current problem faced by medical researchers. A major challenge in tissue engineering is to find materials and processing techniques that allow them to produce extracellular matrices (ECM) mimicking scaffolds that promote cell growth and organization into a specific architecture, inducing cell differentiation and subsequent cell function. The ideal tissue repair material thus should consist of synthetic biomaterials, such as natural polymers mimicking the mechanical and biological functionality of the ECM. Cellulose acetate membranes were used as scaffolds for microvascular cell growth. Hydroxyapatite (HA) is a natural ceramic (responsible for strength and stability in the human skeletal system) operable as a biocomposite coating to improve the biocompatibility of implant substrates. In this work, HA was prepared from low cost natural calcium source — eggshells. Its structural properties were investigated by scanning (SEM), transmission (TEM) electron microscopies and Fourier Transformed Infrared spectroscopy (FT-IR). The composition analyses of HA were measured by the total reflection X-ray fluorescence spectrometer (TXRF) and by prompt gamma activation analysis (PGAA). Hydroxyapatite added biodegradable scaffolds have been prepared by electrospinning method to enhance biological functionality.

Mechanical properties of oxidized silicon nitride ceramics

The effect of oxidation on the room-temperature mechanical properties of silicon nitride ceramics with four different compositions is studied. Room temperature values of bending strength and elastic modulus of the whole oxidized material and of hardness, the fracture toughness and elastic modulus of the internal region (without the strongly oxidized surface layer) are determined for the materials oxidized at five different temperatures up to 1400°C. The strength decreases with increasing oxidation temperature for all the materials investigated. The fracture toughness of the internal region decreases upon oxidation at 1000°C. A reduction of the elastic modulus of the materials oxidized at 1400°C is also observed. The oxidation-induced changes in the mechanical properties are partially explained by the changes in the phase composition.

Comparison of oxidation behaviour of sintered ceramics produced from various silicon nitride powders

Sintered ceramics produced from two kinds of silicon nitride powder were oxidized at 1000 and 1400°C. The density, the mechanical properties and the phase composition of the oxide layer and the internal region (without the oxide scale) of one material were compared with those of the other. It was found that the difference in the starting powder properties caused differences in the oxide layer thickness, and the phase composition and the mechanical properties of the internal part.

Electrical Examination of Silicon Nitride – Carbon Composites

The Si3N4 ceramics are usually known as strongly refractory and enduring materials and they have typical insulating material properties on room temperature. If reinforcing phase of the Si3N4 matrix composite is a good electrical conductor, in that case it is worth to investigate the composite in electrical aspect. In our case carbon nanotubes, black-carbon and graphite with good electrical conductivity were mixed in the base ceramic. During our electrical investigations DC resistivity measurements were used to determine the percolation threshold and the conductivity of the composites. In case of high resistance samples AC impedance spectroscopy was applied. As result of the impedance spectroscopy capacitive properties were found. In some cases of conductor samples combined mechanical – electrical measurements were done to study the integrity of the additions in the matrix.

Preparation of Si3N4 Composites with Single Wall Carbon Nanotube and Exfoliated Graphite

Silicon nitride based composites with 3wt% of single wall carbon nanotubes and exfoliated graphite have been prepared. Optimisation of the manufacturing processes has been conducted to preserve the carbon nanotubes and exfoliated graphite in composites and to avoid damaging during high temperature processing. The first results show that carbon nanotubes and exfoliated graphite have a good contact to the surface of silicon nitride grains. In the case of increase of sintering pressure an increase of bending strength was achieved. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements.

Development of preparation processes for CNT/Si3N4 composites

Silicon nitride based composites with different amount (1, 3 and 5 wt%) of carbon nanotubes have been prepared. Optimisation of the manufacturing processes has been conducted to preserve the carbon nanotubes in composites and to avoid damaging during high temperature processing. The first results show that carbon nanotubes have a good contact to the surface of silicon nitride grains. With increasing the carbon nanotube content a lower densification rate was obtained together with the deterioration of the mechanical characteristics of composites. In the case of 1wt% and 3 wt% carbon nanotube addition the increase of pressure resulted in increase of bending strength. It was found that microstructure features achieved by properly designed sintering parameters are the main responsible factors for the strength improvements.

Production of Polymer Nanofibers Containing Hydroxyapatite by Electrospinning

Hydroxyapatite (HAP) is the main inorganic component of mammal bone and teeth. It is one of the few bioactive materials, which helps cell growing. The objective of this study was to fabricate hydroxyapatite-biopolimer nanofiber mats. To achieve this goal, two different suspensions were used. Approximately 1 μm diameter size fibers with large HAP agglomerates were fabricated using acetone and acetic acid. Fibers with a larger diameter size and homogenous distributed HAP particles were produced applying acetone and isopropanol. During the experiment the effect of the processing parameters: applied voltage, diameter of needle, the distance of the needle tip and the collector, flow rate was analyzed.