Ioan Vida-Simiti

Silicon effect on the composition and structure of nanocalcium phosphates: In vitro biocompatibility to human osteoblasts

Nanostructured calcium phosphates, such as nanohydroxyapatite (HAP) and HAP with silicon content (HAP-Si) of 0.47wt.% (1% SiO2), 2.34wt.% (5% SiO2) and 4.67wt.% (10% SiO2) in the final product, were synthesized by aqueous precipitation, freeze dried and then calcined at 650, 950 and 1150°C. The obtained materials were investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) imaging. From the analysis of the XRD patterns, the HAP and β-tricalcium phosphate (β-TCP) phases were identified and their amounts in the samples were estimated. The size of HAP and β-TCP crystallites was estimated to be in the nanocrystalline domain. FTIR spectra showed the presence of characteristic vibrations for P-O, H-O and Si-O groups and their modification with Si content and calcination temperature. TEM, SEM and AFM images also revealed the morphology of the particles and of their aggregates. These materials have been used to manufacture scaffolds which were tested for their influence on adhesion and proliferation of cells, in human osteoblast culture, considering their further use in bone reconstruction. It was found that an appropriate addition of silicon in nanocalcium phosphate scaffolds leads to an enhanced adhesion and proliferation of cells in osteoblasts in vitro.

Bulk titanium for structural and biomedical applications obtaining by spark plasma sintering (SPS) from titanium hydride powder

Titanium is a low density element with excellent mechanical properties, and is an attractive material for structural and biomedical applications. In recent years, a new process technology is emerging by which titanium and titanium alloys can be obtained by using titanium hydride (TiH2) as a precursor for Ti and its mixture with alloying elements. The feasibility of this manufacturing approach has been fully demonstrated from powder to sintering and from microstructure to mechanical properties. In this paper, a study concerning powder metallurgy processing of Ti by spark plasma sintering (SPS) route is presented. The influence of the technological parameters on the hardness and microstructures change during SPS has been studied. The experimental results are related to microscopic, thermal, and mechanical analysis.

Characterization of Gradual Porous Ceramic Structures Obtained by Powder Sedimentation

Asymmetric membranes present better separation and service characteristics than the symmetric ones. In our preliminary studies the possibility of obtaining sintered porous materials with gradual structure by sedimentation of metallic and ceramic powders was demonstrated. Zirconium silicate (ZrSiC 4 ) particles were used for the manufacturing of the porous supports, and mullite powder was deposited by sedimentation in order to achieve the active layer with pores size gradient. The used powders and the obtained structures were characterized by laser scattering particle size analyzer, scanning electron microscopy and mercury porosimetry. The permeability and the filtration fineness of the structures were also determined. By using a thin active layer made of small particles deposited onto a macro-porous support, one can achieve membranes with high flow rates and filtration fineness in the microfiltration area.

Metallic Foams Obtained from Nickel Based Superalloy Hollow Spheres

In this work, hollow spherical nickel based superalloy powders obtained by liquid phase atomization were used. The obtained powder was divided into six size particle ranges between 200 µm and 630 µm using a shatter box. Samples from all six ranges were obtained by spreading the powder into the sintering die and consolidating them by sintering at 900°C and 1000°C for 30 minutes in vacuum (10-4 Torr). The metallic foams obtained by sintering hollow particles presents high porosity, and can be used as thermal barriers, catalyst support, shock absorbers or lightweight structural elements.

Optimization of Reactive Sputtering Technology for Hard Coatings Deposition

The paper presents the research work carried out in order to optimize the technology and reactive magnetron sputtering system used for the deposition of hard, multielemental, multiphase coatings. On the basis of a model of dynamic pressure developed and validated by us, regulatory structures for dynamic pressure inside the deposition chamber were designed and implemented. By using this optimization, extensive experiments involving nanostructured (Ti, Al, Si)N coatings, with a thickness of approx. 2 μm, were carried out. Using TEM microscopy, SAED and Vickers microhardness characterizations the results of deposition system optimization on the microstructure and microhardness of thin films were investigated.

Corrosion Resistance Measurements of Amorphous Ni40Ti40Nb20 Bipolar Plate Material for Polymer Electrolyte Membrane Fuel Cells

Metallic bipolar plates have the advantages of better manufacturability, higher strength over graphite bipolar plates. The higher strength and toughness of the metallic materials permits the reduction of the width of the bipolar plate so, the volume and mass of the fuel cell can also be reduced. In this paper we are investigating the use of Ni-based amorphous material as a bipolar plate for polymer electrolyte membrane fuel cell (PEMFC). The major requirements of the metallic bipolar plate material are low weight, high corrosion and low contact resistance. The corrosion property of the present alloy has been investigated under conditions that simulate the fuel cell environment. Hydrogen gas and air were bubbled into a 1 N H2SO4 solution at 70 °C, throughout the experiment to simulate the respective anodic and cathodic PEMFC environment. The Ni-base amorphous alloys displayed higher corrosion resistance than stainless steel.

Preliminary Studies and Researches on the Elaboration of Gradual Porous Sintered Structures by Powder Sedimentation

Spherical bronze powders were used for studies the obtaining of gradual porous structures by sedimentation and sintering methods. The powder size classes above 100 μm were used for the manufacturing of the macroporous support by spreading the powder into the sintering die. Sintering was conducted in vacuum (10-4 Torr) at a temperature of 750 °C for 40 minutes. On the macroporous support a layer of fine powder fraction was deposited by gravitational sedimentation. The deposited layers were consolidated by sintering at 750 °C for 30 minutes. The analysis of the gradual porous layers was done using scanning electron microscopy and mercury porosimetry. The fluids viscosity influences the sedimentation velocity of particles. The height of the column directly affects the quality of porous structure. If the sedimentary column is short, the turbulences created by adding the suspension of the dispersed powder in the sedimentary tube are more harmful.

Contributions to Processing of Self-Lubricated, Nanocomposite Wear Resistant Coatings by Reactive UM Magnetron Co-Sputtering

Recently a great deal of attention has been devoted to sputtering technology for nanostructured coatings. Wear resistant nanocomposite coatings are very promising materials, which can be easily scaled up for industrial production. Therefore, reactive magnetron sputtering of alloy targets or co-sputtering of elemental metal targets are now intensively investigated. Present paper presents some results of our research work for optimization of tribological properties by definition of selected parameters for reactive sputtering process conditions of self-lubricated carbon doped TiAlN coating. Tailored nanocomposite thin films of multicomponent and multiphase materials have been performed by DC reactive UM magnetron co-sputtering of TiAl and TiC target materials in Ar–N2 respectively C2H2 and CH4 as carbon precursor gases.

The characteristics of gold films deposited on ceramic substrate

A large quantity of gold (approximately 10 tonnes yearly) is consumed, all over the world, just to decorate ceramic and glassware. Due to their advanced chemical stability gold films are used for different high technology applications. The technologies for obtaining the best “liquid bright gold” were intensively studied, but the quality of the decor coatings (films) were empirically assessed. We proposed a scientific investigation of the characteristics of gold films, deposited on ceramic substrates, from “liquid bright golds”. The composition of the film has been determined by EDS (Energy Dispersive X-ray Spectrometry). The distribution of the elements was determined at the surface of the film and in cross-section. The surface distribution of the elements was uniform. The diffusion process of the film into substrate and the migration of the substrate elements at the interface region and into the film have been highlighted.The morphology of the film was studied by SEM microscopy. The grain size varied between 0.05 – 2 μm as a function of the film composition. The major phases from the film and interface were evidenced by X-ray diffraction. The film consisted of crystalline gold. At the interface region a solid solution of Au-ZrSiO4 was identified. Other phases were in amorphous state. The reflection spectra of the films were recorded from optical properties, using a mirror gold as standard, for comparison. The film with the smaller particle size reflected the UV — VIS wavelengths in the same way as a gold mirror. The adherence of the film on the substrate can be explained by the formation of an interfacial layer from solid solution Au−ZrSiO4 and by diffusion processes.

Ti-Al Membranes for Microfiltration

Porous membranes made of Ti – 48 at. % Al intermetallic compound was obtained by elemental powder synthesis. These disks can be used as microfiltration membranes due to their low pores size and interconnected porosity. During this study titanium (purity 99.5%) and aluminum (purity 99 %) with low particle size range were mixed in corresponding ratios. The powder mixture was pressed at 500 MPa and the samples were heat treated in two stages. In the first step is the forming of Al3Ti compound by a solid state reaction at a temperature of 640 °C, slightly below the melting point of aluminum. In the second step the Ti-Al compound was formed at the temperature of 1300 °C and the sintering the porous structure was accomplished too. The obtained membranes were characterized by X-ray diffraction and scanning electron microscopy (SEM).