Julietta V. Rau

Superhard properties of rhodium and iridium boride films.

Very recently, the superhard properties of rhenium and ruthenium boride films were reported, this research being inspired by the discovery of the ReB(2) bulk superhardness. In this paper, we report the first successful deposition and characterization of rhodium and iridium boride films, other possible candidates for superhard materials. The films were prepared, applying the pulsed laser deposition technique, and studied by X-ray diffraction, scanning electron and atomic force microscopies, and Vickers microhardness. The refined structural parameters for RhB(1.1) and IrB(1.1) films were obtained. The RhB(1.1) film is characterized by the submicrometer crystallite size, whereas for the IrB(1.1) film, the crystallite size is in the tens of nanometers range, and this latter film presents a slightly preferred orientation along the [004] direction. Both the films exhibit very similar morphology, being composed of dense globular aggregate texture. The RhB(1.1) film presents a homogeneously textured surface with an average roughness of 20-50 nm, whereas the IrB(1.1) film possesses a finer texture with an average roughness of 20-30 nm. The intrinsic hardness of both films lies in the superhardness range: the 1.0 microm thick RhB(1.1) film possesses a hardness of 44 GPa, whereas the 0.4 microm thick IrB(1.1) film has a hardness of 43 GPa.

Energy dispersive X-ray diffraction study of phase development during hardening of calcium phosphate bone cements with addition of chitosan.

The aim of this work was to study the phase transformation during the setting reaction of two calcium phosphate bone cements based on either alpha tricalcium phosphate (alpha-TCP) or tetracalcium phosphate (TetCP) initial solid phase, and a magnesium carbonate-phosphoric acid solution as the hardening liquid. Low molecular weight (38.2 kDa) chitosan was used to retard the cements setting reaction. To follow the kinetics of the phase development, an energy dispersive X-ray diffraction technique was applied. This technique allowed the collection of diffraction patterns from the cement pastes in situ starting from 1 min of the setting process. In the case of the TetCP-based cement, the appearance and evolution of an intermediate phase was detected.

Large-bandwidth two-color free-electron laser driven by a comb-like electron beam

We discuss a two-color SASE free-electron laser (FEL) amplifier where the time and energy separation of two separated radiation pulses are controlled by manipulation of the electron beam phase space. Two electron beamlets with adjustable time and energy spacing are generated in an RF photo-injector illuminating the cathode with a comb-like laser pulse followed by RF compression in the linear accelerator. We review the electron beam manipulation technique to generate bunches with time and energy properties suitable for driving two-color FEL radiation. Experimental measurements at the SPARC-LAB facility illustrate the flexibility of the scheme for the generation of two-color FEL spectra.

Real-time monitoring of the mechanism of poorly crystalline apatite cement conversion in the presence of chitosan, simulated body fluid and human blood.

In this study, the real-time monitoring of structural changes, occurring upon poorly crystalline apatite bone cement hardening in the presence of chitosan, simulated body fluid and human blood, was performed. Strong experimental evidence of octacalcium phosphate intermediate phase is provided. The energy dispersive X-ray diffraction was applied in situ to monitor the structural changes upon the transformation process, while the Fourier transform infrared spectroscopy and the scanning electron microscopy supplied information on the vibrational and morphological properties of the system. The cooperative action of chitosan and simulated body fluid induces the formation of a preferentially oriented hydroxyapatite phase, this process being similar to the oriented self-assembling process in collagen-apatite matrix in human plasma, occurring upon in vivo biomineralization. Conversely, the presence of blood does not induce any significant change in hardening kinetics and the final structure of the investigated cement.

Hardness of electron beam deposited titanium carbide films on titanium substrate

Increased use of titanium and titanium-base alloys in medicine is occurring due to their relatively low elasticity modulus and enhanced corrosion resistance as compared to more convenient alloys intended for implantation into the human body [1]. However, the properties of oxides present in the near-surface region of Tibase materials deserve special attention. The titanium oxides from TiO to Ti3O5 can exist in a stable state at the harsh conditions of the body fluids surrounding the implant. Tribo-chemical reactions during use can modify the oxidized surface of the implant producing wear debris accumulation, which results in an adverse cellular response and implant loosening. To improve bone response and reliability of implanted device, the surface modification by coating of implants with various substances can be used. In particular, titanium carbide on titanium can provide protection against oxidation, excellent corrosion resistance, enhanced hardness, and superior wear resistance of the implant. To cover a substrate with a thin carbide film, different methods are commonly used, e.g., chemical vapor phase deposition, pulsed laser ablation deposition (PLAD), magnetron sputtering [2–4]. The present study is aimed at the study of the hardness of electron beam deposited (EBD) titanium carbide films onto Ti substrates. To prepare the targets for EBD, titanium carbide powder (Aldrich, 98% pure) was pressed into 18 mm diameter pellets. The pellets were placed into a crucible made of titanium diboride/boron nitride composite (Advanced Ceramics Corp. Europe, UK). The crucible was then inserted into a water-cooled electron beam gun (EVI-8, Ferrotec, Germany), which has been positioned into a stainless-steel chamber evacuated by a turbomolecular pump supported by a rotation pump. The electron beam gun was controlled by a joypad that permits a complete control of the accelerating voltage in the range between −3.05 and −10 kV, the shape, pattern and position of the beam. The maximum operation power was 5 kW. The gun has a magnetic lenses system that allows a 270 ◦ deflection of the beam for avoiding contamination of the evaporating material with tungsten of the emitting filament. The substrates were heated under vacuum of 5.10−2 mbar in the chamber with a high-power halogen lamp. The deposition process was performed at the accelerating voltage −3.5 kV and the emission current of 130 to 200 mA. The pattern of electron beam was circular and slow, to ensure uniform consumption of the evaporating material. The deposition was performed at the substrate pre-heating temperature 200 or 800 ◦C for several minutes. After the cooling and venting with N2, the samples were of metallic luster and dark grey colored. The thickness of film was evaluated by scanning electron microscopy observation of the cross-sections of the samples (a LEO 1530 SEM apparatus, Carl Zeiss, Germany). An absolute error of the thickness measurement was ±10 nm. The hardness was measured with the use of a Leica VMHT apparatus (Leica GmbH, Germany) equipped with a standard Vickers pyramidal indenter (square-based diamond pyramid of face angle 136 ◦). On each sample indentations were made with 5 to 7 loads ranging from 0.01 to 5 N. Both diagonals were measured to diminish the effects of asymmetry on the imprint. Standard deviation of the diagonal measurements was about 5 to 9% of the diagonal length. The measured hardness was that of the film-substrate composite system. To separate the hardness of the film-substrate system on its constituents from the film and the substrate, a model based on an area “law-of-mixtures” approach was applied [5], where the composite hardness Hc of the film-substrate system is expressed as

Bioactive, nanostructured Si-substituted hydroxyapatite coatings on titanium prepared by pulsed laser deposition

AIMS The aim of this work was to deposit silicon-substituted hydroxyapatite (Si-HAp) coatings on titanium for biomedical applications, since it is known that Si-HAp is able to promote osteoblastic cells activity, resulting in the enhanced bone ingrowth. MATERIALS AND METHODS Pulsed laser deposition (PLD) method was used for coatings preparation. For depositions, Si-HAp targets (1.4 wt % of Si), made up from nanopowders synthesized by wet method, were used. RESULTS Microstructural and mechanical properties of the produced coatings, as a function of substrate temperature, were investigated by scanning electron and atomic force microscopies, X-ray diffraction, Fourier transform infrared spectroscopy, and Vickers microhardness. In the temperature range of 400-600°C, 1.4-1.5 µm thick Si-HAp films, presenting composition similar to that of the used target, were deposited. The prepared coatings were dense, crystalline, and nanostructured, characterized by nanotopography of surface and enhanced hardness. Whereas the substrate temperature of 750°C was too high and led to the HAp decomposition. Moreover, the bioactivity of coatings was evaluated by in vitro tests in an osteoblastic/osteoclastic culture medium (α-Modified Eagles Medium). CONCLUSIONS The prepared bioactive Si-HAp coatings could be considered for applications in orthopedics and dentistry to improve the osteointegration of bone implants.

Stabilization of Carbonate Hydroxyapatite by Isomorphic Substitutions of Sodium for Calcium

Carbonate hydroxyapatite (CHA) is an analogue of the mineral component of bone tissue. Synthetic CHA is thermally unstable: it readily decomposes with carbon oxide evolution when sintered to ceramics. Its thermal stability has been studied as affected by partial isomorphic substitution of sodium for calcium intended to compensate a possible charge imbalance induced by CO32− groups. Investigative tools were thermogravimetry and FTIR spectroscopy of the condensed vapor produced by heating CHA samples doped with 0.4 and 0.8 wt % sodium. Sodium does not improve the thermal stability of CHA: weight loss on heating increases with increasing sodium level; evolution of carbon oxides occurs at lower temperatures and more intensively. Sodium enhances the generation of B-type defects (CO32− → PO43− substitutions); these defects are thermodynamically less stable than AB-type defects (2CO32− → PO43−, OH− substitutions), which are characteristic of sodium-free CHA.

Glass-ceramic coated Mg-Ca alloys for biomedical implant applications.

Biodegradable metals and alloys are promising candidates for biomedical bone implant applications. However, due to the high rate of their biodegradation in human body environment, they should be coated with less reactive materials, such, for example, as bioactive glasses or glass-ceramics. Fort this scope, RKKP composition glass-ceramic coatings have been deposited on Mg-Ca(1.4wt%) alloy substrates by Pulsed Laser Deposition method, and their properties have been characterized by a number of techniques. The prepared coatings consist of hydroxyapatite and wollastonite phases, having composition close to that of the bulk target material used for depositions. The 100μm thick films are characterized by dense, compact and rough morphology. They are composed of a glassy matrix with various size (from micro- to nano-) granular inclusions. The average surface roughness is about 295±30nm due to the contribution of micrometric aggregates, while the roughness of the fine-texture particulates is approximately 47±4nm. The results of the electrochemical corrosion evaluation tests evidence that the RKKP coating improves the corrosion resistance of the Mg-Ca (1.4wt%) alloy in Simulated Body Fluid.

IR and X-ray time-resolved simultaneous experiments: an opportunity to investigate the dynamics of complex systems and non-equilibrium phenomena using third-generation synchrotron radiation sources

Third-generation storage rings are modern facilities working with high currents and designed to host powerful radiation sources, like undulators and wigglers, and to deliver high-brilliance beams to users. Many experiments at high spatial resolution, such as spectromicroscopy at the nanometre scale and with high temporal resolution to investigate kinetics down to the picosecond regime, are now possible. The next frontier is certainly the combination of different methods in a unique set-up with the ultimate available spatial and temporal resolutions. In the last decade much synchrotron-based research has exploited the advantage of complementary information provided by time-resolved X-ray techniques and optical methods in the UV/Vis and IR domains. New time-resolved and concurrent approaches are necessary to characterize complex systems where physical-chemical phenomena occur under the same experimental conditions, for example to detect kinetic intermediates via complementary but independent observations. In this contribution we present scientific cases from original works and literature reviews to support the proposed IR/X-ray simultaneous approach, with both probes exploiting synchrotron radiation sources. In addition, simple experimental layouts that may take advantage of the high brilliance and the wide spectral distribution of the synchrotron radiation emission will be given for specific researches or applications to investigate dynamic processes and non-equilibrium phenomena occurring in many condensed matter and biological systems, of great interest for both fundamental research and technological applications.

Structural study of octacalcium phosphate bone cement conversion in vitro.

The nature of precursor phase during the biomineralization process of bone tissue formation is still controversial. Several phases were hypothesized, among them octacalcium phosphate. In this study, an in situ monitoring of structural changes, taking place upon the octacalcium phosphate bone cement hardening, was carried out in the presence of biopolymer chitosan and simulated body fluid (SBF). Several systems with different combinations of components were studied. The energy dispersive X-ray diffraction was applied to study the structural changes in real time, while morphological properties of the systems were investigated by the scanning electron microscopy. The obtained results evidence that final hydroxyapatite phase is formed only in the presence of chitosan and/or SBF, providing new insights into the in vivo biomineralization mechanism and, consequently, favoring the development of new approaches in biomaterials technology.