Egle Conforto

Osteoblast response to biomimetically altered titanium surfaces

Bioinert titanium (Ti) materials are generally encapsulated by fibrous tissue after implantation into the living body. To improve the bone-bonding ability of Ti implants, we activated commercially pure titanium (cpTi) by a simple chemical pre-treatment in HCl and NaOH. Subsequently, we exposed the treated samples to simulated body fluid (SBF) for 2 (TiCT) and 14 days (TiHCA), respectively, to mimic the early stages of bone bonding and to investigate the in vitro response of osteoblasts on thus altered biomimetic surfaces. Sample surfaces were characterized by scanning electron microscopy, energy-dispersive X-ray analysis, cross-sectional transmission electron microscopy analyses, Fourier transform infrared and Raman spectroscopy. It was shown that the efflorescence consisting of sodium titanate that is present on pre-treated cpTi surfaces transformed to calcium titanate after 2 days in SBF. After 14 days in SBF a homogeneous biomimetic apatite layer precipitated. Human osteoblasts (MG-63) revealed a well spread morphology on both functionalized Ti surfaces. On TiCT, the gene expression of the differentiation proteins alkaline phosphatase (ALP) and bone sialo protein was increased after 2 days. On both TiCT and TiHCA, the collagen I and ALP expression on the protein level was enhanced at 7 and 14 days. The TiCT and the TiHCA surfaces reveal the tendency to increase the differentiated cell function of MG-63 osteoblasts. Thus, chemical pre-treatment of titanium seems to be a promising method to generate osteoconductive surfaces.

Crystallographic properties and mechanical behaviour of titanium hydride layers grown on titanium implants

Commercially pure titanium for bone-anchored dental implants, subjected to a sand-blasting and acid-etching surface treatment, has been mechanically tested and analysed by scanning electron microscopy and transmission electron microscopy observations. A fcc titanium hydride layer grows on the polycrystalline titanium substrate with various epitaxial relationships, whose grains also show epitaxial relationships with each other. Indentations, flexion tests and dislocation analyses indicate that this hydride layer can be plastically deformed.

Pt–Si reaction through interfacial native silicon oxide layers

Abstract High-resolution transmission electron microscopy (HRTEM) and selectedarea electron diffraction (SAED) were used to study the formation of 20 nm thick platinum silicide films in the presence of an interfacial native silicon oxide layer. Pt films 10 nm thick were sputtered on Si[001] substrates covered by a native oxide layer 0–2.2 nm thick and annealed between 165 and 800°C. HRTEM observations on cross-sections show that, when an interfacial oxide layer is present, the reactants interdiffuse through the oxide pinholes. The pinholes influence the Pt–Si reaction over all the annealing temperature range examined. Up to 250°C their influence is observed by differences in the silicide phases formed and in the silicide–Si interface flatness. In the 350–550°C annealing temperature range. films with or without an interfacial oxide layer are continuous, polycrystalline and quite homogeneous in thickness, being equivalent for electrical uses. Silicide films grown through an interfacial oxide layer consist of two adjacent Pt2Si and PtSi layers in contrast with oxide-free wafers, which show only PtSi grains. The continuous PtSi film transforms to an epitaxial island-type film afer annealing at 650°C. The Pt2Si layer, however, does not follow the same evolution but remains unchanged up to 700°C at least. By these means, the continuity of silicide films obtained in presence of an interfacial oxide layer can be preserved even above 700°C. These results explain the evolution of the resisitivity as a function of the temperature obtained for the same samples.

The role of molybdenum in the hard-phase grains of (Ti, Mo)(C, N)–Co cermets

The evolution of the core–rim interface in Ti(C, N)-based cermets containing Mo is studied by scanning electron microscopy and conventional and high-resolution transmission electron microscopy as a function of the annealing temperature. A heavily disordered zone on the nanometric scale is observed close to the interface with the core of Ti(C, N) grains in as-sintered samples. It reorders after annealing at a high temperature. This disorder is correlated with the presence of Mo in the rim during sintering, which enhances the strength of the core–rim interface as a barrier for the diffusion of atoms from the core. It avoids the complete dissolution of small Ti(C, N) grains from the original powder and limits the grain growth. It also acts as a barrier against dislocation movements during plastic deformation. This effect, as well as the small final grain size determined by the presence of Mo, contributes to the good mechanical properties of Mo-containing cermets at intermediate temperatures.

The structure of titanate nanobelts used as seeds for the nucleation of hydroxyapatite at the surface of titanium implants.

The sequence of steps of a chemical treatment having as its goal the induce of nucleation and the growth of hydroxyl carbonated apatite (HCA) at the surface of titanium implants was studied by scanning and transmission electron microscopy in cross-section. In the first step, an acid etching forms a rough titanium hydride layer, which remains unchanged after subsequent treatments. In the second step, soaking in an NaOH solution induces the growth of nanobelt tangles of nanocrystallized, monoclinic sodium titanate. In the third step, soaking in simulated body fluid transforms sodium titanate into calcium titanate by ion-exchange in the monoclinic structure. HCA then grows and embodies the tangled structure. The interfaces between the different layers seem to be strong enough to prevent interfacial decohesion. Finally, the role of the titanate structure in the nucleation process of HCA is discussed.

Comparison of Ni-based alloys with extreme values of antiphase boundary energies: dislocation mechanisms and mechanical properties

Dislocation properties have been studied in several L12 nickel-based alloys with high (Ni74Al26), medium (Ni3(Al, 0.25% Hf)), and low (Ni3Ga) antiphase boundary (APB) energies respectively, deformed in the temperature domain of the yield-stress anomaly. Several APB energies have been measured and compared with those found in the literature. The peak in the temperature variation of the strain-hardening coefficient has been correlated with the unlocking of incomplete Kear–Wilsdorf locks. The corresponding unlocking stresses, as well as the frequencies of octahedral-cube and cube-octahedral cross-slip, are strongly correlated with the respective fault energies. The local pinning of near-edge dislocations in cube planes appears essential for the observation of the yield-stress anomaly in alloys with high APB energies.

Study of Fe(II) sulphides in waterlogged archaeological wood

Abstract Wet organic archaeological materials extracted from seawater may suffer damage as a result of degradation influenced by micro-organisms. One of the most common phenomena is indirectly induced by sulphate-reducing bacteria (SRB). Due to their metabolic activity in anoxic conditions, SRB generate hydrogen sulphide from sulphate ions present in seawater. When steel items are in contact with organic matter in presence of sulphides, corrosion of the metal leads to the precipitation of Fe(II) sulphides. These phases are responsible for dramatic post-excavation damage: their oxidation during storage or exhibition in museums leads to the formation of voluminous crystals, which may cause cracking and crumbling, and lead to the production of sulphuric acid. In order to characterize Fe(II) sulphides and their by-products, 13 waterlogged samples were analysed by environmental scanning electron microscopy, micro-Raman spectroscopy, and X-ray diffraction. Experiments were performed on untreated wood fragments, on a fragment of rope, and on mineral concretions scratched from the surface of wood remains, all extracted from different shipwrecks. Mackinawite was detected inside the fragments and between the fibres of the rope. Greigite was detected in scattered locations. Pyrite and sulphated phases, like gypsum and iron sulphates, were identified at the surface of the wood fragments and in the mineral concretions.

A Buried Roman Bronze Inkwell - Chemical Interactions with Agricultural Fertilizers

Abstract Degradation of archaeological artefacts sometimes leads to unusual corrosion products. Techniques have been used to analyse the upper disc of a rare Roman inkwell. Made of leaded bronze and decorated with silver and copper, the object was well preserved in spite of some changes. Corrosion products have been analysed and found to be mainly lead corrosion products. Among them, lead sulphates and lead phosphates such as anglesite and hydroxypyromorphite have been identified and detected all over the surface. The object was discovered during excavations in the middle of a field in which cereals were cultivated. These particular corrosion products were attributed to the result of specific interactions between the metallic alloy and residues of agricultural fertilizers and soil amendments, extensively used for decades in this field. This information is significant because of the nature of the changes.

Formation and Dissolution of Hydride Precipitates in Zirconium Alloys: Crystallographic Orientation Relationships and Stability after Temperature Cycling

Hydride precipitation due to the spontaneous and fast hydrogen diffusion is often pointed as causing embrittlement and rupture in zirconium alloys used in the nuclear industry. Transmission Electron Microscopy (TEM) and X-Rays Diffraction (XRD) have been used to study the precipitation of hydride phases in zirconium alloys as a function of the hydrogen content. The orientation relationships observed between the hydride phase and the substrate were similar to those previously observed in Titanium hydrides grown on Titanium. Dislocation emission from the hydride precipitates has been directly related to the relaxation of the misfit stresses appearing during the transformation. The stability of the hydride phases after several dissolution-reprecipitation cycles have been studied by DSC, TEM and XRD for different total hydrogen content in several alloys. The energy of precipitation observed is lower than that of the dissolution in each case studied. The temperature associated with these two processes slightly increase as a function of the cycle number, as a result of the homogenizing hydrogen distribution in the alloy bulk. The same hydrides phases present before cycling were also observed after 20 cycles. However, transition phases poorer in hydrogen than the dominant one may precipitate at the interface with the substrate. The evolution of these transitions phases with the temperature increase will be investigated by TEM in-situ heating in the next future.

Hydride Precipitates in Zirconium Alloys: Evolution of Dissolution and Precipitation Temperatures During Thermal Cycling Correlated to Microstructure Features

The fast and spontaneous hydrogen diffusion in zirconium alloys used in the nuclear industry leads to the hydride precipitation which is often pointed as causing embrittlement and rupture. Our studies using X-ray Diffraction (XDR), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy coupled to Back-Scatter Diffraction (SEM-EBSD) have been demonstrating that the nature of the hydride phase precipitate depends on the hydrogen content, and can show crystallographic orientation relationships (ORs) with the substrate. Differential Scanning Calorimetry (DSC) has been used to identify the dissolution and precipitation energies at global scale. The difference of both can be associated to the misfit dislocations contribution to the precipitation. Local In-situ TEM dissolution observations confirm the dissolution temperature identified at a global scale and show the depinning of some misfit dislocations during dissolution process. The consequence of this mechanism is that dissolution and precipitation temperatures shift during thermal cyclic loading. This situation will be correlated to the nature of crystallographic hydride phases and their ORs.