Incorporation of amino acids within the surface reactive layers of bioactive glass in vitro: an XPS study

Surface reaction layers grown on bioactive glass (Bioglass^®), by immersion in either simulated body fluid (SBF) or minimal essential medium (-MEM) for 2, 5, 32 and 72 h, were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Layers grown in -MEM exhibited delamination when observed in SEM. Low resolution XPS analysis detected nitrogen at the surface of the Bioglass^® exposed to -MEM for 72 h (8 relative at%), whereas insignificant nitrogen was found at the surface of any sample immersed in SBF. XPS depth profiling (argon) showed the presence of nitrogen throughout the depth of the surface layer of the sample incubated in -MEM for 72 h. Deconvolution of the nitrogen envelope in a high resolution XPS spectrum demonstrated nitrogen characteristic of the amine bonds present in amino acids. Carbon concentration also considerably increased over time with exposure to -MEM (24–55%), whereas it remained in the 20–25% range in SBF. These results demonstrate that the amino acids contained in the culture medium were incorporated within the growing calcium phosphate rich surface reaction layer of Bioglass^®     

Properties of evaporated Mo-Re thin-film superconductors

Mo-Re films have been deposited by electron-beam coevaporation in ultrahigh vacuum in the composition range between 25 and 40 at % Re. The films had either a single-crystal A15 structure, single-crystal -Mo (bcc) structure, or polycrystalline -Mo structure, depending on the substrate temperature during deposition. The superconducting transition temperature was approximately 12 K for films with both the A15 and -Mo structures, the same as literature values for bulk samples of the -Mo structure, even for films as thin as 20 nm. XPS measurements showed that the surface oxide thickness of samples exposed to ambient air was approximately 0.5 nm. Artificial tunnel barriers of oxidized Al were used with Pb or Mo-Re counterelectrodes to form low-leakage tunnel junctions for measurements of the superconducting energy gap.     

The structure of a rapidly solidified Al-Fe-Ti-C alloy

The microstructures of melt-spun Al-2.03 Fe-0.46 Ti-0.35 C (at %) superheated to 1523 K (ribbon I), and 1673 K (ribbon II), respectively, before quenching, have been characterized using analytical electron microscopy and X-ray diffraction. A duplex microstructure has been observed for ribbon I, consisting of a microcellular region, across a sharp transition, followed by a coarser cellular or dendritic structure. The intercellular phases consisted mostly of Al₆Fe (few of Al₃Fe) and the dispersed TiC particles distributed in the -Al matrix with an exact orientation relationship. However, the microstructure of ribbon II comprised uniform, fine-scale dispersions of Al₆Fe phase in -Al grains, and larger size, elongated amorphous phase particles located along the grain boundaries, and approximately 0.46 at % Ti and 0.35 at % C dissolved in the -Al matrix. During the annealing of ribbon II, the amorphous phase transformed to _T-AlFeSi phase, the Al₆Fe dispersoids grew upwards and Al₃Fe, TiC particles precipitated in the -Al matrix. TiC phase formed both in ribbon I and in annealed ribbon II all had an atomic composition of TiC_0.79 (the nominal atomic percent ratio for the alloy was 0.74) and a lattice parameter of 0.424 nm. Moreover, there is a cube-cube orientation relationship between TiC and -Al matrix with a disregistry =0.049. In addition, the solidification characteristics of rapid solidification processing (RSP) Al-Fe-Ti-C alloy and mechanism of TiC formation have been discussed.     

Optical band gap and refractive index of c-BN thin films synthesized by radio frequency bias sputtering

Boron nitrogen (BN) films with the different cubic phase content were deposited on Si and fused silica substrates by radio frequency bias sputtering from a hexagonal BN target by using a two-stage deposition process. The BN films were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible transmittance and reflection measurements. The optical absorption coefficient and the refractive index n were calculated from the transmittance and reflection spectra. With increasing the c-BN content the absorption edge shifts to the higher energy, indicating that the optical band gap of the BN films increases with cubic BN content. The optical absorption behavior of BN films shows characteristics of amorphous materials. The dependence of on the photon energy was fitted by the Urbach tail model and the band-to-band transition model at the two different energy regions, and the optical band gap of the BN films were obtained from the fits. In addition, the refractive index indicates obvious difference for the BN films with different cubic phase content.     

Grain boundary devitrification of Ca α-sialon ceramics and its relation with the fracture toughness

Grain boundary devitrification was carried out on three Ca -sialon ceramics with different grain sizes and morphologies and various amounts of grain boundary glass. The devitrified product was gehlenite in all samples, indicating that the crystallization of the Ca oxynitride glass was accompanied by a volume reduction. The volume reduction upon crystallization and the thermal expansion mismatch between the devitrified product and -sialon grains would result in tensile residual stresses located at multi-grain junctions. These residual tensile stresses were expected to promote the crack deflection and bridging mechanism and thus to improve the material toughness. However, indentation fracture toughness measurement and scanning electron microscope study showed that there was no significant difference in fracture toughness and the fracture mode in present samples prior to and post heat treatment. This may be attributed to a change in the chemistry of the residual glass as a result of the grain boundary devitrification, which could enhance the bonding strength between the adjacent -sialon grains. The enhanced bonding strength could have to some degree hindered the crack deflection and bridging mechanism.     

Fibrous growth of tricalcium phosphate ceramics

Structural transformation and sintering processes of tricalcium phosphate (TCP) ceramics prepared from defective hydroxyapatite (Ca9HPO4(PO4)5OH) were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). Starting powders with Ca/P ratio 1.5 were obtained by adding 0.5 l of 0.3 M H3PO4 solution to an equal volume of 0.45 M Ca(OH)2. In the prepared ceramics, the onset temperature for transformation of defective hydroxyapatite into TCP (witlokite) agrees with the onset temperature for sintering (800 °C). Sintering occurs through the formation of a fibrous structure, which resembles biological hard tissue. In the 1000–1200°C range, these fibres coalesce into grains of up to 0.6 m in size with a fibrous-laminar morphology. At the end of this sintering stage witlokite transforms into TCP. At about 1450°C, partial decomposition of TCP into Ca2P2O7+Ca4P2O9 is observed. AFM observations suggest that Ca2P2O7 is segregated in the liquid state and increases the velocity of grain growth (up to 12 m).     

Methanation of carbon deposited directly from CO2 on rhodium-bearing activated magnetite

Methanation reactivity was studied for the surface carbon deposited from CO₂ on the surface of Rh-bearing activated magnetite. The most active material (Rh=0.83 wt %) for methanation was prepared by the impregnation method at 60°C and showed 98% conversion at 300°C. The surface carbon was composed of elemental carbon (-carbon) and polymerized carbon (-carbon), the proportion being dependent on the density of carbon deposited. In temperature-programmed surface reaction, the extent of conversion of the - and -carbon to CH₄ was 0.34 (-carbon) and 0.53 (-carbon), respectively, and the total conversion was 0.87. This result indicates that not only elemental carbon but polymerized carbon (-carbon) could be converted to CH₄ on the Rh-bearing activated (-carbon) magnetite, whereas -carbon is not hydrogenated on activated magnetite.     

Pulsed laser deposition of silicon nitride thin films by laser ablation of a Si target in low pressure ammonia

We report the deposition of Si-N films by multipulse excimer laser ( = 308 nm, _FWHM = 30 ns) ablation of Si wafers placed in a slow flow of NH₃ in the pressure range (1 bar-1 mbar). The films are deposited on to a Si collector placed parallel to the Si target. We succeeded in depositing pure amorphous Si₃N₄ films at a pressure of 1 mbar of NH₃. The deposition rate reached a maximum value of 0.2–0.3 nm per pulse. At lower pressures, the deposited films consist of a fine mixture of three amorphous phases (amorphous stoichiometric silicon nitride, amorphous non-stoichiometric silicon nitride and amorphous silicon). The amorphous silicon is prevalent in films deposited at a pressure of several to several tens of bars. Droplets of polycrystalline -Si are sometimes visible on the film surface. The experimental evidence, is analysed with a view to elucidating the participation in the chemical synthesis of the three main stages of the process: the substance expulsion from the target by laser ablation, the transition through the gas of the expulsed substance and it's final impact on the collector. We conclude that silicon nitride is mostly synthesized during the impact on the collector of the flow of the ablated substance.     

Structural analysis of amorphous (Fe1-x Mn x )78B22 alloys by X-ray diffraction and electrical resistance

The structure of amorphous (Fe_1–x Mn _x ) alloys prepared by a single roller technique has been investigated in terms of X-ray diffraction and electrical resistance. The lattice parameter of the crystalline precipitates, which were-Fe and b c t (FeMn)₃B, was determined under different heat treatments. On heating up to 440° C where a mixture of amorphous and crystalline phases exists and up to 550° C corresponding to the completion of crystallization, the lattice parameter of the-Fe phase rises to that of pure-Fe with increasing manganese concentration. In samples annealed at 660° C for 5 h, the opposite behaviour is observed. These results can be explained on the basis of the position of the boron atom occupying the-Fe lattice, the pressure effect exerted by the environment, and the enhancement of the chemical short-range ordering between manganese and boron atoms with manganese concentration. In the b c t phase, which shows a reduction in lattice parameter with manganese concentration independent of heat treatment, the effect of redistribution of the atoms in the unit cell should be also taken into account.     

Ultrasonic attenuation of longitudinal and shear waves in superconducting lead

Longitudinal and shear wave ultrasonic attenuations have been measured in high-purity Pb on two single crystals obtained from the same ingot. The measurements were done at low temperatures, at different frequencies, and in transverse magnetic fields, up to a field of 7.3 kG. The propagation directions in the two crystals were along [100] and [110]. For some propagation and polarization directions the _s / _n ratio is found to be frequency-independent, while for others, large divergences in the _s / _n ratios at different frequencies are observed. A sharp decrease of _s / _n nearT _c is observed for a particular longitudinal wave propagation, but not in any shear wave propagation. In some cases _s / _n is found to be abnormally high and this feature is associated with a peak in attenuation _n and a relatively high _n at 7.2 K. None of the _s / _n curves fits closely to any BCS energy gap. For longitudinal waves the high magnetic field (H) dependence of the normal state attenuation was found to agree qualitatively with the free electron theory for propagation along [100], but not for propagation along [110]. For shear waves the high-field attenuations do not extrapolate to zero asH tends to infinity. For all propagation and polarization directions the high-field attenuations show 1/H ² field dependence.     

Similarity solutions in axisymmetric mixed-convection boundary-layer flow

The similarity equations for mixed-convection axisymmetric boundary-layer flow are considered. The equations involve a buoyancy parameter and a curvature parameter . The equations are solved numerically and it is found that for large , and of O(1), an asymptotic solution is approached, the nature of which is discussed. When is also large, of O(^1/4), the problem, at leading order, becomes independent of the mainstream and the free-convection limit is obtained. This problem is also discussed, including the behaviour for large values of ₀, the free-convection curvature parameter. For < 0 we find that the solution can be continued past the point where the wall heat transfer becomes zero (where previous mixed-convection similarity solutions in plane geometry were terminated) with the solution ending as 0^–. The nature of this limit is also discussed. For < 0 it is also found that there are solutions only in _b = < 0 with two branches of solution bifurcating out of = _b , and values of _b are computed for a range of . The behaviour of the solution for large values of the curvature parameter , and of O(1), is discussed where it is shown that the solution proceeds in inverse powers of log .     

Evaluation of tricalciumphosphate/ hydroxyapatite cement for tooth replacement: an experimental animal study

A calciumphosphate cement, consisting mainly of tricalciumphosphate (85% -TCP and 15% -TCP), was inserted in 16 surgical defects created in the tibia of goats. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) showed that after 3 months of implantation the -TCP was transformed to hydroxyapatite (HA). Histological evaluation revealed that the presence of cement stimulated the ingrowth of bone compared with unfilled cavities. Active resorption and remodelling of cement particles was observed. The cement did not evoke an inflammatory reaction. At 6 months after implantation no further changes in the composition of the cement occurred. All remaining material was surrounded by mature bone.     

Dielectric relaxation in polychlorotrifluoroethylene

The effect of increasing lamellar thickness in bulk polychlorotrifluoroethylene (PCTFE) by various methods (annealing and increasing time and temperature of crystallisation) on the parameters of the and relaxations has been studied.For the a relaxation consistent increase in temperature of maximum loss and activation energy with increasing lamellar thickness confirms the strong suggestion of earlier work [6] on oriented specimens and shows that the relaxation arises mainly in the interior of the lamellae with little contribution from the chain folds.No systematic changes in these parameters with increasing lamellar thickness was found for the relaxation and this is explained by the presence of _c and _a components in crystalline and amorphous regions respectively. The component _a (as well as the _c one) shows a marked anisotropy in magnitude with respect to the draw direction in oriented specimens relative to the direction of the applied electric field. This implies a lining up of the chain molecules parallel to one another in amorphous regions.The non-existence of analogous short chain compounds and experimental scatter prevented detailed checking of the consistency of the data for the relaxation with the theory for the _c-C _c model [5].     

Specific analysis of EBSD data to study the texture inheritance due to the β → α phase transformation

A specific processing of EBSD data is proposed to study the texture inheritance of titanium or zirconium alloys. A non standard misorientation map is calculated to localise the colonies inherited from the same parent grain. The calculation of the parent orientation from its inherited variants detailed in previous works has been adapted to the data obtained from an automated EBSD analysis. Finally, a method to derive the orientation map of the parent phase from that of the inherited phase is proposed. The resulting and COMs are used to study some aspects of the variant selection occurring in the transformation of a T40 sample.     

Anodic oxidation effects on pyrolytic graphite surfaces in acid

Anodic oxidation effects on the basal and edge surfaces of pyrolytic graphite in acid were studied by laser Raman spectroscopy, and by a gas-phase chemical modification method coupled with X-ray photoelectron spectroscopy. Surface covering fractions were also studied by -epichlorohydrin monolayer formation. It was found that the species of surface chemical groups added by anodic oxidation was closely related to the structure of the oxidized surface. In the case of the basal surface, carboxyl groups were added by anodic oxidation, being always accompanied by the destruction of its surface structure. On the other hand, in the case of the edge surface, hydroxyl groups were added without the destruction of its structure with a mild treatment. With more severe treatment, carboxyl groups were added and this addition was also accompanied by destruction of the surface structure. There was a range of treatment in which hydroxyl groups could be added without destroying the structure. Finally it was confirmed that both carboxyl and hydroxyl groups could make covalent bonds with epoxy groups of -epichlorohydrin.     

Synthesis, X-ray diffraction and solid-state 31P magic angle spinning NMR study of α-tricalcium orthophosphate

The effects of synthesis conditions on the quantitative preparation of -tricalcium phosphate (-TCP) have been investigated. The following parameters of the synthesis were considered: nature of the starting material-Ca-deficient hydroxyapatite, DAP, versus hydroxyapatite-anhydrous dicalcium phosphate mixtures (HAP-DCPA); Ca/P atomic ratio of the mixture, calcination temperature and time, and cooling rate. The yield and crystallinity of the final product have been estimated using X-ray diffraction (XRD) and solid state ³¹P magic angle spinning NMR (MAS-NMR) techniques. The results show that pure, well-crystallized -TCP powders exhibiting nearly ideal MAS-NMR spectra, can be obtained by reactive sintering of HAP-DCPA (Ca/P=1.50...1.52) mixtures, at 1400°C for 8 h. The broadening of MAS-NMR spectra can be used as an indicator of structural order in the final product. The -TCP yield with DAP was always less than 50%.     

Influence of substrate temperature on the structural and electrical properties of α-Fe2O3 films prepared by ultrasonic spray pyrolysis

Iron oxide films were prepared by ultrasonic spray pyrolysis (USP) on SiO₂ coated Si wafers using iron acetylacetonate as an iron precursor. The crystallographic properties and surface morphologies of the films were characterized by X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy (XPS) was carried out to determine the Fe oxidation states. The satellite peak associated with Fe³⁺ photoemission at a binding energy of 719 eV was detected in the XPS results for iron oxide films, which is one of the indications of the Fe₂O₃ composition. The as-deposited films exhibit a polycrystalline -Fe₂O₃ structure. In order to observe thermal stability of the films, the resistance variation with ambient temperature was measured. All the iron oxide films deposited in this experiment were found to be -Fe₂O₃ with the thermal stability lower than 2%/ °C.     

Mechanical properties and microstructures of rapidly solidified Al89.5Ni8Zr2.5 and Al88.5Ni8Ti3.5 alloys

Al89.5Ni8Zr2.5 and Al88.5Ni8Ti3.5 alloys extruded from their rapidly solidified powders have tensile strength more than 800 MPa and Young's modulus about 100 GPa. The extruded Al89.5Ni8Zr2.5 alloy is composed of -Al, Al3Ni and a metastable tetragonal Al3Zr, and the extruded Al88.5Ni8Ti3.5 alloy consists of -Al, Al3Ni and equilibrium Al3Ti. Through investigation on microstructure change of rapidly solidified Al89.5Ni8Zr2.5 and Al88.5Ni8Ti3.5 alloys with temperature, it is found that a new tetragonal Al3Zr phase, together with -Al and Al3Ni precipitates from the supersaturated -Al phase in the rapidly solidified Al89.5Ni8Zr2.5 alloy at around 603 K and an equilibrium Al3Ti, together with -Al and Al3Ni forms from the supersaturated -Al phase in the rapidly solidified Al88.5Ni8Ti3.5 alloy at about 523 K. The lattice parameters of the new metastable tetragonal Al3Zr phase were calculated to be a=0.3896 nm and c=0.9006 nm. Both the metastable tetragonal Al3Zr and equilibrium Al3Ti phases keep a nano grain size, less than 50 nm even at 773 K. The existence of the nano scale Al3Zr, Al3Ti phases and fine grains of -Al, Al3Ni phases is the reason that Al89.5Ni8Zr2.5 and Al88.5Ni8Ti3.5 alloys have the high strength. © 1998 Chapman & Hall     

Thermal evolution of Fe62.5Co6Ni7.5Zr6Nb2Cu1B15 metallic glass

Thermal evolution of Fe_62.5Co₆Ni_7.5Zr₆Nb₂Cu₁B₁₅ amorphous alloy prepared by one-roll melt-spinning technique was studied by XRD and DTA. The crystallisation process, occurring in several steps, can be summarised as follows: a a + -Fe a + -Fe + -Fe -Fe + -Fe + ZrB₁₂, where a and a are amorphous phases, and a can be indexed as a -Fe (fcc) structure, with a crystalline order on an average distance of 8 Å. The metallic glass demixed on quenching, but component phases tended to mix by exchanging Fe atoms in a temperature range overlapped with the first crystallisation, which yields -Fe nanocrystals (27 Å). Higher temperature exo-peaks correspond mainly to a recrystallisation of the phases formed at lower temperature. It was found that this alloy has nanocrystalline structure also after heating at a well higher temperature than first crystallization. Even after the last exo-peak, the average crystallite size (D) was considerably smaller than that found in the literature for analogous metallic glasses; D values for our alloy were comparable to those of nanocrystalline phases of other systems heat treated below the temperature of exothermal DTA peaks. Extensive oxidation above 600°C, even at a low oxygen content (c _{o 2} 2 ppm), led to a marked modification of the surface layer: two zirconia polymorphs were identified on the surface of the ribbons, and the ratio of -Fe to -Fe content increased with respect to the bulk. Differences in thermal evolution between outer layer and bulk are attributed to a different phase composition and non-uniform distribution since the as-quenched stage.