Effect of poly(<Emphasis Type="SmallCaps">L</Emphasis>-lactide) surface topography on the morphology of in vitro cultured human articular chondrocytes

Human articular chondrocytes were cultured in vitro on poly(L-lactic) acid, PLLA, substrates. Influence of the surface topography on cell morphology was found. Different surface microtopographies were obtained on PLLA by crystallizing at 120 °C after nucleation treatments that include isothermal stages at temperatures just below (55 °C) and just above (75 °C) the glass transition temperature (T _g = 65 °C). Isothermal crystallization from the melt gave rise to big spherulites (approx. 50 μm diameter) with approx. 1 μm depth. Crystallization after nucleation treatments results in smaller (approx. 5 μm)—difficult to distinguish—spherulites. Cell viability was excellent and not affected by the surface roughness. Cell population on the nucleated samples resembles the result of culture on the reference tissue culture polystyrene (TCPS). However, cells cultured on big spherulites (PLLA isothermally crystallized without nucleation treatment) show a peculiar morphology, with a more isolated disposition and growth oriented in a characteristic direction.     

Structural and chemical changes of thermally treated bone apatite

The thermal behaviour of the animal by-product meat and bone meal (MBM) has been investigated in order to assess how it is affected structurally and chemically by incineration. Initially composed of intergrown collagen and hydroxyapatite (HAP), combustion of the organic component is complete by 650 °C, with most mass loss (50–55%) occurring by 500 °C. No original proteins were detected in samples heated at 400 °C or above. Combustion of collagen is accompanied by an increase in HAP mean crystallite size at temperatures greater than 400 °C, from 10 nm to a constant value of 120 nm at 800 °C or more. Newly formed crystalline phases appear beyond 400 °C, and include β-tricalcium phosphate, NaCaPO₄, halite (NaCl) and sylvite (KCl). Crystallite thickness as judged by small angle X-ray scattering (SAXS) increases from 2 nm (25–400 °C) to 8–9 nm very rapidly at 550 °C, and then gradually increases to approximately 10 nm. The original texture of HAP within a collagen matrix is progressively lost, producing a porous HAP dominated solid at 700 °C, and a very low porosity sintered HAP product at 900 °C.     

Crystallization study of chemically vapour-deposited amorphous silicon films by in situ x-ray diffraction

The solid phase crystallization kinetics of chemically vapour-deposited amorphous silicon films were studied by in situ X-ray diffraction. We determined the crystalline volume directly from the Bragg peak intensities at various times during isothermal annealing in the temperature range 578 °C < T < 658 °C. From these experiments we deduced that the crystallization was due to nucleation predominantly at the substrate-film interface followed by crystal growth perpendicular to this interface. The crystal growth rate was thermally activated with an activation energy E_v of 3.1 eV. A strong 〈111〉 preferred orientation of the growing polycrystal was observed and the grain size remained constant at about 60 nm. Evidence of stresses at the amorphous-crystalline interface during the early stages of crystallization was observed. A comparison with previous conductivity measurements is also carried out.     

Microstructure of a thermotropic random copolymer of hydroxybenzoic acid,isophthalic acid and hydroquinone (HBA-IA-HQ)

Transmission electron microscopy has been used to study microstructural features in a thermotropic copolyester composed of 4-hydroxybenzoic acid, isophthalic acid and hydroquinone residues. Selected-area electron diffraction patterns indicate that thin sheared samples of the pure copolymer, and of an analogue containing glass filler, exhibit a dual molecular orientation in which the meridional maxima are closely periodic in scattering angle. Dark-field (DF) imaging in one set of the diffuse equatorial reflections reveals “bands” which have an average period of 200 nm. Annealing the material in the solid state at 250 °C leads eventually to a change in the structure in which the banded texture is replaced by regions of uniform orientation within which the molecules are aligned with the shear axis. Needle-like diffracting crystalline entities, measuring approximately 80 nm long, in the direction of the molecular chain axis, and 5–8 nm thick, have been imaged in DF using the first meridional reflection as the source of diffraction contrast.     

Synthesis and characterization of indium monoselenide (InSe) nanowires

Indium monoselenide (InSe) nanowires were grown by the thermal evaporation method in argon atmosphere without the presence of any catalysts using InSe polycrystalline powder as the source material. No nanostructure growth was observed at deposition temperatures below 580 °C. The nanostructures were discernable at temperatures above 620 °C. Pure InSe nanowires were obtained at the deposition temperature of 660 °C for 50 min. The diameters of the nanowires were from 50 to 240 nm and their lengths were up to several micrometers. X-ray diffraction spectrum reveals that the synthesized products were single-crystalline of the β-phase hexagonal structure of InSe with lattice constants a = 4.006 Å and c = 16.642 Å. The strong peak due to the reflection from the (004) crystal plane reveals that most nanowires grow with a strong preferred orientation.     

Structural and electrical properties of RuO2 thin films prepared by rf-magnetron sputtering and annealing at different temperatures

Conductive ruthenium oxide (RuO₂) thin films have been deposited at different substrate temperatures on various substrates by radio-frequency (rf) magnetron sputtering and were later annealed at different temperatures. The thickness of the films ranges from 50 to 700 nm. Films deposited at higher temperatures show larger grain size (about 140 nm) with (200) preferred orientation. Films deposited at lower substrate temperature have smaller grains (about 55 nm) with (110) preferred orientation. The electrical resistivity decreases slightly with increasing film thickness but is more influenced by the deposition and annealing temperature. Maximum resistivity is 861 μΩ cm, observed for films deposited at room temperature on glass substrates. Minimum resistivity is 40 μΩ cm observed for a thin film (50 nm) deposited at 540°C on a quartz substrate. Micro-Raman investigations indicate that strain-free well-crystallized thin films are deposited on oxidized Si substrates.     

Characterization of severe matrix distortions during phase separation from the redistribution of diffracted intensities

Severe matrix deformation has been examined at an early stage of age-hardening in a polycrystalline Brush 25 alloy containing Cu–11.50 at % Be–0.23 at % Co aged at 200°C. Simplified anisotropic elastic models for the atomic displacement field about coherent disc-shaped precipitates provide quantitative estimates of the atomic displacement field in the surrounding matrix. This requires a separation of diffracted intensity into Bragg peaks, static diffuse scattering, and quasilines. The latter originates from the severely distorted zone about the precipitates. Elastic models include single discs, and [1 0 1] stair-step pairs. Ageing at 200°C introduces larger changes in the diffraction profiles than at 315°C. This is observed mainly as large variations in quasiline intensities, as well as in their relative peak positions. Comparisons are made at about one-half the maximum hardness. These variations result from the response of the coherent anisotropic copper matrix to large tetragonal Bain strains in disc-shaped precipitates, and a strong preference for the largest deformations to be perpendicular to the free surface. Quasiline shifts are used along with Vegard's Law to extend the metastable Guinier-Preston (GP)-zone boundary to 200°C. This boundary extension is smooth and continuous with published data, and thereby relates the metastable GP boundary to a highly distorted matrix about disc-shaped precipitates. Disc diameters range from 4.8–6.4 nm with a thickness of 0.29 nm after 16–64 h at 200°C. The [1 0 1] stair-step pair model best fits the experimental results. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of hydrogen annealing on the composition and particle size of molybdenum nanopowders

We have studied the behavior of molybdenum nanopowder consisting of particles with an average size of 23.7 nm. The powder was prepared by hydrogen plasma reduction of molybdenum trioxide and contained considerable amounts of oxygen in the form of amorphous molybdenum oxides and hydroxides. Annealing in hydrogen for 1 h at temperatures from 300 to 1000°C is shown to cause crystallization of oxides, which then vaporize to form the volatile hydroxide MoO₂(OH)₂. Most of the oxygen is removed by annealing below 700°C. Starting at this temperature, particle growth is observed. The main mechanism behind the coagulation of molybdenum particles is vapor transport. Annealing at 1000°C for 30–50 min in hydrogen with a dew point of −5°C increases the particle size by about one order of magnitude.     

Thermal and crystallization behavior of zirconia precursor used in the solution precursor plasma spray process

Yttria stabilized zirconia (7YSZ) solution precursor has been successfully used in the deposition of high durability thermal barrier coatings. In this paper, the thermal and crystallization behaviors of 7YSZ precursor were investigated by TG-DTA, FTIR and XRD. The results show that the precursor decomposition and crystallization temperatures greatly depend on heating rate e. g. 74°C for the crystallization temperature when tripping the heating rate. With a 10 °C/min heating rate, the weight loss due to precursor pyrolysis occurs predominantly at temperatures below 500 °C. A small weight loss due to the oxidation of residual carbon is detected from 800 °C to 950 °C. The complete crystallization of the tetragonal phase was determined to be around 500 °C by DTA and XRD analyses with a 10 °C/min heating rate. The crystallization kinetics and the activation energy of amorphous 7YSZ precursor were investigated by variable heating rate DTA. The calculated activation energy is 66.2 kJ/mol. The Avrami parameter value was determined to be 2.68, which indicates that crystallization nucleation and growth is diffusion-controlled. The crystalline phase of 7YSZ coatings deposited by the Solution Precursor Plasma Spray process was identified by XRD and Raman spectrum. The average YSZ grain size in the SPPS coating was determined to be 61 nm.     

Interfacial crystalline behavior in glass-fiber/polypropylene composites modified by block copolymer coupling agents

A kind of di-block copolymer polystyrene-block-poly(γ-methacryloxy-propyltrimethoxysilane) (PS-b-PMPS) with different PS block length and a kind of tri-block copolymer polystyrene-block-poly(n-butylacrylate)-block-poly(γ-methacryloxypropyltrimethoxysilane) (PS-b-PnBA-b-PMPS) with different PnBA block length were synthesized by atom transfer radical polymerization (ATRP), in which PS was a ‘hard’ block and PnBA was a ‘soft’ block. The interfacial crystallization behaviors of glass fiber/polypropylene systems modified with different coupling agents MPS, PS-b-PMPS, and PS-b-PnBA-b-PMPS were investigated on different crystallization conditions. Transcrystallinity could not be induced on non-isothermal crystallization or without maleic anhydride (10%) in polypropylene, but it appeared when glass fibers were treated with common silane coupling agent γ-methacryloxypropyltrimethoxysilane (MPS) and di-block copolymer coupling agent PS-b-PMPS in 135 °C isothermal crystallization without shear and 150 °C isothermal crystallization with shear. However, it disappeared at the interface when the samples were treated with tri-block copolymer coupling agent (PS-b-PnBA-b-PMPS) either under static or shear-induced condition. It might be that the flexible interlayer formed by the flexible block PnBA of PS-b-PnBA-b-PMPS could relax not only the thermal stress resulted from interface temperature gradient arising from sample cooling for crystallization, but also the shear stress induced by fiber/matrix interface shear.     

Crystallization and void formation in ZnO–B2O3–SiO2–MgO sintered solder glasses

The evolution of crystallization and porosity changes with firing temperature were studied in ZnO–B2O3–SiO2–MgO glasses. Those glasses presintered at 610 °C to a low porosity were crystallized in the temperature range of 690–870 °C. The glasses were crystallized by a surface crystallization mechanism. The porosity increased with the crystallization temperature. In the temperature range of 710–790 °C, several crystalline phases, such as 3ZnO–B2O3, willemite (2ZnO–SiO2), 5ZnO–2B2O3, and another form of zinc silicate (2ZnO–SiO2), produced at relatively low temperatures, were produced, while above 800 °C only the 2ZnO–SiO2 phase co-existed with a glass phase. Only an observed density difference between the glass and the crystallized glass cannot be attributed to the void formation during the crystallization reaction. Due to the crystallization the composition of the remaining glass around the crystalline phases is expected to change. The depletion of a certain component in the remaining glass, probably the SiO2 due to the production of the 2ZnO–SiO2 phase, might result in the increase in the vapour pressure of the remaining glass and lead to the observed increase in porosity. Below 800 °C, at which temperature the crystallization rate is fast and only a small amount of the glass phase remained, the porosity remained constant after the completion of the crystallization. Contrarily at 860 °C the porosity continuously increased with firing time. This revised version was published online in November 2006 with corrections to the Cover Date.     

A New Hysteretic Behavior in the Electrical Resistivity of Flexinol Shape Memory Alloys Versus Temperature

The electrical resistivity (ER) of Flexinol nickel-titanium shape memory alloys (SMA) has been measured in the range from −15 to 105°C. The investigated Flexinol wires have two diameters, 150 and 375 μm. The experimental results show new temperatures of phase transformation (TTR) evidencing the unexpected presence of the R-phase. The transformations from austenite to martensite, from austenite to R-phase, and vice versa are simultaneous. In the range [20 to 110°C] the hysteresis is almost negligible, whereas in the range [−15 to 105°C] the accommodation process of the hysteresis is observed.     

Synthesis and electrical properties of Gd<Subscript>2</Subscript>MO<Subscript>5</Subscript> (M = Zr,Hf)

Polycrystalline Gd₂ZrO and Gd₂HfO₅ have been prepared by heat-treating coprecipitated oxide mixtures, and their order-disorder phase transitions have been studied in the range 20–1600°C. The materials have been shown to consist of nanostructured grains with a nanodomain size of ∼40 nm. Their electrical conductivity has been determined by impedance spectroscopy in air between 300 and 1000°C. The 1000°C conductivities of Gd₂ZrO₅ and Gd₂HfO₅ are 3.7 × 10⁻³ and 1.8 × 10⁻³ S/cm, and the respective effective activation energies are 1.37 and 1.56 eV.     

Phase transitions of liquid crystalline polyesters: Poly(heptane-1,7-diyl-4,4′-biphenyldicarboxylate)

Wide-angle X-ray scattering was applied to investigate the non-isothermal and isothermal phase transitions of poly(heptane-1,7-dyil-4,4′-biphenyldicarboxylate). It is suggested that the isotropic–smectic (I–S) transition is controled by a nanophase separation with a critical point T_ns=151 °C. Nanophase separation is followed by a first-order S–Cr (crystal) transition. At isothermal conditions above T_ns only S phase exists, whereas below it the S phase appears first and the Cr phase grows from the S by nucleation and three-dimensional crystal growth.     

Thermo-elastic properties of dense YSZ and porous Ni-ZrO2 monolithic and isotropic materials

Attempts are made to correlate the structure and properties of dense and porous Yittria Stabilized Zirconia to establish optimal thermo-elastic properties for better performance at elevated temperatures. Temperature and compositional dependence of isotropic elastic bulk properties (Young's modulus, Poisson's ratio and Shear and Bulk moduli) are determined using the stiffness constants reported in the literature. Anisotropy of Yittria Stabilized Zirconia increases with composition of Yittria dosage in Zirconia. Optimal composition of 12 mole% Yittria stabilized Zirconia is slightly better than 8 mole% Yittria Stabilized Zirconia based on the improved thermo-elastic properties for better performance at higher temperature (RT-400°C). However 15.5 mole% YSZ seems to be more suitable from the view point of thermo-elastic performance at elevated temperatures (500–800°C). Polycrystalline properties predicted are within 5% error limits of the experimental values for Young's modulus of 12 mole% Yittria Stabilized Zirconia. Numerical prediction of Young's modulus of 12 mole% YSZ for 〈100〉 orientation is 362 GPa as compared to experimental value of 370 GPa reported in literature.     

The influences of firing temperatures and excess PbO on the crystal structure and microstructure of (Pb<Subscript>0.25</Subscript> Sr<Subscript>0.75</Subscript>)TiO<Subscript>3</Subscript> ceramics

Polycrystalline samples of (Pb_0.25Sr_0.75)TiO₃ (PST75) were prepared by the solid-state reaction method. The effects of firing temperatures and excess PbO on PST75 ceramics were investigated. The PST75 was calcined between 600 and 1000 °C for 3 h and the sintering temperature ranged between 1050 and 1250 °C for 2 h. The optimized calcination and sintering conditions were identified as 950 and 1250 °C, respectively. The lattice parameter c increased, while the lattice parameter a decreased with increased firing temperatures. The average particle size and average grain size increased with increased firing temperatures. After the addition of PbO—excess 0, 1, 3, 5, and 10 wt%—in the PST75 samples, the lattice parameter a decreased. The average particle size and the average grain size increased with the increase of PbO. The porous microstructure slightly decreased with an increasing amount of PbO—up to 3 wt%—then slightly increased with the higher excess PbO. The density was improved by adding 3 wt% of excess PbO. A low dielectric loss was observed from the 3 wt% excess PbO sample.     

Microstructure and properties of Mg–5.6%Sn–4.4%Zn–2.1%Al alloy

In a previous study, Mg–Sn–Zn-based alloys showed insufficient structural stability at elevated temperatures. In order to improve the castability and corrosion resistance 2.1%wt Al was added to the Mg–5.6%Sn–4.4%Zn base alloy. At the as-cast condition, SEM micrographs indicate a very fine microstructure (Dendritic Arm Spacing—DAS—smaller than 17 μm). The study focuses on precipitation hardening, phase formation and structural stability, during the aging of solution treated samples at elevated temperatures. After solution treatment and aging at 225 °C, Vickers hardness measurements show that this alloy maintains a constant increase of 30% in hardness for periods of up to 32 days. EDS (SEM & STEM), XRD, and Auger characterization methods were applied to identify the phases presented in the alloy. There is no evidence for the presence of the deleterious γ-Al₁₂ Mg₁₇ phase. SAXS measurement and STEM micrographs reveal very fine precipitations (less than 100 nm) after 32 days of aging, along with homogenously distributed larger precipitations (up to 500 nm).     

Processing and material issues related to lead-free soldering

The European requirement for lead-free electronics has resulted in higher soldering temperature and some material and process changes. Traditional tin–lead solder melts at 183°C, where as the most common lead-free alternatives have a much higher melting temperature—tin–copper (227°C), tin–silver (221°C) and tin–silver–copper (217°C). These have challenged the ingenuity of the materials and process engineers. This chapter will explore some of the issues that have come up in this transition, and which these engineers have understood and addressed. As we enter the lead-free era, we see changes as printed wiring board (PWB) substrates which were designed for lower soldering temperatures are being replaced by newer materials. Factors such as glass transition temperature (T _g), decomposition temperature (T _d) and coefficient of thermal expansion must be considered. Many electronic components are made for lower peak temperatures than those required by the new solders. Solder flux chemistries are changing to meet the needs of the new metal systems, and cleaning of flux residues is becoming more of a challenge. Finally, there is a potential reliability problem—an increased potential for the growth of conductive anodic filament (CAF), an electrochemical failure mechanism that occurs in the use environment.     

Growth of multi-walled carbon nanotubes by catalytic decomposition of acetylene on Ni-supported carbon fibers prepared by the heat-treatment of cellulose fibers

Cellular-type carbon fibers, prepared by heat-treatment of cellulose fibers that ranged from 500 to 2300 °C, were used as catalytic support for the growth of carbon nano-filaments. A comparison of the Raman spectra of products prepared at different heat-treatment temperatures showed significant variation in the carbon structure of the surfaces of the as-prepared carbon fibers. TEM observation clearly revealed that the products heat-treated below 1000 °C had an amorphous phase, and at 1500 °C they were similar to glassy carbon—an example of non-graphitizing carbon. Surface graphitization of the carbon fibers derived by pre-treatment at 1500 °C was accomplished at above 2000 °C. Multi-walled carbon nanotubes (MWCNTs), approximately 15 nm and 8 μm in diameter and length, were synthesized on the surface of the prepared carbon fibers via a tip growth mechanism. TEM images and Raman spectra confirmed that the higher synthesis temperature could lead to the formation of MWCNTs with better crystalline carbon shells.     

Permeability and pore structure evolution of silicocalcareous and hematite high-strength concretes submitted to high temperatures

Two high-strength concretes (HSC) only differing in their aggregates—silico-calcareous and hematite—were heated at temperatures up to 450°C (1°C/min). The evolution of their microstructural parameters—porosity, pore structure, permeability—were analysed. Both concretes showed equivalent initial microstructural characteristics. From 60°C, heating generated a large capillary porosity characterized by pore accesses around 0.1 μm. The intensity and especially the width of the porosity peaks increased with temperature. For silico-calcareous HSC, macropores-50 to 0.3 μm—were detected by MIP studies at 250°C and especially at 450°C. They were correlated to microcracks visually observed at the surface of the probes. Up to 250°C, the intrinsic permeability increased similarly for both concretes. Between 250 and 450°C, permeability remained stable for hematite HSC while, for silico-calcareous HSC, a major change was noticed. A good correlation between permeability and total water porosity was observed. At 450°C, influence of the microcracks on permeability was greater than the impact of the increase of capillary pore size. As both concretes showed similar initial microstructural features, conclusion was reached that the differential behaviour can mainly be attributed to internal thermal gradients discrepancies related to the type of aggregates: hematite allows to limit thermal gradient and thus, thermo-mechanical stresses. It was globally observed that damage due to high temperature thermal treatments was lower for hematite HSC.

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Résumé Deux bétons à hautes performances se distinguant uniquement par leurs granulats—silico-calcaires et hématites—ont subi des traitements thermiques allant jusqu'à 450°C (1°C/min). L'évolution de leurs propriétés microstructurales —porosité, structure des pores, perméabilité—a été examinée. Initialement, les caractéristiques microstructurales des deux bétons sont identiques. Dès 60°C, le chauffage provoque l'apparition d'une importante porosité capillaire dont les accès de pore se situent au voisinage de 0,1 μm. L'intensité et surtout la largeur des pics de porosité augmentent avec la température. Pour le béton silico-calcaire, des macropores—dans la gamme 50 à 0.3 μm—ont également été mis en évidence par la porosimétrie mercure à partir de 250°C et surtout à 450°C. Ceux-ci ont été corrélés à des microfissures détectées visuellement à la surface des éprouvettes. Jusqu'à 250°C, on observe pour les deux bétons une augmentation de la perméabilité au gaz. Entre 250 et 450°C, ce paramètre n'évolue pas pour le béton d'hématite alors qu'une évolution majeure est de nouveau observée pour le béton silico-calcaire. Ces évolutions sont bien corrélées à celles de la porosité totale à l'eau. En tenant compte de la similitude microstructurale initiale de la phase cimentaire des deux bétons, cette différence de comportement a été principalement attribuée à des différences de gradients thermiques internes liées au type de granulats, l'hématite permettant de limiter les gradients thermiques et par conséquent les contraintes d'origine thermo-mécaniques. Globalement, l'endommagement lié aux traitements thermiques est moins conséquent pour le béton d'hématite.

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Editorial Note CEA (Saclay) is a RILEM Titular Member.