Metal-doped apatitic calcium phosphates: preparation,characterization, and reactivity in the removal of hydrogen sulfide from gas phase

With the expansion of human activities, there are more and more living areas adjacent to industrial and/or agricultural activities such as chemical processes, petroleum processes, paint finishing, food processing, livestock farming, composting plants etc. Bad odor is part of several nuisances caused by industrial and/or agricultural activities. Hydrogen sulfide (H₂S) is a typical odorous molecule which causes foul odor at very low concentration. This molecule is formed in different industrial installations, in particular in coal combustion, and petrochemical refinery. The separation and/or transformation of H₂S from gas phase to odorless products are important processes for sustainable development. In this paper, we communicate the preparation of new sorbents for the sorption of H₂S from a synthetic gas effluent. These sorbents consist in an inorganic phase (hydroxyapatite) as host particles, and well-dispersed particles of a metal oxide as guest particles which are the active phase for the removal of H₂S. At room conditions, iron, lead, and zinc doped calcium phosphates were found to be effective for the removal of H₂S. The performance of the sorbents depends on preparation method and the nature of active phases. This opens new prospects for the treatment of H₂S from gas phase.     

In Situ Synchrotron X‐Ray Techniques for Real‐Time Probing of Colloidal Nanoparticle Synthesis

Solution‐phase synthesis of colloidal nanoparticles with precisely tailored properties is one of the fastest growing research topic and represents the most critical foundation to implant nanotechnology in a variety of areas to boost performance of traditional systems. Comprehensive understanding of the nucleation and growth mechanisms involved in the formation of colloidal nanoparticles is very important to realize rational design and synthesis of well‐tailored nanoparticles and requires appropriate in situ techniques to probe the kinetics of the synthetic reactions. Synchrotron hard X‐rays represent a class of promising probes for solution‐phase reactions due to their strong penetration in ambient environment and solutions. This review completely summarizes the in situ synchrotron X‐ray techniques emerged in the recent years for real‐time probing nanophase evolution of colloidal nanoparticles. Typical examples of colloidal nanoparticle syntheses are discussed in detail to shed the light on the advantages and disadvantages of individual techniques.     

Physico-chemical characterization of the fibre/matrix interaction in polyethylene fibre/epoxy matrix composites

The interphase in polyethylene fibre/epoxy matrix composites is studied with FT-IR microspectroscopy using a set-up to investigate the matrix as close to the fibre as a few μm or less. It is shown that moisture present on the fibre surface is able to influence the polymerization reaction of the epoxy/anhydride matrix in an irreversible manner. This effect is enhanced for composites from the more hydrophilic polyvinylalcohol fibre. The fibre/matrix interaction in these thermoplastic fibre composites is also studied with DSC through the characterization of the fibre melting. A decreased 'DSC interaction parameter' is found if the composition of the interphase is changed by moisture. For a composite with an epoxy/amine matrix, on the other hand, the DSC interaction parameter is unaffected by moisture from the fibre surface.     

Interfacial interaction in carbon fiber/thermoplastic composites

This work was undertaken in order to increase the understanding of the mechanism responsible for fiber/matrix interaction in carbon fiber/thermoplastic composite. From results of previous study on carbon fiber/PEEK composite, which suggested that the formation of the fiber/ matrix interaction was primarily related to a chemisorption mechanism, a study was done of the conditions required to obtain efficient fiber/matrix interaction in PA-12 and PP/carbon fiber composites. The interest in studying carbon fiber composite based on PP and PA-12 was that these two matrices are very different in terms of reactivity, polyamide having many more reactive groups than polypropylene. As expected, due to the non-reactive chemical structure of the polypropylene, fiber/matrix interaction in carbon fiber/PP composite occurred only when the matrix was thermally degraded, i.e. when the composite was molded at high temperature or under long residence time at the melt temperature. For the carbon fiber/PA-12 composite, strong fiber/matrix interaction occurred readily at relatively low molding temperature, i.e. well before thermal degradation of the matrix. It was also found that the short beam shear strength in these composites seems to evolve with molding temperature, and a maximum interfacial strength was observed at a molding temperature corresponding to the thermal degradation of the matrix. This indicates that although matrix degradation often results in strong reduction in the composite performance, some matrix degradation can be beneficial in terms of interfacial mechanical properties. Finally, this work demonstrated that while the formation of fiber/matrix interaction seems to be primarily related to a chemisorption mechanism, the contribution of interphase crystallinity to the interfacial strength is not negligible. In fact, interfacial crystallinity was found to be essential to ensure optimum interfacial strength.     

A fibre microbuckling model for predicting the notched compressive strength of composite sandwich panels

Cohesive-zone models have been successfully applied to predicting the damage from notches in engineering materials loaded intension. They have also been used to determine the growth of fibre microbuckling from a hole in a composite laminate under compression. The usual strategy is to replace the in elastic deformation associated with plasticity or microbuckling with a line crack and to assume some form of stress-displacement bridging law across the crack faces. This paper examines recent published experimental data for notched glass-fibre epoxy/honey comb sand wich panels loaded in uniaxial compression. A plastic fibre kinking analysis and a linear softening cohesive-zone model are used for the prediction of the unnotched and open-hole compressive strength and the theoretical results are found to be in a good agreement with experimental data. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 73–84, January–February, 2007.     

Synthesis of poly(1.4.-benzamide) in solutions of randomly coiled polymers

The polycondensation of p-aminobenzoic acid by the use of triphenylphospine and hexachloroethane is described. One way to obtain a mixed solution of rigid rod and flexible coil polymers is the polycondensation of the rigid chains in a solution of a flexible polymer matrix. Results on matrix polycondensation of poly(p-benzamide) in solutions of poly(methyl methacrylate), poly(methyl methacrylate-co-styrene), polystyrene and polyacrylonitrile are reported. It is shown that there exists an interrelation between the phase behavior of the mixed polymer solutions and the influence of the matrix polymer on the synthesis of poly(1.4.-benzamide). The ternary phase diagrams of the rigid rod/flexible coil polymer solutions were determined.     

Design of Microstrip Antennas with Composite Laminates Considering Their Structural Rigidity

Two types of conformal load-bearing antenna structures (CLAS) were designed with microwave composite laminates and Nomex honeycomb cores to secure both the structural rigidity and a good electrical performance. One was a 4 × 8 array for the synthetic-aperture radar (SAR) system and the other was a 5 × 2 array for the wireless local-area network (LAN) system. The design was based on a wide bandwidth, high polarization purity, low losses, and high structural rigidity. The design, fabrication, and structural/electrical performances of the antenna structures were studied. Their flexural behavior was examined by three-point bending, impact, and buckling tests. The electrical measurements were in a good agreement with simulation results. The complex antenna structures obtained have good flexural characteristics. The design of this antenna structure is extended to give a useful guide for sandwich panel manufacturers as well as antenna designers.     

Compaction and Consolidation of Aramid and Composite Fibers. 2. Consolidation of Composite Fibers

The transverse compaction and consolidation of composite fibers obtained from blends of rigid-chain aromatic polyamides and a thermoplastic polycaproamide PA-6 are investigated with the aim to predict the fiber behavior during their compression and processing into plastics. Introduction of the aliphatic polyamide PA-6 into aramid fibers considerably increases their transverse compliance and promotes their sintering. A method for calculating the viscosity of the thermoplastic in the interfiber space from the ratio between the volumetric rate of compaction and the porosity of the material is proposed. It is found that the effective viscosity of the PA-6 melt, during its flow in the thin interfibrillar layers under compression, grows with decrease in its content in the composite fibers.     

Preparation and characterization of exfoliated polystyrene/clay nanocomposites using a cationic radical initiator-MMT hybrid

The exfoliated polystyrene (PS)/clay nanocomposites were prepared via in situ polymerization using a cationic radical initiator-intercalated montmorillonite hybrid. The exfoliated structure resulted from the predominant intra-gallery polymerization over the extra-gallery polymerization owing to the anchored radical initiator inside the clay galleries. Several critical properties of the nanocomposites such as the initial thermal degradation temperature, glass transition temperature, storage modulus, Young’s modulus, and tensile strength were estimated and compared with earlier reported literature values. The improvements in such properties were either comparable or much greater than the reported literature values, mainly due to the efficient exfoliation and dispersion of the clay in the PS matrix.     

Visibly transparent & radiopaque inorganic organic composites from flame-made mixed-oxide fillers

Radiopaque composites have been produced from flame-made ytterbium/silica mixed oxide within a crosslinked methacrylate resin matrix. The refractive index of the filler powder increased with ytterbium oxide loading. A high transparency was achieved for a matching refractive index of the filler powder and the polymer in comparison to commercial materials with 52 wt% ceramic filling. It was demonstrated that powder homogeneity with regard to particle morphology and distribution of the individual metal atoms is essential to obtain a highly transparent composite. In contrast, segregation of crystalline single-oxide phases drastically decreased the composite transparency despite similar specific surface areas, refractive indices and overall composition. The superior physical strength, transparency and radiopacity compared to composites made from conventional silica based-fillers makes the flame-made mixed-oxide fillers especially attractive for dental restoration materials.