Advances in Science and Technology Vol. 77

Abstract: The integration of energy storage into structural multifunctional materials has found use in a wide variety of applications, such as future air and ground vehicles. However, the present realization of these materials cannot be used to increase the structural properties thus limiting its future use in these applications. Here, we developed a novel multifunctional composite material using polyvinylidene fluoride (PVDF) interleaves in carbon fiber composites. The carbon fibers function as both the structural reinforcement as well as the electrodes for the dielectric polymer. It has shown that energy storage functionality can be added into the composites with no reduction in the short beam shear strength. Currently, the breakdown strength is low due to challenges in the processing of the composites and the potential for regions of reduced thickness during pressing. In future research, the manufacturing process of the composites will be investigated to improve the breakdown strength in order to obtain high energy density in addition to preserving the outstanding mechanical properties. This new multifunctional material will open a door to the development of advanced structures that distribute energy storage throughout the composite thus eliminating their current ad hoc implementation.

Abstract: TiB₂ is a superhard, high-temperature and high corrosion resistant material and it is under consideration for tungsten-free cutting tools and high temperature structural applications. Although such a covalent compound requires significantly elevated temperature for the consolidation, great exothermicity of TiB₂ synthesis by means of SHS (Self-propagating High-temperature Synthesis) can be “ïn situ” utilized. In this study, TiB₂-based composites are fabricated from titanium, boron and binder metal. In order to optimize consolidation process and improve fracture toughness of the products, three types of binder, based on cobalt, nickel or copper were investigated. In respect to hardness, limited amount of binder, 5, 10 or 15 vol.% respectively, were applied; each time 5 vol.% of Ti addition for reaction with boron completeness was used. The TiB₂ based composites were fabricated from elements in one process by means of the SHS process combined with p-HIP (pseudo-hot isostatic pressing) method. The raw elemental powders were homogenized by wet mixing using ball milling technique. Dried mixtures were pressed into a compact, coiled by heating element and then exposed to the SHS-p-HIP process. After SHS initiation, the compact was pressed pseudo-isostatically under pressure of 190MPa for 5 min. The sintering additives and their concentrations significantly affected the consolidation process as well as the properties of composites. The highest hardness was obtained for samples sintered with cobalt, containing intermetallic binder. However, elemental metal binder was detected as a main component for samples sintered with copper. The relative density, SEM microstructure, phase composition and hardness are compared in this study.

Abstract: Polymer Impregnation Pyrolysis (PIP) is a cost effective technique for obtaining Ceramic Matrix Composites (CMC) modified with nanoparticles. Commercial UBE polymeric precursor (Tyranno polymer VL-100, diluted in xylene) of a SiC ceramic matrix (with 11 wt% O and 2 wt% Ti) was used to infiltrate 100x85x3 mm^{Superscript text}3 SiC felts (Tyranno ZM fibers, diameter 14 microns, 800 filament/yarn, 270 g/m^{Superscript text}2, with 9 wt% O and 1 wt% Zr), applying different pyrolysis procedures. In particular, pyrolysis was performed in two conditions: 1) at 1000 °C for 60 min; 2) at 900 °C for 120 min. A pyrolysis at 900 °C could be more convenient since it can be easily performed in a steel furnace, without a refractory lining. The SiC felts were pretreated by CVD (Chemical Vapour Deposition) in order to deposit a pyrolytic carbon interphase (about 0.1 microns). Impregnation was performed under vacuum, and drying was carried out in an explosion-proof heating oven. Pyrolysis at 900°C was performed in a AISI 310S austenitic steel furnace, under nitrogen flow. Geometric density was monitored during densification. Mechanical characterisation (bending tests at room temperature, following UNI EN 658-3:2002) was performed after 11 PIP cycles. The results were used to compare the influence of pyrolysis temperature on densification.

Abstract: A novel composite material for the efficient separation of oil from water is presented. It is based on polyurethane (PU) foams modified with colloidal superparamagnetic iron oxide nanoparticles (NPs) in their whole volume and sub-micrometer polytetrafluoroethylene (PTFE) particles on their surface. The hydrophobic and oleophobic original foam becomes water-repellent and oil-absorbing due to the presence of the PTFE particles on its surface. The oil absorption rate is significantly increased by the presence of the colloidal iron oxide NPs. Detailed analysis demonstrates that the NP capping molecules play a significant role in the oil absorption mechanism. Furthermore, the treated foams can be magnetically actuated, and be moved towards oil polluted waters by a weak magnet. As a result, they can absorb the oil contaminants from the water surface, purifying it.

Abstract: PolyHIPEs are highly porous polymeric form, prepared through emulsion templating by polymerizing the continuous phase of high internal phase emulsions (HIPEs). A maleimide-terminated aryl ether sulfone oligomer (MAPES) was copolymerized with divinylbenzene (DVB) in the continuous phase, using a mixed surfactants system (sorbitan monooleate (Span80), cetyltrimethylammonium bromide (CTAB), dodecylbenzenesulfonic acid sodium salt (DDBSS)), and peroxide initiator, to improve CO2 adsorption and the mechanical properties of obtained materials. PolyHIPEs were prepared by two different ratios of mixed surfactants; (SPAN80, DDBSS, and CTAB; 6.3, 0.4, and 0.3 wt%, which was denoted as 7s) and (SPAN80, DDBSS, and CTAB; 11.3, 0.4, and 0.3 wt%, which was denoted as 12s). 0, 2.5, 5, 10, 20, and 30 wt% of maleimide-terminated aryl ether sulfone oligomer were copolymerized with DVB. All PolyHIPE nanocomposites foam were characterized for phase morphology, thermal behavior, surface area, mechanical properties and adsorption of CO2 by using SEM, TG-DTA, N2 adsorption-desorption, LLOYD universal testing machine and CO2 adsorption unit, respectively. The obtained PolyHIPEs showed an open cell and a secondary pore structure with surface areas of approximately 400m2/g. CO¬2 adsorption tests were characterized by pilot gasification unit and the obtained materials showed higher adsorption than neat poly(DVB) without MAPES. Compressive modulus test of the materials showed a higher modulus than for poly(DVB) PolyHIPEs.

Abstract: Atmospheric pressure plasma treatment was used to improve hydrophilic properties and scaffold/cell interaction of poly(S/EGDMA)polyHIPE highly porous foam, prepared from poly(styrene/ethylene glycol dimethacrylate) using high internal phase emulsion technique. With our synthesis procedure and surface treatment, this bioactive material, featuring highly porous structure and good mechanical strength, can be applied as a scaffold for tissue engineering applications. The treatment time and external plasma parameters were investigated in regards to the polyHIPE foam surface’s appropriate for fibroblast implantation. The changes in surface properties were characterized by contact angle measurement, showing that the exposure to air-plasma induced polyHIPE foam with hydrophilic surfaces, as observed by a decrease in contact angle degree. Enhancement of the interaction between the polyHIPE foam and the L929 fibroblast-like cells would imply the hydrophilic improvement of the polyHIPE foam surface due to the polar-like property of the biofluid cell medium.

Abstract: Titanium alloy are widely used in biomedical applications due to their excellent properties such as high strength, good corrosion resistance and excellent biocompatibility. Researches are being developed with elements such as Nb and Zr that reach all criterions for excellent biocompatibility and provide titanium alloys with Young’s modulus close to human bone. The aim of this work was to produce Ti-27Nb-13Zr alloy with different milling times by powder metallurgy process. The mixtures were performed by high energy milling and sintering in high vacuum furnace with temperature of 1300 °C / 3 h. The microstructures of samples were analyzed by SEM and XRD, while the mechanical behavior was evaluated by elastic modulus and Vickers hardness test. The diffraction results of sintering treatment indicate that the alloys are composed of α and β phases. Images obtained by SEM indicate the formation of equiaxial structures. Vickers hardness measurements from sintered samples with 1300 °C / 3 h indicate mean values around 413, 473 and 609 HV for 2, 6 and 10 hours of milling, respectively. The values of elastic modulus enable use the alloy as biomaterial.

Abstract: Silver chloride (AgCl) nanoparticles with the average size of about 45 nm have successfully been doped onto the iron oxide-silica coreshell surfaces by a simple room temperature wet chemistry method under ambient atmosphere. The Stöber process has been used to make the coreshell structure, followed by adsorption of Ag⁺ species on silica surface prior to the addition of hydrochloric acid (HCl) and polyvinylpyrrolidone (PVP). The concentration of HCl acid that was used to induce the growth of AgCl particles was varied from 0.12 mM to 12x10³ mM of concentrations. Results showed that at a very high concentration of HCl (12x10³ mM), large AgCl agglomerates (0.3-0.6 microns) with irregular cubic-like morphology were obtained while at a very low, 12 mM HCl concentration, 30-50nm AgCl particles having a uniform cubic morphology were observed. Concentrations below 12 mM result in irregular and nearly spherical morphology of AgCl particles with a smaller size (28-60 nm). UV-Vis absorption of the composite materials showed absorption in the visible wavelength indicating that Ag nanoclusters might coexist together with AgCl particles.

Abstract: Titanium and its alloys are widely used as biomaterials and interact well with bone tissue. In order, to evaluate more than just morphological osseointegration by histological slides the work aimed to approach a molecular evaluation of bone-implant using lectinhistochemistry (LHC), which binds with high specificity carbohydrates (sugar residues) presents in membrane glycoproteins with the use of lectins. The implanted samples were obtained by powder metallurgy, Ti-13Nb-13Zr alloy with and without gelatin. Pores were achieved by adding gellatin 5 wt% to the hydrogenated metallic powder, after near net shape processing, the samples were thermal treated in vacuum (300 °C/90min) and sintered in high-vacuum (1150 °C/14h). The samples were characterized for porosity (~30%), and subsequently were implanted in rat’s femur bone. After 4 weeks of healing process, bone with implant were sampled to perform LHC in paraffin embedded tissue in histological slides using the lectins PNA, UEA-1, WGA, sWGA and RCA-1. All samples osseointegrated well with the bone, no fibrous capsule was present in the bone which was in contact with the implant. With the molecular approach of osseointegration, adjustments in the processing and structure of macroporous titanium based implants can be performed to achieve friendly structure.

Abstract: We present prototype memory devices using metallic and metal oxide nanoparticles obtained by a physical deposition technique. The two memory device examples demonstrated concern the use of platinum nanoparticles for flash-type memories and the use of titanium oxide nanoparticles for resistive memories. Both approaches give interesting device memory properties with resistive memories being still in an early exploratory phase.