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Abstract

Gelcasting is a new method for forming advanced ceramics based on obtaining intermediary gels promoted by polimerization “in situ” within the ceramic slurry. Gelcast composites of an ALCOA A-1000 alumina and the copolymer obtained using acrylamide and N,N′-metylene-bisacrylamide as monomers were characterized by thermogravimetry. Polymer distribution was determined by thermogravimetric analysis of small size specimens that were taken from different parts of the alumina composites formed in different shapes. Derivative thermogravimetry was used to identify the resulting polymerization stage within the gelcast body, as well as to study the influence of mold materials and operating conditions. All the composites show an even distribution of the polymer in the bulk, which enables machining in the green state and obtaining high density alumina bodies after sintering.

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Abstract  

In the present paper the effect of the thermoexfoliated graphite (EG) content (0–0.310 parts by volume), constituent mixing conditions (a paddle mixer or a disk-and-screw extruder), annealing and aging on thermodestruction processes of polypropylene (PP)/exfoliated graphite composite materials (CM) by means differential thermal analysis and the thermogravimetric method have been investigated. The studies have shown that thermodestruction processes in CM based on PP and EG ran in air for expense of PP thermodestruction. The characteristics of thermodestruction in CM essentially depend on a regime of making and concentration of components. It is established that processes leading to the formation of less perfect crystalline structures or causing amorphization of PP (including formation of continuous space structures from EG particles, cluster traps) advances thermodestruction. The increase in crystallinity extent of PP favors to the decrease in thermodestruction processes.

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Abstract  

Polyaniline/multi-walled carbon nanotube (PANI/MWNT) composites were prepared by in situ polymerization. Transmission electron microscope (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) were used to characterize the PANI/MWNT composites. Thermal stability and glass transition temperature (T g) were measured by thermogravimetry (TG) and temperature modulated differential scanning calorimetry (TMDSC), respectively. The TG and derivative thermogravimetry (DTG) curves indicated that with augment of MWNTs content, the thermal stability of PANI/MWNT composites increased continuously. While, T g increased and then decreased with the MWNTs content increasing from 0 to 20 mass%.

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Abstract  

Conducting polyaniline/Cobaltosic oxide (PANI/Co3O4) composites were synthesized for the first time, by in situ deposition technique in the presence of hydrochloric acid (HCl) as a dopant by adding the fine grade powder (an average particle size of approximately 80 nm) of Co3O4 into the polymerization reaction mixture of aniline. The composites obtained were characterized by infrared spectra (IR) and X-ray diffraction (XRD). The composition and the thermal stability of the composites were investigated by TG-DTG. The results suggest that the thermal stability of the composites is higher than that of the pure PANI. The improvement in the thermal stability for the composites is attributed to the interaction between PANI and nano-Co3O4.

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Abstract  

DTA/TG and X-ray investigations were carried out on different building composites in order to examine their relative hydration processes. The presence of lime, hemihydrate gypsum, ferosilicate, and some other wastes as leaner and hydrophobic additive in different proportions into composites provokes hydration reactions, leading to calcium silicate hydrate (CSH), ettringite and an intermediate phase formation with varying chemical composition of calcium, aluminum, silicon and sulfur. DTA curves indicate several transformations taking place between composites components, related to hydration of some phases. The content of ettringite component corresponds to the properties and it is used as an indicator for the possibility of industrial application. It is found out that gypsum based cementitious binders could be used as building material in the industry. The same time it is confirmed that the selected wastes could be considered as secondary raw materials.

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Abstract  

Three-phase cyanate ester adhesives have been developed using a bisphenol E cyanate ester resin, fumed silica, and negative-CTE (coefficient of thermal expansion) reinforcements: short carbon fiber or zirconium tungstate (ZrW2O8). Fumed silica was used to impart thixotropic behavior on the resin and decrease settling in the adhesives. The cured composites were evaluated using various thermal analysis techniques for their thermal-mechanical properties. Composites with short carbon fiber showed enhanced modulus and decreased thermal expansion (70% reduction for 20 vol%) and showed little phase separation. While settling of the dense ceramic particles could not be completely eliminated for the zirconium tungstate composites through rheological modification of the adhesive with added fumed silica, a reduction in CTE of 84% was achieved in the composite (58 vol%) compared to the neat resin. In addition, the effect of thermal history on the cure and temperature induced ZrW2O8 phase transitions, and their corresponding influence on thermal strains vs. temperature, are examined by thermomechanical analysis.

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Composites made from E-glass/epoxy or aramid/epoxy are frequently used in aircraft and aerospace industries. These materials are prone to suffer from the presence of delamination, which can reduce severely the performance of aircrafts and even threaten their safety. Since electric conductivity of these composites is rather small, they can propagate electromagnetic waves. Detection of delamination damage can then be monitored by using an electromagnetic penetrating radar scanner, which consists of emitting waves having the form of short time pulses that are centered on a given work frequency. While propagating, these waves undergo partial reflection when running into an obstacle or a material discontinuity. Habitually, the radar is moved at constant speed along a straight path and the reflected signal is processed as a radargram that gives the reflected energy as function of the two-way time and the antenna position.In this work, modeling of electromagnetic wave propagation in composites made from E-glass/epoxy was performed analytically. The electromagnetic wave reflection from a delamination defect was analyzed as function of key intervening factors which include the defect extent and depth, as well as the work frequency. Various simulations were performed and the obtained results have enabled to correlate the reflection pattern image features to the actual delamination defect characteristics which can provide quantification of delamination.

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Abstract  

Polyurethane composites with bagasse of sugar cane (BSC) at different proportions: 5, 10 and 20 mass/mass% were prepared by melt mixing method. The thermal behavior of these composites were studied by thermogravimetry (TG/DTG). The influence of fiber concentration on the kinetic parameters of the composites was studied and a better interaction was suggested between PU/BSC with 5mass/mass% of fiber. Scanning electron microscopy was carried out to investigate surface morphology.

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Pollack Periodica
Authors: Patricia Duratna, Jan Bujnak, and Abdelhamid Bouchair

Machacek J., Cudejko M. Shear connection in steel and concrete composite trusses, SDSS’Rio 2010 Stability and Ductility of Steel Structures , Rio de Janeiro, Brazil, 8–10 September, 2010, pp. 847

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Introduction Over the last few years, polyaniline (PANI) composites have been studied with growing interest because of their numerous applications in various electrical and electronic devices. Many articles on PANI

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