Papers by Keyword: Glass Transition Temperature (T_g)

Abstract: In this present study, molecular dynamics (MD) simulation has been performed to investigate the influence of applied hydrostatic compressive and tensile pressure on glass forming process of Ni₆₂Nb₃₈ bimetallic glass using embedded atom method (EAM). During fast cooling (~10 K ps^-1), tensile and compressive pressure has been applied having 0.001 GPa,0.01 GPa and 0.1 GPa magnitude. The glass transition temperature (T_g) for each pressurized (Tensile and Compressive nature) cooling case has been calculated and T_g is found to be dependent on both magnitude and nature of the pressure applied during cooling process.Voronoi cluster analysis has also been carried out to identify the structural evaluation during hydrostatically pressurised fast cooling process. In case of both hydrostatic tensile and compressive pressurised cooling processes, T_g increases with the increase of pressure from 0.001 GPa to 0.1 GPa in magnitude.

Abstract: Glass fibre reinforced epoxy (GRE) composites, used as mechanical support and thermal insulators for superconducting magnets of fusion reactors, have been exposed to gamma irradiations at both higher and lower order ranges of doses. Hand layed E-glass fibre/epoxy composite samples, exposed to gamma-irradiations of cumulative doses of both low strength (10, 20, 30, 40, 50 and 60 kGy) and high strength (0.5, 2.5, 6.5, 8.5 and 10.5 MGy) reveal a huge lowering of the ILSS (inter laminar shear strength) for its exposure to low strength dose irradiation. However, improved ILSS values are recorded for high dose exposures. At both high and low doses of exposure to irradiation the T_g (glass transition temperature) got improved initially with a decreasing trend towards the later stages of exposures. Thermo-gravimetric analysis (TGA) test reveals lowest initial decomposition temperature (IDT) for the composite sample irradiated to maximum dose (10.5 MGy). Activation energy () values of gamma-irradiated composite samples for thermal decomposition were found less compared to that for as-cured composite. FTIR spectra of irradiated samples reveal formation of oligomers confirming the trend of activation energy of irradiated composite. FESEM fractographs of the irradiated composite fracture samples reveal several modes of failure.

Abstract: An aviation polysulfide sealant has been soaked in a water bath at 85 °C to study the effects of hydrothermal treatment on this material. The morphology, Shore A hardness, and mechanical properties of the sealant were measured before and after soaking. The glass transition temperature (Tg) and room temperature storage modulus (E') were measured by means of a dynamic mechanical analyzer (DMA). The results showed that the surface glossiness of the polysulfide disappeared, some bubble defects appeared on its surface, the Shore A hardness and the tensile strength increased, while the elongation at break fluctuated with aging. The Tg and E' of the sealant changed only slightly. The chemical structure of the sealant was not obviously changed, and its aggregation state was changed only slightly, thus indicating that this sealant is characterized by good hydrothermal resistance.

Abstract: This article deals with the classification of glassy and polymer electrolytes for lithium-ion batteries into the so-called “strong/fragile” scale, by the means of the bond-strength-coordination number fluctuation model. We have evaluated the strength parameter, which plays a key role in the understanding of the relaxation phenomena, of each lithium-ion conductor under consideration. We have derived a relationship that not only describes accurately the experimental results, but also provides important details on the interrelation between the strength parameter, the bond strength of the structural unit, the binding energy, the coordination number and the glass transition temperature.

Abstract: To prove the suitability the honeycomb composites structure with VARTM, the mechanical properties of the skin materials and honeycomb composites structure were evaluated with the static strength tests. The mechanical properties of honeycomb composites structure made by VARTM were satisfied with the real using conditions instead of the composites structure made by autoclave process. Accordingly, the honeycomb sandwich composites made by VARTM is available for manufacturing various composites parts. VARTM was very effective method to manufacture the honeycomb sandwich composites. It was possible that the manufacturing process was changed from autoclave process to VARTM to solve the problems on the autoclave process.

Abstract: A new method, which allowed lamination at room temperature without any additional adhesive, was described in this paper. A low Tg styrene-acrylic latex binder was used to forming the green tape via a water-based slurry. The green tapes could adhere to each other at room temperature under low or slight pressure. The density and deformation of laminated green parts depended significantly on lamination pressure, but the density of green parts did not increase after the lamination pressure exceeded a specific value of 4MPa. The interface between the tapes had been investigated in the green and sintered state by SEM. The experimental results showed that the microstructure of interface and density of lamination ceramics was a function of fraction of binder, plasticizer, and laminated pressure.