Search results for " thermal analysis"
showing 10 items of 91 documents
Water diffusion and swelling stresses in ionizing radiation cured epoxy matrices
2017
Abstract In this work a DGEBF epoxy monomer was cured by electron beam radiation in the presence of an iodonium salt and the obtained system was hydrothermally aged as such and also after a thermal treatment, in order to obtain two systems having different uniformity in the cross-linking degree. On both systems, the transient stress field arising from swelling was measured and monitored by an optical Photoelastic technique and the results were commented with reference to a thermally cured epoxy system containing the same monomer and already discussed in a previous work. Beam samples with identical dimensions, obtained from the irradiated systems, have been aged at 80 °C in water, and charac…
Water diffusion and swelling stresses in highly crosslinked epoxy matrices
2016
Abstract The present work investigates the swelling induced stresses arising in two epoxy systems during water uptake. The analysed systems are two epoxy resin based on DGEBA monomer and DGEBF monomer respectively, both fully cured by DDS amine. The systems achieve different cross-link density degrees, and are characterised by high glass transition temperatures ranging between 200 and 230 °C. Both epoxies have been conditioned in deionized water baths at two different temperatures (50 °C and 80 °C). A desorption process at room temperature in a dry airborne environment was performed after saturation. Dynamic Mechanical Thermal Analysis, carried out at the various stages of hydrothermal cond…
Use of kinetic DTA and TG methods for compatibility tests on 2,4,6--trinitrotoluene
1986
We have investigated the suitability of thermoanalytical methods for compatibility tests on explosives and contact materials. DTA and TG curves of various materials were evaluated using two DTA and four TG methods and one DSC method. TNT was used as model substance. The contact materials were paraffin, polyethylene, an epoxy resin paint and an epoxy glue. In earlier tests the first two were found compatible and the latter two incompatible with TNT. None of the methods provides an absolute value for the activation energy. However, in compatibility tests only the relative change in the activation energy is of interest and, for this, three of the methods proved informative.
A green method to prepare nanosilica modified graphene oxide to inhibit nanoparticles re-aggregation during melt processing
2017
Abstract A graphene oxide-silica nanohybrid (GOS), self-assembled into a lasagna -like structure, was prepared in water and used as a filler for the melt preparation of polyamide 6 (PA6)-based nanocomposites. For sake of comparison, PA6-based materials were prepared under the same processing conditions by adding GO only or a physical mixture of GO and silica (GO+S). All the materials were characterized from a morphological, spectroscopic, thermal, dynamic-mechanical (DMA) and mechanical point of view. For all the nanocomposites, the interphase was studied either by analyzing loss factor plots coming from DMA measurements and by implementing a novel approach, i.e. combining solvent extractio…
Li2OSiO2Al2O3MeIIO Glass-Ceramic Systems for Tile Glaze Applications
1991
In order to verify the possibility of using glass-ceramic materials as tile coatings, the devitrification processes of three industrial formulations belonging to the Li2O─Al2O3─SiO2 glass-ceramic system were investigated by differential thermal analysis, X-ray diffractometry, scanning electron microscopy, and IR spectroscopy. Compositional variations were made by addition of large amounts of MgO or CaO or PbO (ZnO) oxides as well as through smaller additions of other oxides. In these systems the surface crystallization contributes appreciably to the bulk crystallization mechanism. All the systems investigated show a high tendency toward crystallization even at very high heating rates, devel…
Investigation of eutectic transformation of Zn−Al alloy by DTA
1995
The paper discusses the investigation of crystallization of metals and alloys by differential thermal analysis (DTA). It was assumed that this method allows determination of the mechanism and kinetics of volumetric crystallization underiso conditions (e.g. anisothermal) on the basis of the parameters of the equation expressing an integral form of the DTA curve. From DTA, a course of eutectic transformation was determined for a technical Zn−Al alloy containing 4wt% Al. Investigations were carried out under continuous cooling at various rates and the kinetics parameters were determined with the KEKAM equation:-ln(1-x)=kln
Effects of ZrO2 precursors on the synthesis of V-ZrSiO4 solid solutions by the sol-gel method
1992
The preparation of V-ZrSiO4 solid solutions starting from different ZrO2 precursors by using sol-gel methods is reported. The starting materials were hydrolysed and the dried gels were fired at a temperature between 500 and 900 °C with soaking times of 12h. The organic character of zirconia precursors was stronger, i.e. the starting material had more carbon atoms, a higher temperature was necessary to make the first crystalline phase appear (ZrO2(tetragonal)) and the temperature range for the whole phase transformation was narrower. In all dried gel samples the presence of infrared bands which might be associated with either Si-O-Zr or Si-O-V was not observed. On the other hand, some bands …
Effect of hydrothermal ageing on the thermal and delamination fracture behaviour of CFRP composites
2014
Abstract This work investigates the hydrothermal ageing behaviour of a carbon fibre reinforced laminate and its epoxy matrix in bulk conditions. A model DGEBA epoxy is employed, and water uptake and dynamic mechanical thermal (DMTA) analyses have been performed on both the composites and bulk resin. Fracture toughness of the bulk resin has been measured, evidencing a substantially unmodified critical stress intensity factor KIC, although the evidence of plasticisation effects given by DMTA. Interlaminar Mode I fracture toughness of the composite showed a variable trend towards slight decreases or slight increases, according to the prevailing toughening or embrittling mechanisms activated by…
Layered-structural monoclinic–orthorhombic perovskite La2Ti2O7 to orthorhombic LaTiO3 phase transition and their microstructure characterization
2014
The layered-structural ceramics, such as lanthanum titanate (La{sub 2}Ti{sub 2}O{sub 7}), have been known for their good temperature and low dielectric loss at microwave frequencies that make them good candidate materials for high frequency applications. However, few studies have been conducted on the synthesis optimization by sol gel reaction, in particular by acrylamide polymerization route. The interest in La{sub 2}Ti{sub 2}O{sub 7} ceramic has been greatly increased recently due to the effect of oriented grains. This anisotropy of the microstructure leads to anisotropy in dielectric, electrical and mechanical properties. In this study, grain oriented lanthanum titanate was produced by t…
Effect of additives on the crystallization of cordierite-based glass-ceramics as glazes for floor tiles
2003
Abstract The effect of several additives such as fluxes and/or nucleants on a parent glass with composition located in the primary field of cordierite within the quaternary system CaO–MgO–Al 2 O 3 –SiO 2 has been examined. Crystallization path of glasses was determined by differential thermal analysis (DTA) and X-ray powder diffraction (XRD). Pressed pellets of powdered glasses containing different additives were submitted at thermal treatments up to 1200 °C. The microstructural development at several temperatures was followed by field emission scanning electron microscopy and energy-dispersive X-ray analysis. The results shown that additions of TiO 2 as nucleant and/or B 2 O 3 as flux to a…