Search results for "DIFFERENTIAL SCANNING CALORIMETRY"
showing 10 items of 285 documents
Structural, thermal, dielectric and ferroelectric properties of Na0.5K0.5NbO3and Na0.5K0.5NbO3+0.5mol%MnO2ceramics
2014
Lead-free Na0.5K0.5NbO3 and Na0.5K0.5NbO3+0.5mol%MnO2 ceramics were fabricated by solid state hot pressing sintering process. The phase structure and thermal, dielectric and ferroelectric properties of these ceramics were investigated. X-ray measurements showed that all samples have a single perovskite structure and possess orthorhombic–tetragonal and tetragonal–cubic phase transitions. Sequence of phase transitions was confirmed by differential scanning calorimetry (DSC) and dielectric measurements. Obtained results showed that optimal temperature sintering of Na0.5K0.5 NbO3+0.5mol%MnO2 ceramics is 1100 °C. The results show that investigated ceramics are one of the promising materials as e…
PHASE TRANSITIONS IN HALOGENOANTIMONATE(V) CRYSTALS: [N(CH3)4]SbCl6 AND [N(C2H5)4]SbCl6
1998
Abstract New crystals of the family of alkylammonium chloroantimonates(V), [N(CH 3 ) 4 ]SbCl 6 and [N(C 2 H 5 ) 4 ]SbCl 6 , have been grown and systematically studied. X-ray studies show that [N(C 2 H 5 ) 4 ]SbCl 6 is composed of isolated cations and ideal SbCl 6 − octahedra. Differential scanning calorimetry, dilatometric and dielectric measurements reveal structural phase transitions in [N(CH 3 ) 4 ]SbCl 6 and [N(C 2 H 5 ) 4 ]SbCl 6 of first order at 236 and 345 K, respectively. The measurements of 1 H-NMR spin-lattice relaxation times, T 1 , show that mechanism of the phase transitions in [N(CH 3 ) 4 ]SbCl 6 and [N(C 2 H 5 ) 4 ]SbCl 6 is due to the reorientations of the tetraalkylammoniu…
Differential scanning calorimetric and Raman studies of phase transition V ⇌ IV of ammonium nitrate
1993
Abstract Differential scanning calorimetry, alone and in conjunction with Raman spectrophotometry for simultaneous calorimetric and spectral measurements, was used to study the solid state phase transitions of ammonium nitrate between − 50 and 100 °C. On heating, two transition paths were observed between − 40 and 0 °C: one showing two separate peaks in DSC and the other showing a single peak. The latter path became dominant when samples were thermally cycled. The double transition was followed by transition IV →II at 51 °C and the single transition by transitions IV → III → II at about 50 and 87 °C. Raman spectra showed that there were two phases present between the two DSC peaks at low te…
Thermotropic polyesters with mesogenic groups based on substituted hydroquinone units and highly flexible siloxan spacer in the main chain
1984
New thermotropic Polyesters having mesogenic groups based on substituted hydroquinone units and highly flexible oligosiloxan spacer in the main chain, are synthesized and characterized. The mesophase formed at low temperature are studied by differential scanning calorimetry (DSC) and polarized light microscopy. The liquid crystalline behaviour of these polyesters, particulary their transition temperatures and the mesophase width could be explained on the basis of their structural features.
Durability of Basalt/Hemp Hybrid Thermoplastic Composites
2019
The Achilles heel of thermoplastic natural fibre composites is their limited durability. The environmental degradation of the mechanical properties of hemp and hemp/basalt hybrid-reinforced high-density polyethylene (HDPE) composites has been investigated with a special focus on the effects of water ageing and accelerated ageing, including hygrothermal and UV radiation. Modification of the matrix was carried out using a maleic anhydride high-density polyethylene copolymer (MAPE) as a compatibilizer. Hybridization of hemp fibres with basalt fibres and the incorporation of MAPE were found to significantly decrease the water uptake (up to 75%) and increase the retention of mechanical propertie…
Protection of active aroma compound against moisture and oxygen by encapsulation in biopolymeric emulsion-based edible films.
2008
International audience; Edible films made of ι-carrageenans display interesting advantages: good mechanical properties, stabilization of emulsions, and reduction of oxygen transfers. Moreover, the addition of lipids to ι-carrageenan-based films to form emulsified films decreases the transfer of water vapor and can be considered to encapsulate active molecules as flavors. The aim of this study was to better understand the influence of the composition and the structure of the carrageenan-based film matrices on its barrier properties and thus on its capacity to encapsulate and to protect active substances encapsulated. Granulometry, differential scanning calorimetry, and Fourier transform infr…
Kinetic parameters of a cyanate ester resin catalyzed with different proportions of nonylphenol and cobalt acetylacetonate catalyst
2005
The isothermal cure of a dicyanate ester monomer has been investigated by differential scanning calorimetry (DSC) in the presence of different quantities of a catalyst system formed by nonylphenol (NP) and cobalt (II) acetylacetonate (Co(AcAc)2). Two sets of experiences were studied. Firstly, the NP composition was varied from 0 to 10 per hundred resin (phr) and secondly, the Co(AcAc)2 loadings were changed at 2 phr of NP. It has been observed that the cyanate conversion increases significantly after the first addition of the metal catalyst and, also, at the same time the thermal stability improves. Moreover, the kinetic data have been fitted with a second-order equation respect to the cyan…
Morphology and thermal behavior of dicyanate ester-polyetherimide semi-IPNS cured at different conditions
2000
A high-temperature thermosetting bisphenol-A dicyanate, BADCy was modified with polyetherimide, PEI, at various compositions. Phase separation and rheokinetics through curing were studied by optical microscopy, dynamic and isothermal differential scanning calorimetry, and rheological measurements. The PEI phase separated at the early stages of curing, well before gelation, and did not affect the polycyclotrimerization kinetics. The phase structure and thermal properties of the final network were investigated as a function of the PEI content and cure temperature. For this purpose, dynamic mechanical analysis, scanning electron microscopy studies, and thermogravimetrical analysis were carried…
Water-soluble and redox-responsive hyperbranched polyether copolymers based on ferrocenyl glycidyl ether
2015
Water-soluble copolymers of ferrocenyl glycidyl ether (fcGE) and glycidol were prepared via anionic ring-opening multibranching polymerization (ROMBP). The resulting hyperbranched materials with molecular weights (Mn) of 3500 to 12 300 g mol−1 and relatively narrow molecular weight distributions (Mw/Mn = 1.40–1.69) exhibit both temperature- as well as redox-responsive behavior, which was studied via turbidity measurements. The cloud point temperatures (Tc) were adjusted between 45 and 60 °C through variation of the fcGE comonomer content. Additionally, these Tcs can be increased by the addition of an oxidizing agent. The extent of oxidation of the materials was quantified by Mosbauer spectr…
A Challenging Comonomer Pair: Copolymerization of Ethylene Oxide and Glycidyl Methyl Ether to Thermoresponsive Polyethers
2014
Motivated by the oxygen-rich and fully amorphous structure of poly(glycidyl methyl ether) (PGME), a series of thermoresponsive poly(glycidyl methyl ether-co-ethylene oxide) copolymers P(GME-co-EO) with molecular weights in the range of 3000–20 000 g mol–1 were synthesized by the activated monomer polymerization technique. Tetraoctylammonium bromide (NOct4Br) was employed as an initiator in combination with triisobutylaluminum (i-Bu3Al) as a catalyst under mild conditions. Polyethers with varying GME content between 31 and 100 mol % were obtained. Triad sequence analysis using 13C NMR spectroscopy proved that no pronounced block structure was obtained. Differential scanning calorimetry (DSC)…