Search results for "CERAMICS"
showing 10 items of 1599 documents
Regioselective C–H amination of free base porphyrins via electrogenerated pyridinium-porphyrins and stabilization of easily oxidized amino-porphyrins…
2020
Four free base aminoporphyrins were synthesized in two steps via regioselective anodic nucleophilic substitution with pyridine followed by ring opening of the electrogenerated pyridinium with piperidine. The X-ray crystallographic structure of the unstable 2-aminotetraphenylporphyrin was solved. Protonation of this latter compound leads to the stable diiminium porphyrin salt.
Spin polarization in electrodeposited thin films of the molecule-based magnetic semiconductor Cr5.5(CN)12·11.5H2O
2013
The magnetoresistance (MR) effect of thin films of the Prussian Blue Analogue (PBA) Cr5.5(CN)12·11.5H2O, prepared by electrochemical deposition, has been measured using the standard two-point probe method. This molecule-based ferrimagnetic material, with a Tc = 240 K, exhibits MR up to 2% at 6 T and 200 K.
H(II) centers in natural silica under repeated UV laser irradiations
2004
We investigated the kinetics of H(II) centers (=Ge'-H) in natural silica under repeated 266nm UV irradiations performed by a Nd:YAG pulsed laser. UV photons temporarily destroy these paramagnetic defects, their reduction being complete within 250 pulses. After re-irradiation, H(II) centers grow again, and the observed recovery kinetics depends on the irradiation dose; multiple 2000 pulses re-irradiations induce the same post-irradiation kinetics of H(II) centers after each exposure cycle. The analysis of these effects allows us to achieve a deeper understanding of the dynamics of the centers during and after laser irradiation.
Metamagnetism in hydrophobically induced carboxylate (phenylmalonate)-bridged copper(II) layers
2006
Self-assembly of copper(II) ions, phenylmalonate and pyrimidine yields the layered compound [Cu(pym)(Phmal)]n ( 1) where intralayer ferro- and interlayer antiferromagnetic interactions occur with three-dimensional antiferromagnetic ordering at Tc = 2.15 K Lloret Pastor, Francisco, Francisco.Lloret@uv.es ; Julve Olcina, Miguel, Miguel.Julve@uv.es
Modular Paradigm for Composites: Modeling Hydrothermal Degradation of Glass Fibers
2021
Fiber-reinforced composite materials are often used in structural applications in humid, marine, and offshore environments. Superior mechanical properties are compromised by environmental ageing and hydrolytic degradation. Glass fibers are the most broadly used type of fiber reinforcement to date. However, they are also most severely affected by environmental degradation. The glass fiber degradation rates depend on: (1) glass formulation; (2) environmental factors: pH, T, stress; (3) sizing; (4) matrix polymer; (5) fiber orientation and composite layup. In this short review (communication), seven modules within the Modular Paradigm are reviewed and systematized. These modeling tools, encomp…
An approach to evaluation of sheet bending force under successive multiaxial stress condition
2009
A new bending under tension test is presented in this paper. This method tries to evaluate bending forces in sheet under successive multiaxial stress condition. This test is carried out in only one step with a pinned cylinder over a material that has been previously deformed to pure shear condition. Due to that, the bending process is made under higher back tension forces than the ones involved in the common methods previously studied in the literature. This entails high pressure values in the sheet-bending tool contact that affects the corresponding friction process. Material is strongly strengthened as a consequence of the deformation practiced in it, and as a result of that, bending forc…
Dynamics of Phase Transition in 0.4NBT-0.4ST-0.2PT Solid Solution
2012
In this paper we present dielectric spectroscopy results of NBT-(0.6-x)ST-xPT with x = 0.2 solid solution. Dielectric investigations clearly showed a relaxor—normal ferroelectric phase transition at TPT = 419 K and low temperature and low frequency dispersion similar to coexistence of dipolar glass and ferroelectric phase. The mean relaxation time above the phase transition follows Vogel—Fulcher law with following parameters: E A = 0.179 eV, τ 0 = 3.39·10−14 s, T VF = 223 K.
Radiation processes in oxygen-deficient silica glasses: Is ODC(I) a precursor of E′-center?
2006
Abstract The accumulation of radiation-induced defects under non-destructive X-ray and destructive cathodoexcitation was studied in pure silica KS-4V glasses possessing an absorption band at 7.6 eV. The correspondence between the existence of this band and the creation of the E′-center by radiation was checked. Detection of induced defects was accomplished by measurement of the luminescence during irradiation, post irradiation afterglow or phosphorescence, induced optical absorption, and thermally stimulated luminescence. In all samples, these observed phenomena associated with charge trapping and recombination on the oxygen-deficient luminescence center. Others centers of luminescence were…
Structure evolution and reaction mechanism in the Ni/Al reactive multilayer nanofoils
2014
Abstract The extremely rapid gasless reactions in binary Ni/Al reactive multilayer nanofoils (RMNFs) are investigated both experimentally and theoretically. The quenching technique is used to study the dynamics of structural transformation on the micro- and nanoscales. The experimentally obtained patterns of structural evolution related to the heterogeneous reactions are compared with the results of molecular dynamics simulations carried out for the same reactive system. Based on the obtained data, the intrinsic mechanism of the reaction in Ni/Al RMNF is considered, which adequately explains the unusual parameters of a gasless combustion wave in such a system.
Irradiation effects on the absorption edge of silica glass
2007
Abstract Vacuum ultraviolet absorption experiments were carried out on a variety of specimens of amorphous silica β-irradiated at different doses from ∼103 to 5 × 106 kGy. Changes in the width of the absorption (Urbach) edge were investigated. These changes strongly depend on the kind of silica considered: in particular the Urbach energy of silica of industrial manufacture increases in the irradiated samples, whereas in sol–gel silica it is poorly influenced by the irradiation. The fictive temperature of the different materials before and after irradiation was also monitored. The changes of the Urbach energy and of the fictive temperature are tentatively discussed considering the disorder d…