EVALUATION OF A FIBER-OPTIC SENSOR FOR STRAIN MEASUREMENT AND AN APPLICATION TO CONTACT MECHANICS

A surface attached fiber-optic sensor has been evaluated for maximum strain measurement capability in simple tension experiments to better understand the basic mechanisms of fiber-optic sensor failure. A fiber-optic sensor was then evaluated for its applicability to measure strains under more complex loading conditions, for example, contact strains. Experimental work has shown that while the surface attached fiber sensor fails at much lower strain levels than that achievable by conventional strain gages, unlike conventional strain gages, the fiber-optic sensor shows linearity up until the failure point. This failure point is well within the parameters for typical experiments in our laboratory. Fiber-optic sensors also showed their applicability to contact mechanics.     

Swelling effects in cross-linked polymers by thermogravimetry

A Brazilian coal power plant generates a waste composed by the fly and bottom ashes produced from coal combustion and by a spent sulfated lime generated after SO₂ capture from combustion gases. This work presents a study of the early stages of the hydration of composites formed by this waste and a type II Portland cement, which will be used for CO₂ capture. The cement substitution degrees in the evaluated composites were 10, 20, 30 and 40%, and the effect of the coal power unit waste on the hydration reaction was analyzed on real time by NCDTA, during the first 40 h of hydration. The results show that the higher is the substitution degree, the higher is the retarding effect on the cement hydration process. Actually, by respective thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis on initial cement mass basis, this effect is caused by double exchange reactions among Ca and Mg components of the waste, during the first 4 h of hydration, which promote a much higher exothermic effect in the NCDTA curve, simultaneously to respective induction periods. The pozzolanic reactions, due to the presence of the waste silica and alumina containing amorphous phases, consume part of the original Ca(OH)₂ content existent in the waste in the case of 30 and 40% substituted pastes, and also from part of the Ca(OH)₂ produced in cement hydration reactions, in the case of the 10 and 20% substituted pastes.     

Dielectric resonator-based resonant structure for sensitive ESR measurements at high-hydrostatic pressures

We present a newly developed microwave probe head that accommodates a gasketed sapphire anvil cell (SAC) for performing sensitive electron spin resonance (ESR) measurements under high-hydrostatic pressures. The system was designed around commercially available dielectric resonators (DRs) having the dielectric permittivity of approximately 30. The microwave resonant structure operates in a wide-stretched double-stacked geometry and resonates in the lowest cylindrical quasi TE(011) mode around 9.2 GHz. The most vital parts of the probe's microwave heart were made of plastic materials, thus making the resonant structure transparent to magnetic field modulation at 100 kHz. The overall ESR sensitivity of the probe was demonstrated for a small speck of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) positioned in the gasket of the SAC, using water as the pressure-transmitting medium. The system was also used for studying pressure-induced changes in spin-relaxation mechanisms of a quasi-1D-conducting polymer, K(1)C(60). For small samples located in the sample hole of the gasket the probe reveals sensitivity that is only approximately 3 times less than that yielded by regular ESR cavities.     

Threshold switching effects in AgTlSe2 and CuTlSe2 films

Switching effects in AgTlSe₂ and CuTlSe₂ chalcopyrite semiconductors films have been investigated. The threshold switching voltage was found to increase linearly with the thickness, moreoverV _th increases exponentially with the temperature. The rapid transition between the highly resistive and conductive states was attributed to an electrothermal origin from Joule's heating of a current channel.     

An ESR on formation of iminoxy free radicals—solvent effect on hyperfine splitting constants

The solvent effect on hyperfine interaction in three different types of iminoxy radicals obtained by oxidation of di-2-pyridiketoxime (1), diethyl hydroxyimino(2-fluorophenyl)methanephosphonate (2) and isonitrosoacetophenone (3) have been analyzed. Linear correlations of hyperfine constants of ¹⁴N (both iminoxyl and pyridyl nitrogens of the iminoxyl derived from 1), ³¹P (isomer Z of the iminoxyl derived from 2) and ¹⁹F (both Z and E isomer of iminoxyls derived from 2 on E_T (30) solvent parameters have been found. Opposite directions of the dependencies for different nuclei of the same radical have been established. Anisotropic spectra of the radical derived from 1 and iminoxy radicals derived from -furildioxime have been obtained by γ-irradiation of solid oximes.     

Viscosity of liquid selenium and selenium-sulphur mixtures

The viscosity of selenium has been studied in the liquid state, and the effect of thallium and sulphur additives was investigated. The rotating cylinder method was used. Experimental measurements show that the viscosity of liquid selenium with sulphur admixtures is higher than that for pure selenium, and a complex molecular structure is formed. The results were explained on the basis of the free volume model and the data for liquid selenium were fitted to the model withE _act=0.6 eV.     

The determination of thermodynamics of oxygen complexes of anions of sulfur dioxide and fluoronitrobenzenes using atmospheric pressure ionization mass spectrometry

The thermodynamic properties of oxygen complexes of the negative ions of 1-fluoro-2,4-dinitrobenzene (FDNB), 1,5-difluoro-2,4-dinitrobenzene (DFDNB), and sulfur dioxide have been determined by measuring the temperature dependence of the pertinent ion ratios by using a mass spectrometer equipped with a⁶³Ni atmospheric pressure ionization source. The values of -H° and -S°are SO ₂ ^–(O₂), 101 ± 2.1 kJ mole¹ and 121 ± 3.8 J/K-mole; FDNB^–(O₂), 51.5 ±3.4 kJ mole^–1 ± 9.2 J/K-mole; and DFDNB^–(O₂), 65.7 ± 0.4 kJ mole^–2 and 110 ± 5.0 J/K-mole.     

Dielectric relaxation and AC conduction of an AgTlSe2 semiconductor in the solid and liquid states

Measurements of the dielectric properties of AgTlSe₂ in the solid and liquid states were carried out in a wide range of frequencies and temperatures. The material displayed dielectric dispersion, and a loss peak was observed. Cole-Cole diagrams have been used to determine the distribution parameter (a) and the molecular relaxation time (). The process of dielectric relaxation (loss) and ac conduction was attributed to the correlated barrier hopping model suggested by Elliott for amorphous solids, where two carriers simultaneously hop over a barrier between charged defectD ⁺ andD ^– states.     

Electrical properties of CuTlSe2 in the liquid state

The electrical conductivity and thermoelectric power of CuTlSe₂ have been investigated as a function of temperature up to 230 °C above its melting point. In the liquid state the experimental data are analyzed in terms of a model developed for the density of states and electrical transport in solid amorphous semiconductors (Mott, 1970). Positive thermoelectric power suggests a large predominance of holes in electrical conduction. It appears that the conduction is due to holes in extended states near the band edge. It is found that the energy gap has a large temperature coefficient =5.5×10^–4eV/K.