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Abstract  

Samples of an organic–inorganic hybrid were prepared by solvolysis and polycondensation in formic acid of tetraethoxysilane and diethylbenzyl phosphonate, simultaneous with the oxidative polymerization of aniline. The thermal behavior of the samples in dynamic air atmosphere and non-isothermal conditions was determined by a coupled thermogravimetric/evolved gas analysis. Two significant thermal events were established: the elimination from the polymeric matrix of low mass molecules, respectively the thermooxidative degradation of the organic part of the matrix. The kinetic analysis was performed with the Flynn-Wall-Ozawa, Friedman and modified Non-Parametric-Kinetic methods. Only the last one allowed an objective analysis of the first process as a process of two simultaneous thermally induced phenomena with the kinetic functions of the type αm(1 − α)n.

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We measured from 5 to 300 K the thermal conductance of different superconducting Bi-2212 thin rods and one superconducting module integrating a hybrid current lead based on such rods. The conductance values of the rods are lower than the measurable limits of the set-up and a detailed evaluation of the heat losses is required. The analysis of the heat exchanges permits to introduce a correction function to the measured values and allows to study low thermal conductivity materials. The dependence of the thermal conductivity of Bi-2212 rods on the sample microstructure is analyzed after this correction. We calculate analytically the time required to reach the steady-state for long bars for which extended relaxation times are expected. From the measured conductance data we estimate the heat load introduced by the current lead into a cryogenic bath in static conditions.

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Abstract  

Bentonite was investigated to remove Ni(II) from aqueous solutions because of its strong sorption ability. Herein, bentonite was modified with sodium carboxymethylcellulose (CMC) and used as an adsorbent to remove Ni(II) from aqueous solutions. The results indicated that CMC-bentonite had higher sorption capacity than bare bentonite in the sorption of Ni(II) from aqueous solutions. Sorption of Ni(II) on CMC-bentonite was mainly dominated by ion exchange or outer-sphere surface complexation at low pH values, but by inner-sphere surface complexation or surface precipitation at high pH values. The thermodynamic data calculated from temperature dependent sorption isotherms indicated that the sorption of Ni(II) to CMC-bentonite hybrids was an spontaneous process and enhanced with increasing temperature.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Ştefănescu, M. Stoia, O. Ştefănescu, A. Popa, M. Simon, and C. Ionescu

Abstract  

Hybrid organic-inorganic materials, silica – polyols (ethylene-glycol – EG; 1,2 propane diol – 1,2PG; 1,3 propane diol – 1,3PG and glycerol – GL), were prepared by a sol-gel process starting from tetraethylorthosilicate (TEOS) and polyols, in acid catalysis. The resulting materials were studied by thermal analysis (in air and nitrogen), FTIR and solid state 29Si-NMR spectroscopy. These techniques evidenced the presence of polyols in the silica matrix both hydrogen bounded and chemically bounded in the silica network. The thermal analysis proves to be the most appropriate technique to evidence the organic chains linked in the matrix network and to follow the thermal evolution of the gels to the SiO2 matrix.

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Abstract  

Valency control of neptunium is an important issue in the partitioning of high level liquid waste (HLLW) from power-reactor spent fuel treatment. The redox behavior of neptunium in HLLW is quite different from that in nitric acid because of the effect of the large amount of ions in HLLW. In order to remove neptunium from HLLW, we studied the reduction of neptunium in synthetic HLLW (SHLLW) to maintain its valency at IV so that it can be extracted by TRPO extractant in the well developed Chinese TRPO process. Five different reductants were tested and the reduction behavior was investigated. The influence of some active elements in SHLLW was studied. The mechanism that the reductants react with neptunium through Fe element was supposed and proved by experiments. The reduction rate of Np(V) was highly enhanced by Fe element. Finally, a hybrid reductant was suggested and good reduction efficiency was obtained.

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Abstract

It is well established that gallium insertion into the hydroxiapatite matrix as practiced in orthopedics protects bone from resorbtion and improves the biomechanical properties of the skeletal system. The research presented in this article is an investigation into the thermal decomposition of gallium nitrate, which is part of a complex process leading to the preparation of a hybrid matrix. It was demonstrated that after melting of the hexahydrate in its own water there occurs a simultaneous condensation of 4 mol of initial monomer Ga(NO3)3·6H2O into a tetramer Ga4O4(NO3)4. The resulting inorganic cycle gradually loses N2O5 and, through the formation of unstable oxynitrates, is transformed into gallium oxide. The use of molecular mechanics for comparing the potential energies of consecutive products of thermal decomposition permitted an evaluation of their stability and an appropriate interpretation of the experimental data.

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JPC - Journal of Planar Chromatography - Modern TLC
Authors: Stefan Kreibik, Virginia Coman, Constantin Măruțoiu, and Gheorghe Mihăilescu

Some of the physical properties of dielectric liquids are influenced by electric fields. Interesting results were obtained in this work by applying external alternating electric fields to chromatographic media (paper or TLC plates) filled with dielectric liquids. Capillary tubes were used to enable understanding of the flow phenomena which occur in porous media. It was observed that the displacement velocity of the liquids confined in the capillary tubes depended on the magnitude of the alternating electric field, the electric properties (conductivity, permittivity) of the liquids, the frequency of the current, the tube diameters, the shapes of the molecules, and the tube material. Evident electrokinetic effects (dielectroosmotic flow) were observed on silica gel layers and paper strips developed with non-polar and polar solvents. As a result the separation resolution of non-ionic compounds was improved. This method is a hybrid of electric forced flow and classical diffusion; we have named it planar dielectrochromatography.

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. Method Quantum chemical calculations were conducted using DFT as implemented in the Gaussian 03 suite of programs [ 45 ]. The chosen DFT method, namely the hybrid B3LYP density functional [ 46 ], combines the exact HF exchange, the Slater local

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Abstract  

Half a century of focused nuclear education in Brazil has resulted in the expansion of applications of nuclear technique in many fields, such as power generation nuclear power plants, environmental monitoring, medical diagnostics and treatments, food irradiation, new materials development using irradiation, archaeological dating, hydrological studies, and so on. Nuclear research is blooming and evolving in Brazil. In the last three years, two master’s degrees and one doctorate have been approved by the Ministry of Education. The scientific capacity building has been enlarging and improving the reservoir of qualified personnel who Brazil expects to operate the current infrastructure and other facilities to be settled in the near future. Only graduate programs allocated by CAPES (Ministry of Education) and CNPq (Ministry of Science & Technology) in the Nuclear Engineering Area (Engenharia II) are considered in this paper. In Brazil, there are also Physics and hybrid graduate programs in what DSc degrees are pursued using nuclear and nuclear-related techniques; CAPES and CNPq do not allocate them in the nuclear engineering area, following their own criteria, since those programs have their own peers, budget and evaluation area.

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Abstract  

57Fe-conversion electron Mössbauer spectroscopy (CEMS) — a sensitive tool to analyze the phase composition of corrosion products on the surface of stainless steel — was applied to study real specimens from the Paks Nuclear Power Plant, Hungary. The primary circuit side of the heat exchanger tubes was studied on selected samples cut out from the steam generators during regular maintenance. Mostly Cr-and Ni-substituted magnetite, amorphous Fe-oxides/oxyhydroxides as well as the signal of bulk austenitic steel of the tubes were detected. The level of Cr-and Ni-substitution in the magnetite phase could be estimated from the Mössbauer spectra. It is suggested that Cr-Ni substitution occurs simultaneously so that the inverse spinel structure of magnetite is preserved up to a certain limit which appears to be roughly at [Fe3+]tet[Fe2+ 1/4Ni2+ 3/4Fe3+ 1/4Cr3+ 3/4]octO4. Further decrease of the iron content of this phase results in the formation of nickel chromite of regular spinel structure, with very low Fe content. This transformation may be responsible for the hybrid structure of the protective oxide layer, being substantially accelerated by previously performed, factory developed and proposed AP-CITROX decontamination cycles.

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