Mircea Nicolae Palamaru

Use of some oxides in radiolytical decomposition of water

Abstract This paper deals with a study on the radiolysis of water in the presence of certain oxides: BeO, SiO2, TiO2, ZrO2 acting as catalysts for the hydrogen production. A radionuclide of 60Co with an activity of about 5×104 Ci was employed as an irradiation γ source. A considerable increase (up to ten times or more) of the amount of hydrogen resulting from the radiolysis of water in the presence of the above mentioned oxides was noticed in comparison with a reference sample, irradiated under the same experimental conditions, but without any catalyst. The radiolysis products have been identified by means of a method based on mass spectrometry.

Humidity sensor characteristics and electrical properties of Ni–Zn–Dy ferrite material prepared using different chelating-fuel agents

Abstract Humidity sensor characteristics and electrical properties of Ni–Zn ferrite material doped with Dy were studied after synthesis via sol–gel self-combustion method. In order to obtain different micro configurations of the material reflected in different porosities, four different fuel agents were involved: citric acid, tartaric acid, cellulose and urea. XRD and XPS techniques were used to certify the composition. The influence of fuel agent and structural features on the electrical properties of ferrite sintered pellets was investigated at room temperature as a function of frequency and humidity. Because the electrical characteristics of a porous material can significantly affect by the humidity, the electrical measurements were carried out in controlled humidity environments. Conduction mechanism is explained in terms of fuel agent influence on phase composition, grain size value, cation distribution and induced strain within spinel lattice by dissolution of voluminous Dy3+ ions. The humidity sensors applicative characteristics of the material are highlight by analyzing the sensitivity, response and recovery times of nickel–zinc–dysprosium ferrite used as active material.

Laboratory analyses of 60Co2+, 65Zn2+ and 55+59Fe3+ radiocations uptake by Lemna minor

The living Lemna minor vascular plant and two different sorbents obtained by chemical treatment of this plant were tested to study the removal process of 60Co2+, 65Zn2+ and 55+59Fe3+ from low radioactive wastewaters. The most effective sorbent was the protonated biomass, indicating the decisive contribution of the complexation process in the assembly of the uptake mechanisms. The uptake performance of the biosorbent obtained from the L. minor can be increased with ∼20% by treatment with 0.1 N HNO3. Concerning the metabolically active mechanism, it can be notice the slow elimination of 65Zn2+ and the continuously increase of 55+59Fe3+ uptake degree. The Na2CO3 generated in situ in systems participates to a double exchange reaction with the metallic cations during the uptake. 60Co2+, 65Zn2+ and 55+59Fe3+ radiocations prefer for coordination N-donor ligands at the expense O-donors ones.

The influence of the chelating/combustion agents on the structure and magnetic properties of zinc ferrite

AbstractThe present study is reporting the influence of the chelating/combustion agents on the magnetic properties of Zn ferrite. Six chelating/combustion agents, citric acid, egg white, tartaric acid, glycine, glucose and urea, were used to obtain monophase zinc nanoferrite via a sol-gel auto-combustion method. The samples were subjected to a comparative study of structural features and magnetic properties by means of infrared spectroscopy, X-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Significant influence of fuel and combustion mode was observed in the magnetic behavior of as-obtained samples. Values of the structural parameters were discovered to vary as a function of fuel choice, and to obtain crystallite size between 38 and 62 nm, inversion degree between 0.239 and 0.807, lattice parameter between 8.4125 and 8.4432 Å. The optimization of sol-gel method synthesis of zinc ferrite nanoparticles by chosing the appropriate fuel is providing structural and magnetic properties of zinc nanoferrite as potential materials to be used in biomedical applications.

Optimization of synthesis conditions and the study of magnetic and dielectric properties for MgFe2O4 ferrite

AbstractNano-sized magnesium ferrites were synthesized by the sol-gel auto-combustion method using a variety of chelating/combustion agents: tartaric acid, citric acid, cellulose, glycine, urea and hexamethylenetetramine. The original purpose of this work was the synthesis of nano-sized magnesium ferrite by using, for the first time, cellulose and hexamethylenetetramine as chelating/combustion agents. Synthesized samples were subjected to different heat treatments at 773 K, 973 K and, respectively 1173 K in air. The disappearance of the organic phase and nitrate phase with the spinel structure formation was monitored by infrared absorption spectroscopy. Spinel structure, crystallite size and cation distribution were evaluated by X-ray diffraction data. The morphology of as-prepared powders was studied using scanning electron microscopy. The magnetic and dielectric properties were studied for the obtained samples.

Radiochemical study of the kinetics of crystal growth in gels

Abstract A kinetic study was performed on nucleation and growth of crystals containing radioactive ions in gelatin and agar gels. The investigated crystals were: 60CoHPO4, 60CoS, 60Co(OH)2, 60Co(SCN)2, 204Tl(OH)3, and 204Tl[(C2H5)2NCS2]3. The study shows that the crystal growth rate depends on the cation size and charge, the nature of anion as well as on the colloidal medium. The crystallisation process in the gel has two distinctive steps: diffusion of reactant ions in the gel followed by a chemical reaction which leads to nucleation of the crystal. Both steps are described quantitatively.

Kinetic study on crystal growth in gels by radioisotopic labelling

The paper deals with a kinetic study of crystal growth in gelatin and agar gels, using a technique based on radioactive tracers.204TlCl,204TlBr,204TlI,60CoC2O4 and60CoH4C4O6 crystals in gels have been obtained. The global kinetic process of appearance of crystals has been found to be made up of two distinct stages: diffusion of the ions in the gel and crystallization, having different rate constants.

Kinetic study for the formation of microcrystalline “disks” of204T1I in gelatin medium

This paper presents a radiochemical study of the appearance of204T1I microcrystals and their development as “disks” resembling Liesegang rings, in gelatin, under different experimental conditions. Thus, kinetic diagrams have been traced, from which gel diffusion rate constants for radioactive ions were calculated, as well as reaction rate constants between reactant species:204T1+ and I−, in colloidal medium, followed by the development of concentrated microcrystals under form of one or more “disks”. There is an interconnection between gelatin concentration of the colloidal medium, on one hand, and204T1I microcrystal “disks” number and dimensions, on the other hand, “disks” which appeared in gel as a result of the global process of nucleation.

Radiometric method for the study of the nucleation of crystals containing134Cs+ ions in gelatin

A radiometric method that permits to follow, in real time, the kinetics of crystals growth:134CsClO4;134CsHC4H4O6;134Cs2CrO4;134Cs2[PtCl6] and134Cs[AgI2], in gelatin medium is presented. Constants of the diffusion of134Cs+ radioactive ions through gel and of the reaction between this cation and anions under study, leading to the formation of crystals were calculated. An approximately invesely proportional ratio was found between the rate of nucleation and the solubility of the crystal.

Influence of the B-site cation nature on dielectric properties of Ca2XBiO6 (X = Dy, Fe, Al) double perovskite

For the synthesis of Ca2XBiO6 (X = Dy, Fe, Al) metal oxides with ordered double-perovskite structure, the sol-gel auto-combustion method has been used for the first time. The synthesis progress was followed by the Fourier transform infrared spectroscopy and the samples structure was investigated by X-ray diffraction. The samples morphology was studied by means of scanning electron microscopy. The influence of the nature of the trivalent B-site cation on the dielectric properties was evaluated by resistivity measurements in vacuum at frequencies between 102–105 Hz. The best dielectric behavior was obtained for Ca2AlBiO6 and Ca2DyBiO6, while the best semiconductor behavior was found for Ca2FeBiO6.