Alexandra Raluca Iordan

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.

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.

Influence of A-site Cation on Structure and Dielectric Properties in A2DyBiO6 (A=Mg, Ca, Sr, Ba) Double Perovskites

Double perovskite metal oxides with formula A2DyBiO6 (A = Mg, Ca, Sr, Ba) were synthesised by a sol–gel auto-combustion method, using citric acid as the combustion agent. The effects of A-site cation on the structure, morphology, and dielectric properties were examined. The synthesis was monitored using Fourier transform infrared spectroscopy (FTIR) to indicate the absence of organic phase. X-ray diffraction (XRD) analysis showed that the compounds have three different perovskite structures. Structural characterisation of the samples was evaluated using XRD patterns. Scanning electron microscopy showed that all samples are formed by agglomerated particles. Dielectric properties were evaluated using dielectric permittivity and dielectric losses. Cole–Cole plots show a single semicircle for all materials, indicating that the double perovskites obtained are composed of well conducting grain boundaries and poorly conducting grains.

Influence of Heavy Metals on the Environmental from Tarnita Mining Area

Abstract This paper presents aspects related to water pollution with heavy metals from the Tarnita mining area before and after the cessation of the mining activity. The impact of heavy metals on waters is important because these metals have a negative impact on both human health and aquatic ecosystems. All research data showed that, even the mining activities from this area were suspended, the sterile still pollutes the soil and water

Synthesis of Polymetallic Oxides with High Organized Structure

Abstract The synthesis and characterization of high organized and nanostructured polymetallic oxides were studied. The samples were synthesized by sol-gel autocombustion method, using glycine as chelating/fuel agent and polyacrylamide-based hydrogel as template agent. This polymer has a porous microstructure with well-individualized and regularly-dispersed pores. The asobtained samples were characterized by IR spectroscopy, XRD, SEM. The magnetic properties were studied. As-synthesized polymetallic oxides have the morphological structure given by the three-dimensional lattice structure of hydrogel used as template agent

Photochemical degradation of polymers containing urethane groups in the solid phase : Influence of S block cations on the degradation

Modification of the physico-mechanical properties of films made of biologically compatible polymers, with urethane groups, complexed with metallic ions from the s-block (Soft Block), have been investigated according to cation nature and photochemical irradiation time. Strain at the break, remnant elongation, elasticity modulus and resistance at the break were the main physico-mechanical properties measured. Experiments were carried out by irradiation with ultraviolet light, on solid film, under condition of accentuated degradation. Ions of both alkaline metals and alkaline-earth metals in the first step of irradiation improve the physico-mechanical properties. But in the middle of the investigated range they strongly decrease, concomitantly with the appearance of some deep photochemical induced structural modifications in the structure of the investigated polyesterurethane.