Zoran Nedić

Identification of protonic species and their dynamic equilibrium in magnesium and calcium salts of 12-tungstophosphoric acid

Abstract This contribution presents the results of the investigation of Mg 2+ and Ca 2+ 12-tungstophosphoric acid (WPA) salts as superionic proton conductors. We have identified protonic species as charge carriers in several hydration degrees of these salts by IR spectroscopy at low, room and high temperatures. In the IR spectra we have found the characteristic frequencies for H 3 O + , OH − , H 2 O, H 5 O 2 + . Also, we have investigated the dynamic equilibrium between protonic entities in the function of temperature, as well as the nature and the strength of hydrogen bonds in those compounds. During the process of calcination, these salts undergo a few phase transformations. The temperatures of interest for the further investigations were taken from data of thermal analysis.

Dielectric investigation of electrical conductivity in the copper salt of the 12-tungstophosphoric acid hydrate

Abstract The electrical and dielectric properties of the copper salt of 12-tungstophosphoric acid (WPA) hydrate have been investigated by broadband dielectric relaxation spectroscopy (DRS). This work is a continuation of our previous investigations on the influence of monovalent and bivalent cations on the dielectric properties of WPA hydrates salts. Measurements were made in the frequency range 10 mHz–1 MHz in order to explore the long-range dynamics, following recent microwave measurements aiming at the local dynamics properties. Experiments were done in the temperature interval 293–350 K. Data treatment included complex permittivity e *, complex electric modulus M * and complex impedance Z * formalism, Arrhenius diagram and Cole–Cole diagrams. The results are discussed in terms of conductivity relaxation and conductivity current relaxation. Rather long conductivity relaxation times measured seem to correspond to ion jumping processes. A phase transition was observed at 323 K.

Dielectric relaxation and conductivity in barium salt of 12-tungstophosphoric acid hydrate

Abstract Barium salt of 12-tungstophosphoric acid (WPA) hydrate BaHPW12O40·7H2O (BaHWPA·7H2O) has been investigated both in the microwave (X-band) region and in the lower frequency (5 Hz–500 kHz) region. This work is a continuation of our previous investigations on the influence of monovalent and bivalent cations on the dielectric properties of WPA hydrate salts. The real and imaginary parts of the permittivity (e′, e″) as a function of frequency and temperature, were determined in both frequency regions. The observed relaxations were attributed to specific relaxation processes. In the lower frequency range, the relaxation time τ=1.0×10−6 s was assigned to barium ion jumps. In the microwave region, the dielectric relaxation time τ=1.7×10−11 s was attributed to polyatomic ions (H3O+) and/or H2O molecules reorientations. A phase transition was observed at 330 K. The low value of the activation energy for reorientation in the microwave frequency region is discussed. The d.c. conductivity and its temperature dependence were determined. Measurements were made in the temperature interval from 286 to 353 K. In the upper part of this temperature interval a PTCR effect was observed.

Synthesis and Characterization of Biphasic Calcium Phosphate/ Poly-(DL-Lactide-Co-Glycolide) Biocomposite

In this paper we report the results on synthesis of a composite biomaterial based on biphasic calcium phosphate (BCP) and poly-(DL-lactide-co-glycolide) (DLPLG). Besides, we have investigated the influence of new synthesis method on the structure and characteristics of the composite. The synthesis of biphasic calcium phosphate from Ca(NO3)2 x 4H2O and (NH4)3 PO4 in alkali environment was performed by means of precipitation technique. Composite material BCP/DLPLG was first prepared from commercial granules using chemical methods. Powdered polymer DLPLG was then homogenized at appropriate ratio with addition of biphasic calcium phosphate into the suspension. All samples were characterized by DSC, IR, X-Ray and SEM techniques.

Dielectric investigation of magnesium salt of 12-tungstophosphoric acid hydrate

Abstract Magnesium salt of 12-tungstophosphoric acid (WPA) hydrate MgHPW 12 O 40 –14H 2 O has been investigated in the microwave (X-band) and in the lower frequency (5 Hz–500 kHz) region. The specimens were obtained by pressing powder. Real and imaginary parts of permittivity were obtained for the specimens in both frequency regions. In the microwave region dipolar relaxation was observed with the relaxation time τ =1.6×10 −11 s. This relaxation is attributed to the fast reorientation of H 2 O molecules. In the lower frequency region ionic jump relaxation was observed with the relaxation time τ =3.9×10 −7 s. Results on ac and dc conductivity are discussed.

Physicochemical Properties of Al-Pillared Montmorillonite Doped with 12-Tungstophosphoric Acid

Bentonite a natural raw material from the x8aipovo mining deposits (Republic of Srpska), which contains a high percentage of montmorillonite, was treated to obtain montmorillonite clay ready for further investigations. Al-pillared montmorillonite was doped with 12-tungstophosphoric acid (WPA) by the sol-gel method. Substantial increase in proton conductivity of this new material was achieved. Different physicochemical methods were used to characterize new materials such as X-ray powder diffraction (XRD), thermogravimetric (TG) analysis, porosity measurements, scanning electron microscopy (SEM), and infrared measurements (IR). Impedance spectroscopy technique was applied in order to study the proton conductivity and its dependence on the frequency and tungstophosphoric acid concentration.

The Stabilizer Influence on Morphological Characteristics of Poly-(DL-Lactide-Co-Glycolide) Nanospheres

Copolymer poly(D,L-lactide-co-glycolide) is used for obtaining the systems for controlled delivery of medicaments. Its specific characteristics make it suitable for various researches where its synthesis is performed in different ways. Using the system for controlled delivery of medicaments, an equal concentration of the medicament is achieved in the body throughout an extended period of time and it has advantages over the conventional methods. In this paper we present a new solvent/non-solvent chemical method for obtaining DLPLG nanospheres. In the experiment various stabilizers were used in order to examine their influence on morphological characteristics of DLPLG particles. The samples were characterized by Infrared Spectroscopy (IR), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM) and Stereological analysis.

Nickel/Silica Precursor from Sodium Silicate Solution - Synthesis and Characterization

The aim of this paper was the investigation of the influence of synthesis parameters, as well as the order of synthesis steps, in procedure of chemical precipitation, on the properties of synthesized nickel precursor. The starting materials were always the same aqueous solutions of Ni(NO3)2×6H2O and Mg(NO3)2×6H2O of constant molar ratio, 2% solution of SiO2 in the form of sodium silicate solution (module SiO2/Na2O = 3.0) and 10% solution of Na2CO3, while synthesis steps and addition modes were varied. Complete pH and temperature monitoring was performed during entire synthesis at 90°C. The formed precipitate aged 30 minutes at synthesis temperature. By changing the order and conditions of adding SiO2 and Na2CO3 solutions and keeping the treatment of precipitates the same (rinsing with hot distilled water followed by drying at 110°C for 24 hours) six different precursors were obtained. Samples characterizations were performed using different experimental techniques: XRD analysis, IR spectroscopy, reflection spectroscopy, TG analysis, N2 physisorption. The relation between synthesis procedure and precursor properties was established.

Thermal and Conductivity Analyses of Alkaline Earth Salts of 12-Tungstophosphoric Acid

Heteropoly compounds can form several different crystallohydrates, but their stability depends on the ambient temperature and relative humidity. Therefore we have investigated 12tungstophosphoric acid (WPA) alkaline earth salts under constant conditions at relative humidity (35%) and room temperature (20°C). Under these conditions, hydration degree and phase transformations have been studied by thermal analyses (TGA, DTA), IR spectroscopy and conductometric measurements. The obtained results proved the influence of the cations nature on the dehydration process.