Z. Nedic

Thermally induced phase transformations of 12-tungstophosphoric acid 29-hydrate : synthesis and characterization of PW8O26-type bronzes

The phase transformations of 12-tungstophosphoric H3PW12O40-29H2O (29-WPA) acid in the temperature range from ambient temperature to 1150°C were investigated and characterized by differential thermal analysis (DTA), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), infrared (i.r.) and Raman spectroscopies. From room temperature to 550°C, 29-WPA passes through a dehydration process, which characterizes the formation of different crystallohydrates, in anhydrous form as well as “denuded” Keggins anions, the D-phase (PW12O38). During these processes, Keggins anions are not disturbed too much and they are preserved up to about 550°C. The “D” phase is transformed by solid-solid recrystallization at about 600°C in a new monophosphate bronze type compound PW8O26. Unit cell dimensions were calculated from XRPD data (ao=0.7515 nm). With the temperature increasing up to 1150°C, novel synthesized cubic bronze passed through three polymorphous phase transitions. According to a general formula for monophosphate tungsten bronzes (WO3)2m (PO4)4 all four polymorphs have m=16.

THE INFLUENCE OF ACID TREATMENT ON THE COMPOSITION OF BENTONITE

Bentonite from the ‘Bogovina’ coal mine in Serbia, was characterized. The influence of acid treatment on its composition, as well as mathematical descriptions of this influence are reported. The purpose of this work was to correlate the concentration of the acid used for the treatment with the resulting bentonite composition. X-ray diffraction (XRD), infrared spectroscopy and quantitative chemical analysis were employed to define the changes caused by acid treatment.The contents of all the cations, except Si, decreased exponentially with increasing concentration of the HCl used for the treatment of the bentonite. This approach was tested on previously published data and was shown to be valid.The basal reflections of smectite decreased gradually and eventually disappeared after intense treatment, while the other reflections remained in the XRD patterns of all the samples, but decreased slightly with increasing acid strength. In addition, the amount of X-ray amorphous matter formed increased rapidly with increasing acid concentration up to 4.5 M. With further increase in the acid strength, the amount of X-ray amorphous matter remained virtually constant.

Characterization of Bronze Surface Layer Formed by Microarc Oxidation Process in 12-Tungstophosphoric Acid

This paper is a brief review of our recent research into novel uses for heteropoly compounds as precursors for thin films that can be used as catalysts and materials with good optical, conductive and other characteristics. In view of this, we have chosen thin film obtained with 12-tungsphosphoric acid on aluminum substrates. In all cases, a relatively new, microarc oxidation technique has been used to prepare oxide coatings on substrate surfaces. Advanced physicochemical methods, AFM and SEM-EDS, XRD, Raman and Micro-Raman, and luminescence spectroscopy, as the most powerful techniques, have been used for the characterization of new materials. Possible applications have been discussed as well.

Synthesis, conductivity and structural characterization of phosphorous bronzes originating from heteropolyacids. Relation with similar proton containing phases

Abstract The phosphorus doped molybdenum oxide compound (P 0.18 Mo 4.00 O 12.66 ), isostructural with molybdite was synthesized in the process of thermally induced phase transformation of 12-molybdophosphoric acid. The synthesized phases (low and high temperature) and the precursor compound ( Q -phase) have been characterized by thermal (DTA and TGA), X-ray powder diffraction, electron scanning microscopy and spectroscopic (IR) methods. The temperature dependence of electric conductivity σ ( ω → 0) is discussed. It was concluded that the electronic conductivities of bronzes obtained from heteropolyacids are very similar to those of corresponding anhydrous polyacids.

Electrochemical lithiation/delithiation kinetics and capacity of phosphate tungsten bronze and its chemically pre-lithiated derivatives in aqueous solutions

Monophosphate bronze (PW8O26, WPB) was synthesized by low-temperature (650xa0°C) heating of 12-tungstophosphoric acid (WPA). Its lithiated derivative with a low lithium content (Li3-WPB) was synthesized by heating lithium salt of WPA at 650xa0°C. Its lithiated derivative with a high lithium content was synthesized by mechanochemical lithiation of Li3WPB (Lin-WPB) (nxa0>xa03), followed by heat treatment at 650xa0°C. X-ray powder diffraction analysis confirmed that the bronze structure changed with the increase of the incorporated lithium content. These bronzes were investigated from the aspect of lithiation/delithiation kinetics in an aqueous saturated LiNO3 electrolyte solution. By cyclic voltammetry, both the kinetics of intercalation/deintercalation and the coulombic capacity were found to decrease with the increase of initial lithium content, in agreement with literature data for electrochemically lithiated tungstophosphate bronzes. Monoclinic lithium-free bronze PW8O26, as the most promising material, was subjected to a further detailed galvanostatic investigation coupled with the LiFe0.95V0.05PO4/C composite as a cathode material in an aqueous battery. In comparison to its behavior in an organic electrolyte, a considerably lower initial capacity of the bronze electrode was measured. However, its cyclic stability was much better in an aqueous than in an organic electrolyte.

Nanocomposite Based on Natural Materials

Milorad Davidovic1, Marina Kutin1, Suzana Linic1, Ubavka Mioc2, Zoran Nedic2, Svjetlana Sredic3, Aleksandra Nikolic4, Dusan Jovanovic4, and Polycarpos Pissis5 1GOSA Institute 2University of Belgrade, Faculty of Physical Chemistry 3Institute of Mining 4IHTM, Center of Catalysis and Chemical Engineering 5National Technical University of Athens, Department of Phisics, Athens 1,2,4Serbia 3Republic of Srpska, Bosnia and Herzegovina 5Greece