Search Results
Abstract
The paper describes the determination and depth profiling of oxygen in thin oxide films using 18O(p,α)15N nuclear reaction. The excitation function of 18O(p,α)15N nuclear reaction exhibits a resonance at 629 keV and a plateau at 730 keV with uniform cross-section. The resonance is used to determine the depth profile of oxygen in films while the plateau, to estimate its overall concentration. The resonance, characterized by a width of 2.1 keV enables high-depth resolution (~20 nm) measurements and has a probing depth of more than a micron. The paper presents depth profile measurements of oxygen in several metal oxide films (SiO2, TiO2 and HfO2) using this resonance. Possible interferences arising from 15N(p,α)12C, 19F(p,α)16O and 11B(p,α)2α nuclear reactions are also discussed. It has been shown that it can serve as a suitable alternative to 3.05 MeV 16O(α,α)16O resonant scattering which is generally used for depth profiling oxygen. It is, in fact, more reliable and precise in materials that witness significant large angle multiple scattering. It can also be advantageously used to monitor 18O, when used as a tracer.
The authors have reviewed the salient features of the thermal behavior of the following systems:(A)Single oxide systems: (i) Cr2O3, (ii) Fe2O3, (iii) Al2O3, (iv) MnO2, (v) ZrO2, (vi) NiO, (vii) ZnO, (viii) TiO2, (ix) SiO2, (x) ThO2.(B)Binary oxide systems: (i) Cr2O3-Al2O3, (ii) Cr2O3-Fe2O3, (iii) Cr2O3-ZnO, (iv) Al2O3-SiO2, (v) Al2O3-Fe2O3, (vi) MnO-Cr2O3, (vii) Cu-Al2O3, (viii) ZrO2-Cr2O3, (ix) NiO-Cr2O3, (x) ZrO2-NiO, (xi) ThO2-Al2O3.(C)Ternary oxide systems: (i) NiO-Cr2O3-ZrO2, (ii) Fe2O3-Cr2O3-Al2O3.(D)Vanadates: (i) tin vanadate, (ii) copper vanadate, (iii) lead vanadate, (iv) cobalt vanadate and (v) silver vanadate.
Abstract
The ion exchange behaviour of the exchanger Na4Ti9O20.xH2O was studied with particular emphasis on Sr2+ exchange. Titration of H4Ti9O20.xH2O with 0.1M [Sr/OH/2+SrCl2] solution yielded a strontium ion exchange capacity of 5.30 meq g–1 corresponding well with the theoretical value. When strontium was absorbed on Na4Ti9O20.xH2O from neutral solutions, Sr2Ti9O20.xH2O was formed. This compound decomposed to SrTiO3 and TiO2 when heated to 870 °C. From alkaline solutions strontium was absorbed both as Sr/OH/+ and Sr2+ with the proportion of the former species increasing with pH. At pH 12.8 only exchange of Sr/OH/+ was observed and the exchanged form was Na2/SrOH/2Ti9O20.xH2O. This compound decomposed to Na2Ti6O13 and an unidentified strontium titanate when heated to 870 °C. Distribution coefficients were determined for alkali and alkaline earth metal ions as a function of pH. The selectivity sequence for alkaline earth metal ions was Ba>Sr
Ca>Mg, and that for alkali metal ions was Cs>K>Li /pH 2–6/ and Li>Cs>K /pH 7/.
Abstract
Glasses are suitable host matrices for the immobilization of high-level radioactive wastes. The corrosion behaviour of nuclear waste glass in water is of considerable importance, since a potential route for returning of radionuclides to the biosphere is their leaching from the waste form into groundwater and subsequent transport by the groundwater to the surface. In this study, the preparation and characterization of borosilicate glasses of different chemical composition were investigated. Borosilicate glasses were doped with simulated nuclear waste oxides. The chemical corrosion in water of these glasses was followed by measuring the leach rates (g·cm–2·day–1), as a function of time. It was found that a simulated nuclear waste glass with the chemical composition (weight %), 15.61% Na2O, 10.39% B2O3, 45.31% SiO2, 13.42% ZnO, 6.61% TiO2 and 8.66% waste oxides, is characterized by low melting temperature and with good corrosion resistance in water. Influence of passive layers on the leaching behaviour of nuclear waste glasses is discussed.
Abstract
The surface properties of titanium hydroxide precipitates, formed under different conditions were studied in the presence of carrier-free radioactive89Sr. It was found that titanium with concentrations equivalent to 24 mg TiO2/litre, was enough to remove by adsorption more than 95% of the carrier-free strontium activity from an alkaline solution (pH≈13) in less than 6 hrs, regardless of whether the precipitate was freshly prepared or aged for a few days. If the precipitate was formed in situ, at the above pH value, the percentage removal of the strontium activity from the solution was even greater, and this was attributed to an internal adsorption process. At a lower pH value (∼2.5), however, the adsorption of strontium activity by titanium hydroxide was very low (<5%), whether the precipitate was preformed or formed in situ. The increase in the adsorption ability of titanium hydroxide precipitate on going from low pH (2. 5) to higher values was attributed to the inversion of the charge of titanium hydroxide sols from cationic particles at pH 2. 5 to negatively-charged particles at pH>3. 5, these latter particles adsorbing any positive strontium ions in solution.
Abstract
Abstract
This paper presents the results obtained in the investigation of the reactions of potassium carbonate with some transition metals oxides (TiO2 , V2 O5 , Cr2 O3 , MnO2 , Fe2 O3 ). The reactions were carried out under non-isothermal conditions, and thermogravimetric analysis was used to monitor the transformation degree a. Experimental data indicated that the reaction of potassium carbonate and iron(III) oxide occurs in one stage, whereas the reactions of the oxides of titanium, vanadium, chromium and manganese are more complex, involving two-stage processes. Activation energies and pre-exponential factors were determined for all the processes taking place in the investigated systems. For the second stage of the reaction of K2 CO3 with Cr2 O3 , and V2 O5 the obtained values of activation energy were 59.2 and 512 kJ mol−1 respectively. Based on the values of activation energy and pre-exponential factor, the existence of a kinetic compensation effect was postulated for the three homologous series of reactions.
Abstract
Synthesis of the green spinel pigment Co0.46Zn0.55(Ti0.064Cr0.91)2O4 by a novel two-step method of preparation have been investigated. Inorganic pigments are almost always prepared by a solid state reaction. It is classical ceramic method which used oxides, hydroxides or carbonates as precursors. The reaction is performed at temperature higher than 1300C and an agent of mineralization is usually present. The presented novel method of preparation decreases the calcining temperature necessary for reaching of bright and clear hue of the pigments prepared. Main attention was focused on the influence of two types of titanium raw materials on the temperature region of the spinel structure formation and on the colour properties of the pigments. The mixture of precursors with TiO2 gives a one-phase system when calcining at 1100C but the colour properties are more interesting at 1150C. Thermal stability of this pigment is limited by temperature 1300C. This temperature is connected with partial oxidation of Cr(III) to Cr(VI). Thermal analysis provided the first information about the temperature region of the pigment formation and determined the thermal stability of pigment.
Abstract
In previous works, the effects on the devitrification mechanism of a certain composition calcium phosphate with additives of TiO2, SiO2, Al2O3, CeO2 have been studied. It was found that some metal oxide additives played a key role as the nucleation agent in calcium phosphate glass-ceramics, and the devitrification mechanism of calcium phosphate glass system was changed drastically by addition such as metal oxide. Hydroxyapatite (HAp), tricalcium phosphate (TCP) and β-calcium phosphate (β-CaP2O6) whisker are the three most biologically compatible materials to human bone in bio-ceramics field. In this work, the effect on devitrification mechanism and the physical properties of certain composition calcium phosphate glass with three above additives were investigated, and the result shown that although no fine crystalline was induced in the certain composition of calcium phosphate glass when a large amount of additive was added, but such additives play a catalyst role by lowering the activation energies of devitrification. It would supplement the mechanical properties and the biocompatibility for the calcium phosphate glasses.
Thermal properties of oxide glasses
Part III. Thermal stability of Li2O·2SiO2·nMeO2 glasses (M=Ti, Zr)
Abstract
Glasses with the composition Li2O·2SiO2·nTiO2 and Li2O·2SiO2·nZrO2, where n=0, 0.03, 0.062, 0.1, were prepared and the onset and peak temperatures have been determined by DTA. From these characteristic temperatures, the kinetic parameters describing the nucleation and crystal growth have been obtained by isoconversional methods. The kinetic parameters have been used for the calculation of nucleation and crystal growth times for individual glasses so determining the order of glass stability at reheating. The stability of glasses increases with the content of TiO2 or ZrO2 where the increase is higher for ZrO2. Within the concentration range under study, the increase of both times with the metal oxide concentration is quadratic. It has been discussed that the crystallization kinetics does not obey the Arrhenius law and, therefore, when using the evaluation methods based on this law, the results should not be extrapolated outside the temperature range of the measurements.
