Kinetic studies for the non-isothermal decomposition of un-irradiated and γ-irradiated ruthenium(III) acetylacetonate

Kinetic studies for the non-isothermal decomposition of un-irradiated and γ-irradiated ruthenium(III) acetylacetonate in air were carried out. The results show that the decomposition proceeds in one major step in the temperature range of 150–250 °C with the formation of RuO₂ as a final solid residue for un-irradiated Ru(acac)₃. For γ -irradiated Ru(acac)₃ with 10² KGy total γ-ray dose, the decomposition goes eventually to completion with almost 100% decomposition and proceeds in one major step, which contains four overlapping decomposition stages in the temperature range of 200–320 °C. The kinetics is shown to be non-isothermal, using both model-fitting and model-free approaches. Infrared (IR) spectroscopy and X-ray powder diffraction techniques were employed to follow the chemical composition of the solid residue obtained at different temperatures.     

Kinetics of isothermal decomposition of unirradiated and γ-irradiated zirconium acetylacetonate

In this study, isothermal decomposition of unirradiated and γ-irradiated zirconium acetylacetonate Zr(acac)₄ using 10³ kGy absorbed γ-ray dose was carried out in static air. The isothermal operating temperatures were selected to be 150, 170, 190 and 210°C. The kinetics of the decomposition were followed using both model-fitting and model-free approaches. The results of the model-fitting approach with regard to the investigated data showed that the decomposition behaviour was best described by a first-order (F1) reaction model. The analysis of the data using the model-free approach signified the dependency of activation energy E _a on the extent of conversion (α). Pre-γ-irradiation of zirconium acetylacetonate Zr(acac)₄ with 10³ kGy absorbed γ-ray dose had no significant effect on the thermal decomposition behaviour of Zr(acac)₄. The thermodynamic and kinetic parameters of the decomposition process were calculated and evaluated.     

Influence of γ-irradiation on the non-isothermal decomposition of calcium-gadolinium oxalate

Thermal decomposition of co-precipitated unirradiated and irradiated Ca-Gd oxalate has been studied by adopting differential thermal analysis (DTA) and thermogravimetric (TG) techniques. The reaction occurs through two stages corresponding to the decomposition of gadolinium oxalate (Gd-Ox) followed by that of calcium oxalate (Ca-Ox). The kinetic parameters for both the stages are calculated by using solid state reaction models and Coats-Redfern's equation. The co-precipitation as well as irradiation alter the DTA peak temperatures and the kinetic parameters of Ca-Ox. The decomposition of Gd-Ox follows the two dimensional Contracting area ( R 2 ) mechanism, while that of Ca-Ox follows the Avrami-Erofeev ( A 2 ) mechanism ( n =2), which are also exhibited by the co-precipitated and irradiated samples. Co-precipitation decreases the energy of activation and the pre-exponential factor of the individual components but the reverse phenomenon takes place upon irradiation of the co-precipitate. The mechanisms underlying the phenomena are explored.     

Isothermal decomposition of γ-irradiated dysprosium acetate

Isothermal decomposition of un-irradiated and pre- n -irradiated dysprosium acetate [Dy(CH₃COO)₃] has been investigated at different temperatures between 603-623 v K. Irradiation was observed to enhance the rate of decomposition without modifying the mechanism of the thermal decomposition. Thermal decomposition of dysposium acetate is shown to proceed by a nucleation and growth mechanism (Avarmi-Erofe'ev equation) both for un-irradiated and pre- n -irradiated samples. The enhancement of the decomposition was found to increase with an increase in the n -ray dose applied to the sample and may be attributed to an increase in point defects and formation of additional nucleation centers generated in the host lattice. Thermodynamic values of the main decomposition process were calculated and evaluated.     

Isothermal decomposition of γ-irradiated palladium acetate

The isothermal decomposition of un-irradiated (pristine) and pre-γ-irradiated palladium acetate was studied in the temperature range (498–508 K) and in air using the isothermal thermogravimetric technique. The data were analysed using various solid state reaction models. The results showed that the kinetics of isothermal decomposition of palladium acetate was governed by random nucleation reaction (Erofe'ev equation A ₃). The activation energies of the main decomposition process for un-irradiated and pre-γ-irradiated samples were calculated. The change in texture and crystal structure of the investigated palladium acetate by γ-irradiation was studied using electron microscopy and X-ray diffraction techniques.     

Kinetic analysis of the thermal decomposition of pristine and γ-irradiated zinc uranyl acetate

Thermal decomposition of pristine and γ-irradiated zinc uranyl acetate was investigated in air using isothermal and dynamic thermogravimetric techniques. The decomposition proceeded via one major process with the formation of triuranates ZnU₃O₁₀ as solid residues. Kinetic analysis of isothermal data, when compared with various solid-state reaction models, showed that the decomposition reaction is best fitted by the phase-boundary model. Kinetic analysis of the dynamic TG curves was discussed with reference to integral methods of modified Coats and Redfern equations. Kinetic and thermodynamic parameters were calculated and evaluated. IR spectroscopy and X-ray powder diffraction techniques were employed to follow the chemical composition of solid residue at different calcination temperatures. The results display that the triuranate ZnU₃O₁₀ starts forming by calcination of zinc uranyl acetate at temperatures?>?300 °C and undergoes decomposition at higher temperatures (>600 °C) with the formation of U₃O₈. The results were evaluated regarding the utilization of zinc uranyl acetate as an important source of diuranates and triuranates.     

EPR spectra of γ-irradiated hydrated barium dithionate single crystals

EPR spectra of barium dithionate hydrate single crystals γ-irradiated at low (80 Gy) and high (10 kGy) doses are studied. Four lines, the strongest of which is due to the SO₃⁻ radical, are observed in the EPR spectrum of the low-irradiated samples. Another line seems to belong to SO₂⁻. The strong line and weak lines with hyperfine structure and lines for pairs of closely spaced SO₃⁻ centers with a strong angular dependence are observed at high irradiation doses. The main values of the SO₃⁻ hyperfine coupling tensor and the dipole-dipole coupling constants of the SO₃⁻ pairs are determined. A quantum-chemical calculation of the electronic structure of isolated SO₃⁻ and SO₂⁻ radicals is performed. Values of the g tensors and hyperfine couplings are calculated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 18–22, January–February, 2008.     

EPR study of γ-irradiated three-furancarboxylic acid

The electron paramagnetic resonance of γ-irradiated single crystals of three-furancarboxylic acid has been studied for different orientations of the crystals in a magnetic field. The radicals produced by γ-irradiation have been investigated between 123 and 350 K. The spectra were found to be temperature dependent, and radiation damage centers were attributed to the radical. The principal values of the g-tensor were determined. The results were found to be in good agreement with the existing literature data and theoretical predictions.     

Correlating the TL response of γ-irradiated natural quartz to aluminum and hydroxyl point defects

This paper investigates the relationship between Al- and OH-related point defects with the thermoluminescent (TL) response of natural quartz sensitized with high doses of γ radiation and heat-treatments. For this, specimens from a single crystal were progressively irradiated with doses of ⁶⁰Co from 2 to 50 kGy. After each step of sensitization, the absorption bands related to [AlO₄]⁰, [AlO₄/H]⁰, [H₄O₄]⁰ and Li-dependent OH point defects were measured by optical absorption and infrared (IR) spectroscopy. The sensitization of the 280 °C TL peak increased up to 15 kGy and then its intensity remained constant. The absorption intensity at 470 nm increased with γ doses suggesting a progressive creation of [AlO₄]⁰ acting as recombination centers for the sensitized peak. At the same time, the TL intensity of the 90 °C peak decreased with the accumulated dose. This effect was not related to the saturation in the number of recombination centers because both [H₄O₄]⁰ and [AlO₄]⁰ bands were increasing after 50 kGy. Compared to the as-received condition, it was found that IR bands associated with [AlO₄/H]⁰ and Li-dependent OH decreased with the effect of heat-treatments. The precursor for [AlO₄]⁰ is [AlO₄/Li]⁰ and the Li species dislodged from [AlO₄/Li]⁰ and Li-dependent OH centers play an important role in the sensitization process.     

EPR study of free radicals in γ-irradiated thiazide compounds

The aim of this paper was to identify the type of radicals formed by γ-irradiation in powdered chlorothiazide (CTZ), hydrochlorothiazide (HCTZ), althiazide (ATZ) and trichloromethiazide (TCTZ) on the basis of analysis of their electron paramagnetic resonance spectra with enhanced resolution. In TCTZ, HCTZ and ATZ the radical was formed by abstraction of a hydrogen atom from the carbon atom C-3, and in the case of CTZ by addition of a hydrogen atom to the nitrogen atom N-4. The hyperfine structure is found. The electron densities at nitrogen atom positions in the N-C-N group in HCTZ, ATZ and TCTZ depend on a single 3-position substitution and are in line with their diuretic potency.     

Analysis of the EPR spectrum of γ-irradiated barium dithionate

An analysis of the experimental EPR spectrum of -irradiated barium dithionate is made. Based on the data obtained, a model of this spectrum is constructed. It is shown that the spectrum results from superposition of four individual signals, for which the following values of the g-factor components have been determined: for I g = 2.0097, g = 2.0044; for II g = 2.0069, g = 2.0023; for III g = 2.0042, g = 2.0032; for IV g = 2.0002 and g = 2.0032.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 71, No. 6, pp. 727–731, November–December, 2004.This revised version was published online in April 2005 with a corrected cover date.     

ESR of γ-irradiated DI-, TRI- and poly-glycin

The effects of γ radiation on glycylglycine, triglycine, and polyglycine have been studied using ESR spectroscopy. The radiation exposures have been performed under vacuum at room temperature. All those irradiated substances show a doublet absorption signal often ascribed to a radical formed on the α carbon of the peptide chain. The magnetic susceptibility has been found to depend on temperature according to the Curie-Weiss law. The radio-sensitivity parameter G_r , the hyperfine splitting constant A_h and the spectroscopic factor g nave been determinated as well as θ which is the temperature corresponding to the Curie temperature of the irradiated substance. The results on C_r , θ and A_h for all peptides studied here agree with the assumption of radiation induced free radicals located at the α carbon of the peptide chain, leading to conclude that the degree of delocalization of the unpaired electron increases for increasing number of glycine units in the peptide. Finally, from negative θ values obtained, a conclusion has been reached on the antiferromagnetic nature of the interaction between unpaired spins.     

Application of M?ssbauer spectroscopy to the study of tannins inhibition of iron and steel corrosion

The inhibitory effect of tannins was investigated using, among others, potentiodynamic polarizations and Mössbauer spectroscopy. These techniques confirmed that the nature, pH and concentration of tannic solution are of upmost importance in the inhibitory properties of the solutions. It is observed that at low tannin concentration or pH, both, hydrolizable and condensed tannins, effectively inhibit iron corrosion, due to the redox properties of tannins. At pH ?? 0, Mössbauer spectra of the frozen aqueous solutions of iron(III) with the tannin solutions showed that iron is in the form of a monomeric species [Fe(H₂O)₆]^3?+?, without coordination with the functional hydroxyl groups of the tannins. The suspended material consisted of amorphous ferric oxide and oxyhydroxides, though with quebracho tannin partly resulted in complex formation and in an iron (II) species from a redox process. Other tannins, such as chestnut hydrolysable tannins, do not complex iron at this low pH. Tannins react at high concentrations or pH (3 and 5) to form insoluble blue?Cblack amorphous complexes of mono-and bis-type tannate complexes, with a relative amount of the bis-ferric tannate generally increasing with pH. Some Fe^2?+? in the form of hydrated polymeric ferrous tannate could be obtained. At pH 7, a partially hydrolyzed ferric tannate complex was also formed. The latter two phases do not provide corrosion protection. Tannin solutions at natural pH react with electrodeposited iron films (approx. 6 ??m) to obtain products consisting only on the catecholate mono-complex of ferric tannate. Some aspects of the mechanism of tannins protection against corrosion are discussed.     

Application of the method of static fluctuational approach to the Bogolyubov–Kolesnikov–Shelah model

A method of calculating the equilibrium correlation functions of any arbitrary order for the Baldwin– Kolesnikov–Shelah (BKSh) model is suggested based on the static fluctuational approach. The method based on only one controllable approach allows the so-called equations of long-range coupling to be obtained which contain all information on the sought-after equilibrium correlation functions within the scope of the BKSh model. Calculations of the sought-after equilibrium correlation functions allow one to go beyond the scope of the conventional molecular field approach and to take into account the effect of field fluctuations on the gap behavior and the heat capacity to the left and right of the critical point. For the simplest case disregarding a dependence of the potential on the wave vector, temperature dependences of the energy gap and heat capacity with allowance for the fluctuations are presented. It is demonstrated that in this case, the fluctuations are small for three-dimensional systems, but sharply increase with decreasing dimensionality of the system.     

An approach to evaluate the efficiency of γ-ray detectors to determine the radioactivity in environmental samples

This work provides an approach to determine the efficiency of γ-ray detectors with a good accuracy in order to determine the concentrations of either naturally occurring or artificially prepared radionuclides. This approach is based on the efficiency transfer formula(ET), the effective solid angles, the self- absorptions of the source matrix, the attenuation by the source container and the detector housing materials on the detector efficiency. The experimental calibration process was done using radioactive(Cylindrical Marinelli) sources, in different dimensions,that contain aqueous152 Eu radionuclide. The comparison point to a fine agreement between the experimental measured and calculated efficiencies for the(NaI HPGe) detectors using volumetric radioactive sources.     

An approach to evaluate the efficiency of γ-ray detectors to determine the radioactivity in environmental samples

This work provides an approach to determine the efficiency of γ-ray detectors with a good accuracy in order to determine the concentrations of either naturally occurring or artificially prepared radionuclides. This approach is based on the efficiency transfer formula (ET), the effective solid angles, the self- absorptions of the source matrix, the attenuation by the source container and the detector housing materials on the detector efficiency. The experimental calibration process was done using radioactive (Cylindrical & Marinelli) sources, in different dimensions, that contain aqueous ¹⁵²Eu radionuclide. The comparison point to a fine agreement between the experimental measured and calculated efficiencies for the (NaI & HPGe) detectors using volumetric radioactive sources.     

Effect of capping on the mechanoluminescence of γ-irradiated ZnS:Cu nanophosphors

Mechanoluminescence (ML) properties of γ-irradiated and non-irradiated capped ZnS:Cu nanophosphors have been investigated. The nanoparticles were prepared by wet chemical method using different capping agents. The samples were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). ML was excited impulsively by dropping a load on to the sample. Two peaks have been observed in the ML intensity versus time curve. It has been found that ML intensity rises with time, attains a maximum and then decays. The ML intensity of γ-irradiated SiO₂ capped ZnS:Cu nanophosphors was found to be the highest amongst the presently investigated nanophosphors. Mechanism of ML has been explained on the basis of piezoelectrically induced charge carrier detrapping model.     

Critical behaviour in the commensurate-incommensurate phase transition of pure and γ-irradiated LiRbSO4 crystals

The effect of γ-irradiation on the incommensurate phase of LiRbSO₄ crystals has been studied by measuring the specific heat C_p . As a result of γ-irradiation, the values of C_p decreased and the transition temperature T_c shifted to lower values. The values of ΔH and ΔS decreased with increasing dose rate. The results are explained on the basis of an energy change due to induced lattice defects.