Effect of gamma-irradiation on the catalyzed bromate oscillator

The oscillatory characteristics of a catalyzed bromate system is altered by gammairradiation. The alterations observed are probably due to the activation of the reduced form of the metal ion catalyst under gamma-irradiation. However, these alterations could not be accounted for in terms of an effective concentration of bromate acting as a quenching agent under gamma-irradiation conditions as reported in the literature.     

The Effect of tetrabutylammonium ion on the uncatalyzed bromate oscillator

The effect of tetrabutylammonium ion (Bu₄N⁺) on the uncatalyzed bromate oscillator with phenol as substrate was monitored at 25 ± 0.1°C under stirred batch conditions. The changes in the oscillatory behaviour with increasing concentration of the Bu₄N⁺ ions have been ascribed to their ability to act as ion-pairing reagent.     

Sequential oscillations in uncatalyzed bromate oscillator in a closed reactor

Two types of oscillatory regimes separated by a time pause occur during the oxidation of aniline with bromate in sulfuric acid (a Körös-Orbán System) in a closed, stirred batch reactor. It is most likely that sequential oscillations are due to aniline and its oxidation/bromination product.     

Iodide-promoted uncatalyzed bromate oscillators

Iodide ions—in a rather narrow concentration range—induce some of the uncatalyzed bromate oscillators to a more pronounced oscillatory activity: the number of oscillations increases considerably and the overall rate of the chemical reaction drops about an order of magnitude. Preliminary suggestion is made on the mechanism of iodide-induced oscillatory reactions.

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Potential response in the uncatalyzed bromate oscillatory system

The potential response of the platinum indicator electrode in the uncatalyzed bromate oscillator (UBO) with three different substrates, namely gallic acid (GA), pyrogallol (PG) and veratraldehyde (VA) has been analyzed. The large amplitude oscillations obtained with a Pt electrode are due to the sequential response of the indicator electrode to the varying concentration ratios of the redox couples present in the reaction mixture.     

Chemical oscillations in the uncatalyzed bromate oxidation of hydroquinone and nitrophenols

Chemical oscillatory behavior in the uncatalyzed bromate oxidation of hydroquinone and nitrophenols is reported. The reaction is strongly inhibited by stirring. Effect of one-electron redox couples (EZ catalysts) on the system is described.

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Effect of gamma-irradiation on the thermal decomposition of pure and doped (Ba2+ caesium bromate

Effect of γ-irradiation on the isothermal decomposition of pure and doped (Ba²⁺, 0.50 mol%) caesium bromate has been studied in the temperature range 633–673 K. It is indicated that though the pure and pure irradiated crystals are immune to decomposition, doped and doped irradiated crystals undergo decomposition rapidly. There is initial rapid gas evolution representing 1–2% reaction, which is completely eleminated in doped irradiated crystals. The other stages exhibited by the crystals are, (1) acceleratory and (2) decay stages. Presence of two decay stages (one short and one long) is indicated in the doped substance, and the short decay diminishes with increase in temperature and virtually remains absent at 673 K. The acceleratory as well as decay periods of doped and doped irradiated crystals are analysed according to Prout-Tompkins, Avrami-Erofeev and Contracting square models. The rate constants in all the stages increase with increase in temperature. The energy of activation for the acceleratory periods of both the substances are almost same (± 10 kJ/mol) irrespective of the kinetic equation employed. Similar is the case with decay stages. But the energy of activation of the decay stages are higher than those of the acceleratory stages. Microscopic observation reveals that the reaction begins essentially on surfaces by the rapid formation of an interface and is followed by the penetration of the interface into the crystallite. The melting of a eutectic formed between the product CsBr and the parent material causes a marked increase in the rate.     

Various dynamic behavior of Ag+-induced oscillations in uncatalyzed bromate oscillators

Silver ion induces the uncatalyzed bromate oscillators /aromatics-bromate-acid/on a variety of dynamic behavior, including high frequency and complex oscillations. The behavior of a reacting system depends on the chemical composition of the armatics, the time of addition of Ag⁺, and the concentration of Ag⁺. The chemistry underlying the phenomena is discussed.

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A comparative study of uncatalyzed and catalyzed oscillatory behavior of different mono-and dihydroxybenzoic acids in acidic bromate

Optimum and boundary conditions for uncatalyzed and catalyzed temporal oscillations in the redox potentials in the oxidation of mono- and dihydroxybenzoic acids in acidic bromate (H₂SO₄) have been established and compared. The number and relative positions of the functional groups, in the aromatic ring have been found to influence the oscillatory behavior. Ferroin has been found to enhance the oscillatory behavior considerably as compared to Ce(IV) and Mn(II). A probable explanation of the oscillatory behaviour of these system is suggested.

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Effect of gamma-irradiation on the acidic properties of Na-Y zeolites

Na-Y zeolite samples were subjected to different doses of γ-irradiation ranging between (10–160 Mrad). The effect of this treatment on the surface acidity was investigated via temperature programmed desorption (TPD) of pyridine and ammonia.The results obtained revealed that γ-irradiation brought about a considerable decrease in the concentration of acidic sites to an extent proportional to the dose employed up to 80 Mrad. A dose as high as 160 Mrad was sufficient to expell completely the labile and moderately bound acidic centres (Bronsted type). These results have been attributed to the stimulation effect of the departure of structural water brought about by γ-irradiation. However, γ-irradiation was found to exert undetectable effect on the Lewis acidity of the investigated zeolites.     

Effect of gamma-irradiation on the thermal decomposition of potassium chlorate

The thermal decomposition of -irradiated KClO₃ was studied by dynamic thermogravimetry. The reaction order, activation energy, frequency factor and entropy of activation were computed using the Coats-Redfern, Freeman-Carroll and Horowitz-Metzger methods and were compared with those of the unirradiated salt. The decomposition increases with the irradiation dose. The energy of activation decreases on irradiation. The mechanism for the decomposition of unirradiated and irradiated KClO₃ follows the Avrami model equation, 1-(1-)^1/3, and the rate controlling process is a phase boundary reaction assuming spherical symmetry.     

Effect of γ-irradiation on the thermal decomposition of strontium bromate

The effect of irradiation on the thermal decomposition of strontium bromate has been studied by dynamic thermogravimetry. Irradiaton enhances the decomposition and decreases the energy of activation but does not change the mechanism of decomposition.     

Effect of gamma-irradiation on the foaming behavior of ethylene-co-octene polymers

Ethylene-co-octene polymers containing different branching levels were irradiated in air and under vacuum at 25, 50 and 100 kGy. Gel fraction measurements, thermal analysis and rheology were used to assess the effect of the treatment on polymer structure modifications. The copolymer with 24 wt% octene was shown to be more sensitive to gamma rays and degradation was observed in some cases. Cross-linking in the amorphous phase also occurred as a consequence of irradiation and affected the foaming behavior of these materials.     

Effect of radiation dose on the thermal decomposition of sodium bromate

Influence of radiation dose in the range of 0.5–2.0 MGy of⁶⁰Co -rays on the isothermal decomposition of sodium bromate at 633.0 K shows that irradiation increases the initial gas evolution {ie37-1}, shortens the induction period (I), enhances the rate of reaction in the accelerating and decay stages. The data fit well the Prout-Tompkins relationship, indicating that nucleation occurs in a chain branching manner during the process. The fraction decomposed, , increases with increasing radiation dose.     

Effect of gamma-irradiation on the thermal decomposition of barium oxalate hemihydrate

The effect of -irradiation (1.0–4.0 MGy) on the thermal decomposition of barium oxalate hemihydrate has been studied at 723K by a gas evolution method. Decomposition isotherms of unirradiated and irradiated crystals are characterized by (i) rapid initial gas evolution, (ii) acceleratory and (iii) decay stages. Irradiation enhances the rate of decomposition without altering the mechanism of the process, the effect being higher at higher irradiation doses. The analysis of the data reveal that the two-dimensional phase boundary reaction model gives the best fit to the results.     

Effect of gamma-irradiation on some structural characteristics of NiO

Pure NiO specimens were prepared by the thermal decomposition of pure basic nickel carbonate in air at 400 and 600°C. The obtained solids were exposed to different doses of γ-irradiation ranging between 10–80 Mrad. The change in residual microstrain, lattice parameter and crystallite size due to the irradiation process were investigated by X-ray diffraction analyses.The results revealed that γ-irradiation effected important changes in the structural characteristics of NiO lattice. No detectable change was observed for the crystalline size of NiO-400°C; however, the crystallite size of NiO-600°C decreased by increasing the dose up to 20 Mrad and increased at higher doses but still remaining smaller than that measured for the unirradiated specimen.The lattice parameters of NiO preheated at 400 or 600°C were found to increase as a function of the dose. These results were attributed to progressive removal of Ni³⁺ ions acting as lattice defects in NiO solid.The microstrains in NiO specimens precalcined either at 400 or 600°C were found to decrease progressively by increasing the dose falling to minimum values at doses of 40 and 80 Mrad for the solids preheated at 600 and 400°C, respectively. The augmentation of the exposure dose above 40 Mrad for NiO-600°C resulted in an increase in microstrain which, however, remained always smaller than those found for the unirradiated solid. The strain-relief in NiO-600°C due to γ-irradiation took place, mainly, via splitting of its crystallites. On the other hand, the progressive removal of lattice defects (Ni³⁺ ions) due to the irradiation process might account for the observed strain-relief in NiO-400°C.     

Effect of gamma-irradiation on the catalytic activity and selectivity of gamma-alumina

Methanol conversion reaction was carried out in contact with a poorly crystalline -alumina pre-irradiated with different doses of -rays. The reaction was conducted at 140–440°C using a flow technique under atmospheric pressure. The results obtained revealed that -irradiation of Al₂O₃ resulted in drastic modifications of its activity and selectivity in methanol conversion reaction. The dose of 15 Mrad was sufficient to suppress completely the formation of dimethyl ether (DME) and stimulated the formation of methane, which started at 200°C instead of 300°C in the case of the unirradiated alumina specimen. However, the rate of CH₄ formation was found to decrease as a function of the dose employed. When the dose reached 140 Mrad, DME was reproduced with a rate comparable to that measured for the unirradiated catalyst sample. These results permitted us to conclude that DME is produced on the weak acidic sites (Brönsted acidity of Al₂O₃) and is not necessarily an intermediate compound for methane formation that takes place directly from methanol on strong acidic sites (Lewis acidity). The doses of 15–75 Mrad expelled completely the Brönsted acidic sites from Al₂O₃ surface, and the doses above this limit brought about a transformation of Lewis acidic sites into Brönsted acidity that is responsible for dimethyl ether formation. This transformation occurs by the action of liberated water from the dehydration of methyl alcohol.     

Effect of gamma-irradiation on thermoluminescence values in dried fruits

Studies were conducted to measure the effect of irradiation treatment on thermoluminescence (TL) values in dried fruits such as apricots, dates and raisins. For this purpose, inorganic dust particulate (minerals) adhering to the fruit surface was collected from untreated and treated (0.5, 1.0 and 1.5 kGy) samples. The TL responses of the isolated minerals was measured in the temperature range of 80–320°C at an increasing rate of 10°C/s. It was observed that peak of the TL signals appeared at 200°C in each case and generally the magnitude of the peak signals was almost 10³ times that of unirradiated samples. Regression and correlation analysis of the data indicated strong relationship between radiation absorbed dose and TL values at each temperature (r≥0.98). It was concluded that TL measurements could serve as a fast and reliable method for distinguishing as well as determining absorbed dose in irradiated dried apricot, date and raisin.     

Effect of gamma-irradiation on adsorption properties of Slovak bentonites

One of the basic prerequisites for the use of bentonite as engineering barrier in deep geological repositories for radioactive waste and spent nuclear fuel is their stability against ionizing radiation stemming from radionuclides present in radioactive waste and spent nuclear fuel. The aim of this study was to compare the changes in the adsorption properties of selected Slovak bentonites in relation to uranium fission products (¹³⁷Cs and ⁹⁰Sr), prior to and after irradiation of bentonites with a ⁶⁰Co γ-source and specifying the changes in the structure of Slovak bentonites induced by γ-radiation. The changes in irradiated natural forms of Slovak bentonites and the changes in their natrified analogues and fractions with different grain sizes were studied from five Slovak deposits: Jelšovy potok, Kopernica, Lastovce, Lieskovec and Dolná Ves. The EPR spectra of bentonites from deposits Jelšovy potok and Lieskovec with absorbed doses of 10⁴ and 10⁵ Gy γ-rays showed no changes in the structure of the studied Slovak bentonites. The changes, which in terms of structure destabilization can be considered insignificant, occurred only in bentonites with absorbed doses of γ-radiation as much as 1 MGy. The absorbed dose of 1 MGy γ-radiation did not have an effect on the adsorption of cesium on every studied bentonite. Changes that can also be regarded as insignificant occurred only during strontium adsorption, especially on Fe–bentonite from deposit Lieskovec and Ca–Mg–bentonite from deposit Jelšovy potok, when an increase in the adsorption capacity occurred. Attention should be paid in further research of this topic which would require carrying out experiments on bentonite samples with absorbed doses higher by several orders of magnitude.