On the use of Diefallah's composite integral method for the non-isothermal kinetic analysis of heterogeneous solid-gas reactions

The paper contains an analysis of the used of Diefallah's composite integral method of kinetic parameters evaluation. It is shown that the application of this method should be preceded by the application of an isoconversional method through which the dependence of the activation energy, E, on the conversion degree,<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>a, should be established. If Edepends on<span style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family:Symbol'>a, Diefallah's composite integral method leads to erroneous results. If Edoes not depend on<span style='font-size: 10.0pt;font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>a, the true kinetic model should be comprised in the pre-established set of kinetic models. These observations were checked for two sets of non-isothermal data, namely: (a) the TG curves corresponding to the dehydration of CaC₂O4·H₂O; (b) the TG curves corresponding to the thermal decomposition of polyvinyl chloride (PVC).     

Highly active and stable immobilized aluminium chloride catalyst for alkylation of benzene with 1-dodecene

Summary An AlCl₃ catalyst immobilized on<span lang=EN-US style='font-family:Symbol;mso-bidi-font-family: Symbol;mso-ansi-language:EN-US'>g-Al₂O₃with meso- and macro-pore bimodal structure was prepared and studied in the alkylation of benzene with 1-dodecene in a suspension bed reactor. The catalyst exhibited high activity, selectivity and stability during 1000 h running, with a 1-dodecene conversion of more than 95%, monoalkylbenzene selectivity of 92%, and 2-phenyldodecane (2-Ph) selectivity of nearly 42%.</o:p>     

Natural radioactivity traces in South-Brazilian cereal flours by gamma-ray spectrometry

Summary Cereal flours are the major component of the Brazilian diet and are also important exportation products. Radioactivity concentrations of ²³² Th, ²²⁶Ra, ⁴⁰K and ¹³⁷Cs were determined in commercial samples of South-Brazilian cereal flours (soy, wheat, corn, manioc, rye and oat flour) to verify the radiological security of these foodstuffs. The measurements were carried out by gamma-ray spectrometry using a 66% relative efficiency HPGe detector. The ⁴⁰K flour activities, at 95% of confidence level were in: soy 474±3 Bq ^. kg^-1; corn 30.0±0.3 Bq ^. kg^-1; rye 94±1 Bq ^. kg^-1; manioc 67±1 Bq ^. kg^-1; oat 76±1 Bq ^. kg^-1 and wheat 36.2±0.4 Bq ^. kg^-1. The lower limit of detection for ⁴⁰K ranged from 0.54 to 1.43 Bq ^. kg^-1. The ¹³⁷Cs activities in flour samples were: soy ￡0.07 Bq ^. kg^-1, corn ￡0.01 Bq ^. kg^-1, oat ￡0.03 Bq ^. kg^-1 and in wheat, manioc and rye ￡0.02 Bq ^. kg^-1. The highest concentrations levels of ²³² Th and ²²⁶Ra were 0.69±0.04 Bq ^. kg^-1 and 0.44±0.03 Bq ^. kg^-1, respectively, in soy flour.     

Kinetic and thermodynamic parameters of 99Mo sorption on thermally treated hydrotalcite

Summary Thermally treated hydrotalcite was synthesized and its ability to sorb ⁹⁹Mo from aqueous solutions was studied under static conditions as a function of initial concentration, amount of sorbent and pH. X-ray diffraction was used to characterize synthesized calcined hydrotalcite. The values of sorption data were fitted to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms. The mean energy of sorption was calculated as 5.24 kJ^. mol^-1from D-R sorption isotherm. The Lagergren equation has been used for the study of the kinetic process. The rate constants of ⁹⁹Mo sorption on calcined hydrotalcite were calculated at various temperatures (293-323 K). The thermodynamic constans have been calculated and the standard enthalpy of the system was found to be<span style='font-size:12.0pt; font-family:Symbol;mso-bidi-font-family:Symbol'>DH°=11.5±0.3 kJ^. mol^-1. The values of calculated<span style='font-size:12.0pt;font-family:Symbol;mso-bidi-font-family: Symbol'>DG° and<span style='font-size:12.0pt;font-family: Symbol;mso-bidi-font-family:Symbol'>DS° were</o:p>-13.9±2.0 kJ^. mol^-1and (8.7±0.2)^. 10^-2kJ^. K^-1. mol^-1, respectively. These results show that the sorption process is endothermic, spontaneous in nature and the degree of freedom of ions is increased by sorption.     

Fractionation of lyophilized MIBI kit for99mTc labeling

Summary The lyophilized MIBI kit was dissolved in 1 ml sterile saline or 250<span style='font-size: 12.0pt;font-family:Symbol;mso-bidi-font-family:Symbol'>mg/ml ascorbic acid and dispensed into 0.2 ml fractions, which were stored at -20 °C for 12 days. The solution was prepared by using two different protection methods. In the first method evacuated vials were used for storage of fractionated solution while in the second method an antioxidant agent, ascorbic acid was employed. The radiochemical impurity of ^99mTc-MIBI in the unprotected fractions rises with time. Exclusion of air as well addition of ascorbic acid in fractionated solutions gave very good results. The labeling efficiency and biodistribution of fractionated solutions was the same as the lyophilized kit even after 12 days.     

Effect of metal loading and carbon support microstructure on the dispersion of Pt/C catalysts prepared viaadsorption of chloroplatinic acid

Summary Adsorption of<span lang=EN-US style='mso-ansi-language:EN-US'>H₂PtCl₆onto a carbon support followed by reduction of the adsorbed platinum species with H₂at 250°C leads to<span lang=EN-GB style='mso-ansi-language:EN-GB'>Pt/C catalysts, which show universal volcano-like dependence of platinum dispersion on the metal loading in the range from 0.01 to 0.55mmol (Pt)/m²(S_BET)<span lang=EN-GB style='mso-ansi-language:EN-GB'>when highly disordered carbons, namely, active carbons and carbon blacks, are used as supports. The maximal dispersion D(CO/Pt) = 0.8 is attained at<span lang=EN-US style='mso-ansi-language:EN-US'>0.18mmol (Pt)/m² (S_BET). With<span lang=EN-GB style='mso-ansi-language:EN-GB'>other factors being equal, the dispersion of platinum supported on carbons with a more regular crystal structure, especially Sibunit-type supports, proves to be the highest and independent of the metal loading.The differences between the two groups of carbon supports are explained by the differences in the state of the adsorbed platinum precursors.     

Stability of the valinomycin - strontium complex in water saturated nitrobenzene

Summary From extraction experiments and<span style='font-size:12.0pt;font-family:Symbol; mso-bidi-font-family:Symbol'>g-activity measurements, the extraction constant corresponding to the equilibrium Ba²⁺(aq)+SrL²⁺(nb)?BaL²⁺(nb)+Sr²⁺(aq) taking place in the two-phase water-nitrobenzene system (L= valinomycin; aq= aqueous phase,</o:p>nb= nitrobenzene phase) was evaluated as logK_ex(Ba²⁺, SrL²⁺)=1.3. Furthermore, the stability constant of the valinomycin-strontium complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: logb_nb(SrL²⁺)=5.4.     

241Pu concentration in southern Baltic Sea ecosystem

Summary ²⁴¹Pu concentrations were calculated indirectly in different compartments of the southern Baltic ecosystem by the activity measurements of²⁴¹Am isotope from the increase of the<span lang=EN-GB style='font-size:12.0pt;font-family:Symbol;mso-bidi-font-family:Symbol; mso-ansi-language:EN-GB'>b-emitting²⁴¹Pu at 16-18 years after the Chernobyl accident. Enhanced levels of²⁴¹Pu were observed in all analyzed samples. Maximum values (0.408 and 0.367 mBq^. g^-1d.w.) of the estimated²⁴¹Pu concentrations were found in sediments of Internal Puck Bay and Gdańsk Bay, respectively, and in the suspended matter from water of Gdańsk Bay (77.8 mBq^.g^-1d.w.). The highest²⁴¹Pu/^239+240Pu activity ratio was found in the suspended matter (1500) and water (140). The²⁴¹Pu activity of the air dust was very high in April 1986, 3643±34.3 mBq^.g^-1d.w., and the²⁴¹Pu/^239+240Pu activity ratio was 56, but the highest²⁴¹Pu/^239+240Pu activity ratio of the air dust was measured in August. Then the²⁴¹Pu concentration in air dust decreased quickly to values similar to those before the Chernobyl accident.<span style='font-size:12.0pt'>This study provides new data for the ²⁴¹Pu concentrations in various compartments of the Baltic Sea ecosystem.     

Ga2O for target, solvent extraction for radiochemical separation and SnO2for the preparation of a68Ge/68Ga generator

Summary The target for the production of⁶⁸Geconsists of a disc of gallium suboxide, Ga₂O, with a 19 mm diameter. The suboxide was primarily prepared by repeatedly mixing metallic Ga and Ga₂O₃at 700 °C. The target (2.4 g) was quite stable under a long-time irradiation with a 34 MeV proton beam at a current of ~80<span lang=EN-ZA style='font-size:12.0pt; font-family:Symbol;mso-bidi-font-family:Symbol;mso-ansi-language:EN-ZA'>mA. The dissolution of the target was performed using 12M sulphuric acid solution, assisted with the dropwise addition of 30% H₂O₂solution, and took less than 4 hours. A solvent extraction method, using a 9M H₂SO₄-0.3M HCl/CCl₄system, was employed for the radiochemical separation of⁶⁸Ge from Ga and Zn radionuclides, while 0.05M HCl was used for the back extraction of⁶⁸Ge from the organic phase. The⁶⁸Ge obtained in the dilute HCl was directly loaded onto a column containing either a hydrous tin dioxide or a crystalline tin dioxide, obtained by calcinations of the hydrous oxide at 450, 700, and 900 °C. The calcinated hydrous tin dioxide at 900 °C showed the highest crystallinity and highest⁶⁸Ga elution yield and was selected for use in the generator. The⁶⁸Ga elution from the column generator packed with 2 g of tin dioxide, using 3 ml of 1M HCl, and yielded an average of 65%. The breakthrough of⁶⁸Ge was 6.1^. 10^-4%.     

Separation of europium from aqueous solutions using Al3+- and Fe3+-doped zirconium and titanium phosphates

Summary The sorption of europium from aqueous solutions (Eu-concentration: 10 to 250 mg/l) by Fe³⁺- and Al³⁺-doped zirconium- and titanium-phosphates was investigated using a batch technique and ¹⁵²Eu tracer. The initial pH of the solutions was adjusted to 3, 4, 5 and 6. All investigations were performed under constant ionic strength, I=0.15 established by NaCl.<span lang=EN-GB style='font-size:12.0pt;mso-ansi-language:EN-GB'>Although zirconium phosphates generally showed a higher Eu-uptake capacity than the titanium ones, all investigated materials possessed the ability to remove considerable amounts of europium from aqueous solutions. The Eu-sorption properties of the studied phosphate materials<span style='font-size:12.0pt'>seem to be not especially affected by the type of trivalent cations used for the doping (i.e., Al³⁺or Fe³⁺).     

Glass transition kinetics of some Se-Te-Ag chalcogenide glasses

Summary The present paper reports the Differential Scanning Calorimetric (DSC) study of some Ag doped Se-Te chalcogenide glasses. DSC runs were taken at different heating rates. Well-defined endothermic and exothermic peaks were obtained at glass transition and crystallization temperatures. The variation of glass transition temperature T_gwith Ag concentration has been studied. It has been found that T_gdecreases with increase in Ag concentration. The heating rate dependence of T_gis used to evaluate the activation energy of glass transition (DE_t). The value of<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>DE_thas been found to increase with increase in Ag concentration followed by nearly constant value at higher concentrations of Ag.     

Mechanism ofb-picoline oxidation to nicotinic acid on V-Ti-O catalyst as studied by in situFTIR

Summary In situFTIR spectroscopy was used to study the interaction of<span style='font-family:Symbol;mso-bidi-font-family:Symbol'>b-picoline with the surface of a V-Ti-O catalyst in the temperature range of 120-300°C.b-picoline was found to react with the Lewis acid sites of the catalyst to form a nitrogen-coordinated complex. This complex turns into an aldehyde-like complex at</o:p>150-250°C and then into a nicotinate, which is a direct precursor of nicotinic acid.</o:p>     

Synthesis and characterization of new borate-vanadate mixed glasses

Summary It has been found that a series of M_xO_y-V₂O₅-B₂O₃glasses (M_xO_y=Li₂O, Na₂O, K₂O and MgO) containing 10 mol%<span style='font-size:12.0pt;font-family: Symbol;mso-bidi-font-family:Symbol'>a-Fe₂O₃exhibited glass-forming regions that shifted with the content of network modifier (NWM) compared to B₂O₃and V₂O₅glasses. The M?ssbauer spectra of a series of M_xO_y-V₂O₅-B₂O₃glasses showed increased quadrupole splitting (D) with increasing NWM content. This suggests that the coordination numbers of the V⁴⁺and V⁵⁺are fixed and that the formation number of non-bridging oxygens (NBO) is considered to increase with increasing NWM content, and with increasing formation number of NBO, the Fe³⁺ion site changes from VO₄to BO₄tetrahedra. Consequently, the quadrupole splitting increases with increasing NWM content.     

Evolution of the Cu/ZnO methanol synthesis catalyst during its reduction and re-oxidation

Summary Cu K EXAFS studies of the structure of Cu-Zn oxide catalyst were performed for the as prepared samples, those after its activation by hydrogen and after its subsequent re-oxidation. It was found that during the primary formation of the CuZnO solid solution, the copper ions are dissolved in the extended stacking faults of the ZnO lattice as ultra-small oxide clusters. Activation by hydrogen at 473 K leads to the reduction of most copper cations to Cu⁰with the formation of nanoparticles with the characteristic size of ca. 1.6 nm. The copper metal particles were re-oxidized to Cu²⁺at 523 K in<span lang=EN-US style='mso-ansi-language:EN-US'>ahelium flow containing 0.05 vol. % oxygen. The re-oxidized cations do not form a CuO phase. Instead, they return to the extended stacking faults of ZnO. However, this time they form stripe-like clusters of square-planar coordinated copper cations.