Application of radioactive tracer technique to study the kinetics of iodide ion-isotope exchange with strongly basic anion-exchange resin Duolite A-116

The kinetics of iodide ion-isotope exchange with strongly basic anion-exchange resin Duolite A-116 was studied. The temperature was varied from 25.0 to 40.0°C, and the iodide ion concentration in solution, from 0.0025 to 0.020 M. Two sets of experiments were performed: exchange of the inactive resin in the iodide form with an iodide solution spiked with ¹³¹I and exchange of the labeled resin with an inactive iodide solution. In both cases, the rate constants, amounts of iodide ions exchanged, and initial rate of iodide ion exchange were calculated. For both forward and reverse exchange, the rate constants are essentially similar. Published in Russian in Radiokhimiya, 2008, Vol. 50, No. 6, pp. 558–560. The test was submitted by the authors in English.     

Application of radiotracer technique to study the ion-isotope exchange reactions using a strongly basic anion-exchange resin duolite A-113

Short-lived radioactive ¹³¹I and ⁸²Br tracers were used to study the kinetics of ion-isotope exchange reaction. The experiments were performed in the temperature range 26.0–43.0°C, ion concentration in solution in the range 0.0025–0.020 M, and amount of labeled ion-exchange resin varying from 0.250 to 1.250 g. For bromide ion-isotope exchange reactions, the calculated values of specific reaction rate, initial rate of bromide ion exchange, and amount of bromide ions exchanged were obtained higher than those for iodide ion-isotope exchange reactions under identical experimental conditions. The observed difference is attributed to the difference in the ionic size of bromide and iodide ions in solution. Published in Russian in Radiokhimiya, 2007, Vol. 49, No. 5, pp. 455–457. The text was submitted by the authors in English.     

Kinetics of bromide ion-isotope exchange with weakly basic macroporous resin Indion-860

Kinetics of bromide ion-isotope exchange with weakly basic macroporous resin Indion-860 was studied. Two sets of experiments were performed. In the first set, inactive ion-exchange resin samples in the bromide form were equilibrated with a radioactive bromide solution spiked with ⁸²Br tracer, and in the second set of experiments, labeled radioactive ion-exchange resin samples in the bromide form were equilibrated with an inactive bromide solution. The temperature was varied from 25.0 to 40.0°C, and the concentration of bromide ions in solution, from 0.005 to 0.100 M. In separate experiments, performed at a fixed temperature of 25.0°C using 0.0100 M bromide ion solution, the amount of the labeled radioactive ion-exchange resin was varied from 0.250 to 1.000 g. Essentially similar rate constants were obtained for the forward and reverse reactions. Published in Russian in Radiokhimiya, 2008, Vol. 50, No. 6, pp. 551–554. The test was submitted by the authors in English.     

Application of radioactive tracer technique for characterization of strongly basic anion-exchange resins duolite A 101D and duolite A 102D<Superscript>1</Superscript>

The radioactive ⁸²Br was used as a tracer to study the bromide self-diffusion reactions. The effect of temperature, concentration of ionic solution, and amount of ion-exchange resin on the kinetics of exchange reactions was examined. Under identical experimental conditions, the specific reaction rate, amount of bromide ions exchanged, and initial rate of bromide ion exchange calculated for Duolite A 101D resin were higher than those calculated for Duolite A 102D resin. The difference in the values calculated for the two resins was attributed to their water-holding capacities. The probable mechanism of bromide isotope exchange reaction was also predicted by comparing the specific reaction rate of rapid and slow exchange process. It is expected that the same technique can be employed to assess the efficiency of various ion exchangers under different operating conditions.     

Contribution to the study of electrocoagulation mechanism in basic textile effluent

Electrocoagulation method with iron electrode is used to treat the industrial textile wastewater in batch reactor. The effects of operating parameters such as time and potential electrolysis on the decolourization and COD removal efficiency have been investigated. The results indicate that electrocoagulation is very efficient and able to achieve 100% colour and 84% COD removal in 3 min at potential 600 mV. The effluent wastewater is very clear and its quality exceed the direct discharge standard. Furthermore, the mechanism of electrocoagulation is elucidated by zeta potential measurement.     

Application of an EWMA combining technique to the prediction of currency exchange rates

Financial forecasting is an important and challenging task for both academic researchers and business practitioners. The recent trend to improve the prediction accuracy is to combine individual forecasts using a simple average or weighted average where the weight reflects the inverse of the prediction error. In the existing combining methods, however, the errors between actual and predicted values are equally reflected in the weights regardless of the time order in a forecasting horizon. In this paper, we propose a new approach where the forecasting results of Generalized AutoRegressive Conditional Heteroskedastic (GARCH), neural network, and random walk models are combined based on a weight that reflects the inverse of the exponentially weighted moving average of the Mean Absolute Percentage Error (MAPE) of each individual prediction model. The results of an empirical study indicate that the proposed method has a better accuracy than the GARCH, neural network, and random walk models, and also combining methods based on using the MAPE for the weight.     

Application of high resolution autoradiography to study the microsegregation of carbon in thin foil microstructures of a 12% Cr steel using 14C as a radioactive tracer

The technique of high resolution microautoradiography has already been applied to study the microsegregation of carbon and tritium in iron and its alloys, but autoradiographs have so far been obtained using liquid nuclear emulsions and carbon replicas on massive specimens. This technique has now been extended to study the distribution of carbon in thin foil microstructures of a 12% chromium steel in the quenched and tempered condition. An experimental procedure has been developed for obtaining autoradiographs on thin foils, and is described in detail. The limitations of the technique with respect to efficiency and resolution have been considered. The results obtained show that high resolution microautoradiography on thin foils permits a more precise localization of the radioactive tracer atoms with respect to the microstructural features and gives a better resolution, even with a radioisotope emitting high energy particles, in comparison with the replica method on massive specimens.     

ESCA study on the destruction mechanism of metal-resin adhesion due to water penetrating through the resin

The mechanism destroying the adhesion between PMMA and mild steel, and the action of water molecules reaching the adhesion interface was investigated. Mild steel and a thin PMMA film were bonded with dental adhesive (4-META resin). After immersion in water, the adhesive layer was peeled from the metal surface. The surface was analysed by ESCA, reflection electron diffraction, and X-ray diffraction to elucidate changes in surface structure. After 2 weeks immersion, there was a very thin brown product and after 2 months a thick black corrosion product composed of Fe₃O₄ formed at the adhesion interface. The thin brown layer showed no X-ray diffraction pattern but reflection electron diffraction showed it to be FeO(OH). After 3 days immersion, the mild steel surface appeared unchanged through the clear resin layer, and ESCA analysis showed the same chemical state as the surface of the specimen immersed for 2 weeks. Destruction of adhesion between metal and adhesive is caused by destruction of the chemical bond by the water molecules permeating through the resin layer. It is followed by corrosion of mild steel which produced iron oxide hydrate.     

Specialized channels to control the kinetics of ion release in hydrophobic resin

Fluoride, as a model ion, has been clinically used to inhibit the development of secondary carious lesions at the interfaces of restored teeth and demineralization. Controlling of its release kinetic is important in the dental restorative composites with respect to enhance biological activities without side effects. To introduce the channels into composites as specialized channels for continuous and controllable fluoride release, this paper suggests the one-dimensional structure with controllable functions. This specialized structure is generated by the novel development of a coaxially aligned tri-nozzle electrospinning technique. The fluoride source, comminuted sodium fluoride nanoparticles, was encapsulated in poly(methyl methacrylate) sheath. Tuned fluoride release was achieved by hydrophilic poly(acrylic acid) incorporated with the NaF nanosuspension with a hollow structure introduced using an inner fluid (ethylene glycol) in the tri-nozzle system. The structures of the multi-functionalized channels were preserved during UV curing of the polymeric dental restorative composites. The resulting composite resins show long-term release profiles controllable by both poly(acrylic acid) content and the hollow structures, which are based on fluoride diffusion and water ingress. Therefore, the functionalized channel can be applied to control the long-term release of ions in hydrophobic matrix at desirable kinetic.     

Application of X-ray scattering technique to the study of supersmooth surfaces

Applications of the X-ray scattering technique for studying supersmooth surfaces with rms roughness of 0.1–0.2 nm are discussed. The experimental schemes are analyzed and systematic errors on the determination of 2D and 1D PSD-functions are evaluated. Results of laboratory and synchrotron experiments are presented on the study of roughness of superpolished substrates made of different materials as well as for B₄C films of different thickness.     

Holography as a technique for the study of photopolymerization kinetics in dry polymeric films with a nonlinear response

A method is reported that makes use of holography to study the kinetics of the radical photopolymerization of acrylamide in a polyvinyl alcohol when the Kogelnik theory is applied. A mechanism of unimolecular termination by the radicals that initiate the polymerization reaction is postulated to calculate the quantum yield, the molar-extinction coefficient, the index of refraction, and the thickness of the film. The conversion percentage of monomers is obtained along with the ratio of rate constants of the mechanism of polymerization from the nonlinear fit of the transmittance curves, their angular response, and the temporal evolution of diffraction efficiency. Compared with previous holographic techniques, this method has the advantage of predicting these chemical parameters using all the data points of the temporal diffraction efficiency variation rather than being restricted to the linear zone of these curves. In this way the whole reaction process, not just the initial process, is taken into account.     

The kinetics and the mechanism of acoustic drying of capillaryporous materials

We present the results of an experimental investigation into the kinetics of acoustic drying of silica gel and felt at a frequency of 500 cps; we examine the mechanism of the intensifying effect of acoustic energy on the drying process.     

Application of the level set method to the simulation of resin transfer molding

A new methodology is presented to simulate mold filling in resin transfer molding (RTM) using a combination of the level set and boundary element methods (BEMs). RTM is a composite manufacturing process where a liquid resin is injected in a closed rigid mold containing a dry fibrous reinforcement. Process simulation is motivated by the importance of tracking accurately the motion of the flow front during the mold filling stage. The BEM solves the equation governing the resin flow and the level set method is implemented to track the resin front in the mold. This formulation opens up new opportunities to improve RTM flow simulations and optimize injection molds. The present paper focuses on isothermal resin flow in undeformable porous medium. The implementation of the numerical algorithm is described and several examples of two-dimensional filling with single or multiple injection gates are presented. The robustness of the coupling and the ability to predict accurately the position of the front by this new model are discussed. It is also shown how dry spot formation can be tracked precisely during the simulation and how a generalization of this approach allows predicting resin flow across obstacles.     

Application of Kissinger analysis to glass transition and study of thermal degradation kinetics of phenolic–acrylic IPNs

Degradation kinetics of sequential IPNs, based on novolac resin and poly (2-ethyl hexyl acrylate), are studied at linear heating rates of 2°C/min, 5°C/min, 10°C/min and 20°C/min by thermogravimetric analyser (TGA). Activation energy (E _a and order (n) of thermal decomposition reaction for IPNs and pure phenolic resin are evaluated from TGA curves using differential method of Freeman and Carroll. Decrease in T _g with an increase of acrylate content in IPNs are seen. Lower activation energy (E _a′), as calculated by applying Kissinger equation, for the concerned transition of IPNs, compared to that of pure phenolic resin is quite evident from DSC study.     

TOF SIMS and XPS study of the interaction of silanized E-glass with epoxy resin

The interaction of a silanized E-glass plate surface with the diglycidyl ether of bisphenol S (DGEBS) has been studied using time-of-flight secondary ion mass spectrometry (TOF SIMS) and X-ray photoelectron spectroscopy (XPS). In the TOF SIMS spectra, in addition to a series of ion fragments readily assigned to the parent DGEBS epoxy resin, some new ion fragments attributable to the reaction product of DGEBS with the polymeric hydrolysed -aminopropyl triethoxysilane (HAPS) precoating have been observed. In the XPS spectra a mixed coating of HAPS and DGEBS was demonstrated by the presence of intense N1s and S2p peaks. With the previous demonstration that the HAPS deposit is strongly bound to the E-glass plate surface, direct confirmation of the formation of chemical bonds at the E-glasssilane-resin interfaces has been obtained. These conclusions were complicated by the presence of polydimethylsiloxane (PDMS) and the incorporation of aluminium and calcium ions from the HAPS silanized glass plate into the mixed coating of HAPS and DGEBS epoxy resin.     

Certain regularities of the kinetics of moisture and heat exchange in drying of moist materials

Methods of calculation of the kinetics of drying of moist materials for the period of the falling rate are considered; they are based on the characteristics of the kinetics of drying: the relative drying rate and the generalized and relative drying times. Miscellaneous  Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 6, pp. 1102–1110, November–December, 2008.     

A study of the effects of phosphorus on the kinetics and mechanism of the order-disorder transformation in an Ni2Cr alloy

Three Ni₂Cr alloys, with phosphorus (P) contents of 0.002, 0.017 and 0.078 wt % were prepared as cast slabs, which were then thermomechanically treated to a final thickness of 0.38mm, after which they were solution annealed at 900° C for 1 h and water quenched. The isothermal order-disorder transformations of the Ni₂Cr alloys were investigated in specimens aged at temperatures between 425 and 550° C, for times ranging from 2 h to 70 days, by surface hardness measurements and microstructural studies. From the surface hardness data, time-temperature-transformation (TTT) curves were constructed for each of the three alloys of different phosphorus content. It was found that increasing the amount of phosphorus greatly reduced the time required to start and complete the order transformation. However, it was found that the effect of phosphorus content on the rate of transformation was significantly reduced at ageing temperatures above 500° C. The results are discussed in terms of models for nucleation and growth of ordered phases.     

EN及SEM在铝锌铟合金活化机理研究中的应用

采用扫描电镜(SEM)及电化学噪声(EN)分析了Al-5Zn-0.03In-1Mg-0.05Ti-X合金腐蚀前后的金相结构、表面形态,探讨了合金初始活化过程.结果表明晶界上存在富AlZnMg及富AlZnMgIn两种偏析相,这些阳极第二相处诱发的孔蚀为合金初始活化的主要方式.对电化学噪声进行小波分解可以清晰地分辨合金表层第二相初始腐蚀的时间段.     

Reaction mechanism and kinetics analysis of the phase transformation of TiO2 from the anatase phase to the rutile phase

The kinetic mechanism of the phase transformation of TiO₂ from the anatase phase to the rutile phase was investigated. TiO₂ powders were prepared with different pH value of the starting solution via the thermal hydrolysis method in this study. The pH values of the starting solutions have significant effects on the phase transformation temperatures of the thermal hydrolysis reaction. As the reaction temperatures were raised, the conversion from the anatase phase to the rutile phase was increased. A core–shell morphology of the prepared TiO₂ samples was suggested via the signals of the anatase phase and the rutile phase in UV–vis spectrum analysis. Through the isothermal heating process of the reaction kinetics, the controlling reaction in the phase transformation process from the anatase phase to the rutile phase was determined to be the three-dimensional phase boundary controlled process. The activation energy of the phase transformation was increased with an increase in the pH value of the starting solution.