Authors:Sameh Othman, Azza Ali, Nabil Mansour, and Bahgat El-Anadouli
In this study, a new mathematical model was suggested to account for the effect of internal and external diffusion on fluid–solid
noncatalytic reactions. The special features of this model are the combination of the transport processes and the chemical
reaction kinetics with the added factor due to the structural properties of the solid reactant. The model was examined theoretically
and experimentally. A reactive cloth filter that separates radionuclides from radioactive waste solutions is used as a practical
application for the model. Analyses of the respective rate data in accordance with another two theoretical models showed that
process is controlled by the rate of the diffusion step. The external and internal mass transfer constants across the liquid
film and the resin matrix were determined from the graphical representation of the proposed model. The practical validation
with the theoretical results offered satisfactory agreement at most of the process stages.
The formation of benzynes derivatives from ortho-trimethylsilyl triflates using tetra-n-butylammonium fluoride (TBAF) as the benzyne-forming trigger was achieved in a straightforward flow reactor at room temperature. These benzynes were immediately trapped in Diels—Alder reactions to deliver the desired cycloadducts.
In this work it has been established which compounds finally are formed in air in the two-component CuO-V2O5 and CuO-α-Sb2O4 systems. Unknown thermal properties of CuV2O6, Cu2V2O7 and Cu11V6O26 have been established. Reactivity of the oxides and phase relations in the ternary V2O5-CuO-α-Sb2O4 system in air have been studied by using XRD and DTA methods. The results have showed the reaction of V2O5, CuO with α-Sb2O4 does not produce any compound where all the three oxides would be involved. It has been established that the α-Sb2O4 reacts and forms binary phases independently with CuO or V2O5. On the base of these results the investigated system was divided into subsidiary subsystem in which CuSb2O6 remains at equilibrium in the solid state with other phases formed in corresponding binary systems.
The results obtained by studying decarbonization of different samples of Estonian limestone and dolomite and the following
sulphation or carbonation of calcined products to estimate their SO2 and CO2 binding ability were presented. Experiments were
carried out with thermogravimetric equipment(Q-Derivatograph, MOM and Labsys™, SETARAM) – calcination of the samples in the
atmosphere of air with the heating rate 10 K per minute using multiplate crucibles, the following sulphation or carbonation
of the calcined products after cooling to the fixed temperature (temperature range 400–900C) under isothermal conditions
in the flow of air-SO2 or air-CO2 mixture. Chemical, X-ray, BET nitrogen dynamic desorption, etc. methods for the characterization of the initial samples,
intermediate and final products were used.
In addition, the possibilities of recurrent use of oil shale ashes taken from different technological points at operating
thermal power plants (Estonian and Baltic TTPs, Estonia) as sorbents for SO2 binding from gaseous phase were studied, as well as the possibilities of activation of these ashes towards SO2 binding.
The results of these studies confirmed the high reactivity of Estonian limestone and dolomite towards SO2 and CO2. Dependence of SO2 binding mechanism on the SO2 concentration has been established. Modelling of SO2 capture of dolomite and limestone was carried out to establish the kinetic parameters of these processes. The possibilities
of activation of oil shale ashes and their effective recurrent use for binding SO2 and CO2 from gaseous phase were confirmed.
In this study gasification in air of activated carbons and carbon blacks is investigated using a simultaneous TG-DTA unit. It is found that a final acid or alkaline treatment can substantially alter their reactivity in the gasification reaction in air. To make a proper assessment of their solid state reactivity with respect to their gasification in air a simple method is advanced which has been used recently in assessing solid state reactivity of other materials. In this method a thermogravimetric (TG) plot is obtained on a reference carbon and then similar TG plots are obtained on the other samples of carbon using identical experimental conditions and the same TG unit. The solid state reactivity is assessed from plots of the αR (the value of αR, the extent of the gasification of the reference carbon) against the sample carbons values of the αS (labeled αS to denote the value of the various carbon samples). The values of appropriate couples of αR and αS at temperaturesT1,T2,T3,...Tn allow an αR-αS plot to be constructed. If the solid state reactivity of the carbon samples matches exactly that of the reference carbon the result will be a linear plot, showing coincidence of αS and αR at all values of αR. If the solid state reactivity of a carbon sample exceeds that of the reference carbon then the lines plotted will be on one side of the coincidence plot, while if they are less than the carbon reference they will lie on the other side. The results show that treatment of a carbon with alkaline or acid may have a significant effect on the reactivity of the carbon sample which is only partly explained by observable differences in surface area.
are produced which are reducing in nature and therefore very low yields of I2 are observed for low -doses. In further irradiation the reformation of –O–O–, peroxy linkages is proposed hence the observed higher yields. All the processes ultimately lead to an oscillatory variation in yields of I2 with -doses.
Reactivity in the solid-state between ZnWO4 and some RE2MoO6 (RE=Y, Sm, Eu, Gd, Dy, Ho, Er and Lu) was investigated by XRD and DTA-TG methods. Four new compounds with the formula ZnRE2MoWO10 (RE=Sm, Eu, Gd, Dy) were synthesized. The obtained compounds are isostructural and crystallize in the monoclinic system. They
melt incongruently within the temperature range of 1016–1033°C. The solid product of melting is an adequate of rare-earths
Authors:P. Pasierb, R. Gajerski, S. Komornicki, and M. Rękas
The mutual reactivity in mixtures containing Nasicon (Na3Zr2Si2PO12) or YSZ (ZrO2:Y2O3) solid electrolytes with Li2CO3 or Li2CO3:BaCO3 sensing electrode materials was investigated using simultaneous DTA and TG and ex situ XRD techniques. The uncontrolled chemical
reaction is suspected to be responsible for the instability of electrochemical gas sensors constructed from these materials.
DTA and TG results obtained for Nasicon-carbonate mixtures indicate the possibility of reaction in the temperature range from
about 470 to 650C, which overlaps the sensor operating temperature range (300–525C). The results obtained for YSZ-carbonate
mixtures indicate that reaction between carbonate and the ZrO2 takes place at higher temperatures and cannot explain the instability drift of investigated sensors. The mechanism of observed
reactions in systems studied is also discussed.