Authors:J. Madarász, T. Leskelä, G. Pokol, and L. Niinistö
Cesium hexachlorocerate(IV), Cs2CeCl6 (I) and sodium pentakis(carbonato)cerate(IV), Na6Ce(CO3)5·12H2O (II) have been investigated in air by simultaneous TG/DTA, FTIR and XRD in order to follow the oxidation state of cerium during their thermal treatment. The thermal decomposition of the hexachloro compound (I) is accompanied by a double change in the oxidation state of cerium. First, in an inner reduction-oxidation reaction, chlorine is evolved and a Cs2CeCl5 phase is obtained. The immediately starting oxidation of this Ce(III) species caused various phase transitions in the CeCl3-CsCl system formed. The presence of Cs3CeCl6 above 400°C can also be assumed and finally this phase also oxidizes into CeO2 with the formation of CsCl as by-product. In the case of the pentacarbonato complex (II), no Ce(III) species were detected. The final products of its decomposition were CeO2 and Na2CO3.
Authors:D. Kozma, J. Sztatisz, K. Tomor, G. Pokol, and E. Fogassy
The optical resolution of racemic mandelic acid (I) by S-2-benzylamino-butanol (II) was performed in water, ethyl acetate,
and water saturated ethyl acetate. It was found that the efficiency of the resolution is three times higher in water saturated
ethyl acetate than in either water or ethyl acetate. The salt mixtures produced during the resolutions and the pure diastereoisomeric
salts were analyzed by TG, DSC and X-ray powder diffraction measurements. The R-(-)-IS-(+)-II salt has the higher melting
point and heat of fusion value which indicates that this is the more stable salt. Though the general assumption is that diastereoisomeric
salt pairs of successful optical resolutions form eutectic systems, the R-mandelic acid-S-2-benzylamino-butanol and the S-mandelic
acid-S-2-benzylamino-butanol system was found to behave in a different way. Melting did not start at or near the estimated
eutectic temperature. The difference can be explained either by miscibility in the solid phase (solid solution) or by a blocked
interaction between the crystals of the two solid salts. This unusual behaviour of the salt pair should be responsible for
the unusual difference in the efficiency of the resolutions performed in different solvents
Authors:S. Békássy, T. Cseri, G. Kenessey, G. Pokol, K. Tomor, and G. Liptay
Montmorillonite-supported iron(III) nitrate and copper(II) nitrate reagents, and other supported metal nitrates prepared in
the same way, were investigated by thermal and X-ray powder diffraction methods. The metal nitrates are present on the support
in the form of crystalline hydrate and not as acetone solvate as supposed earlier. Thermal decomposition of metal nitrates
that are active in model reactions proceeds in a different way from that of the practically inactive nitrates. In the former
case, water release and nitrate decomposition itself are simultaneous process. These and other results contributed to determination
of suitable reaction conditions for the montmorillonite-supported reagents.
Authors:J. Zsakó, G. Pokol, Cs. Novák, Cs. Várhelyi, A. Dobó, and G. Liptay
A number of 30 [Co(en)3 ]Y3 , [Co(en)2 X2 ]Y and [Co(en)2 X(amine)]Y2 type complexes (X =Cl, Br; Y =Cl, Br, I, NCO, NCS, NO3 , ClO4 , etc.; amine =aromatic and alkylamines) were obtained from trans-[Co(en)2 Cl2 ]Cl by double decomposition and by substitution reactions, respectively. The structure of the complexes was proved by means
of far and middle FTIR spectra. The thermal decomposition was studied by TG, DTA and DSC measurements. Mass spectra were also
recorded. In the case of [Co(en)3 ]Y3 complexes the nitrate, perchlorate and dimesoperiodates decompose suddenly, frequently explosion like. The halides and thiocyanates
seem to substitute an ethylenediamine ligand, yielding a rather unstable intermediate. The pyrolysis of [Co(en)2 X2 ]Y type derivatives yields no relatively stable intermediates, but the decomposition temperatures may be correlated with
the nature of Y and with the cis or trans configuration of the compound. With the [Co(en)2 X(amine)]Y2 type complexes one observes the formation of [Co(en)2 XY]Y as intermediate product. From the TG curves kinetic parameters were derived for some dehydration and deamination processes,
by using the nomogram method. The validity of a non-linear kinetic compensation law was observed.
Authors:J. Bajdik, K. Pintye-Hódi, Cs. Novák, P. Szabó-Révész, G. Regdon, I. Erős, and G. Pokol
Dimenhydrinate is a heat-sensitive antihistamine with a low melting point. The heat-sensitive feature is of importance if
direct compression is used. Direct measurement of the heat originating in the texture of tablets during compression is very
difficult. Thermoanalytical methods were used as indirect methods to describe the changes in material properties at high temperature:
differential scanning calorimetry, thermomicroscopy and thermogravimetric analysis. Film coating method is widely used in
pharmaceutical technology. A fluidized bed apparatus was applied to coat the crystals. The coating film forming agent was
hydroxy-propyl-methylcellulose (HPMC), which is a gastric-soluble polymer. Thermoanalytical measurements reveal that dimenhydrinate
crystals are sensitive to heat. Film coating method does not alter the shape of the DSC curve of dimenhydrinate, but increases
the melting point. The presence of a macromolecular film reduces the thermal conductivity, because it separates the particles.
Authors:I. Szilágyi, J. Madarász, G. Pokol, F. Hange, G. Szalontai, Katalin Varga-Josepovits, and A. Tóth
This paper discusses the changes in the structure and thermal reduction of nanosize hexagonal ammonium tungsten bronze (HATB),
(NH4)0.33−xWO3−y, which were caused by K+ ion exchange (doping) and studied by XRD, XPS, 1H-MAS NMR, FTIR, SEM and TG/DTA-MS. Comparison of the cell parameters of undoped and doped HATB revealed that both a and c cell parameters decreased after the ion exchange reaction, which showed that smaller K+ ions partly replaced the larger NH4+ ions in the hexagonal channels of HATB. After the reaction, from the hexagonal channels less NH3 evolved, which also supported the incorporation of K+ ions into the hexagonal channels.
Authors:Cs. Várhelyi Jr., G. Pokol, Á. Gömöry, A. Gănescu, P. Sohár, G. Liptay, and Cs. Várhelyi
chelates of the type [Ni(II)(Diox.H)2], ((Diox.H)2:
various α-dioximes) have been studied by means of FTIR, NMR, MS data
and various thermoanalytical methods (TG, DTA, DTG, DSC). In some cases kinetic
parameters of the thermal decomposition of the complexes were also calculated
using Zsak’s ‘nomogram method’. The mechanism of
the decomposition processes was characterised on the basis of mass spectra.
Authors:H. Simon, Z. Vincze, K. Marthi, G. Lévai, G. Pokol, E. Fogassy, and D. Kozma
A non-isothermal experimental study using thermogravimetry (TG) and differential scanning calorimetry (DSC) was conducted
for investigation the oxidation reactivity of natural phosphate and its demineralised products. The analyses were carried
out in oxygen atmosphere and at different heating rate (5, 10, 20, 30, 50, 60C min-1) up to 1000C. The results indicated that the material washed with HCl from the original phosphate, mainly apatite and carbonates
of calcium and magnesium, as well as with HCl/HF, silicates minreals, had an inhibition effect during oxidation reactions
of organic material. The increase of the heating rate shifted the reactions to higher temperatures. In addition, kinetic parameters
were determined by assuming a single first-order kinetic model, using the Coats-Redfern method. The influences of demineralization
process of natural phosphate and the heating rate were examined and discussed.