Authors:I. Szilágyi, Judit Pfeifer, C. Balázsi, A. Tóth, Katalin Varga-Josepovits, J. Madarász, and G. Pokol
We studied the thermal stability of different hexagonal tungsten trioxide, h-WO3 samples, which were prepared either by annealing hexagonal ammonium tungsten bronze, (NH4)0.33−xWO3−y, or by soft chemical synthesis from Na2WO4. The structure and composition of the samples were studied by powder XRD, SEM-EDX, XPS and 1H-MAS NMR. The thermal properties were investigated by simultaneous TG/DTA, on-line evolved gas analysis (TG/DAT-MS), SEM
and in situ powder XRD. The preparative routes influenced the thermal properties of h-WO3 samples, i.e. the course of water release, the exothermic collapse of the hexagonal framework and the phase transformations
were all affected.
Authors:M. Zaharescu, A. Jitianu, A. Brãileanu, V. Bãdescu, G. Pokol, J. Madarász, and Cs. Novák
The hydrolysis-polycondensation of organically modified Si-alkoxides leads to the obtaining of inorganic-organic hybrid materials
in which the organic moieties remain as permanent groups bonded to the inorganic network.
The molecular species previously determinated by GC-MS during the gelation process have been significantly different according
to the type of the alkoxide used.
In the present work, thermal stability of SiO2-based inorganic-organic hybrid materials starting with TEOS (tetraethoxysilan), MTEOS (triethoxymethylsilan), VTEOS (triethoxyvinylsilan)
and MTMOS (trimethoxymethylsilan) was studied.
The molecular structure of the gels obtained determines differences in their thermal behaviour. Gels obtained starting with
MTEOS show the highest thermal stability, while gels obtained using VTEOS the lowest, among the substituted alkoxides. A particular
behaviour presents the gel obtained with MTMOS that decomposes in four steps. This could be explained by the presence in the
gel of some prevalent types of molecular species with different thermal stability.
Authors:J. M. Ginés, M. J. Arias, J. R. Moyano, Cs. Novak, G. Pokol, and P. J. Sánchez-Soto
A thermal study using DSC and Hot Stage Microscopy (HSM) was carried out to investigate the interaction in solid state of the binary system PEG 4000 — oxazepam, and to establish their phase diagram. The eutectic composition, which melting occurs at lower temperature as compared with the pure components, has been determined. The results obtained by DSC and HSM have indicated that PEG 4000 — oxazepam mixtures displays no obvious incompatibilities, and that the system shows a typical eutectic behaviour. However because of the closeness of the melting of PEG 4000 to the eutectic temperature, it was difficult to determine precisely the eutectic composition and temperature on the basis of DSC measurements alone. The use of heats of fusion corresponding to physical mixtures allowed an estimation of the eutectic composition at 6% w/w oxazepam. Additional information of temperature (57.6‡C) and composition (5–10% w/w oxazepam) of the eutectic was obtained by HSM using the contact method. This low melting temperature in this range of compositions offers advantages in terms of drug stability and easy manufacture.
Authors:M. Crişan, Ana Brăileanu, M. Răileanu, D. Crişan, V. Teodorescu, R. Bîrjega, V. Marinescu, J. Madarász, and G. Pokol
and S-doped TiO2 sol–gel nanopowders were prepared
by controlled hydrolysis-condensation of titanium alkoxides. The influence
of different Ti-alkoxides (tetraethyl-, tetraisopropyl- and tetrabutyl-orthotitanate)
used in obtaining TiO2 porous materials in similar
conditions (water/alkoxide ratio, solvent/alkoxide ratio, pH and temperature
of reaction) has been investigated. The relationship between the synthesis
conditions and the properties of titania nanosized powders, such as thermal
stability, phase composition, crystallinity, morphology and size of particles,
BET surface area and the influence of dopant was investigated. The nature
of the alkyl group strongly influences the main characteristics of the obtained
oxide powders, fact which is pointed out by thermal analysis, X-ray diffraction,
TEM and BET surface area measurements.