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Inclusion compounds do not belong to the group of simple compounds. They consist of molecules of the host and guest components. Some of them form supermolecules and exhibit super-molecular properties.
Abstract
Thermal and thermo-oxidative stability of some poly(siloxane-azomethine)s obtaining starting from bis(formyl-p-phenoxymethyl)tetramethyldisiloxane and different organic diamines have been investigated by TG+DTG+DSC simultaneous analyses performed in argon flow and air static atmosphere, respectively. TG, DTG and DSC curves of each polymer showed three or four successive degradation steps at different temperatures according to the composition of the sample and the gaseous atmosphere in which the thermal analysis was performed. For each process, the following parameters were evaluated: total mass loss, temperature corresponding to the maximum reaction rate, maximum reaction rate, temperature corresponding to certain mass loss. In order to determine the thermal and thermo-oxidative stabilities of investigated polymers, the following values were determined: T x% — temperature corresponding to x% mass loss, and %Δm T — mass loss at a given temperature T. The obtained orders of stability were correlated with the structure of investigated polymers.
Abstract
Two isothermal soot oxidation protocols were tested in a Perkin-Elmer TGA6: (1) the sample was heated under N2 and then the reaction gas was introduced and (2) the sample was introduced after the empty furnace was heated under the reaction gas. The first protocol is common in soot oxidation studies, it gives a measure of the volatiles and is easier to handle, but as it is shown the determined reaction rate may be falsified by the O2 concentration. Using gas analysis it was found that ∼2000 s are necessary for the complete gas change in the instrument. An instrument specific correction function involving the O2 concentration and reaction order n with respect to O2 was developed which allowed the correlation of the rates measured with both protocols.
Absorption heats of hydrogen sulphide in aqueous solutions of monoethanolamine, diethanolamine and triethanolamine were determined by calorimetry. The measured enthalpies were compared to those calculated on the basis of solubility measurement and to the enthalpies of protonation of hydrogen chloride at 25‡.
Abstract
Two integral isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose) and the invariant kinetic parameters method (IKP) were used in order to examine the kinetics of the non-isothermal crystallisation of a silica-soda-lead glass. The objective of the paper is to show the usefulness of the IKP method to determine both the activation parameters and the kinetic model of the investigated process. Thismethod associated with the criterion of coincidence of kinetic parameters for all heating rates and some procedures of the evaluation of the parameter from Johnson–Mehl–Avrami–Erofeev–Kolmogorov (JMAEK) equation led us to the following kinetic triplet: activation energy, E=170.5±2.5 kJ mol–1 , pre-exponential factor, A=1.178±0.350·10 10 min–1 and JMAEK model (A m) m=1.5.
Abstract
A newly synthesized copper-complex exhibiting nonlinear optical properties, crystalline nature, and generating interest as a material for non-linear optical applications was investigated. As thermal stability studies are indispensable before attempting any laser-assisted processing experiments, the thermal behavior of 2,2′-dihydroxy azobenzene with Cu2+ cations that are found to organize themselves as non-central symmetric crystallites, was investigated. The thin films were deposited on silicon substrates by matrix-assisted pulsed laser evaporation using a Nd:YAG laser working at 266 and 355 nm. Thermal analysis of the bulk compound indicates a higher thermal stability in argon flow when compared to the air atmosphere; as well, since, the adhesion of the compound onto the substrate enhances the bonding, the thermal stability of the Cu complex increases. Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy, spectroscopic ellipsometry, and ultraviolet–visible spectroscopy investigations were also performed.
Summary Thermogravimetry (TG) was applied to evaluate the thermal behavior of five refinery atmospheric distillation residues (ATR) obtained from different Brazilian crude oils. The asphaltenes were extracted of each sample and their influence on coke formation was studied. It was observed that they have a great contribution on carbonaceous residues formation during pyrolysis and that the heavier the ATR sample, the higher is the contribution of other heavy components present in ATR samples.
Abstract
A new synthesized 4CN type azomonoether, exhibiting dying properties, crystalline nature and generating interest as a material for non-linear optical applications was investigated. Modern devices incorporating liquid crystals tend to use thin films of such materials because of their special characteristics. Thermal stability studies are indispensable before attempting any deposition experiment. We have investigated the thermal behaviour of 4-[(4-chlorobenzyl)oxy]-4′-cyano-azobenzene (TG, DTG, DTA and DSC) in inert flow atmosphere, under non-isothermal conditions. The phase transitions were studied by repeated heating-cooling regimes, with intercalated isothermal steps. The thin films were deposited on silicon and quartz substrates by matrix assisted pulsed laser evaporation (MAPLE) using a Nd:YAG laser working at 266 nm. FTIR spectroscopy of the obtained thin films confirmed the preservation of the compound’s structure.
We studied the potential role of seed bank in the dynamics of the understorey in a turkey oak-sessile oak forest (Querceteum petraeae-cerris) in Hungary. We used long-term records of the herb layer (1973–2006) and the seed bank composition of 2006 to assess the role of seed bank in the regeneration of herb layer. The total cover of herb layer decreased from 22% (1973) to 6% (1988), and remained low (<10%) till 2006; coinciding with the increasing cover of secondary canopy dominated by Acer campestre. We found a low density seed bank (ca. 1300 seeds/m2). Altogether 33 species were germinated from the soil samples. A few generalist weed species composed the majority of seed bank. It was possible to assign a seed bank type for 19 species; 14 species out of 19 was long-term persistent. We found that the characteristic perennial forest herbs and grasses had only sparse seed bank. The Jaccard similarity between vegetation and seed bank was low (<30%). Our results suggest that the continuous establishment of forest herbs are not based on local persistent seed bank; it should be based on vegetative spreading and/or seed rain.
Diploid Anthoxanthum odoratum and tetraploid A. aristatum were compared with respect to stomatal guard cell lengths, and stomatal density at adaxial and abaxial surfaces of the lamina. Further, the genome size of both species was determined by flow cytometry, and the number as well as the chromosomal distribution of 5S and 45S rDNAs were examined using FISH with ribosomal DNA (rDNA) probes. The average length of stomatal guard cells in A. odoratum was shown to be greater than that for A. aristatum, but the ranges overlapped. Moreover, reduction in stomatal frequency was found at higher ploidy levels.The genome size was 6.863 pg/2C DNA for A. aristatum and 13.252 pg/2C DNA for A. odoratum. A. aristatum has four sites of 5S rDNA in its root-tip meristematic cells, whereas A. odoratum has six. Both species have six sites of 45S rDNA. Chromosomal localization of the rDNA varied, which suggests that chromosome rearrangements took place during Anthoxanthum genome evolution.
