László Pöppl

A melt mechanism for the thermal decomposition of ammonium dichromate

Microscopic examination of (NH4)2Cr2O7 crystallites, previously decomposed to measured extents, has given strong evidence that reaction proceeds through the intervention of a melt. This reaction has previously been accepted as occurring in the solid phase and the use of higher magnifications than were applied previously revealed the progressive development of foam-like zones of active reaction. These structures are termed ‘fusion nuclei’. We conclude that an initial, and probably reversible, dissociation of the reactant (NH4)2Cr2O7⇌ 2NH3+ H2O + 2CrO3 is followed by a sequence of steps by which NH3 and/or NH+4 is oxidized in the CrO3 melt to N2 and N2O, possibly involving the intervention of NH4NO2 and NH4NO3 respectively. Since these various consecutive and concurrent reactions contribute to the overall chemical change we conclude that the quantitative characterization of their kinetics and stoichiometry requires the separate investigation of selected simpler reaction mixtures. Some observations on the reaction of ammonia with molten CrO3 are discussed.

Nitration of polyethersulfone by ammonium nitrate and trifluoroacetic anhydride

Victrex polyethersulfone was nitrated efficiently and controllably on its deactivated aromatic ring with a mixture of ammonium nitrate and trifluoroacetic anhydride. The products were characterized by elemental analysis and IR spectroscopy, their thermal properties were investigated by TGA and DSC methods. A comparison is made between this procedure and the analogous nitration of Udel polysulfone.

Preparation and characterization of brominated polyethersulfones

A novel derivative of aromatic polyethersulfone (PES) was obtained by bromination. Victrex PES was reacted with bromine under various conditions: in solution, in suspension, and without solvent; with or without catalyst; and at low and elevated temperatures. Practically no bromination occurred in solution; in the other cases, brominated PESs to various extents were obtained. The degree of substitution (DS) varied between 0.3 and 2.3. It was found that no catalyst is required for this reaction; the temperature, the concentrations of bromine and of polymer in the reaction mixture, and the duration of the reaction are the determinant factors of the DS. The modified polymers were characterized by elemental analysis, 1H-NMR, 13C-NMR, and PGC-MS, and their thermal properties were investigated by TGA and DSC methods. Further transformations of brominated PES as well as other new chemical reactions of PES will be the subject of later publications.

Determination of fulvic acids in water samples of Hungarian caverns

Abstract Water samples from the region of Beke cavern of Aggtelek and above the Jozsefhegyi and Palvolgyi caverns of Buda, Hungary were analyzed by various chromatographic techniques and fluorescence spectrometry. According to size-exclusion chromatographic (SEC) measurements, the water samples contained only low-molecular-weight components, fulvic acids, which were concentrated and separated from inorganic and non-acidic organic compounds in the water samples at pH 2 using an XAD-8 resin column. Elution from the column was performed with 0.1 M NaOH solution. UV absorbance was monitored at 254 nm and fractions were collected and subsequently separated by applying a size-exclusion high-performance liquid chromatographic (SE-HPLC) method. The mobile phase was ammonium acetate at a concentration of 50 mmol/dm 3 and a flow rate of 0.5 cm 3 /min. The SE-HPLC measurements confirmed the presence of low-molecular-weight compounds in the samples analyzed. Quantitative determination of the fulvic acid content of the concentrated samples was carried out by fluorescence spectrometry. The excitation and emission wavelengths were 325 and 440 nm, respectively. The fulvic acid concentrations of the water samples examined ranged between 2 and 112 μg/cm 3 .

Interaction of kaolinite with organic and inorganic alkali metal salts at 25–1300 °C

Abstract The reactions of Georgian kaolinite with saturated solutions of alkali metal Chlorides, potassium acetate and with solid salts resp. were followed by XRD, FTIR and TA-MS methods. The results show that in the case of solid MCl and solutions thereof already at room temperature alkali metal ions have been incorporated into kaolinite. The quantity of incorporated cations increased with rising temperature. CH 3 COOK was intercalated into the interlayer spaces. The solid state reactions and the gaseous reaction products up to 1000 °C were followed by different methods. The crystal phases formed in the course of the reactions between kaolinite and the decomposed salts have been investigated up to 1300°C. The reaction mechanisms on the basis of experimental data and literature are discussed.

Synthesis and characterizations of hydroxy-aluminum cross-linked montmorillonite

Cross-linked montmorillonite was prepared by reacting homoionic sodium form of bentonite (Na-M) from Istenmezeje (Hungary) with high molecular weight polyhydroxy-aluminum complex. The complex was prepared by controlled hydrolysis of alumina macrocation. The intercalated clay (Na-Al-M) was thermally treated to convert the hydroxy cations to oxide pillars. The pillared products were characterized by X-ray powder diffraction (XRD), Fourie transform infrared spectroscopy (FTIR), (thermogravimetry (TG), differential thermal analysis (DTA) and thermal analysis-mass spectrometry (TA-MS) methods. The specific surface area as well as pore size and pore structure distribution of samples were measured by nitrogen, water and carbon tetrachloride adsorption, and the heat of immersion was also determined. The pillared products were characterized by d(001) reflections of 19 Å, which is stable even at 500°C. The interaction of polymer alumina caused several changes in the obtained FTIR spectra due to the formation of different new bonds. The rate of dehydroxylation of the pillared product is very moderate, the water release occurred in different temperature ranges according to TA-MS results. Dehydration starts at interfaces and at the wall of pores, occurring nearly with uniform rate at 250-500°C. DTA curve indicates the formation of a new phase at 950°C. The obtained surface area of the pillared product by nitrogen adsorption becomes larger (208 m2 g-1) with respect to the non pillared clay, which decreases less than 10% upto 700°C. The pillared sample has a definite pore structure, the quantity of micropores (0-40 Å) decreased with increasing of macropores (>1000 Å). The obtained domestic pillared montmorillonite possesses a high degree of thermal stability and may be used as adsorbent.

Study of the binary CaCO3-SiO2 system by quantatitative DTA

Solid-state reactions in the CaCO3-SiO2 system with different mass ratios (CaCO3:SiO2=from 1∶0.2 to 1∶10) were studied by means of thermogravimetry, quantitative DTA and high-temperature X-ray diffraction up to 1500 °C.It was found that not CaCO3, but CaO reacted with SiO2. The rate of decarboxylation increased and the temperature of formation of silicate phases decreased significantly with increasing silica content. Only mono- and dicalcium silicates could be detected as solid-state reaction products. Above 1400 °C, an intensive melting process took place; the amount of silica had no clear effect on its temperature range.Quantitative DTA and X-ray diffraction data proved that, below 1000 °C, not only the decarboxylation process, but also silicate formation must be taken into consideration.

IBM PC-based multipurpose data-acquisition system for thermal analysis

A multipurpose data-acquisition system based on IBM PC or compatible computers has been developed for analog thermoanalytical equipment (especially for the Mettler TA 1 and TA 2 and Derivatographs). The system is versatile, easily tailored to specific requirements, and permits multitask operation, i. e. the collection of data from current experiments and the evaluation of results from previous experiments simultaneously.ZusammenfassungBasierend auf IBM PC oder kompatiblen Computern wurde ein Mehrzweck-Datenerfassungssystem für analoge thermoanalytische GerÄte (besonders für Mettler TA1 und TA2 und Derivatographen) entwickelt. Das System ist vielseitig, kann spezifischen Anforderungen leicht angepa\t werden und erlaubt den Foreground-Background-Betrieb, d.h. es können gleichzeitig Daten eines laufenden Experimentes erfa\t und Daten früherer Experimente ausgewertet werden.