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Thermal decomposition kinetics of some aromatic azomonoethers

Part II. Non-isothermal study of three liquid crystals in dynamic air atmosphere

Journal of Thermal Analysis and Calorimetry
Authors: A. Rotaru, Anna Kropidłowska, Anca Moanţă, P. Rotaru, and E. Segal

Abstract  

Thermal analysis of three azomonoether dyes, exhibiting liquid-crystalline properties, was performed in dynamic air atmosphere. Thermal stability studies and the evaluation of the kinetic parameters of each physical or chemical transformations are essential for a full characterization, before attempting accurate thin films’ depositions of such materials used in non-linear optical applications. New synthesized dyes with general formula:

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where R is a nematogenic group: CN, CF3 or a highly polarizable group: NO2 were investigated using TG, DTG, DTA and DSC techniques, under non-isothermal regime. The evolved gases were analyzed by FTIR spectroscopy. The activation energies of the first decomposition step were evaluated for each compound, the obtained results revealing complex mechanisms.

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Journal of Thermal Analysis and Calorimetry
Authors: A. Rotaru, Catalin Constantinescu, P. Rotaru, Anca Moanţâ, M. Dumitru, Margareta Socaciu, Maria Dinescu, and E. Segal

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.

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Abstract  

Over the ages, the deposits of dead vegetation buried by rock and mudflows, compacted and compressed out all of the moisture; it slowly carbonized and became coal. Humic acids are natural organic acids — brown coloured biological macromolecules, formed in coal by biochemical changes (decomposition, pyrolysis) of lignocellulosic matter. From lignite coal bed, the humates were extracted in alkaline medium and isolated from the residual fraction. Humic acids were obtained by treating humantes’ solutions with HCl. Thermal analysis (TG, DTG, DTA and DSC) was used in order to establish the decomposition and thermal effects of lignite, humates, humic acids and residual matter extracted from Rovinari mines in Romania. A non-isothermal linear temperature regime was imposed to reveal all decomposition steps.

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Abstract  

Thermochemical properties of two kinds of composite material of synthetic zeolite ZSM5 in potassium form (K-ZSM5) with AgI have been studied. The composites have been prepared by treating the silver form of synthetic zeolite ZSM5 (Ag-ZSM5) with potassium iodide solution under different experimental conditions. One of the composites was additionally sintered at temperature 500C for 20 h. Both composites have been characterized by TG, DTG, DTA, EDS analysis, X-ray powder diffractometry and X-ray photoelectron spectroscopy. The methods of thermal analysis as well as X-ray powder diffractometry and XPS confirmed the differences between the two composites caused by sintering during the synthesis. The content of AgI in the surface layer was different. No changes of the zeolitic mineral dimensions are observed.

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Journal of Thermal Analysis and Calorimetry
Authors: Erika Szunyogová, Dagmar Mudroňová, Katarína Györyová, Radomíra Nemcová, Jana Kovářová, and Lenka Piknová-Findoráková

Abstract  

Spectroscopic (IR), thermoanalytical (TG/DTG, DTA) and biological methods were applied to investigate physicochemical and biological properties of seven zinc(II) complex compounds of the following formula Zn(HCOO)2·2H2O (I), Zn(HCOO)2·tph (II), Zn(CH3COO)2·2H2O (III), Zn(CH3COO)2·tph (IV), Zn(CH3COO)2·2phen (V), Zn(CH3CH2COO)2·2H2O (VI), Zn(CH3CH2CH2COO)2·2H2O (VII), where tph=theophylline, phen=phenazone. The formation of various intermediates during thermal decomposition suggests the dependence on the length of aliphatic carboxylic chain and type of N-donor ligand (tph, phen). The final product of the thermal decomposition was ZnO. The antimicrobial activity of these complexes were tested against G+ and G bacteria. Strong inhibitive effect was observed towards E. coli, salmonellae and Staph. aureus.

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Abstract  

Zinc carboxylate complexes with N-donor ligands exhibit antimicrobial and antifungal effects. The preparation and thermal properties of complex compounds Zn(isobut)2 and Zn(isobut)2L(isobut=(CH3)2CHCOO, L=papaverine — pap, phenazone — phen) are described in this paper. The newly synthesized compounds were characterized by elemental analysis, IR spectroscopy and TG/DTG, DTA methods.During the thermal treatment it was found that the release of organicligands (pap, phen) was followed by pyrolysis of zinc(II) isobutyrate. (C3H7)2CO and CO2 were found as gaseous products and zinc oxide as the final product of thermal decomposition. Gaseous and solid products of thermal decomposition were confirmed by chemical analysis, IR spectra and X-ray powder diffraction.

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Abstract  

The thermal decomposition process of mixtures of CoC2O4⋅2H2O (COD) or Co(HCOO)2⋅2H2O (CFD) or [Co(NH3)6]2(C2O4)3⋅4H2O (HACOT) with activated carbon was studied with simultaneous TG–DTG–DTA measurements under non-isothermal conditions in argon and argon/oxygen admixtures. The results show that the thermal decomposition of the studied mixtures in Ar proceeds in the same manner. It begins with the salt decomposition to Comet+CoO mixture followed by (T>680 K) the simultaneous reduction of CoO to Cometand carbon degasification. The final product of the thermal decomposition of COD-C and CFD-C mixtures, identified by XRD, is β-Co. Cobalt contents determined in the final products fall in the range 71–78 mass%. The rest is amorphous residual carbon. In Ar/O2 admixtures the end product is Co3O4 with ash admixture.

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Abstract  

Mg-Al L(ayered) D(ouble) H(ydroxide) was prepared and its thermal behaviour was characterized by thermoanalytical methods (TG, DTG, DTA), 27Al M(agic) A(ngle) S(pinning) NMR spectroscopy, X-ray diffractometry (XRD) and S(canning) E(lectron) M(icroscopy). Heat treatment destroyed the layered structure, which could only be partially reconstituted by rehydration. On calcination mixed oxide with the predominance of basic sites were formed. Pillaring the LDH with Fe(CN)6 4- anions was also performed. The material was characterized by XRD and BET measurements. Heat stability of the pillared substance was investigated, too. Pillaring proved to be successful, however, decreased heat resistance was found in the intercalated material relative to the guest LDH.

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Abstract  

The thermal behaviour of kaolinites intercalated with formamide, dimethyl sulphoxide and hydrazine has been studied by simultaneous TG-DTG-DTA-EGA and TG-MS techniques. The complexes can be decomposed completely without dehydroxylating the mineral. It was found that the amount of intercalated guest molecules per inner surface OH-group is close to unity for the formamide and dimethyl sulphoxide intercalates. For the intercalation of hydrazine it was found that hydrazine is locked in the expanded mineral as hydrazine hydrate and its amount is somewhat higher than that obtained for the other two reagents. The thermal evolution patterns of the guest molecules revealed that all the three reagents are bonded at least in two different ways in the interlayer space.

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Abstract  

The physicochemical properties of spent fluidized bed cracking catalyst and its influence on hydration process of cement slurry were studied. The samples were cement slurries prepared with water/solid=0.5 and additions of used catalyst amounted to 0, 5, 10, 15, 20 and 25%with resp. to the solid. After definite time they were subjected to thermogravimetric analysis (TG, DTG, DTA) and, in order to determine the progress of reaction with water, the heat of hydration was measured by means of isotherm calorimetry. The studies disclosed that the spent cracking catalyst is not merely an inactive filler in cement slurries, but it modifies the course of the hydration process. The spent catalyst is a pozzolana additive and its presence leads to a decrease of calcium hydroxide contents in the system. The spent catalyst affect on the heat of cement hydration. Small amounts additive accelerate the process of binding.

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