Search Results

You are looking at 101 - 110 of 1,467 items for :

  • "thermal behaviour" x
  • Refine by Access: All Content x
Clear All

Abstract  

Thermal gravimetric (TG) and differential thermal (DTA) analyses were performed to characterize the thermal behavior and the stoichiometry of uranyl bis-1,3-diketonate complexes (R1COCR2COR3)2 UO2 x H2O, where R1,3=CH3; C2H5; C6H5; CF3; pNO2−C6H4; pCl−C6H4; pMe−C6H4; NH−C6H5; R2=H, C6H5 andx=1; 2. Based on the data obtained, a thermal degradation mechanism for each complex was proposed. The final degradation product for all studied complexes was U3O8 oxide. The temperature of the first organic fragment rupture including the U-O (ligand) bond was taken as criterion for the thermal stability of the metal-oxygen donor bond in these complexes. The observed stability order is in good agreement with the IR determined constant force values,k, of the U-O (ligand) bond.

Restricted access

The thermal behaviour of some 2-benzylamino-2-deoxyheptonic acids obtained from 2-benzylamino-2-deoxy-D-glycero-L-gluco, 2-benzylamino-2-deoxy-D-glycero-D-ido and 2-benzylamino-2-deoxy-D-glycero-D-taloheptononitriles (reported) previously has been studied in air (static atmosphere) and N2 (dynamic atmosphere, flow rate 200 ml/min).

Restricted access

Abstract  

The thermal behaviour (from 20 to 500°C) of high-molecular polyoxyethylene-urea mixtures which formed a molecular complex was investigated by means of a derivatograph. Under the conditions of the investigation, there were no indications of an interaction between the thermal decomposition products and the initial components, or of new intermediates with a thermostabilizing effect. A linear coorelation was obtained between the mass loss at 250°C and the urea content of the mixture, which may be used to determine the urea content of similar mixtures.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Jinn-Shing Lee, Chung-King Hsu, Li-Kuo Lin, Chih-Long Chang, Shich Borjinn, and Chin-Wang Huang

Abstract  

Vitreous solder glasses, such as Mansol #40 and FEG-2002, are commercialized solder glasses, which are compression sealing glasses that can be used to solder materials with expansions between 55-68⊙10-7C-1, such as Al2O3. In order to understand and tailor the thermal behaviour of solder glasses, cylindrical-like glasses were first carefully ground with a stainless steel mortar and pestle. Initially, no exothermic or endothermic data were obtained from the DTA/DSC curves except those relating to melting. However, exothermic peaks appeared after the glass samples were re-melted. In this work, kinetic parameters such as the activation energy, and the morphology of the devitrification mechanisms for two kinds of solder glasses were also investigated, using non-isothermal DTA techniques. The activation energies ranged from 220 to 235 kJ mol-1 and the devitrification mechanism parameters were close to 1. This indicates that the devitrification mechanisms of the two kinds of solder glasses involve surface nuclei.

Restricted access

Investigation of the complex thermal behavior of fats

Combined DSC and X-ray diffraction techniques

Journal of Thermal Analysis and Calorimetry
Authors: G. Keller, F. Lavigne, C. Loisel, M. Ollivon, and C. Bourgaux

The thermal behavior of three ural fats (displaying very different composition), cocoa butter (CB)2, lard, and a stearin obtained from anhydrous milk-fat (AMF) fractionation, were studied by both DSC and X-ray diffraction as a function of temperature (XRDT). To perform temperature explorations between −30‡C and +80‡C, at rates identical to those used for DSC and ranging from 0.1 K min−1 to 10 K min−1, a new set of X-ray sample-holders, temperature-controlled by Peltier effect, has been developed. It is shown that the three more stable polymorphic forms of CB were easily characterized by either X-ray diffraction or DSC, and existence of two Β-3L forms was confirmed. On the contrary, the more complex polymorphism of lard and AMF required combined examination by DSC and XRDT and the brightness of the synchrotron source for studies at the highest heating rates. Quantitative analysis of the long spacings of XRDT recordings is invaluable for interpretation of thermal events. For instance, it was found that the simultaneous formation of two polymorphic forms, of apparent long spacing of 34 and 42 å, at the onset of lard crystallization might explain the difficulty of its fractionation.

Restricted access

Abstract  

The western region of the Deccan Volcanic Province (DVP) is constituted of tholeiitic lava flows. They host numerous cavities, varying in size and shape, largely occupied by zeolites and a variety of secondary minerals, amongst which the fibrous zeolites (natrolite group), are particularly gorgeous and attractive. Scolecite and mesolite are the only two members commonly occurring in this region. Our data on their thermal behaviour significantly differs from that reported in previous literature. Scolecite, Ca8(Al16Si24O80)·24H2O shows three distinct steps instead of two and water loss is observed even beyond 550°C. It is held that the first step corresponds to the expulsion of water from the site farthest away from Ca and the next two steps in succession correspond to the two sites nearer to Ca. Mesolite, Na16Ca16(Al48Si72O240)· 64H2O has much more complex behaviour with four or five steps of water expulsion and a major loss around 248–270°C in a double reaction attributed here to the expulsion of water from scolecite type channels. It is further held that the natrolite type channels are emptied in further steps. Loss of water in steps even beyond 400°C is particularly noted and such reactions are well reflected in the TG and the DTG. Peak temperature dependence on sample amounts is also evident. Successive phase transformations above 700°C, up to 1000°C are reflected in the DTA curves.

Restricted access

The thermal behaviour of single-crystals of the title compound has been investigated by means of thermal methods supported by optical microscopy. A complex change takes place on heating. After the loss of the two water molecules, leading to an amorphous phase, recrystallization takes place. This results in a solid (probably an anhydrous form) which reacts further, through partial liquefaction, to yield a red crystalline product whose structure has been characterized via X-ray powder spectra and electronic and IR spectroscopy.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: Mihaela Badea, Rodica Olar, Dana Marinescu, Veronica Lazar, Carmen Chifiriuc, and Gina Vasile

Abstract  

This paper reports the investigation on the thermal stability of new complexes with mixed ligands of the type [Cd(NN)(C3H3O2)2(H2O)m]·nH2O [(1) NN: 1,10-phenantroline, m = 1, n = 0; (2) NN: 2,2′-bipyridine, m = 0, n = 1.5 and (C3H3O2): acrylate anion]. The IR data indicate a bidentate coordination mode for both heterocyclic amine and acrylate. The in vitro qualitative and quantitative antimicrobial activity assays showed that the complexes exhibited variable antimicrobial activity against planktonic as well as biofilm embedded Gram-negative (Escherichia coli, Klebsiella sp., Proteus sp., Salmonella sp., Shigella sp., Acinetobacter boumani, Pseudomonas aeruginosa), Gram-positive (Bacillus subtilis, Staphylococcus aureus) and fungal (Candida albicans) strains, reference and isolated ones from the hospital environment. The thermal behaviour steps were investigated in synthetic air flow. The thermal transformations are complex processes according to TG and DTA curves including dehydration, amine as well as acrylate thermolysis. The final products of decomposition are the most stable metal oxides.

Restricted access

Natural montmorillonite was pillared by various polyhydroxy cations. The resulting pillared layer clays (PILCs) were characterized by X-ray fluorescence, X-ray diffraction (XRD) and infrared (IR) spectroscopies. The thermal behaviour of Al-PILC was investigated in detail by a combonation of XRD, derivatography IR spectroscopy and a comparison to natural montmorillonite is given. It was found that thermal stability of Al-PILC is lower than that of natural montmorillonite. However, heat treatment in the stability region results in significant sintering of natural montmorillonite, while the interlayer spacing of Al-PILC is hardly affected.

Restricted access

The paper deals with the thermal behaviour of trimethoxy silane (MTS) modified ethyl methacrylate (EMA) and butyl methacrylate (BMA). Several copolymer samples were prepared by varying the molar ratio of MTS with respect to EMA or BMA. The copolymerisation was carried out at 78 °C for 120 min using benzoyl peroxide as an initiator. Incorporation of MTS in alkyl methacrylates resulted in an increase in thermal stability. Hydrolytic cross-linking of copolymer having higher mole fraction of MTS gave a cross-linked product with better thermal stability.

Restricted access