Thermal decomposition of the hydrated basic carbonates of lanthanides and yttrium in CO2 atmosphere

The hydrated basis carbonates of lanthanides and yttrium were prepared by precipitation from homogeneous solution via the hydrolysis of urea, without the addition of an auxiliary anion. Thermogravimetry, derivative thermogravimetry (TG-DTG), and differential thermal analysis (DTA) have been used in the study of these compounds in CO2 atmosphere. The results lead to the composition and thermal stability of the studied compounds, and also to a comparative study with reported results in air atmosphere. © 1993.

Thermal decomposition and stability in a series of tetrafluorborate copper(I) complexes

Tetrafluorborate copper(I) complexes containing acetonitrile, triphenylphosphine, 1,10-phenanthroline, 2,2′-bipyridine and 2-quinolinethiol have been prepared in order to study their thermal stabilities as a function of the ligands present. The characterization of the above compounds was carried out by elemental analysis and IR spectroscopy. Their thermal behaviour has been investigated and the final products were identified by X-ray powder diagrams. © 1995.

Influence of polymerization on the synthesis of SrTiO3: Part I. Characteristics of the polymeric precursors and their thermal decomposition

The influence of polymerization on the thermal decomposition of polymeric precursors and phase formation was investigated during synthesis of SrTiO3. The precipitation of polymeric precursor in acetone produced a more thermal stable precursor with lower weight loss during decomposition. This more stable precursor retarded the formation of the SrTiO3 phase. From thermal analysis, XRD and FT-IR the presence of an intermediate phase during decomposition of the precursors was observed. This is a mixed (Sr,Ti) carbonate phase with the proposed composition of Sr2Ti2O5.CO3. © 1995.

Structure and catalytic mechanism of glucosamine 6-phosphate deaminase from Escherichia coli at 2.1 Å resolution

Background: Glucosamine 6-phosphate deaminase from Escherichia coli is an allosteric hexameric enzyme which catalyzes the reversible conversion of D-glucosamine 6-phosphate into D-fructose 6-phosphate and ammonium ion and is activated by N-acetyl-D-glucosamine 6-phosphate. Mechanistically, it belongs to the group of aldose-ketose isomerases, but its reaction also accomplishes a simultaneous amination/deamination. The determination of the structure of this protein provides fundamental knowledge for understanding its mode of action and the nature of allosteric conformational changes that regulate its function. Results: The crystal structure of glucosamine 6-phosphate deaminase with bound phosphate ions is presented at 2.1 Å resolution together with the refined structures of the enzyme in complexes with its allosteric activator and with a competitive inhibitor. The protein fold can be described as a modified NAD-binding domain. Conclusions: From the similarities between the three presented structures, it is concluded that these represent the enzymatically active R state conformer. A mechanism for the deaminase reaction is proposed. It comprises steps to open the pyranose ring of the substrate and a sequence of general base-catalyzed reactions to bring about isomerization and deamination, with Asp72 playing a key role as a proton exchanger.

Thermal decomposition of some diuretic agents

Thermogravimetry-derivative thermogravimetry and differential scanning calorimetry were used to study the thermal behaviour of furosemide, hydrochlorothiazide, spironolactone, and amiloride hydrochloride. The results revealed the extents of their thermal stability and also permitted interpretations concerning their thermal decompositions. © 1996 Akadémiai Kiadó.

Thermal decomposition of some analgesic agents

Thermogravimetry, derivative thermogravimetry (TG, DTG) and differential scanning calorimetry (DSC), were used to study the thermal behaviour of mefenamic acid, ibuprofen, acetaminophen, sodium diclofenac, phenylbutazone, dipyrone and salicylamide. The results led to thermal stability data and also to the interpretation concerning the thermal decomposition. © 1996 Akadémial Kiadó.

Thermal decomposition of acetylsalicylic acid (aspirin)

The thermal decomposition of aspirin in air and dry air flux was investigated. Thermogravimetry-derivative thermogravimetry (TG-DTG), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), infrared absorption spectra and thin layer chromatography have been used to study the thermal decomposition of this compound. The results permit the identification of some compounds revealed in the first step of the TG-DTA curves, and also suggest the thermal decomposition mechanism.

Thermal decomposition of the magnesium, zinc, lead and niobium chelates derived from 8-quinolinol

Solid M-Ox compounds, where M represents Mg(II), Zn(II), Pb(II) and NbO(III), and Ox is 8-quinolinol, have been prepared. Thermogravimetry, derivative thermogravimetry (TG, DTG), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR) and infrared absorption spectra (IR) have been used to characterize and to study the thermal stability and thermal decomposition of these compounds. © 1997 Akadémiai Kiadó.

Synthesis, characterization and thermal decomposition of [Pd2 (C2-dmba) (μ-SO4) (μ-SO4) SO22]

The bridged sulphate complex [Pd2 (C2,dmba) (μ-SO4) (SO2)2] has been obtained by reacting a saturated solution of SO2 in methanol and the cyclometallated compound [Pd(C2,N-dmba)(μ-N3)]2; (dmba = N,N-dimethylbenzylamine), at room temperature for 24 h. Reaction product was characterized by elemental analysis, NMR comprising 13C{1H} and 1H nuclei and I.R. spectrum's measurements. Thermal behavior has been investigated and residual products identified by X-ray powder diffraction.

Influence of canine brain decomposition on laboratory diagnosis of rabies.

Canine brains infected with rabies virus were submitted to decomposition by being left at room temperature of 25 to 29 degrees C for up to 168 h. At 24 h intervals, brain fragments were analyzed by immunofluorescence (IF) and by the mouse intracerebral inoculation (MI) test to confirm the diagnosis of rabies and to measure the putrefaction effect on the accuracy of the diagnosis. Forty eight h after the beginning of the experiment, the MI test showed signs of impairment with four negative results, while after 72 h, 100% of the results were negative to the MI test and only one result was negative to the IF test, indicating that the threshold period for accurate diagnosis is 24 to 48 h before putrefaction. The authors recommend the shipment of suspected cases of rabies to the laboratory for confirmation, but the use of putrid materials for diagnosis is meaningless because of false-negative results.

Preparation and thermal decomposition of solid-state cinnamates of lighter trivalent lanthanides

Some new compounds of cinnamic acid with lighter trivalent lanthanides were prepared in the solid state. The compounds have general formula ML3·H2O, where L is cinnamate (C6H5-CH=CH-COO-) and M is La, Ce, Pr, Nd or Sm. Thermogravimetry, derivative thermogravimetry, differential scanning calorimetry, infrared absorption spectra and X-ray diffraction powder patterns were used to characterize and to study the thermal stability and thermal decomposition of these compounds.

Thermogravimetric studies of the decomposition kinetics of four different Hevea rubber clones using Ozawa's approach

Thermal degradation of natural rubber extracted from four different rubber clones of the Hevea brasiliensis species was investigated by thermogravimetry using Ozawa's approach to assess the kinetic parameters of the decomposition process. The results are discussed in terms of the order of reaction, kinetic parameters such as activation energy as a function of conversion degree, and thermal stability for each of the clones.

Improved activity and stability of Ce-promoted Ni/γ-A1 2O3 catalysts for carbon dioxide reforming of methane

The CO2 reforming of CH4 was carried out over Ni catalysts supported on γ-Al2O3 and CeO 2-promoted γ-Al2O3. The catalysts were characterized by means of surface area measurements, TPR, CO2 and H2 chemisorption, XRD, SEM, and TEM. The CeO2 addition promoted an increase of catalytic activity and stability. The improvement in the resistance to carbon deposition is attributed to the highest CO2 adsorption presented by the CeO2 addition. The catalytic behavior presented by the samples, with a different CH4/CO2 ratio used, points to the CH4 decomposition reaction as the main source of carbon deposition.

An active/reactive predispatch model incorporating ramp rate constraints solved by dual decomposition/lagrangian relaxation

The Predispatch model (PD) calculates a short-term generation policy for power systems. In this work a PD model is proposed that improves two modeling aspects generally neglected in the literature: voltage/reactive power constraints and ramp rate constraints for generating units. Reactive power constraints turn the PD into a non-linear problem and the ramp rate constraints couple the problem dynamically in time domain. The solution of the PD is turned into a harder task when such constraints are introduced. The dual decomposition/ lagrangian relaxation technique is used in the solution approach for handing dynamic constraints. As a result the PD is decomposed into a series of independent Optimal Power Flow (FPO) sub problems, in which the reactive power is represented in detail. The solution of the independent FPO is coordinated by means of Lagrange multipliers, so that dynamic constraints are iteratively satisfied. Comparisons between dispatch policies calculated with and without the representation of ramp rate constraints are performed, using the IEEE 30 bus test system. The results point-out the importance of representing such constraints in the generation dispatch policy. © 2004 IEEE.