Kinetics and mechanism of thermal decomposition of lead carbonate

Results are given on the kinetics and mechanism of the processes in the thermal decomposition of lead carbonate with the application of TG and DTA experimental investigation methods.The following mechanism was established: 3 PbCO₃=2 PbO.PbCO₃+2 CO₂ (1) 2 PbO.PbCO₃=3 PbO+CO₂ (2) PbO — melting (3)The following activation energy values were determined with TG methods for processes (1) and (2): 118.2 and 235.2 kJ/mole, respectively; and with DTA methods for processes (1), (2) and (3): 113.9, 246.6 and 294.9 kJ/mole, respectively.

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Zusammenfassung Die an Hand der TG- und DTA-Untersuchungen erhaltenen Ergebnisse über Kinetik und Mechanismus der bei der thermischen Zersetzung von Bleicarbonat auftretenden VorgÄnge werden beschrieben.Die folgenden Mechanismen des Vorganges wurden festgestellt: 3 PbCO₃=2 PbO.PbCO₃ + 2 CO₂ (1) 2 PbO.PbCO₃=3 PbO + CO₂ (2) PbO — Schmelzen (3)Die folgenden Werte der Aktivierungsenergie wurden durch TG-Versuche für die VorgÄnge (1) und (2) bestimmt: 118.2, bzw. 235.2 kJ/Mol, und durch DTA-Messungen für die VorgÄnge (1), (2) und (3): 113.9, 246.6, bzw. 294.9 kJ/Mol.

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Résumé La cinétique et le mécanisme des réactions qui se déroulent lors de la décomposition thermique du carbonate de plomb ont été étudiés par TG et ATD. Les mécanismes suivants ont été établis: 3 PbCO₃=2 PbO.PbCO₃+2 CO₂ (1) 2 PbO.PbCO₃=3 PbO + CO₂ (2) PbO — fusion (3)Pour les réactions (1) et (2), les valeurs de 118.2 et 235.2 kJ · mol^–1 ont été trouvées à partir des résultats TG et pour les réactions (1), (2) et (3) l'ATD a fourni respectivement 113.9, 246.6 et 294.9 kJ · mol^–1.

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, . : 3 ₃=2 PbO.PbCO₃+2 ₂ (1) 2 PbO.PbCO₃=3 +O₂ (2) — (3) (1) (2), 118.2 235.2 /. (1), (2) (3) : 113.9; 246.6 294.9 /.

     

Zirconium-catalyzed enantioselective [3+2] cycloaddition of hydrazones to olefins leading to optically active pyrazolidine, pyrazoline, and 1,3-diamine derivatives

Asymmetric [3+2] cycloaddition of hydrazones to external olefins has been successfully conducted in high yields with high enantioselectivities using a chiral zirconium catalyst. These reactions open ways to synthetically and biologically important pyrazoline, pyrazolidine, and 1,3-diamine derivatives. Further, several experiments suggested that the reactions proceeded via concerted pathways.     

Characterization of micellar systems by the conductivity method; Sodium salt of perfluoropolyether carboxylic acid

A new method for the interpretation of the conductivity of ionic surfactants is proposed. The model considers the contribution of ions and of charged micelles, and is based on the approximation of constant concentration of surfactant chains above the critical micellization concentration (CMC), and on the equilibrium constant of counterion bindings to the micelles (K). These two parameters evaluated for aqueous solutions of sodium salt of perfluoropolyether carboxylic acid are as follows:K=35800 dm³ mol^–1; CMC=1.19×10^–3 moldm^–3. The third quantity obtained by this procedure is the product of the aggregation number (N) and the size parameter (f=e ² L/6r):Nf=76.5 S cm² mol^–1.     

Axial chirality control of tropos BIPHEP-Rh complexes by chiral dienes: synergy effect in catalytic asymmetric hydrogenation

Diastereopure tropos Rh complexes bearing not only BIPHEP but also chiral dienes can be employed as highly enantioselective hydrogenation catalysts for an olefinic substrate.     

Similarity analysis of protein sequences based on the normalized relative-entropy

Based on the classification of 20 amino acids, we reduce a protein primary sequence to six (0,1) sequences. For each of them, two so-called normalized relative-entropies are calculated and thus a 12-D vector is constructed to describe the protein primary sequence. The examination of similarities/dissimilarities among eight different proteins illustrates the utility of the approach.     

Effect of H<Subscript>2</Subscript>SeO<Subscript>3</Subscript> on the early stages of nucleation and growth during Cu electrocrystallization in acidic medium on glassy carbon electrode

The early stages of Cu electrodeposition onto a GC electrode were investigated in 0.5 M H₂SO₄ + 0.01 M CuSO₄ solution without or with H₂SeO₃ when a molar concentration ratio [Cu(II)]/[Se(IV)] was 1.10⁴ to 2.10². The H₂SeO₃ solution in 0.5 M H₂SO₄ was also used. The electrochemical techniques such as cyclic voltammetry and chronoamperometry and structural investigation using ex situ AFM were applied to study the nucleation and growth of Cu onto a GC electrode. Chronoamperometric results were shown to follow an instantaneous 3D nucleation and diffusion-controlled growth model by Scharifker and Hills. The values of number of Cu nuclei N and average nuclei radius r _av were calculated. It was shown that, in the presence of H₂SeO₃ in amounts of 0.001 to 0.005 mM, N increases and r _av decreases. At higher concentrations of the additive, the changes of these parameters with the deposition potential E _dep were shown to be somewhat more complex. The dependences of N and r _av on the concentration of H₂SeO₃ in different regions of Cu overpotentials were also revealed.     

Barycentric coordinates for Lagrange interpolation over lattices on a simplex

In this paper, a (d?+?1)-pencil lattice on a simplex in ${\mathbb{R}}^d$ is studied. The lattice points are explicitly given in barycentric coordinates. This enables the construction and the efficient evaluation of the Lagrange interpolating polynomial over a lattice on a simplex. Also, the barycentric representation, based on shape parameters, turns out to be appropriate for the lattice extension from a simplex to a simplicial partition.     

Intramolecular energy transfer in a tetra-coumarin perylene system: influence of solvent and bridging unit on electronic properties

The synthesis and characterisation of a novel coumarin donor-perylene bisimide acceptor light-harvesting system is reported, in which an energy-transfer efficiency of >99% is achieved. Comparison of the excited-state properties of the donor-acceptor system with model compounds revealed that although the photophysical properties of the perylene bisimide acceptor unit are affected considerably by the nature of the substituent at the imide positions and the solvent employed, through-bond interaction between the donor and acceptor units is negligible. Energy transfer in the present system can be described as occurring via a through-space energy-transfer mechanism. Careful consideration of the redox properties of the donor relative to the acceptor units allows for avoidance of potentially deleterious excited-state electron-transfer processes.