The phase diagram of KNO3–RbNO3

The phase diagram of the binary system KNO₃–RbNO₃ was studied using simultaneous direct and differential thermal analysis technique and differential scanning calorimetry. This system exhibits six invariants: a eutectic at 293 °C, four eutectoïd reactions at 109, 157, 159, and 291 °C, respectively, and a peritectoïd one at 288 °C.     

Yang–Mills theory à la string

A surface of codimension higher than one embedded in an ambient space possesses a connection associated with the rotational freedom of its normal vector fields. We examine the Yang–Mills functional associated with this connection. The theory it defines differs from Yang–Mills theory in that it is a theory of surfaces. We focus, in particular, on the Euler-Lagrange equations describing this surface, introducing a framework which throws light on their relationship to the Yang–Mills equations. Dedicated to Octavio Obregón, on the occasion of his 60th birthday.     

A thermogravimetric study into the effects of additives and water vapor on the reduction of gypsum and Tunisian phosphogypsum with graphite or coke in a nitrogen atmosphere

The paper reports an investigation on the reduction of synthetic gypsum and a Tunisian phosphogypsum sample in pure nitrogen or loaded with H₂O vapor, using graphite or natural coke. Thermogravimetry analysis in non-isothermal conditions showed that H₂O gas has no effect on the onset temperature of reduction (T _red), whereas the use of coke as a carbon source lowers the T _red of about 50 °C but the reduction rate and the conversion degree into CaS are not significantly affected by the coke proportion. The activation energy and the reaction order were determined using the direct Arrhenius plot and the Coats–Redfern kinetic model. These models led to the same reaction order and to close values of activation energies. The FWO isoconversional method shows that the reduction is more complex than a one step process and leads to lower values of activation energy. Addition of 5% mass of various oxide lowered the activation energy; however, the use of the Co₂O₃/Co₃O₄ as additive seems to enhance more the reduction rate.     

Calcium hydroxyapatite solubilisation in the hydrochloric and perchloric acids

Summary Enthalpy of solution of calcium hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ (CaHap) in hydrochloric and perchloric acid solutions is measured by an isoperibol calorimeter and a C80 microcalorimeter. The former device is adapted to reactions occurring in concentrated acid solutions, whereas the microcalorimeter is suitable for slow processes happening in diluted acid solutions. Some solution mechanisms are suggested for different pH ranges. They are confirmed by complementary solution in the same solvent of the entities produced by the reaction between CaHap and the acid. These entities are CaCl₂; Ca(ClO₄)₂·nH₂O; Ca(H₂PO₄)₂ and H₃PO₄. Extrapolation of solution enthalpies to pH=7 leads to the solution enthalpy of (CaHap) in pure water, which is -406.2 kJ mol^-1 from HCl and -437.3 kJ mol^-1 from HClO₄.     

Kinetics and thermodynamics of the attack of a phosphate ore by acid solutions at different temperatures

A calorimetric study of the kinetics and thermodynamics of the attack of a phosphate ore from Gafsa region (Tunisia) by phosphoric acid and by a mixture of phosphoric acid and sulfuric acids is undertaken at different temperatures. Two samples of the same ore having different grain size have been used. At 25 °C, the dissolution enthalpy in phosphoric acid solution equals −233.6 ± 2.2 J/g for both of the samples. Attack by the mixture of acids is strongly dependent on the solid granulometry. Interpretation of the calorimetric results by Avrami model shows the existence of three domains attributed to phosphate ore dissolution/H₂PO₄⁻ neutralisation, hemihydrate (HH) precipitation and hemihydrate/dihydrate (DH) transformation. The attack by the acid mixture was performed at higher temperatures and showed in addition the transitional formation of the anhydrous sulfate (AH) at T ≥ 55 °C, which transforms into dihydrate after the HH/DH transformation.     

Diagramme De Phases Du Systeme Binaire CsNO3—LiNO3. Activité des constituants du liquide

Phase diagram of the binary system CsNO₃–LiNO₃ has been drawn by using simultaneously direct and differential thermal analysis between 323 and 723 K. This system is characterized by a congruent intermediate equimolar compound with melting point at 463 K, two eutectic reactions at 447 and 433 K; the eutectic points are respectively at 0,47 and 0,63 mol fraction of LiNO₃; a plateau due to the phase transition of CsNO₃ at 428 K and an other one at 333 K due to the formation of CsLi(NO₃)₂. The miscibility in solid state seems to be nil or negligible. These results associated with some other thermodynamic data have been used to calculate the activities of the constituents along the liquidus curve and the activities of the liquid constituents at 723 K. The binary liquid (Cs–Li)NO₃ exhibits a negative deviation from the ideal behaviour.This revised version was published online in November 2005 with corrections to the Cover Date.     

Scalable Synthesis and Cancer Cell Cytotoxicity of Rooperol and Analogues

Plant polyphenols, such as the African potato (Hypoxis hemerocallidea)-derived bis-catechol rooperol, can display promising anticancer activity yet suffer from rapid metabolism. Embarking upon a program to systematically examine potentially more metabolically stable replacements for the catechol rings in rooperol, we report here a general, scalable synthesis of rooperol and analogues that builds on our previous synthetic approach incorporating a key Pd-catalyzed decarboxylative coupling strategy. Using this approach, we have prepared and evaluated the cancer cell cytotoxicity of rooperol and a series of analogues. While none of the analogues examined here were superior to rooperol in preventing the growth of cancer cells, analogues containing phenol or methylenedioxyphenyl replacements for one or both catechol rings were nearly as effective as rooperol.     

A numerical algorithm for the nonlinear Timoshenko beam system

An initial boundary value problem is considered for the dynamic beam system Its solution is found by means of an algorithm, the constituent parts of which are the finite element method, the implicit symmetric difference scheme used to approximate the solution with respect to the spatial and time variables, and also a Picard type iteration process for solving the system of nonlinear equations obtained by discretization. Errors of three parts of the algorithm are estimated and, as a result, its total error estimate is obtained. A numerical example is solved.