Thermal reaction of clCH2CONH2 in molten acetamide

Mixtures composed of amides and electrolytes exhibit interesting properties such as viscoelastic behaviour and a megavalue of the dielectric constant. In order to improve the dielectric properties, the authors are investigating a large number of molten mixtures of CF₃COONa with different types of amides, including the ternary system sodium trifluoroacetate-chloroacetamide-acetamide. The experimental measurements showed that the ternary mixtures are thermally unstable. A yellow oily product is formed; this was purified and tested by means of IR and NMR techniques. The formula and the kinetic mechanism are proposed.     

Surface tension of talc and talc-chlorite mixtures

It is possible to estimate surface tension of high-energy solids combining the immersion microcalorimetry thermodynamics and Van Oss' model. In this study we have applied this method on talc and talc-chlorite samples in order to obtain thermodynamic values which permit to understand surface properties useful in the industrial applications of these solids. Some talcite samples are preferentially used in specific industrial applications because they are less hydrophobic or more lamellar. This method seems to be reliable to classify the solids and predict some properties.     

Behavior of iodododecane in nuclear fuel reprocessing

By simulation experiments with a 10^–5 mol/l solution of iodododecane labeled with¹³¹I in n-dodecane the influence of various materials and conditions, which are possible in nuclear fuel reprocessing, has been investigated. The formation of decomposition products was detected via HPLC with a radioactivity monitor. By means of²⁵²Cf plasma-desorption mass spectrometry (PDMS) the decomposition products were identified. It was found that a temperature of 100°C favored the formation of iodoalkanes with chain lengths of C₁ to C₁₁. The presence of TBP(tri-n-butyl-phosphate) accelerated the decomposition of iodododecane. In pure TBP only iodobutane was formed as a decomposition product.     

Manifestation of biquadratic coupling in the smectic C* phase soft mode dielectric response

The soft mode dielectric response of three ferroelectric chiral smectic C* substances is studied in the vicinity of the smectic C*-smectic A* phase transition. For some substances the soft mode dielectric strength exhibits a pronounced anomaly in the C* phase just below the phase transition. We show how this anomaly can be systematically correlated with a corresponding anomaly in the experimentally determined ratio of spontaneous polarization over tilt. By comparing the experimental results with the theoretical predictions of an extended Landau model, we demonstrate how the crossover behaviour of the system can be interpreted as being the consequence of the presence of a biquadratic coupling between tilt and polarization in the Landau free-energy of the system.     

Working Methods Paper: Critical considerations with respect to the identification of tin species in the environment

Biogeochemical pathways of tin species in the environment are still controversial, e.g. with regard to methylation and transmethylation phenomena, owing to the fact that the identification of methylated tin-compounds is often difficult. The previous tentative identification of a mixed methylbutyltin compound in sediment and biological samples by GC/AAS after hydride generation gave an illustration of this problem. This compound was previously identified in sediments by other authors and also suspected to occur in a contaminated sediment sample from the Boyardville Marina, France. The retention time obtained by GC/AAS corresponded to the actual retention time of a mixed methylbutyltin calibrant. However, additional checks demonstrated that the compound detected was actually monophenyltin. This evidence was produced by a thorough analysis of a selected sediment sample by alternative techniques such as GC/AAS and GC/AES after pentylation, GC/FPD and GC/MS. The results presented highlight the need for a full identification of compounds to avoid mis-interpretation.     

Kinetic model for hydrocarbon-assisted particulate boron combustion

A kinetic model is presented to describe the high temperature (1800 K < T < 3000 K) surface oxidation of particulate boron in a hydrocarbon combustion environment. The model includes a homogeneous gas-phase B/O/H/C oxidation mechanism consisting of 19 chemical species and 58 forward and reverse elementary reactions, multi-component gas-phase diffusion, and a heterogeneous surface oxidation mechanism consisting of ‘elementary’ adsorption and desorption reaction steps. Thermochemical and kinetic parameters for the surface reactions are estimated from available experimental data and/or elementary transition state arguments. The kinetic processes are treated using a generalized kinetics code, with embedded sensitivity analysis, for the combustion of a one-dimensional (particle radius), spherical particle. Model results are presented for the oxidation of a 200 μm boron particle in a JP-4/air mixture at ambient temperatures of 1400 K and 2000 K. These results include temperature and gas-phase species profiles as a function of radial distance and particle burning rates. © 1994 John Wiley & Sons, Inc.     

Kinetics and mechanism of the thermal decomposition reaction of acetone cyclic diperoxide in the gas phase

The kinetics of the thermal decomposition reaction of gaseous 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (ACDP) in the presence of n-octane was studied in the 403.2–523.2 K temperature range. This reaction yields acetone as the organic product. Under optimum conditions, first-order kinetics were observed, included when the S/V ratio of the Pyrex reaction vessel was increased by a nearly six-fold factor. In the range 443.2–488.2 K the temperature dependence of the rate constants for the unimolecular reaction in conditioned vessels is given by In k₁/(s^?1) = (31.8 ± 2.5) ? [(39.0 ± 2.5)/RT]. The value of the energy of activation in kcal/mol correspond to one O? O bond homolysis of the ACDP molecule in a stepwise biradical initiated decomposition mechanism. At the lower reaction temperatures as well in preliminary experiments participation of a surface catalyzed ACDP decomposition process could be detected. © 1994 John Wiley & Sons, Inc.     

Pourquoi, pour qui enseigner les mathématiques? Une mise en perspective historique de l’évolution des programmes de mathématiques dans la société française au XXe siècle

Evolutions of mathematical curricula in French society have been marked by the successive answers intitutions have given to the following question since one century: Why and whom teaching mathematics? Here I present two of these, one given in 1908 and one in 1967. Each symbolises a breaking period of reforms in secondary mathematics teaching in France. We will see in the two first part of this paper that they belong to two different worlds, with social, institutional, ideological and mathematical specific features. In the third part, I’ll focus on geometry, showing the effects of the different answers concerning the public and the aims of mathematical teaching.     

Thermoelectric properties of tin clathrates under hydrostatic pressure

We report the temperature dependence of electrical resistance (R) and thermopower (S) of clathrate Cs₈Sn₄₄ under high pressure up to 1.2 GPa. We observe a reversible gap widening, prominent relaxation effect of R, irreversible increase of |S| under high pressure. We also find that the power factor S²σ (σ: electrical conductivity) reaches a maximum at pressure of 0.3 GPa. Comparison of the experimental results with band structure calculations suggests that the intrinsic vacancy in the clathrate structure of Cs₈Sn₄₄ plays an important role in transport properties under high pressure. Measurements on Cs₈Zn₄Sn₄₂, a clathrate which has defects other than vacancies, are compared with Cs₈Sn₄₄. The results indicate that replacing Sn by Zn has similar effect as the intrinsic vacancy on S.