Q band interferometer for high temperature measurements

A Q band interferometer for determining the complex permittivity of solids and liquids between 20°C and 1300°C has been developed. The Roberts and Von Hippel standing-wave method was used. The technique involves the utilization of a computer-assisted digital voltmeter for data acquisition and treatment. Results for a 67SiO₂–33Na₂O within the temperature range 20–400°C and in the liqid state (950°C) are presented.     

Comportement rheologique de sols d'acide polysilicique. II. Etude de la gélification

Résumé L'analyse du comportement rhéologique de sols d'acide polysilicique en solution aqueuse de concentration supérieure à 7 g 1^–1 de silice en fonction du pH entre 6 et 11 et de la température entre 25 et 45 °C a permis de situer la gélification dans un domaine de pH compris entre 8 et 10. Ce processus prend une intensité maximale à 30°C. Le comportement rhéofluidifiant à bas gradients de cisaillement et antithixotrope donne naissance sur les rhéogrammes à un point d'inversion à pH = 9. L'ionisation des groupes silanols à la surface des particules colloïdales permet la réorganisation du milieu après cisaillement. Un état d'ionisation trop élevé est responsable d'un effet electro-répulsif à pH = 10. L'influence de la concentration et de la température sur ces processus est discutée.

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The rheological behavior of polysilicic acid in aqueous solutions at higher concentrations than 7 g 1^–1 of silice is studied for pH between 6 and 11 with temperature varying from 25° to 45°C. This study indicates that gelification takes place between pH 8 and 10. The process of gel formation attains the highest intensity at 30°C. The shear-thinning behavior at low shear rate gives rise to an inversion point at pH = 9 in shear stress—shear rate curves. The state of ionization at the surface of colloïdal silice particles after shear involve shear thickening observed at pH = 9. A high ionization degree causes an electrostatic repulsion at pH = 10. The concentration and temperature effects upon the organization of network are discussed.

     

Fast dynamic Kerr-effect of lysozyme in solution

Dynamic Kerr effect and dielectric relaxation measurements were carried out for lysozyme at pH 4.7 and pH 7.7. From high dilution measurements we compute the shape of hydrodynamically equivalent ellipsoïd. Relaxation times corrected for viscosity effect are temperature dependent : this implies slight molecular shape variation. Denatured lysozyme relaxation is also observed before transition temperature.     

Exhibition of surface steps by high resolution electron microscopy of monoclinic rare earth sesquioxides

On high resolution structure images, the existence of a superperiod has been observed, linked with the apparition of extraspots in the diffraction diagram. The specimen (B-Sm₂O₃) can be described as composed of layers of thickness 6 Å, nearly perpendicular to the incident electron beam. These layers are of 3 different kinds. We have shown that the apparition of the superperiod can be linked with steps of height 6 or 12 Å (i.e. 1 or 2 layers): computed images, using this hypothesis exhibit the observed superperiod, even for thicknesses around 230 Å. This allows atomic steps to be imaged with a high resolution structure image.     

Determination de microquantites de lithium serique par spectrometrie d'absorption atomique sans flamme: Optimisation des Conditions ExpérimentalesDetermination of traces of lithium in blood serum by electrothermal atomic absorption spectrometry. Optimization of experimental parameters

Electrothermal atomic absorption spectrometry is used to determine traces of lithium in blood serum; the limit of detection had to be decreased by optimizing the experimental conditions. Signal intensity and reproducibility were improved by the addition of Triton X-100 (0.1%). Other additives examined were less effective. The validity of the final method was checked by statistical tests for linearity of response and precision. The method is suitable for the determination of lithium in sera of normal subjects who have not had lithium therapy; the limits of the normal range are 2–17 μg l^?1 with a mean value of 8 μg l^?1.     

Spectres de vibration des acides cyclopentaniques C4H8CHCOOH,C4H8CHCOOD,C4H8CDCOOH,C4H8CDCOOD et de leurs sels de so

The infrared and Raman spectra of C₄H₈CHCOOH, C₄H₈CHCOOD, C₄H₈CDCOOH, C₄H₈CDCOOD and their sodium salts were studied and frequency assignments made; the ring puckering vibrations were observed in the Raman spectrum. The depolarisation values show the existence of a plane of symmetry, perpendicular to the ring compatible with a “bent” structure.