Amélioration De L'aptitude Au Décochage Et Au Débourrage: Des Sables Liés Au selicate De Soude Et Durcis: Par Le Gaz Carbonique

Improvement In the aptitude to discharge and to unstop of sands binded with sodium silicate and hardened by carbon dioxide. Chemically hardened sands offer a large choice of moulding and coring processes by the use of organic and mineral compounds. The use of these binders requires a knowledge of associated risks, to obtain a reduced residual resistance (in order to facilitate the discharging and the unstopping of the parts) and for the success of the products.The aim of this study was to rationalise the utilisation conditions of sodium silicate moulded sands, with additives, hardened by carbon dioxide. This should minimize the eventual defects in the cast parts. Sand resistance is very important right after the casting; it makes more difficult the tasks of discharging and unstopping. The need to incorporate organic matter to the sands becomes a necessity. The role of the organic matter is to reduce the sand resistance. The use of silicate binder requires the identification of the mechanism of the mixture hardening by carbon dioxide. It also calls for a knowledge of the gel structure formation, and of the influence of certain parameters on the properties.The experimental part is concerned with a comparative study of the behaviour of these sands in the foundry.The factors influencing this behaviour are: grain size, carbon dioxide blowing-in time, binder rates, adjuvant ratios and mixing time, etc…A thermographie study was carried out in order to perform the experimental work in real conditions.The obtained results have led to the determination of the optimal values of the above-mentionned parameters. This allows to obtain the smallest residual resistance, hence to improve the discharging and unstopping processes.This approach is clearly exhaustive and shows all possible interactions of the adjuvants with sodium silicate and the considered sands.     

Synthèse Et Cyclisation De Carboxylsulfamides Dérivés D'amines Et D'α-Hydroxyesters. Éavaluation De L'Activité Bactéeriostatique

Abstract

Les carboxylsulfamides sont obtenus à partir de l'isocyanate de chlorosulfonyle, d'amines primaires et d'α-hydroxyesters. Après réduction alcaline, ces carboxylsulfamides sont cyclisés dans les conditions de la réaction de Mitsunobu pour conduire aux N-sulfamoyloxazolidinones chides avec des rendements élevés.

The synthesis of carboxylsulfamides was carried out starting from chlorosulfonyl isocyanate, primary amines and α-hydroxyesters. After reduction, the carboxylsulfamides were cyclised under Mitsunobu conditions giving N-sulfamoyloxazolidinones in good yields.     

Préparation Chimique,Caracterisation Cristallographique,Etudes Thermique et Vibrationnelle du Cyclotriphosphate Hexahydraté de Manganèse et de Tetra-Argent,MnAg 4 (P 3 O 9 ) 2 .6H 2 O

The cyclotriphosphate hexahydrate of manganese and silver, MnAg 4 (P 3 O 9 ) 2 .6H 2 O, was prepared by Boullé's process. MnAg 4 (P 3 O 9 ) 2 .6H 2 O crystallizes in the triclinic system, P-1, Z = 1 and its structure was determined by Rietveld's method. The refinement of 54 parameters by this method, using 1752 independent reflections leads to Rw p = 0.098, R p = 0.065 and R B = 0.033 on the basis of its isotype NiAg 4 (P 3 O 9 ) 2 .6H 2 O. The unit cell parameters of this salt are the following a = 8.824(1)Å, b = 8.485(1)Å, c = 6.609(1)Å, f = 90.30(1)°;, g = 92.89(1)°; and n = 107.28(1)°;. The thermal behavior of this new compound was studied, between 25 and 600°;C, under atmospheric pressure by infrared spectrometry, X-ray diffraction, thermal analyses TGA and DTA coupled. This study allows us the identification and the crystallographic characterization of a new phase, MnAg 2 (PO 3 ) 4 isotype of ZnRb 2 (PO 3 ) 4 , obtained between 350 and 450°;C, mixed with the long-chain polyphosphate of silver AgPO 3 . The kinetic characteristics of the dehydration of MnAg 4 (P 3 O 9 ) 2 .6H 2 O and the thermal phenomena accompanying this dehydration were determined and discussed on the basis of the proposed crystalline structure. The vibrational spectrum of the, MnAg 4 (P 3 O 9 ) 2 .6H 2 O, was examined and interpreted in the domain of the stretching vibrations of the P 3 O 9 rings, on the basis of the proposed crystalline structure and in the light of the calculation of the thirty fundamental IR frequencies for the idealized D 3h symmetry.