Ordre chimique dans les alliages metalliques liquides

Due to improvements of high temperature calorimetry, the quantity of liquid alloys showing large negative departures from ideality increased strongly during the last decades. Such a behaviour is now explained by the occurence of chemical short-range order (CSRO), the stoichiometry of which is often elucidated from direct structural determinations as well as from modelization of the thermodynamic functions. In some extreme cases, the destruction of CSRO by increasing temperature lead to a genuine second order transition. The short rewiev of experimental results concerning the variation of physical properties of some liquid alloysvs. temperature and concentration agrees well with CSRO. Some examples of structural determination of CSRO in metallic melts are given. Finally, links between CSRO and phase diagrams and between CSRO and glass-forming ability are also examined.     

Methode calorimetrique de mesure des enthalpies de formation des alliages liquides a forte tension de vapeur

The heat effects corresponding to the dissolution of solid PbSe in liquid Pb-Se alloys starting from pure Pb were measured with a direct reaction calorimeter. The partial enthalpy of formation of PbSe in the melt and the integral enthalpy of formation of the Pb-PbSe system in the liquid state referred the liquid Pb and PbSe were deduced. Then, from a very simple change of reference state, and in the knowledge of the enthalpy of PbSe, the integral enthalpy of formation of Pb-Se liquid alloys with reference to pure liquid components could be derived. The results agreed very well with those obtained previously on the dissolution of Se in Pb. The method used can be applied whenever the component to be added to the bath has a high vapor pressure.

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Zusammenfassung Die bei der Überführung von festem PbSe in flüssige Pb-Se-Legierungen auftretenden Wärmeeffekte wurden mittels direkter Reaktionskalorimetrie bestimmt. Die auf flüssiges Pb und PbSe bezogene partielle Bildungsenthalpie des Pb-PbSe-Systems im flüssigen Zustand wurde ermittelt. Durch eine geringfügige Veränderung des Referenzzustandes konnte bei Kenntnis der Enthalpie von PbSe die integrale Bildungsenthalpie von flüssigen Pb-Se-Legierungen in Bezug auf die reinen Komponenten abgeleitet werden. Die Ergebnisse stimmen gut mit denen überein, die früher für die Auflösung von Se in Pb erhalten wurden. Die Methode ist anwendbar, wenn dem Bade zuzugebende Komponenten einen hohen Dampfdruck haben.

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Pb-Se Pb-Se, . Pb-Se Pb-PbSe Pb Pb-Se. PbSe, Pb-Se . , . , .

     

Etude thermodynamique de la décomposition thermique des hydroxynitrates de zinc

The reaction scheme of thermal decomposition for four zinc hydroxynitrates was investigated by means of differential scanning calorimetry, thermogravimetry, mass spectrometry, and radiocrystallography. The thermal transformation of Zn(OH)(NO₃) · H₂O and of Zn₃(OH)₄(NO₃)₂ involves the formation of gaseous water and nitric acid from an actual chemical reaction. This reaction is not observed for Zn₅(OH)₈(NO₃)₂ · 2H₂O and Zn₅(OH)₈(NO₃)₂. These results show that the formation of gaseous nitric acid molecules inside the solids is specific to hydroxynitrates of divalent metals M, whose lamellar crystalline structure is characterized by a stacking of hexagonal close-packed layers of formula MX_2+m, where m = 0 or 1 and X = OH^?, H₂O, or NO^?₃.     

Etude thermodynamique de la decomposition thermique des hydrates du chlorure de magnesium

The thermodynamic study of the different compounds of the system MgCl₂, H₂O, HCl allows to draw the stability diagram of the 8 solid phases into a three-dimensional space (temperature, total pressure and ratio of HCl and H₂O partial pressures). The evolution of the composition of solid and gaseous phases during an isobaric heating is described. The conclusions of this study are in good agreement with the experimental results obtained in laboratory and with the industrial requirements set for the different steps of the dehydration of MgCl₂.     

Etude thermodynamique des oxydes TiO2−x a 1050°C

g_O2^M (O/Ti) and h z (O/Ti) have been directly measured at 1050°C within the whole homogeneity range of the rutile phase TiO_2?x, respectively, using the method of equilibration between oxides and buffer gaseous mixtures and by means of a high temperature microcalorimeter. These results are discussed in terms of point defects.     

Etude thermodynamique du systeme plomb—selenium par calorimetrie

The enthalpy of formation of PbSe liquid alloys was measured at nine temperatures by direct reaction calorimetry (drop method) for 0 < x_Se < 0.5 and 883 < T < 1365 K. The enthalpy of formation is strongly negative in the whole range investigated. It is not dependent on the temperature when x_Se < 0.3 but increases strongly with temperature when 0.3 < x_Se < 0.5 (ΔC_p,max ?90 J K^?1 mol^?1 at x_Se = 0.5).     

Etude par analyse thermique différentielle des transformations ordre-désordre dans des alliages or-cuivre riches en or

By differential thermal analysis of some Au-Cu alloys the order-disorder transformation AuCu I? AuCu II of the compound AuCu is shown to be a first order transformation accompanied by a variation of enthalpy. This method has also allowed to detect a certain order in alloys with more than 75 at-% Au.     

Analyse thermique des alliages amorphes de Ni-P et Ni-B

Résumé Les alliages de nickel-phosphore et de nickel-bore préparés pour oxydo-réduction en phase liquide sont dans leur état initial amorphes ou imparfaitement cristallisés.Au cours d'un traitement thermique approprié, une diffusion atomique précède la cristallisation du nickel, des phosphures ou des borures de nickel.Les différentes étapes de l'évolution structurale des alliages sont suivies par ATD et par diffraction X.L'évolution de la résistivité électrique de ces mêmes alliages, au cours de montées linéaires en température, confirme les résultats obtenus par ATD et diffraction X.

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The nickel-phosphorus and nickel-boron alloys prepared for oxidation-reduction in the liquid phase are amorphous or perfectly crystallized in their initial form. An atomic diffusion precedes the crystallization of nickel, nickel phosphides or nickel borides in the course of appropriate thermal treatment. The different stages of the structural development of the alloys were followed by DTA and X-ray diffraction. The changes in the electrical conductivities of the same alloys as a function of linearly increasing temperature confirmed the results obtained with the aid of DTA and X-ray diffraction.

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Zusammenfassung Die für Oxydoreduktionszwecke in flüssiger Phase hergestellten Nickel-Phosphor und Nickel-Bor Legierungen sind in ihrem Ausgangszustand amorf oder teilkristallin.Im Laufe einer geeigneten thermischen Behandlung geht der Kristallisation des Nickels, der Nickelphosphide und Nickelboride eine atomare Diffusion voraus.Die verschiedenen Stufen der strukturellen Entwicklung der Legierungen werden mittels DTA und Röntgendiffraktion verfolgt.Die Verfolgung des elektrischen Widerstands der Legierungen bei linearen Temperaturanstiegen bestätigte die mittels DTA und Röntgendiffraktionen erhaltenen Ergebnisse.

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- , - , . , . . - , , .

     

Mecanismes de durcissement structural des alliages plomb-cadmium (etain,argent) pour grilles de batterie I- alliages plomb-cadmium

The reequilibration of supersatured Pb-Cd alloys was studied by different experimental methods: hardness measurements, optical and electron microscopy, electron microprobe. Two structural states were considered: as-cast alloys, rehomogenised alloys. The Cd contents were 1, 1.5, 2 and 3.2 weight%. The explored temperatures were 20 and 80 °C. This last temperature corresponds to the curing temperature of battery's grids and to the highest operating temperature. The evolution of the quenched structure towards the equilibrium state was studied for the time range one minute to one year. The corresponding aging is characterized by a continuous precipitation and a discontinuous transformation. The hardening process is followed by an overaging which consists of a discontinuous transformation with a reprecipitation of the Cd from the fine hardening precipitates of the same phase.     

Influence des chlorures et des sulfures sur la corrosion des alliages inoxydables en milieu phosphorique

The corrosion resistance of stainless alloys has been studied in 40 % phosphoric acid contaminated by chlorides and/or sulfides. The influence of temperature and impurities on the behaviour of materials was clarified by using electrochemical techniques (polarization curves). The action of Cl⁻ ions results in the local destruction of the passivity layer whereas the S²⁻ ions induce an important incease in the corrosion rate. The simultanous presence of chloride and sulfide ions increases the agressivness of the phosphoric acid medium as a result of a synergic effect.     

Étude thermochimique des alliages de gallium et de sodium

Enthalpies of mixing of liquid alloys of gallium and sodium and enthalpies of formation ΔH_f of the two compounds NaGa₄ and Na₅Ga₈ of this binary system were determined calorimetrically at 723 K. Referred to the simple constituants in the liquid state, the following values were found:

By means of quantitative thermal differential analysis, the value for the melting enthalpy of Na₅Ga₈ was found to be (13.5±0.5) kJ mol^?1.     

Dosage rapide des alliages cuivre-palladium par electrolyse a tension controlee

The optimum conditions for separation by controlled potential electrolysis were determined by linear chronoamperometry. This method can be applied to any alloy which, can be deposited on platinum electrodes. For Cu-Pd alloys, the palladium was deposited at 50° in N sulphuric acid medium at +640 mV (with respect to the normal hydrogen electrode). Copper was deposited in several stages at ambient temperature after adding hydroxylammonium chloride. For ca. 100 mg of deposited metal, the errors were less than l%; they could be reduced by using bigger samples. The two successive electrolyses required less than 3 h.     

Etude MNDO des composes conjugues enneagonaux

We present MNDO calculations of a series of nine-membered conjugated compounds. The geometries have been fully optimized. Cyclononatetraenyl and benzocyclononatetraenyl anions, nonapyrrol, and nonathiophene appear to be planar aromatic compounds. Following MNDO , nonafulvene has a planar prefered conformation, but a polyenic structure, while nonafuran and cyclononatetraene are gauche molecules. The Universal Huckel Method (UHM ), a simple all valence electron empirical technique which describes σ systems using localized MO , gives, qualitatively, the same results as the MNDO method. The quantum calculation carried out with MNDO and UHM have been used to describe the physicochemical properties of ninememberedring conjugated compounds under consideration. To our knowledge, we present here the first theoretical study dealing with nine-membered conjugated molecules.     

Etude microanalytique des phosphates de nickel

Résumé Par spectrographie d'absorption infrarouge, il a été possible d'interpréter les spectres des ortho, pyro, tri et polymétaphosphates de nickel simples et doubles, d'étudier le déplacement des bandes d'absorption par suite du remplacement partiel d'ions Ni²⁺ par des ions étrangers. Conjointement, les trois techniques expérimentales utilisées ont permis d'étudier les transformations subies par quelques uns de ces phosphates au cours de leur chauffage et de mettre ainsi en évidence la formation d'orthophosphate acide, NiHPO₄, dans certaines conditions, cette substance n'ayant pu être préparée à l'état de pureté par simple précipitation.

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Summary By means of infra red absorption spectrography, it is possible to interpret the spectra of the ortho-, pyro-, tri- and tetrapolyphosphates both simple and double, and to study the shifts of the absorption bands resulting from the partial replacement of Ni²⁺ ions by foreign ions. At the same time, the three experimental techniques employed have made it possible to investigate the transformations undergone by some of these phosphates when they are heated, and in this way reveal the formation of the acid orthophosphate NiHPO₄ under certain conditions. This material has heretofore not been obtained pure by simple precipitation.

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Zusammenfassung Durch absorptionsspektrographische Untersuchungen im Infrarot der einfachen und. Doppelsalze des Nickels mit Ortho- und Pyrophosphorsäure, Tri- und Polymetaphosphorsäure gelang es, deren Spektren zu interpretieren und die Verschiebung der Absorptionsbanden bei teilweisem Ersatz des Nickelions durch andere Ionen zu studieren. Gleichzeitig war es auf experimentellem Wege möglich, die Umwandlung einiger dieser Phosphate beim Erhitzen zu beobachten und dabei die Bildung von Nickelhydrogenorthophosphat, NiHPO₄, unter gewissen Bedingungen festzustellen. Diese Verbindung läßt sich durch einfache Fällung nicht in reinem Zustand herstellen.

     

Etude des generateurs d'indium-113m

Methods are proposed for the determination of¹¹³Sn in the eluate of an^113mIn generator as well as for the analysis of its chemical and radionuclidic purity. Two generators of different origin have been studied. The presence of the radioisotopes¹¹³Sn,¹²⁵Sb,^125mTe and the elements Zr, Si and Fe have been found in the eluate. Recommendations are given for the use of such generators.     

Etude par desorption thermique programmee des proprietes des argiles modifiees

The present work tries to emphasize the effect of acid/basis properties of montmorillonite type clays by ion exchange with cations of different natures. The acidity and basicity measuring was made by thermo programated desorption (TPD)1,2, using ammonia like basis agent and carbon dioxide like acid agent. With TPD method we can determine acid/basis proprietes by measuring of the quantity of the ammonia and carbon dioxide termodesorbed. Clays are crystalline aluminosilicates, similar with the zeolyts, who presents the property of ion exchanging. That propriety can be applicated for pollutants cations from aquatic solutions. Ion exchanging propriety depends of a lot of factors: the cation nature, the valence and the ionic ray of the cation present in the impregnated solution. That's an advantage for depollution process of heavy metals by fixing of these metals by montmorillonite structure. By using TPD metod we can obtaine a caracteristic diagram. This revised version was published online in July 2006 with corrections to the Cover Date.