Determination calorimetrique des enthalpies de formation en metallurgie

The calorimetric methods used for the measurement of the enthalpy of formation of metallic systems are described and discussed. Special attention is paid to direct reaction calorimetry, dissolution calorimetry, precipitation calorimetry, combustion calorimetry... and non-reacting calorimetry is considered as an additional method from this point of view. Emphasis is placed on their particular field of application. Some recent developments are given.

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Zusammenfassung Kalorimetrische Verfahren zut Messung der Bildungsenthalpie von metallischen Systemen wurden beschrieben und diskutiert. Besondere Aufmerksamkeit wurde dabei der Hinreaktionskalorimetrie, der Lösungskalorimetrie, der Fällungskalorimetrie, der Verbrennungskalorimetrie geschenkt, Nichtreaktionskalorimetrie wurde als eine zusätzliche Methode in dieser Hinsicht betrachtet. Das spezielle Anwendungsgebiet dieser Verfahren wird hervorgehoben und einige Neuentwicklungen gegeben.

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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 . , . , .

     

Determination de l'enthalpie de formation du pentafluorotellurate iv de potassium KTeF5 par calorimetrie de reaction

The standard enthalpy of formation of KTeF₅ has been determined by reaction in a normal solution of KOH: ΔH°₂₉₈ KTeF₅ = ? 1687.37 ± 4,84 kJ.mol^?1     

Determination de l'enthalpie de formation du pentalfluorotellurate IV de rubidium RbTeF5 par calorimetrie de reaction

The standard enthalpy of formation of RbTeF₅ has been determined by hydrolysis reaction in a molar aqueous solution of NaOH or KOH as ΔH°₂₉₈f RbTeF_{5 cr} = ?1696 ± 1 kJ.mol^?1     

Determination de l'enthalpie de formation standard du tetrafluorure de tellure par calorimetrie de combustion dans le fluor et par calorimetrie de reaction

The standard enthalpy of formation of tellurium tetrafluoride has been determined: by combustion in fluorine:

by reaction in a normal solution of soda:

     

Influence des substituants sur l'activite catalytique des composes arene-chrome tricarbonyle,mise en evidence de l'imfortance d'un α-heteroatome (O,N)

Substituents bearing a heteroatom in α position to an Cr(CO)₃-complexed arene group induce a strong perturbation in the six-electron ligand—metal bond allowing an increased catalytic effiency of these derivatives under mild conditions.     

Reaction de l'acetylene dicarboxylate d'ethyle avec l'oxo-6 (2H) cyclohepta (c) pyrrole ; mecanismes de formation des adduits

The cycloaddition reactions of 6-oxo (2H) cyclohepta (c) pyrroles $\text{4a, b and c}$ with diethyl acetylene dicarboxylate an electron-deficient dienophile of relatively low LUMO energy level, afford the 1:2 adducts $\text{5a, b}{}_1\text{-b}{}_2\text{and c}$ respectively The kinetics of the reactions, investigated By ¹H NMR spectroscopy, have allowed to precise the mechanism of the addition In particular, new-intermediates, 1:2' adducts $\text{6b and c}$ have been observed and isolated for the compound $\text{6c}$.     

Etude de l'equilibre entre l'oxyde de nickel et l'oxygene. Essai d'interpretation des lois de variation de la conductivite electrique en fonction de la temperature

In a previous paper we have shown that at 740°C and under an oxygen pressure less than 1,3 torr the electrical conductance G of a NiO powder reaches rapidly an apparently stabilized signal G_i which sharply decreases after a sufficiently long time to a G₀ value independent of P_O2.From this observation we have studied the influence of the temperature successively on the electrical conductance G_i and G₀. The Arrhenius law is only verified for the G₀ = f(T) curve. G₀ appears as the representative value of the gas-solid equilibrium.     

Alcoylation par l'iodure de butyle,de l'enolate de tetrabutylammonium de l'acetylacetone; nature de l'entite reagissante

The alkylation of tetrabutylammonium acetylacetonate with butyl iodide was studied in order to specify the nature of the reactive anionic species during the nucleophilic reaction of an ambident anion, under similar conditions to those of phase transfer catalysis. The C/O alkylation ratio changes with neither the solvents nor the enolate concentration; however k_obs, varies with the solvent but does not depend on the énolate concentration. The results and spectrophotometric UV data show that only one reactive species, the ion-pair, is involved.     

Etude calorimetrique et analytique de l'adsorption du cyanogene sur la silice

The adsoprtion of C₂N₂ on well outgassed specimens of SiO₂ at temperatures from 35 to 913°C has been studied by heat flow calorimetry, volumetry, and mass spectrometry.Small amounts of cyanogen are adsorbed at low temperature: reversibly by hydrogen bonding with the silanol groups, and irreversibly on strained siloxane bridges or Lewis acid sites. Above 200°C cyanogen reacts, with silanol groups, leading to the formation of HCN (partly reversibly adsorbed on non-reacted silanol groups) and silyl isocyanate:

. The process is complete at 418°C and the measured enthalpy for the reaction

is ΔH = ?12.2 ± 0.3 kcal mole^?.Above 500°C, HCN and C₂N₂ react with ordinary siloxane bridges. At higher temperature, the pyrolysis of

produces CO₂ with CO and N₂ (in smaller quantities), showing that a large proportion of N-atoms are bonded on the surface.     

Contribution des fonctions thermodynamiques en phase vapeur et en solution à l'étude de l'équilibre conformationnel de la chloro-4 cyclohexanone

The thermodynamic properties related to the conformational equilibrium of 4-chloro cyclohexanone have been determined by n.m.r. and i.r. with two unpolar solvents CCl₂ = CCl₂ and CS₂. The predominance of a conformation is discussed by means of the enthalpic and entropic contributions of the isolated and solvated molecules: intramolecular interactions of the isolated molecules and a quadrupolar effect at the time of the solvation explain that result.     

Catalyse par des complexs σ-aryl-nickel de l'electroreduction en biaryles des halogenures aromatiques

In mixed THF/HPMA, electrochemical reduction of NiX₂L₂ (L = PPh₃, X = Cl or Br) yields a zerovalent nickel complex which reacts very rapidly with ArX (X = I, Br, Cl) by oxidative addition to give ArNiXL₂, which also is electroreducible. Thus it is possible to obtain a catalytic electroreduction of ArX which affords mainly biaryls when X = Cl. A mechanism is suggested according the various results especially with a view to explain the loss of catalytic activity. A clear indication of increasing activity is given when aliphatic bromides are added to the solutions.     

Diverses methodes d'analyse des alliages d'etain et de samarium

Several methods of analysis for tin-samarium alloys are studied: chemical analysis, X-ray fluorescence and arc spectrography. Their characteristics and the results obtained are compared. The chemical methods are most precise but are insensitive and tedious. X-Ray fluorescence is suitable for routine work and for control of alloy homogeneity. Arc spectrography is by far the most sensitive method The methods can be applied to alloys of other rare earths with tin.