bluuebunny/crossref_metadata_2025_split huggingface dataset:
Étude du composé d'addition Hg(CN)2.0,80 tétrahydrofuranne. Morphologie et données préliminaires sur la structure cristalline
Authors: Ledésert Margaret , Frey Michel , Monier Jean-Claude 
Published: March 2019

De nombreuses études ont été effectuées pour déterminer le rôle de l'adsorption sur la morphologie cristalline et déduire les mécanismes structuraux qui peuvent intervenir lors de la croissance en solution. Dans le cadre d'une contribution à ces travaux, nous avons entrepris l'étude du solvate Hg (CN)₂ . 0,80 tétrahydrofuranne.
On indique la morphologie de ce composé ainsi que l'étude préliminaire de sa structure (caractéristiques de la maille, groupe spatial, positions des atomes de mercure) .
Contribution à l'étude des transformations hydrothermales des minéraux sulfurés
Authors: Maurel Colette 
Published: March 2019

Reactions between sulphide minerals and aqueous solutions containing metallic salts (Ag, Bi, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) were studied experimentally at 100 and 200° C.
Three essential reaction types were distinguished :
— simple exchange reactions between the metal in the sulphide and that in solution ;
— oxido-reduction reactions producing a sulphide higher in metal content than the initial sulphide with the formation of acid in the solution ;
— oxido-reduction reactions proceeding in the opposite sense : the action of sulphuric acid leads to a sulphide lower in metal content than the initial sulphide.
Qualitative previsions on the direction in wich a reaction will proceed are possible by means of thermodynamic calculations.
Complex transformations are explained by the superpositions of a few simple reactions. The application to natural cementation phenomena is considered.
Étude d'une uraninite provenant de la pegmatite de Rajasthan (Inde)
Authors: Choudari R. , Kosztolanyi Charles , Coppens René 
Published: March 2019

Les études ont été faites sur une uraninite pegmatitique provenant de la mine de mica de Bhunas à Rajasthan ou Rajputana (Inde).
Cet article est le résultat des mesures physiques, d'une analyse chimique complète, d'analyses aux rayons X, ainsi que la détermination de l'âge du minéral par la méthode du plomb. L'étude révèle qu'il s'agit d'un cristal d'uraninite (distance réticulaire : 5,472 ± 0,002 Å), minéral idéal pour la détermination d'âge par les isotopes. L'âge absolu de ce minéral se situe aux environs de 906 ± 20 M. A.
La structure cristalline de la chervétite
Authors: Kawahara Akira 
Published: March 2019

Chervetite Pb₂V₂O₇ is monoclinic, space group P2₁/a with the following unit cell parameters : a = 13.37, b = 7.16, c = 7.11 Å, ß = 106°.
The positions of the lead atoms were determined from (010) and (001) Patterson projections. Vanadium atoms were found by difference series projected on the same planes. Three-dimensional difference series were needed to locate the oxygen atoms. The atomic positions of all atoms were refined by least squares method (R = 0.21).
The structure shows V₂O₇ groups in which the vanadium atoms are at the centre of two oxygen tetrahedra which share a corner. The V-O distances lie between 1.65 and 1.88 Å.
Eight and nine oxygens surround the Pb(1) and Pb(2) atoms respectively, with Pb˗O distances between 2.24 and 3.20 Å.
In order to refine the oxygen positions it would be desirable to use neutron diffraction.
Étude par diffraction de neutrons de la structure cristalline de U2F9
Authors: Laveissière J. 
Published: March 2019

La structure cubique centrée de U₂F₉ a été précisée par diffraction de neutrons : groupe spatial I[-4]3m, a = 8,4716 ± 0,0005 Å, distances moyennes U-F : 2,30 Å.
Étude du pouvoir rotatoire des cristaux˗liquides cholestériques
Authors: Cano René 
Published: March 2019

La théorie de Mauguin˗de Vries exprime le pouvoir rotatoire spécifique d'une préparation cholestérique homogène, considérée comme un empilement hélicoïdal de lamelles biréfringentes, en fonction des indices de ces lamelles et du pas de leur empilement. Cette théorie n'a jamais été vérifiée quantitativement. Il est possible d'atteindre la valeur du pas en mesurant l'équidistance des « plans » de Grandjean ; il est plus difficile de connaître les valeurs des indices. L'addition d'un corps cholestérique à un corps nématique donne une phase cholestérique ; nous avons supposé que, pour des mélanges de faibles teneurs en corps cholestérique, les propriétés optiques des lamelles élémentaires pouvaient en première approximation se déduire de celles du composant nématique pur. Dans ces conditions, l'emploi de la formule de de Vries permet de retrouver quantitativement, avec une bonne précision, les valeurs mesurées du pouvoir rotatoire.
Contribution à l'étude des phosphates ammoniaco˗métalliques monohydratés. II. Structure cristalline du phosphate de cobalt˗ammonium monohydraté : Co NH4 PO4, H2O
Authors: Tranqui Duc , Durif-Varambon André , Guitel Jean-Claude , Averbuch-Pouchot Marie-Thérèse 
Published: March 2019

CoNH₄PO₄, H₂O est orthorhombique avec une maille : a = 5,550, b = 8,850, c = 4,805 Å et deux unités moléculaires par maille. Le groupe d'espace est Pmn2₁-C⁷₂v. La structure cristalline a été déterminée au moyen de deux projections.
Étude de la transformation d'une titanomagnétite en titanomaghémite dans une roche volcanique
Authors: Prévôt M. , Remond Guy , Caye René 
Published: March 2019

Cette étude porte sur un cristal de titanomagnétite largement transformé sur sa bordure en titanomaghémite.
Les courbes de dispersion des pouvoirs réflecteurs des deux plages correspondantes sont comparées à celles de minéraux connus.
L'analyse à la microsonde électronique met en évidence une forte diminution de la teneur en fer et une augmentation importante pour celles du titane et du manganèse dans la bordure du cristal. L'interprétation de ces résultats conduit à penser que la maghémitisation de la titanomagnétite correspond non seulement à une oxydation du fer mais encore à une diffusion de cations qui viennent occuper partiellement les sites cristallographiques théoriquement vacants ; l'enrichissement en titane et en manganèse influe sur la teneur en fer qui ne dépend pas uniquement du degré d'oxydation du minéral. Les propriétés magnétiques des titanomaghémites devraient donc être différentes de celles prévues par la théorie.
L'effet de socle dans le métamorphisme
Authors: Fonteilles Michel , Guitard Gérard 
Published: March 2019

The basement effect has been detected and defined in the Pyrenees where it is well expressed : the presence of a granitic or metamorphic basement before the Hercynian metamorphism influences the form and the distribution of the isograds in the overlying paleozoic cover (the isograds converge around the basement cores) and the position of anatexis. Several examples of the basement effect outside the Pyrenees are given. The various hypotheses which may explain this frequent type of thermal structure are discussed. The peculiarities of the heat transfer in a basement-cover unit during regional metamorphism are investigated by means of two models : series with autochtonous basement and series with the basement involved in nappe-structures. The basement effect — as well as the thickness of the metamorphic zones and the changes of the metamorphic types — are correlated to the form of the temperature-depth curve which is discussed. The heat absorbed by the chemical reactions (initial lithology) plays an important role. The basement effect involves a thermal disequilibrium during metamorphism (the isograds rise up) . Eskola's theory of the « mantled gneiss dome » is discussed and compared with the theory of the basement effect.
Structure cristalline de FeHo4S7 et de certains composés isotypes
Authors: Adolphe Claude , Laruelle Pierre 
Published: March 2019

The crystal structure of FeHo₄S₇ has been derived from that of L₅S₇. On the basis of observed structure factors, several models have been tried with the iron atom in statistical disorder or in special positions. A good agreement was found with iron distributed on two metal sites and a refinement was achieved at R = 0.098. In these positions the metal coordination is six-fold. The only site with seven-fold coordination was found to be iron-free.
Divalent metals have the same repartition in FeY₄S₇. Other sulfides ML₄S₇ exhibit probably similar structures, except perhaps Cd compounds.
Étude structurale des hydroxystannates CaSn(OH)6 et ZnSn(OH)6 par diffraction neutronique, absorption infrarouge et résonance magnétique nucléaire
Authors: Cohen-Addad Claudine 
Published: March 2019

The complete structure of cubic hydroxystannates, CaSn (OH)₆ and ZnSn(OH)₆, of space group Pn₃, has been determined by neutron diffraction at 4° K (powder techniques), and with the study of the spectrum of CaSn (OD)₅,₄₅ (OH)₀,₅₅. The 24 hydrogen atoms of the unit cell form two sorts of hydrogen bonds with double well-distributions and are on two sites 24 h statistically half occupied with some probability of movement from one position to another at 300° K. The hydrogen bonds, with lengths of 2,75-2,9 Å link different octahedra MO₆ — M = Ca, Zn or Sn — and form distorted squares around empty sites, near planes perpendicular to the three crystallographic axes. The double maxima of the infrared absorption spectrum are attributed to these two different hydrogen bonds. Any supplementary resolution is not observed at low tempera tures. The nuclear magnetic resonance of protons, observed in CaSn (OH)₆ and ZnSn (OH)₆, shows a line width in agreement with this model. Moreover, a narrow line shows the existence of inclusions of some supplementary water molecules in the crystals.
La structure cristalline du tétracyanoplatinate de potassium et sodium trihydraté
Authors: Moreau-Colin M.-L. 
Published: March 2019

KNaPt (CN)₄. 3H₂O est monoclinique avec 4 unités formulaires par maille ;
a = 11,77 Å ; b = 13,74 Å ; c = 6,50 Å ; β = 94° 47'.
La détermination de la structure est basée sur l'analyse des projections (001) et (010). Le facteur R est 7,9 % pour l'ensemble des plans (hk0) et 9,3 % pour l'ensemble des plans (h0l).
L'auteur donne aussi une discussion de la structure.
Application de la sphère de Poincaré à l'ellipsométrie de précision
Authors: Robert André 
Published: March 2019

Polarimetry problems can be dealt with simply the help of Poincaré's representation ; as this method is not widely appreciated its properties are developped in section 1. Theafter in section 2, an automatic method for measuring polarisation forms is described ; in this method the ellipticity and the orientation of the main axis of the light ellipse are given on digital voltmeters. This method uses a photomultiplier tube, a rotating analyser with a constant frequency w, the gain of the photomultiplier circuit being automatically controlled to eliminate fluctuation of the preceding results to both automatic two-dimensional photoelasticity and three-dimensional photoelasticity by scattered light ; any transparent body is an operator on the form of light and this operator is related to the state of deformation of the body.
Heterogeneous nucleation on a substrate
Authors: Chakraverty Benoy K. 
Published: March 2019

Nucleation theory in the case of condensation on a substrate is reviewed. The thermodynamics of adsorbed layer formation is briefly discussed. It was shown that three distinctly different condensation regions exist :
a) that of medium supersaturation and an adsorbed layer which is less than a monolayer,
b) very high supersaturation and an adsorbed layer which is much less than a monolayer,
c) supersaturation very low and adsorbed atoms in one or more monolayers before condensation begins.
Nucleation theory is very suitable for application to case a).
The kinetics of nucleii formation was derived and the frequency of nucleation was obtained as a function of supersaturation. Collision between nucleii was taken into account and saturation density of the number of nucleii was obtained analytically.
Experimental results are shown confirming the theoretical predictions ; in particular ad-atom concentration is shown to exist as well as a saturation density of nucleii controlled by collision process.
L'interface cristal˗bain fondu
Authors: Mutaftschiev Boyan 
Published: March 2019

The main purpose ol this paper is to underline the fundamental structural as well as interfacial energy differences existing between the crystal-melt interface and other interfaces such as crystal-vapour, liquid-vapour and crystal I-crystal II.
After a short review of the existing theories of liquids and melting process, an approach towards understanding the crystal-melt interfacial structure based on the Bernal random-liquid model is suggested.
Finally, some preliminary experimental results on the measurement of contact angle and adhesion energy between the densest crystal plane and the melt for close packed metals are presented.
Tendances actuelles des méthodes de détermination des structures cristallines
Authors: Mornon Jean-Paul 
Published: March 2019

On évoque quelques-unes des causes et des conséquences de l'évolution actuelle des méthodes de détermination des structures cristallines. On fait mention de l'intérêt que peut revêtir la création de programmes visant à une automatisation poussée de ces méthodes ainsi que les perspectives offertes par les dernières recherches théoriques et expérimentales.
Spinelles déformés dans le système rhodite de nickel et de cuivre
Authors: Dulac Jean 
Published: March 2019

The spinel compounds NiRh₂O₄ et CuRh₂O₄ show tetragonal deformations in opposite directions ; one with c/a > 1, the other with c/a < 1 (if one takes as a reference the face-centered cubic cell of the spinels).
A study, at room temperature, of the solid solution Rh₂CuₓNi₁₋ₓO₄ (0 < x < 1) has led to the discovery of a new orthorhombic phase with : 0.12 < x < 0,175. The formation of this phase may be explained by an extension of the theory of the Jahn-Teller effect (theory of Kanamori).
La distinction géochimique ortho˗para des leptynites
Authors: Davoine Philippe 
Published: March 2019

A study of the chemical characteristics (main elements Cu, Cr, Ni and Pb) of four families of sample rocks : rhyolites, dacites, arkoses and leptynites, was effected. It revealed geochemical criteria which permit the distinction between ortho and para leptynites by the main elements only, particularly Ca, Na and K.
The validity of the selected criteria is discussed.
It seems that the position of the composition the leptynites in the quartz, albite, orthose diagram can be considered as an additional critérium.
Étude thermochimique des sulfures de la formation ferrifère de Pierrefitte (Hautes-Pyrénées)
Authors: Besson Maurice 
Published: March 2019

Le gisement plombo-zincifère de Pierrefitte est formé de sulfures contenus dans une roche magasin constituée de silicates essentiellement ferreux, de magnétite, de quartz et de carbonates subordonnés à Barbazan et plus abondants à Garaoulère. L'évaluation des conditions physiques correspondant aux assemblages de sulfures est recherchée par l'analyse des sphalérites et des pyrrhotites par diverses méthodes. Ces conditions sont estimées voisines de t = 380° C, P = 2,9 kbar, log f [S₂] = — 6,6 , log f [O₂] = — 25,4. Les enregistrements de décrépitométrie des inclusions fluides contenues dans les sphalérites conduisent à des estimations voisines. Ces conditions sont compatibles avec les conditions de formation des assemblages de silicates du magasin ; toutefois la température d'équilibre constatée pour les assemblages de sulfures semble légèrement inférieure à la température d'équilibre des assemblages de silicates, fait confirmé par les relations mutuelles de formation des minéraux.
Structures magnétiques des chromates de cobalt et de nickel
Authors: Pernet Marc , Quezel G. , Coing-Boyat Jean , Lewy-Bertaut Erwin Félix 
Published: March 2019

Les structures magnétiques des chromates de cobalt et de nickel isotypes de CrVO₄ (groupe spatial Cmcm) ont été déterminées par diffraction neutronique. Les quatre ions magnétiques sont en position 4 (a) : 0 0 0, 0 0 1/2, 1/2 1/2 1/2, 1/2 1/2 0. Dans CoCrO₄, l'arrangement des vecteurs de spins S1, S2, S3, S4, est caractérisé par les modes (+--+) et G2 (+-+-) ; ils font un angle de 55° avec l'axe des x et leur module est 1,20. Dans NiCrO₄, l'arrangement est colinéaire selon le mode Aₓ et S = 0,64. On observe donc une réduction importante de spin, due à des effets de covalence. Les mesures magnétiques ont permis de déterminer les températures de Néel (14° et 23° K respectivement), les températures de Curie paramagnétiques (— 24° et — 105° K) et les constantes de Curie, CM (3,39 et 1,60).
Étude par microscopie optique et radiocristallographie des sulfates de calcium semihydratés
Authors: Barriac Pierre , Murat Michel , Chevreton Maurice 
Published: March 2019

The comparative study of the textures of the three calcium-sulfate-hemihydrates (α, α low pressure and β), by optical microscopy observation on thin layers, allows us to consider that liquid water is the recrystallisation medium of the hemihydrate during dehydration of gypsum.
Diffractometer patterns of these three varieties differ in the intensity of the lines. According to the texture of the original gypsum, the α variety crystallizes either in thin needles or in large elongated crystals having their axis parallel to the (010) planes containing the water molecules of the dihydrate.
The three hemihydrates (α, α low pressure and β) may be considered as structuraly identical, the β form showing a very porous submicronic texture.
Sur les compositions chimiques des minéraux des lherzolites pyrénéennes et leur signification génétique
Authors: Monchoux Pierre , Besson Maurice 
Published: March 2019

New chemical analyses of coexisting minerals in four samples of Pyrenean lherzolites (Moncaup body), are here used as a basis for a study of the conditions of formation of those rocks. The problem has been handled through the Fe⁺⁺ and Mg distribution coefficients among clino- and orthopyroxenes, olivines and orthopyroxenes, and from the clinopyroxenes composition. Formation conditions of about 1 100°-1 200° C and 8-12 kbar are inferred, and are in good agreement with recent experimental data on peridotites.
The compositional join muscovite˗pyrophyllite at moderate pressures and temperatures
Authors: Velde Bruce 
Published: March 2019

An investigation of compositions between muscovite, KAl₃Si₃O₁₀ (OH)₂ and pyrophyllite Al₂Si₄O₁₀ (OH)₂ was undertaken under hydrothermal conditions of 1, 2 and 3,5 kilobars water pressure and temperatures between 250° C and 440° C. The resulting five silicate phases were identified by X-ray diffraction, electron microscope and cation exchange capacity methods. The study permits the determination of the stability of expandable and mixed-layered phases under various physical and chemical conditions. A brief discussion of possible applications to natural mineral assemblages is made.
Vue d'ensemble sur la rhéologie des magmas silicatés naturels
Authors: Carron Jean-Paul 
Published: March 2019

The results of viscosity measurements concerning melted rocks and natural glasses may be interpreted by the same model as used for binary glasses SiO₂-M₂O. At a given temperature, the viscosity rj depends on the percentage of broken bonds between the tetrahedra of the aluminosilicate structure (R). The relations are of the form η = k /R[m], and may be applied to granitic glasses as well as to molten basalts, to anhydrous melts as well as to hydrated magmas. Diagrams are given between 800° C and 1400° C, which account for the main rheological properties of natural materials, and they may be used to estimate the viscosity of any silicate melt, if one knows its chemical composition, its water content, and its temperature, in the range 10² to 10¹⁵ poises, with an error of about an order of magnitude.
Étude de la macle de disiliciure de fer β
Authors: Dusausoy Yves , Wandji Roland 
Published: March 2019

Iron disilicide, β-FFeSi₂, has orthorhombic symmetry. Crystals are often twinned. X-ray study of the twins shows that the twinning element is a pseudosymmetry element of the orthorhombic unit cell : [011] axis or (011) plane. This simulates a pseudotetragonal symmetry. Goniometric investigations of twinned crystals show that the two individuals are twinned by juxtaposition with the composition plane (011). The β-FeSi₂ twin is pseudomerohedral.
Contribution à l'étude de quelques tétraisocyanato, tétraisothiocyanato et tétraisosélénocyanatométallates de tétraméthylammonium [(CH3)4N]2M (NCX)4 avec M = Co et Zn ; X = O, S, Se
Authors: Kergoat René , Guerchais Jacques-E. , Genêt Françoise 
Published: March 2019

Les complexes de formule [(CH₃)₄N]₂ M (NCX)₄ où M = Co ou Zn et X = S ou Se cristallisent dans le système quadratique, groupe P₄/nbm. Leurs paramètres sont :
[(CH₃)₄ N]₂ Co (NCS)₄ a = 10,98 Å ; c = 10,69 Å
[(CH₃)₄ N]₂ Zn (NCS)₄ a = 11,00 Å ; c = 10,70 Å
[(CH₃)₄ N]₂ Co (NCSe)₄ a = 11,18 Å ; c = 10,90 Å
[(CH₃)₄ N]₂ Zn (NCSe)₄ a = 11,19 Å ; c = 10,91 Å
Les isocyanates correspondants ont été synthétisés. Ils ne sont pas isomorphes des précédents. Des études magnétiques, conductimétriques et par les infrarouges montrent que le métal a une coordinence tétraédrique et que la liaison sur le métal se fait par l'azote du groupement (NCO).
Structure de Mn5 Si C
Authors: Spinat Pierre , Fruchart Robert , Kabbani Mayer , Herpin Paulette 
Published: March 2019

Crystals of Mn₅ Si C belong to the orthrhombic system, space group Cmc2₁, with Z = 8 in a unit cell of dimensions a = 10.198 Å, b = 8.035 Å, c = 7.630 Å.
The stuctural hypothesis stablished from isomorphous compound Mo Mn₄ Si C by Patterson and Fourier syntheses, was completed on Mn₅ Si C by electron density maps. A least-squares refinement gave R = 0.06 using 565 observed structure factors.
The structure consists of a succession of perpendicular plans to [100]. Carbon atoms may be located in the center of right prisms, bases of which are triangular.
Structure cristalline de la parabutlérite
Authors: Borène Jacques 
Published: March 2019

La parabutlérite est un sulfate basique de fer hydraté, Fe SO₄OH, 2H₂O.
Ses paramètres réticulaires sont a = 7,38 Å, b = 20,13 Å, c = 7,22 Å et son groupe de symétrie Pmnb. Sa structure cristalline a été résolue à l'aide des mesures de diffraction des rayons X faites sur un diffractomètre automatique. Le facteur R obtenu après affinement sur les facteurs d'agitation thermique anisotrope est de 0,038.
Étude de l'eau d'hydratation des cations compensateurs de smectite homoioniques
Authors: Poinsignon Christiane , Cases Jean-Maurice 
Published: March 2019

The quantitative study by infrared spectrometry of residual water of homoionic smectite with alkaline and alkaline-earth cations as exchangeable cations allows the measure of water different species and their characterization by its integrated extinctions coefficient.
It appears a lineary relation between absolute intensity A 3 microns of the residual waters stretching band and the electric field of hydrated cations. It reveals the perturbation induced by the cation on its hydration shell.