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The i.r. and Raman spectra of the niobate and tantalate of “1 × 2 block” type structure AIIBV2O6 (AII = Ca, Sr, Ba, Pb) are presented and analyzed. The complete vibrational analysis of BaNb2O6 is presented and a force field is proposed for this type of compounds, the potential energy distribution is given and some characteristic normal modes are drawn in comparison with the normal modes of the double octahedron B2O10 which is the basic motif of the “1 × 2 block” type structure.

The i.r. and Raman spectra of antimonates MIISb2O6 and tantalates MIITa2O6 belonging to the trirutile structure are studied. The vibrational assignment is obtained by means of the comparison of the spectra, the use of the correlation method and normal coordinate calculations. A force field characteristic of this type of compounds is proposed.

The i.r. absorption and Raman scattering spectra of some aluminium and gallium garnets have been studied. They show a stronger force field in the aluminates than in the gallates and the influence of the ionic radius of the Ln 3+ cation on the frequencies of the aluminium—oxygen or gallium—oxygen network. The study of the system Er 3 Ga 5 O 12 -Er 3 Al 5 O 12 permitted us to propose an assignment of the different ranges of frequencies and to point out that the tetrahedra vibrations are higher than the octahedra ones. The i.r. spectrum of the perovskite NdGaO 3 is compared to the garnet Nd 3 GasO 12 one.

We present the synthesis conditions and structural features of perovskite type phases in which the B IV cation is replaced by a weighed association of M III and M V cations. The A II cation may be substitued by a cation of the same valence. The distribution on the B sites of the M III and M V cations is statistical or ordered depending on the M III cation radii.

The i.r. and Raman spectra of antimonates M II Sb 2 O 6 (M II = Pb, Ca, Sr, Ba, Cd) belonging to the ‘PbSb 2 O 6 type’ structure are studied. A vibrational assignment is proposed and the normal coordinate calculations permitted us to calculate the force field and to characterize the chemical bonds in these compounds.

L'etude de la resolution de l'equation du bilan-matiere d'une colonne chromatographique est presentee. Une solution numerique est proposee pour un isotherme d'adsorption parabolique dans le cas de fortes courbures. Une solution numerique, basee sur une methode de discretisation, a ete egalement mise au point pur les isothermes d'adsorption de forme quelconque.

The Raman and infrared spectra of CaNb2O6 are assigned by normal coordinate analysis according to Shimanouchi’s method. The Raman spectroscopy results enabled us to refine the force field, which was then checked by the infrared spectroscopy results. The obtained force constants show that there are three different types of Nb–O bonds in the columbite structure and that the Ca–O bonds are of electrostatic nature. The potential energy distribution calculation gives us a precise assignment for all the observed frequencies.

Unpolarized Raman spectra of the compounds M 3 UO 2 F 5 ( M = K, Rb, Cs, NH 4 ) were recorded in the region 1000-100 cm −1 at room and liquid nitrogen temperatures. Polarized Raman spectra of single crystals K 3 UO 2 F 5 , Rb 3 UO 3 F 5 were measured at room temperature and permitted a complete assignment of the A 1 ′, E 2 ′ and E 1 ′ fundamental modes of the UO 2 F 5 3− ion of the D,7, symmetry group. Factor group analysis was applied to the interpretation of the spectra. Site and correlation splitting due to the internal modes of the UO 2 F 5 3− ion are discussed.

A study of the system Rb2OTa2O5 shows the existence of six phases. One phase α (1-1) stable up to 600°C, two phases β1 and β2(2–3) with orthorhombic unit-cells. The phase δ(2–5) is a cubic pyrochlore. The structure of the ζ phase (3–8) with a monoclinic unit-cell is intermediate between pyrochlore and hexagonal bronze-type. Lastly, the structure of the η phase (about 1–3, 7) belongs to the hexagonal bronze type.

A systematic study has been made of the influence of two factors on the synthesis of titanium dioxide gels: (i) the acidity of the reaction medium and (ii) the presence of a solvent. This study demonstrates that, in an aqueous acid medium, the development of textural properties is related to the concentration of free hydrogen ions. The presence in an acid reaction medium of a solvent, such as butanol or benzene, of low dielectric constant, inhibits the development of the structural properties by lowering the ionic dissociation of the acid. Our results provide an explanation for the apparently divergent measurements in the literature.

A comparison is made between the force fields calculated for the MIINbV2O6 and MIITaV2O6 columbite series and the MIITaV2O6 and MIISbV2O6 trirutile series. The trirutile structure is shown to be particularly more rigid than the columbite structure. For this reason, the trirutile structure exists only for divalent cations of small size. The stability of the two structures and their relative modifications are then compared. From a comparison of the vibrational spectra of the rutile FeSbO4 with those of the trirutile MSb2O6 compounds, a short-range order in the rutile structure is proposed.

The normal coordinate analysis of PbNb 2 O 6 and PbTa 2 O 6 compounds of “1 × 2 block” structural type has been carried out using a crown model unit corresponding to the pseudo-cell unit of the crystal structure. The results permitted the assignment of the observed i.r. and Raman frequencies and the force fields obtained have been compared to the “1 × 2 block” homologues, i.e. BaNb 2 O 6 , CaTa 2 O 6 , BaTa 2 O 6 (II), SrNb 2 O 6 whose force fields have been previously determined.

The structural characteristics of the columbite niobates MNb 2 O 6 (M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) from their X ray diffraction powder patterns and indexed according to the Pbcn space group are given. Cell parameters are refined for each compound. Previous spectroscopic studies by normal coordinate analysis provide the basis for a discussion of the precise nature of the NbO and MO bonds. Force constants and bond order are given and the influence of the electronegativity of the M 2+ cations upon these bonds is shown.

The vibrational assignment of compounds A2IIIB2IVO7 (A = La, Nd; B = Zr, Hf) belonging to the pyrochlore structure is proposed. A normal coordinate analysis permitted us to calculate their force field which is discussed.

The Raman spectra of partially deuterated ethylenediamine (5 and 95% on NH 2 groups) have been recorded between − 46 and − 196°C in the region of the NH and ND stretching vibrations. The vibrational frequencies of the isotopically diluted NH and ND bonds enabled us to demonstrate the importance of the hydrogen bonds in the cohesion of the crystals and during the allotropic transformation, and also to show the influence of the asymmetric effect on the form of the normal modes of vibration of the NH 2 groups.

Solid solutions between different perovskite-type compounds A+++ B+++O3 is described. An immiscibility gap, often narrow, exists between the pseudo-monoclinic and rhombohedral symmetries. Near this zone exists a solid solution with pseudocubic symmetry which differs from the pseudo-monoclinic one by a larger movement of cations.

The Raman spectra of the solid compounds LiI, 3 en; LiX, 2 en (X = Cl, Br, I; en = NH 2 CH 2 CH 2 NH 2 ) and their analogues with en-d 4 (en-d 4 = ND 2 CH 2 CH 2 ND 2 ) have been investigated. The assignment of all the observed bands in the region of the NH 2 (ND 2 ) and CH 2 stretching vibrations is made according to the crystal structure of these compounds. The influence of hydrogen bonding and of Fermi resonance between the ν s (NH 2 ) and 2δ(NH 2 ) levels and between the corresponding levels of the ND 2 and CH 2 groups has been discussed. The spectroscopic results obtained are in good agreement with the crystallographic structures of the compounds.

The structural characteristics from X ray diffraction powder patterns and indexed according to the Pnma space group are given for SrTa 2 O 6 isomorphous with SrNb 2 O 6 and for a modification of BaTa 2 O 6 isomorphous with CaTa 2 O 6 . Cell parameters are refined for each compound. The force field of different niobates and tantalates of “1×2 block” type structure calculated from a vibrational analysis is then compared and the relative stability of the two modifications of BaTa 2 O 6 is shown.

Infrared (4000-100 cm −1 ) and Raman (1000-100 cm −1 ) spectra of the complexes M 4 (UO 2 ) 2 F 8 -2H 2 O (M = Rb, Cs) were reported. Factor group analysis was used to classify the normal vibration modes of the binuclear ion (UO 2 ) 2 F 4− 8 and to interpret the spectra. Polarized Raman spectra of Rb 4 (UO 2 ) 2 F 8 -2H 2 O made it possible to assign the Raman fundamental vibrations of the anion (UO 2 ) 2 F 4− 8 . The infrared fundamental vibrations of this anion was made by comparison with those of the mononuclear UO 2 F 3− 5 anion. The result of the normal coordinate analysis of the (UO 2 ) 2 F 4− 8 ion was used to support the preceding assignment and to analyze the effect of the association of a double fluorine bridge with two UO 2 F 5 groups on the spectra and on the G.V.F.F. constants, compared to those of the mononuclear ion UO 2 F 3− 5 .

The vibrational study of the three families of the niobates and tantalates of “1 × 2 block”-type structure shows that some vibrational frequencies are characteristic of this structure. The relation between the calculated force constants and the structural characteristics permitted us to distinguish the different types of Nb O and Ta O bonds from each other, and to establish a relation between the polarizability of the divalent cation and the mode of linkage of the double octahedra in the layer planes. Finally, the comparison of these results with those obtained for other niobates and tantalates of various structures permitted us to determine the relative stability of all these compounds.

The normal coordinate analysis of CaTa 2 O 6 , BaTa 2 O 6 (II) and SrNb 2 O 6 compounds (type II) of “1×2 block” structural type was performed in order to define more precisely the assignment of the observed i.r. and Raman vibration frequencies. The results obtained showed that the I and II types of “1×2 block” type structure (I: BaNb 2 O 6 , BaTa 2 O 6 (I) and the values of the force constants agreed with the nature of the Nb(Ta)O bridge.

Simulation and optimization of multi-stage adiabtic catalytic reactors is now well developed in chemical industries, design and companies and universities. In a first part we present briefly a program package developed in our laboratory, first for chemical industry, and secondly for chemical engineering education. In this presentation we show how it is possible to take into account new possibilities in direct optimization procedures and new terms in objective functions. In a second part we examine design problems of optimization, including many sub-problems in the definition of objective functions. Then we try to show how it is possible to sensibilize our students on the possibilities of choice for decision variables by using this package.

Resume Infrared and Raman spectra of the niobates of columbite structure M Nb2O6 (M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd) were recorded in the region 1100-50 cm−1. All of them are similar at the shorter wavelengths (> 400 cm−1) but depend on the cation at lower frequencies. By comparison of i.r. and Raman spectra, the main vibration frequencies have been assigned.

Heat and mass transfer are studied for drying of a semi-infinite solid in warm air. The mathematical model, a system of partial differential equations, gives an exact analytical solution if transfer coefficients are constant and free water present at the surface. An analogy has been found for heat transfer with and without drying. A finite-difference solution of broader application than the analytical method has been developed, and the two methods agree closely. Experiments are described which show fair agreement with calculations of heat transfer during the first step of drying. Water content profiles remain flat during that period and no precise comparison can be made

Potentiometric and conductimetric measurements of solutions of sodium hydroxide and lead nitrate at 27 ± 0.2 °C have established the existence of hydrated lead monoxynitrate, dioxynitrate, heptoxytrinitrate and pentoxynitrate. It was shown that the presence of silica inhibits the formation of anhydrous lead oxide but favors that of hydrated lead oxide. The preparation of lead oxynitrates and hydrated lead oxide was carried out over a wide range of temperatures at various concentrations of reactants.

A study on interaction potential between polar molecules is made for fitting the potential. A solution is proposed for returning to a potential that is independent of molecule orientation. This solution uses a weighted Boltzmann factor in the calculation of potential energy. The method of calculation is given.

A new application of small-angle scattering of X-rays to the determination of particle size distributions is discussed, without any hypothesis concerning the shape of these distributions. The practical utilization of this method is described for the case of carbons. In the discussion, a comparison with the results of nitrogen adsorption on an oxidized pile-grade graphite sample is presented.

In the optimal design of multistage reactors for oxidation of sulfur dioxide, two important cost factors are considered: catalyst and heat exchange. The way to obtain the associated economic function is presented. A complete solution of the reactor train equation must be carried out to obtain each value of this implicit function of ten variables (injections of gas and temperatures in catalyst beds). To optimize the multistage reactor, three direct methods are adapted for a specific treatment of constraints on the variables. Two of these methods (Hooke and Jeeves, simplex) give satisfactory results and it appears possible to make a rational choice between exchangers and injections Dans le calcul optimal d'un reacteur multietage d'oxydation de l'anhydride sulfureux, deux postes importants du coǔt sont pris en compte: catalyseur et echangeurs. Le moyen de calculer la fonction economique associee est presente; chaque valeur de cette fonction implicite de dix variables (injections et temperatures dans les lits catalytiques) necessite le calcul complet du reacteur. L'optimisation est realisee au moyen de trois methodes directes adaptees pour un traitement specifique des contraintes, deux de ces methodes (Hooke et Jeeves, simplex) donnent des resultats satisfaisants rendant possible un choix entre les echangeurs et les injections.

It it shown in this paper that the process of evaporation of liquids into a turbulent gas flow in a wetted-wall column can be represented by the film-penetration model. The numerical values of the two parameters S and L of this model, estimated from mass transfer data, appear to be well defined functions of flow conditions. The surface renewal mechanism used in the considered mass transfer model was shown to be consistent with the momentum transfer concept. The results may be used to predict mass transfer processes with chemical reactions in similar flow systems, by applying the theoretical developments using the film-penetration theory [7–10]. The same procedure may be used to estimate the film-penetration parameters in other flow systems, such as the flow of liquid films in a wetted-wall column, or other complicated system such as stirred tanks, bubble columns, packed columns etc.

The enthalpies of mixing in the system 3-ethyl-3 pentanol–carbon tetrachloride were measured by microcalorimetry. The classic theory of associated solutions leads to an expression for the excess enthalpy which we have simplified by introducing the heat at infinite dilution for the alcohol. The resulting expression allows the enthalpy of formation of a hydrogen bond to be calculated using calorimetric and tonometric results. The calculations show that this enthalpy is independent of the concentration of the solution (up to 0.45 in molar fraction) and is in agreement with the literature.

La determination de l'equilibre liquide-vapeur, de la chaleur latente de vaporisation et de la pression de vapeur en coordonnees reduites est effectuee pour cinq potentiels d'interaction (6-n) en mettant en evidence le role du parametre de la repulsion n. Determination of liquid-vapour equilibrium, latent heat of vaporization and vapour pressure is made with reduced variables for five (6-n) interaction potentials, while studying the influence of repulsion parameter n. La confrontation theorie-experience a necessite un choix parmi les valeurs des parametres physiques d'interaction des premiers hydrocarbures prises dans la litterature. Elle a mis en evidence l'influence de la repulsion et celle du coefficient d'entropie communautaire. Une variation continue de ce coefficient a ete determine pour le methane et l'ethane. A theoretical-experimental confrontation implied a choice among values of interaction physical parameters of first saturated hydrocarbons from literature. Influence of repulsion and ...

Rb3UO2F5 crystallizes in the tetragonal lattice with the space group 14 1 a . The dimensions of the cell are a = 9·53 8 A ; c = 18·57 3 A . Most of the crystals formed are twinned. One type of the twin observed is described. The compound is isostructural with K3UO2F5.

The following six compounds: PbNb4O11, Pb5Nb4O15, Pb2Nb2O7, ZnNb2O6, Zn3Nb2O8 and Pb2−xZnyNb2−zO7−x+y-2, 5z are described with a view to characterizing their crystallographic unit-cells (parameters and symmetry) by X-ray diffraction on single-crystals; their structures belong to one of three types: tungsten-bronzes, pyrochlorite or columbite. Stabilization of orthorhombic PbNb2O6 is studied with regard to chemical and thermic properties.

Polarized Raman spectra of Cs3UO2F5 in which the UO2F5 3− ion is in its statistical position have made it possible to assign definitely the Raman fundamental vibration modes as follows : v1(A′1) = 784, v2(A′1) = 423, v8(E′2) = 325, v8(E′2) = 219 and v10(E″1) = 259 cm−1.

Resume Cs 3 UO 2 F 5 forme a la temperature ambiante presente deux varietes cristallines I et II. Les traitements thermiques et l'analyse thermique differentielle montrent que I est une forme ordonnee tandis que II presente un desordre du aux atomes lourds. Les resultats de diffraction des rayons X ont montre que la structure de I est cubique a faces centrees et les atomes de fluor et d'oxygene occupent statistiquement leurs sites dans la maille. Cependant l'ion UO 2 F 5 3− conserve la symetrie D 5 h tout comme dans les composes K 3 UO 2 F 5 et (NH 4 ) 3 UO 2 F 5 .

Two modifications of SrNb2O6 were disclosed by systematic studies: a monoclinic pseudo-orthorhombic modification with cell parameters a = 11, 02 A, b = 7, 73 A, c = 5, 60 A, r = 90;°2, space group P21a, isostructural with orthorhombic CaTa206, and a tetragonal modification having the potassium tungsten bronze structure. The conditions of reversible transformation of the two phases in one another were delimited.

This work presents a study of the mixed oxides of vanadium(V) and lanthanides by dry methods. The study includes all elements of the rare earth group except cerium and promethium.All orthovanadates of the formula TVO4 were prepared and their lattice parameters redetermined for all lanthanides. New materials were synthesized: lanthanides 4T2O3•V2O5, for elements from samarium to ytterbium the compounds 5T2O3•V2O5• and for praseodymium and neodymium the compounds 6T2O3•V2O5. Identification of these materials was carried out by X-ray diffraction.

Phase equilibria studies in the systems (PbxBa1−x)Nb2O6, (PbxSr1−x)Nb2O6 and (BaxSr1−x)Nb2O6 have been made. Tetragonal 0, 2

Cette mise au point porte sur l'utilisation de la technique de chromatographie en phase gazeuse pour la determination des coefficients d'activite a dilution infinie. Deux points particuliers seront developpes: - Elaboration des modeles mathematiques, - Problemes experimentaux poses en vue de l'exploitation des resultats chromatographiques.

Des conditions de selection des solutions du modele cellulaire sont presentees et appliquees aux molecules d’azote et d’oxygene pour le calcul de la chaleur de vaporisation qui est comparee aux donnees experimentales.