Framework Vibrations Research Articles

ChemInform Abstract: Preparation of High‐silica Faujasites by Treatment with Silicon Tetrachloride.

AbstractDie Dealuminierung eines NaY‐Zeolithes mit SiCl4 gemäß Gleichung A führt nur dann reproduzierbar zu hoch kristallinen Materialien, wenn unter exakt kontrollierten Bedingungen gearbeitet wird.

The effects of incommensurability on the phonon modes in the one-dimensional superionic conductor K-hollandite

Polarized Raman and infrared spectra of the one dimensional (1-D) superionic conductor ( K 2 x Mg x Ti( 8− x ) O 16; x = 0.77) have been measured over the phonon frequency region 10–1000 cm −1 as a function of temperature and pressure. The majority of the IR and Raman active modes predicted by group theory for the (Ti, Mg)O 6 framework were observed. The frequencies and their IR and Raman scattering cross-sections for the incommensurate lattice of K + ions were calculated using a one dimensional linear chain model. This model assumes Coulomb interaction between nearest neighbors that are located in a sinusoidal potential due to the framework lattice. Several broad Raman bands were attributed to amplitudon type modes from the one dimensional incommensurate K + ion sublattice. The IR active phason modes could not be identified unambiguously due to the underlying TiO framework vibrations which are known to possess large anharmonicity and oscillator strenghts.

Preparation of high-silica faujasites by treatment with silicon tetrachloride

NaY has been dealuminated in highly controlled conditions by SiCl4. The materials thus obtained, after subsequent washing and ammonium exchange, were characterized by chemical analysis, thermogravimetry, X-ray diffraction, infrared spectroscopy of the framework and surface hydroxyl groups and 29Si nuclear magnetic resonance spectroscopy.In order to obtain highly crystalline materials in a reproducible way, a very specific dealumination and washing procedure has to be followed. The mechanism of the dealumination is complex and always combines direct isomorphic substitution with acid leaching of aluminium. The materials obtained have continuously varying properties as far as unit-cell dimensions and framework vibrations are concerned. In contrast, the amount of extra-lattice aluminium retained in the zeolite reaches a maximum at intermediate degrees of dealumination.

Vibrational study of H 3OUO 2PO 4·3 H 2O (HUP) and related compounds. Phase transitions and conductivity mechanism: Part II, H 3OUO 2PO 4·3 H 2O

Infrared and Raman spectra of polycrystalline H 3OUO 2PO 4·3 H 2O (HUP) and its D and P 18O 4 derivatives, in the form of dense transparent disks and wet powder, have been investigated at various temperatures in the 100–300 K region. The bands due to framework vibrations are similar to those of KUP, whereas those for the protonic species are different. OH stretching and bending bands of the oxonium ion have been identified at 2920, 1740 and 1160 cm −1 in the low-temperature spectrum of HUP. Differential scanning calorimetry (DSC) and infrared (IR) intensity investigations show a phase transition between 274 and 260 K. The mechanism of the phase transition consists, as in the case of KUP, of ordering of the protonic species, which induces ordering of PO 4 tetrahedra. The ordering can be influenced by excess water content, stacking faults and stress (ferroelastic behaviour is evidenced). The conductivity mechanism in HUP is discussed.

Influence of gravity forces in the response of framed structures to earthquake excitations

This paper presents an algorithm which accounts for the instability effects of gravity forces in the dynamic analyses of plane frameworks with uniform members subject to earthquake excitations. A nonlinear static analysis, the formulation of a stress dependent stiffness matrix and the solution of a nonlinear eigenvalue problem are the basic steps of the algorithm. Numerical results are provided to show the effects of gravity forces on the frequencies and modes of vibrations of tall frameworks and on their response to earthquake excitations. These results are compared with those available elsewhere and some extensions and applications are given.

A note on the Raman spectra of water-bearing albite glasses

The Raman spectra of albite glasses with 4.5 and 6.6 weight percent water have been obtained, and are compared with that of a dry sample. The hydrous glasses show bands near 3600 cm −1 due to O-H stretching, and a previously unreported weak band near 1600 cm −1 due to bending of molecular H 2O. Other weak spectral features are discussed, and the effect of dissolved water on the aluminosilicate framework vibrations is considered.

Optimal Control for Extinction in Minimum Time of Spatial Structure Vibrations

Publisher Summary This chapter discusses the feasibility of applying the optimum active control theory for extinction in minimum time of a spatial structure vibration. Modern control theories have been applied successfully to the control of the trajectory and motions of space vehicles and aeronautical systems. The dangerous vibrations are based on the kl-th form, and will be extinguished in minimum time T. the chapter explains the way in which an optimal control for the vibrational process can be obtained, in which the time T of extinguishing an arbitrary kl-th form of the double layer framework vibrations will be a minimum and the energy of the control device is bounded.

Infrared and thermal studies of the interaction of transition-metal ions with the framework of type-X zeolites

Zeolites NaMX (m = Mn(II), Co(II), Ni(II), Cu(II)) were prepared by ion exchange and characterised by chemical analysis, sorption measurements, and X-ray powder photography. The cation-framework interactions were investigated using thermal methods (DTA) and infrared spectroscopy. During dehydration of the zeolites, changes occurred in the infrared spectra, associated with framework vibrations which were attributed (mainly) to cation migration and cation-framework interactions. The patterns of these changes for the Mn(II)-, Co(II),- adn Ni(II)-exchanged zeolites were similar but somewhat different from the observed for the NaCuX zeolites. The thermal stability of the zeolites, as measured by the temperature of the first exotherm (DTA), was not dependent on the extent of the cation exchange for the Mn(II), Co(II), or Ni(II) zeolites but, in the case of the NaCuX zeolites, decrease with increasing copper concentrations. This decrease in stability was correlated with the amount of reactive oxygen available in the NaCuX zeolites.

Numerical operational methods for time‐dependent linear problems

AbstractA general and systematic discussion on the use of the operational method of Laplace transform for numerically solving complex time‐dependent linear problems is presented. Application of Laplace transform with respect to time on the governing differential equations as well as the boundary and initial conditions of the problem reduces it to one independent of time, which is solved in the transform domain by any convenient numerical technique, such as the finite element method, the finite difference method or the boundary integral equation method. Finally, the time domain solution is obtained by a numerical inversion of the transformed solution. Eight existing methods of numerical inversion of the Laplace transform are systematically discussed with respect to their use, range of applicability, accuracy and computational efficiency on the basis of some framework vibration problems. Other applications of the Laplace transform method in conjunction with the finite element method or the boundary integral equation method in the areas of earthquake dynamic response of frameworks, thermaliy induced beam vibrations, forced vibrations of cylindrical shells, dynamic stress concentrations around holes in plates and viscoelastic stress analysis are also briefly described to demonstrate the generality and advantages of the method against other known methods.

Fourier transform infrared photoacoustic spectroscopy of pyridine adsorbed on silica-alumina and .gamma.-alumina

Relative numbers of Bronsted acid to Lewis acid sites on silica-alumina have been determined photoacoustically by an infrared analysis of chemisorbed pyridine compared to similar adsorption of ..gamma..-alumina that has only Lewis sites. Results are similar to those obtained by earlier IR transmission studies that suggested the use of framework vibrations of silica as an internal reference standard. The 20% coverage of the silica-alumina surface by pyridine adsorbed at Bronsted sites found photoacoustically is in good agreement with a previous value of 17% estimated from transmission spectroscopic data. Reproducibility of the photoacoustic measurements is excellent.

Schwingungsspektren von primären, sekundären und tertiären Organoplumbylaminen

The vibrational behaviour of the organolead amines of the type R 3PbNH 2 (R= t-C 4H 9), [R 3Pb] 2NH (R = i-C 4H 9, t-C 4H 9, (CH 3) 3CCH 2) and [R 3Pb] 3N (R = CH 3) and their ND- and 15N-isotopomeres has been investigated. The assignment of the lead-nitrogen framework vibrations for this class of compounds is discussed. The Fermi resonance corrigated difference of frequency Δν s,as (NH 2) of ( t-C 4H 9) 3PbNH 2 yields a HNH-bonding angle ϕ = 107.9°. The temperature dependence of δ(NH 2) is reported in order to characterize the different hydrogen bridging association of the primary amines of the fourth main group. The Δν(CD) values for several organolead compounds in CDCl 3 solution are reported, concerning the different relative basicity of these compounds. The organolead amines are the strongest bases of the organometal amines of the main group IV.

Symmetry Coordinates and Force Field Analysis of a Heptamolybdate, Mo7O24, Model

A complete vibrational analysis is performed for a heptamolybdate, Mo7O24, niodel of C2V symmetry. The symmetry coordinates are classified into those of (a) framework vibrations, (b) ligand vibrations, (c) framework-ligand couplings, and (d) interligand vibrations. A simple valence force field is estimated, and a relative scale for the force constants of the angles is pre­sented. Vibrational frequencies are calculated and the influence of inclusion of redundancies is investigated. The final result is compared with experimental data from infrared and Raman. In the calculation of species A1 a correlation is found to all except one of the polarized Raman frequencies.

Symmetry Coordinates and Tentative Force Field Analysis of a PMo12O40 Model with the Keggin Structure

Abstract A complete vibrational analysis is performed for the 53 atomic PMo12O40 model of Td symmetry. The symmetry coordinates are classified into those of (a) ligand vibrations, (b) framework-ligand couplings, (c) framework vibrations, and (d) interligand vibrations. Simple valence force fields are estimated, and the influence of inclusion of redundancies on the calculated frequencies and symmetry force constants is investigated. Comments are made on calculated symmetry force constant values up to 345 mdyne/Å. Vibrational frequencies are calculated for the Mo3O7 and Mo3O13 units and for the PMo12O40 3- complex ion. For the latter compound the calculated values are compared with experimental data from infrared and Raman spectra.

Molecular vibrations of complexes with trigonal ligands: VII: Hexammines with an octahedral skeleton, application to [Ni(NH 3) 6] 2+

A vibrational analysis is performed for [Ni(NH 3) 6] 2+, which has an octahedral framework structure. The D 3d structure was assumed for the whole complex. Symmetry coordinates are given for all the vibrational modes, which are classified as (a) ligand vibrations, (b) ligand-framework couplings, and (c) framework vibrations. The correlations with the framework O h and ligand C 3v symmetries are worked out. An approximate force field based on the ligand-framework correlated coordinates is developed. It reproduces satisfactorily the observed frequencies for four isotopic ions of[Ni(NH 3) 6] 2+. Approximate calculations for the point-mass model (XY 6) are compared with those of the whole complex. The validity of the point-mass model approximation is confirmed.

Molecular vibrations of complexes with trigonal ligands: VI: Tetrammines with a square-planar-skeleton- the infrared spectrum of [Cu( 15NH 3) 4] 2+

A vibrational analysis is performed for [Cu(NH 3) 4] 2+, which has a square-planar frame work structure. Two versions of symmetry coordinates are produced assuming the C 4V and C 4h structures, respectively. The IR spectrum of [Cu( 15NH 3) 4] 2+ was recorded, and the observed frequencies used as supplementary data in a normal coordinate analysis along with data available for other isotopic compounds. An approximate force field which reproduces satisfactorily the observed frequencies for all the isotopic compounds is developed. The force constants may be classified as pertaining to the (a) ligand vibrations, (b) ligand-framework couplings and (c) framework vibrations. These calculations for the whole complex are compared with (i) results for free NH 3, (ii) the analysis of the XY 4 ( D 4h) point-mass model and (iii) calculations for the pyramidal-axial CuNH 3 ( C 3V) fragment. It is concluded that the effects of kinematic coupling are small. The validity of the point-mass model approximation is confirmed.

Molecular vibrations of free and complexed ligands:symmetry coordinates for the Ni(PF 3) 4 model

Symmetry coordinates of molecular vibrations for the Ni(PF 3) 4 type model are deduced. They are classified as the coordinates for (a) ligand vibrations, (b) ligand-framework couplings, (c) framework vibrations, and finally (d) the redundant coordinates.

Complex formation and kinematic coupling: complexed ethylene

The hypothetical system of an ethylene-thallium(III)-water complex, C 2H 4-Tl 3+-H 2O, was used to demonstrate in principle the possibility of kinematic couplings between internal ligand and complex framework vibrations in an organometallic complex.

Location of cations in zeolites by infrared and Raman spectroscopy

For various hydrated monovalent cationexchanged forms of the synthetic zeolite Linde A a linear relationship has been found between the frequency of some of the framework vibrations and the reciprocal of the sum of the cation and framework oxygen ionic radii; this regularity implies that the Tl+,Ag+, and Li+ions probably occupy similar positions in the crystal structures to those determined for the Na+ and K+ ions by X-ray crystallography.

Vibrations of Timoshenko Beams and Frameworks

A general matrix formulation suitable for a use of the digital computer is presented for dynamic analysis of frameworks composed of prismatic members. The dynamic stiffness coefficients are derived in the form of nondimensional parameters corresponding to the effects of rotatory inertia, shear deformation, and of bending deformation. The individual parameter may be dropped when the appropriate effect is not considered; hence, the stiffness coefficients can be applied to a problem with various considerations of Timoshenko theory, Rayleigh theory, bending and shear, and of Bernoulli-Euler theory. Input data for the computer include the configurations of the framework and the elastic properties of constituent members. The method may be applied to irregular frameworks composed of sloping members with and without sidesway. Numerical examples presented indicate that the effect of rotatory inertia and of shear deformation on the frequencies of frameworks without sidesway is more significant than that of swayed structures.

Infrared Spectra of Acylureas and NN′-Deuterated Acylureas

Abstract The infrared spectra of seven monoacylureas and their NN′-deuterated compounds have been measured in the region between 3600 and 450 cm−1. A number of characteristic absorption bands of the –CONHCONH2 and –CONDCOND2 groups have been found and assigned by referring to the infrared spectra of related compounds and the isotopic frequency shifts. Partial deuteration by mixtures of water and heavy water has been made to distinguish the absorptions due to the NH and NH2 groups from each other. The features of infrared spectra of monoacylureas can be explained by regarding them as composite spectra of aliphatic imides and urea. From the effect of the alkyl frame-work vibrations for the imide III frequency, it is suggested that the RCONH– group of monoacylureas takes the trans conformation.