Crystal structure and magnetic structure of TbOOH

The monoclinic modification of terbium oxide hydroxide, TbOOH, was prepared using hydrothermal technique. The crystal structure was investigated by three-dimensional single-crystal X-ray analysis and was refined to a conventional R-value of 8.1%. The space group is $\text{P2}{}_1\text{m}$, No. 11, with a = 6.04 Å, b = 3.69 Å, c = 4.33 Å, and β = 109.0°. The terbium atom is seven coordinated with oxygen atoms, and the structure is not hydrogen bonded.The compound is antiferromagnetic with a Néel temperature of 10°K. Neutron diffraction powder patterns were measured at 300°K and 4.2°K. The magnetic super lattice reflections were indexed on the basis of a monoclinic unit cell with the dimensions a_M = 2a, b_M = b, c_M = c, and β_M = β, where a, b, c, and β are the dimensions of the chemical unit cell. The structure contains two independent magnetic atoms. A nonclinear antiferromagnetic arrangement of the spins describes the magnetic structure. The spin at one atom has an angle of 43° with the ac plane and the projection of the spin on the ac plane has an angle of 59° with the a axis. The spin on the other atom has an angle of ?43° with the ac plane, the projection having the same angle of 59° with the a axis.     

Algebraic structure count

Further studies of an efficient graphical algorithmic method for determining algebraic structure count of polycyclic polyene systems possessing 4n rings are presented.     

Typical fiber structure

Model fibers of polyethylene and nylon 6 were strained in the direction of the fiber axis and the internal deformation of the samples was studied by large-angle and small-angle x-ray diffraction. The compression of samples along the fiber axis was successfully carried out, and the results obtained by x-ray methods yielded more interesting information on the structure of the fibers than was obtained in extension. A model for the structure of the fiber was constructed on the basis of the results on compressed fibers. In this model, crystals are distributed in cylindrical symmetry around the fiber axis keeping a crystal axis tangential to circles in the section normal to the fiber axis. The characteristic crystal axis is the b axis in polyethylene and the a axis in nylon 6. The chain axis of the crystals varies in orientation with respect to the fiber axis. In compression of fibers with such a structure, the crystals rotate around the characteristic axis indicated above. In the case of nylon 6 fiber, only this simple rotation seems to occur, while additional changes occur in polyethylene fibers. However, the simple rotation predominates even in polyethylene fibers. This fiber structure is correlated with the structure of thin films of the materials. This similarity proves the existence of a common mechanism for the origin of the structure of fibers and films.     

Kaolinite flocculation structure

Effective flocculation and dewatering of mineral processing streams containing colloidal clays has become increasingly urgent. Release of water from slurries in tailings streams and dam beds for recycle water consumption, is usually slow and incomplete. To achieve fast settling and minimization of retained water, individual particles need to be bound, in the initial stages of thickening, into large, high-density aggregates, which may sediment more rapidly with lower intra-aggregate water content. Quantitative cryo-SEM image analysis shows that the structure of aggregates formed before flocculant addition has a determinative effect on these outcomes. Without flocculant addition, 3 stages occur in the mechanism of primary dewatering of kaolinite at pH 8: initially, the dispersed structures already show edge-edge (EE) and edge-face (EF) inter-particle associations but these are open, loose and easily disrupted; in the hindered settling region, aggregates are in adherent, chain-like structures of EE and stairstep face-face (FF) associations; this network structure slowly partially rearranges from EE chains to more compact face-face (FF) contacts densifying the aggregates with increased settling rates. During settling, the sponge-like network structure with EE and FF string-like aggregates, limits dewatering because the steric effects in the resulting partially-gelled aggregate structures are dominant. With flocculant addition, the internal structure and networking of the pre-aggregates is largely preserved but they are rapidly and effectively bound together by the aggregate-bridging action of the flocculant. The effects of initial pH and Ca ion addition on these structures are also analyzed. Statistical analysis from cryo-SEM imaging shows that there is an inverse correlation of intra-aggregate porosity with Darcian inter-aggregate permeability whereas there is a strong positive correlation of Darcian permeability with settling and primary dewatering rate as a function of pH in suspension. Graphs of partial void contributions also suggest that it is not total porosity that dominates permeability in these systems but the abundance of larger intra-aggregate voids.     

Computer-assisted structure elucidation

Summary Program CASE, an evolving computer model of the structure elucidation process, treats three major tasks: reduction of the chemical and spectral properties of a compound of unknown structure to their structural implications, generation of all complete molecular structures compatible with the structural features identified, and ranking these structures on the basis of the degree of fit between predicted and observed spectral properties. The current program status is described and program application is illustrated.

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Strukturaufklärung mit Computer-Hilfe

Zusammenfassung Ein in Entwicklung befindliches Computer-Modell (program CASE) wird beschrieben, das hauptsächlich folgende drei Aufgaben erfüllt: Zuordnung der chemischen und spektralen Eigenschaften einer Verbindung unbekannter Struktur zu ihren strukturellen Bedeutungen; Aufstellung aller Strukturen, die mit den gefundenen Eigenschaften im Einklang stehen; Einordnung dieser Strukturen je nach Übereinstimmung mit den vorhergesagten und gefundenen Parametern. Der derzeitige Entwicklungsstand des Programms wird erläutert und die Anwendung diskutiert.

     

Selenoketene substitution structure

Microwave studies (26.5–40 GHz) of further isotopic species of selenoketene formed by pyrolysis of 1,2,3-selenodiazole (¹²CH₂¹²C^76,77,82Se, ¹²CH₂¹³C⁸⁰Se and ¹³CH₂¹²C⁸⁰Se) and by pyrolysis of 5-deuterio-1,2,3-selenodiazole (¹²CHD¹²C^78,80Se) are reported. In conjunction with earlier results for ¹²CH¹²C^78,80Se an r_s structure has been derived with distances SeC (1.706 Å), CC (1.303 Å), CH (1.0908 A) and a HCH bond angle of 119.7°. The geometry of the CH₂C moiety of selenoketene is closer to allene, CH₂CCH₂, than to ketene, CH₂CO.     

Multiphase structure of segmented polyurethanes: Its relation with spherulite structure

Small-angle light-scattering (SALS), Polarized light microscopy (PLM), differntial scanning calorimetry (DSC), and small-angle x-ray scattering (SAXS) were used to study morphological changes in segmented polyurethanes with 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) as the hard segment. It was found. for the first time, that spherulites could form from the melt by quenching the polyurethanes in the melt state to annealing temperatures between 120°C and T_h, the highest annealing temperature for spherulite formation. T_h ranged from 140°C to ca. 170°C and depended upon the hard-and soft-segment compatibility. Within the range 120°C to T_h, the radius of the spherulite increased with increasing hard-segment content at each fixed annealing temperature. Annealing at 135–140°C gave rise to the largest spherulites. SAXS was used to investigate the phase-separated structures corresponding to the spherulite formation. The interdomain spacing increased with increasing hard-segment content and with increasing annealing temperature.The degree of phase separation first increased with increasing annealing temperature from room temperatures (ca. 25°C), reached a maximum at ca. 107°C, and then decreased with further increase in the annealing temperature. On the basis of these observations, the mechanisms of phase separation, crystallization, and spherulite formation are discussed. © 1993 John Wiley & Sons, Inc.     

The analysis of emulsion structure changes during flow through porous structure

The aspects of emulsion flow through porous media are crucial for many industrial processes, especially in the development of Enhanced Oil Recovery (EOR) techniques and also during oily wastewater purification. In this paper we investigated the hydrodynamics of gravitational flow of emulsions with inner phase of different concentrations. We also tried to determine the quantitative changes in the droplet diameter distribution and concentration of emulsion flowing out of the bed. On the basis of experimental data, it was possible to describe the influence of emulsion concentration on the hydrodynamics process and to characterize the changes of the structure of emulsion.     

Self-assembly patterning of colloidal crystals constructed from opal structure or NaCl structure

We developed a novel self-assembly process to fabricate an orderly array of particle wires constructed from a close-packed colloidal crystal without preparation of patterned templates. A substrate was immersed vertically into a SiO2 colloidal solution, and the liquid surface moved downward upon evaporation of solution. Particles formed a mono-/multiparticle layer, which was cut by the periodic drop-off of solution. The orderly array of particle wires was successfully fabricated, showing the suitability of the self-assembly process for the fabrication of nano-/microstructures constructed from nano-/microparticles or blocks. The mechanism of the assembly process and control of thickness, width, and interval of particle wires were further discussed. Moreover, an array of particle wires constructed not from close-packed face-centered cubic (or hexagonal close packed) structure but from two kinds of particles was realized to fabricate an array of particle wires with NaCl structure by this self-assembly process.