Comparative Study of Sol-Gel Derived 2.5% and 11.3% Y2O3-ZrO2 by Perturbed Angular Correlations Spectroscopy

Powders and thin films of zirconia doped with 2.5 and 11.3 mole% Y₂O₃ have been fabricated via the sol-gel route. The phase structure and its thermal evolution have been investigated using mainly the hyperfine nuclear technique of Perturbed Angular Correlations. Both resulting structures, tetragonal and cubic, exhibited at least two different configurations around zirconium sites. The tetragonal powder involves an activation energy for vacancy fast diffusion lower than the cubic powder. Conclusions have also been drawn regarding the thermal stability of the ceramics under different heat treatments. Member of Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina. Member of Comisión de Investigaciones Científicas de la Provincia de Buenos Aires (CICPBA), Argentina.     

Simultaneous determination of Co,Mo, Ni,W and moisture content in hydrodesulfurization catalysts by neutron capture gamma-ray spectrometry

Neutron capture γ-ray spectrometry has been applied for the simultaneous determination of Co, Mo, Ni, W and moisture in hydrodesulfurization catalysts. The Co, Mo and water content are determined in a 10 min irradiation using a 500–2500 keV calibration. Ni and W, if present, require, and additional 30 min irradiation, using a 5000–9000 keV calibration. In both cases TiO₂ is used as internal standard. Results are in good agreement with those obtained by NAA for metals and by TGA for moisture. This work was supported by Grant N⁰ 31.26-Sl-0304 from the Consejo Nacional de Investigaciones Científicas y Technológicas.     

Liquid crystals formed in sodium alkyl sulfates-water systems studied by positron annihilation techniques

Lyotrophic phase transitions were investigated in liquid crystalline systems of sodium alkyl sulfate-water. The positron annihilation parameters indicated the presence of a nematic phase in sodium dodecyl sulfate water-system in absence of additives. The effect of the hydrocarbon chain-length and unsaturation of the surfactant on the nematic phase formation were also studied. Liquid crystals of sodium 10-undecenoate were polymerized by ultraviolet irradiation. Polymerization is seen to cause a gradual change from the hexagonal to the lamellae phase.This research is in furtherance of the USA-Mexico Cooperative Science Program through the National Science Foundation and the Consejo Nacional de Ciencia y Tecnología     

Disclination and molecular director studies on bowlic columnar nematic phase using mosaic-like morphology decoration method

Two bowlic cyclotriveratrylene CTV-1 and CTV-2, with different peripheral groups of —OCH₃ and —OCH₂CH₃ for CTV-1 and —OCH₃ and —OCH₂COOCH₃ for CTV-2, respectively, were synthesized by typical trimerization via a multistep sequence from vanillin. Both bowlic CTV molecules were thermotropic liquid crystals, and presented typical grainy textures of the nematic phase and homogeneous texture of the single domain nematic phase. It is of interest to observe the regular and beautiful mosaic-like morphologies after cooling from liquid crystalline phases, which appeared and vanished repeatedly in several circles of cooling and heating. The size of each mosaic was several dozens of micron. In nature, the mosaic-like morphologies are the optical pattern of cracks formed by the shrinking, due to the crystallization of frozen texture of nematic phases. By means of scanning electron microscopy, the mosaic-like morphologies were observed to consist of lamellae, and each mosaic is a rectangular multi-layer lamella, which is composed of packed single-layered lamellae. The fibrils in the diameter of about 1 μm were observed, which are the structural units of lamellae and would be the bundles of the bowlic molecular columns. The mosaic-like morphologies decorate the bowlic molecular columnar nematic phase, therefore, a novel mosaic-like morphologies decoration method was applied to reveal the director distribution of several kinds of point disclinations, such as s = +1(δ=0° and δ =90 °) and s = ±1/2, and Nèel domain walls. It was shown that the bowlic molecular columnar nematic phase behaved as normal nematic phases; however, the basic structural units ordered were the bowlic molecular column or the bundles of bowlic molecular column (i.e. fibrils), but not the bowlic molecules themselves. The bowlic molecular columns acted as the rod-like molecules in a normal nematic phase. Therefore, a new term BCN (bowlic columnar nematic phase) is used to describe the anomalous nematic phase in this paper. Supported by the National Natural Science Foundation of China (Grant No. 20774077), the Natural Science Foundation of Fujian, China (Grant Nos. E0510003 & E0710025) and the Project of Science and Technology of Xiamen, China (Grant No. 3502Z20055013)     

Liquid crystal and solution phases of sodium dodecyl-p-benzene sulphonate (NaLAS) and octa-oxyethylene glycol hexadecyl ether (C16E8): 1:1 mixtures in water

The liquid crystals and other phases formed when the mixed surfactant system sodium dodecyl-p-benzene sulphonate (NaLAS) and octa-oxyethylene glycol hexadecyl ether (C₁₆E₈, 1:1 by weight) is dispersed in water have been investigated using optical microscopy, X-ray diffraction and differential scanning calorimetry. Despite the fact that neat LAS is a multi-phase solid and C₁₆E₈ is a crystalline solid, when the two are mixed at temperatures above the melting temperature of the C₁₆E₈ with no water present, what appears to be a metastable gel phase formed containing only a small volume fraction of un-dissolved LAS (ca. 5%). Moreover, when water is added to the system, the phase behaviour of the mixture considerably differs to that of either of the individual components. We report a detailed phase study on this mixture here particularly focussing on the ‘neat’ mixture. The phase behaviour when water is added is also discussed. Particularly interesting is the presence of a micellar phase between the hexagonal and lamellar phases thought to be due to weak interactions between micelles during the transition from rods to discs. In addition, the presence of a low temperature intermediate phase is discussed.     

Magnesium and calcium surfactants Ternary phase diagrams of magnesium and calcium dodecylsulphate with decanol and water

The isothermal ternary phase diagrams for the systems magnesium dodecylsulphate-decanol-water at 40 °C and calcium dodecylsulphate-decanol-water at 50 °C are determined by water deuteron NMR and polarizing microscopic studies. In the magnesium system, three liquid crystalline phases (lamellar and normal and reverse hexagonal) and two isotropic (normal and reverse) solution phases are characterized and their ranges of existence are obtained. The calcium system yields the same liquid crystalline phases, but only the lamellar liquid crystalline phase is investigated in detail. The important observations made are: (i) The lamellar liquid crystalline phase for the magnesium and calcium systems can incorporate, respectively, a maximum of 22.5 and 14.3 mole water per mole surfactant ion against 139 mole water for the corresponding sodium system. (ii) The reverse hexagonal liquid crystalline phase is formed for both the magnesium and calcium systems while no such liquid crystalline phase exists for the corresponding sodium system. (iii) The²H NMR quadrupole splittings obtained in the liquid crystalline phases for C₈SO ₄ ^– and C₁₂SO ₄ ^– surfactant systems with different counterions (Ca²⁺,Mg²⁺,Be²⁺,Na⁺) reveal that surfactant hydration is almost independent of alkyl chain length and counterions.     

Interaction independent π bond orders for certain excited states

Particular solutions of the bond order equations are shown for certain excited states, common to different conjugated systems and interaction-independent. The P matrix for these states has: 1 in the principal diagonal (charges), ± 1 in the secondary one, zero otherwise.Consejo Nacional de Investigaciones Cientificas y Técnicas.     

Phase diagram of water between hydrophobic surfaces

Molecular dynamics simulations demonstrate that there are at least two classes of quasi-two-dimensional solid water into which liquid water confined between hydrophobic surfaces freezes spontaneously and whose hydrogen-bond networks are as fully connected as those of bulk ice. One of them is the monolayer ice and the other is the bilayer solid which takes either a crystalline or an amorphous form. Here we present the phase transformations among liquid, bilayer amorphous (or crystalline) ice, and monolayer ice phases at various thermodynamic conditions, then determine curves of melting, freezing, and solid-solid structural change on the isostress planes where temperature and intersurface distance are variable, and finally we propose a phase diagram of the confined water in the temperature-pressure-distance space.     

Comparison of analytical methods for the determination of trace amounts of strontium and yttrium by photon induced X-ray fluorescence techniques in lateritic materials

Three different analytical methods for the determination of strontium and yttrium in Venezuelan latterites by radioisotope induced X-ray fluorescence are compared, also with results from conventional wavelength dispersive X-ray fluorescence. The samples analyzed were from Cerro Impacto, Venezuela. The photon-induced energy dispersive X-ray fluorescence system consisted of a¹⁰⁹Cd (7 mCi) source for excitation of the characteristic K X-rays for strontium and yttrium. The detection system employed a high resolution Si(Li) detector and was completely controlled by a PDP-11/05 processor. Of the three analytical methods described, the internal standard-thin film technique was shown to be slightly superior to the conventional standard calibration curve method and the standard additon/dilution procedure. This can be explained by considering the effectiveness of the compensation of the sources of errors by these methods. It should also be noted that in the case of wavelength dispersive X-ray fluorescence, an about 5–10 times greater sample is needed, which is a limitation compared to energy dispersive X-ray fluorescence in some cases. Finally, typical relative standard deviations of the energy dispersive X-ray fluorescence methods were about 10–15% for the range of about 100–100 ppm of strontium and yttrium; these values are acceptable considering the large degree of heterogeneity in this type of geological material. This project was funded by Consejo Nacional de Investigaciones Científicas y Technológicas (CONICIT) and performed as part of UNESCO's IGCP-129 “Lateritization Processes” project.     

Application of radioisotope excited energy dispersive X-ray fluorescence determination of palladium in catalysts and doped venezuelan laterites

A rapid procedure for determining palladium in catalysts and geoiogical materials is presented. This method involves the use of an²⁴¹Am (100 mC) source for excitation and employs a PDP-11/05 processor for the data acquisition and analysis by energy-dispersive X-ray fluorescence. The relative standard deviation for 5 independent determinations is less than 3% for 100 seconds of fluorescent time. The calculated and measured values agreed well for both, the prepared standards and the doped Venezuelan laterites. Finally, data on the different sources of error is given including counting time, sample preparation, and total error. This investigation was funded in parts by CONICIT (Consejo Nacional de Investigaciones Científicas y Technológicas).     

On a SC method for determining bond orders in alternant hydrocarbons

A method proposed by Hall allowing direct calculation of bond orders of even AH without computing first the MO's is extended a) so as to take into account some states which include singly occupied MO's and b) to odd AH.Consejo Nacional de Investigaciones Científicas y Técnicas     

The self-organization properties of <Emphasis Type="Italic">n</Emphasis>-dodecylammonium α-glutamate/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>5</Subscript>H<Subscript>11</Subscript>OH/water system

A biocompatible surfactant-n-dodecylammonium α-glutamate (GDA) with biodegradable and biocompatible properties was synthesized, and the phase behavior and the structural properties of GDA/n-pentanol/water system was studied by small-angle X-ray diffraction, electron spin resonance, and freeze-fracture transmission electron microscopy (FF-TEM). In the ternary phase diagram of GDA/n-pentanol/water system, there exist three isotropic regions—O/W, bicontinuous, and W/O structures, and two anisotropic regions—hexagonal liquid crystal (HEX), and lamellar liquid crystal (LLC) regions. UV irradiation causes the decrease in the interlayer space, d, of lamellar liquid crystal and in the radius, r, of column aggregates of hexagonal liquid crystal, but it has little effect on the structure of O/W and W/O microemulsions.     

Phase diagrams of the systems (I) Sodium dodecyl sulphate — octyl trimethyl ammonium bromide-water, (II) Sodium dodecyl sulphate — dodecyl trimethyl ammonium bromide-water

Summary Ternary phase diagrams of the pseudo three component systems sodium dodeoyl sulphate (SDS) + octyl trimethyl ammonium bromide + water (I) and SDS + dodecyl trimethyl ammonium bromide + water (II) at 298.2 K are presented. In (I) the liquid crystal region stretches continuously between the two surfactant/water axes and (for a 1∶1 surfactant ratio) penetrates very deeply into the water corner. There also appears to be a two liquid region near this corner. In (II) solid, probably 1∶1 complex, is formed over much of the diagram. An explanation of the transition between neat and middle phases at constant water content is forwarded.

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Zusammenfassung Es werden die tern?ren Phasendiagramme der Pseudodreikomponentensysteme von Natriumdodecylsulfat (NaDS) + Oktyltrimethylammoniumbromid + Wasser (I) sowie NaDS + Dodecyltrimethylammonium-bromid + Wasser (II) bei 298,2 °K dargestellt. In (I) streckt sich das kristallin-flüssige Gebiet endlos zwischen den zwei Tensid/Wasser-Achsen und (für ein Tensidverh?ltnis 1∶1) dringt sehr tief in die Wasserecke ein. In (II) wird ein fester Komplex — wahrscheinlich 1∶1 — über einen wesentlichen Teil des Diagramms gebildet. Es wird eine Erkl?rung des übergangs zwischen der reinen („neat“) und der mittleren Phase bei konstantem Wassergehalt vorgestellt.

     

Purete radionucleidique du solute injectable d'eau tritiee

Conclusion Nous avons mis au point une méthode simple permettent de détecter les impuretés β^-, à l'aide d'un compteur à scintillation liquide. La courbe établie en mesurant la variation du taux de comptage en fonction du seuil de discriminateur pour la préparation à l'essai, doit être parallèle à celle obtenue, dans les mêmes conditions, avec une solution étalon d'eau tritiée. Le mélange scintillant dioxane-naphtalène, 2,5-diphényloxazole (PPO), 1,4-bis-2-(4-méthyl-5-phényloxazolyl)-benzène (diméthyl POPOP) [1 litre/100 g/7 g/0,3 g] permet de détecter la présence d'au moins 0,005% de³⁵S, 0,004% de¹⁴C et 0,04% de⁴⁵Ca.

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The radionuclidic purity of tritiated water is checked by an easy and rapid method using a liquid scintillation counter. The liquid scintillator: dioxane (1 liter)/naphtalene (100 g)/(PPO (7 g)/dimethyl POPOP (0.3 g) allows the detection of, at least, 0.005% of sulfur—³⁵S, 0.004% of carbon—¹⁴C and 0.004% of⁴⁵Ca.

     

Polarization transfer solid-state NMR for studying surfactant phase behavior

The phase behavior of amphiphiles, e.g., lipids and surfactants, at low water content is of great interest for many technical and pharmaceutical applications. When put in contact with air having a moderate relative humidity, amphiphiles often exhibit coexistence between solid and liquid crystalline phases, making their complete characterization difficult. This study describes a (13)C solid-state NMR technique for the investigation of amphiphile phase behavior in the water-poor regime. While the (13)C chemical shift is an indicator of molecular conformation, the (13)C signal intensities obtained with the CP and INEPT polarization transfer schemes yield information on molecular dynamics. A theoretical analysis incorporating the effect of molecular segment reorientation, with the correlation time τ(c) and order parameter S, shows that INEPT is most efficient for mobile segments with τ(c) < 0.01 μs and S < 0.05, while CP yields maximal signal for rigid segments with τ(c) > 10 μs and/or S > 0.5 under typical solid-state NMR experimental conditions. For liquid crystalline phases, where τ(c) < 0.01 μs and 0 < S < 0.3, the observed CP and INEPT intensities serve as a gauge of S. The combination of information on molecular conformation and dynamics permits facile phase diagram determination for systems with solid crystalline, solid amorphous, anisotropic liquid crystalline, and isotropic liquid (crystalline) phases as demonstrated by experiments on a series of reference systems with known phase structure. Three solid phases (anhydrous crystal, dihydrate, gel), two anisotropic liquid crystalline phases (normal hexagonal, lamellar), and two isotropic liquid crystalline phases (micellar cubic, bicontinuous cubic) are identified in the temperature-composition phase diagram of the cetyltrimethylammonium succinate/water system. Replacing the succinate counterion with DNA prevents the formation of phases other than hexagonal and leads to a general increase of τ(c).     

Thermal,physicochemical and microstructural studies of binary organic eutectic systems

Solid–liquid phase equilibrium data of three binary organic systems, namely, 3-hydroxybenzaldehyde (HB)—4-bromo-2-nitroanilne (BNA), benzoin (BN)—resorcinol (RC) and urea (U)—1,3-dinitrobenzene (DNB), were studied by the thaw–melt method. While the former two systems show the formation of simple eutectic, the third system shows the formation of a monotectic and a eutectic with a large immiscibility region where two immiscible liquid phases are in equilibrium with a liquid of single phase. Growth kinetics of the pure components, the monotectic and the eutectics, studied by measuring the rate of movement (v) of solid–liquid interface in a thin U-tube at different undercoolings (ΔT) suggests the applicability of the Hillig–Turnbull’s equation: v = u (ΔT) ⁿ , where v and n are the constants depending on the nature of the materials involved. The thermal properties of materials such as heat of mixing, entropy of fusion, roughness parameter, interfacial energy, and excess thermodynamic functions were computed from the enthalpy of fusion values, determined by differential scanning calorimeter (Mettler DSC-4000) system. The role of solid–liquid interfacial energy on morphologic change of monotectic growth has also been discussed. The microstructures of monotectic and eutectics were taken which showed lamellar and federal features.     

Influence of biomass on hydrodynamics of an internal loop airlift reactor

The effect of the biomass presence on the overall circulation velocity, the linear velocities both in the riser and the downcomer and the overall gas hold-up was studied in a three-phase internal loop airlift reactor (ILALR). The measured data were compared with those obtained using a two-phase system (air—water). All experiments were carried out in a 40 dm³ ILALR at six different biomass concentrations (ranging from 0 g dm⁻³ to 7.5 g dm⁻³), at a temperature of 30°C, under atmospheric pressure. Air and water were used as the gas and liquid model media, respectively. Pellets of Aspergillus niger produced during the fermentation of glucose to gluconic acid in the ILALR were considered solid phase. In addition, liquid velocities were measured during the fermentation of glucose to gluconic acid using Aspergillus niger. All measurements were performed in a bubble circulation regime. At given experimental conditions the effect of the biomass on the circulation velocities in the ILALR was negligible. However, increasing of the biomass concentration led to lower values of the total gas hold-up. Presented at the 33rd International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 22–26 May 2006.     

Synthesis,characterization and fungicidal activity of zinc diethyldithiocarbamate and phosphate

Monolayers of amphiphilic di-block copolymer, PEO₄₀-b-PMA(Az)₁₉ on water surface and solid surfaces, such as silicon wafer and quartz glass, were analyzed by surface pressure — molecular area (π-A) isotherm, UV-Vis spectroscopy, atomic force microscopy (AFM) and total X-ray reflectivity (TXR). The monolayer prepared at 22 mN m-1 consisted of H aggregated azobezene (Az) moieties, which orientated perpendicular to the solid surface. The monolayer structure, including H aggregated Az and orientation of Az, was stable after annealing at 98°C, at which temperature the hydrophilic PEO domain was the liquid phase and the hydrophobic PMA(Az) was in the smectic A phase.     

The simultaneous determinations of cobalt,nickel and molybdenum in hydrodesulfurization catalysts by photon induced X-ray fluorescence

A rapid radioisotope induced energy-dispersive X-ray fluorescence procedure for the simultaneous determinations of Cobalt, Nickel and Molybdenum in hydrodesulfurization catalysts is presented. A¹⁰⁹Cd (7 mCi) source is used as the excitation system coupled to a high resolution Si(Li) detector. A PDP-11/05 processor is employed as a multichannel analyzer and also to automatically control the complete system by means of a prewritten computer program. The relative standard deviations for the three determinations (CoO, NiO and MoO₃) are less than 5% for 300 seconds of fluorescent time for a typical sample. Finally a comparison of results by different methods is given to check the accuracy since no standard reference materials are available for catalytic material. This project was funded by Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICIT).     

A thermodynamic approach to the selectivity of liquid crystalline reentrant phases

The thermodynamic characteristics and selectivity of sorption of disubstituted benzene, pyridine, and naphthalene by the p-n-nonyloxybenzoyloxy-p′-cyanoazobenzene, p-n-hexyloxycinnamoyloxy-p′-cyanoazobenzene liquid crystalline phases and their mixture was studied by gas chromatography. The reentrant nematic phase of a mixture of mesogens was found to possess high selectivity to structural isomers. The results of manifestation of liquid crystalline phase selectivity are discussed on the basis of the enthalpy and entropy characteristics of solution of sorbates.