Chemical control of quartz suspensions aggregative stability

This article studies the influence of zeta potential on the fluidization of quartz suspensions and the possibility of its chemical control by changing the aggregative stability of the system using a reagent whose main component is the reaction product of amines and phosphoric esters. It is shown that aggregation of quartz, when treated by the specified chemical system, takes place due to an electrokinetic potential decrease resulting from reduction in the thickness of the diffuse portion of the electrical double layer around the quartz particles. It was found that chemical treatment of the quartz suspension contributes to a significant increase in fluidization onset velocity and fluid filtration coefficient. The article also proposed a correction to the Richardson–Zaki equation to take into account the aggregation of quartz particles. In order to explain the filtration properties of treated sand, a model was developed that takes into account the influence of aggregation on the porosity of the porous medium. The results presented here can be of use when developing oil fields composed of poorly consolidated sandstones.     

Density functional calculations on CO attached to PtnRu(10−n) (n = 6–10) clusters

B3LYP and SCF‐Xα calculations have been performed on Pt_nRu_(10−n)CO (n = 6–10) clusters. The work aims to simulate the adsorption of CO on the (111) surface of platinum metal and to examine the electronic effects that arise when some Pt atoms are replaced with Ru. Adsorption energies and Pt C and C O stretching frequencies have been calculated for each cluster. Ru does affect the electronic structure of the clusters, the calculated adsorption energies, and frequencies, the Pt C frequency more than the C O. The donation‐backbonding mechanism that accompanies the shift in CO stretching frequency that occurs when CO adsorbs on platinum does not explain the differences in frequency shift observed in CO on various Pt/Ru surfaces. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 77: 589–598, 2000     

Higher temperature order–disorder transition,electrical and optical properties of [N(C2H5)4]2Pd2Cl6 compound

[N(C₂H₅)₄]₂Pd₂Cl₆ hybrid compound with semiconducting character was synthetized and characterized by X-ray diffraction, the thermal, optical and electrical properties. X-ray diffraction indicates that the compound crystallize at room temperature in the orthorhombic system and (Immm) space group. Two endothermic peaks at, 343 K and 440 K were observed in the DSC measurements corresponding to the evaporation of water molecules and order-disorder transition, respectively. The optical band gap (E_g = 4.34 eV) was deduced by the Tauc relation. The electrical properties was studied using the impedance spectroscopy in the frequency range of 0.1 Hz to 1 MHz and over the temperature range of 270 K to 480 K. The analysis of Nyquist plots revealed the presence of grains, grain boundaries and the electrode effects. The equivalent circuit was determined. The Ac conductivity was analyzed by the Jonsher low and the conduction mechanism was deduced based in the Elliot theory and indicate that the correlated barrier hopping model (CBH) was described the two regions II and IV and the overlapping polaron model (OLPT) the right model described the conduction in the regions I and III.     

Optical and electrical properties and conduction mechanism of [(CH3)2NH2]2CoCl4

Monoclinic crystals of [(CH₃)₂NH₂]₂CoCl₄ are of the space group P2₁/n. Unit cell dimensions are as follows: a = 8.5393 Å, b = 11.3905 Å, c = 13.4069 Å and β = 91.02°. This compound undergoes several phase transitions. The optical properties were measured by means of UV–visible absorption spectroscopy in the range 200–800 nm. Analysis of the data revealed the existence of direct allowed optical transition mechanisms with bandgap energy equal to 3.84 eV. The electrical conductivity of [(CH₃)₂NH₂]₂CoCl₄ was studied in the frequency range 10⁻¹–10⁶ Hz and in the temperature range 411–449 K by means of impedance spectroscopy. Impedance and modulus analyses indicated temperature-independent distribution of relaxation times and non-Debye behavior in this material. A super-linear power law was observed for the AC conductivity, which was analyzed based on the jump relaxation model σ_ac = σ_dc + A₁ω^s1 + A₂ω^s2. Accordingly, the first AC term A₁ω^s1 corresponds to translational hopping motion and the second term A₂ω^s2 to well-localized hopping and/or reorientational motion. Conduction takes place via correlated barrier hopping in phases I and II.     

Tailoring of Polarizing Agents in the bTurea Series for Cross‐Effect Dynamic Nuclear Polarization in Aqueous Media

A series of 18 nitroxide biradicals derived from bTurea has been prepared, and their enhancement factors ? (¹H) in cross‐effect dynamic nuclear polarization (CE DNP) NMR experiments at 9.4 and 14.1 T and 100 K in a DNP‐optimized glycerol/water matrix (“DNP juice”) have been studied. We observe that ? (¹H) is strongly correlated with the substituents on the polarizing agents, and its trend is discussed in terms of different molecular parameters: solubility, average e–e distance, relative orientation of the nitroxide moieties, and electron spin relaxation times. We show that too short an e–e distance or too long a T_1e can dramatically limit ? (¹H). Our study also shows that the molecular structure of AMUPol is not optimal and its ? (¹H) could be further improved through stronger interaction with the glassy matrix and a better orientation of the TEMPO moieties. A new AMUPol derivative introduced here provides a better ? (¹H) than AMUPol itself (by a factor of ca. 1.2).     

A note on Hermite polynomials of several variables

The present paper deals with an extension of certain results obtained by Burchnall for Hermite polynomials to similar results for Hermite polynomials of several variables.     

Properties of amorphous carbon nitride prepared by RF reactive sputtering

The local microstructure and optical and electrical properties were investigated of amorphous carbon nitride (a-CN) films deposited by reactive radio-frequency (RF) sputtering. Two series prepared in nitrogen or in a nitrogen and argon mixture were studied. The optical properties were investigated by transmittance/reflectance and photothermal deflection spectroscopies. Combined infrared measurements and Raman scattering spectroscopies were used to investigate the microstructure of a-CN films in terms of nitrogen incorporation within the films and C sp ² content. These experiments were completed by dark electrical conductivity measurements performed in coplanar configuration in the temperature range 50–450?K. The films exhibit semiconductor behaviour and the temperature dependence suggests two types of conduction. An increase in nitrogen incorporation induces an increase with clustering of sp ² phase replacing C=C olefinic groups with aromatic groups.     

VCl3 catalyzed imine-based multicomponent reactions for the facile access of functionalized tetrahydropyridines and β-amino carbonyls

Abstract  

A simple, mild, and highly efficient method has been developed for the preparation of functionalized tetrahydropyridines and β-amino carbonyls from the multicomponent reactions involving in situ imines and vanadium (III) chloride as a Lewis acid. The multicomponent reaction of two equivalents of aromatic aldehyde, two equivalents of amine, and one equivalent β-keto ester in the presence of catalytic amount of VCl₃ provides highly atom economic five-component tetrahydropyridines in very good yields. The same catalyst was found useful for the efficient synthesis of a wide variety of β-amino ketones using direct-type Mannich reaction of aromatic aldehyde, amine, and aromatic ketones. The notable advantages of this method are simple procedure, short reaction time and good yields, and applicable to broad range of substrates.