Methodical Thermolysis of [Ba2Ti2(thd)4(OnPr)8(nPrOH)2] under Autogenous Pressure Followed by Combustion for the Synthesis of Dielectric Tetragonal BaTiO3 Nanopowder

Tetragonal powders : Dielectric tetragonal BaTiO₃ nanopowder was synthesized in a solvent‐less, efficient process by the thermolysis of a single [Ba₂Ti₂(thd)₄(OnPr)₈(nPrOH)₂] precursor in a closed reactor at 700 °C under autogenous pressure, followed by combustion. The BaTiO₃ nanopowder is characterized thoroughly, employing advanced morphological, compositional, structural, and thermal techniques, and the dielectric constant is accounted.

     

Achieving fast convergence of ab initio free energy perturbation calculations with the adaptive force-matching method

This paper studies the possibility of improving the convergence of ab initio free energy perturbation (FEP) calculations by developing customized force fields with the adaptive force-matching (AFM) method. The ab initio FEP method relies on a molecular mechanics (MM) potential to sample configuration space. If the Boltzmann weight of the MM sampling is close to that of the ab initio method, the efficiency of ab initio FEP will be optimal. The difference in the Boltzmann weights can be quantified by the relative energy difference distribution (REDD). The force field developed through AFM significantly improves the REDD when compared with standard MM models, thus improving the convergence of the ab initio FEP calculation. The static dielectric constant ε_s of ice-Ih was studied with PW-91 through ab initio FEP. With a customized force field developed through AFM, we were able to converge ε_s to 80 ± 4 with 3,600 configurations. A similar ab initio FEP calculation with the TIP4P model would require 220 times more configurations to achieve the same accuracy. Our study indicates that the PW-91 functional underestimates ice-Ih ε_s by about 20%.     

Preparation and characterization of alumina supported silicalite membranes by sol–gel hydrothermal method

Two types of unsupported zeolites (silicalite-1 and silicalite-2) and porous alumina discs supports were prepared by the hydrothermal sol–gel synthesis method. The influence of the raw materials used as SiO₂ source, the temperature of the thermal treatment and the presence of the ceramic support on the crystallization of zeolites were studied. The reaction products were characterized by X-ray diffraction (XRD), IR spectroscopy (IR) and scanning electron microscopy (SEM) studies. The SiO₂ source had a significant effect on the final zeolite obtained: the use of colloidal silica sol (ZCS) as SiO₂ source in the synthesis led to ZSM-11 (silicalite-2) crystals, while the sodium silicate solution (ZSS) produced the ZSM-5 (silicalite-1) type. The presence of the alumina support influences the crystallization process of ZSM-5, as it improves nucleation and the ordering of the crystals.     

Selectivity Aspects in Cross Metathesis Reactions

When certain catalysts that display a low apparent metathesis activity on terminal olefins are employed on mixtures of terminal and internal olefins, they lead to a selective formation of cross metathesis products. Critical experimentation using deuterated 1-pentene reveals that terminal olefins prefer to scramble “head-to-tail”. A study of the macrocyclics distribution produced at various conversions during 1,5-cycloocta-diene polymerization suggests that these are being formed exclusively via an intramolecular transalkylidenation. The significance of the two sets of results is discussed in terms of two basic mechanistic schemes.     

Ring-opening polymerization of unsaturated alicyclic compounds

The ring-opening polymerizations of cyclooctene, cyclododecene, 1,5-cyclooctadiene, 1,5,9-cyclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene have been carried out by using a two-component catalyst system composed of ethylaluminum dichloride and tungsten hexachloride. NMR and infrared analyses of the respective polymers indicate structures which are consistent with a ring-cleavage mode of propagation. No evidence for double-bond shifts or transannular reactions during the polymerizations of 1,5-cyclooctadiene, 1,5,9-cyclododecatriene, 3-methylcyclooctene, and 3-phenylcyclooctene was found. The polymerizability of substituted, unsaturated, mediumsized alicyclic monomers suggests a convenient method for synthesis of certain perfectly alternating terpolymers. Since polymerizations occurred rapidly with little evolution of heat, it was concluded that entropy is a substantial contributor to the free energy of the ring-opening polymerization of medium-sized, unsaturated alicyclic monomers.     

Intralamellar dislocation networks formed by glide in γ-TiAl I. The mechanism of formation

In a lamellar TiAl alloy deformed at room temperature under an orientation that activates slip parallel to the interfaces, the nphase exhibits intralamellar dislocation networks parallel to the primary slip plane and entirely glissile in their habit plane. Their meshes are mainly rectangular with branches all coplanar, screw or near-screw in character and with Burgers vector of and types. Dislocation organization at and in the near-vicinity of these intralamellar networks suggests a reaction between a family of primary coplanar d011] dislocations that slip in the network habit plane and a family of dislocations that cross-slip from a plane inclined to the lamellae into the network. The reactions result in junctions with Burgers vector that subsequently transform into rectangular units. The presence of these networks is consistent with that of a residual elastic twist between adjacent nlamellae.     

Experimental study of a swept reflectometer with a single antenna for plasma density profile measurement

The feasibility of a swept microwave reflectometer, with one antenna only, for plasma electron density measurement is studied. Experimental results obtained in the laboratory by simulating the plasma with a metallic mirror are presented.Permanent address Departamento de Electromagnetismo Facultat de Ciencas-Universitad de Santander Avda los Castros s/n Santander-Spain