No abstract

Pore structure of coal has a great influence on its behavior during mining, preparation, and utilization. Characterization of the pore structure of twelve Turkish coals from different geographic locations and with carbon contents varying between 61 and 84% (on dry ash-free basis) was carried out using different techniques. The volume and area of macropores were determined by mercury intrusion porosimetry. Mesopore volumes and areas were determined by N2 gas adsorption at 77 K using the Barrett−Joyner−Halenda (BJH) method. Brunauer−Emmet−Teller (BET) areas were calculated using the same data. Micropore volumes and areas were determined by the application of the Dubinin−Radushkevich (DR) equation to the CO2 adsorption data at 298 K. True and apparent densities of coals were measured by helium and mercury displacement. Pore size distributions were evaluated using data thus obtained. Small-angle X-ray scattering (SAXS) technique was also employed to determine the surface area of some samples. The highest BET surface area, 34 m2/g, was found for Tunçbilek coal which has a significant mesoporous volume; while the corresponding values for the rest of the coals were less than 7 m2/g. DR surface areas which varied in the range 19−115 m2/g were larger than BET areas indicating molecular sieve character of coals. SAXS areas were larger than DR areas for some coals which can be explained by the presence of closed pores in these samples. For some coals having relatively small porosities, SAXS areas were found to be smaller than DR areas which is attributed to the inability of the method to distinguish ultramicropores of molecular dimensions which are probably accessible to CO2 molecules. SAXS surface area of Illinois No. 6 coal and a synthetic char (Spherocarb) were also measured and the values found agreed well with the ones given in the literature.

The crystal and molecular structures of an o-hydroxy Schiff base derivative, (E)-2-ethoxy-6-[(2-methoxyphenylimino)methyl]phenol, have been determined by single crystal X-ray diffraction analyses at 296 and 100 K. The results from temperature-dependent structural analysis regarding the tautomeric equilibrium of the compound were interpreted with the aid of quantum chemical calculations. To clarify the tautomerization process and its effects on the molecular geometry, the gasphase geometry optimizations of two possible tautomers of the title molecule, its OH and NH form, were achieved using DFT calculations with B3LYP method by means of 6-31 ? G(d,p) basis set. In order to describe the potential barrier belonging to the phenolic proton transfer, nonadiabatic Potential Energy Surface (PES) scan was performed based on the optimized geometry of the OH tautomeric form by varying the redundant internal coordinate, O-H bond distance. The Harmonic Oscillator Model of Aromaticity (HOMA) indices were calculated in every step of the scan process so as to express the deformation in the aromaticities of principal molecular moieties of the compound. The results show that there is a dynamic equilibrium between the aromaticity level of phenol and chelate ring and furthermore p-electron coupling affecting overall molecule of the title compound. Charge transfer from phenol ring to pseudo-aromatic chelate ring increases with increasing temperature, whereas p-electron transfer from chelate ring to anisole ring is decreased as temperature increases. The most strength intramolecular H-bonds are observed for conformers close to transition state.

Measurements of the ll5In Knight shift and the NMR linewidth in liquid In-Ni have been carried out over the concentration range (0-50) at.% Ni at high temperatures. With changes of the Ni concentration important changes occur in the hyperfine interactions referring to 115In. The experimental results for higher Ni concentrations are in good agreement with a model involving a significant d-d exchange interaction.In liquid alloys of simple metals with 3 d elements (magnetic impurities) the polarization of the surrounding electrons, caused by the magnetic moment of the impuri ties, influences both the Knight shift of the solvent nucleus and the relaxation time of the NMR process.Recent NMR studies on liquid Bi-Mn [1] show that the Mn impurities possess a local magnetic moment. The im purities affect very strongly the -() Bi-Knight shift Kim^. A concentration of 3 at% Mn causes a relative change AK^Bl/ K to»B i = 33%, which is indeed a very strong effect.In this work we present measurements concerning the concentration dependence of the "-In-Knight shift and the NMR linewidth in liquid In-Ni for concentrations up to 50 at% Ni at high temperatures. To our knowledge this is the first investigation of the ll5In-Knight shift in the liquid In-Ni system.For the relatively difficult sample preparation we used metals with a purity of 99.999% (Ventron Corporation). Alloys of the required composition, particularly those with higher Ni concentration, were left several hours at 1850 A T in an A120 3 container sealed under vacuum, to get a uniform distribution of the components. The measure ments were carried out using a high temperature NMR spectrometer, of which details are given elsewhere [2. 3], Figure 1 shows our experimental results. We plotted the relative change of K,v,in defined as AK/K0 = (K(c) -K0)/ K0, where K(c) and K0 are the ll5In-Knight shifts in the alloy and in pure Indium at the melting point, respectively.The function AK(c)/K0 shows a pronounced maximum at c = 20 at% Ni and becomes negative at c = 50 at% Ni. In this respect it is interesting to consider earlier NMR in vestigations on binary liquid alloys of simple with transi tion metals [1.4-6]. In most of these systems the transition metal concentration was about 6 at% and the relative Knight shift of the simple metal was found to increase linearly with the concentration of the transition metal. NMR investigations of liquid systems with higher transi

No abstract