Epitaxial growth of nonpolar GaN films on r-plane sapphire substrates by pulsed laser deposition

Single-crystalline nonpolar GaN epitaxial films have been successfully grown on r-plane sapphire (Al₂O₃) substrates by pulsed laser deposition (PLD) with an in-plane epitaxial relationship of GaN[1-100]//Al₂O₃[11-20]. The properties of the ~500 nm-thick nonpolar GaN epitaxial films grown at temperatures ranging from 450 to 880 °C are studied in detail. It is revealed that the surface morphology, the crystalline quality, and the interfacial property of as-grown ~500 nm-thick nonpolar GaN epitaxial films are firstly improved and then decreased with the growth temperature changing from 450 to 880 °C. It shows an optimized result at the growth temperature of 850 °C, and the ~500 nm-thick nonpolar GaN epitaxial films grown at 850 °C show very smooth surface with a root-mean-square surface roughness of 5.5 nm and the best crystalline quality with the full-width at half-maximum values of X-ray rocking curves for GaN(11-20) and GaN(10-11) of 0.8° and 0.9°, respectively. Additionally, there is a 1.7 nm-thick interfacial layer existing between GaN epitaxial films and r-plane sapphire substrates. This work offers an effective approach for achieving single-crystalline nonpolar GaN epitaxial films for the fabrication of nonpolar GaN-based devices.     

Hydrophobic Flocculation Flotation for Beneficiating Fine Coal and Minerals

ABSTRACT

It is shown that hydrophobic flocculation flotation (HFF) is an effective process to treat finely ground ores and slimes so as to concentrate coal and mineral values at a fine size range. The process is based on first dispersing the fine particles suspension, followed by flocculation of fine mineral values or coal in the form of hydrophobic surfaces either induced by specifically adsorbed surfactants or from nature at the conditioning of the slurry with the shear field of sufficient magnitude. The flocculation is intensified by the addition of a small amount of nonpolar oil. Finely ground coals, ilmenite slimes, and gold finely disseminated in a slag have been treated by this process. Results are presented indicating that cleaned coal with low ash and sulfur remaining and high Btu recovery can be obtained, and the refractory ores of ilmenite slimes and fine gold-bearing slag can be reasonably concentrated, leading to better beneficiation results than other separation techniques. In addition, the main operating parameters affecting the HFF process are discussed.     

Realization of nonpolar a-plane ZnO films on r-plane sapphire substrates using a simple single-source chemical vapor deposition

Nonpolar (112?0) ZnO thin films (a-plane ZnO) have been grown on (11?02) sapphire substrates (r-plane sapphire) by a simple atmospheric pressure single-source chemical vapor deposition (SSCVD) approach. The crystallinity, surface morphology and optical property of the films were investigated using high-resolution X-ray diffraction (HRXRD), scanning electron microscope (SEM) and transmission spectrum, respectively. XRD results revealed that the ZnO films were grown on the substrates epitaxially along (112?0) orientation, and the epitaxial relationship between the ZnO films and the substrates was determined to be (112?0)ZnO∥(11?02) Al2O3, and [1?101]ZnO∥[022?1]Al₂O₃. The SEM image exhibited that the a-plane ZnO films showed a high density of well-aligned ZnO sheets with rectangular structure. The transmission spectrum showed that the ZnO films were highly transparent in the visible region.     

COMPARISON OF PREDICTIVE CORRELATIONS FOR THE NORMAL BOILING DENSITY OF NONPOLAR FLUIDS

Seven empirical correlations for the calculation of the normal boiling density of non polar pure fluids are studied for their accuracy and applicability. One of the correlations is specific only for the normal boiling density, five are based on the corresponding states method (these need the critical parameters and acentric factor as inputs), and the other is a new kind of correlation that uses the Lennard-Jones molecular parameters and the acentric factor as input data. As reference, we take the value for the normal boiling density given by the specific correlation functions proposed in the DIPPR project for 252 nonpolar fluids, grouped into 17 families. In view of the results, we recommend the use of the Yamada-Gunn expression because of its simplicity and because other, less simple, models represent no clear improvement over its accuracy. We also recommend the use of the molecular-parameter model because it gives very good results for some families of fluids.     

Epitaxial growth of nonpolar m-plane ZnO (10-10) on large-size LiGaO2 (100) substrates

Nonpolar m-plane ZnO epitaxial film with [10-10] orientation was successfully grown on a large-size (100) LiGaO₂ single crystal substrate by chemical vapor deposition method. The dependence of growth characteristics on the different growth conditions was investigated. Following CVD growth, the surface morphologies and epi-film crystallinity were examined by scanning electron microscopy and X-ray diffraction. Room-temperature photoluminescence spectra exhibit a strong near-band-edge emission peak at 377 nm with a negligible green band. Raman spectroscopy showed that the as-grown (10-10) ZnO epilayer on (100) LiGaO₂ are under compressive stress. Further structural characterization and defect analysis of nonpolar ZnO material was performed using transmission electron microscopy.     

Evaluation of nonpolar methyl esters by column and gas chromatography for the assessment of used frying olive oils

The measurement of unaltered methyl esters separated from polar methyl esters by column chromatog-raphy was used to evaluate the alteration of an olive oil that had been used 15 times to fry potatoes. Unaltered methyl ester (the nonpolar fraction) decreased significantly (94.9 ± 0.8%vs 98.2 + 0.5%; p < 0.05), while the polar fraction increased significantly (4.0 ± 0.7%vs 2.1 ± 0.7%; p < 0.05) after 15 fryings. The unrecoverable fraction also increased. In order to avoid column contamination the gas Chromatographic analysis was only done on the nonpolar fractions. Linoleic and oleic acids showed a tendency to decrease while saturated fatty acid tended to increase. The unsaturated/saturated fatty acids ratio decreased from an initial value of 7.05 to 6.40 in the last frying. Quantitative gas Chromatographic analysis using both the percentage fatty acid composition and the relative amount of unaltered methyl esters showed a significant oleic acid decrease after 15 fryings (75.8 ± 0.6vs 78.9 ± 0.2 mg/100 mg oil; p < 0.05). To whom correspondence should be addressed     

COMPARISON OF PREDICTIVE CORRELATIONS FOR THE NORMAL BOILING DENSITY OF NONPOLAR FLUIDS

Seven empirical correlations for the calculation of the normal boiling density of non polar pure fluids are studied for their accuracy and applicability. One of the correlations is specific only for the normal boiling density, five are based on the corresponding states method (these need the critical parameters and acentric factor as inputs), and the other is a new kind of correlation that uses the Lennard-Jones molecular parameters and the acentric factor as input data. As reference, we take the value for the normal boiling density given by the specific correlation functions proposed in the DIPPR project for 252 nonpolar fluids, grouped into 17 families. In view of the results, we recommend the use of the Yamada-Gunn expression because of its simplicity and because other, less simple, models represent no clear improvement over its accuracy. We also recommend the use of the molecular-parameter model because it gives very good results for some families of fluids.     

CALCULATION OF THE VAPORIZATION ENTHALPY OF NONPOLAR FLUIDS AT THE STANDARD TEMPERATURE

Different analytical models were used to calculate the enthalpy of vaporization of nonpolar fluids at the standard temperature of 298.15 K. The models considered were some general classical expressions, three group contribution models that allow the property to be calculated at any temperature, another group contribution model specifically designed for calculations at the standard temperature, and finally a molecular model proposed by our research group. The results for 42 nonpolar fluids are compared with the value obtained in the correlation proposed in the DIPPR project.     

CALCULATION OF THE VAPORIZATION ENTHALPY OF NONPOLAR FLUIDS AT THE STANDARD TEMPERATURE

Different analytical models were used to calculate the enthalpy of vaporization of nonpolar fluids at the standard temperature of 298.15 K. The models considered were some general classical expressions, three group contribution models that allow the property to be calculated at any temperature, another group contribution model specifically designed for calculations at the standard temperature, and finally a molecular model proposed by our research group. The results for 42 nonpolar fluids are compared with the value obtained in the correlation proposed in the DIPPR project.     

A new synthetic approach for difficult benzoxazines: Preparation and polymerization of 4,4′-diaminodiphenyl sulfone-based benzoxazine monomer

The first successfully synthesized benzoxazine in high purity from 4,4′-diaminodiphenyl sulfone (DDS), paraformaldehyde and phenol using high boiling point nonpolar solvent is reported. The solution method for benzoxazine synthesis is modified by using a nonpolar solvent of high boiling point. For comparison, the synthesis of such difficult benzoxazine monomer was prepared in high boiling point polar solvent, dimethylsufoxide. ¹H NMR indicates the purity of the monomer prepared by this novel method to be quite high in comparison with that obtained using dimethylsulfoxide (DMSO). The thermally activated polymerization of the monomer affords polybenzoxazine with T_g at ca. 203 °C. The 5% and 10% decomposition temperatures of the polymer are 324 and 368 °C with 58% char yield, reflecting the excellent thermal stability than the typical polybenzoxazine based on bisphenol-A and aniline.