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131.
K.R. Poeppelmeier M.E. Leonowicz J.C. Scanlon J.M. Longo W.B. Yelon 《Journal of solid state chemistry》1982,45(1):71-79
Low-temperature synthesis of the oxygen-deficient compound CaMnO2.5 from polycrystalline CaMnO3 preserves the existing structural framework of the oxidized precursor. The crystal structure of CaMnO2.5 was determined using neutron powder diffraction data analyzed by the Reitveld profile refinement method. The structure of the reduced phase can be described by the orthorhombic distortion , where ac is the simple cubic distance (~3.7 Å) characteristic of the Mn4+O2?Mn4+ framework in CaMnO3. The unique features of the structure are five-coordinate Mn3+ cations with nearly square pyramidal (~C4v) coordination and ordered oxygen vacancies. The preparation, structure refinement, and noncubic distortions of single crystals of CaMnO3 are also described. Attempts to transform single crystals of CaMnO3 into CaMnO2.5 by well-ordered topotactic changes have not been successful. 相似文献
132.
Giovanni A. Longo 《Experimental Thermal and Fluid Science》2009,33(2):284-291
This paper presents the heat transfer coefficients and the pressure drop measured during HFC-410A condensation inside a commercial brazed plate heat exchanger: the effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature and great sensitivity to refrigerant mass flux and vapour super-heating. At low refrigerant mass flux (<20 kg/m2 s) the saturated vapour condensation heat transfer coefficients are not dependent on mass flux and are well predicted by Nusselt [W. Nusselt, Die oberflachenkondensation des wasserdampfes, Energy 60 (1916) 541–546, 569–575] analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (>20 kg/m2s) the saturated vapour condensation heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [W.W. Akers, H.A. Deans, O.K. Crosser, Condensing heat transfer within horizontal tubes, Chem. Eng. Prog. Symp. Series 55 (1959) 171–176] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8–10% higher than those of saturated vapour and are well predicted by Webb [R.L. Webb, Convective condensation of superheated vapor, ASME J. Heat Transfer 120 (1998) 418–421] model. A simple linear equation based on the kinetic energy per unit volume of the refrigerant flow is proposed for the computation of the frictional pressure drop. 相似文献
133.
134.
Márcia R. S. Silva L. E. B. Soledade S. J. G. Lima E. Longo A. G. Souza Iêda M. G. Santos 《Journal of Thermal Analysis and Calorimetry》2007,87(3):731-735
The present work investigates
the influence of milling and calcination atmosphere on the thermal decomposition
of SrTiO3 powder precursors. Both pure and neodymium-modified SrTiO3 samples
were studied. Milling did not significantly influence numerical mass loss
value, but reduced the number of decomposition steps, modifying the profiles
of the TG and DTA curves. On the other hand, milling increases the amount
of energy liberated by the system upon combustion of organic matter. It was
also observed that the milling process, associated to the calcination in an
oxygen atmosphere, considerably decreases the amount of organic matter and
increases the final mass loss temperature. 相似文献
135.
We have investigated the plasmonic resonance characteristics of canonical circular and square cylinders, with gap defects, that are illuminated by a plane wave. The circular and square cylinders have vee shaped gaps and constant width gaps, respectively. The electric and magnetic fields are obtained by solving the Lippmann–Schwinger equation from which we compute the far-field scattering cross-section and near-field local electromagnetic energy density.Numerical results are given for numerous wavelength and gap dimensions to qualitatively present the effects of gap defects on the scattering cross-section and local electromagnetic energy density. 相似文献
136.
137.
M. Capitelli D. Cappelletti G. Colonna C. Gorse A. Laricchiuta G. Liuti S. Longo F. Pirani 《Chemical physics》2007
The interaction energy in systems (atom–atom, atom–ion and atom–molecule) involving open-shell species, predicted by a phenomenological method, is used for collision integral calculations. The results are compared with those obtained by different authors by using the complete set of quantum mechanical interaction potentials arizing from the electronic configurations of separate partners. A satisfactory agreement is achieved, implying that the effect of deep potential wells, present in some of the chemical potentials, is cancelled by the effect of strong repulsive potentials. 相似文献
138.
We have investigated linear, starbranched and hyperbranched XnHm polymers and determined the number of atoms, rotors, internal coordinates, valence and HOMO molecular orbitals as well as molecular mass for each generation and valency. We use the semi-empirical MNDO model to obtain full geometry optimization for increasingly larger clusters for each generation in order to obtain total relative energies. We then generate analytical functions, which correlate the total relative energies with the generation, for each valency, for the hyperbranched polymers. We have also generated analytic functions, which correlate total relative energies, experimental van der Waals coefficients and standard enthalpy of combustion with the number of carbon atoms in each chain of the linear alkanes. These results are used to predict the enthalpy of combustion for higher generations of alkanes in good agreement with experiment. Due to the exponential increase in size with generation of the hyperbranched polymers alternative analytical models may be of interest to theoretical chemists working in this line of research. 相似文献
139.
140.
S. H. Leal J. C. Sczancoski L. S. Cavalcante M. T. Escote J. M. E. Matos M. R. M. C. Santos F. M. Pontes E. Longo J. A. Varela 《Journal of Sol-Gel Science and Technology》2010,53(1):21-29
Pb1−x
Sr
x
)TiO3 powders with different compositions (x = 0, 0.10, 0.50, 0.90 and 1) were synthesized by the polymeric precursor method and heat treated at 800 °C for 2 h under
air atmosphere. The thermogravimetric and differential scanning calorimetry analyses were performed in the range from 25 to
800 °C in order to estimate the stages corresponding to the water evaporation, organic decomposition and crystallization of
these materials. X-ray diffraction patterns and Rietveld analyses showed that the (Pb1−x
Sr
x
)TiO3 phases with strontium content up to x = 0.1 crystallize in a tetragonal structure. The micrographs obtained by scanning electron microscopy and transmission electron
microscopy showed that the powders have agglomerated nature, presenting irregular morphologies and polydisperse particle size
distribution. The energy dispersive X-ray spectrometry indicated the presence of pure (Pb0.50Sr0.50)TiO3 phase. 相似文献