Papers by Keyword: Polymorphs

Abstract: Polymorphs is present in many crystalline drug, different crystal type tend to produce different effects. Drug quality and curative effect of the important quality index is drug heteromorphic stability .The change of drug heteromorphic will change the nature, quality, efficacy of the drug. Generally speaking, the greater the crystal particle size, heating melting needs more energy, the more stable. The crystal type which has high melting point, the chemistry stability is good, but the solubility and digestion rate is low. HMP has different polycrystalline forms, at present reports in the literature there are two kinds of crystal type, form Ⅰ and form Ⅱ. The form Ⅰ is more stable than form Ⅱ, and has higher melting point. This article research the relationship between HMP polymorphism and melting point based with the drug melting point meter and DSC.

Abstract: Geometric mobiles is a new kinetic art which become a new technique combined with basic science and modern art. Geometric mobiles design and calculation by mechanics and mathematics in order to have a slowly and elegant movements. An innovative and efficient design method is first established based on virtual technology and polymorphs small cell centroid point analytical rule. The method reveals the intrinsic relationship between Geometric mobiles and mathematics & mechanics modeling, provides the mathematics foundation for art works innovative and next research.

Abstract: The zirconia in its cubic phase (C-ZrO2) has gained scientific and technological interest because it has high ionic conductivity and is useful in applications where the transport of oxygen ions prevails, for example, in the oxygen sensors and solid oxide fuel cells [1,. In the pure zirconia, the Zr4+ ion is too small to sustain the fluorite structure at low temperatures, so it has to be partially replaced by a higher atomic radius cation and lower valence number, for example, the Y3 +, Mg2 +, Ca2 + and the rare earth cations TR3 +, [. Currently there are several synthesis methods used to obtain cubic zirconia, the most popular being the mixture of oxides and coprecipitation used industrially in the research labs, but these methods provide powders with different characteristics which will be decisive for a specific application. In this context, the objective of this study was the preparation of homogeneous mixtures of zirconia-rare earth in different concentrations in order to stabilize the C-ZrO2, using the technique of heterogeneous coprecipitation for potential applications in oxygen sensors.

Abstract: In this paper we propose the stabilization of zirconium oxide with controlled additions of a rare earth elements concentrate, in the system ZrO2: ƞ wt% Re2O3 (with ƞ=5.36, 10.47, 13.74, 16.91 e 20) where Re₂O₃ is a rare earth elements concentrate composed mainly of 76.88% of yttrium oxide, 12.1% of Dysprosium oxide, 4.04% of Erbium oxide and 1.94% of Holmium oxide. The synthesis method used was the Pechini method. The results show that additions of 5.36 and 20 wt% of the concentrate are enough to stabilize the tetragonal and cubic zirconia phases respectively, and that zirconium oxide polymorphs can coexist with additions within these limit. In the characterization of the obtained powders are presented and discussed the following results: differential scanning calorimetry, transmission electron microscopy and X-ray diffraction. Also, it was necessary to make analysis by Rietveld refinement because they had severe overlap in the diffraction peaks. One of the most relevant results is obtaining a raw material, cheap to be used in many technological applications.

Abstract: The phase stability of silicon nitride is examined using a series of first principles phonon calculations. -phase shows slightly higher free energy than  in the temperature range from 0 to 2000K. The difference between  and is only 0.02 eV/Si3N4 or 2 kJ/mol at 300 K. The result is consistent with the experimental report by high-temperature oxide-melt-drop solution-calorimetry. Similar calculations are made for ZrO2, Ga2O3, BN and some perovskites. Using cluster expansion technique combined with a large set of first principles calculations, the cation disordering of II-III spinel oxides and the phase diagram of diamond vs. c-BN are theoretically investigated. Theoretical results on the atomic structures of  and  sialons are also shown.