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Hydrated Phases (hydrated + phase)
Selected AbstractsA new tetrahydrated form of sodium naproxenJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2007Piera Di Martino Abstract The anhydrous sodium naproxen (ASN) can form several hydrated phases if maintained at different relative humidities (RH). The water uptake can promote crystallographic modifications, according to the amount of water. In a previous work, the authors showed that a dihydrated form could be obtained either by crystallization in water or by exposure of the anhydrous form to a RH of 55%. In the present work, the authors report about the formation and characterization of a new tetrahydrated form, obtained by exposing the ASN to RH,,,75%. All the hydrated compounds were characterized by the combined use of several spectroscopic, thermal, and crystallographic techniques. The thermal stability of both the dihydrated and tetrahydrated compounds was also tested. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96:156,167, 2007 [source] Order-disorder enantiotropy, monotropy, and isostructurality in a tetroxoprim-sulfametrole 1:1 molecular complex: Crystallographic and thermal studiesJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2003Mino R. Caira Abstract Two enantiotropic polymorphs of a tetroxoprim (TXP)-sulfametrole (SMTR) 1:1 molecular complex monohydrate and two isostructural TXP-SMTR 1:1 molecular complex solvates with methanol and ethanol were grown and studied by X-ray diffraction and thermal methods (thermogravimetric analysis and differential scanning calorimetry). Interconversion of the polymorphic hydrates is essentially an order/disorder transition involving a substituent on the TXP molecule. These hydrated phases may be described as "nearly isostructural" with the methanol and ethanol solvates. Thermal data for decomposition of the solvates were rationalized on the basis of the location and topologies of solvent crystallographic sites. Solid-state properties of two monotropic polymorphs of the unsolvated TXP-SMTR 1:1 molecular complex were also investigated and the theoretical and experimental phase diagrams of the individual components were assessed. The existence of polymorphic and pseudopolymorphic forms is determined by conformational flexibility of the TXP-SMTR bimolecular complex components, a tendency for molecular disorder in TXP, the ability of the drug complex to form intricate, highly stabilized hydrogen-bonded frameworks, and the competition between nonspecific van der Waals and specific hydrogen bond interactions. © 2003 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 92:2164,2176, 2003 [source] Use of micro-Raman spectroscopy to study reaction kinetics in blended white cement pastes containing metakaolinJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Moisés Frías Abstract Curing temperature is known to play an important role in the formation, development, and stability of the hydrated phases appearing during pozzolanic reactions (chemical reaction between puzzolanic addition, metakaolin (MK), and calcium hydroxide from cement hydration). A typical example of this important reaction is to be found in metakaolin-bearing cement pastes, characterized by hexagonal phases whose thermodynamic stability declines with rising temperature. These phases cannot be exhaustively researched with traditional techniques (such as X-ray diffraction) due to their poor crystallinity. Consequently, micro-Raman spectroscopy was used in the present study to explore the behavior of white cement paste blends containing 0, 10, and 25% MK at two curing temperatures (20 and 60 °C). This led to the identification, for the first time using Raman spectroscopy, of phases C2ASH81 (stratlingite) and C3ASH6, which appear in the MK,white cement reaction. The CSH gel formed was characterized by Q1 dimers and a C/S ratio of 1.3,1.5. Raising the curing temperature favored the formation of C4AH13. Copyright © 2009 John Wiley & Sons, Ltd. [source] Characterization of CaCO3 hydrates by micro-Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 1 2002M. M. Tlili The Raman spectra of the three varieties of hydrated calcium carbonate, monohydrate, hexahydrate and ,amorphous,' are reported for the first time and discussed according to the already known crystal structures. The transformation by dehydration of these hydrated phases into the usual anhydrous forms was followed by in situ micro-Raman spectroscopy. It is shown that the dehydration of the hexahydrate proceeds through the formation of the ,amorphous' phase. The latter is better described as microcrystalline monohydrate. Copyright © 2002 John Wiley & Sons, Ltd. [source] Influence of Activation Temperature on Reaction Kinetics in Recycled Clay Waste,Calcium Hydroxide SystemsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 12 2008Moisés Frías Obtaining pozzolanic materials from recycling of industrial waste and byproducts is a priority action of environmental policy all over the world. This paper describes the effect of activation conditions on the reaction kinetics in calcined clay waste (CCW)/calcium hydroxide systems. The CCW used in this work shows excellent qualities for use as supplementary cementing material in the manufacture of commercial blended cements. This research work presents an exhaustive study about the kinetics of a pozzolanic reaction in this cementing system. The results obtained by different techniques (DTA/TG, X-ray diffraction, and SEM/EDAX) confirm that the activation conditions (in the range 700°,800°C and 2,5 h of retention) have a direct effect on the formation and evolution of hydrated phases. Low activation temperatures favor the CSH gels' formation, while at higher temperatures aluminates (C4AH13) and aluminum silicate hydrates (C4ASH8, hydrotalcites) are predominant. [source] Chemically Bonded Phosphate Ceramics: II, Warm-Temperature Process for Alumina CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2003Arun S. Wagh This is the second of three papers on a dissolution model that describes the formation of chemically bonded phosphate ceramics. In this paper, we discuss the kinetics of formation of aluminum phosphate ceramics between 100° and 150°C. Using basic thermodynamic formulations, we calculated the temperatures of maximum solubility of alumina and its hydrated phases and predicted the temperatures of formation of ceramics. Differential thermal and X-ray diffraction analyses on samples made in the laboratory confirm these temperatures. The resulting ceramics of alumina bonded with aluminum phosphate (berlinite) show a high compressive strength of 16 000 psi. We have concluded that rapid evaporation of excess water in the slurry generates porosity in the ceramics, and that better processing methods are needed. A consolidation model is presented that describes the microstructure of the ceramic. It predicts that a very small amount of alumina must be converted to form the bonding phase; hence, the product is mostly alumina with a thin coating of berlinite on the surface of alumina particles. [source] | ||||||||||