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Precipitated Crystals (precipitated + crystal)
Selected AbstractsSelective preparation of poly(p -oxybenzoyl) by using fractional polycondensationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 8 2006Kunio Kimura Abstract Selective preparation of poly(p -oxybenzoyl) (POB) in the copolymerization system of p -acetoxybenzoic acid (p -ABA) and m -acetoxybenzoic acid (m -ABA) was examined by using reaction-induced crystallization of oligomers. Polymer crystals mainly composed of p -oxybenzoyl moiety were precipitated when the content of m -ABA in the feed was 30 mol %. The formation of the polymer crystals was attributed to both the reactivity of monomer and the phase-separation behavior of oligomer. Reactivity of p -ABA was twice higher than that of m -ABA, and thereby, the homo-oligomers of p -oxybenzoyl moiety were more rapidly formed in solution than do co-oligomers at the early stage in polymerization. They were selectively precipitated by crystallization to form crystals because of low miscibility. Co-oligomers containing m -oxybenzoyl moiety were also formed in solution, but they were unable to be phase-separated because of higher miscibility. Further polycondensation occurred between oligomers in the precipitated crystals, leading to the formation of POB. This polymerization proceeded with selecting certain monomers by crystallization and afforded a new methodology for fractional polycondensation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2732,2743, 2006 [source] Preparation and Optical Property of Glass Ceramics Containing Ruby CrystalsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010Jumpei Ueda We have developed the glass ceramics containing ruby crystals by heat treatment of a Cr3+ -doped SiO2,Al2O3,Y2O3 glass at 1550°C. The shape of precipitated crystals in the glass matrix was rod type whose average width and length were around 10 and 200 ,m, respectively. From an X-ray diffraction measurement and an electron probe X-ray microanalysis, it was confirmed that the rod crystals were ,-Al2O3. Intense emission bands of Cr3+ at 694 nm, called the R -lines, were observed in the glass ceramics heat treated above 1300°C. In addition, the intense red luminescence was observed only in the ,-Al2O3 rod crystals by a photoluminescence mapping image. [source] Fiber Reinforced Calcium Phosphate CementARTIFICIAL ORGANS, Issue 3 2000Luís Alberto Dos Santos Abstract: The term calcium phosphate cement was introduced by Gruninger et al. (1). This type of cement can be prepared by reacting a calcium phosphate salt with an aqueous solution, which causes it to set by the crossing of the precipitated crystals. These cements offer a series of advantages that allow their use as grafts and substitutes of damaged parts of the bone system. However, these cements have low mechanical strength compared to human bones. This work studied the influence of the use of polyamide fibers in the mechanical properties of a calcium phosphate cement based on ,-tricalcium phosphate as well as the mechanisms involved in the increase of mechanical strength. The results demonstrate the feasibility of the use of polymeric fibers to increase mechanical strength and the need for coupling agents for the effective performance of the fibers as reinforcement in these materials. [source] The Influence of Shear Stress on Crystallization in an Ultrasound LevitatorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2007S. Sacher Abstract Industrial precipitation processes often use chemical agents to influence crystal morphology and size distribution. This experimental study deals with the investigation of physical parameters including an alternative method to affect crystal growth, thus, avoiding the presence of additives as intrinsic impurities. The influence of shear stress acting on growing crystals within a droplet is investigated in an ultrasound levitator. An ultrasound levitator enables the suspension of a single droplet against gravity and the study of containerless precipitation with specific mechanical forces acting on crystals. The levitator is used as a three-phase reactor with precipitation from the gas and liquid, and as a reactor for precipitation from two different solutions. Calcium carbonate is used as a model system. The variation of temperature and the amount of applied shear stress leads to different amounts of calcium carbonate morphologies. An increase in the shear stress results in more rounded or spherical crystals. The intensity of the shear stress also influences the particle size distributions of the precipitated crystals, i.e., with increasing shear stress, particle size distributions are shifted to smaller sizes. [source] | ||||||||||