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Melt Crystallization (melt + crystallization)
Selected AbstractsMelt Crystallization and Morphology of Poly(p -phenylene sulfide) under High PressureMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2007Jun Lu Abstract The high-pressure melt-crystallization behaviors of poly(p -phenylene sulfide) (PPS) were investigated using WAXD, DSC, TEM and SEM. PPS extended-chain crystals with c -axis thickness exceeding 4.5 µm were formed at high pressure. The DSC results showed that the melting temperature and melting enthalpy of high-pressure crystallized PPS samples were up to 327.53,°C and 94.96 J,·,g,1, respectively, which were higher than the values of ideal PPS perfect crystals used by some researchers, and the melting enthalpy of the samples fluctuated regularly during the thickening growth of the PPS crystals. Other characteristic morphologies obtained at high pressure, i.e. spherulites and rod-like crystals, were also presented with the SEM measurements. [source] Thermal properties and phase morphology of melt-mixed poly(trimethylene terephthalate)/poly(hexamethylene isophthalamide) blendsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2008Fang-Chyou Chiu Abstract This work examines the thermal properties and phase morphology of melt-mixed poly(trimethylene terephthalate) (PTT)/poly(hexamethylene isophthalamide) (PA 6I) blends. Two temperatures, i.e., 250 and 260°C, are used to prepare the blends, respectively. Differential scanning calorimetry results indicate the immiscible feature of the blends. It is thus concluded that the ester-amide interchange reaction hardly occurred in the PTT/PA 6I blends. Depending on the composition and mixing temperature, the crystallization ability of PTT in the blends is either enhanced or hindered. Basically, a lower PA 6I content shifts the PTT melt crystallization to a higher temperature, whereas a higher PA 6I content causes an opposing outcome. The original complex melting behavior of neat PTT becomes more regular after the incorporation of 60 wt % or 80 wt % of PA 6I. Thermogravimetry analyses (TGA) show that the thermal stability of the blends improves as the PA 6I content increases. The two-phased morphology of the blends is examined by scanning electron microscopy (SEM). Polarized light microscopy (PLM) results reveal that the PTT spherulites become coarser with the inclusion of PA 6I; only smaller/dispersed crystallites are observed in the blend with 20 wt % of PTT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Retrograde melt,residue interaction and the formation of near-anhydrous leucosomes in migmatitesJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2010R. W. WHITE Abstract Considering physical segregation of melt from its residue, the chemical potentials of the components (oxides) are the same in both when segregation occurs. Then, as P,T conditions change, gradients in chemical potential are established between the melt-rich domains and residue permitting diffusional interaction to occur. In particular, on cooling, the chemical potential of H2O becomes higher in the melt segregation than in the residue, particularly when biotite becomes stable in the residue assemblage. Diffusion of water from the melt to the residue promotes crystallization of anhydrous products from the melt and hydrous products in the residue. This diffusive process, when coupled with melt loss from the rocks subsequent to some degree of crystallization, can result in a significant degree of anhydrous leucosome being preserved in a migmatite with only minor retrogression of the residue. If H2O can diffuse between the melt segregation and all of the residue, then no apparent selvedge between the two will be observed. Alternatively, if H2O can diffuse between the melt segregation and only part of the residue, then a distinct selvedge may be produced. Diffusion of H2O into the residue may be in part responsible for the commonly anhydrous nature of leucosomes, especially in granulite facies migmatites. Diffusion of other relatively mobile species such as Na2O and K2O has a lesser effect on overall melt crystallization but can change the proportion of quartz, plagioclase and K-feldspar in the resultant leucosome. The diffusion of H2O out of the melt results in the enhanced crystallization of the melt in the segregation and increases the amount of resulting anhydrous leucosome relative to the amount produced if melt crystallized in chemical isolation from the residue. For high residue:melt ratios, the proportion of resulting near-anhydrous leucosome can approach that of the proportion of melt present at the onset of cooling with only minor loss of melt from a given segregation required. Crystallization of melt segregations via the diffusion of H2O out of them into the host may also play a major role in driving melt-rich segregations across key rheological transitions that would allow the expulsion of remaining melt from the system. [source] Formation of spinel-cordierite-feldspar-glass coronas after garnet in metapelitic xenoliths: reaction modelling and geodynamic implicationsJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2007A. M. ÁLVAREZ-VALERO Abstract Spinel + cordierite + K-feldspar + plagioclase + glass form coronas around garnet in metapelitic xenoliths at El Hoyazo and Mazarrón, two localities of the Neogene Volcanic Province (NVP) of SE Spain. The presence of fresh glass (quenched melt) in all phases shows that corona development occurred under partial melting conditions. Algebraic analysis of mass balance in the NCKFMASH system suggests the reaction Grt + Sil + Bt + Pl = Spl + Crd + Kfs + melt as the most plausible model for the development of coronas in the El Hoyazo sample, and indicates that biotite was required as reactant for the formation of cordierite. The P,T conditions for the formation of coronas are estimated at ,820 ± 50 °C, 4.5 ± 0.6 kbar at El Hoyazo, and ,820 ± 50 °C, 4.0 ± 0.4 kbar at Mazarrón. The El Hoyazo xenoliths record a complex P,T history, characterized by early melt production during heating and additional melting during decompression. A local cooling event characterized by minor retrograde reaction and melt crystallization preceded ascent and eruption. This study shows that detailed xenolith analysis may be used to track magma evolution in a chamber. [source] Ordovician high-grade metamorphism of a newly recognised late Neoproterozoic terrane in the northern Harts Range,central AustraliaJOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2001I. S. Buick Abstract Granulite facies rocks from the northernmost Harts Range Complex (Arunta Inlier, central Australia) have previously been interpreted as recording a single clockwise cycle of presumed Palaeoproterozoic metamorphism (800,875 °C and >9,10 kbar) and subsequent decompression in a kilometre-scale, E-W striking zone of noncoaxial, high-grade (c. 700,735 °C and 5.8,6.4 kbar) deformation. However, new SHRIMP U-Pb age determinations of zircon, monazite and titanite from partially melted metabasites and metapelites indicate that granulite facies metamorphism occurred not in the Proterozoic, but in the Ordovician (c. 470 Ma). The youngest metamorphic zircon overgrowths from two metabasites (probably meta-volcaniclastics) yield 206Pb/238U ages of 478±4 Ma and 471±7 Ma, whereas those from two metapelites yield ages of 463±5 Ma and 461±4 Ma. Monazite from the two metapelites gave ages equal within error to those from metamorphic zircon rims in the same rock (457±5 Ma and 462±5 Ma, respectively). Zircon, and possibly monazite ages are interpreted as dating precipitation of these minerals from crystallizing melt within leucosomes. In contrast, titanite from the two metabasites yield 206Pb/238U ages that are much younger (411±5 Ma & 417±7 Ma, respectively) than those of coexisting zircon, which might indicate that the terrane cooled slowly following final melt crystallization. One metabasite has a second titanite population with an age of 384±7 Ma, which reflects titanite growth and/or recrystallization during the 400,300 Ma Alice Springs Orogeny. The c. 380 Ma titanite age is indistinguishable from the age of magmatic zircon from a small, late and weakly deformed plug of biotite granite that intruded the granulites at 387±4 Ma. These data suggest that the northern Harts Range has been subject to at least two periods of reworking (475,460 Ma & 400,300 Ma) during the Palaeozoic. Detrital zircon from the metapelites and metabasites, and inherited zircon from the granite, yield similar ranges of Proterozoic ages, with distinct age clusters at c. 1300,1000 and c. 650 Ma. These data imply that the deposition ages of the protoliths to the Harts Range Complex are late Neoproterozoic or early Palaeozoic, not Palaeoproterozoic as previously assumed. [source] Miscibility in Blends of Isotactic/Syndiotactic Polystyrenes at Melt or Quenched Amorphous Solid StateMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2006Shu Hsien Li Abstract Summary: Miscibility in amorphous phase and behavior in a crystalline phase of blends of two semicrystalline and isomeric polymers, isotactic polystyrene (iPS) and syndiotactic polystyrene (sPS), was probed. Optical and scanning electron microscopy results indicate no discernible heterogeneity in iPS/sPS blends in either melt state or rapidly quenched amorphous super-cooled state, while the Tg behavior of the quenched amorphous blends shows an intimately mixed state of two polymer chains. The crystal forms of the blends were further analyzed to provide additional evidence of miscibility in the amorphous domain. The sPS in the iPS/sPS blends upon melt crystallization was found to predominantly exist as the more stable , -form (rather than mixed , -form and , -form in neat sPS), which also suggests evidence of miscibility in the iPS/sPS blends. The melting behavior of semicrystalline sPS in the iPS/sPS mixtures was analyzed using the Flory-Huggins approach for estimation of interactions. By measuring the equilibrium melting point of the higher-melting sPS species in the sPS/iPS blends, a small negative value, for the interaction parameter (,,,,,0.11) was found. Further, by introducing a third polymer, poly(2,6-dimethyl- p -phenylene oxide) (PPO), a ternary iPS/sPS/PPO blend system was also proven miscible, which constituted a further test for stable phase miscibility in the iPS/sPS blend. General nature of miscibility in blends composed of two crystalline isomeric polymers is discussed. Issues in dealing with blends of polymers of the same chemical repeat unit but different tacticities were addressed. X-ray diffractograms for neat sPS and iPS/sPS blends, each having been isothermally crystallized at 245,°C for 4 h. [source] A petrological, mineralogical, and chemical analysis of the lunar mare basalt meteorite LaPaz Icefield 02205, 02224, and 02226METEORITICS & PLANETARY SCIENCE, Issue 7 2006Katherine H. Joy They consist mainly of zoned pyroxene and plagioclase grains, with minor ilmenite, spinel, and mesostasis regions. Large, possibly xenocrystic, forsteritic olivine grains (<3% by mode) contain small trapped multiphase melt inclusions. Accessory mineral and mesostasis composition shows that the samples have experienced residual melt crystallization with silica oversaturation and late-stage liquid immiscibility. Our section of LAP 02224 has a vesicular fusion crust, implying that it was at one time located sufficiently close to the lunar surface environment to have accumulated solar-wind-implanted gases. The stones have a comparable major element composition and petrography to low-Ti, low-Al basalts collected at the Apollos 12 and 15 landing sites. However, the LAP stones also have an enriched REE bulk composition and are more ferroan (Mg numbers in the range of 31 to 35) than similar Apollo samples, suggesting that they represent members of a previously unsampled fractionated mare basalt suite that crystallized from a relatively evolved lunar melt. [source] Crystallization and biodegradation of polylactide/carbon nanotube compositesPOLYMER ENGINEERING & SCIENCE, Issue 9 2010Defeng Wu The crystallization behavior of polylactide/carbon nanotube composites was studied using differential scanning calorimeter and polarized optical microscope. The nucleation mechanisms and the crystallization kinetics were explored. The results show that the presence of nanotubes has nucleating effect on both the melt crystallization and the cold crystallization of PLA. However, the nanotubes also play the role of physical barrier, impeding the crystal growth dynamically. In the experimental range of temperatures, the presence of nanotubes accelerates the melt crystallization, while retards the overall kinetics of the cold crystallization. The biodegradability of the samples with various crystallization histories was then further examined. The results show that the presence of nanotubes reduces the biodegradation rate of PLA, and the amorphous sample shows the highest degradation levels. Moreover, a lower degradation level is observed both on the surface and inside the sample with melt crystallization history in contrast to the one with cold crystallization history. POLYM. ENG. SCI., 50:1721,1733, 2010. © 2010 Society of Plastics Engineers [source] Nonisothermal crystallization behavior of a luminescent conjugated polymer, poly(9,9-dihexylfluorene- alt -2,5-didodecyloxybenzene)POLYMER INTERNATIONAL, Issue 2 2007Gui-Zhong Yang Abstract The nonisothermal crystallization kinetics of poly(9,9-dihexylfluorene- alt -2,5-didodecyloxybenzene) (PF6OC12) from the melt were investigated using differential scanning calorimetry under different cooling rates. Several analysis methods were used to describe the nonisothermal crystallization behavior of PF6OC12. It was found that the modified Avrami method by Jeziorny was only valid for describing the early stage of crystallization but was not able to describe the later stage of PF6OC12 crystallization. Also, the Ozawa method failed to describe the nonisothermal crystallization behavior of PF6OC12. However, the method developed by combining the Avrami and Ozawa equations could successfully describe the nonisothermal crystallization kinetics of PF6OC12. According to the Kissinger method, the activation energy was determined to be 114.9 kJ mol,1 for the nonisothermal melt crystallization of PF6OC12. Copyright © 2006 Society of Chemical Industry [source] Two modes of O,H...O hydrogen bonding utilized in dimorphs of racemic 6- O -acryloyl-2- O -benzoyl- myo -inositol 1,3,5-orthoformateACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2009Shobhana Krishnaswamy The title compound, C17H16O8, yields conformational dimorphs [forms (I) and (II)] at room temperature, separately or concomitantly, depending on the solvent of crystallization. The yield of crystals of form (I) is always much more than that of crystals of form (II). The molecule has one donor ,OH group that can make intermolecular O,H...O hydrogen bonds with one of the two acceptor C=O groups, as well as with the hydroxyl O atom; interestingly, each of the options is utilized separately in the dimorphs. The crystal structure of form (I) contains one molecule in the asymmetric unit and is organized as a planar sheet of centrosymmetric dimers via O,H...O hydrogen bonds involving the OH group and the carbonyl O atom of the acryloyl group. In the crystal structure of form (II), which contains two independent molecules in the asymmetric unit, two different O,H...O hydrogen bonds, viz. hydroxyl,hydroxyl and hydroxyl,carbonyl (benzoyl), connect the molecules in a layered arrangement. Another notable feature is the transformation of form (II) to form (I) via melt crystallization upon heating to 411,K. The higher yield of form (I) during crystallization and the thermal transition of form (II) to form (I) suggest that the association in form (I) is more highly favoured than that in form (II), which is valuable in understanding the priorities of molecular aggregation during nucleation of various polymorphs. [source] Confocal Raman Microscopy as a Tool to Investigate Concentration Profiles of Melt Crystallized Ibuprofen/Carnauba WaxCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2009H. Qu Abstract Coatings are of great significance for pharmaceutical solid dosage forms. They fulfil a number of functions and are often necessary to control drug delivery, to mask bitter taste, or to protect the active pharmaceutical ingredient from detrimental environmental factors. The process of self-coating by melt crystallization of a suitable binary mixture eliminates the need for an additional process step in the manufacture of a solid drug. Self-coating relies upon the physical and spatial separation of individual components in a melt during solidification. This paper focuses on the use of confocal Raman microscopy as a nondestructive technique for quantifying the spatial distribution of the components in self-coated pastilles manufactured from the binary system ibuprofen/carnauba wax. Pastilles are produced from the melt. Raman spectroscopy allows the direct analysis of concentration profiles across the surface of the pastille. Here, the samples are cleaved and the cleaved surface is investigated in order to establish the distribution of the components in the interior of the solid. A univariate calibration model was developed and statistically validated with standard mixtures of ibuprofen and carnauba wax. Different regression models (linear or polynomial, using different significant peaks for the respective compounds) were assessed and a linear model was found to be adequate to determine the concentration gradient in the pastilles. [source] | |||||||||||||