Abstract: Th e growth rate C of the cr ys tallin e bodies a ppearing in each of a se t of 35 characte rized po ly. e th ylene fractions ra ngin g from 3600 to 807 ,000 in molec ular we ight has been meas ured as a fun ction of the unde rcooling tJ.T. In isothe rmal c rys tallization, only ax ial ites we re found from M\",= 3600 to 18 ,000. (For th ese runs, tJ.T < 17.5 °C.) From M\".= 18,000 to M\". \"\" 115,000 coa rse·grained non ·banded s phe ru · lit es we re found for tJ.T > 17.5 °C , and axialites for tJ.T < 17.5 °C : a rathe r s ha rp break occurred in th e log .o C ve rsus T data at tJ.T \"\" 17.5 0c. The morphologica l changes we re more gradual. Above Mil' \"\" 115,000, only nea rly s tructureless \" irregular\" spherulit es we re found a t all unde rcoolings corresponding to isothermal growth. Typica l ringed sphe rulites were o btained only on quenching. Wide·ang le x·ray data showed that the usual orthorhombic subce ll predominated in all the morphologies encounte red. Low· angle x·ray data showed tha t the s pecime ns exhibit ed lamellar crystallization irrespective of the particular gross morphology involved. The growth rat e data on each frac tion we re analyzed us ing

Abstract: Surface crystallization of a Au+‐ion‐implanted lithia‐alumina‐silica glass has been realized. Annealing of a glass sample implanted with 285‐keV Au+ ions at 550 °C results in the growth of colloidal Au particles of 18–35‐A radius. The Au particles constitute sites for the precipitation of lithium metasilicate crystals at 550 °C. Further annealing at 750 °C allows the growth of quartz and β‐spodumene crystals. The crystallized surface obtained after the high‐temperature anneal was characterized by a Knoop microhardness number of 626, which is of the order of that obtained for commerical volume‐crystallized glass‐ceramics of similar composition.

Abstract: In this study, optical microscopy, differential scanning calorimetry, and infrared spectroscopy are used to study the high‐temperature isothermal crystallization of high‐molecular‐weight poly(vinylidene fluoride) It is shown that there exists a temperature domain in which both the α and β phases of PVF2 can be grown concurrently and in competition with each other to form two distinct populations of spherulites which are characterized by different diameters, band periods, and melting points In addition, a time‐ and temperature‐dependent crystal‐crystal transition from the α phase to the γ form can be induced in this high‐temperature crystallization region to produce spherulites which melt 15–20 ° above the melting point of the original α phase This transformation exhibits nucleation and propagation characteristics which in some regions can compete with the normal growth of the α phase to produce unique ’’wagon‐wheel’’ spherulitic structures

Abstract: The transformation behavior of roller-quenched amorphous Pd 0.82− x Au x Si 0.18 and Pd 0.835− x Au x Si 0.165 alloys, where x ⩽ 0.10, after rapid heating to temperatures near to or above T g , is reported. The calorimetrically determined glass ( T g ) and kinetic crystallization ( T c ) temperatures both increased with x up to x ≈ 0.04. With increasing x , at x ⩾ 0.04, T c decreased rapidly while T g varied little. Binary Pd 0.82 Si 0.18 alloys crystallized to an fcc phase without apparent composition segregation. The tendency to phase separate at T near T g , as manifested by small- (SAXS) and large-angle X-ray scattering and calorimetry, increased with increasing Au substitution. Pd 0.8 Au 0.035 Si 0.165 alloy apparently phase separated by a nucleation and growth mechanism, with a growth rate limited by the melt viscosity, to form an fcc phase dispersed in an amorphous phase which later crystallized. Pd 0.74 Au 0.08 Si 0.18 alloy phase separated initially to two melts, each of which later crystallized in turn. The initial separation behavior was generally consistent with the predictions of the spinodal theory but with some deviation from Cahn's linear relation.

Abstract: This work examines the effect that appreciable molecular extension has on the crystallization of long chain molecules. Elementary theoretical considerations presented indicate that to achieve high molecular extensions in solution a longitudinal velocity gradient of strain rate about 103s-1 is required. A method of generating such a velocity gradient, involving flow between opposed jets, is reported and the nature of this flow pattern is examined and quantitatively analysed. The behaviour of polyethylene-xylene solutions in the flow field is presented, notably birefringence observations and measurements indicate that a high degree of molecular alinement can be achieved in specific localized areas of the flow field; also concentration effects are observed which are discussed in terms of entanglement concepts. The effect chain alinement has on crystallization is examined in detail, in particular the ‘shish kebab ’ morphology of the crystals so produced is examined in relation to the hydrodynamic conditions in which they were grown.

Abstract: Poly(vinylidene fluoride) exists in three crystalline forms. Optimum conditions for preparing form III were established by infrared spectroscopy, differential scanning calorimetry, and x-ray diffraction measurements. Form III is easily obtained by annealing mats of solution-grown crystals of form II at 175–185°C and is also preferentially formed by isothermal crystallization from the melt between 165 and 175°C. Below 165° crystallization of form II is favored. The melting point of form III is higher than that of form II.

Abstract: Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO-Al2O3-SiO2 system were studied by DTA, X-ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO2 or TiO2. Up to 10 wt% CeO2 was also added to some glasses. Metastable solid solutions with the high-quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce2Ti2O4 (Si2O7). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO2, but no crystalline TiO2 was detected. In the presence of CeO2, TiO2 was a more effective catalyst than ZrO2. Although CeO2 lowered the melting temperatures of the glass-ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crystallization.

Abstract: Amorphous silk fibroin with random coil conformation shows endothermic and exothermic peaks and endothermic shift on the DSC (differential scanning calorimetry) curve. The endothermic shift observed at 175°C was due to the glass transition. The exothermic peak at 212°C is recognized to be the crystallization, which later was confirmed by x-ray diffraction pattern. The endothermic peak at 280°C is shown to be the degradation.

Abstract: Crystals of monellin, a sweet protein from Dioscoreophyllum cumminsii, were grown by vapor diffusion of 20% ethanol into buffered protein solution. The crystals are orthorhombic, belonging to space group P21212, with a = 54.4 A, b = 113.0 A, c = 40.8 A, and V = 250,300 A3. The asymmetric unit contains two complete molecules of monellin. The diffraction pattern of this crystal form extends to at least 2.5 A, indicating that x-ray structural analysis is possible to near-atomic resolution.

Abstract: The conversion of amorphous calcium phosphate (ACP) to crystalline hydroxyapatite (HA) was studiedin vitro in the presence or absence of phosphatidyl serine (PS) and other phospholipids. ACP transformation and HA crystal growth were monitored by electron microscopy, selected-area electron diffraction and X-ray diffraction, and by measuring supernatant calcium and phosphate. PS, and other acidic phospholipids, had a significant stabilizing effect on ACP. With preformed ACP at ratios of only 1 lipid molecule per 30–50 Ca atoms, PS markedly delayed HA crystal formation. When PS was present during ACP precipitation, inhibition of conversion to HA was less pronounced, but crystal habit and aggregation were greatly altered resulting in stacks of thin, membrane-like sheets approximately 38–42 A thick. PS appeared to be most effective in blocking ACP to HA conversion when oriented primarily on the surface; it most affected subsequent crystal formation when distributed throughout the amorphous precursor. Phospholipids possessing anionic, and hence Ca-binding properties, were effective in stabilizing ACP; neutral zwitterion lipids, which have amphipathic properties but do not bind Ca, were not. In view of the presence of anionic lipids in matrix vesicles and their association with early mineral deposits, the current findings add further evidence that lipids may play a role in the control of normal mineralizationin vivo.

Abstract: The crystallization kinetics of a Pd 0.775 Cu 0.06 Si 0.165 metallic glass have been determined by calorimetry over the temperature interval 665–680 K. We observe a change in the time dependence from t 4 at 665 K to t 3 at 680 K. In this temperature interval the activation enthalpy for crystallization was observed to be (95 ± 5) kcal/mol, in good agreement with the activation enthalpy for viscous flow as determined previously by Chen.

Abstract: In the melt crystallization of isotactic polypropylene, poly(ethylene oxide) and poly(butene-1) in contact with substrates, the existence of a fixed number of nucleating sites on the substrate surfaces has been established. When these sites become active successively (the transient in the number of nuclei is long) during crystallization, pseudohomogeneous nucleation on the substrate occurs. Nucleation rates for poly(butene-1) and poly(ethylene oxide) on substrates and in bulk have been measured. These data can be used for comparing the nucleating ability of substrates. Estimates of the variation of bulk nucleation rates from one volume element to another as well as for repeated crystallization within a given volume element have been included. Finally, the temperature coefficients of heterogeneous nucleation rates have been combined with the temperature coefficient of spherulitic growth rate of poly(butene-1), to yield values of the interfacial energy parameters appearing in the theory of heterogeneous nucleation. The quantitative characterization of the nucleating ability of substrates by this method is an improvement over the mere use of nucleation densities or nucleation rates.

Abstract: Melting and crystallization behavior of polytetrafluoroethylene as polymerized in emulsion and suspension is shown to depend on molecular weight. DSC heating curves for virgin PTFE with low molecular weight below 3 × 105 have a single peak, whereas curves for higher molecular weight samples have double peaks. With increasing heating rate the areas of higher melting peaks become larger than the lower melting peaks. The morphology of polymer exhibiting double melting peaks is mainly folded ribbons or granular particles. The phenomenon of double melting is explained on the basis of two different crystalline states which correspond to the “fold regions” and the “linear segments” in a folded ribbon. The melting temperature of virgin PTFE is almost constant at ca. 330°C for molecular weights below 1 × 106, and rises as the molecular weight increases above 1 × 106. The heat of melting of virgin PTFE is nearly independent of molecular weight. On the basis of these results, we propose a model for melting and crystallization of low and high molecular weight PTFE and for the crystal structure.

Abstract: Results of experimental studies in the system NaAlSi 3 O 8 -KAlSi 3 O 8 -SiO 2 -H 2 O, at 4 kb and from 650° to 1000°C, have been used to generate composition paths for liquid and crystal fractions as functions of temperature and bulk composition. In both the experimental work and the analyses of crystallization, attention has been devoted mainly to silicate liquid that is saturated with quartz and an alkali feldspar but unsaturated with respect to an aqueous vapor phase. Such liquid can be represented on a compound T-X surface that slopes, with decreasing H 2 O content in the system, toward SiO 2 for NaAlSi 3 O 8 -rich compositions and away from SiO 2 for KAlSi 3 O 8 -rich compositions. Compositions of the crystal fraction that separates from the liquid under equilibrium conditions in the temperature range 700° to 655°C have been calculated for an array of bulk compositions. Equilibrium crystallization history is characterized by numerous shifts and some reversals along paths that describe the composition of the crystal fraction. The various paths demonstrate that intensive parameters such as temperature, pressure, and H 2 O fugacity cannot be uniquely determined from the composition of a specific fraction. Paths also have been outlined, for a variety of bulk compositions, from the maximum temperature for separation of quartz ± alkali feldspar to the solidus temperature of 655° C under conditions of perfect fractional crystallization in which successive precipitates are immediately isolated from the silicate liquid. These crystal fraction paths are marked by discontinuities that indicate abrupt, discrete changes in composition, and with falling temperature, they tend to focus toward a compositional area centering about 20 NaAlSi 3 O 8 , 45 KAlSi 3 O 8 , 35 SiO 2 . The melting of crystalline assemblages that represent the haplogranite system can be considered as the inverse of equilibrium crystallization, fractional crystallization, or some combination of these idealized processes. Thus the composition path for an equilibrium crystal fraction can also serve for the tracing of compositional changes in a residue formed during equilibrium melting. A residue of given composition can be produced at constant elevated pressure under conditions representing many different combinations of temperature and bulk composition. The experimentally determined complexities of crystallization are reasonable indications of what can occur under natural plutonic conditions. They are potentially most useful, however, for the testing of genetic models based upon detailed studies of rocks in a geologic and petrographic context. They also lead to the conclusions that (1) the bulk composition of a granitic plutonite is not by itself sufficient for estimating conditions under which the rock was formed and (2) experimental data obtained for the haplogranite system under conditions that include the presence of an aqueous fluid phase ( P H 2 O ≈ P fluid = P tot ) are highly restricted in their pertinence to the crystallization histories of most granitic plutonites.