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Showing papers on "Crystallization published in 1986"


Journal ArticleDOI
TL;DR: A number of approaches to the synthesis of a class of anionic clay minerals (M a 2+ M b 3+ (OH) 2 a +2 b (X − ) 2 b · x H 2 O; M 2+ = Mg, Ni, Co, Zn, Cu, etc., M 3+ = Al, Cr, Fe, Sc; m 2+ /M 3+ ∼ 1−5; X − = water and base stable anion; x = 0−6) have been sumarized.

772 citations


Journal ArticleDOI
01 Aug 1986-Polymer
TL;DR: In this article, a study has been made of the crystallization behavior of poly(ether-ether-ketone), PEEK, under isothermal and non-isothermal conditions.

635 citations


Journal ArticleDOI
TL;DR: In this paper, it is shown that there is a window in the acid concentration which provides long-term solution stability, and that the gels formed from these clear solutions shrink in their liquor under certain conditions and the introduction of hydrogen peroxide into the liquor causes vigorous gel shrinkage.
Abstract: Titanium alkoxides hydrolyse vigorously with water producing polycondensates whose equivalent oxide content varies from ∼ 70% to over 90%. This variation reflects the average molecular size and the nature of the terminal bonds. Hydrolysis conditions also affect the molecular and particle morphologies modifying the crystallization and sintering behaviour of oxide materials derived from polycondensates. It is also possible to form clear polymer solutions under excess water hydrolysis with the addition of certain acids. Investigations show that there is a window in the acid concentration which provides long-term solution stability. The gels formed from these clear solutions shrink in their liquor under certain conditions and the introduction of hydrogen peroxide into the liquor (surrounding the gel) causes vigorous gel shrinkage.

375 citations


Journal ArticleDOI
TL;DR: In this article, a series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates, assuming local equilibrium between phases, and that the system remains chemically closed during crystallization of the trapped liquid.
Abstract: A series of calculations have been carried out to evaluate the effect on cumulus mineral compositions of solidification of trapped intercumulus liquid in orthocumulates. The calculation assumes local equilibrium between phases, and that the system remains chemically closed during crystallization of the trapped liquid. The latter assumption is held to be valid on a scale of tens to hundreds of centimeters. It is not necessary to know the composition of the trapped liquid, as the calculation only requires an estimate of FeO content and trapping temperature. The change in composition of a mineral from that of the initially precipitated cumulus crystals to the final composition after complete solidification is termed the “trapped liquid shift”. Its magnitude depends on the modal proportions of cumulus phases and the initial porosity, and is only weakly dependent on initial phase compositions. Trapped liquid shifts are significant when compared with mineral composition changes occurring during fractional crystallization. Crystallization of 30% trapped liquid gives rise to shifts of up to 10 mol. percent in Mg number of olivine or pyroxene. The size of the shift becomes greater when the initial cumulus assemblage has a lower total FeO+MgO content, and vice versa. As a result of the relationship between trapped liquid shift and cumulus mode, mineral composition variations and trends may be generated in sequences of cumulates which originally had constant compositions of cumulus minerals. For example, in a cyclic unit grading from a pyroxenitic base to an anorthositic top, crystallization of a uniform proportion of trapped liquid will result in an apparent iron enrichment trend from bottom to top of the cycle, as has been observed in the Upper Critical Zone of the Bushveld Complex.

341 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the transition from amorphous to crystalline state and back can be achieved simultaneously with long term data (amorphous phase) stability, provided the melting temperature of the compound is sufficiently high.
Abstract: Results of rapid (laser induced) and slow (heating stage induced) crystallization studies on Te1−xGex, 0≤x≤0.6, are reported. The time it takes to laser crystallize varies with x by more than four orders of magnitude. Films with stoichiometric compositions, Te and GeTe, can be crystallized using laser pulses of less than 100 ns duration. Unlike Te, which spontaneously crystallizes at room temperature, GeTe has a crystallization temperature of >150 °C. From these results we argue that, in general, compound materials allow realization of fast‐switching, reversible, phase‐change optical recording media. Furthermore, this fast‐switching capability, from the amorphous to the crystalline state and back, can be attained simultaneously with long term data (amorphous phase) stability, provided the melting temperature of the compound is sufficiently high.

337 citations


Journal ArticleDOI
TL;DR: In this article, the oxidation kinetics of several single-crystal and polvcrystalline silicon carbide materials and singlecrystal silicon in dry oxygen over the temperature range 1200° to 1500°C were fitted to the linear-parabolic model of Deal and Grove.
Abstract: The oxidation kinetics of several single-crystal and polvcrystalline silicon carbide materials and single-crystal silicon in dry oxygen over the temperature range 1200° to 1500°C were fitted to the linear-parabolic model of Deal and Grove. The lower oxidation rates of silicon carbide compared to silicon can be rationalized by additional consumption of oxidant in oxidizing carbon to carbon dioxide. The (000J) Si face of the silicon carbide platelets exhibited lower parabolic oxidation rates than the (0001) C face, by a factor of 10 at 1200°C. Apparent activation energies increased from a value of ∼120 kJ/mol below 1400°C to a value of ∼300 kJ/mol above this temperature. The (0001) Si face exhibited this high activation energy over the entire temperature range. The controlled nucleation thermally deposited material exhibited the highest oxidation rates of the polycrystalline materials followed by the hot-pressed and sintered α-silicon carbides. In general, the oxidation rates of the polycrystalline materials were bracketed by the oxidation rates of the basal planes of the single-crystal materials. Higher impurity concentrations and higher density of nucleation sites led to a greater susceptibility to crystallization of the scale which significantly complicated the oxidation behaviors observed. When crystallization of the oxide scale occurred in the form of a layer of spherulitic cristobalite crystals, a retardation of the oxidation rates was observed. An accelerated oxidation behavior was found when this coherent layer was superseded by the formation of fine mullite crystals.

323 citations


Journal ArticleDOI
TL;DR: In this article, the microstructure of the crystallized products was analyzed by observing the micro-structure properties of the parent glass in a bulk form, which led to the occurrence of large cracks in the crystallised product.
Abstract: Formation of a high-strength bioactive glass-ceramic in the system MgO-CaO-SiO2-P2O5 was investigated by observing the microstructure of the crystallized products. Crystallization of the parent glass in a bulk form led to the occurrence of large cracks in the crystallized product. This was attributed to the precipitation of fibrousβ-wollastonite crystals growing perpendicular to the outer surfaces of the glass after uniform precipitation of fine oxyapatite/fluoroapatite crystals. On the other hand, crystallization of the same glass in a powder compact led to the formation of a crack-free dense crystallized product due to uniform precipitation of both apatite and wollastonite fine crystals throughout the glass article. The uniform precipitation of the wollastonite crystals was attributed to the simultaneous formation of fine crystals in the individual glass particles.

310 citations


Patent
25 Apr 1986
TL;DR: In this article, a porous and transparent hydrated gel is prepared from a poly(vinyl alcohol) solution in a mixed solvent consisting of water and an water-miscible organic solvent.
Abstract: A porous and transparent hydrated gel is prepared from a poly(vinyl alcohol) solution in a mixed solvent consisting of water and an water-miscible organic solvent. Upon cooling the poly(vinyl alcohol) solution below room temperature, a gel is formed as a consequence of crystallization of poly(vinyl alcohol) molecules. Exchange of the organic solvent included in the gel with water produces a hydrated gel of poly(vinyl alcohol) which has a high tensile strength, a high water content, and a high light transmittance.

279 citations


Journal ArticleDOI
TL;DR: Differential scanning calorimetry (DSC) and density gradient technique (DGT) were used to determine, both isothermally and dynamically, the crystallization kinetics of polyetheretherketone (PEEK) as mentioned in this paper.
Abstract: Differential scanning calorimetry (DSC) and the density gradient technique (DGT) were used to determine, both isothermally and dynamically, the crystallization kinetics of polyetheretherketone (PEEK). The data were analyzed by a model utilizing, for the first time, two crystal nucleation and growth processes which were observed experimentally in a typical Avrami plot of the isothermal data. Thus, by modeling the data as two separate Avrami type crystallization processes occurring in parallel, both isothermal and dynamic data could be predicted with the same model constants. The first process provided an Avrami exponent of 2.5 and an onset temperature of 320°C. The second process displayed an Avrami exponent of 1.5 and an onset temperature of 342°C. The validity of this dual mechanism crystallization model was proven in practice by predicting with best fit model constants, a wide range of crystallinities of both neat and carbon fiber-reinforced PEEK samples that had been made at different cooling rates from the melt.

272 citations


Book ChapterDOI
TL;DR: In this article, high resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework, showing that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination.
Abstract: Silica-rich, Al-, B- and (Al + B) MFI zeolites called Zeosilites, Aluzeosilites, Borozeosilites and Aluborozeosilites respectively were obtained by hydrothermal crystallization at 60–200°C from mixtures containing F anions and tetra-, tri- and di-propylamraonium cations as templates; pH values were 3–10. Crystal size is a function of the Si substitution degree, it may reach 800 um in some cases. DSC, DTA and TG curves corresponding to the decomposition of the templates occluded as fluoride salts are different from those observed for samples obtained in alkaline medium. Mass spectrometer analysis shows that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination. High resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework.

241 citations


Journal ArticleDOI
TL;DR: Amorphous alloy powders of the types NiZr, Cozr, FeZr and CuZr are produced by mechanical alloying from crystalline elemental powders as discussed by the authors, which is monitored by microstructural investigations, x-ray diffraction, and, where applicable, by magnetization measurements.
Abstract: Amorphous alloy powders of the types NiZr, CoZr, FeZr, and CuZr are produced by mechanical alloying from crystalline elemental powders. The alloying and amorphization process is monitored by microstructural investigations, x‐ray diffraction, and, where applicable, by magnetization measurements. The crystallization temperatures, determined by differential scanning calorimetry, are comparable to those measured for rapidly quenched and solid state reacted amorphous metals of the same compositions.

Journal ArticleDOI
TL;DR: In this article, the tendency of carbon fiber to nucleate the crystallization of PEEK has been evaluated by DSC and other techniques and it was found that PEEK with carbon fiber had a higher nucleation density than PEEK itself.
Abstract: : The tendency of carbon fiber to nucleate the crystallization of PEEK has been evaluated by DSC and other techniques. As the carbon fiber content was increased, the supercooling necessary for PEEK crystallization decreased. The repeated melting (at 396 C) of thhe same PEEK sample results in a decrease of the number of nuclei for crystallization. At equivalent thermal histories, PEEK with carbon fiber was found to have a higher nucleation density than PEEK itself. The surface growth of carbon fiber and nuclei in the PEEK matrix compete for crystallization growth. As the holding time in melt was increased, the number of matrix spherulites formed on cooling decreased, hence a more pronounced transcrystalline region was developed. Correspondingly, the composites preheated in the melt for 100 min. showed about two times the transverse tensile strength and strain-to-failure of those preheated for only 30 min. Corresponding fracture surface produced in tension showed that the former samples had a greater matrix adhesion to the carbon fiber than the latter. A strong interfacial bond is thus developed by crystallization on carbon fiber surface. Destroying nuclei in the PEEK matrix by long preheating enhances crystallization on the carbon fiber.

Journal ArticleDOI
TL;DR: In this paper, the authors derived an equation to calculate the efficiency of removal of elements from magmas into aqueous fluids as a function of (1) the bulk solid-liquid partition coefficient of these elements; (2) the initial and saturation water concentrations in the melt; and (3) the chlorine concentration of the melt.
Abstract: Equations have been derived which model element partitioning between silicate melts, aqueous fluids, and crystalline phases during crystallization. These equations can be used to calculate the efficiency of removal of elements from magmas into aqueous fluids as a function of (1) the bulk solid-liquid partition coefficient of these elements; (2) the initial and saturation water concentrations in the melt (which together determine the amount of melt crystallized before water saturation); and (3) the chlorine concentration of the melt (in the case of chlorine-complexed cations).The efficiency with which copper and molybdenum can be removed from silicate melts, E(Cu) and E(Mo), respectively, has been calculated. Based on geologic data, copper is modeled as a compatible element and molybdenum is modeled as an incompatible element. Under these conditions the ratio E(Mo)/E(Cu) increases as the initial water concentration of the melt decreases for a given depth of vapor evolution and a given Cl/H 2 O ratio and increases as the depth of vapor evolution increases for a given Cl/H 2 O ratio and a given initial water concentration of the melt.Cu is concentrated so efficiently into a moderately to highly saline aqueous phase that liquid-vapor extraction seems to be a reasonable process to account for the concentration of Cu in porphyry Cu deposits. Efficient extraction of Cu results when aqueous fluids are evolved early in the crystallization of the intrusion. The value of D(Mo) is small relative to D(Cu) at moderate to high chloride concentrations, and the extraction of Mo from the melts into aqueous fluids therefore tends to be less efficient. However, vapor-liquid partitioning can extract the requisite quantities of Mo from granitic melts of batholithic size if Mo acts as an incompatible element and if the water content of the magma at water saturation is on the order of several weight percent.

Journal ArticleDOI
TL;DR: Melange polyoxyde d'ethylene-polymethacrylate de methyle, etudie en fonction de la composition, de la masse moleculaire de chaque composant et de la temperature de cristallisation.
Abstract: Melange polyoxyde d'ethylene-polymethacrylate de methyle, etudie en fonction de la composition, de la masse moleculaire de chaque composant et de la temperature de cristallisation

Journal ArticleDOI
TL;DR: The water of hydration in myoglobin crystals and solutions was studied at subzero temperatures by calorimetry and infrared spectroscopy and a hydrogen bond network model is proposed to explain these features.

Journal ArticleDOI
TL;DR: In this paper, it was shown that amorphous alloy powders of Cu and Ti can be produced over a broad composition range by mechanical alloying of the elemental powders in a high-energy ball mill.
Abstract: We show that amorphous alloy powders of Cu and Ti can be produced over a broad composition range by mechanical alloying of the elemental powders in a high-energy ball mill. The amorphous powders are compared with liquid-quenched amorphous alloys of the same compositions using the techniques of x-ray diffraction and thermal analysis of crystallization. The two types of samples are found to have similar characteristics. Chemical analysis shows that only trace amounts of impurities are introduced in the alloys by the milling process.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the compositional dependence of the partitioning of chromite between spinels and silicate melts by considering the exchange of FeCr2O4 component between the crystalline and melt phases.

Journal ArticleDOI
TL;DR: In this paper, the melting and crystallization processes of a model system composed of 864 LJ particles under periodic boundary conditions are simulated by means of constant temperature, constant pressure molecular dynamics techniques.
Abstract: By means of constant‐temperature, constant‐pressure molecular dynamics techniques, we simulate the melting and crystallization processes of a model system composed of 864 Lennard‐Jones (LJ) particles under periodic boundary conditions. On heating an fcc crystal of LJ particles, it is ascertained that melting takes place. On the other hand, a LJ liquid, when quenched slowly, crystallizes into a stacking of layers with stacking faults where each layer forms a close‐packed structure with occasional point defects. The atomic configuration is not always nucleated into a completely ordered structure. A large hysteresis in the volume‐temperature curve is observed. The volume contraction at the transition is characterized by two different growth rates, relatively slow at the first stage and relatively fast at the final stage. The critical cooling rate which separates the crystal‐forming cooling rates and the glass‐forming cooling rates is between 4×1010 and 4×1011 K/s for argon. On taking advantage of computer si...

Journal ArticleDOI
TL;DR: In this paper, a pure β-modification of polypropylene has been prepared and the thermodynamic equilibrium melting point of the β modification has been determined, which is a complex process consisting of three partially overlapping processes (β-melting→ recrystallization in the α modification (βα-recrystallisation)→ βαmelting).
Abstract: The pureβ-modification of polypropylene has been prepared. It has been found that the nature of the melting of theβ-modification strongly depends on the thermal history of the sample (melting memory effect). The melting of samples cooled to room temperature after crystallization is a complex process consisting of three partially overlapping processes (β-melting→ recrystallization in theα-modification (βα-recrystallization)→ α-melting). If heating starts at the temperature of crystallization, theβ-modification melts separately, withoutβα-recrystallization. Under melting conditions free from the interference caused byβα-recrystallization, theβ-modification exhibits the melting characteristics of thermodynamically stable modifications. The thermodynamic equilibrium melting point of theβ-modification has been determined to beT m 0 (β)=456 K.

Journal ArticleDOI
TL;DR: In this article, a new equation was derived from Johnson-Mehl-Avrami equation to calculate the activation energy of crystallization for metallic glass E, d [ ln (d x d t ) p ]/d (1/T p ) = − E R, where x is the volume fraction of transformation, t the effective time, Tp the peak temperature of crystallisation at d2x/dt2=0, R the gas constant.
Abstract: A new equation is derived from Johnson-Mehl-Avrami equation to calculate the activation energy of crystallization for metallic glass E, d [ ln ( d x d t ) p ]/ d (1/T p ) = − E R , where x is the volume fraction of transformation, t the effective time, Tp the peak temperature of crystallization at d2x/dt2=0, R the gas constant. It demonstrates that (dx/dt)p can be used instead of the cooling rate B in a Kissinger plot. This new equation has successfully predicted the activation energy of crystallization for Pd76Y9Si15 during non-isothermal annealing; and indicated, as expected, that the maximum rate of crystallization in DSC increases by the same factor as the heating rate does.

Journal ArticleDOI
TL;DR: In this article, the authors investigate the interaction of thermal convection and crystallization in large aspect-ratio magma chambers and show that the convective instability occurs at different stages of crystallization.

Journal ArticleDOI
TL;DR: In this article, a study has been made of the mechanical, thermal, and morpholigical characteristics of melt-crystallized isotactic polypropylene containing high levels of the β or pseudohexagonal crystalline form.
Abstract: A study has been made of the mechanical, thermal, and morpholigical characteristics of melt-crystallized isotactic polypropylene containing high levels of the β or pseudohexagonal crystalline form Different levels of β-form crystallinity were produced in the polymer by blending in low levels of quinacridone dye nucleating agent Microscopical studies of the crystallization process revealed that both α-form (monoclinic), and β-form spherulites nucleated on the dye particles, with α-spherulite growth commencing at a higher temperature These observations were able to qualitatively explain the dependence of β-form level on both the nucleant concentration and its state of dispersion in the polymer Improving the dispersion of the nucleant was found to reduce the level of β-form crystallinity if the nucleant concentration exceeded an optimum level A new procedure for quantifying the volume fraction of β spherulites in a sample was developed which utilized the technique of selective solvent extraction From volume-fraction, x-ray, and density data, the pure α and β crystal densities were obtained Dynamic mechanical measurements-obtained on unoriented specimens containing varying levels of β-form crystallinity showed an increase in the magnitude of the damping in the post-Tg region with increasing β content High levels of the β form lead to lower values of the modulus and yield stress, and higher values of the elongation at break and impact strength

Book ChapterDOI
TL;DR: Porin has proven to be rather useful for the optimization of conditions to crystallize membrane proteins as it is very stable over a wide range of conditions Crystallization experiments (at 20°) are successful also using several other detergents with a moderate to high carboxymethyl cellulose (CMC) initial problems with reproducibility of porin crystallization revealed that a high degree of purity of this protein is required, and that the removal of tightly bound lipoprotein and glycolipid is critical for success as mentioned in this paper.
Abstract: Publisher Summary This chapter describes isolation and crystallization of bacterial porin The unusual aspects of porin crystallization are consistent with the micellar interactions involved in crystal formation The resulting porin crystals are relatively sensitive to the environment Care must be taken in handling and mounting crystals for X-ray analysis to avoid significant or abrupt changes in the solvent or detergent environment and uncontrolled variations of temperature Porin has proven to be rather useful for the optimization of conditions to crystallize membrane proteins as it is very stable over a wide range of conditions Crystallization experiments (at 20°) are successful also using several other detergents with a moderate to high carboxymethyl cellulose (CMC) Initial problems with reproducibility of porin crystallization revealed that a high degree of purity of this protein is required, and that the removal of tightly bound lipoprotein and glycolipid is critical for success Although current experience is limited, it seems fair to conclude that with a better understanding of protein–amphiphile interactions, of micellar physical chemistry, and with improvement in crystallization techniques, the outlook for understanding membrane protein structure appears bright

Journal ArticleDOI
TL;DR: In this paper, the authors show that heterogeneous nucleation is essential for the formation of porphyritic textures, and that the textures are more likely to be dendritic or radial.


Journal ArticleDOI
TL;DR: Although indomethacin remained as a glass for 2 years at room temperature, pulverized glassy indometHacin was found to crystallize, and the rate of crystallization was determined by the X-ray diffraction method and followed first-order kinetics.
Abstract: Glassy indomethacin was prepared by cooling the melt, and the glassy state was confirmed by the jump of heat capacity and the anomalous endothermic park (heat capacity maximum) in the differential scanning calorimetry (DSC) curve. The influences of the cooling rate of the melt and the heating rate of the glass formed on the glass transition temperature (Tg) were examined, and the apparent activation energy of glass transition was calculated to be 212.5kJ/mol. The relaxation process below Tg was traced in terms of the area under the anomalous endothermic park of the DSC curve and the rate of relaxation during annealing was found to reach the maximum at about 303 K. The rate of dissolution of glassy indomethacin was far greater than that of crystalline indomethacin. Although indomethacin remained as a glass for 2 years at room temperature, pulverized glassy indomethacin was found to crystallize, and the rate of crystallization was determined by the X-ray diffraction method. The degree of crystallization was determined by Hermans' method, and was found to reach a maximum of 60% after 2 months. The process of crystallization followed first-order kinetics.

Journal ArticleDOI
TL;DR: In this paper, a new lattice model of polymer crystallization is described, and results of numerical solutions of rate equations for crystallization of a two-dimensional "crystal" are presented.
Abstract: A new lattice model of polymer crystallization is described. Results of numerical solutions of rate equations for crystallization of a two-dimensional "crystal" are presented. It is shown that the crystal thickness varies inversely with supercooling and that kinetics similar to secondary nucleation occurs. This is true even though the growth face is intrinsically rough and hence there cannot be any nucleation. The presence of a low-entropy saddle point during growth is explained, and its influence on the crystal thickness and lamellar morphology is discussed.

Journal ArticleDOI
01 Dec 1986-Polymer
TL;DR: In this article, the authors examined the initial stages of polymer crystallization in the melt, registered in situ by time-resolved small-angle X-ray scattering using a synchrotron Xray source, and found that the NIF state had a more disordered layer surface as compared to the final E and F2 structures.

Journal ArticleDOI
TL;DR: In this article, the ferrisilicate molecular sieve analog of the zeolite ZSM-5 can be obtained from a gels containing low-molecular-weight silica species.

Journal ArticleDOI
TL;DR: In this article, the authors reviewed transport and interface kinetic concepts for the design and control of inorganic crystal growth experiments, and their applications and limitations in protein crystal growth were considered.