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Showing papers on "Crystallization published in 1980"


Journal ArticleDOI
TL;DR: In this article, the modified Kissinger-type equation was derived on the basis of the nucleation and growth equations, and the validity of the equation was ascertained by applying to the crystallization of Li 2 O·2SiO 2 glass whose kinetic data regarding crystallization are already well-known.
Abstract: For the purpose of analyzing the crystallization process of glass by DTA, the modified Kissinger-type equation was derived on the basis of the nucleation and growth equations, and the validity of the equation was ascertained by applying to the crystallization of Li 2 O·2SiO 2 glass whose kinetic data regarding crystallization are already well-known. The modified Kissinger-type equation is identical with the so-called Kissinger equation only when the crystallization starts at the surface and grows towards the inside of the glass one-dimensionally. The conditions required for applying the Kissinger plot or modified Kissinger-type plot to the crystallization of glass were discussed, and it was concluded that the crystallization mechanism should be known in order to obtain the meaningful activation energy.

451 citations



Journal ArticleDOI
01 Jun 1980-Polymer
TL;DR: In this paper, a study has been made of the general crystallization behavior of poly(L-lactic acid), PLLA, and is intended to be the basis for further work on fibre formation processes.

393 citations



Journal ArticleDOI
TL;DR: In this paper, the technique of preparing oxide glasses from metal alcoholates through hydrolysis, gelling and heating at low temperatures has been reviewed, which makes it possible to produce very high purity and compositions which the conventional melting technique could not give because of immiscibility, crystallization and high melting temperatures.
Abstract: Developments in the technique of preparing oxide glasses from metal alcoholates through hydrolysis, gelling and heating at low temperatures have been reviewed. This technique makes it possible to produce (1) glasses of very high purity and (2) glasses of compositions which the conventional melting technique could not give because of immiscibility, crystallization and high melting temperatures. This technique can provide glasses having various shapes such as fibers, thin coating films, isolated films and bulk glasses. Discussion was made on the microscopic processes leading to fibers and bulk glasses.

321 citations



Journal ArticleDOI
TL;DR: In this paper, a model for the fomation of thermally sprayed alumina coatings is proposed and the spreading and crystallization of liquid droplets on impact with the substrate are analyzed and the thermal history of individual particles related to the kinetics of nucleation of γ-Al2O3 to other forms.
Abstract: A model for the fomation of thermally sprayed alumina coatings is proposed. The spreading and crystallization of liquid droplets on impact with the substrate are analysed and the thermal history of individual particles related to the kinetics of nucleation of γ-Al2O3 to other forms. The results suggest that under the usual spraying conditions undercooling of the liquid droplets is such that γ-Al2O3 nucleates in preference to α-Al2O3 and the cooling rate after solidification is sufficiently rapid to prevent transformation to δ-Al2O3 or α-Al2O3. Transformation of initially formed γ-Al2O3 to α-Al2O3 appears to be possible only if the lamellae formed on impact are thicker than about 10 μm if the substrate is heated to about 1000° C, or if the thickness is greater than about 20 μm on an unheated substrate. The α-Al2O3 generally observed in thermally sprayed coatings is the result of crystallization from pre-existing nuclei arising from incomplete melting of the feed material.

287 citations



Journal ArticleDOI
TL;DR: In this paper, a temperature-dependent small-angle x-ray scattering and electron microscopic study on a sample of low-density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting.
Abstract: A temperature-dependent small-angle x-ray scattering and electron microscopic study on a sample of low-density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting. The analysis of SAXS data is based upon some general properties of the electron-density correlation function. Electron micrographs are obtained from stained sections γ irradiated at elevated temperatures and are analyzed quantitatively by statistical means. According to the model proposed here the thickness distribution in the amorphous layers, rather than that of the crystalline regions, is the essential factor governing the crystallization and melting behavior. The temperature-dependent changes in this thickness distribution provide a natural explanation for the large reversible changes in long-spacing.

267 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that rigid microfibrils of wholly aromatic polyamides such as poly(p-phenylene terephthalamide) (PPTA), poly-p-benzamide (PBA), and their block copolymers with blocks of nylon 6 or nylon 66 were dispersed in a matrix of nylon 2 or nylon 6.
Abstract: As an extension of reinforcing principles of composite materials in which macroscopic fibers are dispersed in a ductile matrix, rigid microfibrils of wholly aromatic polyamides such as poly(p-phenylene terephthalamide) (PPTA), poly-p-benzamide (PBA), and their block copolymers with blocks of nylon 6 or nylon 66 were dispersed in a matrix of nylon 6 or nylon 66. On blending polyaramides with aliphatic polyamides, the spherulitic texture disappeared and a locally birefringent homogeneous texture was obtained. Electron microscopy revelaed that microfibrils of PPTA with diameter of 15-30 nm were dispersed in a fractured surface of the polymer composite. Strong interaction between the fibril surface and the matrix was suggested by the fact that the crystallization of matrix polyamides was induced by the rigid polyaramides. Wide-angle x-ray diffraction intensity curves, DSC curves of cooling process from the melt, and isothermal crystallization curves indicated a marked tendency for induced crystalliza...

207 citations


Journal ArticleDOI
TL;DR: In the presence and absence of magnesium ion, calcite growth-rate reduction was shown to follow a Langmuir adsorption model, suggesting that the magnesium ion is adsorbed at growth sites on the crystal surface as discussed by the authors.


Journal ArticleDOI
TL;DR: In this article, the effects of different molecular diffusion rates on the formation of layered igneous rocks have been examined in a simple laboratory system and the results suggest that stratification in the melt and double-diffusive effects during solidification of the magma should be taken into account when developing theories of the layering.
Abstract: The experiments reported here are a first attempt to model in a simple laboratory system some of the physical processes occurring during crystallization in magma chambers and to examine possible effects of different molecular diffusion rates on the formation of layered igneous rocks. Our laboratory results suggest that stratification in the melt and ‘double-diffusive’effects during solidification of the magma should be taken into account when developing theories of the layering. Explicitly, we have extended earlier experiments on double-diffusive convection, which show how layers may readily form from smooth gradients when two components with different molecular diffusivities have opposing effects on the density gradient. The new experiments included the influence of crystallization and have used an aqueous solution Of Na2CO3 cooled in various configurations. When cooling was from the top, the crystals formed in horizontal layers, whether the initial fluid was homogeneous, was stratified with a constant gradient, or was stratified in several distinct layers. The dominant effect was the formation of a cold but light fluid layer against the cooled upper boundary as the denser crystals grew. The crystals were small and closely packed in the upper layer (which was vigorously converting) and larger and more loosely packed in the lower, more quiescent fluid. In the case where there were preexisting layers there was an abrupt increase in the growth rate of crystals as they crossed an interface. With sidewall cooling and a constant gradient the lighter solution left behind after crystallization streamed upward in a thin boundary layer right to the top of the tank. The outer flow consisted of circulation in nearly horizontal converting layers, each of which was depressed slowly as the light fluid collected at the top. When a constant gradient of Na2CO3 was cooled from below, crystallization produced a ‘finger’ instability, leading to the growth of a mixed layer in the fluid above. An experiment using opposing gradients of Na2CO3 and K2CO3 (with Na2CO3 rich on top) showed that crystals settling to their own density level and then redissolving can reverse the original sense of the gradient and produce small-scale double-diffusive layering in the liquid.

Journal ArticleDOI
TL;DR: In this article, clear titania glasses were formed by a low temperature chemical polymerization technique in the TiO2SiO2 binary, which required initial formation of soluble intermediate species capable of polymerizing into an oxide network.
Abstract: Clear titania glasses were formed by a low temperature chemical polymerization technique in the TiO2SiO2 binary. The chemical method developed requires initial formation of soluble intermediate species capable of polymerizing into an oxide network. The process provides formation of an essentially organic-free, often monolithic, oxide network at temperatures below 500°C. Since the glass formation takes place by low temperature chemical polymerization, the high-temperature reactions such as crystallization, phase separation, etc., which restrict glass formation, can be avoided in the entire SiO2TiO2 binary.

Journal ArticleDOI
TL;DR: A detailed description of the morphology and the complex melting behavior of poly(ethylene terephthalate) crystallized isothermally in the range 100-245°C is presented in this article.
Abstract: A detailed description of the morphology and the complex melting behavior of poly(ethylene terephthalate) crystallized isothermally in the range 100–245°C is presented. Double or single melting endotherms can deliberately be obtained by varying the heating rate in the differential scanning calorimeter (DSC). In the case of double melting peaks, the first endotherm (I) corresponds to the melting of the crystalline material formed at the crystallization temperature Tc. The second melting endotherm (II) originates from the melting of a fraction of the original crystalline material reorganized during the DSC scan. The appearance of one melting endotherm (I or II) relates to the melting of the original structure or the melting of a completely transformed structure. Taking the end of the melting endotherm I as the final melting temperature TM of the material, an equilibrium melting temperature of 290°C is obtained from a plot of TM vs. Tc. A detailed morphological study of the isothermally crystallized samples by electron microscopy and both small-angle and wide-angle x-ray scattering raises questions about the use of the two-phase concept in relating morphological parameters and melting behavior at low crystallization temperatures.


Journal ArticleDOI
Farid F. Abraham1
TL;DR: In this article, it is demonstrated that one can distinguish between a supercooled liquid that becomes a glass and a super-cooling liquid that nucleates to a defect crystal during a quench using the isothermal-isobaric Monte Carlo method.
Abstract: It is demonstrated that one can easily distinguish between a supercooled liquid that becomes a glass and a supercooled liquid that nucleates to a defect crystal during a quench using the isothermal–isobaric Monte Carlo method.(AIP)

Journal ArticleDOI
01 May 1980-Nature
TL;DR: In this paper, the process of differentiation is demonstrated explicitly: starting with a homogeneous mixture of two solutes in water, crystallization at a vertical boundary produces overall vertical composition gradients, as well as density stratification accompanied by smaller scale layering.
Abstract: Large igneous intrusions characteristically have a systematic gradation in mineral composition from top to bottom, often associated with a horizontally layered structure on several scales1,2. Current theories3 invoke the settling of denser crystals as the mechanism responsible for separating the various components from the solidifying melt. However, recent laboratory experiments4,5, using crystallization from aqueous solutions to model the essential fluid-dynamical processes, have documented another significant way in which chemical differentiation of the liquid can be caused by relative motion between crystals and the remaining melt. The growth of crystals of a denser component on a side-wall boundary leaves behind less dense fluid. (This corresponds to the behaviour of many common magmas, notably those of the calc-alkaline series. However, in tholeiitic basalt magmas, of the type which commonly form layered intrusions, crystallization lends to an increase in density of the remaining melt.) The lighter fluid rises to the top of the chamber in a boundary layer flow, which builds up a stable density gradient, by the ‘filling box’ mechanism6,7 previously discussed in other contexts. In the latest experiments reported here, the process of differentiation is demonstrated explicitly: starting with a homogeneous mixture of two solutes in water, crystallization at a vertical boundary produces overall vertical composition gradients, as well as density stratification accompanied by smaller scale layering.

Journal Article
TL;DR: In this paper, the authors studied the crystallization phenomena of glasses of fused natural basalt rocks by DTA, X-ray phase analysis, electron microscopy, and other techniques.
Abstract: Crystallization phenomena of glasses of fused natural basalt rocks were studied by DTA, X-ray phase analysis, electron microscopy, and other techniques. Crystallization was catalyzed by the addition of either chromite ore or P₂O 5 , both up to 5 wt %. Various heat treatments were used, and their influences on controlling the microstructures and properties of the products were studied to develop high strength glass-ceramic material of the CaO-Al₂O₃(Fe₂O₃)-MgO(FeO)-SiO₂ system from the domestic basalts. Magnetite precipitates were found to be a nucleation initiator in every case of the crystallization. Diopside, anorthite, clinoenstatite and monticellite were identified as silicate crystalline phases contained in the crystallized products. The crystallite size was in the range of 0.1-2.5㎛. The fine crystallites were approximately cubic, but large crystallites were either plate or needle shape. The thermal expansion coefficient, microhardness and modulus of rupture of glass-ceramics were ranged from 78.5 to 81.8×10 -7 ㎝/㎝/℃, from 820 to 930㎏/㎟, and from 1800 to 2800㎏/㎠, respectively.

Journal ArticleDOI
TL;DR: In this paper, a non-isothermal differential scanning calorimetry (DSC) was used to determine the activation energy for amorphous arsenic crystallization over a selected range of temperatures.
Abstract: Careful analysis of the Avrami equation [ x = 1 −exp(− At n )] shows that an activation energy for crystallization ( E c ) for amorphous materials can be defined over a selected range of temperatures. This activation energy can be determined experimentally using non-isothermal differential scanning calorimetry (DSC) by determining the crystallization temperature ( T c ) as a function of heating rate (φ). A plot of (ln( φ / T c ) has a slope equal to E c / n . The activation energy for the crystallization of amorphous arsenic obtained by this non-isothermal method is found to be in fair agreement with that obtained from an isothermal DSC experiment.

Journal Article
TL;DR: In this article, single-step and multistep undercooling experiments using both Fe,Mg-free and Fe,mgbearing model granitic compositions were conducted to investigate the influence of mafic components on the crystallization of granitic melts.
Abstract: Single-step and multistep undercooling experiments using both Fe,Mg-free and Fe,Mgbearing model granitic compositions were conducted to investigate the influence of mafic components on the crystallization of granitic melts. Crystallization of granite and granodiorite compositions in the system NaAlSi3O6-KAlSirOr-CaAlzSi2Os-SiOr-H2O produces assemblages containing one or more of the following phases: plagioclase, alkali feldspar, qloartz, silicate liquid, and vapor. The observed phase assemblages are generally in good agreement with equilibrium data reported in the literature on the same bulk compositions. With the addition of Fe and Mg to these bulk compositions six new phases participate in the equilibria (orthopyroxene, clinopyroxene, biotite, hornblende, epidote, and magnetite). However, crystalline assemblages produced in phase equilibrium and crystal grofih experiments brought to the same fnal P-Z-X6,. conditions are in general not equivalent. In crystal-growth experiments, nucleation of the feldspars and quartz is greatly inhibited in the presence of Fe and Mg. Indeed, plagioclase is the only tectosilicate to nucleate in the granodiorite composition. Mafic phases nucleate and grow outside of their thermal stability fields as defined by the equilibrium phase diagrams. This contrast in mineral assemblages between the equilibrium and crystal growth experiments is in marked contrast to the results obtained for Fe- and Mg-free compositions. Perhaps the addition of Fe and Mg has caused a breakdown of the Si-O framework in the melt, thereby promoting the more rapid nucleation of the inoand phyllosilicates rather than the framework silicates. Border zones of granitic plutons, com-only rich in mafic minerals, may result from the more rapid nucleation of mafic phases from the silicate liquid. These zones are thought to develop by early crystallization along the walls of the pluton. Our results suggest the mafic phases should nucleate more quickly than the feldspars and quartz and thus should enrich the early crystallization products in ferromagnesian minerals.

Journal ArticleDOI
TL;DR: In this article, the surface and bulk crystallization of Li2O · 2 SiO2 glass has been studied by differential thermal analysis and the influence of the specific surface area of the sample and the nucleation heat treatment on the crystallization kinetics is pointed out.

Journal ArticleDOI
TL;DR: In this article, a SiO2 cap, either intentionally deposited or produced by laser crystallization in the presence of oxygen, was found to be necessary for Si graphoepitaxy.
Abstract: Silicon graphoepitaxy has been achieved using a strip‐heater oven and a sample configuration consisting of a relief grating in a SiO2 substrate, a deposited amorphous silicon film, and a deposited SiO2 overlayer or ’’cap.’’ The resulting films are free of cracks and superior in crystallographic orientation and surface smoothness to graphoepitaxial films produced by laser crystallization. Enhancement‐mode, n‐channel, insulated polysilicon gate field‐effect transistors were fabricated and gave surface mobilities of 400 cm2/V sec at a p doping of 1016 cm−3. A SiO2 cap, either intentionally deposited or produced by laser crystallization in the presence of oxygen, was found to be necessary for Si graphoepitaxy. We attribute this effect to shear stresses produced by the SiO2 cap during crystallization.

Journal ArticleDOI
TL;DR: In this paper, the isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated and it is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction.
Abstract: The isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated. It is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction. The effects are discussed in terms of the diffusion of heterogeneities in the bulk due to interaction and the adsorption on the fibers.

Journal ArticleDOI
TL;DR: In this article, the doping efficiency of the resulting Si:H films has been remarkably improved, achieving room temperature conductivity as high as 27 Ω−1 cm−1 at a doping ratio of NPH3/NSiH4=5.6×10−3 for a specimen deposited at 30 C. Optical emission spectroscopy during the plasma deposition has revealed that a weak emission intensity of the SiH band with respect to hydrogen lines and the absence of emission from the doubly excited states of hydrogen molecules are necessary conditions for the crystallization of doped Si
Abstract: Crystallization of phosphorus‐doped a‐Si:H has been initiated at a substrate temperature below 200 °C, under the deposition conditions of a low flow rate of silane and in the presence of an external magnetic field. Along with the crystallization, the doping efficiency of the resulting Si:H films has been remarkably improved. Room‐temperature conductivity as high as 27 Ω−1 cm−1 has been achieved at a doping ratio of NPH3/NSiH4=5.6×10−3 for a specimen deposited at 30 C. Optical emission spectroscopy during the plasma deposition has revealed that a weak emission intensity of the SiH band with respect to hydrogen lines and the absence of emission from the doubly excited states of hydrogen molecules are necessary conditions for the crystallization of doped Si:H films.

Journal ArticleDOI
TL;DR: In this paper, a direct measurement of solid phase epitaxial crystallization during cw laser annealing of ion-implanted silicon is reported, which utilizes optical interference effects between reflected light from the sample surface and from the growth plane to time-resolve the growth process with high spatial resolution.
Abstract: Direct measurement of solid phase epitaxial crystallization during cw laser annealing of ion‐implanted silicon is reported. The measurement technique utilizes optical interference effects between reflected light from the sample surface and from the epitaxial growth plane to time‐resolve the growth process with high spatial resolution. Laser‐induced solid phase epitaxial growth was monitored for two values of incident laser power; corresponding epitaxial growth rates and calculated surface temperatures are given.

Journal ArticleDOI
01 Oct 1980-Geoderma
TL;DR: In this paper, the effects of increasing amounts of fulvic acid (FA) on the crystallization of aluminum hydroxides from AlCl3, solution, neutralized to different degrees, were investigated.

Journal ArticleDOI
TL;DR: In this article, the formation of CaO-SiO2 glasses, which could not have been prepared with the conventional glass-melting technique because of the presence of the stable liquid-liquid immiscibility zone, was investigated by the gel method.
Abstract: The formation of CaO-SiO2 glasses, which could not have been prepared with the conventional glass-melting technique because of the presence of the stable liquid-liquid immiscibility zone, was investigated by the gel method. The monolithic transparent glasses of CaO·9SiO2 and CaO·4SiO2 composition were obtained by slowly heating to 800° C the transparent gels formed by hydrolysis with atmospheric moisture. In this binary system, the promotion of hydrolysis by the addition of water was not so favourable, because it caused the precipitation of the hydrolysed product, i.e. Ca(OH)2, and therefore the gels obtained were translucent or opaque. The values of true density and refractive index measured for the transparent glasses were comparable with those calculated from the corresponding compositions. Crystallization occured during heat-treatment above 800° C and wollastonite was precipitated.

Journal ArticleDOI
TL;DR: Vibrational spectroscopy provides direct information about the structural arrangement of glass networks such as degree of polymerization of network-forming polyhedra and structural arrangements of silicategermanate, silicate-borate, and related ternary glasses as mentioned in this paper.
Abstract: Vibrational spectroscopy provides direct information about the structural arrangement of glass networks such as degree of polymerization of network-forming polyhedra and structural arrangements of silicate-germanate, silicate-borate, and related ternary glasses. The Raman spectrum provides a probe for the onset of crystallization in some glasses and for the identification of metastable phases that crystallize from glasses.

Patent
16 Apr 1980
TL;DR: In this paper, a crystallization process is described for separating a crystallizable material and an excluded material which is at least partially excluded from the solid phase obtained upon freezing a liquid mixture of the materials.
Abstract: A crystallization process is disclosed for separating a crystallizable material and an excluded material which is at least partially excluded from the solid phase obtained upon freezing a liquid mixture of the materials. The solid phase is formed and melted at spaced locations in a liquid mixture of the materials and, within the liquid mixture, internal solid and liquid flows are maintained in opposite directions to effect separation of the materials. The solid phase is formed by evaporative cooling of the liquid mixture and melted by direct contact with a condensing vapor phase of the materials, each of these operations being performed substantially at the prevailing triple point locus conditions in the respective locations in the liquid mixture.