Showing papers on "Nucleation published in 1979"
TL;DR: In this paper, a theory for the plastic deformation of metallic glasses below their glass transition temperature is presented based on two modes of thermally activated shear transformations initiated around free volume regions under an applied shear stress.
2,336 citations
TL;DR: A review of the literature concerning cavity nucleation as a result of plastic deformation indicates that at low temperatures there is a critical plastic strain required to nucleate a cavity.
874 citations
TL;DR: A discriminant analysis of the data, which took into account both the CSI and the nucleation time for each sample, allowed a sharp distinction between bile samples of cholesterol gallstone patients and controls.
494 citations
TL;DR: In this article, microstructural development during aging of supersaturated solid solutions of cubic ZrO, stabilized with MgO, was studied, principally using transmission electron microscopy, and the starting materials were commercial Mg-PSZ, solution-annealed at 1850°C for 4 h.
Abstract: Microstructural development during aging of supersaturated solid solutions of cubic ZrO, stabilized with MgO was studied, principally using transmission electron microscopy. The starting materials were commercial Mg-PSZ, solution-annealed at 1850°C for 4 h. Optimum mechanical properties are obtained at aging temperatures of 1400° to 1500°C, where homogeneous intragranular precipitates of tetragonal ZrO2 form. The best materials are those in which the precipitation reaction is about two-thirds complete and the precipitates have not lost coherency. Under these conditions, the particles do not transform to monoclinic symmetry when cooled to room temperature, except near propagating cracks, where the stress-induced transformation contributes to the high fracture toughness and strengths observed. Aging at lower temperatures causes eutectoid decomposition, as expected from phase-equilibria considerations. Nucleation of the eutectoid reaction product invariably occurs at grain boundaries.
353 citations
TL;DR: A review of the theoretical and experimental aspects of bubble nucleation and explosive boiling is given in this paper, where only kinetic limits are discussed, and two major applications of concepts are concerned with the hazardous phenomenon known as contact vapor explosives and with volcanoes.
301 citations
TL;DR: In this article, it was shown that amorphous silicon hydrogen films from silane or silane/argon mixtures are formed by nucleation and growth of islands of average lateral dimensions ∼100 A. If these islands do not coalesce into a homogeneous film, subsequent growth produces columnar morphology with low density interstitial regions.
Abstract: Using transmission and scanning electron microscopy, it is shown that plasma deposition of amorphous silicon hydrogen films from silane or silane/argon mixtures proceeds via nucleation and growth of islands of average lateral dimensions ∼100 A. If these islands do not coalesce into a homogeneous film, subsequent growth produces columnar morphology with low‐density interstitial regions. There is a strong correlation between the columnar structure and the presence of nonradiative recombination centers.
257 citations
TL;DR: In this article, a critical examination is made of a recently suggested experimental technique which utilizes the Johnson-Mehl-Avrami transformation rate equation to describe nonisothermal transformations, and it is shown that for transformations involving nucleation and growth the technique has limited applicability.
Abstract: A critical examination is made of a recently suggested experimental technique which utilizes the Johnson-Mehl-Avrami transformation rate equation to describe nonisothermal transformations. It is shown that for transformations involving nucleation and growth the technique has limited applicability.
221 citations
TL;DR: In this article, the growth rate of crystallization and the nucleation rate of amorphous silicon layers produced by evaporation were investigated. But the results of the analysis were limited to a single sample.
Abstract: Crystallization has been studied in amorphous silicon layers produced by evaporation. The crystalline fraction is deduced from conductivity measurements. Depending upon the conditions of evaporation homogeneous or heterogeneous nucleation is observed and the crystallization is induced at the surface or in the bulk. The variations with temperature of the growth rate of crystallization and of the nucleation rate are obtained from the kinetics of the crystallization measured at various temperatures. The results allow one to provide orders of magnitude for the thermodynamical parameters which characterize the crystallization.
180 citations
TL;DR: In this article, the formation of martensite was observed in stainless steel specimens with diameters of less than 0.5 μm, and was associated with dislocation pile-ups on the active slip plane.
177 citations
TL;DR: In this paper, an analysis for the nucleation of microcracks from the inhomogeneous flow lines in soda-lime glass under Vickers indentations is considered, and the minimum loads for crack nucleation are shown to depend on the hardness, H, and critical stress intensity factor, KIC.
Abstract: An analysis for the nucleation of microcracks from the inhomogeneous flow lines in soda-lime glass under Vickers indentations is considered. The minimum loads for crack nucleation are shown to depend on the hardness,H, and the critical stress intensity factor,K
IC. Unlike the Lawn and Evans analysis, the present model does not require the presence of any fortuitous flaws of critical dimensions in the material, since the flaws are nucleated by the deformation in the deformed zone.
171 citations
TL;DR: In this paper, a model for non-isothermic crystallization of Al23Te77 glasses was developed on the basis of the Avrami theory, which is in agreement with isothermic results.
Abstract: The crystallization of Al23Te77 glasses has been studied by DSC techniques. Two peaks occur, showing an earlier excess Te crystallization and a later one of the remaining amorphous matrix. Isothermal determination of the kinetics is only possible for the second process, so a model for non-isothermic crystallization is developed on the basis of the Avrami theory, which is in agreement with isothermic results. The shift of the crystallization peaks with the scan rate allows knowledge of the activation energy for both processes. Those are found to be 1.9 and 2.8 eV respectively. Fitting of the experimental data with this model also indicates a diffusion mechanism for the Te crystallization and a homogeneous nucleation and growth process for the second stage. Re-scanning of the sample after the completion of the first peak shows a second Tg commonly associated with phase separation. Results are discussed in terms of the studies of structure recently reported.
TL;DR: In this paper, the effects of interparticle spacing, particle size, particle strength, and strain on recrystallization kinetics of alloys containing a stable, dispersed second-phase are reviewed.
Abstract: The recrystallization kinetics of alloys containing a stable, dispersed second-phase are reviewed, and the effects of interparticle spacing, particle size, particle strength, and strain are considered. An outline is given of the deformation mechanisms in two-phase alloys, the origin of the misoriented zones associated with large second-phase particles is discussed, and new results are presented. The nucleation of recrystallization at large second-phase particles is discussed in terms of the annealing behaviour of the deformation zones, and the effect of particle spacing is considered. The effect of small second-phase particles on the nucleation of recrystallization is shown to depend upon their effect on the stored energy of cold work, the nature of the nucleation sites and the pinning of boundaries. Grain growth during primary recrystallization is discussed and attention is drawn to the effect of recovery on the driving force.
TL;DR: In this paper, the importance of kinetic factors in determining the nature of growing phases is discussed and the mechanism of the retardation of crystal growth by added crystallization inhibitors is illustrated by the influence of organic phosphonate molecules upon precipitation of calcium carbonate.
TL;DR: The behavior of palm oil during crystallization related well to that of high polymers as discussed by the authors, and the crystallization process was divided into nucleation and crystal-growth phases to facilitate a theoretical treatment similar to high polymer, providing crystals possessing overall structural regularity.
Abstract: Polymorphic behavior of palm oil crystals was studied by DSC isothermal analysis and microscopic observation. Different crystal forms developed specific spherulites depending on the degree of super-cooling from the melt. The A-form crystal was capable of forming a dotted spherulite and the B-form crystal of forming a dendritic spherulite. Experimental results of B form crystallization studied by the DSC and a microscope under kinetic conditions were evaluated using Avarami’s theory, since the behavior of the oil during crystallization related well to that of high polymers. The crystallization process was divided into nucleation and crystal-growth phases to facilitate a theoretical treatment similar to that of high polymers, providing crystals possessing overall structural regularity.
TL;DR: In this paper, the influence of pre-existing grain size on the kinetics of dynamic recrystallization at a specified temperature and strain rate was investigated in two austenitic stainless steels.
Abstract: Dynamic recrystallization in two austenitic stainless steels has been monitored by (i) observations of the high-temperature stress/strain behaviour, and (ii) metallographic measurements on rapidly quenched, partially reacted specimens. Particular effort has been put into assessing the influence of pre-existing grain size on the kinetics of dynamic recrystallization at a specified temperature and strain rate. A theory due to Cahn, which is intended to describe the kinetics of transformations where nucleation is strictly confined to pre-existing grain boundaries, has been applied to the dynamic recrystallization problem. Some measure of agreement with observation is obtained but only on the proviso that proper attention is paid to repeated nucleation at the recrystallization front, and that a distinct variation of active grain boundary area during the reaction is recognized and considered.
TL;DR: In this paper, the effect of the interaction potential on crystal nucleation and the symmetry of the nucleated phase has been studied and the results from both types of calculations are consistent: the rubidium potential leads to a b.c. structure while the other three potentials give an f.c order.
Abstract: Molecular dynamics technique has been used to study the effect of the interaction potential on crystal nucleation and the symmetry of the nucleated phase. Four systems, namely rubidium, Lennard‐Jones, rubidium‐truncated, and Lennard‐Jones‐truncated, have been studied each at reduced density 0.95. Two types of calculations were performed. Firstly, starting from a liquid state, each system was quenched rapidly to a reduced temperature of ∼0.1. The nucleation process for these systems was monitored by studying the time dependence of temperature and the pair correlation function, and the resulting crystalline structure analyzed using among other properties the Voronoi polyhedra. Only in the case of rubidium was a b.c.c. structure nucleated. In the other three cases we obtained a f.c.c. ordering. Secondly, we have studied the effect of changing the interaction potential in a system which has already achieved an ordered state under the action of some other potential. After establishing a b.c.c. structure in a rubidium system, the change in the symmetry of the system was studied when the pair potential was modified to one of the other three forms. The results from both types of calculations are consistent: the rubidium potential leads to a b.c.c. structure while the other three potentials give an f.c.c. structure. Metastable disordered structures were not obtained in any of the calculations. However, the time elapse between the moment when the system is quick‐quenched and the moment when nucleation occurs appears to depend upon the potential of interaction.
TL;DR: The spinodal decomposition (SD) mechanism is based on the Ginzburg-Landau expression for the free energy of an inhomogeneous system as mentioned in this paper, and it has been shown to be effective in the experimental study of SD in alloys, glasses, and binary liquid mixtures.
Abstract: Considerable deviations from equilibrium conditions are observed for nonstatic, first-order phase transitions. In some cases, unstable (labile) phase states may precede the onset of the phase transition. The relaxation of the system is then accompanied by an enhancement of random inhomogeneities and the appearance of a modulated intermediate structure. This mechanism of the initial stage of a phase transition is called spinodal decomposition (SD). Theoretical and experimental studies of SD in two-component systems are reviewed in this paper. Thermodynamic stability and the possibility of SD in one-component liquid-vapor systems and an alternative nucleation mechanism are discussed. The phenomenological theory of SD is based on the Ginzburg-Landau expression for the free energy of an inhomogeneous system. A linearized diffusion equation is derived, for which thermodynamically unstable states have exponentially increasing solutions for the Fourier components of composition. Subsequent refinements of SD theory take into account thermal fluctuations and involve the derivation of the kinetic equation for the distribution functional. Diffraction methods are the most effective in the experimental study of SD in alloys, glasses, and binary liquid mixtures. So far, the agreement between theory and experiment must be regarded as only qualitative.
TL;DR: In this paper, the growth rate of crystallization and the nucleation rate of amorphous germanium layers produced by evaporation were studied. But the results only provided orders of magnitude for the thermodynamical parameters which characterize the crystallization.
Abstract: Crystallization has been studied in amorphous germanium layers produced by evaporation. The crystalline fraction is deduced from conductivity measurements. Depending upon the conditions of evaporation homogeneous or heterogeneous nucleation is observed and the crystallization is induced at the surface or in the bulk. The variations with temperature of the growth rate of crystallization and of the nucleation rate are obtained from the kinetics of the crystallization measured at various temperatures. The results allow to provide orders of magnitude for the thermodynamical parameters which characterize the crystallization.
TL;DR: A detailed study of the crystallography and strain field contrast at chromium needles precipitated in a Cu-0,55 wt.c.% alloy was made in this article, where the orientation relationship between the Cu matrix and Cr needles was found to be Kurdjumov-Sachs, with a 〈651〉Cu growth axis being preferred.
TL;DR: In this article, an isothermal metastable phase transformation diagram was developed for the Na-TPA system and a gismondine-like phase was added to the metastable phases coexisting with ZSM-5 and the crystallization sequence.
TL;DR: In this paper, the moment of nucleation and the explosive growth of the nucleus to engulf the whole system have been monitored by studying the characteristics of Voronoi polyhedra in addition to quantities such as temperature, pressure, pair correlation functions, etc.
Abstract: Molecular dynamics technique is used to study the homogeneous nucleation of an ordered stable phase from a liquidlike state of aggregation. The rubidium potential is used for a 500 particles system with reduced density 0.95. At the start of the calculation the system is quenched rapidly from a reduced temperature of 0.8 to 0.1. The moment of nucleation and the explosive growth of the nucleus to engulf the whole system have been monitored by studying the characteristics of Voronoi polyhedra in addition to quantities such as temperature, pressure, pair correlation functions, etc. After nucleation, the surface of the nucleus is found to advance at a rate of about 130 m/sec; the size of the critical nucleus is estimated to contain 40 to 70 particles. The ordered stable phase is found to have a bcc structure. In spite of the very rapid rate of cooling which was used to start the calculation, a metastable disordered structure was not obtained.
TL;DR: In this paper, two sets of glasses were studied with compositions close to Li2O·2SiO2 and Na2O ·2CaO·3SiO 2, and with water contents ranging from 0.019 to 0.136 wt% and 0.007 to 0.040 wt%, respectively.
Abstract: Two sets of glasses were studied with compositions close to Li2O·2SiO2 and Na2O·2CaO·3SiO2, and with water contents ranging from 0.019 to 0.136 wt% and 0.007 to 0.040 wt%, respectively. The crystal nucleation and growth rates increased markedly with increase in water content, whereas the viscosities of the glasses decreased. For the lithia glasses, increases in nucleation rates at various temperatures closely corresponded to reductions in viscosity, indicating that the main effect of water was to lower the kinetic barrier to nucleation (ΔGD), rather than to alter the thermodynamic barrier to nucleation (W*). For the soda-lime glasses, ΔGD was also lowered by water content but additional effects due to differences in base compositions were observed. The kinetic barriers to growth were lowered by water content for both sets of glasses, increases in growth rates corresponding closely to reductions in the viscosities. It is suggested that the large effects of water on nucleation and growth may be due to an increase in the oxygen ion diffusion coefficient. In the soda-lime glasses addition of sodium fluoride produced similar effects to the addition of water. Liquidus temperature measurements, and the results of DTA, optical microscopy and electron microscopy are also reported.
TL;DR: In this article, the authors show that the delay in nucleation of olivine in basaltic melts increases systematically with decreasing degree of supercooling, cooling rate, superheat, olivines content of the melt and with increasing melt viscosity.
Abstract: The delay in nucleation of olivine in basaltic melts increases systematically with decreasing degree of supercooling, cooling rate, superheat, olivine content of the melt and with increasing melt viscosity. These findings imply homogeneous nucleation of olivine in melts run in the Pt-wire loop sample container used. Unlike plagioclase nucleation, the appearance of the first olivine crystal in a melt is predictable (to within 0.1–1 h of the event). The ‘metastable region’ (i.e., the minimum degree of supercooling necessary for nucleation) is less than 13 ° C. The cause of the delay in nucleation is discussed in terms of the finite growth rate of embryos and the progressive polymerization of the melt with decreasing temperature and increasing time. At degrees of superheat <18 ° the melts are inferred to be more highly disordered than expected. Some implications of the results for petrology and experimental petrology are discussed, including the possibility that continuous zoning may develop under isothermal conditions due to the sluggish attainment of equilibrium of melt structure following a sudden change in temperature.
TL;DR: A survey of recent studies of homogeneous and heterogeneous nucleation and condensation processes and associated flows can be found in this article, where the phenomenological (classical) theory of the quasi-steady droplet-formation model with appropriate correction factors can be made to fit homogeneous nucleations and condensing processes in cloud-chamber, supersonic-nozzle and shock tube flows.
TL;DR: In this article, the saturation vapor pressure over a flat surface of pure (99%) sulfuric acid has been determined to be 2.5 × 10-5 torr at 23°C.
TL;DR: In this paper, a study by transmission electron microscopy and diffraction is presented in which the various phase transitions in this complex system are analysed and it is shown that the transition at high temperatures from the disordered A3 to the ordered B19 structure proceeds by a heterogeneous nucleation and growth process whereas the transition from the B19 to the metastable L10 phase occurs by way of a shear transformation whereby B19 ordering in the close packed planes seems to be conserved and also polytypes are formed as intermediate phases.
TL;DR: In this article, the tetrahedral carbon phases (diamond, lonsdaleite etc.) were crystallized under reduced pressure (10 -3 / Pa) using a coaxial plasma generator.