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Understanding the origins of the diversity in terrestrial planets is a fundamental goal in Earth and planetary sciences. In the Solar System, Venus has a similar size and bulk composition [...]

The classical homogeneous nucleation rate theory for the solidification of metals has been in use for over 50 years, but it is almost universally used incorrectly. Because of this, solid-liquid surface energies calculated from nucleation rate theory are also incorrect. Herein, the correct usage of the homogeneous nucleation rate equation for the solidification of metals is presented. It is shown that because of the assumption of thermodynamic equilibrium, the homogeneous nucleation rate cannot be accurately calculated but is likely in the range [10.sup.12]-[10.sup.14] [s.sup.-1]. Also, it is shown that the homogeneous nucleation temperature for a pure metal is essentially a material property. Calculations for the solidification of pure Ni are included. PACS No.: 64.60.Q. La theorie du taux de nucleation homogene classique pour la solidification des metaux est en usage depuis 50 ans, mais est universellement utilisee incorrectement. A cause de cela, les energies de surface liquide-solide calculees a partir de cette theorie sont egalement incorrectes. Nous presentons ici l'utilisation correcte de l'equation de taux de nucleation homogene pour la solidification des metaux. Nous montrons qu'a cause de l'hypothese d'equilibre thermodynamique, le taux de nucleation homogene ne peut pas etre calcule exactement, mais est dans le domaine [10.sup.12]-[10.sup.14] [s.sup.-1]. Nous demontrons aussi que la temperature de nucleation homogene pour un metal pur est une propriete essentielle du materiau. Nous incluons des calculs pour la solidification du Ni. [Traduit par la Redaction], 1. Introduction Many aspects of the structure and behaviour of both solid metals and gases, such as crystal structure, diffusion in solids and gases, and kinetic behaviour of gases, are [...]

Although liquids typically flow around intruding objects, a counterintuitive phenomenon occurs in dense suspensions of micrometre-sized particles: they become liquid-like when perturbed lightly, but harden when driven strongly (1-5). Rheological [...]

Phase morphology and evolution during solidification process of polypropylene and poly(ethylene-co-octene) (PP/PEOc) blend in an internal mixer was investigated by means of scanning electron microscopy (SEM) and in-line back small-angle laser scattering (BSALS). The average particle diameter ([d.sub.p]) and the average characteristic length ([L.sub.m]) were calculated by the pattern analysis of SEM micrographs to describe morphological variation with temperature during solidification process under the natural cooling condition. Furthermore, a fractal dimension ([D.sub.f]) based on the probability density of the character length was calculated in this study to describe the distribution of main sizes of the dispersed phase particles. Structure parameters, such as heterogeneity distance (Ic) and integral invariant (Q), were also calculated using BSALS to describe solidification process. The results obtained from BSALS were in agreement with those obtained from SEM, which means BSALS was valid to study the phase morphology and evolution during solidification process of polymer blend. POLYM. ENG. SCI., 51:609-616, 2011. [C]2011 Society of Plastics Engineers, INTRODUCTION Blending of two or more polymers has proved an effective and important alternative method to introduce raw materials with tailor and improved properties. There has been an extraordinary growth [...]

Core melt solidification phenomena in the lower plenum of pressurized reactor vessel during external reactor vessel cooling is investigated in late in-vessel phase experiment tests under different external cooling conditions and melt pouring positions. The melt solidification behavior, which has not yet been given sufficient attention, is an important issue since it influences not only the transient but also the steady state of melt pool thermal hydraulics. A noneutectic melt (80 mol % KN[O.sub.3]-20 mol % NAN[O.sub.3]) was used to simulate the core melt. It has been found out that when the vessel is cooled with water during the whole test period (water cooling), the cooling is more effective than the case that the vessel lower head is first cooled with air and flooded by water (air/water cooling). Water cooling at the beginning leads to faster buildup of crust layer on the vessel inner wall and lower crust thermal conductivity compared with air/water cooling. In comparison with the air/water cooling, the water cooling also achieves shorter time period of crust growth. During the solidification period in all tests, the constitutional supercooling condition is fulfilled. Pouring position near the vessel wall results in considerable asymmetry, in the heat flux distribution through the vessel wall. [DOI: 10.1115/1.400108l] Keywords: core melt, in-vessel, crust, solidification, lower head, heat flux, IVR, PWR, PRV

Problem statement: The solidification of materials depends on the cooling rate of the materials which is governed by heat flow in the mould and alloy composition. Solidification rate also affects the structure and properties of the materials. Approach: In the present study, the heat flow of cold set resin bonded sand mould was simulated using JL Analyzer FEM analysis software. To verify the model, the gray cast iron was melted at 1350[degrees]C temperature and poured into a resin bonded sand mould at 1300[degrees]C. Results: It showed that most of the heat-reserve at the junction of the mould which was nearer to the source of liquid metal and the lowest heat-reserve at the end of the mould. So, the solidification rate was very high at the end of the mould wall whereas it was comparatively low near the sprue of the mould. Conclusion: Finally, depending on the heat-flow through the mould, the solidification rate changed the microstructure from chill, mottled and gray cast iron and hardness changed from 95.1 HRB-78.78 HRB. Key words: Heat transfer, FEM, solidification, hardness, INTRODUCTION Casting is the most important process in manufacturing and sand casting is the most convenient process in foundry. Most of the liquid metal can be poured into the sand [...]

Tin samples subjected to high pressure laser shocks of short duration are studied. It gives clear evidence of melting, provide information on the sizes of the fragments and their velocities and indicate qualitative trends regarding the influence of shock pressure.

Two-dimensional mathematical model of laser cladding with droplet injection was developed to understand the influence of fluid flow on the mixing, dilution depth, and deposition dimension, while incorporation melting, solidification, and evaporation phenomena. The calculation show that melt pool shape and size become smaller when considering the power injection since a large part of energy is absorbed by the power particle, and melt pool shape also depends on the size and velocity of the droplet and the mass flow rate.

A robust on-line detection system for estimating the gate freezing-off time, which is useful for monitoring and control of injection molding, was developed based on an analysis of the correlation changes around the gate freeze-off time, as reflected in the changes of the screw movement and nozzle pressure (NP). Experiments showed that the gate freezing-off time can be accurately detected under different molding conditions. POLYM. ENG. SCI., 45:33-41, 2005. [c] 2004 Society of Plastics Engineers, INTRODUCTION In injection molding, packing-holding commences at the end of filling. Additional polymer is packed into the mold at high pressure to compensate for the material shrinkage associated with solidification. [...]

Lower-level chemistry and physical science courses introducing the field of materials science can integrate the information around previous studies of physical and chemical change and the transition from a liquid state to a solid one. Historical information like that in this article can help students to appreciate more fully the benefits of the modern material culture. Fluidizing of materials and discovery of solidifying processes has opened the way to shape-solidify technology and expanded the types of artifacts that can be made and made possible the material culture that now exists. Topics include solidification by cooling, covering metals, glass and thermoplastics, solidification by removal of water covering clay and wood pulp, and solidification by chemical reactions, covering clay, inorganic cements and thermoset polymers.

Three types of seed/barrier layers with nontexture and (111) texture were used in studying the room-temperature recrystallization of electroplated copper films. Results indicate that the initial texture of the plated films plays a significant role in the self-annealing behavior such as reduction rate of sheet resistance and texture changes during self-annealing. The reduction rate of sheet resistance is also higher on the nontextured seed than in the (111) textured seed.

The stability of a planar solid/liquid interface during resolidification of the molten surface of silicon-tin alloys is analyzed by examining the time evolution of an infinitesimal harmonic perturbation of the planar interface. The temperature distributions in the melt and solid and the concentration profile in the melt are divided into a base state and a state due to the perturbation. One of the conclusions is that destabilization of the solid/liquid interface must happen during the establishment of the solute pileup.

The article examines isothermal viscoelastic behavior of glassy polymers at compression. Experiments to analyze stress-induced densification of polymers are described.

Research was conducted to examine the theory of interaction between a solid inclusion in a liquid with nonuniform viscosity with an advancing solidification front. A model was used in which the weight of the particle, its buoyancy and that of viscous drag were essential. Focus was made on the velocities of the inclusion and of the solidification front move in the same direction. The investigation into the inclusion behavior was carried out in terms of three dimensionless variables.

An analysis on how the chemical reaction during partial melting and solidification is affected by the per-annealing and intermediate rolling (PAIR) process. The thermal analysis found no remarkable difference in the partial melting behavior between PAIR processed and control samples. However, results of the analyses using high temperature X-ray diffraction and scanning electron microscopes suggest that the (CaSr)CuO2 crystals did not grow in the samples processed by the PAIR technique.

A study on dendritic alloy solidification was conducted to investigate the grain structural development and columnar-to-equiaxed transition during directional dendritic solidification using the NH4Cl-H2O model alloy. The experiment is the first phase of a continuing effort to ultimately model and simulate the columnar-to-equiaxed transition in the presence of crystal sedimentation and melt convection using a multiphase model developed by two researchers in a previous study.

The glass forming ability (GFA) of the ternary alloys Pd(sub 83.5-x)Cu(sub x)Si(sub 16.5) apparently correlate with the formation of crystalline-compounds/solid-solutions. This was gleaned from the results of an attempt to correlate the GFA of the alloys with the crystalline phases formed upon their solidification from the molten state. The molten alloys were allowed to crystallize at temperatures close to their liquidus, which allowed the identification of the crystalline phases in the as-crystallized specimens.

A study was conducted on thermal stresses in an inwardly solidifying sphere. A solution was presented which accounts for thermal expansion associated with temperature gradients and volume changes linked with phase transition.The frozen medium was modeled as an elastic-perfectly plastic. Parametric studies using appropriate material properties and cryopreservation protocols indicated that strains associated with phase transition led to higher stresses than those associated with thermal expansion.

A study was conducted to analyze gravitational, thermoelectric and magnetohydrodynamic influences on solidification processes using a physics-based framework. The Bridgman-Stockbarger configuration was determined using directional solidification with Peltier Interface Demarcation under different gravitational environments. Results showed that the buoyancy-induced convection die not significantly affected temperature fields.

The magnetic characteristics of cast permanent magnets, such as samarium-cobalt magnets, produced by solidification in a magnetic field are examined. The different materials, samarium, cobalt, copper, iron and zirconium, were melted in a cold inductive crucible and casting into a copper mold to create precursor alloys. It is shown that the chemical composition used to prepare them might be adapted from those used for sintered Sm2 magnets to optimize their magnetic properties.

In part I of this paper, we presented two efficient front-tracking methods to simulate the growth of a spherulite within an imposed temperature field. In this second part we present a method that predicts the final microstructure in a macroscopic part by coupling these front-tracking techniques with (a) a stochastic model for the nucleation of individual spherulites, (b) a cellular model for spherulite impingement and solid fraction evolution and (c) a Finite Difference Method (FDM) for latent heat release and heat diffusion. The method tracks the physical phenomena on several length scales: a coarse grid for the heat diffusion, a fine grid for solid fraction evolution and a very fine grid for the shape of the individual spherulites and the lamellae within them. To our knowledge this is the first time that a fully coupled multiscale model has been applied to the solidification of polymers which gives realistic microstructure evolution, orientation of the different lamellae within spherulites and maps of the solid fraction and temperature fields during solidification. The model provides us with a quantitative predictive tool that can be used to optimize industrial processes., BACKGROUND The mechanical and chemical properties of polymers (as with most engineering materials) depend very strongly on the microstructure (1, 2). The microstructure, in turn, is determined by the conditions [...]

A study was conducted on hypercooled Co-Pd melt nonequilibrium solidification. The electromagnetic levitation method and time-resolved recalescence detection were employed in growth velocity measurements for Co-Pd alloy metals in an undercooling range over the limit of hypercooling. The experimental results suggest that high undercoolings significantly influence interface kinetics.

A simple model shows that a rocky planet close to its star may solidify so slowly that its water is lost to space and the planet becomes desiccated, whereas a [...]

Solidification of metal castings can be modeled by an implicit real-valued function whose behavior is determined by physical parameters prescribed on the boundary of a casting. We show how to construct such functions using theory of R-functions for two-dimensional castings represented by their boundaries. The parameterized form of the constructed functions is convenient for studying, controlling, and optimizing their behavior in terms of the physical parameters specified on the boundary of the casting. The proposed approach can also be used for modeling multiple cavities in a same sand mold, generalizes to three-dimensional castings, and is applicable to other physical phenomena that may be suitable for analysis based on empirical knowledge.

This paper presents a numerical algorithm for the microprestress-solidification theory developed in a companion paper and verifies this theory by comparisons with typical test data from the literature. A model for cracking is incorporated in the algorithm.

A new physical theory and constitutive model for the effects of long-term aging and drying on concrete creep are proposed. The previously proposed solidification theory, in which the aging is explained and modeled by the volume growth (into the pores of hardened portland cement paste) of a nonaging viscoelastic constituent (cement gel), cannot explain long-term aging because the volume growth of the hydration products is too short-lived. The paper presents an improvement of the solidification theory in which the viscosity of the flow term of the compliance function is a function of a tensile microprestress carried by the bonds and bridges crossing the micropores (gel pores) in the hardened cement gel. The microprestress is generated by the disjoining pressure of the hindered adsorbed water in the micropores and by very large and highly localized volume changes caused by hydration or drying. The long-term creep, deviatoric as well as volumetric, is assumed to originate from viscous shear slips between the opposite walls of the micropores in which the bonds or bridges that cross the micropores (and transmit the microprestress) break and reform. The long-term aging exhibited by the flow term in the creep model is caused by relaxation of the tensile microprestress transverse to the slip plane. The Pickett effect (drying creep) is caused by changes of the microprestress balancing the changes in the disjoining pressure, which in turn are engendered by changes of the relative humidity in the capillary pores. Numerical implementation, application, and comparison with test data is relegated to a companion paper that follows in this issue.

The solidification/stabilization (S/S) process is applicable to soil contaminated by metals and other inorganics. However, this process is not currently viewed by the U.S. Environmental Protection Agency (EPA) as applicable for remediation of soils contaminated solely with volatile organic compounds, because these organic compounds have been shown to have a detrimental effect on the macrostructural properties of ordinary portland cement (OPC) and could be released during the mixing and curing process. The aim of the present study is mainly to investigate the feasibility of using quaternary ammonium-modified clays (organophilic clays) to stabilize organics (phenol, 2-chlorophenol, and 2,4-dichlorophenol) in contaminated soils prior to conventional cement-based solidification. The effectiveness of the S/S process, using organophilic clays, was evaluated, based on experimental findings from batch sorption, leachability of hazardous constituents, unconfined compressive strength, and permeability tests. Results from these experimental tests indicate that the use of organophilic clay as a presolidification adsorbent gives a successful S/S process in the treatment of phenol-contaminated soils.

Solidification characteristics of oil droplets ascending in a cold water solution layer have been studied by the direct-contact cooling method. The frozen oil column is produced at the outlet of the nozzle in the lower temperature condition, whereas normal injection is carried out at the higher temperature condition. A decrease in injection oil temperature T(sub n) under normal injection conditions increases the solidification rate R of the oil droplet. However, under frozen oil column formation condition, R decreases with a decrease in T(sub n).

Solidification studies show that frozen gelatinized 2% corn starch-water mixture is homogeneous at freezing conditions when the solid-liquid interface is more than a minimum critical cell velocity. Freezing at cell velocities less than or equal to 7.5 micrometer/second pushes the starch granules in such a way that they form a segregated band with alternating high- and low-starch bands. The product is homogeneous at a cell velocity of 10 micrometer/second. The relation of the segregation behavior to the solid- liquid interface velocity is quantified and compared to an existing model.

A thermodynamic model is proposed for predicting the aqueous solubility of calcium silicate hydrates (C-S-H) as the major solid-solution component of hydrated cement. The model, which is based on solid solution-aqueous solution theory, considers the role of the C-S-H phase in cementitious waste solidification/stabilization systems. It may be used for predicting solid solution solubility and the distribution of trace components between solid and aqueous phases.

The solidification of a molten layer of amorphous thermoplastic between cooled parallel plates is used to model the mechanics of part warpage in the injection-molding process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The model allows material to be added to fill the space created by the pressure applied during solidification so that this model can be used to assess packing-pressure effects in injection molding. Parametric results are presented on the effects of the mold temperatures and the packing pressure - the pressure applied during solidification to counteract the effects of volumetric shrinkage of the thermoplastic - on the in-plane and through-thickness shrinkages, on warpage, and on residual stresses in plaque-like geometries. The packing pressure is shown to have a significant effect on part warpage. While the results are presented in terms of normalized variables based on the properties of bisphenol-A polycarbonate, they can be interpreted for other amorphous thermoplastics, such as modified polyphenylene oxide, polyetherimide, and acrylonitrile-butadiene-styrene., INTRODUCTION This paper addresses the warpage of plastic parts induced by forming processes, such as injection molding, in which molten resin is injected into a relatively cold mold. As the [...]

Real time microholography is employed in measuring the transient concentration field in the vicinity of a growing dendrite. The growth of the dendrite is monitored by a charge-coupled device camera and a video recording system between the crystallization and solidification stages. Results show that concentration distribution directly next to a group of sharp dendritic tips is smoother than the structure of the interface itself.

Numerical models are used to analyze the infiltration and solidification/remelting of a pure metal in a two-dimensional porous preform. Momentum and energy equations are incorporated in the model to account for the effect of liquid flow and heat transfer phenomenon. Results indicate that the infiltration and solidification processes are governed by several dimensionless variables, such as the melting temperature and the total infiltration time.

Carbonation is seen to have a major influence on the properties of cement-solidified waste forms. It significantly alters CSH gel products which play a large role in the fixation of toxic species. Calcite is also produced from the direct reaction of portlandite with CO2. The formation of calcium carbonate leads to the increase in hydration of C3S, thus achieving higher strength values. A significant reduction in leachable metals extracted is also noted.

The basic creep of concrete is the time-dependent strain caused by a sustained stress in absence of moisture movements. It is the strain observed on sealed specimens. Similar to other properties of concrete, it is dependent on the age of concrete, as a consequence of long-time chemical reactions associated with the hydration of cement. This paper formulates the solidification theory with a continuous retardation spectrum, and shows how this spectrum can be readily and unambiguously identified from arbitrary measured creep curves and how it then can be easily converted to a discrete spectrum for numerical purposes. The identification of the continuous spectrum is based on Tschoegl's work on viscoelasticity of polymers. Attention is limited to basic creep.

Linear and nonlinear perturbation analyses help examine the morphological stability of the solid-liquid interface in dilute binary alloy solidification and incorporate the effects of excess enthalpy in the condition describing the local energy balance at the solid-liquid interface. A direct method of undetermined coefficients helps calculate the Landan coefficient representing the nonlinear growth rate. The excess-energy correlation is significant at large growth velocities and low frequencies of interface perturbation in metallic and nonmetallic systems.

Splat cooling of two liquid metal droplets, impacting sequentially on a substrate, results in higher cooling rate of the bottom droplet compared to top droplet. This is preceded by non-equilibrium crystallization due to significant undercooling at the initiation of solidification. The theoretical findings substantiate the presence of a two-dimensional temperature field in the substrate during solidification at the splat. The reduced cooling rate of the lower droplet leads to coarser grain structure.

A study has investigated the solidification/stabilization (S/S) of waste in portland cement. Solid-state deuterium spectroscopy techniques were used to to assess interaction between waste and cement. Such techniques are non-destructive and non-invasive. The study used phenol as used as a model waste. The study identified a liquid and rigid environment for phenol in cement. The liquid phenol does not bind to the cement matrix. The study therefore reveals that total immobilisation does not occur in the S/S of phenol in portland cement.

Research has investigated the chemical reactions involved in fixation systems in solidification/stabilisation processes. Information is relevant to the safe disposal of industrial waste. Tricalcium aluminate and copper oxide/hydroxide were tested as fixing agents. Energy-dispersive X-ray analysis and X-ray diffractometer technology established interaction of chemicals. Research revealed fixation occurred by chemical interaction and physical entrappment.

The rapid solidifaction of Si-As alloys by pulsed-laser melting at regrowth velocities was investigated using time-resolved measurements and Rutherford backscattering. The results showed that the congruent melting temperature was 1565 +/- 25 K for 4.5 at.% As and 1425 +/- 25 K for 9 at.% As. Fusion enthalpy was not affected by the composition. There was good agreement between experimental results and values derived from heat flow simulations.

The solidification of the undercooled melts of the eutectic Ag-Cu alloy is studied. Experiments are performed wherein the melts ofan Ag-Cu alloy pellet are undercooled at various gas pressure levels by means of the glass slag method. The specimen is solidified by radiation, convection and conduction processes. Temperature measurements reveal that the solidification of the Ag-Cu alloy is governed by two different mechanisms whichare both dependent on the undercooling temperature.

A study was conducted as an extension of studies on the solidification of flowing liquid in a pipe. The current study considers the radiation effect and process window for both radiation and forced convection cases on the pipe's outside. Results show that the development of a first-order logarithmic profile serves as a viable approximation for a cylindrical geometry in the solidified layer.

The thermal contact and latent heat evolution involved in solidification modeling are studied for the identification of important criteria functions. These criteria functions are very important for determining the porosity level of thematerial being modeled. Experimental and computational analyses are carried outon a horizontally cast bar to investigate how its criteria functions are distributed. Results indicate that the treatment of thermal contact and phase change in solidification affects the values of the criteria functions.

The solidification structure of a gas-tungsten arc spot weld is studied through numerical simulations. An algorithm is used to simulate the macrograph of the spot weld. The melting phase involved in the welding process is also investigated with respect to the thermal gradient and solidification rate. Results reveal that the solidification phase is characterized by a flow dominated process of boundary smoothing and superheat reduction.