Solid-liquid Region Research Articles

An ultra‐sulfur Hastelloy alloy C‐4

AbstractThe effect of sulfur on solidification‐segregation and corrosion resistant properties of Hastelloy C‐4 corrosion‐resistant alloy was studied. It was found that strict controlling the content of sulfur can reduce the width and temperature interval of the solid‐liquid biphase region and the segregation degree of the alloy, resulting in a higher corrosion resistance. An improved low segregation Hastelloy C‐4 corrosion resistant alloy was developed.

Evolution of particle morphology in semisolid processing

Experimental results are summarized of the formation of spheroidal grain structures in an Al-4.5 wt pct Cu alloy by (1) isothermally holding very fine equiaxed dendrites in the liquid-solid region and (2) direct spheroidal solidification from the melt. The fine-grained dendritic structure was obtained by very rapid solidification in a thin-section (0.8 mm) permanent-mold plate casting under conditions such that solidification took place during the filling process and, hence, during rapid fluid flow. Grains of approximately 30 µm in diameter (representing a grain density of about 3×104 mm−3) were obtained; these ripened to a spheroidal morphology in the liquid-solid region in less than 5 seconds. A similarly high grain count was then obtained in the bulk melt by vigorous agitation and rapid cooling near the liquidus temperature; the melt was thereafter cooled more slowly. Under these conditions, a spherical morphology formed early in solidification and grew in that form. The evolution of particle size with time in the liquid-solid region is shown to be essentially identical in the initially dendritic and spherical-growth experiments.

Microstructural Evolution of Electromagnetically Stirred Al Alloy during Isothermal Reheating in Solid-Liquid Region

The effects of reheating in solid-liquid region on the microstructure of electromagnetically stirred Al alloy have been investigated. The billet of Al alloy was produced at a various casting speed from 200 to 500 mm/min in a continuous casting machine with an electromagnetic stirring device. The microstructure of the billet, which was isothermally reheated in a solid-liquid region during holding for from 0.5 to 15 min, was examined. The roundness and size of primary α phase of electromagnetic stirred Al alloy was measured according to the reheating time. The roundness of primary α phase was obtained a minimum during holding for from 3 to 7 min at a holding temperature of 584°C and was deteriorated at a longer reheating time due to a dominant coalescence. Also the spheroidization of primary α phase during reheating in solid-liquid region was significantly dependent on initial microstructure of the billet.

Influence of the Electromagnetic Stirring on Globularization of Primary Solid Phase in Solid-Liquid Region

Forming of alloy and composite within a solid-liquid region, i.e. thixo-forming and rheo-forming, has been recognized as a technology offering several potential advantages over casting and forging such as a low forming pressure, reduction of macrosegregation, and reduction of porosity. In this paper, a globularization for primary solid phase by a forced fluid flow in melt due to electromagnetic stirring during solidification and isothermal stirring at solid-liquid region, was examined to produce Al alloy having a globular solid phase to get a thixotropic behavior. The electromagnetic stirrer was specially designed and manufactured to create all kind of fluid flow pattern such as a circumferential, vertical, helicoidally and contra-rotating flow pattern during the solidification of a melt. The size and roundness of primary solid phase of the quenched sample after isothermal stirring at solid-liquid region were measured with respect to a stirring time and frequency. The globularization of solid phase was enhanced with incresing the stirring time and electromagnetic flux density, i.e. stirring strength.

Computational Model of the Freezing of Jet Fuel

A computational fluid dynamics model is developed that simulates the solidification of jet fuel due to freezing in a buoyancy-driven flow. Flow resistance caused by porous crystal structures that exist in liquid-solid regions is simulated through the use of a momentum resistance source term. Experiments are performed in which jet fuel samples are cooled below their pour point temperatures in an optical cell. Polarized light is used to record images during the freezing process. In addition, low-temperature properties of jet fuel samples are determined, using a differential scanning calorimeter, pycnometer, and a low-temperature viscometer. The validity of the simulations is demonstrated by comparing temperature and solid area measurements with predicted values for various thermal boundary conditions and fuel samples. Reasonable agreement between experiments and simulations is obtained. Thus, the modeling technique is useful for aircraft fuel system designers in the prediction of fuel tank hold-up.

Cationic surfactant-based polyfluorate salts: Phase separation and analytical applications in the extraction and preconcentration of ionic species prior to liquid chromatography

The liquid–solid phase separation originating from the formation of cationic surfactant-based polyfluorate salts (CSBPS) has been explored for extracting and preconcentrating ionic species. Two cationic surfactants were tested; one with aliphatic hydrocarbon tail [Cetyltrimethylammonium bromide (CTAB)]and the other containing a heterocyclic ring [Hexadecylpyridinium bromide (HPyBr)]. Phase separation possibility was investigated with the use of hexafluorophosphates (PF 6 −) and tetrafluoroborates (BF 4 −). The effect of added acid, base and salt on the phase separation and analyte extraction was also investigated. In all cases the obtained phase diagrams consisted of two regions: a homogeneous liquid region and a solid–liquid region. Analytes of hydrophilic and hydrophobic nature such as amines, amino acids and organic chromophores were used as test compounds in both their anionic and cationic forms. The respective recoveries ranged from over 90% for anionic species and in the proximity of 50% for cationic species, remaining below 20% for neutral species. Extracts from alkaline aqueous and plasma samples spiked with tyrosine and phenylalanine were also subjected to HPLC separation with UV detection with satisfactory results. On line application was also enabled using a flow through-solid phase extraction-HPLC hyphenated apparatus, thus adding the element of automatization and increased reproducibility.

High Temperature Phase Relations in FeO<I><SUB>X</SUB></I>(<I>X</I>=1 and 1.33)–CaO–SiO<SUB>2</SUB> Systems under Various Oxygen Partial Pressure

As a fundamental study of slags in metallurgical processes, liquidus lines in the FeO(wustite)-CaO-SiO 2 and Fe 3 O 4 (spinel)-CaO-SiO 2 systems were determined at temperatures between 1573 and 1673 K and partial pressures of oxygen between 10 - 4 and 36Pa using a quenching method with a crucible of platinum foil. It was found that the two phases (solid wustite and liquid) region in the FeO-CaO-SiO 2 system (1573 K) increased remarkably by changing the partial pressure of oxygen from 10 - 4 to 10 - 3 Pa. It was also found that the two phases (solid spinel and liquid) region in the Fe 3 O 4 -CaO-SiO 2 system (1573 K) at PO 2 of 10 - 2 Pa was a little larger than that in the FeO-CaO-SiO 2 system at PO 2 of 10 - 3 Pa but it was extended considerably when the oxygen pressure was increased to 10 - 1 Pa. However, the two liquids region did no change too much in the range of oxygen pressure above 10 - 1 Pa even though the liquidus line became almost parallel to the Fe 3 O 4 -CaO axis in the ternary diagram when the oxygen pressure was increased. Furthermore, it was found that the two phase region in the Fe 3 O 4 -CaO-SiO 2 system at PO 2 of 10 - 1 Pa decreased remarkably with increasing temperature. On the basis of the obtained and reported data, the homogeneous liquid regions in the FeO x -CaO-Si0 2 systems (1573K) at PO 2 of 10 - 3 Pa, 10 - 1 Pa and in air were compared.

E222 自然物質を利用した水溶液スラリーの研究(OS-9 単相混相機能性流体の流動と熱伝達II)

In recent years, slurries of ice have been commonly used as environmentally-friendly secondary refrigerants because they provide solutions to such issues as establishment of uniformity in electrical loads, effective use of unavailable energy for use and savings in energy. In addition to ice-slurries, ice-water mixtures in slurry-state have also been put to practical use at temperatures below 0℃. A binary mixture such as a water-solution has a solid-liquid coexistent region where a solid phase coexists with the liquid phase. This solid-liquid phase can be used as a high-performance secondary refrigerant if it is possible to form a two-phase flow involving the two phases. Another possibility is that it can also be used as a natural secondary refrigerant because the constituents of the refrigerant are substances existent in the nature.

Iron-carbide cluster thermal dynamics for catalyzed carbon nanotube growth

Molecular dynamics simulations have been used to study the thermal behavior of FeN−mCm clusters where N, the total number of atoms, extends up to 2400. Comparison of the computed results with experimental data shows that the simulations yield the correct trends for the liquid–solid region of the iron-carbide phase diagram as well as the correct dependence of cluster melting point as a function of cluster size. The calculation indicates that, when carbon nanotubes (CNTs) are grown on large (>3–4 nm) catalyst particles at low temperatures (<1200 K), the catalyst particles are not completely molten. It is argued that the mechanism of CNT growth under these conditions may be governed by the surface melting of the cluster.

Lattice dynamics and the high-pressure equation of state of Au

Elastic constants and zone-boundary phonon frequencies of gold are calculated by total energy electronic structure methods to twofold compression. A generalized force constant model is used to interpolate throughout the Brillouin zone and evaluate moments of the phonon distribution. The moments are used to calculate the volume dependence of the Gruneisen parameter in the fcc solid. Using these results with ultrasonic and shock data, we formulate the complete free energy for solid Au. This free energy is given as a set of closed form expressions, which are valid to compressions of at least V/V_0 = 0.65 and temperatures up to melting. Beyond this density, the Hugoniot enters the solid-liquid mixed phase region. Effects of shock melting on the Hugoniot are discussed within an approximate model. We compare with proposed standards for the equation of state to pressures of ~200 GPa. Our result for the room temperature isotherm is in very good agreement with an earlier standard of Heinz and Jeanloz.

Multilayer adsorption and wetting of acetone on graphite.

Adsorption/desorption isotherms of acetone on highly oriented pyrolytic graphite have been measured by ellipsometry for temperatures above the bulk triple point. The behavior in the monolayer and submonolayer regime is conventional, with 2D gas-liquid and 2D liquid-solid coexistence regions. Further liquid monolayers grow on top of the completed monolayer. The growth is basically layer-by-layer. For temperatures between 190 K and the triple point a prewetting-type transition occurs with a thin-thick jump of the layer thickness on adsorption but a layer-wise removal of the film on desorption. In this temperature regime the first monolayer is solid and its molecules are oriented perpendicular to the substrate whereas the higher layers are orientationally disordered polar liquid.

Non-thermal equilibrium melting of granular packed bed in horizontal forced convection. Part II: numerical simulation

A mathematic model based on the theory of interacting continua is developed to describe the complex liquid–solid two-phase flow with phase-change particles as encountered in non-thermal equilibrium melting of granular packed bed subject to horizontal, forced convection. The model is solved numerically using the SIMPLE method, in which the pressure correction based on two-phase mixture continuity equation is implemented. Conservation equations are solved in the entire computational domain including both the liquid–solid region and liquid-only region. It is ensured that the global mass, momentum, and energy of two phases are conserved. The local volume-averaged solid velocity and solid volume fractions are predicted as variables so that the moving and repacking of solid particles can be simulated. This is a step forward from the results published in the open literature where the assumptions of zero-relative motion of solid particles and constant porosity or the constant volume are often used. In addition, the model provides the detailed information about the motion of two phases and phase-change characteristics. Within the uncertainty, the simulation results agree reasonably with the available experimental data presented in Part I of this study [1].

過共晶Ａｌ‐Ｓｉ合金の初晶Ｓｉの恒温晶出形態

In hyper-eutectic Al–Si alloys fabricated by 4–N aluminum and 5–N silicon, the morphology of primary silicon crystals at constant temperature of the solid-liquid co-existent temperature region was investigated. Supersaturated, non crystallization of silicon, alloy made by rapid solidification process were re-melted at the solid-liquid co-existent temperature region. The primary silicon was crystallized to the blocky shape. In the case of quenching by the solid-liquid temperature region after the melting, the primary silicon crystals grew to the petal shape. These crystallizations grew with same shape during isothermal holding at the solid-liquid co-existent temperature region. The primary silicon grew that the ration of length/width was reduced slightly, in the case of continuous cooling.

Magic number behavior for heat capacities of medium-sized classical Lennard-Jones clusters

Monte Carlo methods were used to calculate heat capacities as functions of temperature for classical atomic clusters of aggregate sizes 25⩽N⩽60 that were bound by pairwise Lennard-Jones potentials. The parallel tempering method was used to overcome convergence difficulties due to quasiergodicity in the solid-liquid phase-change regions. All of the clusters studied had pronounced peaks in their heat capacity curves, most of which corresponded to their solid-liquid phase-change regions. The heat capacity peak height and location exhibited two general trends as functions of cluster size: for N=25 to 36, the peak temperature slowly increased, while the peak height slowly decreased, disappearing by N=37; for N=30, a very small secondary peak at very low temperature emerged and quickly increased in size and temperature as N increased, becoming the dominant peak by N=36. Superimposed on these general trends were smaller fluctuations in the peak heights that corresponded to “magic number” behavior, with local maxima found at N=36, 39, 43, 46, and 49, and the largest peak found at N=55. These magic numbers were a subset of the magic numbers found for other cluster properties, and can be largely understood in terms of the clusters’ underlying geometries. Further insights into the melting behavior of these clusters were obtained from quench studies and by examining rms bond length fluctuations.

Metastable phase formation during solidification of undercooled melt

Undercooling behaviour of micron-sized droplets entrained in the matrix of the primary phase of Ag–Ge, Al–Ge and Cu–Ag alloys was investigated. Thermal cycle consisted of equilibration of hypoeutectic alloys above the eutectic temperature in two phase liquid–solid region followed by their slow cooling or quenching from the mushy state. Repeated thermal cycling generated a wide size range of droplets. During slow cooling droplets exhibited a large undercooling below the eutectic temperature of alloys. Solidification structure of the undercooled droplets revealed presence of metastable phases in Ag–Ge and Al–Ge alloys and a non-equilibrium solid solution phase in Cu–Ag alloy. Solidification behaviour of undercooled melt and formation of metastable microstructure are discussed.

Critical phenomena of water bridges in nanoasperity contacts

This article discusses capillary forces measured by scanning force microscopy (SFM), which, as recently reported, show a discontinuous behavior at a low relative humidity between 20% and 40% depending on the solid surfaces. A capillary force discontinuity is very interesting in terms of a possible phase change or restructuring transition of bulk water in the interfacial solid–liquid region. Unfortunately, we have found that SFM measurements show an inherent weakness in the determination of the origin of the forces that are obtained during pull-off measurements. This article critically discusses the origin of the adhesive interactions as a function of relative humidity with chemically modified probing surfaces. Our measurements indicate that force discontinuities in pull-off measurements are strongly affected by the inability of the liquid to form capillary necks below a critical threshold in relative humidity. In the course of this article, we will discuss roughness effects on capillary forces and provide a modified capillary force equation for asperity nanocontacts.

Role of substrate corrugation in helium monolayer solidification

We investigate the first layer of helium adsorbed on graphite with path-integral Monte Carlo, examining the role of substrate corrugations on the phase diagram. When no corrugations are present, the equilibrium state of the system is a liquid phase, with solidification occurring only under compression but before layer promotion. We determine the solid-liquid coexistence region and compare our results to recent Green's function Monte Carlo calculations on the same system. When substrate corrugations are included, we find that the equilibrium phase is the $\sqrt 3 \times \sqrt3$ commensurate solid phase that is well known from experiment. The melting behavior, heat capacity, and single particle binding energy are determined and compared to experiment. We further find that for densities below the commensurate coverage, the low temperature phase of the system consists of solid clusters in coexistence with coalesced vacancies. We find no first layer liquid phase and so no superfluidity in this layer, in contrast to some rather recent suggestions.

Effects Of Liquid Distribution On Flame Spread Over Porous Solid Soaked With Combustible Liquid

Effects of phase change on the flame spread over the porous solid soaked with a combustible liquid has been analyzed for the case when the main mode of heat transfer is conduction. In the model, the fuel-soaked layer is assumed to be divided into three regions: liquid-solid region; three-phase region; vapor-solid region. It is shown that the flame spread rate increases with the thickness of three-phase region. The thickness of the three-phase region increases with the decrease of the diameter of solid particles because of the capillary effects. These results imply that the flame spread rate decreases with the increase of the diameter of solid particles. Thus, the decreasing tendency of the flame spread rate can be explained. The flame behavior as well as the temperature distributions predicted in the present study fairly well coincide with the experimental results, and the model developed here is shown to be valid.

Refining Behaviors in the Fractional Melting Process.

Fractional melting process involves heating an alloy within its liquid–solid region simultaneously ejecting liquid from solid–liquid mixture. The extent of purification obtained is comparable to that obtained in multi-pass zone refining. The fractional melting process in which centrifugal force was used for separating liquid from mixture has been developed. The refining behaviors of present F.M. process were analyzed quantitatively using new parameter called the refining partition coefficient, k' . The effects of process parameters such as a rotating speed and a heating rate on coefficient, k' and refining behaviors were also studied.

Structural and Energetic Behavior of Mixed Samples in the Hexacosane (n-C26H54)/Octacosane (n-C28H58) System; Solid-Solid and Solid-Liquid Equilibria

The combination of the experimental (microcalorimetric and X-ray diffraction) methods and thermodynamic analyses enabled us to determine the phase diagram of the system hexacosane (n-C26H54)/octacosane (n-C28H58). Isothermal X-ray measurements performed on mixed samples at `low temperature' (T 308 K) revealed three crystalline forms: two monoclinic (M011 and Mdci) and one orthorhombic (Op). Four of the five rotator phases were observed at `high temperature': RI, RII, RIV, and RV. Fourteen solid-solid and two solid-liquid two-phase regions were observed, as well as one peritectic, one eutectoid, one metatectoid, and five peritectoid three-phase equilibria. The thermodynamic calculations of the phase-equilibrium relations, carried out with the polynomial functions described in a previous paper and new ones given here, showed full consistency with the experimental data, evidencing the reliability of these polynomial functions.