Experimental study of convection in a mushy layer during directional solidification

1995 ◽  
Vol 293 ◽  
pp. 81-98 ◽  
Author(s):  
C. F. Chen
Keyword(s):  
Directional Solidification ◽  
Solid Fraction ◽  
Convective Motion ◽  
Mushy Layer ◽  
Liquid Region ◽  
Dye Tracing ◽  
X Ray ◽  
Local Permeability ◽  
Before And After ◽  
Theoretical Predictions

Results of experiments using a number of techniques to study the nature of convection in a mushy layer generated by directional solidification of aqueous ammonium chloride solutions are reported. The techniques include flow visualization using a dye tracing method to study convection within the mushy layer before and after the onset of plume convection, and X-ray tomography to measure the solid fraction of a growing mush. The principal results are as follows. (i) Prior to the onset of chimneys, there is no convective motion in the mush, in spite of the vigorous finger convection at the mush-liquid interface. (ii) When the plume convection is fully developed, the flow of fluid in the mush consists of a nearly uniform downward motion toward the bottom of the tank, horizontal motion along the bottom toward the chimneys, then upward plume motion through the chimneys in the liquid region above the mush. (iii) The solid fraction of a growing mush as determined by X-ray tomography shows a significant decrease toward the bottom of the tank after the chimneys are fully developed. As a result, the concomitant increase in the local permeability can be as much as 50%. Some of the results reported herein confirm theoretical predictions of Worster (1992) and Amberg & Homsey (1993). Others reveal phenomena not observed heretofore.

A numerical investigation of steady convection in mushy layers during the directional solidification of binary alloys

1998 ◽  
Vol 356 ◽  
pp. 199-220 ◽  
Author(s):  
T. P. SCHULZE ◽  
M. GRAE WORSTER
Keyword(s):  
Directional Solidification ◽  
Solid Fraction ◽  
Stokes Equations ◽  
Numerical Study ◽  
Vertical Channel ◽  
Navier Stokes ◽  
Mushy Layer ◽  
Navier Stokes Equations ◽  
Strongly Nonlinear ◽  
Steady Convection

We present a numerical study of steady convection in a two-dimensional mushy layer during the directional solidification of a binary mixture. The calculations reveal the internal structure of strongly nonlinear states featuring upflow which has been focused into solid-free regions known as chimneys. The mushy layer is modelled as a porous medium whose permeability is a function of the local solid fraction. The mushy layer is coupled to a chimney that is modelled as a narrow vertical channel where lubrication scalings are used to simplify the Navier–Stokes equations. We use these methods to exhibit solutions which give the detailed structure of the temperature, solute, flow and solid-fraction fields within the mushy layer. A key finding of the numerics is that there are two distinct chimney solutions at low Rayleigh numbers, presumably corresponding to stable and unstable portions of a subcritical solution branch. We also explore the relationship between convective solutions with and without chimneys.

Weak convection, liquid inclusions and the formation of chimneys in mushy layers

1999 ◽  
Vol 388 ◽  
pp. 197-215 ◽  
Author(s):  
T. P. SCHULZE ◽  
M. GRAE WORSTER
Keyword(s):  
Solid Fraction ◽  
Stokes Equations ◽  
Numerical Study ◽  
Solidification Rate ◽  
Mushy Region ◽  
Mushy Layer ◽  
Liquid Region ◽  
Interfacial Conditions ◽  
Buoyancy Driven Convection ◽  
Steady Convection

We present a numerical study of steady convection in a two-dimensional mushy layer during solidification of a binary mixture at a constant speed V. The mushy layer is modelled as a reactive porous medium whose permeability is a function of the local solid fraction. The flow in the liquid region above the mushy layer is modelled using the Stokes equations (i.e. the Prandtl number is taken to be infinite). The calculations follow the development of buoyancy-driven convection as the flow amplitude is increased to the level where the solid fraction is driven to zero at some point within the mushy region. We show that this event cannot occur before the local buoyancy-driven volume flux exceeds the solidification rate V. Further increases in the flow amplitude lead to the formation of a region with negative solid fraction, indicating the need to switch from the Darcy approximation to the Stokes flow approximation. These regions ultimately become what are known as chimneys. We exhibit solutions which give the detailed structure of the temperature, solute, flow and solid fraction fields within the mushy layer. A key finding of the numerics is that these fledgling chimneys emerge from the interior of the mushy layer, rather than eating their way down from the top of the layer, as the amplitude of the steady convection is increased. We discuss some qualitative features of the resulting liquid inclusions and, in the light of these, reassess the interfacial conditions between mushy and liquid regions.

Evaluation of Freezing Methods by Low Temperature X-Ray Diffraction

1977 ◽  
Vol 35 ◽  
pp. 330-333
Author(s):  
T. Gulik-Krzywicki ◽  
M.J. Costello
Keyword(s):  
Biological Materials ◽  
Molecular Organization ◽  
X Ray Diffraction ◽  
Glass Capillary ◽  
X Ray ◽  
Rate Dependent ◽  
Before And After ◽  
Freeze Etching ◽  
Diffraction Patterns ◽  
Set Up

Freeze-etching electron microscopy is currently one of the best methods for studying molecular organization of biological materials. Its application, however, is still limited by our imprecise knowledge about the perturbations of the original organization which may occur during quenching and fracturing of the samples and during the replication of fractured surfaces. Although it is well known that the preservation of the molecular organization of biological materials is critically dependent on the rate of freezing of the samples, little information is presently available concerning the nature and the extent of freezing-rate dependent perturbations of the original organizations. In order to obtain this information, we have developed a method based on the comparison of x-ray diffraction patterns of samples before and after freezing, prior to fracturing and replication.Our experimental set-up is shown in Fig. 1. The sample to be quenched is placed on its holder which is then mounted on a small metal holder (O) fixed on a glass capillary (p), whose position is controlled by a micromanipulator.

The Precipitation of Si in AlCuSi Thin Films

1973 ◽  
Vol 31 ◽  
pp. 34-35 ◽  
Author(s):  
R. M. Anderson
Keyword(s):  
Electron Microscopy ◽  
Thin Films ◽  
Heat Treatment ◽  
Solid Solution ◽  
Integrated Circuit ◽  
Copper Film ◽  
Solution Concentration ◽  
X Ray ◽  
Silicon Thin Films ◽  
Before And After

Aluminum-copper-silicon thin films have been considered as an interconnection metallurgy for integrated circuit applications. Various schemes have been proposed to incorporate small percent-ages of silicon into films that typically contain two to five percent copper. We undertook a study of the total effect of silicon on the aluminum copper film as revealed by transmission electron microscopy, scanning electron microscopy, x-ray diffraction and ion microprobe techniques as a function of the various deposition methods.X-ray investigations noted a change in solid solution concentration as a function of Si content before and after heat-treatment. The amount of solid solution in the Al increased with heat-treatment for films with ≥2% silicon and decreased for films <2% silicon.

A New Polyethylene Corrosion Protecting Coating with Ion Selectivity

2011 ◽  
Vol 314-316 ◽  
pp. 273-278
Author(s):  
Yu Hua Dong ◽  
Ke Ren ◽  
Qiong Zhou
Keyword(s):  
Ion Selectivity ◽  
Nano Particles ◽  
Ammonium Bromide ◽  
Linear Low Density Polyethylene ◽  
X Ray Diffraction ◽  
Sulfosalicylic Acid ◽  
X Ray ◽  
Chemically Modified ◽  
Before And After ◽  
Industrial Standards

Linear low density polyethylene (LLDPE) was chemically modified with grafting maleic anhydride (MAH) monomer on its backbone by melting blending. Nano-particles SiO2 was modified by cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) and anionic surfactant sulfosalicylic acid (SSA) and added to PE coating respectively. Measurement of membrane potential showed that the coating containing modified SiO2 nano-particles had characteristic of ion selectivity. The properties of the different coatings were investigated according to relative industrial standards. Experimental results indicated that PE coating with ion selectivity had better performances, such as adhesion strength, cathodic disbonding and anti-corrosion, than those of coating without ion selectivity. Crystal structure of the coatings before and after alkali corrosion was characterized by Fourier transform infrared spectra (FTIR) and X-ray diffraction (XRD). Structure of the coating without ion selectivity was damaged by NaOH alkali solution, causing mechanical properties being decreased. And the structure of the ion selective coatings was not affected.

scholarly journals Hot gaseous atmospheres of rotating galaxies observed with XMM–Newton

2020 ◽  
Vol 499 (4) ◽  
pp. 5163-5174
Author(s):  
A Juráňová ◽  
N Werner ◽  
P E J Nulsen ◽  
M Gaspari ◽  
K Lakhchaura ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Active Galactic Nuclei ◽  
Spiral Galaxy ◽  
Galactic Nuclei ◽  
X Ray ◽  
Hot Gas ◽  
Heating And Cooling ◽  
Theoretical Predictions ◽  
Central Regions ◽  
Gaseous Atmospheres

ABSTRACT X-ray emitting atmospheres of non-rotating early-type galaxies and their connection to central active galactic nuclei have been thoroughly studied over the years. However, in systems with significant angular momentum, processes of heating and cooling are likely to proceed differently. We present an analysis of the hot atmospheres of six lenticulars and a spiral galaxy to study the effects of angular momentum on the hot gas properties. We find an alignment between the hot gas and the stellar distribution, with the ellipticity of the X-ray emission generally lower than that of the optical stellar emission, consistent with theoretical predictions for rotationally supported hot atmospheres. The entropy profiles of NGC 4382 and the massive spiral galaxy NGC 1961 are significantly shallower than the entropy distribution in other galaxies, suggesting the presence of strong heating (via outflows or compressional) in the central regions of these systems. Finally, we investigate the thermal (in)stability of the hot atmospheres via criteria such as the TI- and C-ratio, and discuss the possibility that the discs of cold gas present in these objects have condensed out of the hot atmospheres.

scholarly journals Synthesis of Novel Arginine-Based Flame Retardant and Its Application in Lyocell Fabric

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3588
Author(s):  
Jiayi Chen ◽  
Yansong Liu ◽  
Jiayue Zhang ◽  
Yuanlin Ren ◽  
Xiaohui Liu
Keyword(s):  
Fourier Transform ◽  
Heat Release ◽  
Flame Retardant ◽  
Photoelectron Spectroscopy ◽  
Fourier Transform Infrared ◽  
Ftir Analysis ◽  
Excellent Thermal Stability ◽  
X Ray ◽  
Cone Calorimeter Test ◽  
Before And After

Lyocell fabrics are widely applied in textiles, however, its high flammability increases the risk of fire. Therefore, to resolve the issue, a novel biomass-based flame retardant with phosphorus and nitrogen elements was designed and synthesized by the reaction of arginine with phosphoric acid and urea. It was then grafted onto the lyocell fabric by a dip-dry-cure technique to prepare durable flame-retardant lyocell fabric (FR-lyocell). X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR) analysis demonstrated that the flame retardant was successfully introduced into the lyocell sample. Thermogravimetric (TG) and Raman analyses confirmed that the modified lyocell fabric featured excellent thermal stability and significantly increased char residue. Vertical combustion results indicated that FR-lyocell before and after washing formed a complete and dense char layer. Thermogravimetric Fourier-transform infrared (TG-FTIR) analysis suggested that incombustible substances (such as H2O and CO2) were produced and played a significant fire retarding role in the gas phase. The cone calorimeter test corroborated that the peak of heat release rate (PHRR) and total heat release (THR) declined by 89.4% and 56.4%, respectively. These results indicated that the flame retardancy of the lyocell fabric was observably ameliorated.

scholarly journals Determination of the Height of Hard X-Ray Sources in the Solar Atmosphere by Measurement of Photospheric Albedo Photons

1975 ◽  
Vol 68 ◽  
pp. 239-241
Author(s):  
John C. Brown ◽  
H. F. Van Beek
Keyword(s):  
Solar Atmosphere ◽  
The Other ◽  
X Ray ◽  
Theoretical Predictions ◽  
Source Models ◽  
The One

SummaryThe importance and difficulties of determining the height of hard X-ray sources in the solar atmosphere, in order to distinguish source models, have been discussed by Brown and McClymont (1974) and also in this Symposium (Brown, 1975; Datlowe, 1975). Theoretical predictions of this height, h, range between and 105 km above the photosphere for different models (Brown and McClymont, 1974; McClymont and Brown, 1974). Equally diverse values have been inferred from observations of synchronous chromospheric EUV bursts (Kane and Donnelly, 1971) on the one hand and from apparently behind-the-limb events (e.g. Datlowe, 1975) on the other.

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