Oscillatory Morphological Instabilities During Rapid Solidification A The Role of Diffusion In The Solid

1985 ◽  
Vol 51 ◽  
Author(s):  
Atul Bansal ◽  
Arijit Bose
Keyword(s):  
Diffusion Coefficient ◽  
Crystal Growth ◽  
Solid Phase ◽  
Constitutional Supercooling ◽  
System Stability ◽  
Segregation Coefficient ◽  
Critical Wavelength ◽  
Equilibrium Segregation ◽  
Diffusivity Ratio

ABSTRACTRecent results by Coriell and Sekerka [J. Crystal Growth, 61, 499(1983)] on the oscillatory instability of a planar rapidly solidifying binary melt are extended to include diffusion in the solid phase. Under assumptions equivalent to those made by Coriell and Sekerka, it is shown that no matter how small the diffusion coefficient is in the solid, the system is stable to all oscillatory and non-oscillatory disturbance modes if the modified constitutional supercooling criterion is satisfied and if the nonriequilibrium segregation coefficient is zero. Thus, a range of the non-equilibrium segregation parameter exists where these results allow the possibility of instability, whereas Coriell and Sekerka predict that the system will be stable.System stability is increased for both oscillatory and non-oscillatory modes. It is necessary for the diffusivity ratio Ds/D1 to be nearly 0.1 before oscillatory modes are affected. Both the critical wavelength of the disturbance as well as the oscillation frequency are reduced slightly from the case where diffusion in the solid is ignored.

Equilibrium segregation coefficient and liquid diffusion coefficient of some impurities in tellurium

1987 ◽  
Vol 43 (3) ◽  
pp. 219-222 ◽  
Author(s):  
A. Zaiour ◽  
M. Hage-Ali ◽  
J. M. Koebel ◽  
A. Bentz ◽  
P. Siffert
Keyword(s):  
Diffusion Coefficient ◽  
Segregation Coefficient ◽  
Liquid Diffusion ◽  
Equilibrium Segregation

Equilibrium segregation coefficient and solid solubility of B in Czochralski Ge crystal growth

2010 ◽  
Vol 518 (9) ◽  
pp. 2409-2412 ◽  
Author(s):  
Toshinori Taishi ◽  
Yutaka Ohno ◽  
Ichiro Yonenaga
Keyword(s):  
Crystal Growth ◽  
Solid Solubility ◽  
Segregation Coefficient ◽  
Equilibrium Segregation

Role of glycopeptides and pepddes in inhibition of crystallization of water in polar fishes

1984 ◽  
Vol 304 (1121) ◽  
pp. 575-588 ◽  
Keyword(s):  
Crystal Growth ◽  
Basal Plane ◽  
Solid Phase ◽  
Freezing Point ◽  
Body Fluids ◽  
Molecular Masses ◽  
Polar Oceans

In the ice-laden polar oceans, water temperatures of — 2 °C are common. This temperature is 1.1 °C below the equilibrium freezing point ( — 0.9 °C) of the fishes’ body fluids. Avoidance of freezing in these environments has been linked to the presence of unusual blood peptides and glycopeptides. These molecules have molecular masses ranging from 2.5 to 20 kDa and are viewed as having antifreeze properties because they lower the freezing point of water by a non-colligative process. A 2% solution of antifreeze has a freezing point of — 1.2 °C and ice formed in their presence melts at — 0.02 °C. Measurements of antifreeze concentrations in ice indicate that these molecules, unlike other proteins of similar size and conformation, are incorporated into the solid phase during freezing and adsorb to it. Adsorption of the antifreezes to ice appears to inhibit growth along the preferred axes ( a -axes) by raising the curvature of the growth steps on the basal plane. At temperatures below — 1.2 °C, crystal growth occurs in the form of long spicules whose axes are parallel to the c -axis, the non-preferred axis of growth.

Stress Driven Instability in Non-Hydrostatically Stressed Crystals and its Role in the Problems of Crystalline Thin Films

1991 ◽  
Vol 239 ◽  
Author(s):  
Michael A. Grinfeld
Keyword(s):  
Thin Films ◽  
Surface Tension ◽  
Crystal Growth ◽  
Solid Phase ◽  
Elastic Solids ◽  
Phase Boundaries ◽  
Crystalline Film ◽  
Physical Mechanisms ◽  
Epitaxial Crystal Growth

ABSTRACTIt was demonstrated in [1] that, in the absence of surface tension aflat boundary of non-hydrostatically stressed elastic solids is always unstable with respect to “mass rearrangement”. The physical mechanisms of the rearrangement can be different, for instance, a)melting-freezing or vaporization-sublimation processes at liquid-solid or vapor-solid phase boundaries, b»surface diffusion of particles along free or interfacial boundaries, b)adsorption-desorbtion of the atoms in epitaxial crystal growth, etc… We discuss the role of this instability in the problems of epitaxy and, in particular, the opportunities delivered by this instability for explanation of the recently discovered phenomena of the dislocation-free Stranski-Krastanow pattern of growth [2]. These phenomena cannot be interpreted in the framework of traditional viewpoints since, according to the classical theory, the Stranski-Krastanow pattern is a result of proliferation of the misfit dislocation appearing on the interface “crystalline film-substratum” [3].

Introduction to geomicrobiology

2018 ◽  
Author(s):  
David L. Kirchman
Keyword(s):  
Fossil Fuels ◽  
Solid Phase ◽  
Direct Reduction ◽  
Iron Oxidation ◽  
Mineral Dissolution ◽  
Precipitation Process ◽  
Soluble Ions ◽  
Chemolithoautotrophic Bacteria ◽  
The Impact

Geomicrobiology, the marriage of geology and microbiology, is about the impact of microbes on Earth materials in terrestrial systems and sediments. Many geomicrobiological processes occur over long timescales. Even the slow growth and low activity of microbes, however, have big effects when added up over millennia. After reviewing the basics of bacteria–surface interactions, the chapter moves on to discussing biomineralization, which is the microbially mediated formation of solid minerals from soluble ions. The role of microbes can vary from merely providing passive surfaces for mineral formation, to active control of the entire precipitation process. The formation of carbonate-containing minerals by coccolithophorids and other marine organisms is especially important because of the role of these minerals in the carbon cycle. Iron minerals can be formed by chemolithoautotrophic bacteria, which gain a small amount of energy from iron oxidation. Similarly, manganese-rich minerals are formed during manganese oxidation, although how this reaction benefits microbes is unclear. These minerals and others give geologists and geomicrobiologists clues about early life on Earth. In addition to forming minerals, microbes help to dissolve them, a process called weathering. Microbes contribute to weathering and mineral dissolution through several mechanisms: production of protons (acidity) or hydroxides that dissolve minerals; production of ligands that chelate metals in minerals thereby breaking up the solid phase; and direct reduction of mineral-bound metals to more soluble forms. The chapter ends with some comments about the role of microbes in degrading oil and other fossil fuels.

scholarly journals The Role of Electric Pressure/Stress Suppressing Pinhole Defect on Coalescence Dynamics of Electrified Droplet

Coatings ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 503
Author(s):  
Jaehyun Lee ◽  
Ehsan Esmaili ◽  
Giho Kang ◽  
Baekhoon Seong ◽  
Hosung Kang ◽  
...  
Keyword(s):  
Solid Phase ◽  
Critical Factor ◽  
Air Pressure ◽  
Conical Shape ◽  
Electric Stress ◽  
Bottom Interface ◽  
Electric Pressure ◽  
Pressure Stress ◽  
Air Film

The dimple occurs by sudden pressure inversion at the droplet’s bottom interface when a droplet collides with the same liquid-phase or different solid-phase. The air film entrapped inside the dimple is a critical factor affecting the sequential dynamics after coalescence and causing defects like the pinhole. Meanwhile, in the coalescence dynamics of an electrified droplet, the droplet’s bottom interfaces change to a conical shape, and droplet contact the substrate directly without dimple formation. In this work, the mechanism for the dimple’s suppression (interfacial change to conical shape) was studied investigating the effect of electric pressure. The electric stress acting on a droplet interface shows the nonlinear electric pressure adding to the uniform droplet pressure. This electric stress locally deforms the droplet’s bottom interface to a conical shape and consequentially enables it to overcome the air pressure beneath the droplet. The electric pressure, calculated from numerical tracking for interface and electrostatic simulation, was at least 108 times bigger than the air pressure at the center of the coalescence. This work helps toward understanding the effect of electric stress on droplet coalescence and in the optimization of conditions in solution-based techniques like printing and coating.

Segmental Volatility in Ethnically Divided Societies: (Re)assessing Party System Stability in Southeast Europe

2021 ◽  
pp. 1-19
Author(s):  
Damir Kapidžić ◽  
Olivera Komar
Keyword(s):  
Ethnic Identity ◽  
Party System ◽  
Ethnically Diverse ◽  
Party Systems ◽  
System Stability ◽  
Southeast Europe ◽  
East European ◽  
Ethnic Parties ◽  
Stabilizing Factors

Abstract This article examines the role of ethnicity and ethnic parties as stabilizing factors in Southeast European party systems. It compares two ethnically divided countries in Southeast Europe: Bosnia and Herzegovina, where ethnic identities that form the political cleavage are firm, and Montenegro, where they are malleable. Theoretically, it addresses the debate between scholars who either find stability or instability in East European post-communist party systems. The article traces the role of ethnicity in the formation and development of electoral contests and compares the two cases by utilizing measures of block volatility, based on analysis of official electoral data. We argue that party systems in ethnically diverse countries are stable at the subsystems level, but unstable within them. In BiH, firm ethnic identity stabilizes the party system by limiting competition between blocks, leading to closure. Malleable ethnic identity in Montenegro opens competition to non-ethnic parties seeking to bridge ethnic divisions, leading to more instability. We find that party system dynamics in ethnically divided new democracies depend on identity rigidity and cleavage salience, in addition to levels of heterogeneity.

Molecular-Dynamics Simulations of Recrystallization Processes in Silicon: Nucleation and Crystal Growth in the Solid-Phase and Melt

2019 ◽  
Vol 3 (8) ◽  
pp. 207-213
Author(s):  
Teruaki Motooka ◽  
Shinji Munetoh ◽  
Ryuzo Kishikawa ◽  
Takahide Kuranaga ◽  
Tomohiko Ogata ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Crystal Growth ◽  
Molecular Dynamics Simulations ◽  
Solid Phase ◽  
Dynamics Simulations
Sign in / Sign up

Export Citation Format

Share Document