scholarly journals Snow lines can be thermally unstable

2020 ◽  
Vol 495 (3) ◽  
pp. 3160-3174 ◽  
Author(s):  
James E Owen
Keyword(s):  
Temperature Profile ◽  
Thermal Instability ◽  
Solid Phase ◽  
Turbulent Viscosity ◽  
Vapour Phase ◽  
Snow Line ◽  
Total Opacity ◽  
Planetary Migration ◽  
Solid Distribution ◽  
Protoplanetary Discs

ABSTRACT Volatile species in protoplanetary discs can undergo a phase change from vapour to solid. These ‘snow lines’ can play vital roles in planet formation at all scales, from dust coagulation to planetary migration. In the outer regions of protoplanetary discs, the temperature profile is set by the absorption of reprocessed stellar light by the solids. Further, the temperature profile sets the distribution of solids through sublimation and condensation at various snow lines. Hence, the snow line position depends on the temperature profile and vice versa. We show that this coupling can be thermally unstable, such that a patch of the disc at a snow line will produce either runaway sublimation or condensation. This thermal instability arises at moderate optical depths, where heating by absorption of reprocessed stellar light from the disc’s atmosphere is optically thick, yet cooling is optically thin. Since volatiles in the solid phase drift much faster than volatiles in the vapour phase, this thermal instability results in a limit cycle. The snow line progressively moves in, condensing volatiles, before receding, as the volatiles sublimate. Using numerical simulations, we study the evolution of the carbon monoxide (CO) snow line. We find the CO snow line is thermally unstable under typical disc conditions and evolves inwards from ∼50 to ∼30 au on time-scales from 1000 to 10 000 yr. The CO snow line spends between ${\sim}10{{\ \rm per\ cent}}\,\mathrm{ and}\,50{{\ \rm per\ cent}}$ of its time at smaller separations, where the exact value is sensitive to the total opacity and turbulent viscosity. The evolving snow line also creates ring-like structures in the solid distribution interior to the snow line. Multiple ring-like structures created by moving snow lines could potentially explain the substructures seen in many ALMA images.

The dance of snow-lines

2020 ◽  
Author(s):  
James Owen
Keyword(s):  
High Resolution ◽  
Planet Formation ◽  
Solid Phase ◽  
Outer Region ◽  
Vapour Phase ◽  
Vital Role ◽  
Sublimation Temperature ◽  
New Process ◽  
High Resolution Images ◽  
Protoplanetary Discs

<p>Snow-lines are thought to play a vital role in the evolution of protoplanetary discs and planet formation at all scales. Snow-lines occur in regions of the protoplanetary discs where the temperature reaches the sublimation temperature and volatiles transition from the solid phase to the vapour phase (or vice-versa). However, in the outer region of protoplanetary discs (beyond a few AU), the temperature is set by the distribution of solids and their ability to absorb stellar light. Thus, the thermodynamics of the disc and the volatile phases are inextricably linked. In this talk, I will show this coupling is thermally unstable, and snow-lines continually evolve in regions of the disc that are marginally optically thick. Patches of the disc proceeding through a limit cycle, where volatiles in a region of the disc continually condense and then sublimate. Using numerical simulations of the CO snow-line I will show it can move 10s AU over 10,000 years, repeatedly. I will use these simulations to discuss how this new process may effect measured Carbon abundances, solid evolution and ultimately planet formation, making connections to high-resolution images of protoplanetary discs. </p>

Nanomaterials, Novel Preparation Routes, and Characterizations

2015 ◽  
pp. 1-40 ◽  
Author(s):  
Irshad A. Wani
Keyword(s):  
Electron Microscopy ◽  
Solid Phase ◽  
Arc Discharge ◽  
Hydrogen Plasma ◽  
Sol Gel ◽  
Chemical Vapour ◽  
Chemical Properties ◽  
Vapour Phase ◽  
Inorganic Materials ◽  
Primary Focus

The important aspect of nanotechnology is the remarkable size dependant physico-chemical properties of nanomaterials that have led to the development of synthesis protocols for synthesizing nanomaterials over a range of sizes, shapes, and chemical compositions. This chapter describes the various aspects of nanotechnology: its dimensions and manipulation of matter with primary focus on inorganic materials. Detailed accounts of various methods lying within top-down and bottom-up synthesis approaches are discussed, like Chemical Vapour Condensation (CVC), arc discharge, hydrogen plasma-metal reaction, and laser pyrolysis in the vapour phase, microemulsion, hydrothermal, sol-gel, sonochemical taking place in the liquid phase, and ball milling carried out in the solid phase. The chapter also presents a brief account of the various characterization techniques used for the identification of the nanomaterials: X-ray diffraction, UV-visible spectroscopy, and electron microscopy (e.g. Transmission Electron Microscopy [TEM], Scanning Electron Microscopy [SEM], Atomic Force Microscopy [AFM]).

scholarly journals Effect of wind-driven accretion on planetary migration

2019 ◽  
Vol 633 ◽  
pp. A4 ◽  
Author(s):  
C. N. Kimmig ◽  
C. P. Dullemond ◽  
W. Kley
Keyword(s):  
Turbulent Viscosity ◽  
Protoplanetary Disks ◽  
High Mass ◽  
Quantitative Prediction ◽  
Migration Behavior ◽  
Secular Evolution ◽  
Accretion Process ◽  
Planetary Migration ◽  
Outward Migration ◽  
Orbital Region

Context. Planetary migration is a key link between planet formation models and observed exoplanet statistics. So far, the theory of planetary migration has focused on the interaction of one or more planets with an inviscid or viscously evolving gaseous disk. Turbulent viscosity is thought to be the main driver of the secular evolution of the disk, and it is known to affect the migration process for intermediate- to high-mass planets. Recently, however, the topic of wind-driven accretion has experienced a renaissance because evidence is mounting that protoplanetary disks may be less turbulent than previously thought, and 3D non-ideal magnetohydrodynamic modeling of the wind-launching process is maturing. Aims. We investigate how wind-driven accretion may affect planetary migration. We aim for a qualitative exploration of the main effects and not for a quantitative prediction. Methods. We performed 2D hydrodynamic planet-disk interaction simulations with the FARGO3D code in the (r, ϕ) plane. The vertical coordinate in the disk and the launching of the wind are not treated explicitly. Instead, the torque caused by the wind onto the disk is treated using a simple two-parameter formula. The parameters are the wind mass-loss rate and the lever arm. Results. We find that the wind-driven accretion process replenishes the co-orbital region in a different way than the viscous accretion process. The former always injects mass from the outer edge of the co-orbital region, and always removes mass from the inner edge, while the latter injects or removes mass from the co-orbital region depending on the radial density gradients in the disk. As a consequence, the migration behavior can differ strongly, and can under certain conditions drive rapid type-III-like outward migration. We derive an analytic expression for the parameters under which this outward migration occurs. Conclusions. If wind-driven accretion plays a role in the secular evolution of protoplanetary disks, planetary migration studies have to include this process as well because it can strongly affect the resulting migration rate and migration direction.

scholarly journals Vapour-Phase and Solid-Phase Epitaxy of Silicon on Solid-Phase Crystallised Seed Layers for Solar Cells Application

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Wei Li ◽  
Sergey Varlamov ◽  
Miga Jung ◽  
Jialiang Huang
Keyword(s):  
Electron Microscopy ◽  
Solar Cell ◽  
Seed Layer ◽  
Solid Phase ◽  
Short Circuit ◽  
Vapour Phase ◽  
Solid Phase Epitaxy ◽  
Cross Sectional ◽  
Vapour Phase Epitaxy ◽  
Planar Defects

Vapour-phase and solid-phase epitaxy are used for thickening of a solid-phase crystallised silicon seed layer on glass. Cross-sectional transmission microscope images confirm that a transfer of crystallographic information has taken place from the seed layer into the epilayers. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy reveal that the density of planar defects (mainly on{111}plains) in the vapour-phase epitaxial sample is much higher than in the solid-phase epitaxial sample. These planar defects can act as recombination centres for free-charge carriers. Consequently, PC1D modelled minority carrier diffusion length in the vapour-phase grown epilayer is 50% shorter than that in the solid-phase grown epilayer. As a result, a solar cell grown by solid-phase epitaxy achieves open circuit voltage of 468 mV, short circuit current of 9.17 mA/cm2, and photovoltaic conversion efficiency at 2.75% which are all higher than those of the solar cell grown by vapour-phase epitaxy on the same seed layer, 400 mV, 7.28 mA/cm2, 1.69%, respectively. It proves that solid-phase epitaxy is more suitable for the solar cell growth on the solid-phase crystallised silicon seed layer than vapour-phase epitaxy.

scholarly journals High-temperature spectrophotometry of indium chloride vapours as a method of study of the In – Se system

2021 ◽  
Vol 23 (4) ◽  
pp. 482-495
Author(s):  
Nikolay Yu. Brezhnev ◽  
Andrey V. Kosyakov ◽  
Anastasia V. Steich ◽  
Alexander Yu. Zavrazhnov
Keyword(s):  
High Temperature ◽  
Binary Systems ◽  
Materials Science ◽  
Solid Phase ◽  
Vapour Phase ◽  
Point Of View ◽  
Indium Chloride ◽  
Component Method ◽  
Auxiliary Component ◽  
Temperature Dependences

The goals of this work are as follows: (а) searching for a method of study of the In – Se system taking into account the specified problems and difficulties, (b) choosing a way for the instrumental implementation of this method, and (c) obtaining experimental evidence that this method and its implementation are promising. The choice of the In – Se system is related to the fact that indium selenides, layered structures and semiconductor phases with stoichiometric vacancies, are promising from the point of view of materials science. This choice is also related to the use of binary precursors for the synthesis of heterostructures based on CIS compounds.We studied the possibility of applying the auxiliary component method using the equilibrium with the participation of indium chloride vapours which were made to contact the condensed phases of the In – Se system. Equilibrium was achieved using high-temperature spectrophotometry of the vapour phase. The experiment had two stages. During the first stage we determined the absorption characteristics of the InCl3 vapour. During the second stage we studied the heterogeneous equilibrium of the unsaturated indium chloride vapour with several phases of the In – Se system. Over the course of the study, we determined the molar attenuation coefficients of the InCl3 vapour and plotted the temperature dependences of the value KP.It was found that the phase composition of the alloys significantly influences the position of the corresponding lines on the KP–T diagram, which proves the possibility of using the suggested auxiliary component method in its specific instrumental (spectrophotometric) implementation in order to study the In – Se system. We also showed the additional possibilities of using this method for plotting T-x diagrams of binary systems in such high-temperature areas where the binary solid phase is in equilibrium with the melt. This application of the method is related to the solubility of a vapour of an auxiliary component (chlorine in the form of indium chlorides) in the melts of binary phases (indium selenides).

Eulerian-Eulerian Modeling of Non-Newtonian Slurries Flow in Horizontal Pipes

2009 ◽  
Author(s):  
Boris M. Bossio ◽  
Armando J. Blanco ◽  
Franz H. Herna´ndez
Keyword(s):  
Experimental Data ◽  
Base Fluid ◽  
Solid Phase ◽  
Flow Behavior ◽  
Turbulent Viscosity ◽  
Pressure Gradients ◽  
Wide Range ◽  
Slurry Flows ◽  
Mean Pressure ◽  
Eulerian Models

Slurries transport through circular pipelines is present in many industries: oil, mineral, water and others. There are many variables involved in slurry flows, causing the flow behavior of these slurry systems to vary over a wide range, and therefore, different approaches have been used to describe their behavior in various flow regimes. At some typical applications, the rheology of the base fluid is itself non-Newtonian. Due to the wide range of variables and their variations, the experimental approach is necessarily limited by geometric and physical scale factors. For a non-Newtonian base fluid, only some particular cases that cover a limited range of conditions have been reported. For these reasons, numerical simulation constitutes an ideal technique for predicting the general flow behavior of these systems. Models in this area can be divided in two different classes: Eulerian-Eulerian and Lagrangian-Eulerian. Lagrangian-Eulerian models calculate the path and motion of each particle, while Eulerian-Eulerian models treat the particle phase as a continuum and average out motion on the scale of individual particles. This work focuses on the Eulerian-Eulerian approach for modeling the flow of a mixture of sand particles and a non-Newtonian fluid in a horizontal pipe. The steady-state rheological behavior of the base fluid was expressed by the three-parameter Sisko model. Homogeneous and heterogeneous flow regimes are considered. For the present study, the widely used “k-ε model” is employed to model turbulent viscosity. The k-ε turbulence model introduces two additional variables: the kinetic energy of the fluid turbulence, k, and the dissipation rate of this kinetic energy, ε. These two variables are solved throughout the fluid domain via two additional differential transport equations. The k-ε model is therefore commonly referred to as a “two-equation” turbulence model. The turbulent viscosity is then determined as a function of k and ε. Additionally, closure of solid-phase momentum equations requires a description for the solid-phase stress. Constitutive relations for the solid-phase stress, considering the inelastic nature of particle collisions based on kinetic theory concepts, have been used. Governing equations were solved numerically using the control volume-based finite element method. An unstructured non-uniform grid was chosen to cover the entire computational domain. A second-order scheme in space was used. Precise numerical solutions in a fully developed turbulent flow were found. Flow behavior for different sand concentrations was simulated. Results for the mean pressure gradients were compared with experimental data. The results turned out to be in compliance with those from the experimental data, for a sand concentration of less than 5%. Numerical simulations of non-Newtonian slurry flows provide a method that can relate properties of the fluid and solid component of the slurry, and does not entail the time and expenses needed for empirical studies. This also might provide a further sight to develop correlations between mean pressure gradients and slurry mean velocity.

Relativistic contribution: an electronic explanation to the thermal disproportionation of PtF5

2017 ◽  
Author(s):  
Robson de Farias
Keyword(s):  
Experimental Data ◽  
Gaseous Phase ◽  
Thermal Instability ◽  
Solid Phase ◽  
Electronic Configuration ◽  
Thermochemical Study ◽  
Energy Diagram ◽  
Unpaired Electrons

<div> <p>In the present work, is performed a computational thermochemical study of platinum tetrafluoride (PtF<sub>4</sub>) and platinum pentafluoride (PtF<sub>5</sub>). The results are compared to those previously [1] obtained to PtF<sub>6</sub> as well as experimental data. Is concluded that in gaseous phase PtF<sub>4</sub> and PtF<sub>5</sub> retain their structures and number of unpaired electrons exhibited in the solid phase. Furthermore, is proposed that the generally accepted t<sub>2g</sub><sup>5</sup>e<sub>g</sub><sup>0 </sup>configuration to Pt<sup>5+</sup> is not correct. Based on the calculated results, an energy diagram is proposed to PtF<sub>5</sub>, which explain why, upon heating, platinum pentafluoride disproportionates readily [7]: 2PtF<sub>5</sub> → PtF<sub>4</sub> + PtF<sub>6</sub>, providing a clear, elegant and straightforward explanation to the thermal instability of PtF<sub>5</sub> as consequence of the electronic configuration. </p> </div>

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