scholarly journals The efficiency of grain growth in the diffuse interstellar medium

2021 ◽  
Vol 502 (2) ◽  
pp. 2438-2445
Author(s):  
F D Priestley ◽  
I De Looze ◽  
M J Barlow
Keyword(s):  
Interstellar Medium ◽  
Size Distribution ◽  
Gas Phase ◽  
Grain Growth ◽  
Common Assumption ◽  
Small Grains ◽  
Far Ultraviolet ◽  
Dust Evolution ◽  
Charged Ions ◽  
Positively Charged

ABSTRACT Grain growth by accretion of gas-phase metals is a common assumption in models of dust evolution, but in dense gas, where the time-scale is short enough for accretion to be effective, material is accreted in the form of ice mantles rather than adding to the refractory grain mass. It has been suggested that negatively charged small grains in the diffuse interstellar medium (ISM) can accrete efficiently due to the Coulomb attraction of positively-charged ions, avoiding this issue. We show that this inevitably results in the growth of the small-grain radii until they become positively charged, at which point further growth is effectively halted. The resulting gas-phase depletions under diffuse ISM conditions are significantly overestimated when a constant grain size distribution is assumed. While observed depletions can be reproduced by changing the initial size distribution or assuming highly efficient grain shattering, both options result in unrealistic levels of far-ultraviolet extinction. We suggest that the observed elemental depletions in the diffuse ISM are better explained by higher initial depletions, combined with inefficient dust destruction by supernovae at moderate ($n_{\rm H}\sim 30 \, {\rm cm}^{-3}$) densities, rather than by higher accretion efficiences.

scholarly journals Thermal Infrared Emission by Dust in the Planetary Nebula NGC 3918

1989 ◽  
Vol 131 ◽  
pp. 201-201
Author(s):  
J. P. Harrington ◽  
D.J. Monk ◽  
R.E.S. Clegg
Keyword(s):  
Infrared Spectrum ◽  
Interstellar Medium ◽  
Size Distribution ◽  
Gas Phase ◽  
Amorphous Carbon ◽  
Planetary Nebula ◽  
Size Range ◽  
Line Emission ◽  
Infrared Emission ◽  
Size Distribution Of Particles

Models of the dust grains in the planetary nebula NGC 3918 are presented. The models, which are calculated for four grain materials -graphite, amorphous carbon, silicate, and iron- have a size distribution of particles based on that found for the diffuse interstellar medium. The infrared spectrum of the nebula -described mainly by IRAS photometry corrected for line emission- can be matched either with graphite grains with a size range of 0.04 - 0.30 μm, or with amorphous carbon grains having a size range 0.0005 - 0.25 μm. The implied depletions of gas phase carbon are only 11% and 4%, respectively. It is shown that iron grains cannot be the dominant dust material.

scholarly journals The cycling of carbon into and out of dust

2014 ◽  
Vol 168 ◽  
pp. 313-326 ◽  
Author(s):  
Anthony P. Jones ◽  
Nathalie Ysard ◽  
Melanie Köhler ◽  
Lapo Fanciullo ◽  
Marco Bocchio ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cosmic Rays ◽  
Shock Waves ◽  
Interstellar Medium ◽  
Gas Phase ◽  
Molecular Clouds ◽  
Observational Evidence ◽  
Electron Collisions ◽  
Uv Photons ◽  
Dust Evolution

Observational evidence seems to indicate that the depletion of interstellar carbon into dust shows rather wide variations and that carbon undergoes rather rapid recycling in the interstellar medium (ISM). Small hydrocarbon grains are processed in photo-dissociation regions by UV photons, by ion and electron collisions in interstellar shock waves and by cosmic rays. A significant fraction of hydrocarbon dust must therefore be re-formed by accretion in the dense, molecular ISM. A new dust model (Jones et al., Astron. Astrophys., 2013, 558, A62) shows that variations in the dust observables in the diffuse interstellar medium (nH ≤ 103 cm−3), can be explained by systematic and environmentally-driven changes in the small hydrocarbon grain population. Here we explore the consequences of gas-phase carbon accretion onto the surfaces of grains in the transition regions between the diffuse ISM and molecular clouds (e.g., Jones, Astron. Astrophys., 2013, 555, A39). We find that significant carbonaceous dust re-processing and/or mantle accretion can occur in the outer regions of molecular clouds and that this dust will have significantly different optical properties from the dust in the adjacent diffuse ISM. We conclude that the (re-)processing and cycling of carbon into and out of dust is perhaps the key to advancing our understanding of dust evolution in the ISM.

The Relationship between Grain Boundary Energy, Grain Boundary Complexion Transitions, and Grain Size in Ca-Doped Yttria

2013 ◽  
Vol 753 ◽  
pp. 87-92 ◽  
Author(s):  
Stephanie A. Bojarski ◽  
Jocelyn Knighting ◽  
Shuai Lei Ma ◽  
William Lenthe ◽  
Martin P. Harmer ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Size Distribution ◽  
Grain Growth ◽  
Lower Energy ◽  
Boundary Energy ◽  
Grain Boundary Energy ◽  
Entire Sample ◽  
Small Grains ◽  
The Relationship

The thermal groove technique has been used to measure relative grain boundary energies in two 100 ppm Ca-doped yttria samples. The first has a normal grain size distribution and the boundaries have a bilayer of segregated Ca. In the second sample, there is a combination of large grains and small grains. The boundaries around the large grains are known to have an intergranular film. The results show that the relative energies of boundaries in the sample with normal grain growth and the boundaries around small grains far from larger grains in the second sample are similar. Also, boundaries surrounding the largest grains and small grains immediately adjacent to them have the same and significantly lower energies. The results indicate that grain boundaries with an intergranular film have a lower energy than those with bilayer segregation and that the intergranular film extends beyond the periphery of the largest grains, but not throughout the entire sample.

scholarly journals Evolution of dust porosity through coagulation and shattering in the interstellar medium

2021 ◽  
Author(s):  
Hiroyuki Hirashita ◽  
Vladimir B Il’in ◽  
Laurent Pagani ◽  
Charléne Lefévre
Keyword(s):  
Grain Size ◽  
Interstellar Medium ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Collision Energy ◽  
Size Distributions ◽  
Curve Shape ◽  
Grain Size Distributions ◽  
Small Grains ◽  
Porous Grains

Abstract The properties of interstellar grains, such as grain size distribution and grain porosity, are affected by interstellar processing, in particular, coagulation and shattering, which take place in the dense and diffuse interstellar medium (ISM), respectively. In this paper, we formulate and calculate the evolution of grain size distribution and grain porosity through shattering and coagulation. For coagulation, we treat the grain evolution depending on the collision energy. Shattering is treated as a mechanism of forming small compact fragments. The balance between these processes are determined by the dense-gas mass fraction ηdense, which determines the time fraction of coagulation relative to shattering. We find that the interplay between shattering supplying small grains and coagulation forming porous grains from shattered grains is fundamentally important in creating and maintaining porosity. The porosity rises to 0.7–0.9 (or the filling factor 0.3–0.1) around grain radii $a\sim 0.1~{\rm \mu m}$. We also find that, in the case of ηdense = 0.1 (very efficient shattering with weak coagulation) porosity significantly enhances coagulation, creating fluffy submicron grains with filling factors lower than 0.1. The porosity enhances the extinction by 10–20 per cent at all wavelengths for amorphous carbon and at ultraviolet wavelengths for silicate. The extinction curve shape of silicate becomes steeper if we take porosity into account. We conclude that the interplay between shattering and coagulation is essential in creating porous grains in the interstellar medium and that the resulting porosity can impact the grain size distributions and extinction curves.

scholarly journals Kinetics of Normal Grain Growth Depending on the Size Distribution of Small Grains

2003 ◽  
Vol 44 (11) ◽  
pp. 2239-2244 ◽  
Author(s):  
Byung-Nam Kim ◽  
Keijiro Hiraga ◽  
Koji Morita
Keyword(s):  
Size Distribution ◽  
Grain Growth ◽  
Small Grains ◽  
Kinetics Of

Grain Refinement in Titanium-Erbium Alloys

1974 ◽  
Vol 32 ◽  
pp. 522-523
Author(s):  
B. B. Rath ◽  
J. E. O'Neal ◽  
R. J. Lederich
Keyword(s):  
Electron Microscopy ◽  
Size Distribution ◽  
Grain Refinement ◽  
Grain Growth ◽  
Volume Fraction ◽  
Pure Titanium ◽  
Systematic Investigation ◽  
Second Phase ◽  
Titanium Matrix ◽  
Average Size

Addition of small amounts of erbium has a profound effect on recrystallization and grain growth in titanium. Erbium, because of its negligible solubility in titanium, precipitates in the titanium matrix as a finely dispersed second phase. The presence of this phase, depending on its average size, distribution, and volume fraction in titanium, strongly inhibits the migration of grain boundaries during recrystallization and grain growth, and thus produces ultimate grains of sub-micrometer dimensions. A systematic investigation has been conducted to study the isothermal grain growth in electrolytically pure titanium and titanium-erbium alloys (Er concentration ranging from 0-0.3 at.%) over the temperature range of 450 to 850°C by electron microscopy.

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

scholarly journals Mean Field Analysis of Orientation Selective Grain Growth Driven By Interface-Energy Anisotropy

1994 ◽  
Vol 343 ◽  
Author(s):  
J. A. Floro ◽  
C. V. Thompson
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Growth ◽  
Texture Evolution ◽  
Mean Field ◽  
Orientation Distribution ◽  
Interface Energy ◽  
Abnormal Grain Growth ◽  
Field Analysis ◽  
Energy Anisotropy

ABSTRACTAbnormal grain growth is characterized by the lack of a steady state grain size distribution. In extreme cases the size distribution becomes transiently bimodal, with a few grains growing much larger than the average size. This is known as secondary grain growth. In polycrystalline thin films, the surface energy γs and film/substrate interfacial energy γi vary with grain orientation, providing an orientation-selective driving force that can lead to abnormal grain growth. We employ a mean field analysis that incorporates the effect of interface energy anisotropy to predict the evolution of the grain size/orientation distribution. While abnormal grain growth and texture evolution always result when interface energy anisotropy is present, whether secondary grain growth occurs will depend sensitively on the details of the orientation dependence of γi.

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