Toward a Molecular Theory of Homogeneous Bubble Nucleation: II. Calculation of the Number Density of Critical Nuclei and the Rate of Nucleation

2013 ◽  
Vol 117 (41) ◽  
pp. 12491-12504 ◽  
Author(s):  
Korosh Torabi ◽  
David S. Corti
Keyword(s):  
Bubble Nucleation ◽  
Molecular Theory ◽  
Number Density ◽  
Critical Nuclei

Preparation of open microcellular polylactic acid foams with a microfibrillar additive using coreback foam injection molding processes

2018 ◽  
Vol 54 (4) ◽  
pp. 765-784 ◽  
Author(s):  
Shota Ishihara ◽  
Yuta Hikima ◽  
Masahiro Ohshima
Keyword(s):  
Injection Molding ◽  
Polylactic Acid ◽  
Bubble Nucleation ◽  
Number Density ◽  
Cell Content ◽  
Open Cell ◽  
Cooling Conditions ◽  
Nucleation Sites ◽  
Fast Cooling ◽  
Foam Injection Molding

Open microcellular polylactic acid foams with a fibrous polytetrafluoroethylene additive were prepared by a coreback foam injection molding technique. The effects of this fibrous additive on the foam cell structure were investigated. Fibrous polytetrafluoroethylene forms a network structure in polylactic acid in metering and mixing processes. The fibrous polytetrafluoroethylene network increased the viscoelasticity of polylactic acid and provided polylactic acid with a strain-hardening property. The network also provided heterogeneous bubble nucleation sites for physical foaming. However, because of the slow crystallization rate of polylactic acid, the fibrous polytetrafluoroethylene additive did not promote the nucleation of polylactic acid crystals under fast cooling conditions. During fast cooling, such as injection molding cooling conditions, the crystals induced by the fibrous polytetrafluoroethylene network could not behave as bubble nucleation sites. Thus, changes in rheological properties and the increased number of heterogeneous sites contributed to the decrease in cell size, the increase in the number density of cells and the increase in the open cell content. As the number density of cells increased, the cell walls with the fibrous polytetrafluoroethylene fibrous additive became so thin that they could be easily fibrillated by a stretching operation during the coreback operation, while their strain-hardening property prevented the walls from complete breakage. Synergistically conducting cell reduction and stretching (coreback) operations, high expansion ratio foams with high open cell content were prepared. When we adjusted the foaming temperature and holding time, five-fold expansion (i.e. 80% void ratio) foams with cell diameters less than 25 µm and open cell contents (OCC) higher than 80% were produced.

The effect of nanolites on degassing of silica-rich magma

2020 ◽  
Author(s):  
Francisco Cáceres ◽  
Fabian Wadsworth ◽  
Bettina Scheu ◽  
Mathieu Colombier ◽  
Claudio Madonna ◽  
...  
Keyword(s):  
Ambient Pressure ◽  
Volcanic Eruptions ◽  
Bubble Nucleation ◽  
Magma Ascent ◽  
Explosive Eruptions ◽  
Initial Water Content ◽  
Primary Control ◽  
Number Density ◽  
Bubble Number ◽  
Bubble Number Density

<p>Magma degassing dynamics play an important role controlling the explosivity of volcanic eruptions. Some of the largest explosive eruptions in history have been fed by silica-rich magmas in volcanic systems with complex dynamics of volatiles degassing. Degassing of magmatic water drives bubble nucleation and growth, which in turn increases magma buoyancy and results in magma ascent and an eventual eruption. While micro- to milli-meter sized crystals are known to cause heterogeneous bubble nucleation and to facilitate bubble coalescence, the effects of nanolites remains mostly unexplored. Nanolites have been hypothesized to be a primary control on the eruptive style of silicic volcanoes, however the mechanisms behind this control remains unclear.</p><p>Here we use an experimental approach to show how nanolites dramatically increase the bubble number density in a degassing silicic magma compared to the same magma without nanolites. The experiments were conducted using both nanolite-free and nanolite-bearing rhyolitic glass with different low initial water content. Using an Optical Dilatometer at 1 bar ambient pressure, cylindrical samples were heated at variable rates (1-30 °C min<sup>-1</sup>) to final temperatures of 820-1000 °C. This method allowed us to continuously monitor the volume, and hence porosity evolution in time. X-ray computed microtomography (µCT) and Scanning Electron Microscope (SEM) analyses revealed low and high bubble number densities for the nanolite-free and nanolite-bearing samples respectively.</p><p>Comparing vesicle number densities of natural volcanic rocks from explosive eruptions and our experimental results, we speculate that some very high naturally occurring bubble number densities could be associated with nanolites. We use a magma ascent model with P-T-H<sub>2</sub>O starting conditions relevant for known silicic eruptions to further underpin that such an increase in bubble number density caused driven by the presence of nanolites can feasibly turn an effusive eruption to an eventually explosive behavior.</p>

scholarly journals Can nanolites enhance eruption explosivity?

Geology ◽  
2020 ◽  
Vol 48 (10) ◽  
pp. 997-1001 ◽  
Author(s):  
Francisco Cáceres ◽  
Fabian B. Wadsworth ◽  
Bettina Scheu ◽  
Mathieu Colombier ◽  
Claudio Madonna ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Growth Dynamics ◽  
Nucleation And Growth ◽  
Bubble Nucleation ◽  
Magma Ascent ◽  
Primary Control ◽  
Number Density ◽  
Starting Conditions ◽  
Bubble Number ◽  
Bubble Number Density

Abstract Degassing dynamics play a crucial role in controlling the explosivity of magma at erupting volcanoes. Degassing of magmatic water typically involves bubble nucleation and growth, which drive magma ascent. Crystals suspended in magma may influence both nucleation and growth of bubbles. Micron- to centimeter-sized crystals can cause heterogeneous bubble nucleation and facilitate bubble coalescence. Nanometer-scale crystalline phases, so-called “nanolites”, are an underreported phenomenon in erupting magma and could exert a primary control on the eruptive style of silicic volcanoes. Yet the influence of nanolites on degassing processes remains wholly uninvestigated. In order to test the influence of nanolites on bubble nucleation and growth dynamics, we use an experimental approach to document how nanolites can increase the bubble number density and affect growth kinetics in a degassing nanolite-bearing silicic magma. We then examine a compilation of these values from natural volcanic rocks from explosive eruptions leading to the inference that some very high naturally occurring bubble number densities could be associated with the presence of magmatic nanolites. Finally, using a numerical magma ascent model, we show that for reasonable starting conditions for silicic eruptions, an increase in the resulting bubble number density associated with nanolites could push an eruption that would otherwise be effusive into the conditions required for explosive behavior.

Toward a Molecular Theory of Homogeneous Bubble Nucleation: I. Equilibrium Embryo Definition

2013 ◽  
Vol 117 (41) ◽  
pp. 12479-12490 ◽  
Author(s):  
Korosh Torabi ◽  
David S. Corti
Keyword(s):  
Bubble Nucleation ◽  
Molecular Theory

scholarly journals Reconciling bubble nucleation in explosive eruptions with geospeedometers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sahand Hajimirza ◽  
Helge M. Gonnermann ◽  
James E. Gardner
Keyword(s):  
Volcanic Eruptions ◽  
Bubble Nucleation ◽  
Explosive Eruptions ◽  
Number Density ◽  
Proxy Record ◽  
Decompression Rate ◽  
Large Numbers ◽  
Magmatic Volatiles ◽  
Bubble Number ◽  
Bubble Number Density

AbstractMagma from Plinian volcanic eruptions contains an extraordinarily large numbers of bubbles. Nucleation of those bubbles occurs because pressure decreases as magma rises to the surface. As a consequence, dissolved magmatic volatiles, such as water, become supersaturated and cause bubbles to nucleate. At the same time, diffusion of volatiles into existing bubbles reduces supersaturation, resulting in a dynamical feedback between rates of nucleation due to magma decompression and volatile diffusion. Because nucleation rate increases with supersaturation, bubble number density (BND) provides a proxy record of decompression rate, and hence the intensity of eruption dynamics. Using numerical modeling of bubble nucleation, we reconcile a long-standing discrepancy in decompression rate estimated from BND and independent geospeedometers. We demonstrate that BND provides a record of the time-averaged decompression rate that is consistent with independent geospeedometers, if bubble nucleation is heterogeneous and facilitated by magnetite crystals.

Mass Determination by Direct Measurement of Electron Scattering

1975 ◽  
Vol 33 ◽  
pp. 240-241
Author(s):  
M. K. Lamvik ◽  
A. V. Crewe
Keyword(s):  
Cross Section ◽  
Electron Scattering ◽  
Mass Density ◽  
Variable Mass ◽  
Scattering Cross Section ◽  
Mass Determination ◽  
Number Density ◽  
Cross Sectional ◽  
Thin Slice ◽  
Scattering Cross

If a molecule or atom of material has molecular weight A, the number density of such units is given by n=Nρ/A, where N is Avogadro's number and ρ is the mass density of the material. The amount of scattering from each unit can be written by assigning an imaginary cross-sectional area σ to each unit. If the current I0 is incident on a thin slice of material of thickness z and the current I remains unscattered, then the scattering cross-section σ is defined by I=IOnσz. For a specimen that is not thin, the definition must be applied to each imaginary thin slice and the result I/I0 =exp(-nσz) is obtained by integrating over the whole thickness. It is useful to separate the variable mass-thickness w=ρz from the other factors to yield I/I0 =exp(-sw), where s=Nσ/A is the scattering cross-section per unit mass.

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