scholarly journals Surface phase transitions and crystal habits of ice in the atmosphere

2020 ◽  
Vol 6 (21) ◽  
pp. eaay9322 ◽  
Author(s):  
Pablo Llombart ◽  
Eva G. Noya ◽  
Luis G. MacDowell
Keyword(s):  
Phase Transitions ◽  
Crystal Growth ◽  
Growth Rates ◽  
Large Scale ◽  
Crystal Surface ◽  
Climate Modeling ◽  
Ice Surface ◽  
Snow Crystal ◽  
Surface Phase Transitions ◽  
Step Density

With climate modeling predicting a raise of at least 2°C by year 2100, the fate of ice has become a serious concern, but we still do not understand how ice grows (or melts). In the atmosphere, crystal growth rates of basal and prism facets exhibit an enigmatic temperature dependence and crossover up to three times in a range between 0° and −40°. Here, we use large-scale computer simulations to characterize the ice surface and identify a sequence of previously unidentified phase transitions on the main facets of ice crystallites. Unexpectedly, we find that as temperature is increased, the crystal surface transforms from a disordered phase with proliferation of steps to a smooth phase with small step density. This causes the anomalous increase of step free energies and provides the long sought explanation for the enigmatic crossover of snow crystal growth rates found in the atmosphere.

Low Energy Electron Microscopy of Surface Processes on Clean Si(111) and Si (100)

1989 ◽  
Vol 159 ◽  
Author(s):  
E. Bauer ◽  
M. Mundschau ◽  
W. Swiech ◽  
W. Telieps
Keyword(s):  
Electron Microscopy ◽  
Phase Transitions ◽  
Crystal Growth ◽  
Surface Defects ◽  
Low Energy ◽  
Energy Electron ◽  
Surface Processes ◽  
Surface Phase ◽  
Surface Phase Transitions ◽  
Low Energy Electron

ABSTRACTLow energy electron microscopy (LEEM) is briefly introduced and its application to the study of surface defects, surface phase transitions on Si(111), crystal growth and sublimation on Si(100) is illustrated.

Kinetic aspects of major and trace elements in olivines from variably cooled basaltic melts

2020 ◽  
Author(s):  
Sarah Lang ◽  
Silvio Mollo ◽  
Lyderic France ◽  
Manuela Nazzari ◽  
Valeria Misiti ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Trace Elements ◽  
Crystal Growth ◽  
Cooling Rate ◽  
Crystallization Kinetics ◽  
Growth Rates ◽  
Crystal Surface ◽  
Major And Trace Elements ◽  
Diffusive Boundary Layer ◽  
Diffusive Boundary

<p>Olivine is an important mineral phase in naturally cooled basaltic rocks. The texture and composition of olivine are strictly related to the interplay between the degree of magma undercooling and crystal growth rate. Crystals formed at low undercoolings and growth rates generally show polyhedral-hopper textures and quite homogeneous compositions, while skeletal-dendritic textures and evident crystal zonations occur at high undercoolings and growth rates. In this context, we have performed equilibrium and disequilibrium (i.e., cooling rate) experiments to better understand, by a comparatively approach, the effects of crystallization kinetics on the incorporation of major and trace cations in olivine lattice. The experiments were carried out in a 1 atm vertical tube CO-CO2 gas-mixing furnace to perform experiment at atmospheric pressure and oxygen fugacity of QFM-2 using a basaltic glass (i.e., OIB) as starting materials. The equilibrium experiment was performed at 1175 °C. These target temperatures were kept constant for 240 h and then quenched. Conversely, the disequilibrium experiments were performed at the superliquidus temperature of 1250, and 1300 °C, which was kept constant for 2 h before cooling. The final target temperatures of 1150 (undercooling -ΔT = 50 °C), and 1175 °C (-ΔT = 25 °C) were attained by applying cooling rates of 2 °C/h, 20 °C/h, and 60 °C/h. Then the experimental charges were quenched. Results show that the olivine texture shifts from euhedral (i.e., equilibrium) to anhedral (i.e., disequilibrium) under the effect of cooling rate and rapid crystal growth. In equilibrium experiments, the composition of olivine is homogeneous and non chemical gradients are found in the melt next to the crystal surface. In contrast, a diffusive boundary layer develops in the melt surrounding the olivine crystals growing rapidly under the effect of cooling rate and degree of undercooling. The compositional gradient in the melt increases with increasing cooling rate and undercooling, causing the diffusive boundary layer to expand towards the far field melt. Because of the effects of crystallization kinetics, skeletal-dendritic olivines incorporates higher proportions of major and trace elements that are generally incompatible within their crystal lattice under equilibrium conditions.</p>

scholarly journals Snow-crystal Growth with Varying Surface Temperatures and Radiation Penetration

1989 ◽  
Vol 35 (119) ◽  
pp. 23-29 ◽  
Author(s):  
S.C. Colbeck
Keyword(s):  
Temperature Field ◽  
Crystal Growth ◽  
Solar Radiation ◽  
Surface Temperature ◽  
Growth Rates ◽  
High Altitudes ◽  
Snow Crystal ◽  
Wet Snow ◽  
Snow Crystals ◽  
Polar Snow

AbstractThe temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration. The growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals (i.e. depth hoar) that form just below the surface at high altitudes and in polar snow. The solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub-freezing.

scholarly journals Structure and water attachment rates of ice in the atmosphere: role of nitrogen

2019 ◽  
Vol 21 (35) ◽  
pp. 19594-19611 ◽  
Author(s):  
Pablo Llombart ◽  
Ramon M. Bergua ◽  
Eva G. Noya ◽  
Luis G. MacDowell
Keyword(s):  
Crystal Growth ◽  
Computer Simulations ◽  
Growth Rates ◽  
Ice Surface

In this work we perform computer simulations of the ice surface in order to elucidate the role of nitrogen in the crystal growth rates and crystal habits of snow in the atmosphere.

Comparison of copper sulphate pentahydrate growth rates determined by different methods

1990 ◽  
Vol 55 (7) ◽  
pp. 1691-1707 ◽  
Author(s):  
Miloslav Karel ◽  
Jiří Hostomský ◽  
Jaroslav Nývlt ◽  
Axel König
Keyword(s):  
Growth Rate ◽  
Crystal Growth ◽  
Fluidized Bed ◽  
Growth Rates ◽  
Copper Sulphate ◽  
Crystal Growth Rate ◽  
Effect Of Temperature ◽  
Rotating Disc ◽  
Shape Factors ◽  
Data Treatment

Crystal growth rates of copper sulphate pentahydrate (CuSO4.5 H2O) determined by different authors and methods are compared. The methods included in this comparison are: (i) Measurement on a fixed crystal suspended in a streaming solution, (ii) measurement on a rotating disc, (iii) measurement in a fluidized bed, (iv) measurement in an agitated suspension. The comparison involves critical estimation of the supersaturation used in measurements, of shape factors used for data treatment and a correction for the effect of temperature. Conclusions are drawn for the choice of values to be specified when data of crystal growth rate measurements are published.

Kinetics of the Crystallization of Potassium Sulfate

1993 ◽  
Vol 58 (8) ◽  
pp. 1848-1854 ◽  
Author(s):  
Miroslav Karel ◽  
Jaroslav Nývlt
Keyword(s):  
Experimental Data ◽  
Crystal Growth ◽  
Growth Rates ◽  
Potassium Sulfate ◽  
Kinetics Of

The kinetics of the crystallization of potassium sulfate has been determined using the MSMPR technique. Values of the nucleation and crystal growth rates evaluated from the experimental data are compared with the corresponding literature data.

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