Download - Lpsc 2016-presentation
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New Experimental Evidence of Silicate Formation with Meteorite Like Oxygen Isotopes on a Dust Surface Analog
Subrata ChakrabortyHaiyang Kehoe and M. H. Thiemens
University of California, San DiegoDepartment of Chemistry and Biochemistry, 9500 Gilman Drive, La Jolla, CA 92093-0356
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•Dust particles are obiquitous throughout the universe•Dying stars are the ‘dust factories’ •Constitutes ~1 mass % in the ISM•As high as 10 % in planetary nebula•Dust particles are mainly of two types: carbonaceous and silicates•Long lifetime journey– stellar region through diffuse, dense or molecular clouds to the new born star or its planetary system •Significantly processed during this journey
Background
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Rational
Condensation of oxides in gas phase were theoretically calculated
Ferrarotti and Gail, AA, 2002Mg + H2O → MgO(s) + H2Fe + H2O → FeO(s) + H22Fe + 3H2O → Fe2O3(s) + 3H23Fe + 4H2O → Fe3O4(s) + 4H2
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Rational
Oxidation Reaction on the surface of an existing oxide: SiO, FeO, Al2O3 etc….
With absorbed water molecule Specifically in colder environments
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Experimental
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Experimental
Sample: Si, SiO, Al2O3…..
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Experimental
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Experimental
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Experimental
Four different sets of experiments:1.SiO vapor deposit + H2O2 vapor deposit2.SiO vapor deposit + H2O vapor deposit3.(Al2O3 + Si) vapor deposit + H2O vapor
deposit4.(Al2O3 + SiO) vapor deposit + H2O vapor
deposit
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1 mm
1.SiO Vapor Deposit + H2O2@ 150 K
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1.SiO Vapor Deposit + H2O2
Collection Plate
Side Wall- Foil
Collection Plate- Foil
Element
Atomic (%)
Si 44.2O 55.8
SiOx (<2)
Element
Atomic (%)
Si 38.9O 61.1
Element
Atomic (%)
Si 34.9O 65.1
SiO2
SiO2
@ 150 K
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SiO2
1.SiO Vapor Deposit + H2O2@ 150 K
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2. SiO Vapor Deposit + H2O @ 150 K
2 mm
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Element
Atomic (%)
Si 45.5O 54.5
Stoichiometry: SiO1.2
2. SiO Vapor Deposit + H2O @ 150 K
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Element
Atomic (%)
Si 41.8O 58.2
Stoichiometry: SiO1.4
2. SiO Vapor Deposit + H2O @ 150 K
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2. SiO Vapor Deposit + H2O @ 150 K
Oxygen Isotopes
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2. SiO Vapor Deposit + H2OTime Progression
27 Hrs
19 Hrs
5 Hrs
2.5 Hrs
1 Hr
@ 150 K
@ 300 K
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3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
2 mm
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3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
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3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
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3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
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3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
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3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
Element
Atomic (%)
Si 63.8Al 9.4O 26.8
Stoichiometry: AlSi6.7O2.9
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4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
2 mm
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4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
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4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
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4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
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4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
Element
Atomic (%)
Si 38.6Al 16.9O 44.5
Stoichiometry: AlSi2.3O2.6
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4. (Al2O3 + SiO) Vapor deposit + H2O vapor deposit
Element
Atomic (%)
Si 42.3Al 13.3O 44.4
~ 10 micron particle
Stoichiometry: AlSi3.2O3.3
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Mechanism
Duley and Millar, 1978….. Model (theoretical) for the reaction of +ve ions
with –ve charged species on oxide grain surfaces
Recombination of gas phase ions with surface O- and OH-
Explains selective depletion of Al, Ca, Cr, Ti, Mn etc…..
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MechanismDuley and Millar, 1978….. Model (theoretical) for the reaction of +ve ions
with –ve charged species on oxide grain surfaces
Recombination of gas phase ions with surface O- and OH-
Explains selective depletion of Al, Ca, Cr, Ti, Mn etc…..Other way round….
Reaction of adsorbed species (H2O) with the host species (Si, Al etc…)
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Bikondoa et al., Nature 2006
MechanismSteps: Water adsorbs into O vacancies Dissociates into OH and H
fragments. The OH fragment is pinned at the
position of the O vacancy The H fragment attaches to
another oxygen from the bridging-O rows forming a second OH groupHypothesis:XO + OH → (XOOH)* → XOO + H
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Mechanism
Based on Marcus, 2004
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ComparisonGas Phase Reactions
Chakraborty et al., Science, 2013
Group-2H2 + O → OH + HSiO + OH → SiO2 + HOH + OH → H2O + HOH + O2 → HO2 + O SiO + HO2 → SiO2 + OH
Group 1SiO (g) + O2 → SiO2 + OSiO (g) + O → SiO2
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ComparisonGas Phase Reactions
Chakraborty et al., Science, 2013
Group 1SiO (g) + O2 → SiO2 + OSiO (g) + O → SiO2
Group-2H2 + O → OH + HSiO + OH → SiO2 + HOH + OH → H2O + HOH + O2 → HO2 + O SiO + HO2 → SiO2 + OH
Surface Reactions
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ConclusionsSurface assisted oxidation reation is a
possible mechanismEffective in the dark and cold molecular
clouds and colder parts of the solar nebula
Observed: Growth of new particles through reactions
Observed: Mass-independent oxygen isotopic compositions in the newly formed SiOx particles
Multicle element oxide grains do form in this process
Need more studies in this direction
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3. (Al2O3 + Si) Vapor Deposit + H2O @150 K