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
•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
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
Rational
Oxidation Reaction on the surface of an existing oxide: SiO, FeO, Al2O3 etc….
With absorbed water molecule Specifically in colder environments
Experimental
Experimental
Sample: Si, SiO, Al2O3…..
Experimental
Experimental
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
1 mm
1.SiO Vapor Deposit + H2O2@ 150 K
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
SiO2
1.SiO Vapor Deposit + H2O2@ 150 K
2. SiO Vapor Deposit + H2O @ 150 K
2 mm
Element
Atomic (%)
Si 45.5O 54.5
Stoichiometry: SiO1.2
2. SiO Vapor Deposit + H2O @ 150 K
Element
Atomic (%)
Si 41.8O 58.2
Stoichiometry: SiO1.4
2. SiO Vapor Deposit + H2O @ 150 K
2. SiO Vapor Deposit + H2O @ 150 K
Oxygen Isotopes
2. SiO Vapor Deposit + H2OTime Progression
27 Hrs
19 Hrs
5 Hrs
2.5 Hrs
1 Hr
@ 150 K
@ 300 K
3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
2 mm
3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
Element
Atomic (%)
Si 63.8Al 9.4O 26.8
Stoichiometry: AlSi6.7O2.9
4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
2 mm
4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
4. (Al2O3 + SiO) Vapor Deposit + H2O @150 K
Element
Atomic (%)
Si 38.6Al 16.9O 44.5
Stoichiometry: AlSi2.3O2.6
4. (Al2O3 + SiO) Vapor deposit + H2O vapor deposit
Element
Atomic (%)
Si 42.3Al 13.3O 44.4
~ 10 micron particle
Stoichiometry: AlSi3.2O3.3
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…..
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…)
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
Mechanism
Based on Marcus, 2004
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
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
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
3. (Al2O3 + Si) Vapor Deposit + H2O @150 K
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