HR: 0800h
AN: OS21A-1200    [Abstracts]
TI: Reaction Vessel Design for Sampling Nanoparticles During Growth Under Controlled T, P, pH and Oxidation State
AU: * Gerke, T L
EM: erebus@choice.net
AF: Department of Geological Sciences, Arizona State University, Tempe, AZ 85287-1404 United States
AU: Voglesonger, K M
EM: kendoo@imap4.asu.edu
AF: Department of Geological Sciences, Arizona State University, Tempe, AZ 85287-1404 United States
AU: Holloway, J R
EM: john.holloway@asu.edu
AF: Department of Geological Sciences, Arizona State University, Tempe, AZ 85287-1404 United States
AU: Williams, L B
EM: lynda.williams@asu.edu
AF: Department of Geological Sciences, Arizona State University, Tempe, AZ 85287-1404 United States
AB: Simulation of authigenic mineral formation and mineral catalysis of aqueous reactions requires experimental systems that simulate natural environments by buffering the pH and fO$_{2}$ to relevant environmental conditions. The fO$_{2}$ is commonly buffered in experiments using minerals (e.g., Ni-NiO; Fe$_{2}$O$_{3}$-Fe$_{3}$O$_{4}$), however at low temperatures, the kinetics of the mineral buffer reactions are too slow for accurate control of oxidation state, and the minerals themselves may interfere with the reactions under investigation. To study authigenic clay mineral reactions ($<$200nm particles), we built a new titanium reaction vessel that utilizes a Pd/Ag alloy (75%/25%) semi-permeable hydrogen membrane. At temperatures above 200\deg C, a known pressure of hydrogen on the backside of the membrane controls the concentration of dissolved hydrogen within the vessel, and therefore controls the fO$_{2}$. The pH can be controlled either by the mineral reaction or by addition of acid/base. The reaction system can run at conditions up to 400\deg C and 30 MPa. The fO$_{2}$ dictated by the hydrogen membrane is monitored by the electrochemical potential between a Pt wire in Hg/HgO within an Yytrium doped zirconium (YSZ) reference electrode and a gold source electrode. The reference electrode can also be used to monitor pH with the addition of a titanium source electrode. A Pt-Rd thermocouple continuously monitors the temperature within the vessel, and a liquid chromatography pump and adjustable pressure relief valve control pressure. A sampling valve system allows capture of a 2 ml aliquot of mineral/fluid suspension at T and P for analysis of suspended minerals or of aqueous species. The use of the hydrogen membrane in concert with the hydrogen electrode allows for in situ control and monitoring of the oxidation state within the vessel, without the addition of mineral phases that may influence the reaction progress during crystal growth.
DE: 2194 Instruments and techniques
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting