| Slow heating of standard silicate mineral powders by a focused CO2-laser beam in a CIF3 environment gave different oxygen isotopic results depending on the types of materials used to contain the powders. Stainless steel, nickel, gold-plated nickel, and pure gold sample holders were evaluated. Nickel was most reactive to the oxygen gas released from the silicates in the presence of CIF3, followed by stainless steel and gold. Preferential release of the heavier isotope, 18O, on the surface and release of the lighter isotope, 16O, caused the residual gas collected from quartz to be isotopically lighter than expected by ∼1‰. However, ferromagnesian garnet and olivine gave higher than expected δ18O values, possibly due to fluoride melt phases that formed during laser fluorination.; Rapid heating of NBS28 and NCSU-Q quartz in the pure gold sample holder by a defocused beam also produced lower than expected values. However, Achala and Rose quartz, UWG-2 garnet, and San Carlos olivine gave results that agreed with conventionally accepted values. The offsets from the laser-based to the accepted values were not always consistent from one standard to another, irrespective of heating rate. Gold silicide was identified on the surface of the pure gold sample holder by X-ray diffraction analysis. The presence of oxygen with silicon indicated simultaneous release from the silicate and incorporation in the silicide during laser fluorination.; An empty nickel reaction vessel previously acid etched and exposed to atmospheric oxygen, released large aliquots of gas extremely depleted in 18O (−8, −30, and −27‰), when fluorinated and heated externally to ∼100°C. Continued fluorination and heating at >600°C for 5hrs released a much smaller amount of oxygen enriched in 18O (+12‰).; The experiments performed as part of this study indicate that metal surfaces may serve as hosts for oxygen, and that strong oxygen isotopic fractionation may accompany oxygen release and exchange. The importance of metal substrates in oxygen isotopic fractionation was highlighted by the replacement of the stainless steel chamber by a nonmetallic one made of chlorotrifluoroethylene. NBS28 quartz gave results that nearly coincided with the standard value of +9.6‰ on three separate occasions, averaging +9.5‰ (n = 7). |
