ToF-SIMS analysis of iron oxide particle oxidation by isotopic and multivariate analysis

A procedure for quantitative time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis of the re-oxidation thermally-reduced of iron oxide particles in a ceramic matrix is discussed. Iron oxide is reacted with yttria stabilized zirconia (YSZ) to create a composite that facilitates the high-temperature reduction of CO2 and H2O to produce CO and H-2 (syngas). The reactivity of this two-step solar-thermochemical process is being investigated by varying the concentration of iron in YSZ up to and past its solid solubility point, thus affecting the size of iron oxide particles in the matrix, and hence their rate and extent of re-oxidation. YSZ samples containing natural abundance iron oxide were mixed with an organic binder, isostatically pressed into a disc and calcined in air at 1450 degrees C. The discs (similar to 10mm diameter, 2mm thickness) were thermally reduced in inert gas at 1400 degrees C and then re-oxidized at 1100 degrees C in the presence of (CO2)-O-18. The ratio of O-18 to O-16 shows the extent of oxygen exchange for each iron oxide particle. ToF-SIMS data are acquired in a fashion that maximizes the ability to correct for detector saturation, thus providing quantitative oxygen isotopic results with little error. The data analysis method uses a combination of multivariate analysis for particle identification and conventional analysis for quantitative isotopic ratioing. The results indicate that large iron oxide particles are only poorly utilized, likely due to slow transport, as O-18 penetration into the particles is limited. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.