The ‘Qin & Han Iron Smelting Site Investigation Project’ aims to illuminate the early use and production of iron during the Qin and Han Dynasties in south and south-west China. Here, the authors report on attempts to discover the origins of iron objects from the Lingnan region.

A series of uranium-containing gadolinium zirconate samples have been fabricated at 1723 K in air. X-ray diffraction and Raman spectroscopy have confirmed pyrochlore or defect fluorite structures, while diffuse reflectance, X-ray absorption near edge structure and X-ray photoelectron spectroscopies indicate a predominantly U6+ oxidation state, even when Ca2+ was added to charge balance for U4+. The results demonstrate the potential of gadolinium zirconates as host materials for actinides.

Hydrothermal treatment has been applied successfully to convert amorphous titania films to crystalline anatase at 120 °C, a temperature compatible with most polymeric substrates. The amorphous films were deposited at 80 °C using atomic layer deposition (ALD). The crystallinity of the films was monitored by x-ray absorption near edge structure (XANES), and the film composition was determined by x-ray photoelectron spectroscopy (XPS). The effect of precursor chemistry and substrate material was investigated. It was found that titania films produced from Ti isopropoxide are easier to crystallize than those from Ti tetrachloride as the Ti precursor. The amorphous to crystalline transformation can be achieved more readily with films deposited on Si than polycarbonate substrates. The effect of a “seed” layer on the amorphous to crystalline transformation was also studied. Preformed anatase crystallites between the Si substrate and the amorphous film were shown to accelerate the crystallization process. The possible mechanisms responsible for the phase transformation are discussed.

We have characterized thermally annealed perovskite (CaTiO3) surfaces, both before and after aqueous dissolution testing, using scanning electron microscopy, cross-sectional transmission electron microscopy, x-ray photoelectron spectroscopy, and atomic force microscopy. It was shown that mechanical damage caused by polishing was essentially removed at the CaTiO3 surface by subsequent annealing; such annealed samples were used to study the intrinsic dissolution behavior of perovskite in deionized water at RT, 90 °C, and 150 °C. Our results indicate that, although mechanical damage caused higher Ca release initially, it did not affect the long-term Ca dissolution rate. However, the removal of surface damage by annealing did lead to the subsequent spatial ordering of the alteration product, which was identified as anatase (TiO2) by both x-ray and electron diffraction, on CaTiO3 surfaces after dissolution testing at150 °C. The effect of Ca2+ in the leachant on the dissolution reaction of perovskite at 150 °C was also investigated, and the results suggest that under repository conditions, the release of Ca from perovskite is likely to be significantly slower if Ca2+ is present in ground water.

Epitaxial anatase TiO2 thin films were successfully grown on lattice-matched SrTiO3 (001) substrates by a novel hydrothermal method at very low temperatures (120–200 °C). This method is extremely simple and inexpensive in that the SrTiO3 substrate itself provides the source material for the TiO2 film. X-ray diffraction confirmed the high crystallinity and phase purity of the anatase films. The epitaxial relationship between the film and the substrate was determined as (001)[100]anatase // (001)[100]SrTiO3. Atomic force microscopy revealed the average size of the anatase crystallites as approximately 50 to 200 nm.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

We have studied the aqueous durability of pyrochlore-structured yttrium-titanate (Y2Ti2O7) and Nd/Al-bearing zirconolite [(Ca0.8Nd0.2)Zr(Ti1.8Al0.2)O7] in both neutral and acidic solutions, with and without the presence of 0.001 M of NaF. Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) were used to characterize the composition, structure and morphology of the pyrochlore (Y2Ti2O7) and zirconolite surfaces, both before and after static dissolution testing at 90 and 150°C for four weeks. The leachates were also analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to estimate the individual elemental releases. The results show that the presence of F- ions only has a significant effect in acidic media on the dissolution behavior of pyrochlore and zirconolite. This detrimental effect is more pronounced for pyrochlore than zirconolite; the Y2Ti2O7 surface was replaced completely by alteration products after dissolution testing at 150°C for 4 weeks in acidic media with 0.001 M fluoride ions.

Nd-bearing zirconolite was leached at 90°C for 6 months in 0.001M citric acid, and also in deionised water, to determine the effect of organic-bearing solutions on durability. The pH of the citric acid solution was adjusted to 5 using KOH, approximating that of the water in the parallel tests, to avoid the influence of pH on chemical durability of the zirconolite.

Releases were incongruent in the tests carried out in water. Release rates of Ti, Zr and Nd were comparatively very low (commonly too low to be measured) over the first 80 days of leaching. Rates for Ca and Al were 2 to 4 orders of magnitude higher than Ti, Zr and Nd over this same period. At about 80 days, there was an anomalous decrease in pH from 6 to 4 which enhanced release rates of Ti and Nd in particular. There was development of titania crystals, and the suggestion of hydrolysed titania, on the surface after 6 months. Thermodynamic equilibrium between the leachates and hydrolysed species on the surface of the zirconolite may be the key to apparent cessation of alteration, at least during thefirst 80 days of leaching.

By contrast, zirconolite leached in 0.001M citric acid maintained release rates of Ti, Zr and Nd 2 to 4 orders of magnitude greater than those in water for the first 80 days, values sustained, within an order of magnitude, for the remainder of the leach tests. Releases were congruent. The surface of the zirconolite showed no signs of secondary phase development. This suggests complexation by citrate ions prevented control by hydrolysed species on zirconolite solubility.

Polished tiles (7×7×2 mm3) of Nd-bearing zirconolite were fabricated and then some were irradiated on both large faces with 3 MeV or 2 MeV Au2+ ions (total fluence of ≥ 1 × 1015 ions/cm2) in order to render the zirconolite amorphous and so simulate displacement damage caused by alpha decay. Both the irradiated and non-irradiated tiles were then subjected to static dissolution tests in 0.01M nitric solution (pH2) at 90 C, for periods of 0–1, 1–7, 7–14 and 14–28 days. It was found that radiation damage did not affect the dissolution rate of zirconolite as indicated by the elemental leach rates of Nd, Ti, Ca and Al. The results of solution analyses are consistent with those obtained from X-ray Photoelectron Spectroscopy (XPS) in that the Ca, Nd, Ti and Al concentrations in the top surface layer (< 5 nm) all decreased with respect to that of Zr after dissolution testing, and the leached surface composition of the non-irradiated zirconolite is very similar to that of the two irradiated specimens. The implications of these results are discussed in the context of previous work.

Static dissolution tests on Nd-bearing zirconolite were conducted in deionized water at 150°C for up to 6 months. Surfaces, both before and after aqueous dissolutions, were examined using X-ray Photoelectron Spectroscopy (XPS) and Scanning Electron Microscopy (SEM). Individual submicron-sized crystals wereobserved only on some zirconolite grains after hydrothermal treatment for one week, and were identified as brookite (possibly plus anatase) by Transmission Electron Microscopy (TEM). The number of secondary crystals present on the zirconolite surface was, however, reduced significantly after 6 months of durability testing. The results of electron microscopy studies are consistent with those obtained from XPS in that the average Ca and Ti concentrations of the top surface layer (< 5 nm) decreased slightly with respect to Zr, while the average Al concentration increased after durability testing.