Wilhelm van Bronswijk

Experimental hydrothermal alteration of partially metamict zircon

Abstract We present the results of a series of hydrothermal experiments on grains from two partially metamict zircon samples from Sri Lanka in the temperature range 350 to 650 °C and with different solutions (2 M AlCl3, 2 M CaCl2, pure H2O, and a multi-cation solution). Under these conditions, sharply bounded reaction fronts penetrated into the zircon grains and developed complex lobate and rim structures that resemble structures found in natural zircon systems. The reaction zones are characterized by a marked increase in the cathodoluminescence intensity, a decrease of the back-scattered electron emission, and an increased degree of structural order, as revealed by micro-Raman and infrared spectroscopy. Sensitive high-resolution ion microprobe and electron microprobe measurements revealed that the altered areas gained solvent cations (e.g., Ca2+, Ba2+, Mg2+, Al3+) from the solution and lost variable amounts of Zr, Si, Hf, the REE, U, Th as well as radiogenic Pb. A comparison between “dry” and “hydrothermal” annealing trends shows that the kinetics of structural recovery, including recrystallization of the amorphous phase in metamict zircon, is strongly enhanced under hydrothermal conditions. This finding suggests that water “catalyzes” structural recovery processes in metamict zircon. We found that the structure of the reacted areas does not resemble that of crystalline zircon, i.e., is still characterized by a temperature-dependent degree of disorder, which would not be expected if the reaction is controlled by a coupled dissolution and re-precipitation process. Instead, the alteration process can be described best by a diffusion-reaction-recrystallization model. In this model, it is postulated that the diffusion of water into the metamict structure is the driving force for moving recrystallization fronts. We found that the rate and the extent of solid-state recrystallization of the amorphous phase is an important factor in determining the mobility of trace elements. This interpretation is indicated by the observation that trace elements, including U and Th, were preferentially lost during the reaction with a fluid at low temperatures, where recrystallization of the amorphous material was slow or not activated at all. The observed chemical alteration patterns are believed to reflect a competition between the kinetics of long-range diffusion and ion exchange and the kinetics of the short-range diffusion necessary for the recrystallization process.

Sulphur speciation of leached chalcopyrite surfaces as determined by X-ray photoelectron spectroscopy

Abstract A key factor in improving the bioleaching route for chalcopyrite processing is a better understanding of the surface speciation that exists under chemical leaching conditions that mimic the acid bioleach. The surface sulphur speciation of chalcopyrite under such conditions has been revisited using X-ray photoelectron spectroscopy (XPS). Objectives of the study were to resolve the issue of possible passivation candidates and to understand the relative roles of ferric and ferrous ions in the oxidative leaching process. Neither severely metal-deficient sulphides nor polysulphides were found to be major surface layer components during initial leaching. The primary surface species produced with an acid ferric leach is elemental sulphur. This is largely volatilisable and coats the underlying unleached sulphide mineral but not adjacent minor sulphate domains. It is important to distinguish between the loss of multilayer elemental sulphur and the loss of monolayer or submonolayer quantities of the same species, especially as it impacts on polysulphide identification. The second major leach product on the chalcopyrite surface is disulphide S 2 2− . Although the cation association of the S 2 2− is not known, evidence from the Cu 2p spectra discounts the formation of any CuS 2 type species. Both acidic ferric and ferrous leaches produced the elemental sulphur and disulphide surface, though the more aggressive ferric produced a greater quantity of elemental sulphur. Evidence for polysulphides with a chain length greater than 2 remains an open question. There is some evidence that such polysulphides might form with acidic ferrous leaching, but the prime candidate for any initial leaching inhibition (prior to jarosite formation) is elemental sulphur.

Kinetics of thermal recovery and recrystallization of partially metamict zircon: a Raman spectroscopic study

Isothermal annealing of two partially metamict zircon from Sri Lanka were carried out at 870 K, 968 K, 1071 K, and 1166 K for 0.5 min up to ∼; 210 hours. Raman spectroscopy was used to monitor the amorphous-to-crystalline transformation. The evolution of the phonon frequency and the linewidth of the v 3 Si-O stretching band in zircon with annealing time clearly shows two recovery stages within the temperature and time ranges of the experiments. Both annealing stages form distinct linear segments in the frequency vs . linewidth plot, which are clearly separated from the trend defined by untreated metamict zircons. The first stage is characterized by the recovery of the short-range order, i.e . by the recovery of pre-existing, disordered crystalline domains as indicated by a fast recovery rate of the phonon frequency at the beginning of the transformation. This process dominates at temperature below ∼; 1000 K. In the case of the less metamict zircon, first stage recovery was activated after significant incubation periods, which follow an Arrhenius relationship. The second stage involves epitaxial recrystallization, which is activated within the first few minutes at temperatures > 1000 K ( e.g ., after ∼ 1–2 min at 1166 K). At this stage, the decrease of the linewidth is most probably related to the relaxation of phonon confinement associated with the growth of crystalline domains. We have estimated empirical activation energies of E A = 2.24 ± 0.04 eV and E A = 2.6 ± 0.2 eV for the first stage from the isothermal frequency and linewidth transformation curves. These activation energies are most likely related to recombination of point defects in the crystalline domains of partially metamict zircon. A single activation energy of E A = 3.8 ± 0.4 eV was obtained for epitaxial recrystallization by assuming Johnson-Mehl-Avrami growth kinetics as a first approximation. We suggest that a comparison of frequency versus linewidth relationships observed for natural zircons with experimental trends provides a potential means for recognizing an annealing history of natural zircons, provided that post-annealing radiation damage did not completely obscure the annealing effect.

Molecular modeling of water adsorption on hematite

This paper describes the results of modeling the surface hydration configurations formed when different planes of the hematite crystal were exposed to water using empirically derived potentials able to replicate the hematite, goethite and lepidocrocite structures to within 2% of their measured values. The planes chosen were the {111}, {011} and {210} planes expressed in rhombohedral coordinates. It was found that of all the surfaces studied there was a preference for hydration on the O-terminated basal {111} plane. This plane had the lowest hydrated surface energy and it was also the most stabilised by reaction with water. The Fe-terminated {111} plane was found to be unstable in the presence of excess water (67% coverage). The surface iron atoms relax away from the simulation cell to leave the O-terminated hydrated layer behind. Chemisorption may be energetically feasible at low surface coverages (<67% coverage). The {011} plane of hematite showed a preference for 100% water coverage (full coordination of the surface iron atoms). The surface energy of adsorbing water on this plane was lower than for the {210} plane particularly at high water coverages. The {210} plane was not stabilised by reaction with water at any coverage. The surfaces underwent relaxations depending on the water coverage. Large relaxations were observed at lower coverages for the {011} plane while the largest relaxations were observed at higher coverages on the {210} plane.

Intracrystalline Proteins and Urolithiasis: A Synchrotron X‐ray Diffraction Study of Calcium Oxalate Monohydrate

The existence of intracrystalline proteins and amino acids in calcium oxalate monohydrate was demonstrated by X‐ray synchrotron diffraction studies. Their presence has implications for the destruction of calcium oxalate crystals formed in the urinary tract and the prevention of kidney stones.

In situ Raman spectroscopic studies of the teeth of the chiton Acanthopleura hirtosa

Abstract In situ Raman spectroscopy, in combination with energy dispersive spectroscopy, has been used for the first time to determine the identities and locations, at the micron level, of mineral phases present in single chiton teeth that have been extensively mineralized. At the later stages of development the major lateral teeth of the chiton Acanthopleura hirtosa show characteristic spectroscopic evidence for the presence of lepidocrocite (γ-FeOOH), magnetite (Fe3O4), and an apatitic calcium phosphate. Goethite (α-FeOOH) and ferrihydrite (5 Fe2O3·9 H2O), which have been detected previously in teeth at the early stages of mineralization, were not detected in this mature tooth. The spatial distribution of these phases was determined, providing evidence for the presence of a discrete layer of lepidocrocite between the magnetite and apatite regions, illustrating the complexity of the biomineralization process. The technique of laser Raman microscopy is shown to be ideal for the examination of small biomineralized structures in situ, such as chiton teeth.

The importance of a clean face: the effect of different washing procedures on the association of Tamm–Horsfall glycoprotein and other urinary proteins with calcium oxalate crystals

This study was undertaken to determine whether the use of different washing procedures could explain dissident findings in published studies examining the role of urinary macromolecules in urolithiasis. Calcium oxalate monohydrate (COM) crystals were deposited from or added to the same sieved urine, washed with copious or limited amounts of distilled water, or with methanol, and examined by field emission scanning electron microscopy (FESEM). Demineralized extracts were analysed by SDS-PAGE and Western blotting for Tamm–Horsfall glycoprotein (THG), human serum albumin (HSA), osteopontin (OPN) and prothrombin fragment 1 (PTF1). Synchrotron X-ray diffraction (SXRD) with Rietveld whole-pattern peak fitting and profile analysis was used to determine non-uniform crystal strain and crystallite size in crystals generated from inorganic solutions in the presence of increasing concentrations of THG and prothrombin (PT). HSA and PTF1 were present in all demineralized crystal extracts, confirming their inclusion within COM. OPN was present in all extracts except those derived from pure inorganic COM crystals, because of its occlusion within small numbers of calcium oxalate dihydrate (COD) crystals contaminating the COM population. THG was absent from the demineralized extracts of all crystals washed copiously with water, but present in those washed with methanol or limited amounts of water. FESEM showed extraneous organic material associated only with crystals whose extracts contained THG, confirming that the protein does not bind permanently to the COM crystal surface and is not occluded within the mineral bulk. This was confirmed by SXRD, which showed that non-uniform strain and crystallite size remained unaltered in crystals grown in the presence of increasing THG concentrations. However, non-uniform strain increased and crystallite size decreased with increasing PT concentrations, demonstrating unambiguously that PT is included in COM crystals. It was concluded that scrupulous care must be taken to ensure the complete removal of extraneous THG adventitiously associated with CaOx crystals in order to avoid inaccurate analysis of crystal matrix protein content and possible misinterpretation of experimental data.

Chemical fingerprinting of adhesive tapes by GCMS detection of petroleum hydrocarbon products.

Abstract:  Pressure‐sensitive adhesive tapes often represent key evidence of crimes such as assault, rape or homicide; thus, the development of analytical techniques able to contribute to a detailed characterization of these materials is of forensic importance. The gas chromatography‐mass spectrometry (GCMS) analysis of the solvent extractable fractions of a suite of electrical and gaffer adhesive tapes spanning a range of colors and manufacturers identified a number of petroleum‐derived hydrocarbons. Molecular and isotopic analyses of hydrocarbon constituents of complex materials have found wide analytical utility including the forensic investigation of oil spills and arson. Here, we investigate the utility of these techniques for characterizing the hydrocarbon composition of pressure‐sensitive adhesive tapes for forensic correlation purposes. Subtle distinction of tape samples was evident in the GCMS distribution of several hydrocarbon groups including alkyl‐naphthalenes, hopane and sterane biomarkers. Linear discriminant analysis of the abundances of these products provided high level differentiation of tape manufacturer. The distinction of different adhesive tape samples was further extended by measurement of their stable carbon isotopic values. The molecular and isotopic differences of the petroleum content of tapes are consistent with the use of different petroleum materials used in the manufacturing process and demonstrate the benefits of the combined use of complementary oil hydrocarbon characterization approaches. This study reveals the forensic potential of using established petroleum characterization methods for characterizing materials with a petroleum‐derived hydrocarbon element.

A new biomineral identified in the cores of teeth from the chiton Plaxiphora albida

The hydrated iron(III) oxide limonite is reported for the first time as a biomineral. In situ laser Raman spectra of the tooth cores from major lateral teeth of the chiton Plaxiphora albida are compared with those of synthetic and mineral iron phosphates and iron oxides. Raman spectra measured on iron phosphate and iron oxide standard materials are shown to be easily distinguishable from one another. The central tooth cores of mature P. albida teeth do not show any evidence for the presence of a separate iron phosphate mineral. Rather, in each tooth a narrow band of the hydrated iron(III) oxide limonite is shown to separate the magnetite of the tooth surface from a central core region comprising both lepidocrocite and limonite. The high concentration of phosphorus in P. albida tooth cores, previously observed by energy dispersive spectroscopy, is not associated with a separate iron phosphate mineral, indicating that this element may be adsorbed onto the surface of the iron oxide minerals present. The failure to detect a separate iron(III) phosphate is discussed with reference to other chiton species that display high levels of iron and phosphorus in the cores of their mature major lateral teeth.

Rapid characterisation and classification of automotive clear coats by attenuated total reflectance infrared spectroscopy

Attenuated total reflectance infrared spectroscopy was employed to characterise the clear coats from a collection of automotive paint samples representing 130 vehicles, encompassing a range of Australian and international vehicle manufacturers. Principal component analysis revealed nine distinct classes, which were associated with the country of vehicle manufacture. Further statistical analysis identified variations in the samples from Australian and Japanese vehicles, which ultimately provided information regarding the manufacturer. Linear discriminant analysis gave excellent differentiation between the classes, with 100% of the calibration and test set samples being correctly classified. This ability to rapidly provide information concerning the vehicle origin and manufacturer will facilitate the procuring of investigative leads from questioned paint samples located at crime scenes. Although presented here in an Australian context, the strategy employed is universal and by extension could be utilised in other jurisdictions if they were to generate statistically significant data sets.