Thermal expansion of troilite and pyrrhotite determined by in situ cooling (873 to 373 K) neutron powder diffraction measurements

The thermal expansion coefficients for natural troilite, FeS, Ni-rich pyrrhotite, Fe0.84Ni0.11S, and Ni-poor pyrrhotite, Fe0.87Ni0.02S, were measured during cooling by in situ neutron powder diffraction over the temperature range 873–373 K. Between 873 and 573 K, the mean thermal expansion coefficients for the three compositions are 7.4(3) × 10-5 {FeS}, 8.0(4) × 10-5 {Fe0.84Ni0.11S} and 8.5(4) × 10-5 K–1 {Fe0.87Ni0.02S}. Below 573 down to 373 K, the first two increase considerably to 14.1(7) × 10-5 {FeS} and 9.3(5) × 10-5 {Fe0.84Ni0.11S} while the latter sample shows no significant variation, 8.4(5) × 10-5 K-1. Below 573 K, the thermal expansion is highly anisotropic, with Deltaa/100 K-1 ranging from 0.89(9)% {FeS} to 0.48(12)% {Fe0.87Ni0.02S} while Deltac/100 K-1 ranges from -0.39(11)% {FeS} to -0.13(2)% {Fe0.87Ni0.02S}. Upon cooling through 573 K, troilite and pyrrhotite undergo a transition where the FeS6 octahedra distort and in the case of pyrrhotite, cation-vacancy clustering occurs. The thermal expansion coefficients are bigger for low cation-vacancy concentrations and decrease as the pyrrhotites become less stoichiometric. This indicates that the thermal expansion in these minerals is damped by vacancy ordering or clustering. The thermal expansion coefficients for troilite and pyrrhotite are amongst the largest reported for sulphide minerals and their role in the formation of ore textures is discussed briefly

Ruthenium polypyridyl complexes and their modes of interaction with DNA : is there a correlation between these interactions and the antitumor activity of the compounds?

Various interaction modes between a group of six ruthenium polypyridyl complexes and DNA have been studied using a number of spectroscopic techniques. Five mononuclear species were selected with formula [Ru(tpy) L1L2](2-n)?, and one closely related dinuclear cation of formula [{Ru(apy)(tpy)}2{l-H2N(CH2)6NH2}]4?. The ligand tpy is 2,20:60,200-terpyridine and the ligand L1 is a bidentate ligand, namely, apy (2,20-azobispyridine), 2-phenylazopyridine, or 2-phenylpyridinylmethylene amine. The ligand L2 is a labile monodentate ligand, being Cl-, H2O, or CH3CN. All six species containing a labile L2 were found to be able to coordinate to the DNA model base 9-ethylguanine by 1H NMR and mass spectrometry. The dinuclear cationic species, which has no positions available for coordination to a DNA base, was studied for comparison purposes. The interactions between a selection of four representative complexes and calf-thymus DNA were studied by circular and linear dichroism. To explore a possible relation between DNA-binding ability and toxicity, all compounds were screened for anticancer activity in a variety of cancer cell lines, showing in some cases an activity which is comparable to that of cisplatin. Comparison of the details of the compound structures, their DNA binding, and their toxicity allows the exploration of structure–activity relationships that might be used to guide optimization of the activity of agents of this class of compounds

Orientational Effects and Random Mixing in 1‑Alkanol + Nitrile Mixtures

1-Alkanol + alkanenitrile or + benzonitrile systems have been investigated by means of the molar excess functionsenthalpies (Hm E ), isobaric heat capacities (Cp,m E ), volumes (Vm E ), and entropiesand using the Flory model and the concentration−concentration structure factor (SCC(0)) formalism. From the analysis of the experimental data available in the literature, it is concluded that interactions are mainly of dipolar type. In addition, large Hm E values contrast with rather low Vm E values, indicating the existence of strong structural effects. Hm E measurements have been used to evaluate the enthalpy of the hydroxyl−nitrile interactions (ΔHOH−CN). They are stronger in methanol systems and become weaker when the alcohol size increases. In solutions with a given short chain 1-alkanol (up to 1-butanol), the replacement of ethanenitrile by butanenitrile weakens the mentioned interactions. Application of the Flory model shows that orientational effects exist in methanol or 1- nonanol, or 1-decanol + ethanenitrile mixtures. In the former solution, this is due to the existence of interactions between unlike molecules. For mixtures including 1-nonanol or 1-decanol, the systems at 298.15 K are close to their UCST (upper critical solution temperature), and interactions between like molecules are dominant. Orientational effects also are encountered in methanol or ethanol + butanenitrile mixtures because self-association of the alcohol plays a more important role. Aromaticity effect seems to enhance orientational effects. For the remainder of the systems under consideration, the random mixing hypothesis is attained to a rather large extent. Results from the application of the SCC(0) formalism show that homocoordination is the dominant trend in the investigated solutions, and are consistent with those obtained from the Flory model

Genetic implications of pyrite chemistry from the Palaeoproterozoic Olary Domain and overlying Neoproterozoic Adelaidean sequences, northeastern South Australia

Copyright © 2004 Elsevier B.V. All rights reserved.Chris Clark, Ben Grguric and Andreas Schmidt Mummhttp://www.elsevier.com/wps/find/journaldescription.cws_home/503354/description#descriptio

Woodallite, a new chromium analogue of iowaite from the Mount Keith nickel deposit, Western Australia

AbstractWoodallite is a new Cr-rich member of the hydrotalcite group from the large, low-grade Mount Keith nickel deposit, in the northeastern Goldfields district of Western Australia. Woodallite occurs as whorls and clusters of minute platelets up to 6 mm across in lizardite+brucite-altered dunite. Individual platelets are typically 10–100 µm in maximum dimension and are often curved. Associated minerals include chromite, lizardite, iowaite, pentlandite, magnetite, tochilinite and brucite. Electron microprobe analysis gave: Mg 25.90 wt.%; Cr 10.81; Fe 4.86; Al 0.68; Cl 9.89; S 0.03; Si 0.01; Ni 0.01; Na 0.01, yielding (after correction for loss of volatiles) an empirical formula of Mg6.19(Cr1.21Fe0.51Al0.15)∑1.87(OH)16[Cl1.62(CO3)0.17(SO4)0.01]·4H2O, by analogy with the hydrotalcite group. The simplified formula is Mg6Cr2(OH)16Cl2·4H2O. Combined thermogravimetric analysis and mass spectroscopy showed a two-stage weight loss of 12.7% and 27.3% occurring over the ranges 25–300°C and 300–660°C, respectively. The first weight loss is attributed to loss of interlayer water, chlorine-bearing species (e.g. HCl) and some CO2, the second to loss of hydroxide water, remaining CO2 and Cl species. The mineral is deep magenta to purple in colour, transparent, with a resinous to waxy lustre, and a perfect basal {0001} cleavage. Woodallite has a Mohs hardness of 1.5–2, and a pale-pink to white streak. The strongest lines in the X-ray powder pattern are [dobs (Iobs) (hkl)] 8.037 (100) (003); 4.021 (48) (006); 2.679 (1) (009); 2.624 (3) (012); 2.349 (5) (015); 2.007 (6) (0,0,12); 1.698 (2) (0,1,11); 1.524 (2) (23). These lines were indexed on a hexagonal cell with a = 3.103(2), c = 24.111(24)Å, V = 201.14 Å3 and Z = 3/8. The new mineral is isostructural with the hydrotalcite group and has space group Rm. The measured density is 2.062 gm/cm3. Woodallite is uniaxial negative with ω = 1.555 and ε = 1.535 (white light); pleochroism is distinct from violet to pinkish lilac. Woodallite forms as a result of hydrothermal alteration of primary magmatic chromite by Clrich solutions at temperatures <320°C. Relict chromite fragments are frequently present in the whorls, and associated magnetite is altered extensively to iowaite. The mineral is named after Roy Woodall, eminent Australian industry geologist.B. A. Grguric, I. C. Madsen, A. Prin

A kinetic study of the exsolution of pentlandite (Ni,Fe)9S8 from the monosulfide solid solution (Fe,Ni)S

The kinetics of the exsolution of pentlandite from the monosulfide solid solution (mss) have been investigated using a series of anneal/quench and in situ cooling neutron diffraction experiments. Five mss compositions were examined by anneal/quench techniques covering the composition range Fe0.9Ni0.1S to Fe0.65Ni0.35S and using annealing temperatures between 423 and 773 K for periods from 1 h to 5 months. In situ cooling experiments were performed on four mss compositions in the range Fe0.9Ni0.1S to Fe0.7Ni0.3S. The samples of these solid solutions were heated to 973 K. and then cooled to 373 K in steps of 50 K over a 24 h period. The extent of exsolution was monitored by Rietveld phase analysis using powder neutron diffraction data. The anneal/quench experiments established that initial exsolution of pentlandite from mss above 573 K is very rapid and is effectively complete within 1 h of annealing. However, the mss/pyrrhotite compositions remained Ni rich (17 at% Ni) after 5 months annealing, indicating that compositional readjustment at low-temperatures occurs over long periods. Below 573 K, exsolution is less rapid with rate constants in the range 6 × 10-6 to 1 × 10-5/s and the activation energy for exsolution of pentlandite from mss Fe0.8Ni0.2S between 473 and 423 K is 5 kJ/mol. The in situ cooling experiments showed that the temperature at which exsolution commences upon cooling decreases from 873 K for Fe0.7Ni0.3S to 823 K for Fe0.9Ni0.1S and that exsolution effectively ceased on the time scale of the experiments at temperatures between 598 and 548 K. The kinetic data were analyzed using the Avrami model where y = 1 - exp(-kntn) and the initial rates of exsolution were found to increase with Ni content from 2 × 10-6/s for Fe0.9Ni0.1S to 4 × 10-5/s for Fe0.7Ni0.3S. Both high Ni content and high M:S ratio served to facilitate nucleation rate, indicating that nucleation occurs at S vacancies within mss crystals rather than at grain boundaries. Values of the Avrami geometric constant n vary during exsolution upon cooling indicating three possible changes in the growth mechanism during the reaction. The roles of impurities and S fugacity on reaction rates are discussed. The rate constants for exsolution of pentlandite from mss/pyrrhotite in nature are estimated to be 4 or 5 orders of magnitude slower than those reported here, still very rapid on a geological time scale. High metal mobility persists in this system at low temperatures, even at room temperature, and the textures and compositions observed in nature are a consequence of very low-temperature (<100 °C) equilibration of assemblages over geological time scales

The transformation of pentlandite to violarite under mild hydrothermal conditions: a dissolution-reprecipitation reaction

Allan Pring, Christophe Tenailleau, Barbara Etschmann, Joel Brugger & Ben Grguri