Refinement of iron ore sinter phases: a silico-ferrite of calcium and aluminium (SFCA) and an Al-free SFC,and the effect on phase quantification by X-ray diffraction     

David C. Liles  Johan P. R. de Villiers  Volker Kahlenberg 《Mineralogy and Petrology》2016,110(1):141-147

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V oxidation state in Fe–Ti oxides by high-energy resolution fluorescence-detected X-ray absorption spectroscopy     

Amélie Bordage  Etienne Balan  Johan P. R. de Villiers  Robert Cromarty  Amélie Juhin  Claire Carvallo  Georges Calas  P. V. Sunder Raju  Pieter Glatzel 《Physics and Chemistry of Minerals》2011,38(6):449-458

The oxidation state of vanadium in natural and synthetic Fe–Ti oxides is determined using high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS). Eleven natural magnetite-bearing samples from a borehole of the Main Magnetite Layer of the Bushveld Complex (South Africa), five synthetic Fe oxide samples, and three natural hematite-bearing samples from Dharwar supergroup (India) are investigated. V K edge spectra were recorded on the ID26 beamline at the European Synchrotron Radiation Facility (Grenoble, France), and the pre-edge features were used to determine the local environment and oxidation state of vanadium. In the case of the magnetite samples (natural and synthetic), we show that vanadium is incorporated in the octahedral site of the spinel structure under two oxidation states: +III and +IV. The variations of the pre-edge area are interpreted as various proportions in V³⁺ and V⁴⁺ (between 9.5 and 16.3% of V⁴⁺), V³⁺ being the main oxidation state. In particular, the variations of the V⁴⁺/V³⁺ ratio along the profile of the Main Magnetite Layer seem to follow the crystallization sequence of the layer. In the case of the hematite samples from India, the pre-edge features indicate that vanadium is substituted to Fe and mainly incorporated as V⁴⁺ (between 40 and 72% of V⁴⁺). We also demonstrate the potentiality of HERFD-XAS for mineralogical studies, since it can filter out the unwanted fluorescence and give better resolved spectra than conventional XAS.  相似文献   

Numerical Simulations of Self-Gravitating Magnetized Disks     

S. Fromang  J.P de Villiers  S.A Balbus 《Astrophysics and Space Science》2004,292(1-4):439-444

We present the first global simulations of self-gravitating magnetized tori. The simulations are performed with Zeus-2D and GLOBAL. We find the magnetorotational instability (MRI) to behave similarly in a self-gravitating environment as in previous simulations of non self-gravitating systems: enhancement of turbulent angular momentum transport follows the linear phase. The torus quickly develops a two component structure composed of an inner thick disk in Keplerian rotation and an outer massive disk. We compare this result with zero mass global simulations in 2D, and also present preliminary results of 3D simulations.  相似文献   

The role of facilitation in seedling recruitment and survival patterns, in the Strandveld Succulent Karoo, South Africa     

A. J. De Villiers  M. W. Van Rooyen  G. K. Theron 《Journal of Arid Environments》2001,49(4):809

Several studies in arid ecosystems have demonstrated that seedling establishment and survival were greater underneath the canopies of shrubs than in the open spaces between shrubs. These results led to the formulation of the hypothesis that seedling recruitment and survival were dependent on the shelter provided by shrub species (nurse-plant hypothesis). Seedling emergence and survival beneath and between the canopies of selected perennial shrub species were investigated at five localities in the Strandveld Succulent Karoo, each dominated by a different shrub species. Seedling emergence and survival were also examined at three localities dominated by annual species. In general, species richness and seedling densities were significantly higher in open areas than underneath shrubs, while seedling survival percentages did not differ significantly between microsites. Therefore, no evidence could be found to support the hypothesis that seedling recruitment and survival were facilitated by the presence of shrub species. Although most species will be able to establish in the absence of shrubs, the presence of woody species may have other advantages when restoring vegetation in mined areas.  相似文献   

Ore dust pollution and body temperatures of intertidal animals     

T. Erasmus  A.F. De Villiers 《Marine pollution bulletin》1982,13(1):30-32

Intertidal animals were dusted with iron ore dust and, even after two full tidal cycles, when exposed to direct sunlight during low tide the treated animals heated faster, reached higher temperatures and cooled faster than controls. No short term mortalities were observed. Ore coating changes the colour of the animals and it would appear that colour is one of the important mechanisms controlling the heat budget. Ore dust pollution may therefore have a long-term effect on intertidal animals through its effect on their heat balance.  相似文献