Search results for "engineering.material"
showing 10 items of 2352 documents
An integrated view of the chemistry and mineralogy of martian soils
2005
The mineralogical and elemental compositions of the martian soil are indicators of chemical and physical weathering processes. Using data from the Mars Exploration Rovers, we show that bright dust deposits on opposite sides of the planet are part of a global unit and not dominated by the composition of local rocks. Dark soil deposits at both sites have similar basaltic mineralogies, and could reflect either a global component or the general similarity in the compositions of the rocks from which they were derived. Increased levels of bromine are consistent with mobilization of soluble salts by thin films of liquid water, but the presence of olivine in analysed soil samples indicates that the…
Exploration of Victoria Crater by the Mars Rover Opportunity
2009
“Lake” Victoria? After having explored the Eagle and Endurance craters, which are separated by only 800 meters, the Mars Exploration Rover Opportunity spent 2 years at Victoria, a much larger impact crater located 6 kilometers south across Meridiani Planum. Sedimentary rocks previously analyzed at Eagle and Endurance point to local environmental conditions that included abundant liquid water in the ancient past. Now, an analysis of rocks in the walls of Victoria by Squyres et al. (p. 1058 ) reveals that the aqueous alteration processes that operated at Eagle and Endurance also acted at Victoria. In addition, sedimentary layering in the crater walls preserves evidence of ancient windblown du…
Iron mineralogy and aqueous alteration on Mars from the MER Mössbauer spectrometers
2008
The twin Mars Exploration Rovers Spirit (Gusev crater) and Opportunity (Meridiani Planum) used MIMOS II Moessbauer spectrometers to analyze martian surface materials in the first application of extraterrestrial Moessbauer spectroscopy. The instruments acquired spectra that identified the speciation of Fe according to oxidation state, coordination state, and mineralogical composition and provided quantitative information about the distribution of Fe among oxidation states, coordination states, and Fe-bearing phases. A total of 12 unique Fe-bearing phases were identified: Fe(2+) in olivine, pyroxene, and ilmenite; Fe(2+) and Fe(3+) in magnetite and chromite; Fe(3+) in nanophase ferric oxide (…
Wetting of polymer liquids: Monte Carlo simulations and self-consistent field calculations
2003
Using Monte Carlo simulations and self-consistent field (SCF) theory we study the surface and interface properties of a coarse grained off-lattice model. In the simulations we employ the grand canonical ensemble together with a reweighting scheme in order to measure surface and interface free energies and discuss various methods for accurately locating the wetting transition. In the SCF theory, we use a partial enumeration scheme to incorporate single-chain properties on all length scales and use a weighted density functional for the excess free energy. The results of various forms of the density functional are compared quantitatively to the simulation results. For the theory to be accurate…
Forming Processes Design Oriented to Prevent Ductile Fractures
1996
During cold forming processes ductile fractures are sometimes encountered, depending on the operating parameters and on the material properties and determining the production of defective components to be discarded; for this reason the development of a general approach for the prediction of this type of defects is particularly suitable and this aim has been pursued by a large number of researchers in the last two decades. In the paper the most important and diffused models are described and analysed in order to outline the advantages offered by each of them. Some applications to typical metal forming processes are presented, carrying out a comparison between the numerical predictions and th…
Ten Facets, One Force Field: The GAL19 Force Field for Water - Noble Metal Interfaces
2020
<div>Understanding the structure of the water/metal interfaces plays an important role in many are as ranging from surface chemistry to environmental processes. Due to their intrinsic complexity, the water/metal interfaces cannot yet be adequately described by quantum mechanical approaches and accurate force-fields are therefore needed. We develop and parametrize GAL19, a novel force-field to describe the interaction of water with two facets (111 and 100) of five metals (Pt, Pd, Au, Ag, Cu). To increase transferability compared to its predecessor GAL17, the water-metal interaction is described as a sum of pair-wise terms. The interaction energy has three contributions: (i) physisorption …
A Review of using spray pyrolysis through Sol-gel materials in the synthesis of cathode materials for lithium-ion batteries
2016
Over the years, new synthesis routes of the cathode electrochemical active material for lithium-ion batteries have improved remarkably to optimize their capacity and cycle life performance. This review study focused on the use of some techniques to synthesize the common cathode materials (LiCoO2, LiMn2O4, LiFePO4). The most common and simplest synthesis method was the mixing of powders in their solid-state form and heating them at relatively high temperatures over long periods. Other methods included the formation of sol-gel products that could be either heat-treated more or could be used directly by means of a spray pyrolysis method producing the desired active material. The spray pyrolysi…
Thermal decomposition of chromite spinel with chlorite admixture
2008
Abstract The behaviour of minerals in a South African chromite ore during the increasing of the temperature has been studied. Firstly, the changes produced during the ignition process have been examined by means of thermal and differential analysis (TGA–DTA) until 1200 °C. The characterization of the initial mineral and those obtained after heating at several temperatures in room atmosphere has been performed by X-ray diffraction (XRD). Moreover, voltammetric analyses have allowed to determine the variation of the iron oxidation degree in the studied materials. Light microscopy was applied to find more information about the different phases by their colour. During the heating, a wide range …
Clockwise, low- metamorphism of the Aus granulite terrain, southern Namibia, during the Mesoproterozoic Namaqua Orogeny
2013
Abstract The Aus granulite terrain forms part of the Mesoproterozoic Namaqua Metamorphic Complex (NMC) of southern Africa. The terrain consists of pre- to syn-tectonic granitoid gneisses containing subordinate aluminous metasediments, metapsammites, mafic granulite and calc-silicate, all of which have been metamorphosed and migmatised to varying degrees. Pseudosection modelling of garnet–sillimanite–cordierite–biotite aluminous metapelitic samples constrain peak metamorphic conditions at 5.5 kbar and 825 ° C. Pseudomorphs of sillimanite after andalusite constrain early prograde conditions of ∼ 550–600 ° C at below 4 kbar, whereas the replacement of sillimanite by garnet–cordierite and sub…
Exhumation of the lower crust during crustal shortening: an Alice Springs (380 Ma) age for a prograde amphibolite facies shear zone in the Strangways…
2000
Foliated garnet-bearing amphibolites occur within the West Bore Shear Zone, cutting through granulite facies gneisses of the Strangways Metamorphic Complex. In the amphibolites, large euhedral garnet (up to 3 cm) occurs within fine-grained recrystallized leucocratic diffusion haloes of plagioclase–quartz. The garnet and their haloes include a well-developed vertical foliation, also present in the matrix. This foliation is the same as that cutting through the unconformably overlying Neoproterozoic Heavitree Quartzite. The textures indicate syn- to late kinematic growth of the amphibolite facies mineral assemblages. All mineral assemblages record an arrested prograde reaction history. Notewor…