Search results for "MINERALOGY"
showing 10 items of 1516 documents
Solidification kinetics of hard-sphere colloidal suspensions
2007
We investigate the solidification dynamics of hard-sphere colloidal suspensions applying simultaneously small-angle and Bragg light scattering. These experiments allow a consistent picture of nucleation and crystal growth on the level of large-scale density fluctuations and of density fluctuations on the level of individual crystallites. We observe a temporally almost constant nucleation rate after an induction time that decreases with supersaturation. The classical expectation for the nucleation rate density as a function of supersaturation is in accordance with our data. We investigate the validity of the Wilson—Frenkel growth law for hard-sphere systems, which also fits our data satisfac…
NC-AFM contrast formation on the calcite ($10\bar {1}4$) surface
2012
Calcite, the most stable polymorph of calcium carbonate, is one of the most abundant simple salts in the geological environment. Consequently, its natural cleavage plane has been studied extensively by a wide range of surface-sensitive techniques, giving indications for two reconstructions, namely a (2 × 1) and a so-called ‘row-pairing’ reconstruction. The existence of the (2 × 1) reconstruction has been discussed controversially in the literature, but is now confirmed as a true surface property. In contrast, a comprehensive discussion on the existence of the row-pairing reconstruction is lacking so far.Here, we present a non-contact atomic force microscopy (NC-AFM) study of the calcite s…
Atomistic simulation of SrTiO3 and BaTiO3 (110) surface relaxations
2000
Abstract The (110) surface relaxations were calculated for SrTiO 3 and BaTiO 3 perovskites in a cubic phase. Using a shell model, the positions of atoms in 16 near- surface layers placed atop a slab of rigid ions are calculated. The strong surface rumpling and induced surface dipole moments perpendicular to the surface are predicted for both the O-terminated and TiO-terminated surfaces.
Unravelling the atomic structure of cross-linked (1 × 2) TiO2(110).
2010
The cross-linked (1 × 2) reconstruction of TiO(2)(110) is a frequently observed phase reflecting the surface structure of titania in a significantly reduced state. Here we resolve the atomic scale structure of the cross-linked (1 × 2) phase with dynamic scanning force microscopy operated in the non-contact mode (NC-AFM). From an analysis of the atomic-scale contrast patterns of the titanium and oxygen sub-structures obtained by imaging the surface with AFM tips having different tip apex termination, we infer the hitherto most accurate model of the atomic structure of the cross-linked (1 × 2) phase. Our findings suggest that the reconstruction is based on added rows in [001] direction built …
Method of Discrimination of Surface Fractality
1993
Abstract A simple method for the discrimination of surface fractality is proposed. This method is based on the comparison of the nitrogen adsorption isotherm on a given sample with the "standard" isotherm on a smooth surface. The proposed comparative method makes it possible to determine the lower limit of the scale range of surface fractality. A thermodynamic method is recommended as a complement to fractal analysis in the scale range of about 10-1000 A. The results of the investigation of surface roughness are presented with examples of typical samples of silica gels, porous glasses, apatite, and coal.
Application of fractal geometry to dissolution kinetic study of a sweetener excipient
2001
Abstract In the context of relationship study between dissolution kinetic and particle morphology using the fractal geometry tool, we use a commercially available quality of saccharin powder. The characterization of molecular feature and image analysis study allows us to conclude to the statistic self-similarity of particles of four sieved particles size fractions, permitting the fractal approach. Calculation of reactive fractal dimension is performed using two forms of mass transfer equation: −d Q /d t = kQ D R /3 Δ C and −d Q /d t = k′R D R −3 Δ C , with Δ C ={ C f /[ln C s /( C s − C f )]}. Based on comparison of the surface fractal dimension D S on the two values of reactive fractal di…
Surface and volume non-invasive methods for the structural monitoring of the bass-relief ‘Madonna con Bambino’ (Gorizia, Northern Italy)
2016
Structural analysis of marble statues, carried out by non-invasive and in situ methods, is crucial to define the state of conservation of the artworks and to identify the deterioration phenomena that can affect them. In this work, we combined in situ non-destructive techniques, ultrasonic tomography (US), ultraviolet-induced visible fluorescence (UV-IF) and X-ray fluorescence (XRF) to study the bass-relief ‘Madonna con Bambino’ (Gorizia, Italy). The US revealed the presence of some metallic pivots, associated with areas of high sound velocity; moreover, a more degraded area has been identified in the lower part of the bass-relief. The acquired UV-IF image confirmed the presence of surface d…
Mechanical properties and accommodation processes on metallic interfaces
1998
Bimetallic joints Al/Pb, Al/Sn, Pb/Sn, Pb/Pb, etc. with clean interfaces, obtained by a special cold welding method, are used as a model of phase boundaries for investigation of accommodation processes and strength properties of interfaces. To reduce the volume diffusion-induced relaxation processes, investigations were carried out at relatively low temperatures 0.1-0.5 T m . The role of surface diffusion and the effect of phase boundary energy on the healing of micropore ensembles on interfaces was investigated. The accommodation processes on the phase boundaries are considered as a result of mechanoactivation of both the interaction and structure formation of such non-equilibrium systems.…
Effects of organic aerosol constituents on extinction and absorption coefficients and liquid water contents of fogs and clouds
1978
We have speculated on the influence of organic material on extinction and absorption coefficients and liquid water content of fogs and of clouds immediately after their condensational stage. It results therefore, that the reduction of the speed of growth from fog to cloud droplets due to the presence of organic films largely reduces the properties mentioned. Compared to that their increase coming from the surface tension reduction due to organic material being dissolved or building up films is expected to be less effective.
Assessment of particle suspension conditions in stirred vessels by means of pressure gauge technique
2002
In this work the quantitative assessment of the mass of suspended solid particles in stirred vessels is performed using the Pressure Gauge Technique. This is based on the measurements of the pressure increase on the tank bottom due to the presence of suspended solid particles at any agitation speed. The method has the advantages of not utilising visual observations and of easy and inexpensive application to both laboratory and industrial equipment. Very few data are available in literature and the experimental results collected using the present PGT technique and the correlations here proposed are of considerable academic and industrial interest.