Анализ способов и устройств для уплотнения мелкофракционных шихт

Выполнен анализ способов уплотнения мелкофракционных сыпучих материалов. Предложена схема уплотнения на основе валковых прессов с многоступенчатым уплотнением

Characterizing the hydraulic properties of paper coating layer using FIB-SEM tomography and 3D pore-scale modeling

AbstractPaper used in the printing industry generally contains a relatively thin porous coating covering a thicker fibrous base layer. The three-dimensional pore structure of coatings has a major effect on fluid flow patterns inside the paper medium. Understanding and quantifying the flow properties of thin coating layers is hence crucial. Pore spaces within the coating have an average size of about 180nm. We used scanning electron microscopy combined with focused ion beam (FIB-SEM) to visualize the nano-scale pore structure of the paper coating layer. Post-processing of the FIB-SEM images allowed us to reconstruct the three-dimensional pore space of the coating. The 3D FIB-SEM images were analyzed in detail to obtain pore size distribution and porosity value. The permeability was estimated using the GeoDict software, based on solutions of the Stokes equation. By determining the porosity and permeability of increasingly larger domain sizes, we estimated the size of a representative elementary volume (REV) for the coating layer to be 60µm3, which is well within the volume analyzed using FIB-SEM. The estimated porosity and permeability of the REV domain were 0.34 and 0.09 mDarcy, respectively. Using the pore morphology method, capillary pressure-saturation (Pc-S) and relative permeability curves of the REV domain could be constructed next. The Pc-S curves showed that the coating had a high air entry suction, which is very favorable for printing in that ink will invade the coating as soon as it is applied to the coating. Our results are essential for macroscale modelling of ink penetration into a coating layer during inkjet printing. Macroscopic models can be valuable tools for optimization of the penetration depth and the spreading of ink on and within paper substrates

Electron-beam-induced deposition of platinum at low landing energies

Electron-beam-induced deposition of platinum from methylcyclopentadienyl-platinum-trimethyl was performed with a focused electron beam at low landing energies, down to 10?eV. The deposition growth rate is maximal at 140?eV, with the process being over ten times more efficient than at 20?kV. No significant dependence of composition with landing energy was found in the deposits performed at energies between 40 and 1000?eV. This study provides further evidence for the dissociation process being primarily driven by the sub-20-eV secondary electrons.IST/Imaging Science and TechnologyApplied Science

Intergrowth structure of zeolite crystals and pore orientation of individual subunits revealed by electron backscatter diffraction /focused ion beam experiments

Zeolites are of tremendous scientific and technological importance, since a number of processes in modern chemical industry, such as crude oil refining, rely on their unique combination of catalytic activity and shape selectivity.[1–3] Consequently, significant efforts have been directed at obtaining in-depth insight into the molecular processes taking place within zeolite pores during catalysis.[4–6] A popular strategy is to investigate large zeolite crystallites, which are well-defined, ordered, and reproducible and can be used as model systems for diffusion and catalysis studies.[7–15] However, this taskis complicated by the complex structure of zeolite crystals comprising several intergrown building blocks. The interfaces of these subunits may constitute diffusion boundaries due to potential mismatch in the alignment of the microporous network,[16] and this can render certain regions of the zeolite crystals inaccessible for reactant molecules and consequently affect the catalytic activity of the material.[8, 10, 17

Frictional properties and microstructure of calcite-rich fault gouges sheared at sub-seismic sliding velocities

We report an experimental and microstructural study of the frictional properties of simulated fault gouges prepared from natural limestone (96 % CaCO3) and pure calcite. Our experiments consisted of direct shear tests performed, under dry and wet conditions, at an effective normal stress of 50 MPa, at 18–150 °C and sliding velocities of 0.1–10 μm/s. Wet experiments used a pore water pressure of 10 MPa. Wet gouges typically showed a lower steady-state frictional strength (μ = 0.6) than dry gouges (μ = 0.7–0.8), particularly in the case of the pure calcite samples. All runs showed a transition from stable velocity strengthening to (potentially) unstable velocity weakening slip above 80–100 °C. All recovered samples showed patchy, mirror-like surfaces marking boundary shear planes. Optical study of sections cut normal to the shear plane and parallel to the shear direction showed both boundary and inclined shear bands, characterized by extreme grain comminution and a crystallographic preferred orientation. Cross-sections of boundary shears, cut normal to the shear direction using focused ion beam—SEM, from pure calcite gouges sheared at 18 and 150 °C, revealed dense arrays of rounded, ~0.3 μm-sized particles in the shear band core. Transmission electron microscopy showed that these particles consist of 5–20 nm sized calcite nanocrystals. All samples showed evidence for cataclasis and crystal plasticity. Comparing our results with previous models for gouge friction, we suggest that frictional behaviour was controlled by competition between crystal plastic and granular flow processes active in the shear bands, with water facilitating pressure solution, subcritical cracking and intergranular lubrication. Our data have important implications for the depth of the seismogenic zone in tectonically active limestone terrains. Contrary to recent claims, our data also demonstrate that nanocrystalline mirror-like slip surfaces in calcite(-rich) faults are not necessarily indicative of seismic slip rates

Nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation: Crystal plasticity at sub-seismic slip rates at 18–150 °C

A central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic-seismic transitions in fault gouges, and to identify microstructural indicators for such transitions. We present new data on the slip stability of calcite fault gouges, and on microstructural development down to the nanometer scale. Our experiments consisted of direct shear tests performed dry at slip rates of 0.1–10 μm/s, at a constant normal stress of 50 MPa, at 18–150 °C. The results show a transition from stable to (potentially) unstable slip above ~80 °C. All samples recovered showed an optical microstructure characterized by narrow, 30–40-μm-wide, Riedel and boundary shear bands marked by extreme grain comminution, and a crystallographic preferred orientation (CPO). Boundary shear bands, sectioned using FIB-SEM (focused ion beam scanning electron microscopy), revealed angular grain fragments decreasing from 10 to 20 μm at the outer margins to ~0.3 μm in the shear band core, where dense aggregates of nanograins also occurred. Transmission electron microscopy, applied to foils extracted from boundary shears using FIB-SEM, combined with the optical CPO, showed that these aggregates consist of calcite nanocrystals, 5–20 nm in size, with the (104)[201] dislocation glide system oriented parallel to the shear plane and direction. Our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity. Because crystal plasticity is strongly thermally activated, we infer that the transition to velocity-weakening slip is likely due to enhanced crystal plasticity at >80 °C. This implies that tectonically active limestone terrains will tend to be particularly prone to shallow-focus seismicity

Nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation: Crystal plasticity at sub-seismic slip rates at 18–150 °C

A central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic-seismic transitions in fault gouges, and to identify microstructural indicators for such transitions. We present new data on the slip stability of calcite fault gouges, and on microstructural development down to the nanometer scale. Our experiments consisted of direct shear tests performed dry at slip rates of 0.1–10 μm/s, at a constant normal stress of 50 MPa, at 18–150 °C. The results show a transition from stable to (potentially) unstable slip above ~80 °C. All samples recovered showed an optical microstructure characterized by narrow, 30–40-μm-wide, Riedel and boundary shear bands marked by extreme grain comminution, and a crystallographic preferred orientation (CPO). Boundary shear bands, sectioned using FIB-SEM (focused ion beam scanning electron microscopy), revealed angular grain fragments decreasing from 10 to 20 μm at the outer margins to ~0.3 μm in the shear band core, where dense aggregates of nanograins also occurred. Transmission electron microscopy, applied to foils extracted from boundary shears using FIB-SEM, combined with the optical CPO, showed that these aggregates consist of calcite nanocrystals, 5–20 nm in size, with the (104)[201] dislocation glide system oriented parallel to the shear plane and direction. Our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity. Because crystal plasticity is strongly thermally activated, we infer that the transition to velocity-weakening slip is likely due to enhanced crystal plasticity at >80 °C. This implies that tectonically active limestone terrains will tend to be particularly prone to shallow-focus seismicity

Frictional properties of megathrust fault gouges at low sliding velocities: new data on effects of normal stress and temperature

Friction data used in modelling studies of subduction zone seismogenesis are often poorly representative of in situ conditions. We investigated the influence of in situ effective stresses and temperatures on the frictional properties of (simulated) fault gouges, prepared either from Nankai ODP material or illite shale, at sliding velocities approaching those relevant for earthquake nucleation and SSEs. Biaxial (double direct shear) experiments were performed at room temperature, normal stresses of 5e30 MPa, and sliding velocities of 0.16e18 mm/s. All materials exhibited velocity strengthening under these conditions, along with an increase in the friction coefficient and slip hardening rate with increasing normal stress. Illite gouge showed increased velocity strengthening towards higher normal stresses. The effect of temperature was investigated by means of ring shear experiments on illite gouge at 200e300 C, an effective normal stress of 170 MPa, a pore-fluid pressure of 100 MPa and sliding velocities of 1e100 mm/s. These experiments showed a transition from velocity strengthening to velocity weakening at w250 C. Our results provide a possible explanation for the updip seismogenic limit within subduction zone megathrusts and imply an enhanced tendency for earthquake nucleation and SSEs at low effective normal stresses

Sol-gel transitions and liquid crystal phase transitions in concentrated aqueous suspensions of colloidal gibbsite platelets

In this paper, we present a comprehensive study of the sol-gel transitions and liquid crystal phase transitions in aqueous suspensions of positively charged colloidal gibbsite platelets at pH 4-5 over a wide range of particle concentrations (50-600 g/L) and salt concentrations (10-4-10-1 M NaCl). A detailed sol-gel diagram was established by oscillatory rheological experiments. These demonstrate the presence of kinetically arrested states both at high and at low salt concentrations, enclosing a sol region. Birefringence and iridescence show that in the sol state nematic and hexagonal columnar liquid crystal phases are formed. The gel and liquid crystal structures are studied in further detail using small-angle X-ray scattering (SAXS) and cryo-focused ion beam/scanning electron microscopy (cryo-FIB-SEM). The gel formed at high salt concentration shows signatures of a sponge-like structure and does not display birefringence. In the sol region, by lowering the salt concentration and/or increasing the gibbsite concentration, the nematic phase gradually transforms from the discotic nematic (ND) into the columnar nematic (NC) with much stronger side-to-side interparticle correlations. Subsequently, this NC structure can be either transformed into the hexagonal columnar phase or arrested into a birefringent repulsive gel state with NC structure