Angular Quartz Sand Research Articles

Evaporation-induced salt crystallization and feedback on hydrological functions in porous media with different grain morphologies

Evaporation from porous media in the presence of dissolved salts is an important topic in relation to several environmental issues. In this study, we investigated the interaction of evaporation, salt crystallization and the internal structure of the porous material. Porous columns with different internal structures were generated through random packing of angular quartz sand and round glass beads. Evaporation-induced salt efflorescence on the surface of porous media was recorded by a camera with micro lens. The internal pore structure before and after salt crystallization was visualized using the x-ray computed tomography and quantified by the extracted pore networks. Hydraulic properties in the absence/presence of salt crystals were simulated numerically using the pore-network approach and partially measured experimentally. The evaporative water loss ratio in the angular quartz sand was greater than that in the glass beads with the same sieving size. The evaporation of saline water in angular quartz sand and round glass beads can be separated into three stages similar to water evaporation. Salt efflorescence was generated a crust dome architecture on the surface of the angular sand, but was in tight patchy contact with the round glass beads. The presence of salt crust interrupted the exchange of vapor between the porous media and atmosphere, hindering evaporation. Salt subflorescence clogged some of the pores, and the pore size distribution shifted to smaller sizes part. The porosity decreased and the geometric tortuosity of the porous materials increased owing to salt subflorescence. The presence of subflorescence salt crystals decreased the intrinsic permeability and relative diffusion coefficient of different porous media. The relationship between the vapor diffusion coefficients and porosity is linear in the presence/absence of salt crystallization, considering the geometric tortuosity. The findings indicate that the feedback of salt precipitation on hydraulic properties and vapor diffusion must be considered to accurately quantify hydrological processes, particularly in arid and semi-arid areas where intensive evaporation is accompanied by soil salinization and water shortage.

Experimental and numerical studies on rebound characteristics of non-spherical particles impacting on stainless-steel at high temperature

In this paper, innovative test methods including aerodynamic acceleration, PIV measurement, separate statistics of incidence and rebound information were used to systematically investigate the rebound characteristics of flaky oxide particles and angular quartz sand impacting stainless steel at high temperature. Through the statistical analysis of a large number of experimental results and the measurement of the microscopic erosion morphology of the target surface, combined with the numerical simulation of the gas-solid two-phase flow of the test section, the intrinsic relationship between the rebound behavior of the particles and their erosion behavior was systematically explored for the first time. Meanwhile, the effects of the incident parameters, particle size and accelerated airflow on the rebound characteristics of the particles were revealed. The results have important guiding significance for further understanding the physical properties of particle-wall interaction and predicting the particle erosion characteristics and erosion distribution of industrial equipment components.

Abrasive Wear Behavior of Cryogenically Treated Boron Steel (30MnCrB4) Used for Rotavator Blades.

Rotavator blades are prone to significant wear because of the abrasive nature of sand particles. The aim of this research work is to investigate the effect of cryogenic treatment and post tempering on abrasive wear behavior, in the presence of angular quartz sand (grain size of 212–425 μm), of rotavator blade material of boron steel (30MnCrB4). Cryogenic treatment has caused an improvement in the abrasive wear resistance and microhardness of 30MnCrB4 by 60% and 260.73%, respectively, compared to untreated material due to enhancement in hardness, the conversion of retained austenite into martensite, and the precipitation of secondary carbides in boron steel after exposure to cryogenic temperature. Economic analysis justifies the additional cost of cryogenic treatment.

Frictional response of a thick gouge sample: 1. Mechanical measurements and microstructures

A 10‐cm‐thick layer of synthetic fault gouge (angular quartz sand with millimetric grains) is sheared over several meters at low confining pressures (0.1–0.5 MPa) using a ring shear apparatus (inner radius of 10 cm). The shear strength of the gouge exhibits a significant slip‐weakening behavior active over decimetric slip distances. Tests on the influence of particle size, particle geometry, and boundary conditions are reported. A long‐term compaction of the gouge samples is also observed but appears to be decoupled from the frictional slip weakening. At microscale, series of photographs taken during the runs enable us to follow the formation of a shear band in which most of displacements and strains localize. From image analysis we estimate the strain field in the material surrounding the shear band and show that this outer region accounts for most of the global volumetric strain. We argue that the mechanical coupling between this outer region and the shear band is responsible for the frictional slip weakening. Accordingly, the complex structure of the fault zone is shown to be crucial for its frictional behavior. Implications of our results for fault mechanics are discussed in the companion paper.

Pore-scale Observation of Microsphere Deposition at Grain-to-Grain Contacts over Assemblage-scale Porous Media Domains Using X-ray Microtomography

The prevalence of colloid deposition at grain-to-grain contacts in two porous media (spherical glass beads and angular quartz sand, 710-850 microm) was examined using X-ray microtomography (XMT) under conditions where the colloid-grain surface interaction was solely attractive (lacking an energy barrier to deposition), and under fluid velocity conditions representative of engineered filtration systems. XMT allows pore-scale observation of colloid deposition over assemblage-scale porous media domains. Colloids visible in reconstructed images were prepared by coating gold on hollow ceramic microspheres (36 microm in size) (to render densities only slightly higher than water). A significant fraction of the deposited microspheres were deposited at grain-to-grain contacts (about 20% in glass beads, 40% in quartz sand) under the conditions examined. The deposited microsphere concentrations decreased log-linearly with increasing transport distance regardless of the environment of deposition (grain-to-grain contact versus single-contact deposition). The profile shape was, therefore, consistent with filtration theory, and the observed deposition rate coefficients were also well predicted by filtration theory. The ability of filtration theory to predict the magnitude and spatial distribution of deposition demonstrates that filtration theory captures the essential elements of deposition in the absence of an energy barrier despite a lack of accounting for grain-to-grain contacts. The observed factor of 2 greater deposition at grain-to-grain contacts in quartz sand relative to equivalently sized glass beads is consistent with greater grain-to-grain contact lengths and greater fraction of small pores in the quartz sand relative to the glass beads, as determined via a pore structure analysis algorithm (medial axis algorithm).

Deglacial ocean and climate seasonality in laminated diatom sediments, Mac.Robertson Shelf, Antarctica

The palaeoceanography and climate history of the East Antarctic Margin (EAM) are less well understood than those of West Antarctica. Yet, the EAM plays an important role in deep ocean circulation and the global ocean system and has likely done so in the past. Deglacial-age marine sediments from the EAM provide clues about its past role during this critical period of rapid climate change. Several deep basins across the EAM such as Iceberg Alley (∼67°S, 63°E) on the Mac.Robertson Shelf (MRS) accommodate thick marine sequences that archive the deglaciation in the form of diatom-rich, continuously laminated (varved) sediments. These laminated sediments are pristinely preserved and contain seasonal and long-term information on the cryospheric and palaeoceanographic changes associated with the rapid retreat of the glacial ice sheet across the MRS. We present results of microfabric analysis of the lower ∼2 m of deglacial varves from jumbo piston core JPC43B (Iceberg Alley). Backscattered electron imagery (BSEI) of polished thin sections and scanning electron microscope secondary electron imagery (SEI) of lamina-parallel fracture surfaces are used to analyze the varves. One hundred and ninety-two laminations are investigated and their nature and temporal significance are discussed in terms of seasonal deposition and cyclicity of diatom species. Our high-resolution palaeodata record exceptionally high diatom production and silica flux associated with the retreat of the East Antarctic Ice Sheet, and seasonal sea-ice changes along the EAM. This information is invaluable for assessing cryospheric-oceanographic variation and, therefore, the local and regional response to this period of rapid climate change. Varves are made up of lamina couplets comprising (i) thickly laminated to thinly bedded orange/orange-brown very pure diatom ooze dominated by Hyalochaete Chaetoceros spp. vegetative cells and resting spores, and (ii) brown/blue-grey terrigenous angular quartz sand, silt and clay with an abundant mixed diatom flora. The colour variation between these two types of lamination is striking. Using floristic and textural information we interpret the diatom oozes as spring flux and the terrigenous laminae as summer flux. Each couplet pair represents one annual cycle and reflects seasonal changes in nutrient availability and stratification associated with the cyclical advance and retreat of seasonal sea-ice. The diatom oozes can reach up to ∼7.5 cm in thickness indicating enormous silica flux to the sea floor associated with ice sheet retreat.

The effect of particle dimensionality on Granular friction in laboratory shear zones

To match the boundary conditions of numerical models and to examine the effect of particle dimensionality on granular friction, we conducted laboratory experiments on rods sheared in 1‐D and 2‐D configurations, glass beads (3‐D), and angular quartz sand (rough 3‐D). The average coefficient of friction during stable sliding for 1‐D, 2‐D, smooth 3‐D, and rough 3‐D particles is 0.15, 0.3, 0.45, and 0.6, respectively. Frictional strength of 2‐D layers exceeds 1‐D friction by an amount associated with dilatancy and the additional contact plane in 2‐D. We show that 3‐D granular friction exceeds 2‐D friction by the amount of interparticle friction on the out‐of‐plane particle contacts that do not exist in 2‐D. Data from our 2‐D experiments are remarkably similar to numerical results based on 2‐D particle dynamic simulations. Our data indicate that application of numerical models of granular friction to tectonic faults will require computations involving rough, 3‐D particles.

Influence of grain characteristics on the friction of granular shear zones

Numerical models of granular shear show lower friction and a greater tendency for stick slip than laboratory studies designed to investigate fault mechanics. Here we report on laboratory experiments designed to reproduce the conditions of numerical models and to test the role that grain characteristics play in controlling frictional behavior. Friction and microstructural data are compared for direct shear experiments on thin layers (2–3 mm) of angular quartz sand and spherical glass beads. We study the effect of grain shape, roughness, size distribution, and comminution. In a nonfracture loading regime, sliding friction for smooth spherical particles (μ ∼ 0.45) is measurably lower than for angular particles (μ ∼ 0.6). A narrow particle size distribution (PSD) of spherical beads (105–149 μm) exhibits unstable stick‐slip behavior, whereas a wide PSD of spheres (1–800 μm) and the angular gouge display stable sliding. At higher stress, where grain fracture is promoted, initially spherical particles become stable with accumulated slip, and friction increases to the level observed for angular gouge. We find that frictional strength and stability of a granular shear zone are sensitive to grain shape, PSD, and their evolution. We suggest that a low friction translation mechanism, such as grain rolling, operates in gouge composed of smooth particles. Our results show that the first‐order disparities between laboratory and numerical studies of granular shear can be explained by differences in grain characteristics and loading conditions. Since natural faults predominantly contain angular gouge, we find no evidence for a fault‐weakening mechanism associated with the presence of gouge.

Sand erosion performance of CVD boron carbide coated tungsten carbide

The erosion performance and the interaction between the micro-mechanisms of erosion and the microstructure of a chemical vapour deposited boron carbide coating are presented. Samples were tested using both water–sand slurry and air–sand jet impingements at 90° incidence. Tests used angular quartz sand with a mean diameter between 135 and 235 μm and jet impingement velocities between 16 and 268 m s −1. The chemical vapour deposition (CVD) boron carbide coatings were 15–20 μm thick and deposited on a range of substrates of sintered tungsten carbide with 6 to 15 wt.% metal binder. The results, relative to the erosion resistance of the uncoated substrates, show the coatings to have higher resistance (10 times) under lower energy impacts but similar resistance at higher energy impacts. The sintered boron carbide had a similar erosion resistance to that of sintered tungsten carbide except at high energy impacts where it outperforms tungsten carbide and CVD boron carbide by a factor of 2. The performance of these coatings against erodent mass and impact energy are discussed and related to the nano and micro brittle fracture mechanisms identified by detailed microscopy and predicted by Hertzian cone crack theory. Partial concentric spalling of the coating was also evident in regions where circular Hertzian surface cracks are present. These erosion mechanisms, primarily nano-chipping and crack propagation, are also related to the microstructure and composition identified by XRD analysis and Raman spectroscopy. These results, in conjunction with fracture toughness and micro-hardness measurements, suggest that the coating composition is not pure B 13C 2 but has less erosion resistant forms of boron carbide present such as B 50C 2.

Grain shape and sorting effects on shear wave attenuation in unconsolidated laboratory sediments

Shear wave attenuation measurements were made using ceramic bimorph transducers to excite transverse vibrations in a cylindrical column of unconsolidated sediment. Three different water-saturated sediments were used in an attempt to determine the effects of grain shape and sorting on the frequency dependence of attenuation. The mean grain size of the sediments was held constant while the grain shape and size distributions were varied. The sediment assemblages used in the attenuation measurements included a moderately sorted angular quartz sand, a well-sorted angular quartz sand, and well-sorted spherical glass beads. The moderately sorted sand showed the greatest attenuation over the measurement frequency range of 1–20 kHz. The well-sorted sand and the glass beads showed generally lower attenuation with the beads being the least lossy propagation medium. All three sediments showed evidence of viscous attenuation due to fluid-to-grain relative motion. This mechanism leads to a nonlinear relationship between attenuation and frequency. [Work supported by NORDA.]

A comparison between Biot model predictions and shear wave attenuation measurements in unconsolidated laboratory sediments

Shear wave attenuation measurements were made using three different water-saturated sediments. The sediment assemblages used in the attenuation measurements included well-sorted spherical glass beads, a well-sorted angular quartz sand, and a moderately sorted angular quartz sand. The median grain size of the sediments was held constant while the grain shape and size distributions were varied. Sediment physical properties were measured under the same conditions prevailing during the acoustic measurements. The properties were used as inputs to a theoretical attenuation model based on the Biot theory of propagation of waves in porous media. The model allowed attenuation versus frequency predictions to be made for each of the three sediment assemblages over the measurement frequency range of 1–20 kHz. The resultant comparisons between the measured and predicted attenuations demonstrated the importance of using measured model inputs obtained under controlled laboratory conditions when theoretical model capabilities are being evaluated. The model comparisons shed significant light on the ability of this particular model to predict shear wave attenuation in nonideal sediments. [Work supported by NORDA.]

Grain shape and sorting effects on the frequency dependence of shear wave attenuation in water saturated sediments

Laboratory measurements of shear wave attenuation as a function of frequency were made using previously developed ceramic bimorph transducers [B. A. Brunson and R. K. Johnson, J. Acoust. Soc. Am. 68, 1371–1375 (1980)]. Transverse particle motion was excited in three water‐saturated laboratory sediments of the same mean grain size but differing in their degree of grain size sorting and grain shape. The sediments included a moderately sorted angular quartz sand; a well‐sorted angular quartz sand; and well‐sorted spherical glass beads. The attenuation values increased with frequency over the measurement range from 1 to 20 kHz, but exhibited dependencies more complicated than a simple first‐power frequency relationship. Comparisons were made with predictions based on a two‐component model [R. D. Stoll, Geophys. 42, 715–725 (1977)] using inputs derived in part from laboratory measurements of key sediment properties. Insight into the adequacy of this model to predict attenuation in nonideal sediments, and the importance of using model inputs obtained under controlled conditions was demonstrated. [Work supported by NORDA and NAVELEX 320.]

Tuscaloosa Formation in Tennessee

Late Cretaceous Tuscaloosa Formation occurs as discontinuous remnants that cap many of the ridges in the Western Highland Rim. Typically the formation consists of well-rounded, poorly sorted chert gravel which is trimodal in size distribution. The gravel fraction (mode 15 to 40+ mm) consists of Devonian and Mississippian chert and a small percentage of sandstone pebbles. The medium sand fraction (mode 0.5 mm) consists mainly of angular to well-rounded chert grains developed by attrition during transport. Well-rounded and frosted quartz grains also are present. The fine fraction (mode 0.15 mm) consists of clay, authi-genic (?) mica, and quartz. At its eastern limit the Tuscaloosa is locally well sorted and contains quartz pebbles and a large proportion of quartz sand. Also present in the same area are well-sorted, heavy-mineral-bearing sands and bimodal (0.04, 0.2 mm) siltstone, which contains sand-sized pellet aggregates and fragmentary plant fossils. The finest fraction (less than 0.044 mm) of both eastern and western facies of the Tuscaloosa consists of 60-80 per cent quartz, 5-30 per cent kaolin, and 5-30 per cent montmorillonite, all of which are present in Devonian and Mississippian bedrock. Minor exotic constituents include volcanic(?) glass and heavy minerals. The Mississippian chert gravel in the Tuscaloosa is of local origin, but the Devonian chert was transported from a western source. Other components from a western source are sandstone pebbles and frosted sand grains, both of which probably were derived from Cambrian or Ordovician formations that cropped out on the Pascola arch, an eastward-sloping extension of the Ozark dome. Quartz pebbles, heavy minerals, and some of the angular quartz sand present at the eastern edge of the Tuscaloosa may have been derived from Pennsylvanian sandstone and conglomerates that cropped out north and south of the Pascola arch. Most of the Tuscaloosa Formation is believed to be of nonmarine origin, deposited on the eastward-sloping flank of the Pascola arch. The eastern facies of the Tuscaloosa is believed to be partly marine in origin, the exotic components having been swept in by longshore currents. During deposition of the Tuscaloosa, the Ozark dome and the Cincinnati arch were connected by the Pascola arch, which is now deeply buried beneath the Mississippi Embayment, At that time the Pascola arch stood structurally about 3000 feet higher than at present, and its structural shape and dimensions were comparable to the present Nashville dome. During deposition of the Tuscaloosa the Nashville dome was structurally about 1000 feet lower than at present, and its crest probably was submerged beneath the sea.

The flotation phenomenon, a by-passing and sorting process

ABSTRACT The tidal rivers of Cape York, Australia, transport well-sorted, angular quartz sand into the Gulf of Carpentaria by flotation. The combination of the environmental conditions causing this process are firstly, the peneplanation of the coastal area; secondly, the tidal rivers which run upstream for several miles; thirdly, the semi-tropical climate; fourthly, the lateritic and bauxitic soil containing a high percentage of very angular, quartz grains. The flotation phenomenon acts as a by-passing and sorting agent, and large amounts of clean sand are transported in this manner in various parts of the world, where other environmental combinations may permit the flotation of sand.