Spherical Quartz Research Articles

Photocatalytic degradation of ofloxacin on Gd2Ti2O7 supported on quartz spheres

Gd2Ti2O7 layer was coated on the surface of micrometer-sized quartz spheres by a sol-gel method. Although pyrochlore structured Gd2Ti2O7 does not change after loading, crystallite size of Gd2Ti2O7 reduces from 53.3 to 33.6 nm. Surface area and pore volume of Gd2Ti2O7 are significantly enlarged after supporting on SiO2 spheres. Both Ti4+ and Ti3+ oxidation states exist in the unsupported Gd2Ti2O7, while there is only fully oxidized Ti4+ state in the 30%Gd2Ti2O7/SiO2. The characteristic groups in ofloxacin molecule can be decomposed during photocatalytic oxidation. The reaction rate constant for photocatalytic degradation of ofloxacin on Gd2Ti2O7 is 7.8 × 10−3 min−1, while it is 1.7 × 10−2 min−1 on 30%Gd2Ti2O7/SiO2. The maximum ofloxacin degradation efficiency occurs when using 800 mg/L 30%Gd2Ti2O7/SiO2. When ofloxacin concentration is more than 10 mg/L, the reactant concentration goes beyond the capacity of the photocatalyst.

High-energy-resolution diced spherical quartz analyzers for resonant inelastic X-ray scattering.

A novel diced spherical quartz analyzer for use in resonant inelastic X-ray scattering (RIXS) is introduced, achieving an unprecedented energy resolution of 10.53 meV at the Ir L3 absorption edge (11.215 keV). In this work the fabrication process and the characterization of the analyzer are presented, and an example of a RIXS spectrum of magnetic excitations in a Sr3Ir2O7 sample isshown.

Characteristics of a Micro Quartz Stylus Probe Fabrication by Using the Micro-discharge Plasma Method

Micro-stylus probes and tactile sensing structures are key components in high precision micro-coordinate measuring machines. Micro-spherical styli with a diameter of 0.125mm are available in commercial markets. A tungsten micro-spherical stylus with a diameter of less than 0.08 mm has been successfully fabricated by using a hybrid process which combines one pulse electro discharge and wire electro discharge grinding methods. However, the low controllability is still a critical problem and the electric discharge process is not suitable for the fabrication of non-conductive materials such as quartz and glass. In order to fabricate a non-conductive quartz-based micro-stylus probe, a micro-discharge plasma process was proposed in this paper. A micro-quartz pipe was mounted on a V-shaped block with a low rotation speed and feeding to the plasma zone in order to enable a sphere formation. The experimental results show that a spherical quartz stylus with a diameter of 0.12mm is produced by using the micro discharge plasma process. The machining characteristics such as machining time, feeding length, accuracy, and diameter, will be also investigated. It is possible to produce a micro-spherical quartz stylus probe by using the low-cost micro-discharge plasma method.

A Thermodynamic Consideration on the Mechanism of Ultrasensitive Moisture Sensing by Amorphous Silica

We detected the change in the phase velocity of surface acoustic waves propagating along the amorphous silica layer on a spherical single-crystal quartz due to the very small amount of moisture at less than 1~upmu hbox {mol}{cdot } hbox {mol}^{-1} in the ambient hbox {N}_{2} gas. This was made possible for the first time because this system, called a ball SAW moisture sensor, was extremely sensitive. The measured phase velocity changed as a function of moisture density and temperature and was fitted strikingly well with a thermodynamic model assuming that dissociated hbox {H}^{+} and hbox {OH}^{-} dissolved into the amorphous silica layer at room temperature.

Solar electricity via an Air Brayton cycle with an integrated two-step thermochemical cycle for heat storage based on Co3O4/CoO redox reactions III: Solar thermochemical reactor design and modeling

A two-step solar thermochemical cycle based on Co3O4/CoO redox reactions integrated into an Air Brayton cycle is considered for thermochemical heat storage. The two-step cycle encompasses (1) the thermal reduction of Co3O4 to CoO and O2 driven by concentrated solar irradiation and (2) the re-oxidation of CoO with O2 to Co3O4, releasing heat and completing the cycle. An evacuated horizontal solar thermochemical reactor is proposed with an inclined slope and quartz window for promoting direct irradiation of dense, granular Co3O4/CoO flows. Mechanical analysis of flat and spherical quartz window designs for a 5kWth scale prototype was performed to ensure window stability. Detailed mass and heat transfer analysis for a 5kWth scale prototype was performed coupling Monte Carlo ray tracing for radiative heat exchange to the energy balances for the bed and the reactor. A parametric study of the reactor design was performed with varying cavity depth, particle inlet temperature, and solar concentration ratio. The optimal solar reactor design maximized conversion of Co3O4 to CoO and particle outlet temperature while preventing particle overheating and achieved a Co3O4 to CoO conversion of 0.91, particle outlet temperature of 1385K, maximum flow temperature of 1572K, and absorption efficiency of 0.76.

Role of clay particle electrostatics and the dielectric permittivity of suspended silt particles in sound attenuation in mud

Sound attenuation in marine mud sediments is partly caused by viscous dissipation of acoustically induced flow past suspended silt particles. Clay particles in the surrounding lattice carry electrostatic charges, causing high porosity, so one asks why silt particles do not settle because of gravity to the bottom of the mud layer. Explanation of the suspension and the associated attenuation of sound proceeds from consideration of a quartz sphere immersed in mud. The somewhat-random electric field created by the clay particles causes an electric dipole moment to arise in the sphere because of its dielectric permittivity. This is proportional to the electric field and varies with position, and the result is an electrostatic force on the sphere, the force being proportional to the gradient of the electric field. In equilibrium, this force is balanced by a gravity force. There is a natural spring constant associated with deviations from equilibrium, and the resulting dynamical model is a fixed-mass sphere subjected to a spring force, the force of gravity, and the viscosity-associated force caused by the motion of the surrounding fluid and the no-slip condition at the sphere’s surface. Paper quantitatively discusses the model’s implications on the suspension theory of sound attenuation. Results suggest approximate validity for representative acoustic frequencies of model where sphere has same density as water. [Work supported by ONR.]

The Maturity Myth In Sedimentology and Provenance Analysis

Abstract: We often resort to mythical thinking in the face of natural phenomena that we hardly understand. Sedimentary petrology has several long-standing myths. One is that sediments increase their “maturity” through time by winnowing and sorting, physical wear, chemical weathering, diagenesis, and recycling, as if their destiny were to reach a final stage of perfection represented by quartz spheres of equal size. Such an armchair representation of supermature purity is embodied in white recycled desert sand, whereas a modern analogue for its opposite, the dark dirty rock improperly called graywacke, is yet to be found. Clay matrix does not occur in sand deposited from tractive currents, which is sorted at the instant of settling. Sand grains get rounded relatively rapidly during transport in air but very slowly when transported in water. The degree of winnowing, sorting, and rounding (“textural maturity”) has little to do with the accumulation of “modifying energy” through time. “Mineralogical maturity” does not increase notably even after thousands of kilometers of transport in high-energy environments, and not even during recycling, a physical process that in a weathering-limited denudation regime tends at most to reproduce the mineralogy of parent clastic rocks. Rather, “mineralogical maturity” decreases drastically where sedimentary rock fragments are eroded in abundance from mudrocks interbedded in the source, and sand recycled entirely from orogenic flysch or molasse may contain less than 10% quartz. If natural sediment factories were quartz distilleries, then quartzose sand should become more common through geological time. Pure quartz sand, however, is relatively rare in the modern world, and largely confined to hyperhumid equatorial latitudes or recycled eolian dunefields. A relative increase in more durable minerals is achieved effectively only by chemical processes such as selective leaching in soils, or especially during burial diagenesis, when the time and temperature available for chemical reactions are much longer and higher than at the Earth9s surface. If recycled sediments are commonly quartz-rich with very poor assemblages dominated by zircon, tourmaline, and rutile, it is because their parent sandstones have undergone diagenetic dissolution prolonged for many millions of years at temperatures of many tens of degrees before final exhumation and erosion.

Compression testing spherical particles for strength: Theory of the meridian crack test and implementation for microscopic fused quartz

We show that uniaxial compression testing of spherical particles can give unambiguous access to their tensile strength as governed by surface flaws if one uses pairs of elasto-plastic platens, tailoring their hardness in order to control the relative area of particle-to-platen contact during the test. This eliminates the development of contact microcracks that are typically found to govern particle fracture when hard platens are used. We show that, if the platen materials are well chosen, one can probe a range of stress states for which it is known that particle failure was initiated along the surface, under elevated hoop stress within a region situated remote from the points of load application. Specifically, platens must be chosen such that particles tend to fracture when the ratio of projected contact area radius to particle radius exceeds a specific value that depends on the Poisson ratio of the particles. With fused quartz of Poisson ratio 0.17, this specific ratio value equals 0.65. We demonstrate the approach using microscopic fused quartz spheres 40±20µm in diameter as a testbench material; with those particles hardened steel serves as an appropriate platen material. Their strength values are statistically distributed; this is addressed using several platen materials. The resulting bank of data is interpreted using established survival-analysis methods, namely the non-parametric product-limit estimator. We also give a maximum likelihood estimation of the particle strength Weibull distribution parameters derived from the ensemble of data after left-truncation and/or right-censoring of data points situated inside of the range of unambiguous surface fracture strength measurement for each platen material. This gives a Weibull modulus of 6.3 and characteristic strength of 890MPa for the fused quartz particles. These values are significantly lower than what is produced in high-strength fused quartz fibers of comparable diameter; the difference is most likely a result of surface damage caused during powder storage and manipulation in the absence of a protective coating.

Particle shape-controlled sorting and transport behaviour of mixed siliciclastic/bioclastic sediments in a mesotidal lagoon, South Africa

This study investigates the effect of particle shape on the transport and deposition of mixed siliciclastic-bioclastic sediments in the lower mesotidal Langebaan Lagoon along the South Atlantic coast of South Africa. As the two sediment components have undergone mutual sorting for the last 7 ka, they can be expected to have reached a highest possible degree of hydraulic equivalence. A comparison of sieve and settling tube data shows that, with progressive coarsening of the size fractions, the mean diameters of individual sediment components increasingly depart from the spherical quartz standard, the experimental data demonstrating the hydraulic incompatibility of the sieve data. Overall, the spatial distribution patterns of textural parameters (mean settling diameter, sorting and skewness) of the siliciclastic and bioclastic sediment components are very similar. Bivariate plots between them reveal linear trends when averaged over small intervals. A systematic deviation is observed in sorting, the trend ranging from uniformity at poorer sorting levels to a progressively increasing lag of the bioclastic component relative to the siliciclastic one as overall sorting improves. The deviation amounts to 0.8 relative sorting units at the optimal sorting level. The small textural differences between the two components are considered to reflect the influence of particle shape, which prevents the bioclastic fraction from achieving complete textural equivalence with the siliciclastic one. This is also reflected in the inferred transport behaviour of the two shape components, the bioclastic fraction moving closer to the bed than the siliciclastic one because of the higher drag experienced by low shape factor particles. As a consequence, the bed-phase development of bioclastic sediments departs significantly from that of siliciclastic sediments. Systematic flume experiments, however, are currently still lacking.

Sol-gel Preparation and Properties of Bi4Ti3O12 Photocatalyst Supported on Micrometer-sized Quartz Spheres

AbstractComposite Bi

Light interaction with nano-structured diatom frustule, from UV-A to NIR

ABSTRACTDiatoms are found in nearly every aqueous environment and play a vital part of the global primary production system contributing with up to 25 % and are efficient light harvesting organisms. Unique to diatoms are the hard cell wall, called the frustule surrounding the single cell. The frustule is made from bio-synthesized silicate, perforated by wavelength sized features where the morphology of the nano-structured “greenhouse” is species dependent. Diatoms would therefore make for one of the most interesting “green” resources since it has not only potential as a biomass production system but also for nano-structured inorganic material. To understand the biological significance and to integrate diatomic frustules as active material in devices a fundamental understanding of how light interacts with the frustule is needed. In this study we focus on centric diatoms, i.e. having rotational symmetry where morphological parameters vary between the different investigated species. We report how light interacts with the frustule in the wavelength range from UV-A (320-380 nm) to NIR (900 nm). High resolution spectroscopy and CCD images are used to identify photoluminescence (PL) and variations in the transmitted light caused by the nano-structured frustule. Furthermore we show, by placing the frustule on a quartz half sphere how light transmission is a function of the angle of incidence and wavelength.

Silicate impact-vapor condensate on the Moon: Theoretical estimates versus geochemical data

We numerically simulated the impacts of asteroids and comets on the Moon in order to calculate the amount of condensate that can be formed after the impacts and compare the results with data for lunar samples. Using available equations of state for quartz and dunite, we have determined pressure and density behind shock waves in these materials for particle velocities from 4 to 20km/s and obtained release adiabats from various points on the Hugoniot curves to very low pressures. For shock waves with particle velocities behind the front below 8km/s the release adiabats intersect the liquid branch of the two-phase curve and, during the following expansion, the liquid material vaporizes and does not condense, forming a two-phase mixture of melt and vapor. The condensate can appear during expansion of material compressed by a shock with higher (>8km/s) velocities. Using our hydrocode SOVA, we have conducted numerical simulations of the impacts of spherical quartz, dunite, and water–ice projectiles into targets of the same materials. Impact velocities were 15–25km/s for stony projectiles and 20–70km/s for icy impactors, and impact angles were 45°and 90° to the target surface. Along with the masses of condensates we calculated the masses of vaporized and melted material. Upon the impact of a projectile consisting of dunite into a target of quartz at a speed of 20km/s at an angle of 45°, vaporized and melted masses of the target are equal to 1.6 and 11 in units of projectile mass, respectively, and the mass of condensate is 0.19. Vaporized and condensed masses of the projectile are 0.16 and 0.02, more than 80% of the projectile mass is melted. The calculated ratio of vaporized to melted mass proved to be on the order of 0.1. However, we calculated that, at impact velocities below 20km/s, the condensate mass is only a small fraction of the vaporized and melted masses and, consequently, the major part of vapor disperses in vacuum in the form of separate molecules or molecular clusters. At an impact velocity of 15km/s, the abundance of silicate condensates relative to melt is 0.001–0.0001, in agreement with data from lunar samples. Should the observed condensate abundances be representative, the velocities of major asteroid impacts on the Moon could not substantially exceed 20km/s. Comet impacts at the same velocities produce much smaller amounts of vapor condensate because the low densities of cometary material induce lower shock pressures in the target.

Spherical quartz crystals investigated with synchrotron radiation.

The quality of x-ray spectra and images obtained from plasmas with spherically bent crystals depends in part on the crystal's x-ray diffraction across the entire crystal surface. We employ the energy selectivity and high intensity of synchrotron radiation to examine typical spherical crystals from alpha-quartz for their diffraction quality, in a perpendicular geometry that is particularly convenient to examine sagittal focusing. The crystal's local diffraction is not ideal: the most noticeable problems come from isolated regions that so far have failed to correlate with visible imperfections. Excluding diffraction from such problem spots has little effect on the focus beyond a decrease in background.

Ultrafine spherical quartz formation during seismic fault slip: Natural and experimental evidence and its implications

In recent works on the determination of pseudotachylyte within the principal slip zone (PSZ) of the Chelungpu fault (Taiwan), we demonstrated that frictional melting occurred at shallow depths during the 1999 Mw 7.6 Chi-Chi earthquake. Thus, the characteristics of melts are of paramount importance to investigate processes controlling dynamic fault mechanics during seismic slips. We conducted rock friction experiments on siltstone recovered from the Taiwan Chelungpu fault Drilling Project (TCDP) at a slip rate of 1.3m/s and a normal stress of 1MPa. Here we not only target to characterize experimental pseudotachylyte and evaluate the associated frictional behavior, but also compare it with natural frictional melts of TCDP. Our results show that (1) initial shear stress drop was related to the generation of low viscosity melt patches, (2) the evolution of shear stress in the postmelting regime was congruent with frictional melt rheology, and (3) the slip strengthening presumably resulted from the extremely low content of water of the frictional melt. In particular, the state-of-art of in situ synchrotron analyses (X-ray diffraction and Transmission X-ray Microscope) determine the presence of ultrafine spherical quartz (USQ) grains (~10nm to 50nm) in the glassy matrices presumably produced at high temperature. Our observations confirm that the USQ grains formed in rock friction experiments do occur in natural faults. We surmise the USQ is the result of frictional melting on siltstone and represents the latest slip zones of the Chelungpu fault, and further infer that the viscous melts may terminate seismic slips at shallow crustal conditions.

Simulation of Collapse of Granular Columns Using the Discrete Element Method

AbstractIn this study, a three-dimensional (3D) numerical investigation of axisymmetric collapse of granular columns has been conducted using the discrete element method (DEM). The simulated granular columns have a constant initial radius of 5.68 mm and three aspect ratios: 0.55, 1.0, and 2.0. The columns consist of uniform spherical quartz particles with a diameter of 0.32 mm. In the DEM model, rotational velocities of particles are reduced by a factor at every time step to partially account for the additional rolling resistance due to the effect of particle shape and hysteretic contact behavior. The simple linear contact model is used; however, its performance is improved by using different stiffness values calculated by nonlinear Hertz–Mindlin contact model for each aspect ratio. The simulated final deposit heights, runout distances, and energy dissipation values are in good agreement with experimental observations reported in the literature. The effects of initial porosity and rotational resistance on...

Prediction of sonic velocities in shale from porosity and clay fraction obtained from logs — A North Sea well case study

Prediction of sonic velocities in shales from well logs is important for seismic to log ties if the sonic log is absent for a shaly section, for pore pressure anomaly detection, and for data quality control. An anisotropic differential effective medium (DEM) was used to simulate elastic properties of shales from elastic properties and volume fractions of silt and wet clay (a hypothetical composite material that includes all clay minerals and water). Anisotropic elastic coefficients of the wet clay were assumed as a first-order approximation to be linearly dependent on wet clay porosity (WCP). Here, by WCP we mean a ratio of a pore volume occupied by water to a total volume of the wet clay. Effects of silt inclusions on elastic coefficients of shales were taken into account by using the anisotropic differential effective medium model. Silt inclusions were modeled as spherical quartz particles. Simulated elastic coefficients of shales were used to calculate compressional and shear velocities, and these were in a good agreement with the sonic velocities observed on a test data set from an offshore Mid-Norway well penetrating a 500-m vertical section of shale. To further study the elastic properties of wet clays, elastic coefficients calculated from compressional and sonic velocities measured in shales were inverted for vertical profiles of wet clay elastic coefficients. Analysis of these coefficients found that in the well considered, the increase in elastic coefficients of shales was controlled by the increase of silt fraction with depth. Elastic coefficients of wet clay found no increase with depth. The inverted elastic moduli of wet clay found much stronger correlation with WCP than do the moduli of shale. This confirmed the hypothesis that silt fraction is one of the key parameters for the modeling of elastic properties of shale.

Fluence Measurements Employing Iodide/Iodate Chemical Actinometry as Applied to Upper‐Room Germicidal Radiation

To measure the fluence distribution in the upper room of a facility equipped with germicidal UV lamps a method has been developed utilizing iodide/iodate chemical actinometry together with spherical (1 cm) quartz irradiation chambers. The use of spherical vessels allows radiation from essentially all directions to be measured. Such a measurement allows an estimate of the radiation flux at a given point in space, i.e. the fluence rate. When a battery of spheres located at various points in a room are simultaneously irradiated, a measure of the fluence distribution can be obtained. The use of the iodide/iodate chemical actinometer is uniquely qualified to measure germicidal UV radiation. The purpose of this report is to provide details on how this system can be used to measure fluence rates. In particular, it describes how a hand-held colorimeter can be used to measure the absorbance changes in irradiated spheres.

Digital implant planning for a minimally invasive surgery approach: a case letter of a full-arch rehabilitation.

Digital implant planning for a minimally invasive surgery approach: a case letter of a full-arch rehabilitation.

Towards the use of mushroom-capped dry adhesives in outer space: Effects of low pressure and temperature on adhesion strength

Instrumented indentation apparatus and techniques were applied to the testing of synthetic gecko adhesives in an attempt to characterise their ability to function in a space environment. The indentation apparatus was capable of operating at reduced pressures, allowing a higher vacuum level (1×10−5 mbar) than dry adhesives have previously been tested under. Using a 1.5 mm spherical quartz indenter on polydimethylsiloxane (PDMS), mushroom-capped, structured dry adhesives, the effective Youngʼs Modulus of the material was found to change negligibly as a result of pressure, while no changes in adhesion were observed. The effect of time spent in vacuum was also examined. Significant changes in effective Youngʼs Modulus were observed, but no changes were noted in adhesion. Tests also showed that no significant changes to adhesion could be detected from −50 to 75 °C. These results are important for space applications because it shows that the adhesion of a mushroom-capped, synthetic, PDMS, dry adhesive is constant in various thermal and pressure environments.

The legacy of impact conditions in morphometrics of percussion marks on fluvial bedrock surfaces

Percussion, or impact, marks are a common type of bedrock bedform found on many fluvial bedrock channels and have been attributed to bedload impact. Little is known about the conditions under which they form and how these affect morphology and dimensions of impact mark craters. We present data from a set of experiments exploring the formation of percussion marks by bedload impact under controlled conditions (impact velocity, angle, and particle diameter) by quartz spheres onto polished marble plates through a water interface. Particle impact causes impact craters consisting of a central depressed pit and a surrounding raised crater rim under all impact conditions. Data from 699 impact experiments show that crater rims are always circular and crater diameter (ϕc, in m) scales with the kinetic energy of the particle normal to the surface immediately prior to impact (K.E., in J) by the relationship K.E.=2.48×107ϕc3.188. We test this relationship on impact marks produced in a series of controlled flume experiments for a range of surface inclinations found in natural fluvial channel outcrops. Measurements of impact crater diameter were used to estimate K.E. using our empirical equation. Our model estimates very similar K.E. for impact craters produced in this quasinatural setting to those calculated from flume conditions when realistic values for mean impact velocity and mean impact angle are assumed. Applying this relationship to measurements of crater rim diameter in natural settings will allow the mapping of impact K.E. along and across channel reaches where these bedforms are found. Future numerical models of fluvial bedrock erosion based on impact K.E. could be field calibrated from measurements of percussion marks in marble channels or from installed marble slabs in other bedrock channel reaches.