Main Deposition Mechanisms Research Articles

Arquitetura e mecanismos deposicionais em sistemas aluviais holocênicos de clima árido no oeste argentino e comparação com depósitos neocretáceos brasileiros

The Pre-Cordillera in the northwest of Argentine is characterized by geomorphological features formed during Miocene Andes Cordillera uplifting. The arid weather and compressive tectonic regime propitiated the origin of countless sedimentary basins filled by alluvial fans and playa-lakes deposits. Because of the outcrops abundance and their qualities these basins are important sites for direct observation of depositional alluvial architectures and facies analyses. The description of some deposits in the Rio Jáchal valley (neighborhood of San Jose de Jáchal), and Pie de Palo desert alluvial plain in San Juan, allowed the recognition of main depositional mechanisms in these environments. The analyses were based in the longitudinal cross sections that show intertonguing of the alluvial fans, playa-lakes and eolian deposits. It was characterized the internal and external geometries of the bodies by hierarchical surfaces and macroforms analyses to make the interpretation of the sedimentary process and the depositional dynamics. The facies variation from proximal to distal deposits recorded the evolution of confined or unconfined non-cohesive debris flow to turbulent and laminar flows, resulting by the transport stream energy decrease of ephemeral torrential currents associated with storm periods. Due to the annual low pluviosity (70 mm/y), the sedimentation rate is very low, mainly suggested by the vegetation and soil developed. Although this study has been made in a restrict area with a very recent sedimentary history initiated only in the Late Pleistocene to Holocene, the facies distribution and the depositional mechanisms conditioned by geomorphologic positions in the alluvial fan systems and the sedimentologic characteristics conditioned by the arid climate allow to compare these deposits with the Brazilian neocretaceous, in the Bauru Basin, that shows similar sedimentologic and architecture characteristics.

Particle deposition mechanisms during processing of advanced composite materials

Liquid composite moulding of advanced composite materials often comprises infiltration of a particle-filled resin into a multi-scale porous fabric. These injections/infusions are subject to severe particle depositions inside the reinforcement, leading to undesired inhomogeneous mechanical and functional properties. Hence, the mechanisms for particle depositions are investigated by detailed meso-scale experiments, analysed by microscopic imaging and micro-particle image velocimetry, and macroscopic infusions of a biaxial non-crimp fabric. It is shown that two main particle deposition mechanisms are filtration during fibre bundle impregnation and filtration induced by stationary flow through fibre bundles. It is also clarified where in the reinforcement the particles will deposit. Finally, a number of suggestions on how to process advanced composite materials with a more homogeneous particle distribution are launched.

Meteoric smoke concentration in the Vostok ice core estimated from superparamagnetic relaxation and some consequences for estimates of Earth accretion rate

We measured the magnetization of glacial and interglacial ice from the Vostok core to estimate the meteoric smoke concentration in Antarctic ice. We have found that, within the uncertainty of the method, the smoke concentration in ice in Antarctica is equivalent to that previously measured in Greenland ice. The virtually identical smoke concentrations despite the different ice accumulation rates in Greenland and Antarctica suggest that wet deposition is the main deposition mechanism for such ultra‐small particles. Given the typical scavenging ratios for atmospheric aerosols, this would imply that previous estimates of accretion rate based on dry deposition are likely to be appreciably overestimated.

Mineralizing fluids of the shallow epithermal Au–Ag deposits of the El Barqueño district, Jalisco, Mexico

The El Barqueño district, Jalisco, consists of several polymetallic (Au–Ag–Cu–Zn–Pb) epithermal veins hosted by a volcanoplutonic assemblage of andesitic rocks, granites and granodiorites that belong to the Lower Volcanic Supergroup of the Sierra Madre Occidental. The paragenetic sequence indicates two main mineralization stages. Stage I occurs as breccias with base-metal sulfides and virtually no gold and silver. Stage II is made up of several crustiform quartz bands that form symmetrical vein fillings and contain the precious-metal mineralization. Rhombohedral adularia crystals and quartz pseudomorphs of bladed calcite are widespread in stage II, providing evidence for boiling. Au- and Ag-bearing metallic minerals locally precipitated directly on adularia crystals, an association indicating boiling as the main mechanism of metal deposition. Temperature and salinity of mineralizing fluids range from 101 to 252 °C and 0.2 to 19.1 wt.% NaCl equiv., respectively. While temperatures cluster in the range from 120 to 160 °C, salinities have a bimodal distribution, with most of them falling either below 3 wt.% NaCl equiv. or higher than 10 wt.% NaCl equiv. These two arrays of salinity values describe mixing trends only locally, and may reflect different sources of mineralizing fluids, possibly dominated by meteoric and magmatic sources, respectively. An adularia separate from stage II was dated by 40Ar / 39Ar geochronology at 57.91 ± 0.44 Ma (isochron age). Thus, El Barqueño is the oldest known epithermal deposit in Mexico, and suggests the existence of a previously unrecognized Paleocene metallogenic event in southwestern Mexico.

MINERALOGY, FLUID CHARACTERISTICS, AND DEPOSITIONAL ENVIRONMENT OF THE PALEOCENE EPITHERMAL Au-Ag DEPOSITS OF THE EL BARQUENO DISTRICT, JALISCO, MEXICO

The El Barqueno epithermal vein district is located in the southwestern part of the Sierra Madre Occidental of Mexico. It is made up of several polymetallic (Au-Ag-Cu-Zn-Pb) epithermal veins hosted by a volcanoplutonic assemblage of andesitic rocks, granites, and granodiorites, which belong to the Lower Volcanic Supergroup of the Sierra Madre Occidental, within the Jalisco block. The veins trend from 45° to 100°, dipping to the southeast and south, and steepening with depth. The maximum strike length of the veins at El Barqueno is about 5 km, and the maximum vein thickness is about 10 m (avg 2–3 m), narrowing with depth. The paragenetic sequence indicates two main mineralization stages. Stage I occurs as breccias with base metal sulfides and virtually no gold or silver. Stage II consists of crustiform quartz bands that form symmetrical vein fillings and contain the precious metal mineralization. Rhombohedral adularia crystals and quartz pseudomorphs after bladed calcite are widespread in stage II, providing evidence for boiling. Gold- and silver-bearing metallic minerals locally precipitated directly on adularia crystals, an association indicating boiling as the main mechanism of metal deposition. Conductive cooling and mixing also may have been important. The temperature and salinity of the mineralizing fluids ranged from 101° to 252°C and 0.2 to 19.1 wt percent NaCl equiv, respectively. Whereas temperatures cluster in the range of 120° to 160°C, salinities have a bimodal distribution, most of them falling below 3 or higher than 10 wt percent NaCl equiv. These two arrays of salinity values only locally reflect mixing and may represent different sources of mineralizing fluids, possibly dominated by meteoric and magmatic sources, respectively. An adularia separate from crustiform quartz bands of stage II was dated by 40 Ar/ 39 Ar geochronology at 57.91 ± 0.44 Ma (isochron age). Thus, El Barqueno has the oldest absolute age of any epithermal deposit in Mexico and suggests the existence of a previously unrecognized Paleocene metallogenic event in southwestern Mexico associated with several types of ore deposits, including iron oxide-copper-gold, porphyry-type skarn and epithermal deposits. This further suggests that older rocks beneath the Upper Volcanic Supergroup of the Sierra Madre Occidental may be prospects for other epithermal veins and that exploration for epithermal deposits and related mineral deposit types should be focused in the oldest outcrop portions of the Sierra Madre Occidental.

Electroless Deposition of Ni–Sn–P and Ni–Sn–Cu–P Coatings

The surface morphology and the elemental distribution of low- and high-tin Ni–Sn–P coatings have been investigated. It is shown that in low-tin Ni–Sn–P coatings there is a uniform distribution of the alloy components, both on the surface and through the thickness. The main mechanism of electroless alloy deposition in this case is based on the well-known hypophosphite oxidation as a source of electrons for the metals (Ni and Sn) and phosphorus reduction. In high-tin coatings, a nonuniform distribution of the components is observed, both on the surface and through the coating thickness. Three-dimensional areas enriched in tin and impoverished in Ni and especially in P have been observed using scanning electron microscopy with energy-dispersive X-ray spectroscopy, scanning Auger electron spectroscopy, and Auger electron spectroscopy. The disproportionation reaction of Sn(II) is suggested as being predominant over the hypophosphite oxidation in these three-dimensional areas and is responsible for their formation. The introduction of copper in the solution is giving an additional opportunity to reveal the role of the oxidation of Sn(II) into Sn(IV) as a source of electrons.

Droplet deposition in steam turbines

Research since the 1960s on the deposition of droplets from wet steam is reviewed, concentrating mainly on low-pressure turbines but also covering the limited work related to nuclear high-pressure turbines. The context is first set, outlining the motivation in terms of blade erosion and, to a lesser extent, wetness losses. Details of measurements in turbines and in simulated turbine flows are followed by descriptions of theoretical work on the main inertial and turbulent deposition mechanisms; possible additional contributory mechanisms are summarized. A major combined experimental and computational effort in the 1980s led to broad agreement between measured and calculated fog deposition fractions in low-pressure turbine final stages, attributed largely to the development of more accurate droplet size measurement and computational fluid dynamics techniques. An attempt has been made to correlate advances with the history of steam turbine development and to speculate on the future of deposition studies in the light of recent theoretical developments and trends in power generation.

Geologic implications of seawater circulation through peridotite exposed at slow-spreading mid-ocean ridges

Peridotite denuded by tectonic extension and exposed at the seafloor adjacent to slow-spreading centers hosts hydrothermal circulation of seawater. The reaction of seawater with peridotite causes serpentinization, which generates a high-pH, strongly reducing fluid rich in methane and hydrogen, and is accompanied by as much as 40% volume expansion. Complete serpentinization of peridotite requires tectonic activity to open fluid paths sealed by volume expansion. Diffuse venting of serpentinization fluids causes lithification of calcareous ooze on the seafloor to chalk-like limestone. This may be the main mechanism of deposition of ophicarbonates common in ophiolites. The degree of induration is a function of the fluid flux through the sediment column. Calcareous ooze infiltrates faults and fractures and can be deformed following lithification. Focused venting of serpentinization fluids may lead to deposition of large chimneys composed of calcite, aragonite, and brucite, such as those in the recently documented Lost City vent field (30°N, Mid-Atlantic Ridge). Geophysical implications of serpentinization include (1) creation of magnetic anomalies due to growth of magnetite in serpentinite and (2) lowered seismic velocity. Integrated studies of geologic and geophysical effects of serpentinization may aid in a more complete understanding of the structure of oceanic lithosphere and the mechanisms that expose mantle peridotite at the seafloor.

Transient pressure drop of diesel particulate filters

This paper focuses on challenges associated with the description of the transient filtration/loading behavior of diesel particulate filters and especially the problem of predicting the pressure drop behavior of these filters. Filters separate the typically sub-μm diesel particulate from the exhaust with a variety of transport mechanisms. Main deposition mechanisms are those of Brownian diffusion and direct interception while thermophoresis can be important in the presence of temperature gradients. This article describes the extension and experimental validation of the filter model of Konstandopoulos and Johnson, initially developed for clean filters into the domain of transient filtration/loading.

Experimental Investigation of Pressure Drop with Particle Loading in Nuclepore Filters

This paper presents an experimental investigation of the increase in pressure drop with particle loading in Nuclepore filters. The average increase in pressure drop per unit time and particle mass concentration was measured as a function of particle size, density, and hygroscopicity. Two different Nuclepore filter pore diameters were tested (2 and 5 mu m, respectively) at filter face velocities ranging from 4 to 52 cm/s. Our results showed that the increase in the pressure drop with particle loading inversely proportional to the square root of particle specific gravity and depends weakly on particle diameter (to the power of- 0.2). Furthermore, the increase in the pressure drop with particle loading is proportional to the filter face velocity and inversely proportional to the cube of the pore diameter. Particle interception and impaction on the pore edges are the main deposition mechanisms that are responsible for raising the pressure drop over time across the filter, especially for particles having Stokes numbers below 5. Particle deposition due to diffusion inside the pores is important for particles smaller than 0.2 mu m. These observations agree well with previously published studies on particle deposition on the pore edges in Nuclepore filters. Our tests also showed a dramatic decrease in the pressure drop with loading for hygroscopic particles as the relative humidity increases from 10% to 50%. The pressure drop with loading decreases almost inversely proportional to the relative humidity for ammonium sulfate particles.

Deposition of Ultrafine Aerosols and Thoron Progeny in Replicas of Nasal Airways of Young Children

The deposition efficiencies of ultrafine aerosols and thoron progeny were measured in youth nasal replicas. Clear polyester-resin casts of the upper airways of 1.5-yr-old (Cast G), 2.5-yr-old (Cast H), and 4-yr-old (Cast I) children were used. These casts were constructed from series of coronal magnetic resonance images of healthy children. The casts extended from the nostril tip to the junction of the nasopharynx and pharynx. These casts were similar in construction to those used in previous studies (Swift et al. 1992; Cheng et al. 1993). Total deposition was measured for monodisperse NaCl or Ag aerosols between 0.0046 and 0.20 (Jim in diameter at inspiratory and expiratory flow rates of 3, 7, and 16 L min−1 (covering a near-normal range of breathing rates for children of different ages). Deposition efficiency decreased with increasing particle size and flow rate, indicating that diffusion was the main deposition mechanism. Deposition efficiency also decreased with increasing age at a given flow rate and...

Manufacture of composite electrophoretic coatings using very finely divided Mo and Mo2C powders

An electroplating-electrophoretic procedure for producing composite coatings using a combination of electroplating and electrophoretic methods, followed by liquid phase sintering at the eutectic formation temperatures, has been studied. Finely divided Mo and Mo2C powders produced by low-temperature catalytic reduction of molybdenum trioxide and subsequent molybdenum carbiding were employed, and the main electrophoretic deposition mechanisms have been estabished. Electrophoresis parameters have been examined in terms of their effect on the precipitates formation rate and their structure. This procedure enables components operating under corrosion-erosion wear conditions to be protected and their service life increased by a four or fivefold factor.

Wall temperature and the soiling of murals

A balance is made here of the intensities of the main deposition mechanisms (i.e. Brownian diffusion, thermophoresis, inertial impaction, gravitational settling and Stefan flow) in the case of vertical wall surfaces, and thus frescoes or other murals. When the wall is colder than the air, the temperature gradient forces negative thermophoresis and develops a downward free-convection layer. This generates inertial impaction and increases gravitational settling. A further contribution due to the Stefan flow may be generated. When the wall is warmer, thermophoresis partially counteracts other deposition mechanisms for fine particles, but the temperature gradient generates an uprising flow, and inertial impaction of the largest particles occurs. The deposition rate is reduced for fine particles, but increased for the largest ones. As the mass of the suspended paniculate matter is concentrated in the coarsest particles, the net effect is a heavy soiling. Up-rising flows transport upwards the majority of particles, causing soiling also of the ‘downward facing’ parts of the surface irregularities. Warm floor or cold ceiling may cause atmospheric instability and convective motions, with the above mentioned negative effects. Cold floor and warm ceiling form stable temperature profiles and attenuation of turbulence. Under the warm ceiling a cushion of stable air forms without motion (and inertial deposition) and with thermophoresis (partially) counteracting Brownian diffusion. The best situation appears to be offered by cold floor, warm ceiling, walls in thermal equilibrium with ambient air, and air with stable temperature gradient.

Nonlinear absorption in ionic crystals determined by pulsed photothermal deflection

Intensity-induced nonlinear absorption in several ionic crystals have been investigated at 308 nm by pulsed phototermal deflection in the prebreakdown region. The main mechanism of energy deposition is two or three photon absorption.

Holocene sediments in a shallow bay, southern coast of Kuwait, Arabian Gulf

The texture, composition, distribution and origin of sediments in a shallow open bay of the northwestern part of the Arabian Gulf have been investigated. Evaluation of 67 samples shows that sediments are mostly sands and silts with large but variable carbonate contents. The bottom of the bay has a very irregular morphology with many N-S submarine ridges which could represent an older Holocene land surface. The grain size of the surficial sediments is partly related to depth. Finer sediments, in the central part of the bay, are surrounded towards the shore by coarser deposits. Two promontories strongly influence the sediment distribution. Unidirectional currents (mainly longshore currents and to a lesser extent rip currents) are the main depositional mechanisms. Shell fragments and calcareous rock fragments from wave-cut cliffs are the main components of the coarse fractions. Aragonite and high-Mg calcite are the main carbonate minerals accompanied by smaller amounts of low-Mg calcite. The main differences between the studied area and some of the other arid areas elsewhere in the southern Arabian Gulf are (1) the considerable amount of the aeolian admixture and (2) the carbonates are mostly composed of angular shell fragments.

Deposition of indoor aerosols as determined by PIXE analysis

In indoor air the main deposition mechanisms are sedimentation on horizontal surfaces, diffusion on vertical and horizontal surfaces and electrical interaction. In our study the deposition coupons (three different types) were situated in different locations in a room. Four coupons were placed on a vertical plane and six on a horizontal plane at a height of 5–190 cm. Simultaneously, suspended particles were collected by 2-fraction filter collectors. The average airborne concentrations and surface accumulations were analyzed by the internal beam PIXE facility. Final results were calculated for ten elements. The sulphur concentrations were also analyzed by ion-chromatography. The results were in good agreement with the PIXE values. This deposition study is a part of successive investigations, where the behaviour of indoor aerosols are studied.

Migration, modification and merging in aeolian systems and the significance of the depositional mechanisms in Permian and Triassic dune sands of Europe and North America

The main depositional mechanisms acting in aeolian systems can be assessed in two different and independent ways: first by the internal anatomical approach with analysis of the cross-stratification fabric, and second by the external morphological approach with study of shape and surface features of dunes. Anatomical investigations of various ancient aeolian systems in the Permian and Triassic of Europe and North America and an extensive literature review concerning both internal anatomy and external morphology of ancient and modern dunes reveal three main depositional mechanisms operating in aeolian systems: migration, modification and merging. Migration comprises downwind movement of isolated dunes or trains of aeolian bedforms under predominantly constant wind direction. The orientation of the interset surfaces partially depends on the angular relationship between the path of bedform climb and the depositional surface and also on subsidence. Simple systems are characterized by successive dunes of similar size, whereas compound systems originate by superimposition of smaller aeolian bedforms on larger dunes or draas. Compound migration gives rise to the hierarchy of diastems. Modification comprises overprinting of existing dunes by winds coming from directions other than those that govern migration of the original aeolian bedforms. The anatomical elements representing modification include both intrasets and extensive intersets, depending on duration and on the scale of the changes of the winds. Simple modification comprises occasional origin of either only cross-dipping erosional boundaries or both diastems and intraset laminae oriented in different directions. A special case of modification is the creation of intrasets dipping in the same direction as the foreset inclination, comprising either reactivation or relaxation surfaces, depending on whether the foreset slope is steepened or lowered in angle. Complex modification takes place under repeatedly alternating winds of changing effectiveness. Small-scale modification comprises minor alterations of existing dune types, and medium-scale modification is characterized by conversion of primary aeolian bedforms into secondary dune types. Small-scale and medium-scale modification take place during short-term to smaller-scale long-term changes of effective wind direction. Large-scale modification originates by large-scale long-term changes, accompanied by a certain subsidence, which result in burial of the older dunes by a younger train of aeolian bedforms within the same sand sea migrating obliquely to perpendicularly to the former wind direction. Very large-scale modification is induced by very large-scale long-term changes which result int deflationary erosion of older dune fields and subsequent superimposition of a new sand sea on top of the eroded remnants of the former erg. Merging comprises coalescing of bedforms with only negligible erosion during burial of the first bedform by subsequent dunes. Merging is induced mainly when migration of dunes is stopped by a morphological barrier or ceases as a consequence of weakening winds. Merging further occurs during coalescence of numerous isolated barchans in rows to parallel wavy barchanoid ridges as a consequence of increasing availability of sand. The main depositional mechanism in compound systems is migration of hierarchically superimposed bedforms with subordinate modification under predominantly unidirectional winds. In complex systems, migration, modification and merging take place in different amounts under unidirectional, bidirectional and multidirectional winds. Depending on direction and strength of both earlier and subsequent winds, complex systems are either charcterized by mainly migration with subordinate modification or by considerable modification with either conversion or dissection of older dunes. The effects of migration, modification and merging are discussed in the light of both internal anatomy of ancient cross-stratification fabrics and external morphology of recent dunes. A classification of dune types based on these mechanisms divides the aeolian bedforms into primary, secondary and tertiary types. Primary dunes originate by simple or compound migration with minor modification and comprise mainly transverse dunes. Secondary dunes originate by complex interaction of migration and modification or even predominantly by modification, with the best examples being longitudinal dunes. Tertiary dunes form by merging of transverse and longitudinal elements with varying amounts of migration and modification and are mainly represented by star dunes. The results of various anatomical case studies of ancient aeolianites indicate that simple migration was the dominant mechanism for construction of ergs in the northern hemisphere in Permian and Triassic times.

Regional deposition of 2.5–7.5 μm diameter inhaled particles in healthy male non-smokers

Airborne monodisperse particles in the size range 2.5–7.5 μm dia., labelled with 99mTc, were systematically administered to mouth breathing subjects under different but predetermined breathing patterns ranging from 0.5–2.01, tidal volume and 10–25 breaths/min. The subjects were all healthy, non-smoking males. Measurements were made of both total and regional deposition. The results show the increasing significance of pulmonary deposition as the particle size decreases and consequently the importance of accurate data in this range for the purposes of radiological protection. Both total and regional deposition are a function of the impaction parameter ( D 2 F) suggesting that inertial impaction is the main mechanism of deposition under the conditions studied. The work supports the predicted values of deposition given in the lung model of the International Commission on Radiological Protection. Subsidiary experiments showed the value of faecal sampling in establishing the accuracy of total deposition estimates and in elucidating full regional deposition.