Blocky Structures Research Articles

Formation mechanism of sealing edge pores for vacuum glazing using laser brazing technique

In view of the pore defect of vacuum glazing sealing layer, the research on side edge sealing of laser was made. The phase analysis of microstructure on sealing layer was investigated using scanning electron microscope (SEM) and energy spectrum analysis (EDS) to study the formation mechanism of sealing pores. The influence of laser power and welding rate on sealing edge porosity was researched. The results show that the sealing layer has evenly distributed bilayer structure of wetting layer with few pores caused by the residual gases between the solder particles (external) –melting layer with a large number of mutually disconnected isolated pores (inside). As the increase of laser power, the interface layer is compact and smooth and the pores decline in numbers. When the power exceeds a certain value, the interface becomes unsmooth with the increasing number of pores. The phenomenon of surface defects and blocky structures is generated with lower welding speed and greater energy output. On the other hand, the blocky structures, unmelted solders, pores and cracks are formed by the higher welding speed and smaller energy output. Therefore, the pore defect can be effectively avoided and reduced by the reasonable control of laser power and welding rate.

Tutorial: Spectral bandwidth extension — Invention versus harmonic extrapolation

Various postprocessing methods can be applied to seismic data to extend the spectral bandwidth and potentially increase the seismic resolution. Frequency invention techniques, including phase acceleration and loop reconvolution, produce spectrally broadened seismic sections but arbitrarily create high frequencies without a physical basis. Tests in extending the bandwidth of low-frequency synthetics using these methods indicate that the invented frequencies do not tie high-frequency synthetics generated from the same reflectivity series. Furthermore, synthetic wedge models indicate that the invented high-frequency seismic traces do not improve thin-layer resolution. Frequency invention outputs may serve as useful attributes, but they should not be used for quantitative work and do not improve actual resolution. On the other hand, under appropriate circumstances, layer frequency responses can be extrapolated to frequencies outside the band of the original data using spectral periodicities determined from within the original seismic bandwidth. This can be accomplished by harmonic extrapolation. For blocky earth structures, synthetic tests show that such spectral extrapolation can readily double the bandwidth, even in the presence of noise. Wedge models illustrate the resulting resolution improvement. Synthetic tests suggest that the more complicated the earth structure, the less valid the bandwidth extension that harmonic extrapolation can achieve. Tests of the frequency invention methods and harmonic extrapolation on field seismic data demonstrate that (1) the frequency invention methods modify the original seismic band such that the original data cannot be recovered by simple band-pass filtering, whereas harmonic extrapolation can be filtered back to the original band with good fidelity and (2) harmonic extrapolation exhibits acceptable ties between real and synthetic seismic data outside the original seismic band, whereas frequency invention methods have unfavorable well ties in the cases studied.

Traveltime tomography of crosshole ground-penetrating radar based on an arctangent functional with compactness constraints

Regularization has been an effective technique to provide unique and stable solutions for crosshole ground-penetrating radar (GPR) traveltime tomography. The traditional form of this method, in which a low-order differential operator was used, commonly yields a smooth solution that may not be appropriate when anomalies occur in block patterns, such as voids or irregular objects. The minimum support (MS) functional can be used to improve the resolution of blocky structures; however, in crosshole GPR traveltime tomography, the MS functional is unable to resolve residual artifacts, whose departure from an a priori model are smaller than the focusing parameter selected from a trade-off curve. In addition, it would result in severe instability and yield a trade-off curve with poorly defined corners when the focusing parameter nears the precision of the apparatus. We have developed a new stabilizing functional based on the arctangent (AT) function that effectively removes the artificially small values in the crosshole GPR traveltime tomography, and ultimately is more efficient because it does not require the user to select a focusing parameter. We inverted three 2D synthetic data sets based on the reweighted regularized conjugate gradient algorithm. Compared with the low-order differential and MS functional, the user will be able to clearly distinguish the anomaly boundary using this method, which will yield results that are closer to the actual structure. We also discussed the impact of some influencing factors caused by the noise contained in the data, the central frequency of the antenna, the anomalous trends, and the ray coverage angle. We further inverted an experimental data set to test the effectiveness and robustness of the method.

Grain Refinement Efficiency in Commercial-Purity Aluminum Influenced by the Addition of Al-4Ti Master Alloys with Varying TiAl₃ Particles.

A series of Al-4Ti master alloys with various TiAl3 particles were prepared via pouring the pure aluminum added with K2TiF6 or sponge titanium into three different molds made of graphite, copper, and sand. The microstructure and morphology of TiAl3 particles were characterized and analyzed by scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). The microstructure of TiAl3 particles in Al-4Ti master alloys and their grain refinement efficiency in commercial-purity aluminum were investigated in this study. Results show that there were three different morphologies of TiAl3 particles in Al-4Ti master alloys: petal-like structures, blocky structures, and flaky structures. The Al-4Ti master alloy with blocky TiAl3 particles had better and more stable grain refinement efficiency than the master alloys with petal-like and flaky TiAl3 particles. The average grain size of the refined commercial-purity aluminum always hereditarily followed the size of the original TiAl3 particles. In addition, the grain refinement efficiency of Al-4Ti master alloys with the same morphology, size, and distribution of TiAl3 particles prepared through different processes was almost identical.

Performance of silicone rubber composites with SiO2 micro/nano-filler under AC corona discharge

Outdoor insulators are often subject to corona discharges and the problem is becoming more prevalent with the increasing use of higher transmission voltage levels. For polymeric insulators, exposure to such discharges can alter the chemical structure of basic polymer and degrade surface properties. This paper investigates the effect of micro and/or nano fillers in silicone rubber composites in suppressing such damage. Four different types of samples are fabricated: pristine silicone rubber (PR), 30wt% micron-sized silica/silicone rubber (MC), 27.5wt% micron + 2.5wt% nano silica/silicone rubber (NMC), and 5wt% nano silica/silicone rubber (NC) composites. Samples are exposed to AC corona using a needle to ground-plane electrode setup. Experimental results are analyzed based on five different measurement methods: phase-resolved partial discharge (PD), hydrophobicity loss-recovery, Scanning Electron Microscopy (SEM), Surface roughness and Fourier Transform Infrared Spectroscopy (FTIR). Results indicate that NC shows a strong resistance to partial discharges and hydrophobicity loss. In the area below the needle tip, higher hydrophobicity loss and higher recovery are observed as compared to the vicinity region. Variations in surface roughness, appearance of crackles, voids, pits, surface splitting into blocky structures and damages to chemical structure of silicone rubber are appreciably retarded in NC as compared to PR, MC and NMC. Based on NMC results, it is found that addition of nano-sized silica can be an attractive approach to improve the corona resistance of micron-sized silica filled silicone rubber.

A fast automatic multichannel blind seismic inversion for high-resolution impedance recovery

The inversion of seismic reflection data for acoustic impedance (AI) is a common and accepted method for the interpretation of poststack seismic data. The original mathematical problem is nonlinear due to the nonlinearity of relation between the AI and the earth reflectivity series and also the insufficiency of information about the source wavelet. Furthermore, the problem is ill posed due to the lack of low and high frequencies in the data. We have developed a multichannel blind inversion and solved it for obtaining the AI model and the wavelet directly from seismic reflection data. We found a solution to the overall problem by alternating between two subproblems, corresponding to the AI and wavelet recovery. Having an estimation of the wavelet, the algorithm directly inverts multichannel data for a high-resolution AI model, having blocky structures in the sense of total variation (TV) regularization, while satisfying a priori low-frequency information. The advantages of the split Bregman technique and the discrete cosine transform are used to build a fast and efficient algorithm for solving the nonlinear impedance inversion with TV regularization. Having an estimate of the AI model, the wavelet is updated by restricting it to have a sparse representation in a wavelet transformation domain while predicting the observed data. Numerical tests using simulated 2D data obtained from the benchmark Marmousi model and also 2D field data confirm that the proposed algorithm stably generates accurate estimates of complex AI models and complicated wavelets, simultaneously.

Monte Carlo Study of Degenerate Behavior of AB Diblock Copolymer/Nanoparticle under Cylindrical Confinement.

Degenerate behavior (i.e., forming different self-assembled structures for a given block copolymer (BCP) under the same confinement) commonly exists in various confined systems. Understanding degenerate behavior is crucial for precise control over the structures formed by self-assembly systems under confinement. In this study, the degenerate behavior of a self-assembled AB diblock copolymer/nanoparticle (NP) mixture in a cylindrical pore is studied using Monte Carlo simulation. We find that the degenerate behavior of such a mixture depends on the introduction of the NP. Under different pore sizes, four typical degenerate structures [i.e., single helices (S-helices), double helices (D-helices), parallel cylinders, and stacked toroids] can be obtained if the NP content is zero. However, when the NP content in the mixture is increased, it is found that the number of degenerate structures decreases, that is, only blocky structures can be obtained in the case of high NP content. Moreover, the probability of forming S-helices decreases, whereas the probability of forming D-helices increases with increase in the NP content. Analysis of the interactive enthalpy densities and the chain conformation of the systems indicates that entropy plays an important role in the degenerate structure formation. This study provides some new insights into the degenerate behavior of a BCP/NP mixture under confinement, which can offer a theoretical reference for further experiments.

Soils Characteristics in Maize Based Farming System of Western Oromia, Ethiopia

Understanding soil fertility status is a prerequisite to implement appropriate soil management practices for sustainable agricultural production and productivity. In view of this, a study was conducted at Kejo and Ongobo farmers’ fields, located at GobuSeyo District of East Wollega Zone of Oromia region in 2011. To investigate soil characteristics, Soil samples were collected from the profiles of the genetic horizons for the analyzing the selected physicochemical properties. The results of the study revealed that the soils had strong coarse sub angular blocky structure at Ap horizon, whereas to angular blocky structures at the B horizon. The soil textural class of both profiles was clayey with the clay fractions being the highest and increased consistently with depth. The bulk density values ranging from 1.25 g cm-3 at the Ap horizon to 1.40 g cm-3 at the Bt4 horizon. The pH-H2O were strongly acidic ranging from 5.27 at the Ap horizon to 5.83 at Bt2 horizon. The soil organic matter (SOM) contents of the soils ranging from 0.62% at the Bt2 horizon to 3.78% at the surface horizon, whereas total N ranging from 0.03 to 0.19%, available P from 0.62 to 4.0 mg kg-1 and CEC from 11.84 to 22.47 cmolckg-1 soil.Available Fe ranging from 7.24 to 33.68 mg kg-1, Mn from 2.37 to 83.91 mg kg-1, Zn from 0.013 to 0.314 mg kg-1 and Cu from 0.16 to 2.32 mg kg-1 in the soil and showed decreasing trend with profile depth. The result of the study showed that the soils of the study sites had poor chemical fertility and integrated soil fertility management practices can improve the current situation.

Nonlinear multichannel impedance inversion by total-variation regularization

The analysis of acoustic impedance (AI) allows for the mapping of seismic reflection data to lithology, and hence it plays an important role in the interpretation of poststack seismic data. The AI is obtainable from the inversion of the earth reflectivity series. Efficient deconvolution methods have been developed for recovering the reflectivity series from band-limited poststack data, which are multiple free, zero offset, and migrated. However, calculation of the AI from the reflectivity, when considering the spatial correlation of the impedance parameters, demands the solution of a constrained nonlinear inverse problem. Two efficient algorithms are proposed for solving the nonlinear impedance problem in multichannel form with the total-variation (TV) constraint to recover impedance maps with blocky structures. The first uses the continuous earth model for reflectivity, which allows linearizing the problem in the logarithm domain. The second uses the discrete (layered) earth model for reflectivity. In this case, a nonlinear problem is solved in the original domain. The main properties of the algorithms, which are built based on the split-Bregman technique and the discrete cosine transform are as follows: (1) They are multichannel inversion procedures, so they respect the spatial and temporal correlation of the data, (2) they impose the TV constraint on the parameters to generate blocky structures, (3) they are fast such that a large 3D impedance model with a blocky structure can be recovered easily on a personal computer, and (4) the computational complexities of both algorithms are the same. Numerical tests using simulated 2D data obtained from a benchmark Marmousi model and also 2D and 3D field data confirmed that the proposed algorithm generates more accurate with higher resolution impedance models compared with the conventional methods.

Selective Etching Procedure for Observation of Primary Silicon Morphologies in V-AlSi20 Master Alloy

Abstract Aluminium castings with silicon content above the eutectic are becoming an increasingly important product, meeting a wide range of high end engineering specifications, particularly in automotive and aerospace industries. Its outstanding properties highly depend on their cast microstructures; conventional casting will produce large primary silicon particles in a variety of morphologies. This causes drastically shortened tool life when machining this material, reason for which melt refinement is an ongoing field of investigation. An ultrasound assisted chemical deep etching procedure could be proven to reveal primary and eutectic silicon crystals in all detail while preserving the spatial distribution they had when precipitating from the eutectic during solidification. Different polyhedral growth morphologies, mostly coarser platelets, star-like and blocky structures, were observed in an as cast alloy using Scanning Electron Microscopy. As this metallurgic sample treatment provides to a certain extend spatially resolved information about morphology and distribution of silicon crystals, it is suitable to assess the grade of success of refinement processes aiming to achieve fine and well dispersed silicon particles in the eutectic phase.

Controllable Supramolecular Architectures for Modulating Optical Properties on the Molecular Aggregation Level

AbstractDriven by the association of chemical weak forces and solvent effects, zero‐ to two‐dimensional nanostructures of thiophene‐substituted perylene bisimide such as spheres and blocky structures were obtained. Light‐controlled intramolecular charge transfer from the trithiophene unit to the perylene bisimide in the solid state can induce a hypochromatic shift and enhanced fluorescent emission.

Two-Dimensional DDA Contact Constitutive Model for Simulating Rock Fragmentation

Due to the difficulties of fracture mechanics in dealing with multicrack problems, the continuum-based numerical methods always encounter mathematical problems when modeling rock fragmentation, so the alternative discontinuum-based numerical approaches are worth trying. This paper presents a new two-dimensional contact constitutive model for the discontinuous deformation analysis (DDA) method to simulate the fragmentation of jointed rock. This contact constitutive model consists of a two-phase force-displacement relation in the nomal direction and the Mohr-Coulomb criterion in the shear direction. The two-phase force-displacement relation is imposed in the normal direction of the block interface, instead of the penalty contacting spring. The first phase functions as the original penalty spring, and the second phase serves as a cohesive component. This new contact constitutive model was incorporated into the original DDA code, and four examples were computed for verification. The simulated results agree favorably with those obtained from physical tests and other numerical simulation, showing that the proposed method can simulate the whole process of rock fragmentation and can deal with cases of intact rock, rock mass with nonpenetrative joints, and even blocky rock structures. Furthermore, due to the nature of the triangular block shape, the proposed model can avoid the mesh dependence problem. DOI: 10.1061/(ASCE)EM.1943-7889.0000319. (C) 2012 American Society of Civil Engineers.

Investigation of structural and optical anisotropy of m-plane InN films grown on γ-LiAlO2(1 0 0) by metal organic chemical vapour deposition

In this paper a systematic investigation of structural and optical anisotropy of m-plane InN film grown on γ-LiAlO2(1 0 0) substrate by metal organic chemical vapour deposition, which is believed to be much more difficult than molecular beam epitaxy, is presented. The InN film showed pure m-plane phase as confirmed by x-ray diffraction ω/2θ scan together with polarized Raman spectroscopy. The epitaxial relationship between the m-plane InN and the substrate was found to be [0 0 0 1]InN ∥ [0 1 0]LAO and [1 1 − 2 0]InN ∥ [0 0 1]LAO. The inherent film mosaic anisotropy was studied by x-ray rocking curve analysis. Atomic force microscopy revealed that stripe-like features appear on the surface of the m-plane InN film, which originated from the replication of the surface morphological anisotropy of the substrate. Scanning electron microscopy showed blocky surface structures that were indicative of three-dimensional growth mode, which was related to the anisotropic structural mismatch of the film and the foreign substrate. A small direct band gap of ∼0.7 eV of the m-plane InN film was confirmed by low-temperature photoluminescence spectra, which showed evident polarization anisotropy in terms of both intensity and peak energy. Finally, a blue-shift of absorption edge as compared with the photoluminescence peak energy was observed and fully accounted for by the Burstein–Moss effect.

Micromorphology and Stable-Isotope Geochemistry of Historical Pedogenic Siderite Formed in PAH-Contaminated Alluvial Clay Soils, Tennessee, U.S.A.

Abstract Alluvial clay soil samples from six boreholes advanced to depths of 400–450 cm (top of limestone bedrock) from the Chattanooga Coke Plant (CCP) site were examined micromorphologically and geochemically in order to determine if pedogenic siderite (FeCO3) was present and whether siderite occurrence was related to organic contaminant distribution. Samples from shallow depths were generally more heavily contaminated with polycyclic aromatic hydrocarbons (PAHs) than those at greater depth. The upper 1 m in most boreholes consisted of mixtures of anthropogenically remolded clay soil fill containing coal clinker, cinder grains, and limestone gravel; most layers of coarse fill were impregnated with creosote and coal tar. Most undisturbed soil (below 1 m depth) consisted of highly structured clays exhibiting fine subangular blocky ped structures, as well as redox-related features. Pedogenic siderite was abundant in the upper 2 m of most cores and in demonstrably historical (< 100 years old) soil matrices. Two morphologies were identified: (1) sphaerosiderite crystal spherulites ranging from 10 to 200 μm in diameter, and (2) coccoid siderite comprising grape-like “clusters” of crystals 5–20 μm in diameter. The siderite, formed in both macropores and within fine-grained clay matrices, indicates development of localized anaerobic, low-Eh conditions, possibly due to microbial degradation of organic contaminants. Stable-isotope compositions of the siderite have δ13C values spanning over 25‰ (+7 to −18‰ VPDB) indicating fractionation of DIC by multiple microbial metabolic pathways, but with relatively constant δ18O values (−4.8 ± 0.66‰ VPDB) defining a meteoric sphaerosiderite line (MSL). Calculated isotope equilibrium water δ18O values from pedogenic siderites at the CCP site are from 1 to 5 per mil lighter than the groundwater δ18O values that we estimate for the site. If confirmed by field studies in progress, this observation might call for a reevaluation of low-temperature siderite-water 18O fractionations. Investigations at the CCP site thus provide valuable information on the geochemical conditions under which siderite can form in modern soils, and thus insight on controls on siderite formation in ancient soils.

Polyhedral modelling of underground excavations

Abstract The use of key-block theory for the analysis of blocky rock mass structures in mining and civil engineering is well established. Such methods have traditionally been used to analyse the stability of rock blocks at free surfaces only. These methods have also been limited to the analysis of relatively few discontinuities, usually assumed to be infinitely persistent. Development of more advanced algorithms has removed these limitations and allowed the development of a modeller capable of handling multiple curved, finite persistent discontinuities. We discuss this modeller and its capability of predicting the existence of polyhedra with unlimited facets and morphologies. This paper describes the use of this polyhedral modeller for the study of the stability of an underground excavation and offers significant advantages over the algorithm recently reported by Menendez-Diaz et al. (2009) [3] which is restricted to the analysis of pentahedral blocks formed by four discontinuity sets.

Morphological characteristics and classification of soils derived from diverse parent Materials in Central Cross River State, Nigeria

Variation in soil characteristics is usually a reflection of the difference in materials from which the soil was formed. This study sought to investigate the characteristics of soils formed on different parent materials with a view to classifying them. This study was carried out in selected soils derived from three major types of parent materials in central Cross River State, South Eastern Nigeria. A total of six (6) pedons were excavated, two (2) pedons in each of the identified parent materials. The parent materials were Sandstone-shale-siltstone intercalations. Basement complex and Basalt. The study indicated that soils derived from sandstone-shale-siltstone materials are characterized by ochric sandy loam and loamy sand epipedons with moderate medium sub-angular blocky structures. These soils are also light coloured with dominant hues of 7.5YR with hard to slightly hard and hard to very hard dry consistence at the surface and sub-soil respectively. Soils of basement complex are characterized by the possession of loamy sand epipedons with weak medium crumb and sub-angular blocky structures having predominantly dull yellowish brown and bright yellowish brown colours at the surface and sub-soils. The dry consistences of the surface soils are slightly hard while the sub-soils are hard to very hard. The Morphology of basaltic soils is characterized by sandy loam to clayed texture with strong medium to moderate medium sub-angular block structures. These soils are deep in effective depth and dark reddish brown in colour. Its dry consistence is usually hard to very hard to very hard. Soils of sandstone – shale-siltstone and basement complex origin are classified as Topic Tropustalfs while those of basalt origin are classified Topic Tropustults. Proper fertilization and irrigation programmes based on their inherent characteristics will make these soils more productive and enhance their potentials for sustainable agricultural use Keywords: Parent materials, Soil Morphology and sustainability Global Journal of Pure and Applied Sciences Vol. 14 (3) 2008: pp. 271-278

Micromorphological properties of salt affected soils in Northeast Thailand

A micromorphological study was carried out on salt affected soils from three locations on erosional terraces overlain by wash and alluvium under tropical savanna climate in Northeast Thailand where salinity problem has been acute. This aimed at providing detailed data for a better agricultural land use planning of the area. Five or six profiles at each location were sampled along a linear traverse that included the soils with highest and lowest levels of salt accumulation. Sixteen soil profiles were described, sampled and analyzed using physio-chemical, optical microscope and scanning electron microscope with energy dispersive spectrometer (SEM/EDS) techniques. The highest salt affected profiles show salt crusts, bare surfaces and halophytic plants and these soils have been left idle. All soils are deep, poorly drained, moderately to highly developed and with various salinity levels. They are fourteen Natraqualfs and two Endoaqualfs. Soil textures are sandy for location 1, clayey for location 2 and with a sandy topsoil and clayey subsoil for location 3. The soils at locations 1 and 2 mostly have high values of electrical conductivity (EC) and exchangeable sodium percentage (ESP). Soils at location 3 may have been affected by desalinization and alkalization as is indicated by low EC, high basic cations and high pH. Field morphology, optical micromorphology and SEM/EDS analysis results show clear accumulation of salt in some profiles. Their microstructures are different due to the difference in their texture. Compact grain and bridge grain structures are common in sandy-textured soil whereas channel and subangular blocky structures are common in the clayey soils. Quartz and runi-quartz grains are common as skeleton materials, but are present in different sizes and amounts. Halite occurs in voids in soils at locations 1 and 2 and is abundant in Pedons 1 and 6 where salt crusts exist. Calcite is present only in one profile (Pedon 1). Amorphous pedofeatures are manganiferrous impregnative nodules and iron and manganese oxide impregnated s-matrix. The EDS spectra indicate the presence of barite (BaSO 4) and sylvite (KCl) crystals in voids in some of the soils. The element composition of the soil matrix in a triangle graph of SiO 2: Al 2O 3: Fe 2O 3 is displaced from the ‘kaolin line’ towards the SiO 2 apex, indicating that very fine-grained quartz and/or a Si-rich clay mineral (s) is present in the matrix. The presence of Si-rich clay minerals is supported by XRD results that identified smectite in addition to kaolin and may be an evidence of the resilication process that can occur in salt affected soils. The data points near the Fe 2O 3 apex of the triangle graphs represent iron oxide nodules and their position on the matrix Al 2O 3/SiO 2 line indicates that induration of the matrix with iron oxide has occurred and that the nodules have formed in situ. The normalized element composition of the matrix in triangle graph between SiO 2: Al 2O 3: Na 2O + CaO + MgO indicates that in some instances the salts of Na, Ca and Mg have indurated the soil matrix as data points for salt-rich matrix fall on the clay matrix composition line.

Coexistence of halloysite and kaolinite: a study on the genesis of kaolin clays of Campo Alegre Basin, Santa Catarina State, Brazil

Kaolin at Campo Alegre Basin, Santa Catarina State, Brazil was formed from alteration of volcanic acid rocks. Halloysite clays dominate the clay fraction of the matrix of the kaolin body, whereas a poorly crystalline kaolinite is abundant in veins. Some primary blocky structures have high amounts of illite, in one mine, but in general, only low contents of illite-smectite, illite, chlorite-vermiculite, vermiculite and quartz were identified in the clay fraction of the samples. Toward the top of the mines, hematite and lepidocrocite appear in horizontal red and ochre colored levels and the amount of kaolinite increases compared to halloysite. The vertical zoning of alteration levels, the changes in mineralogy, the positive correlation between depth and Cation Exchange Capacity of the clays, the preservation of different types of rock textures in the kaolin bodies, the dominant tube morphology of the halloysite clays indicate a supergene genesis for the deposits. Criteria to distinguish between supergene and hypogene kaolin are discussed. Transmission Electron Microscopy of the cross sections of halloysite tubes showed polygonal forms that are ascribed to be transitional between kaolinite and halloysite. It is proposed that some of the kaolinite of these deposits be inherited from the dehydration of halloysite tubes.

Effect of Low Frequency Electromagnetic Field on Microstructures and Macro-Segregation of Direct Chill Casting Al-19.2%Si Alloys

The influences of low frequency electromagnetic field on microstructures and macro-segregation in direct chill casting process were investigated in the experiments，Al-19.2%Si alloys were semi-continuously cast into ingots with 100 mm in diameter. Microstructures and macrostructures of samples taken from different part of the cast with different electromagnetic field conditions were characterized by optical microscopy. The results showed that low frequency electromagnetic field refines the microstructures and reduces macro-segregation. Unlike casting without electromagnetic field, the primary Si grains were homogeneous with fine dimensions and the morphology of the primary silicon exhibited small blocky structures or near-spherical structures. Further more, decreasing frequency is beneficial to the improvement. In the range conditions in the experiments, the optimum frequency is found to be 15Hz. During casting, the temperature of the liquid metal in the sump was monitored. The results shown, under LFEC the width of the liquid-solid region became narrowed and the temperature field in the sump also became homogeneous.

Soil genesis along a chronosequence on marine terraces in eastern Taiwan

Soil chronosequences developed on elevated marine terraces are ideal for studying changes in soil-forming processes with time. The coastal range of eastern Taiwan is a product of active arc–continent collision. Vertisols, Mollisols and Entisols are generally found on the different levels of marine terraces herein, but no detailed investigations of soil chronosequence have been conducted by integrating field morphology, physio-chemical characterization, micromorphology and mass-balance interpretations. Five soil pedons were selected on the three marine terraces including Tt-1 and Tt-2 pedons (Typic Hapluderts) on the first higher level with the oldest soil age (9–10 ka), Tt-3 (Vertic Hapludolls) and Tt-4 pedons (Typic Hapludolls) on the second intermediate level (5–6 ka), and Tt-5 pedon (Typic Udipsamments) on the third lower level with the youngest soil age (≤ 3.5 ka). The morphological characteristics showed that strongly developed angular blocky structures, pressure faces and slickensides are more common in higher terrace soils than in lower terrace soils. In this study, depth to C horizon, solum thickness, and thickness of the clay-enriched zone increase with relative terrace age. Although only one to two profiles per terrace were characterized, the following soil analytical characterizations increase with time: the degree of sand grains weathering, pH (H 2O), organic carbon, CEC, contents of Fe d, Fe o and Mn d. Based on X-ray diffraction analysis of the clay-size fraction, soils on all terraces have a mixed mineralogy. Mica, smectite, and kaolinite have slightly increased with increasing terrace age. Furthermore, the dominant processes identified with mass-balance analysis include loss of bases (Ca and Mg), iron, and clay with time. The soil properties, including analytical and mineralogical characterizations, which do not have notable changes with time are primarily due to relatively young soil age (< 10 ka).