Mean Grain Size Research Articles

Effects of indentation depth and grain size on scratching behavior of nanograin FCC Fe polycrystalline substrate

Owing to their high grain boundary (GB) density, nanograin materials have excellent mechanical and physicochemical properties. The variation of GB density can dominate their plastic deformation mechanism. This work investigated the effects of indentation depth and mean grain size (MGS) on the scratching plastic deformation of FCC Fe nanograin substrates by molecular dynamics method. The contact strengths of the models with MGSs of 2.05 and 8.71 nm were the smallest (9.26 GPa) and largest (11.67 GPa), respectively. When the MGS was refined smaller than the critical size (5.07 nm), the Hall–Petch breakdown occurred in the nanograin polycrystalline substrate. With the increase in the indentation depth, plastic deformation became dominant, and abrasion volume first increased and then decreased with a decrease in the MGS. The lateral friction force and normal forces (including their increments) increased with the indentation depth. Models with moderate grain sizes could maintain larger "acceleration" of friction and normal force increments. After grain refinement, dislocations increased during the scratching process, and all of them were short dislocations limited by grain boundaries; in particular, there was no long straight stair-rod dislocation. The shear strain in ultrafine grain model was distributed along GBs. Grain lattice rotation extends throughout small grains with the MGS decrease to 2.05 nm. The deformation mechanism changed from dislocation-mediated mechanism to that involving grain lattice rotation and GBs sliding. This work can provide a theoretical basis for the design, machining, and performance prediction of nanograin polycrystalline materials.

Evolution of sedimentary environment in the Eastern Henan Basin since the Late Pliocene

The Eastern Henan Basin is situated within the downstream alluvial plain of the Yellow River, harboring an impressive accumulation of over 500 m of fluviolacustrine strata since the Pliocene. However, the evolutionary characteristics and driving factors of the sedimentary environment in this region remain unclear due to a lack of reliable chronological constraints on the sedimentary sequence. Here, two cores were retrieved from Hangkonggang (HKG, 303.5 m) and Baisha (BS, 320.2 m) in the Eastern Henan Basin for comprehensive analyses of chronology and sedimentology. A combination of paleomagnetism, electron spin resonance (ESR), and optically stimulated luminescence (OSL) dating results indicates that sediments of two boreholes were accumulated spanning the last ∼3.48 Ma. Grain size distributions (GSDs) of typical sedimentary facies show that the boreholes predominantly encompass three types of sedimentary facies: riverbed, levee, and floodplain. Downcore variations of mean grain size (MGS) reveal that the sedimentary environment in this basin evolved from a dominant riverbed setting during the late Pliocene (3.48–2.72 Ma) to alternations between the floodplain and levee facies during the early Pleistocene (2.72–1.25 Ma) and subsequently between the riverbed, levee, and floodplain after 1.25 Ma. It was closely associated with the decrease in East Asian monsoon precipitation at ∼2.72 Ma and the increase at 1.25 Ma. Notably, the abrupt coarsening of MGS after ∼1.25 Ma was synchronized with the formation of the Sanmenxia terraces, implying the significant influence of the evolution of the Yellow River. Our results suggest that the sedimentary environment of the Eastern Henan Basin was predominantly affected by the stepwise evolution of the East Asian monsoon since ∼3.48 Ma and complementary landform transformation of the Yellow River since at least ∼1.25 Ma.

Formation and evolution of a loess sinkhole in the southern Chinese Loess Plateau

Sinkholes are formed by the collapse of the overlying strata or the subsidence of the ground from cracks or holes in the underlying strata, which are widely developed in the karst and loess regions over southern and northern China. These sinkholes have been explored intensively to infer their climatic and ecological significances, as well as the management of geological disasters. In this study we investigated the Sanyuan (SY) sinkhole in the southern Chinese Loess Plateau to understand how it was formed and evolved. Two 30-m cores were retrieved from the SY sinkhole and a detailed chronological framework was established by applying radionuclides dating for the top 1-m sediments as well as 14C dating for the two 30-m cores. These dating results show that SY sinkhole was formed 23.7 m below the sinkhole surface at ca. 6.0 kyr BP (before 1950 CE). Changes in lithology, sedimentation rate, magnetic susceptibility, lightness, and mean grain-size of these two cores reveal that the sinkhole has undergone two-stage evolution. The first stage was characterized by a relatively slow deposition of loess sediments during 6.0–1.9 kyr BP, and the second stage was a rapid accumulating period since 1.9 kyr BP likely affected by human activities. Our results suggest that SY sinkhole can well document the combined influence of climate change and human activities, offering an ideal archive to decipher the natural and anthropogenic imprints since the mid-Holocene.

One million years of Mediterranean outflow strength

An orbitally tuned age model is established, based principally on sortable silt mean grainsize (SS¯, proxy for flow speed), for sediments deposited under the influence of the Mediterranean Outflow (MO) at IODP Site U1389 in the Gulf of Cadiz. The possibility of tuning sortable silt grainsize to insolation was indicated by close agreement between these two parameters on an earlier isotopically-based age model for the upper 130 m of the core. This led to tuning of the whole 390 m-long record with addition of a magnetic susceptibility control at Marine Isotope Stage 16, and the last occurrence of R. asanoi datum at around 900 ka (now dated at 910 ka in this core).The strongest variability in SS¯ is precessional with speed maxima at insolation minima superimposed on an increase in flow speed from 620 ka to the present. Although the Gibraltar sill exercises a major control on the inflow and outflow to the Mediterranean, there is little change in flow depth over most 20 ka precessional cycles, and therefore minor hydraulic control. Accelerations in average flow speed are also seen in interglacial to glacial (IG-G) cycles, particularly after 550 ka, with strong speed maxima at maximum glacial lowering of sealevel. This has allowed calculation of the sensitivity of flow speed to sea-level (SL) change of ∼0.074 cm s−1/m. From 990 to 620 ka the average amplitude of precessional speed changes is 3.7 cm s−1, but this increases to 7.7 cm s−1 from 620 ka to present.Deep ocean flow speeds are mainly density driven. Previous work has demonstrated that the major drivers of this system's density on precessional timescales are the evaporation - precipitation - inflow balance in the eastern Mediterranean plus cooling in the Gulf of Lions. Published benthic δ18O for 125–235 ka (corrected for ice volume changes) which tracks the combination of seawater temperature and salinity that controls density, demonstrates that flow speed and density maxima are coincident for that period and probably for the whole record. Although precessional SL changes are too small to affect flow speed significantly, SL does control accelerations at glacial maxima because shallower flow depth reduces inflow and leads to longer evaporation time, resulting in increased outflow density and speed. The sensitivity of flow speed to sill depth changes has allowed estimation of the long-term shallowing of the Gibraltar sill of ∼68 m over the last 620 ka in agreement with dated terrace uplift.

Sediment transport trend and its influencing factors in coastal bedrock island sea areas-a case study of Chudao island, China

Coastal bedrock islands sea areas have a unique natural environment, frequent human activities, and complex sedimentary dynamic processes. In this paper, we select the Chudao Island sea area off the coast of Shandong Peninsula, China, as a typical research area to investigate the sediment transport trends and influencing factors by means of high-precision bathymetric survey, high-density sediment sampling, grain-size trend analysis and hydrodynamic numerical modeling. Results and analysis indicate that the grain size parameters including mean grain-size, sorting coefficient and skewness are zonal distributed, roughly parallel to the isobaths. While the overall sediment transport trend is from island shore to sea, with several convergence centers near the loop centers of bottom flow and at the edge of the agriculture area. The near-bottom flow velocity is primary factor that controlling the significance of sediment transport trend, while the flow decides the general patterns of sediment transport trend and sediment distribution. Submarine topography can either directly transport sediments down its slope, or indirectly affect the direction of sediment transport by constraining the near-bottom flow from shallow to deep waters. Besides the natural factors of bottom flow and submarine topography, human activities represented by aquaculture also affect the sediment transport trend in coastal bedrock island sea areas. First, the increased sedimentation rate caused by organic matters and the diffusion of scallop fragments may cause sediment coarsening. Second, the artificial aquaculture facilities can reduce flow velocity and therefore hinder the initiation, suspension and transport of sediment near the aquaculture areas. Our methods and findings provide high-resolution details to insight into the sediment transport trends to improve the understanding of the modern sediment dynamics in small-scale coastal bedrock island sea areas and provide reference for corresponding engineering and agriculture activities.

Laboratory insights into the effects of methane hydrate on the anisotropic joint elastic-electrical properties in fractured sandstones

Fractured hydrate-bearing reservoirs show significantly anisotropic geophysical properties. The joint application of seismic and electromagnetic explorations is expected to accurately assess hydrate resources in the fractured reservoirs. However, the anisotropic joint elastic-electrical properties in such reservoirs that are the key to the successful application of the joint explorations, remain poorly understood. To obtain such knowledge, we designed and implemented dedicated laboratory experiments to study the anisotropic joint elastic-electrical properties in fractured artificial silica sandstones (with fracture density of about 6.2%, porosity of approximately 25.7%, and mean grainsize of 0.089 mm) with evolving methane hydrate. The experimental results showed that the anisotropic compressional wave velocities respectively increased and decreased with the forming and dissociating hydrate, and the variation in the increasing trend and the decreasing extent of the velocity perpendicular to the fractures were more significant than that parallel to the fractures, respectively. The experimental results also showed that the overall decreasing trend of the electrical conductivity parallel to the fractures was steeper than that perpendicular to the fractures during hydrate formation, and the general variations of the two conductivities with complex trend were similar during hydrate dissociation. The variations in the elastic and electrical anisotropic parameters with forming and dissociating hydrate were also found to be distinct. Interpretation of the experimental results suggested that the hydrate binding to the grains evolved to bridge the surfaces of fractures when saturation exceeded 10% during hydrate formation, and the bridging hydrate gradually evolved to floating in fractures during dissociation. The experimental results further showed that the anisotropic velocities and electrical conductivities were correlated with approximately consistent trends of different slopes during hydrate formation, and the joint elastic-electrical anisotropic parameters exhibited a sharp peak at the hydrate saturation of about 10%. The results suggested that the anisotropic joint properties can be employed not only to accurately estimate hydrate saturation but also possibly to identify hydrate distribution in the fractures.

Soil texture influences soil bacterial biomass in the permafrost-affected alpine desert of the Tibetan plateau.

Under warm climate conditions, permafrost thawing results in the substantial release of carbon (C) into the atmosphere and potentially triggers strong positive feedback to global warming. Soil microorganisms play an important role in decomposing organic C in permafrost, thus potentially regulating the ecosystem C balance in permafrost-affected regions. Soil microbial community and biomass are mainly affected by soil organic carbon (SOC) content and soil texture. Most studies have focused on acidic permafrost soil (pH < 7), whereas few examined alkaline permafrost-affected soil (pH > 7). In this study, we analyzed soil microbial communities and biomass in the alpine desert and steppe on the Tibetan plateau, where the soil pH values were approximately 8.7 ± 0.2 and 8.5 ± 0.1, respectively. Our results revealed that microbial biomass was significantly associated with mean grain size (MGS) and SOC content in alkaline permafrost-affected soils (p < 0.05). In particular, bacterial and fungal biomasses were affected by SOC content in the alpine steppe, whereas bacterial and fungal biomasses were mainly affected by MGS and SOC content, respectively, in the alpine desert. Combined with the results of the structural equation model, those findings suggest that SOC content affects soil texture under high pH-value (pH 8-9) and that soil microbial biomass is indirectly affected. Soils in the alpine steppe and desert are dominated by plagioclase, which provides colonization sites for bacterial communities. This study aimed to highlight the importance of soil texture in managing soil microbial biomass and demonstrate the differential impacts of soil texture on fungal and bacterial communities in alkaline permafrost-affected regions.

Grain-size composition of the surface sediments in Chinese deserts and the associated dust emission

Chinese deserts are one of the essential source areas for global dust emission, and the intensity of dust emissions varies significantly depending on the grain-size composition of sediments, wind force, and vegetation coverage. To obtain complete and accurate information on the grain-size compositions of the surface sediments in these deserts and to assess the contribution of Chinese deserts to Asian dust emission, we systematically collected surface sediments from 12 deserts in northern China, and analyzed their grain-size composition. We also calculated dust emissions from 2010 to 2019 based on the sand transport rate and clay content. The mean grain-size of surface sediments was 2.34Φ, and the clay and silt contents were only 0.6 and 6.7%, respectively. The Taklimakan Desert had the finest surface sediment, with a mean grain-size of 2.75Φ, whereas the Kumtag Desert had the coarsest sediment, with a mean grain-size of 2.00Φ. The total annual dust emission of the Chinese deserts from 2010 to 2019 was 70.6 Tg y-1. The Taklimakan Desert in the western region, the Badain Jaran Desert and the adjacent Tengger and Ulan Buh deserts in the central region, and the Otindag Sandy Land in the eastern region were the greatest contributors to dust emission. These core areas of dust emission are also the regions with the highest dust storm frequency, indicating that the deserts are significant regions for dust storms in northern China and an important surface type for dust emission in China. We found a significant positive correlation between dust emission and dust storm frequency.

Grain size variation in the swash zone of Lhoong Beach, Aceh Besar

The spatio-temporal texture characteristics are key parameters for understanding the dynamics of the sedimentary environment. This study was conducted to determine the sediment characteristics in swash zone of Lhoong Beach, Aceh Besar Regency. The analysis emphasizes the seasonal variation of sediment mean grain size (MGS) based on vertical stratification. Sediment samples were taken during November 2018, January 2019 and March 2019, from 3 stations. Samples from station 3 had the coarsest grain characteristics, where the highest MGS value at station 3 was recorded in the mid-layer (5-10 cm) in November. The grain size was found to vary with changing seasons and the depth of the sediment layer. Based on depth stratification, the highest standard deviation was obtained by the mid-layer (5-10 cm); while by period, the highest standard deviation of the MGS value was generated during November.

Disturbed climate changes preserved in terrigenous sediments associated with anthropogenic activities during the last century in the Taiwan Strait, East Asia

Accelerated human activity has greatly reduced sediment discharge into the global oceans in recent decades; however, the potential influence on climate change signals carried by sediments during source-to-sink transport processes remains poorly understood. To this end, multiple sedimentological analyses, including X-ray fluorescence scanning, grain-size composition, clay mineralogy, and 210Pb dating, of three short sediment cores retrieved from the Taiwan Strait, East Asia were performed. The results show that the terrigenous sediments of these cores spanning the last 150 years are mainly derived from the Yangtze River, with relatively small contributions from the Taiwan, Zhejiang, and Fujian rivers. The grain-size compositions are predominantly silt and clay (>90%), with minor sand, and the clay mineral assemblages consist of primarily illite, smectite, and chlorite, with moderate kaolinite. Both the clay mineral assemblage and grain-size compositions inferred from both end-member (EM) modeling and standard deviation analysis provide indirect indicators to reveal the East Asian monsoon variations, realized mainly through the current transport processes. The decreased smectite/(illite + chlorite) ratios since the 1850s represent a relatively long-term weakened East Asian winter monsoon (EAWM), while the overall decreased mean grain-size of the fine sensitive component and EM3/(EM1 + EM2) ratio during the 1850s–1950s also implies a gradually weakened EAWM associated with the synchronously weakened Zhe-Min Coastal Current. These sedimentary records of the East Asian monsoon variations can be compared with numerous published paleoclimate records. However, the largely increased mean grain-size of the fine sensitive component and EM3/(EM1 + EM2) ratios since the 1950s indicates a false strengthened EAWM signal, which conflicts with instrumental data and the clay mineralogy record. This observation, coupled with the coarsened terrigenous grain-size and reduced terrigenous fluxes (decreased Ti/Ca ratios), is mainly attributed to intense anthropogenic influences associated mainly with dam proliferation. Therefore, disturbed climate change information preserved in the terrigenous sediments can be linked to increased anthropogenic activities, perhaps representing an additional feature during the Anthropocene epoch.

Predicting the Strength of Granitic Stones after Freeze–Thaw Cycles: Considering the Petrographic Characteristics and a New Approach Using Petro-Mechanical Parameter

The strength of stones is a determining factor for evaluating their durability after freeze–thaw (F–T) phenomenon in cold regions. In this study, a new petro-mechanical predictor parameter (PMPP) is proposed for predicting the strength of granitic stones after F–T. This criterion considers two parameters namely initial strength (IS) and petrographic characteristics including mineralogical composition and textural features. For this purpose, eight samples of granitic stones were selected to determine their IS (uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS)), mineralogical indices (including Feldspathic Index (IF), Coloration Index (IC), and Quartz-Feldspar Index (IQF)), and textural indices (including Texture Coefficient (TC), Index of Interlocking (g), Index of Grain Size Homogeneity (t), and Index of Mean Grain Size (MGS)). Then, the samples were subjected to the F–T test up to 60 cycles, and their UCS and BTS were measured. The results showed the F–T has the most and least effect on BTS and UCS, respectively. Also, the results obtained from correlation equations prove that influence of mineralogical indices on the UCS and BTS of samples after F–T is more significant than textural indices. Moreover, among the mineralogical and textural indices, IQF and MGS indicated a more significant effect on the UCS and BTS of samples after F–T. Finally, it was concluded that the PMPP has acceptable accuracy for predicting the UCS and BTS of samples after F–T, and thereby the durability of stones. Consequently, PMPP saves much time and provides significant practical advantages for a rapid durability assessment of granitic stones after F–T.

Fabrication of (SiC-AlN)/ZrB2 Composite with Nano-Micron Hybrid Microstructure via PCS-Derived Ceramics Route.

In this work, a (SiC-AlN)/ZrB2 composite with outstanding mechanical properties was prepared by using polymer-derived ceramics (PDCs) and hot-pressing technique. Flexural strength reached up to 460 ± 41 MPa, while AlN and ZrB2 contents were 10 wt%, and 15 wt%, respectively, under a hot-pressing temperature of 2000 °C. XRD pattern-evidenced SiC generated by pyrolysis of polycarbosilane (PCS) was mainly composed by 2H-SiC and 4H-SiC, both belonging to α-SiC. Micron-level ZrB2 secondary phase was observed inside the (SiC-AlN)/ZrB2 composite, while the mean grain size (MGS) of SiC-AlN matrix was approximately 97 nm. This unique nano-micron hybrid microstructure enhanced the mechanical properties. The present investigation provided a feasible tactic for strengthening ceramics from PDCs raw materials.

Sedimentary Dynamic and Composition of a Tidal Channel in a Tropical Hot Semi-Arid Environment, NE Brazil

Tidal channels comprise a peculiar and dynamic environment. This paper aims to recognize the sedimentary distribution and composition of a tidal channel located in a semi-arid climate area in order to understand the sedimentary dynamics of the region. This region has economic and environmental importance considering that several activities are developed in the area such as; salt industry and aquaculture with shrimp farming. The results and discussion presented here on the Barra Grande Port tidal channel are based on 43 superficial samples distributed in the area, in which we analyzed the grain-size distribution and the calcium carbonate and organic matter contents. The data enabled the characterization and compartmentalization of the tidal channel on five sections and the interpretation of the sedimentary dynamics of the area. The sections present an important variation in the composition and selection. The section 1 is located in supratidal zone while sections 02, 03, 04 and 05 are in intertidal zone. The grain-size mean has a tendency to decrease toward the end of the channel as well as the gravel percentage, and the carbonate and organic matter contents. Differently, the mud content and the sorting increase toward the end of the channel and the skewness becomes more positive. In a general way, the carbonate content is high throughout the tidal channel ranging from 20 to 98% while the organic matter content is low ranging from 0 to 3%. This sedimentary distribution occurs due to the development of a hydraulic dam on section 3, causing a morphological growth of this sand bar, which acts as a natural hydraulic dam, hampering the access of the tide and consequently reducing the effectiveness of the transport, resulting in the deposition of fine sediments in the sheltered areas of the channel (sections 04 and 05). The high temperatures and low rainfall of the tropical hot semi-arid climate allowed the development of carbonate sedimentation as well as the development of anthropic activities such as salt extraction in artificial salt pans which may have influenced the low levels of organic matter.

Microstructure evolution dependence of work-hardening characteristic in cold deformation of a difficult-to-deform nickel-based superalloy

The work-hardening characteristic of nickel-based GH4141 superalloy was investigated using uniaxial compression tests with different cold deformations. Prior to compression, the solution treatment was optimized using the dissolving temperature of precipitations, the mean size of grains, and the microhardness of the samples. The typical true strain-stress curve included elastic deformation (ε ≤ 0.03), elastoplastic transition (0.03 ≤ ε ≤ 0.05), and plastic deformation (ε ≥ 0.05) stages. The true strain-stress relationship was formulated on the basis of Tian-Zhang model. During the plastic deformation stage, the true stress gradually increased due to the increase in dislocation slip resistance caused by the formation of dislocation tangles and different boundaries. The hardening rate gradually decreased because of the tardy dynamic recovery, and the decreasing dislocation density increment caused by the formation of grain boundaries.

Sedimentation and sediment geochemistry in a tropical mangrove channel meander, Sungai Kerteh, Peninsular Malaysia

Tropical mangrove swamps are commonly characterized by dense networks of tidal channels that may show pronounced meandering and dendritic patterns. Channel meanders are sometimes accompanied by cut-offs, and, like classical fluvial meanders, record changes in hydrology and sedimentation over time. Channel meandering can, thus, be an important process that contributes to spatial and temporal variability in the preserved record of the sedimentology and geochemistry of mangrove sediments. The aim of this study is to highlight changes in channel meander sedimentation in response to a meander cut-off in a tropical mangrove swamp. Two short sediment cores were sampled, respectively from a point bar (core KR1, 122 cm) at the junction with the neck cut-off and inside the cut-off (core KR2, 98 cm) in the Sungai Kerteh mangroves of Peninsular Malaysia. The profile comparison was based on sediment characteristics, total organic carbon (TOC), and selected elements (Fe, Na, Mg, Mn, Ba, and Sr). A smaller standard deviation of mean grain size (MGS) was found at the point bar (4.37 ± 0.51 ϕ) than in the cut-off (4.43 ± 1.76 ϕ), indicating a difference in flow velocity between the two settings. In turn, these changes in grain size influence channel meander evolution via associated changes in TOC and heavy metals. In order to clarify these relationships, we used principal components analysis and factor analysis. An increased accumulation of selected elements and TOC at the cut-off site from a depth of ~ 60 cm to the core-top segment was probably associated with a slowing down of sediment settling. A higher TOC recorded in the cut-off (2.74 ± 1.42%) compared to the point bar (1.14 ± 0.46%) suggests a propensity for prolonged in situ accumulation of organic matter in the abandoned meander bend. This study provides grain size and sediment geochemical information that is consistent with patterns of active and inactive sedimentation in the meander bends of mangrove channels.

Influence of Al3+ substituted cobalt nano-ferrite on structural, morphological and magnetic properties

The report focuses on studying the structural and magnetic properties of Al3+ substituted cobalt ferrite (CoAlxFe2-xO4, 0.0 ≤ x ≤ 1.0) nanoparticles. The samples have been synthesized by co-precipitation route, followed by annealing at 850 °C during 2 h in air. The X-ray diffraction patterns depict the formation of single cubic spinel structure with Fd-3m space group. Average crystallite size (DX) as well as unit cell parameter (a) were remarkably influenced by increasing Al content. The transmission electron microscopy (TEM) images reveal that grains have an irregular shape and that the mean size of grains decreases with Al content, as seen by XRD experiments with the crystallites behavior. In addition, the energy dispersive X-ray spectrometry analyses show that the samples are chemically homogeneous and the obtained chemical compositions are in agreement with the desired stoichiometry. The scanning electron microscopy exhibits consistence investigations with those observed by TEM. Magnetization-field M(H) curves at 4 and 300 K, highlight that the saturation magnetization and coercivity are considerably influenced by Al content. Thermal variation of the magnetization, M(T), results reveal the existence of inter-particle interactions in the studied samples, further the blocking temperature is found higher than 300 K. Room Mössbauer spectra collected for all samples show a wide effect of Al content on hyperfine properties of Co-ferrite. Indeed, their fits were performed with different components reflecting the incorporation of Fe3+ into A and B sub-structures of ferrite spinel system as the Al content increases. The variation of the hyperfine field, Hhyp, agrees with behavior of Ms as the Al substituent increases from 0.0 to 1.0.

Microstructural and Micromechanical Characteristics of Tin-Based Solders Under Self-Propagating Exothermic Reaction Heating

In this study, a rapid solder melting process has been examined through a self-propagating exothermic reaction using Al/Ni nanofoil as a localized heat source. Four kinds of tin-based solder preforms were partly melted under this process, and the thicknesses of the fusion zone in solder preforms around the Al/Ni nanofoil were experimentally analyzed. The microstructure and morphology of the fusion zone in different kinds of solder preforms were studied by metallographic analysis. In Sn42Bi58 solder, the mean grain size of Bi-rich phases in the fusion zone was finer than the original structure, and decreased from ~ 2.7 μm to ~ 0.8 μm away from the Al/Ni nanofoil. Similar trends of mean size of grains in the fusion zone were also found in the Sn, Sn-3 wt.%Ag-0.5 wt.%Cu(SAC), and SnPb solder preforms. The widths of the fusion zone in the Sn, SAC, SnPb, and SnBi solder preforms were 150 μm, 173 μm, 188 μm, and 233 μm, respectively. In addition, the nano-hardness and distribution in the fusion zones were evaluated. The results show that the value of nanohardness increased along with the decrease of distance from Al/Ni nanofoil. The average hardness and the lower and upper bounds of Sn, SnPb, SAC, and SnBi solder in the fusion zone are 0.260 (−0.045, +0.039) GPa, 0.246 (−0.059, +0.114) GPa, 0.260 (−0.014, +0.070) GPa, and 0.404 (−0.072, +0.134) GPa, respectively. The statistical significance of solder hardness is related to its alloy component, element content, and microstructure.

Using electrical resistivity logs and short duration pumping tests to estimate hydraulic conductivity profiles

Hydraulic conductivity profiles (HCPs) are of crucial importance for 3-dimensional flow and transport groundwater models. Easy and inexpensive methods for the estimation of such profiles increase their availability and strengthen the efficiency of the models. In this study a method is presented, which combines the electrical resistivity (ER) measured over the depth of the aquifer in a borehole and the response of the aquifer to the short duration pumping from the borehole. The hydraulic conductivity profile is calculated from the Kozeny-Carman equation, in which the profiles of the porosity and the mean grain size (MGS) are required. Porosity is calculated from Archie’s law using the intrinsic formation factor, which results from the ER. MGS is calculated from the porosity using a relationship between them. The initial form of this relationship is obtained from literature data and is then adjusted to the conditions of each particular case. The adjustment is achieved by calibrating a MODFLOW based groundwater model, so that it sufficiently simulates the temporal variation of the water level measured in the borehole during the short pumping. The method is applied to the estimation of the HCP in an unconsolidated alluvial aquifer in Greece. The sensitivity of the results to the parameters and assumptions used in the method is investigated and discussed.

Improved ferroelectric and piezoelectric properties of (Na0.47Bi0.47Ba0.06)0.97Sr0.03TiO3 lead-free ceramics sintered in nitrogen atmosphere

The dense ceramics (Na0.47Bi0.47Ba0.06)0.97Sr0.03TiO3 were sintered in nitrogen atmosphere. The weight loss during sintering is 0.2%. The mean size of grains is about 1.5 μm. The dielectric permittivity and dielectric loss of the ceramics at room temperature and 1 kHz are 1836 and 0.05, respectively. The dielectric spectra of the unpoled and poled ceramics were measured. The diffuse dielectric behavior was studied via the Curie-Weiss law and modified Curie-Weiss law. The ceramics exhibit excellent ferroelectric properties. At room temperature, the d33 is as high as 157 pC/N. The ceramics exhibit excellent temperature stability of d33 between room temperature and 115 °C.

Investigation of the effect of grain size on liquefaction potential of sands

Due to the permanent damage to structures during earthquakes, soil liquefaction is an important issue in geotechnical earthquake engineering that needs to be investigated. Typical examples of soil liquefaction have been observed in many earthquakes, particularly in Alaska, Niigata (1964), San Fernando (1971), Loma Prieta (1989), Kobe (1995) and Izmit (1999) earthquakes. In this study, liquefaction behavior of uniform sands of different grain sizes was investigated by using the energy-based method. For this purpose, a total of 36 deformation-controlled tests were conducted on water-saturated samples in undrained conditions by using the cyclic simple shear test method and considering the relative density, effective stress and mean grain size parameters that affect the cumulative liquefaction energy. The results showed that as the mean grain size decreases, the liquefaction potential of the sand increases. In addition, with increasing effective stress and relative density, the resistance of sand against liquefaction decreases. Multiple regression analysis was performed on the test results and separate correlations were proposed for the samples with mean grain size of 0.11-0.26 mm and for the ones with 0.45-0.85 mm. The recommended relationships were compared to the ones existing in the literature and compatible results were obtained.