Densification Rate Research Articles

Microstructure, electrical conductivity, and wear behavior of aluminum-carbon nanotubes and biosynthesized silver nanoparticles composites

Low-cost biosynthesized silver nanoparticles (GAgNPs) were used to enhance the properties of Al-carbon nanotube (CNTs) composites. Al-x% CNTs (× =0, 1, 2, 3, 4) and Al-x% CNTs (× =0, 1, 2, 3, 4) with 2%GAgNPs were produced using high intensive ball milling and spark plasma sintering. The densification, electrical conductivity, microstructure, hardness values, and wear rate were determined. The balling milling of the powders and the SPS method used in the production of the nanocomposites help to close the micro-voids in the materials with high values of densification. Higher dislocation density was obtained for the Al-4%CNTs+2%GAgNPs nanocomposites. A 7.8% and 93.11% raise in the electrical conductivity was obtained for Al, Al-4%CNTs, and Al-4%CNTs-2%GAgNPs composites. It can be concluded that the wear behavior of the Al-CNTs-GAgNPs nanocomposites was affected by the good densification of the composites, homogenous distribution of the reinforcement, and hardness values of the nanocomposites. It was established that a lower coefficient of friction and wear rate with higher electrical conductivity can be obtained with the developed Al-CNTs+GAgNPs nanocomposites.

Urban Gardens and Soil Compaction: a Land Use Alternative for Runoff Decrease

After several landscape transformations caused by human activities, finding a suitable environment becomes increasingly challenging in urbanized regions. The predominance of non-permeable areas results in a low level of water infiltration. Notwithstanding, even green areas can have high runoff rates, since soil compaction has a decisive influence on the water movement. In places that have a natural predisposition to overflow, these problems are more significant. This study aimed to investigate causes of flooding, highlight the benefits of urban gardening and to propose urban gardening as an alternative to soil improvement in the Corujas Watershed, Sao Paulo, Brazil. The evaluation was based on: (a) the physical characteristics of the watershed, provided by morphometric analysis and land-use analysis; and (b) the soil compaction rates of an urban garden compared to a riparian forest and a grass area. The morphometric results indicated that the watershed has a significant flood tendency, and the land use map demonstrated that 29.55 % of the soil has some permeability. Nevertheless, this permeability currently varies according to soil management and cover. The grass area presented the highest compaction rates, the riparian forest a medium rate, and Corujas Garden the lowest rate. The garden also has green infrastructures and good management practices, which have led to the appearance and perpetuation of diffuse springs. These results showed that the urban garden activities could improve the physical characteristics of the soil and optimize water infiltration. Subsequent studies will investigate whether this characteristic also applies to other gardens located in different urban watersheds.

Modeling the Effect of Particle Packing Density for Sintering

This research studies the effect of particle packing density on sintering TiO2 microstructure. Sintering experiment was conducted on compacts involving of monodisperse spherical TiO2 particles. The experimental results are modeled using L2-Regression technique in studing the effect of two theoretical values of 55% and 69% of initial packing densities. The mathematical simulation shows that the lower values of density compacts sintered fast to theoretical density and this reflects that particle packing density improved densification rate because of the competing influence of grain growth at higher values of densities.

In situ formation of Si3N4–SiC nanocomposites through polymer-derived SiAlCN ceramics and spark plasma sintering

In this paper, fully dense Si3N4/SiC nano-composites were fabricated through polymer-derived ceramics (PDCs) method and spark plasma sintering technique. Polymer-derived SiAlCN ceramic was synthesized by using polysilazane as preceramic precursor, aluminum tri-sec-butoxide as Al source. Then Si3N4/SiC composites with nanometer sized Si3N4 and SiC phases were formed spontaneously during spark plasma sintering through in-situ phase separation of amorphous SiAlCN ceramics. It's found that with the increasement of Al contents, the densification rate was accelerated significantly and serious degradation of Si3N4 phase was avoided by restricting carbothermal reaction. At the same time, Al contained composites show excellent oxidation/corrosion resistance at 1350 °C and 50% H2O - 50% O2 water vapor environment than that of Al free samples. The Si3N4/SiC composites derived from Al contained PDCs overcomes the trade-off between abnormal grain growth and serious degradation of Si3N4 phase, which is a very tough problem for traditional PDC route (without Al) to fabricate Si3N4/SiC composites. For traditional PDC route, (I) if with traditional sintering additives, abnormal grain growth occurs, nano grains cannot be achieved; (II) if without traditional sintering additives, serious degradation of Si3N4 occurs, Si3N4 and SiC composite cannot be formed. Therefore, Al contained polymer-derived ceramics route opens a promising avenue to fabricate Si3N4/SiC nano-composites with fine grain size, uniform microstructure and excellent oxidation/corrosion resistance.

Effect of strong mineral fluxes on sintering of porcelain stoneware tiles

Strong fluxes are needed to fire vitrified ceramics at temperatures significantly lower than those usually reached in industrial firing cycles. This work is aimed at understanding the role of strong fluxes in the microstructural evolution during sintering. Six fluxes (colemanite, ulexite, wollastonite, diopside, spodumene and phonolite) were individually added to a porcelain stoneware batch and processed in standard conditions. Compacts and fired bodies were characterized by optical dilatometry, XRD-Rietveld, SEM and measuring technological properties. Strong fluxes change the firing behaviour with a complex interplay of sintering kinetics, microstructural features, and phase composition. Every flux has its own repercussion on the properties of the liquid phase (chemical composition, degree of polymerization, viscosity and surface tension) which are key points to explain the observed microstructure, densification rates, and stability at high temperature. Batches with phonolite, wollastonite or diopside exhibit characteristics closer to standard porcelain stoneware, while spodumene and borates suffer from unsatisfactory microstructures and lower densification efficiency.

Thermodynamic and experimental approach of the effect of Si on the sintering of Y3NbO7

The effect of silicon on the natural sintering of Y3NbO7 powders is studied. Characterizations shows that Si increases densification rate and grain growth but it also leads to the apparition of a secondary silicate phase. The silicate precipitation results from the segregation of silicon favored by matter transport through a liquid phase. The distribution of the secondary phase have been studied by electronic microscopy and mapped by micro-luminescence. Thermodynamic calculations of Gibbs energy of the different phase as well as binary and ternary phase diagrams have been conducted to support interpretation of the sintering experimental results.

Revealing dehydrogenation effect and resultant densification mechanism during pressureless sintering of TiH2 powder

The use of TiH2 powder as a sintering precursor can produce nearly full-density titanium and titanium alloys with good mechanical properties. Unfortunately, there is a lack of research on the effect of lattice defects generated during the dehydrogenation of TiH2 powder, and the underlying sintering diffusion mechanism and activation energy have yet to be determined. In this work, we report a two-step sintering strategy to reveal the dehydrogenation effect and resultant densification mechanism during the pressureless sintering of a TiH2 powder precursor. The results show that, compared with hydrogenated-dehydrogenated (HDH) Ti powder, TiH2 powder, an intermediate of HDH-Ti powder, exhibited a higher instantaneous densification rate, greater onset relative density, rapid grain growth, and thus a smaller grain size. It also showed a grain boundary diffusion mechanism below 91% relative density and half the sintering activation energy in the intermediate sintering stage. Fundamentally, this was attributed to lattice defects generated during the dehydrogenation of TiH2 powder, which was confirmed by the greater relative density of a sintered TiH2 compact due to the two-step sintering strategy designed herein. Interestingly, the sintered sample obtained from the TiH2 powder precursor has a satisfying combination of strength and ductility that is far superior to other bulk Ti materials, especially sintered bulk Ti obtained from HDH-Ti powder. The results obtained in this paper provide theoretical guidance for using pressureless sintering to produce nearly full-density Ti and Ti alloys with good mechanical properties for structural applications.

Effect of La2O3 content on the densification, microstructure and mechanical property of W-La2O3 alloy via pressureless sintering

In the present work, the influences of La2O3 content (0–5.0 wt%) on the densification and grain growth of tungsten (W) nanopowders during pressureless sintering were systematically investigated. The densification inhibitory effect was enhanced with the increase of the amount of La2O3 addition, resulting in that the densification rate decreases from pure W to W/5.0wt%La2O3 composite powder. However, the grain size of W first decreases from 0 wt% to 2.0wt%La2O3 addition due to the increase of number density of La2O3 particles, and then increases from 2.0 wt% to 5.0wt%La2O3 addition because of the significant increase of the particle size and the decrease of the number density. On the premise of achieving near full density, the grain size of all W-La2O3 alloys sintered by pressureless sintering is very small, only 0.47–1.90 μm. The W-2.0wt%La2O3 alloy sintered at 1650 °C with the grain size of 0.47 μm possesses the highest Vickers microhardness of 739.3 HV0.2.

Measuring and Interpreting Multilayer Aquifer‐System Compactions for a Sustainable Groundwater‐System Development

AbstractEver decreasing water resources and climate change have driven the increasing use of groundwater causing land subsidence in many countries. Geodetic sensors such as InSAR, GPS and leveling can detect surface deformation but cannot measure subsurface deformation. A single‐well, single‐depth extensometer can be used to measure subsurface deformation, but it cannot delineate the depths of major compaction and provide insight about the deformation mechanism throughout a complex aquifer system, unless man extensometers at different depths are used. We present a multilayer compaction well (MLCW), installed in a borehole, that uses magnetic rings to detect stratum compaction at 25 depths as deep as 300 m below land surface. Our laboratory and field assessments indicate 1 mm precision and accuracy for one single‐depth magnetic reading. We tested the performance of MLCW by measuring aquifer‐system compaction over the proximal, middle, and distal fans of the Choushui River Alluvial Fan (CRAF) that has long experienced severe land subsidence. The MLCW measurements were used to create time‐depth diagrams of compaction, showing different compaction rates at different layers of aquifers and aquitards to identify the depths of major compactions. The elastic (reversible) and inelastic (irreversible) compactions from MLCW were used in stress‐strain analyses to estimate skeletal specific storages and the safe groundwater levels, below which groundwater extractions have caused irreversible compactions. The hydrogeological parameters derived from MLCW measurements can help governmental agencies to determine effective land‐use and water‐use policies, and ascertain the best strategy for utilizing artificial recharge to prevent land subsidence and achieve sustainable groundwater management.

Dynamic compaction of the Baltic basin silty Sand - quality assurance with CPT, DPM, DMT and PLT

Post-glacial evolution of the Baltic basin sedimented Quaternary soils at the great thickness (up to 30 m) in Riga, Latvia. There are present zones of different combinations of postglacial, alluvial, limnological and dune formations within the metropolitan area of Riga. The geomorphological evolution of this territory is dominated by the Baltic sea former stages, distinguishing these areas as rather complicated. The dynamic compaction was proposed below the warehouse floor of area about 40K m2 in Baltic basin silty Sand. The effect of compaction was evaluated to the depth of 10 m and extensive quality assurance using cone penetration and piezocone tests (CPT(U)), dynamic probing (DP) tests, flat dilatometer tests (DMT) and plate loading tests (PLT), was introduced. CPT(U) and DMT results were compared in terms of soil stiffness parameter evaluation prior and after dynamic compaction. The limitation of DP tests were investigated and finally also warehouse test embankment verified by PLT evaluating shallow compaction rates.

Experimental settling, floatation and compaction of plagioclase in basaltic melt and a revision of melt density

Centrifuge-assisted piston cylinder experiments were conducted on plagioclase in basaltic melt at 1140–1250 °C, 0.42–0.84 GPa and mostly 1000 g. One set of experiments assesses the settling velocity of a dilute plagioclase suspension; a second sinks or floats plagioclase in a MORB-type melt exploring conditions of neutral buoyancy; and a third set examines floatation of plagioclase from an evolved lunar magma ocean composition. A compaction rate for plagioclase cumulates is established. The experiments demonstrate that neutral density of plagioclase An74 in a MOR-type tholeiitic basalt occurs at 0.59 ± 0.04 GPa (1200 °C), contrasting predictions by present models on melt density which yield a density inversion pressure at 0.10–0.15 GPa. In nature, the level of neutral buoyancy depends on melt composition; nevertheless, for the onset of plagioclase crystallization in dry tholeiitic basalts, our result is robust. As the molar volume of plagioclase is well known, the experimentally determined pressure of neutral buoyancy indicates a correction of -1.6% to previous density models for silicate melts. It follows that for (tholeiitic) layered mafic intrusions, plagioclase is negatively buoyant for early, relatively primitive, parent melts. In contrast, the extreme Fe enrichment of a fractionating lunar magma ocean leads to melt densities that let anorthite always float. Compaction φ/φ0 of experimental plagioclase cumulates is quantified to φ/φ0 = − 0.0582 log (Δρ·h·a·t) + 1.284, where φ0 is the porosity after settling (67 ± 2%), h the cumulate pile height, a acceleration and φ porosity as a function of time t. Gravitational-driven compaction in tens of m-thick plagioclase cumulate in basaltic magmas reaches down to ~ 40% porosity within hundreds of years, a timescales competing with characteristic cooling times of cumulate layers of mafic intrusions. To achieve plagioclase modes > 80% due to compaction, an additional overload of ~ 100 m (layers) of mafic minerals would be required. Compaction of a lunar anorthosite crust of 35 km to 20% porosity (i.e. ~ 90% plagioclase after crystallization of the interstitial melt) would require 30 kyrs.

Firn Evolution at Camp Century, Greenland: 1966–2100

Camp Century is an American military base built in 1959 under the surface of the Greenland ice sheet and decommissioned in 1967. Here, we use outputs from RACMO2.3p2 and CanESM2 climate models, adjusted to meteorological observations, and a firn model to simulate the firn density and temperature at Camp Century between 1966 and 2100. The model output is evaluated against an extensive set of firn 3observations and three Representative Concentration Pathways (RCP2.6, 4.5 and 8.5) are considered as future scenarios. Our model suggests that the upper horizon of the Camp Century debris field – observed at a depth of 32 m in 2017 – will continue to be buried by persistent net accumulation over the next eighty years under all RCP scenarios. This horizon depth will be between 58 and 64 m in 2100, depending on the RCP scenario. We estimate a maximum meltwater percolation depth of 1.1 m under all RCP scenarios. We therefore find it extremely unlikely that surface meltwater interacts with the subsurface debris field at Camp Century before 2100 under all RCP scenarios. Camp Century’s future is representative of the firn area in northwestern Greenland, bound to shift from dry snow to a percolation regime. Our model suggests that 10 m firn temperatures at Camp Century will increase from −24.0°C in 1966 to −21.3, −20.0 and −18.6°C in 2100 under the RCP2.6, 4.5 and 8.5 scenarios, respectively. We reveal a previously unknown warm bias in air temperatures simulated at Camp Century by both RACMO2.3p2 and CanESM2 climate models which needs to be accounted for when using these models to predict melt, firn evolution and sea-level contribution of the Greenland ice sheet. We also present novelin situmeasurements of firn compaction rates, which indicate that about 25% of firn compaction of the top 62 m of firn occurs below 20 m depth. This highlights the importance of deep-firn compaction measurements for model evaluation and correction of altimetry products.

Constitutive Model of Solid Backfill Materials and Numerical Simulation of Overburden Movement and Deformation in Backfill Mining

Solid backfill mining is an efficient and environmental-friendly coal mining technology, which can effectively solve the problems of coal gangue pollution, water resource loss, and surface subsidence. Based on the mechanical behavior of backfill materials in the compaction process, volume strain was used to express the deformation modulus, and a constitutive model of backfill materials was proposed in this study. The ABAQUS UMAT was used to develop the numerical calculation subroutine of the model. Finally, the rationality of the model was verified that simulated stress-strain curves of the backfill materials during the compaction process agree well with experiments. Based on the proposed constitutive model, the influence of three factors (the initial compaction rate of the filling body, the mining height, and the mining depth) on the key strata and surface subsidence was analyzed systematically. The results show that the initial compaction rate and the height of coal seams have significant influences on surface subsidence. When the thickness of topsoil is only changed and the structural composition and lithology of overburden are not changed, the mining depth has little influence on surface subsidence, but a significant influence on surface subsidence range. The influence of mining height and mining depth on the deformation of key strata of overburden and surface subsidence is approximately linear, while the influence of the initial compaction rate is nonlinear.

Manufacture and Faraday magneto-optical effect of highly transparent novel holmium aluminum garnet ceramics

A novel transparent magneto-optical holmium aluminum garnet (HoAG) ceramic with a high in-line transmittance of ~80.3 % at 589 nm (~97.0 % of the theoretical transmittance of HoAG single crystal) and a maximal infrared cut-off at ~6.5 μm was successfully fabricated by vacuum sintering at 1650 °C. The facile co-precipitation strategy was employed to yield the precipitation precursor with hollow structures upon calcination into the sphere-like HoAG particle with a narrow particle distribution. Silica sintering aid creates point defect of Ho3+ vacancies to promote the HoAG densification rate during sintering by Si4+ substitution for Al3+ in tetrahedrally coordinated 24 (d) sites. The magneto-optical HoAG ceramic has Verdet constants of ~-154 rad/(T·m) at 635 nm and ~-36 rad/(T·m) at 1064 nm, which are higher than or similar to that of the commercial TGG single crystal. The thermal conductivity of the transparent HoAG ceramic was determined to be ~10.5 W/(m·K) at room temperature.

Fabrication of Highly Transparent Y2O3 Ceramics with CaO as Sintering Aid.

Highly transparent Y2O3 ceramics were successfully fabricated with CaO as sintering aid. The microstructure evolution, optical transmittance, hardness and thermal conductivity of the Y2O3 ceramics were investigated. It was found that doping a small amount (0.01–0.15 wt.%) of CaO could greatly improve the densification rate of Y2O3. With an optimized CaO dosage of 0.02 wt.% combined with the low temperature vacuum sintering plus hot isostatic pressing (HIP-ing), Y2O3 ceramics with in-line transmittance of 84.87% at 1200 nm and 81.4% at 600 nm were obtained.

Modeling Subsurface Drainage in Compacted Cultivated Histosols

Reclaiming histosols in Montéregie region, Québec, Canada, increases peat decomposition and compaction rate and decreases the effectiveness of subsurface drainage. The objective of this paper was to use HYDRUS-2D to model the behavior of subsurface drainage systems, in order to evaluate the compaction effect on drain depth and spacing, and to determine the compact layer thickness and saturated hydraulic conductivities (Ksat) resulting in an improvement of subsurface drainage]. The drainage model was calibrated [Nash-Sutcliffe efficiency coefficient (NSE) = 0.958, percent bias (PBIAS) = −0.57%] using Ksat, meteorological data, and matric potential (h) data measured on the project site from June 10 to July 19, 2017. The calibrated and validated model was used to analyze the variation of h values (Δh in cm d−1) as a function of drain spacing (2–7 m) and drain depth (1 and 1.2 m) and to identify the response surface of Δh to various compact layer thickness and Ksat combinations. The results showed that Δh was on average 58% greater below the compact layer than above it and that reducing drain spacing or increasing drain depth does not improve the drainage rate. The analysis of the compact layer thickness and Ksat effect on Δh showed that for a Δh of 40 cm d−1, Ksat actual values in the two uppermost layers should be multiplied by 50 for compact layer thickness varying from 12 to 35 cm. Water percolation in the soil is reduced by the compact layer. Soil management methods for improving Ksat should therefore be better than deepening the drains or and reducing the spacing.

Understanding the mixed alkali effect on the sinterability and in vitro performance of bioactive glasses

Bioglass 45S5 is widely known for its ability to regenerate bone. However, this glass cannot be fully densified by viscous flow due to its very high tendency for crystallization. In this work, we evaluate the sintering and bioactivity of Bioglass 45S5-based compositions in which Na2O is incrementally replaced by K2O. Our sintering tests demonstrated that the densification of Bioglass 45S5 powders can be significantly enhanced due to a decreased crystallization tendency. The composition in which half of the original Na2O content was substituted by K2O exhibits the highest densification rate, evidencing the mixed alkali effect (MAE) in the viscous-flow-driven sintering process. The replacement of Na2O by K2O significantly improved both the densification rate and the in vitro performance. These results are very relevant for this particular glass and also for the design of new bioactive glasses with improved sinterability.

Electric-field-assisted processing of ceramics: Nonthermal effects and related mechanisms

Field-assisted processing methods, such as spark plasma sintering and flash sintering, have considerably expanded the toolbox of ceramic engineering. Depending on the conditions, substantial electric currents may flow through the material resulting in fast heating rates due to Joule heating. Here, we focus on nonthermal effects induced by electric fields during processing of fluorite- and perovskite-based ceramics. The fundamentals of how a field can directly modify defect formation and migration in crystals are discussed. In addition, the interplay of ion transport and electrical conductivity is considered, this interplay being crucial to understanding nonthermal effects caused by electric fields (as in memristive switching). Electrochemical reactions leading to new phases or reduction are also described, as are densification rates and sintering parameters that are significantly affected even though the sample temperature is held constant. Finally, as grain-boundary properties and segregation are changed by ion transport, we describe how both retardation and acceleration of grain growth can be achieved including graded microstructures.

Neck growth kinetics during polymer sintering for powder-based processes

To prevent texture defects in powder-based processes, the sintering time needs to be adjusted such that a certain amount of coalescence is achieved. However, predicting the required sintering time is extremely challenging to assess in materials such as polymers because the kinetics exhibit both elastic and viscous characteristics when undergoing deformation. The present work introduces a computational approach to model the viscoelastic effect in the sintering of particles. The model contains three stages, three different mechanisms driven by adhesive inter-surface forces and surface tension, which describes the non-linear sintering behaviour. Experimental data from the binary coalescence of Polystyrene (PS), Polyamide (PA) 12 and PEEK 450PF particles are employed to calibrate the contact model, as implemented in MercuryDPM, an open-source software package. Using machine learning-based Bayesian calibration, good agreement is obtained between the experimental data and the numerical results. The findings will be used in future studies to predict densification rates in powder-based processes.

Investigation of fluorescent lamp glass waste as a fluxing agent in porcelain bodies

In this research the effect of fluorescent lamp glass waste (FLGW) as a fluxing agent for preparing porcelain bodies has been investigated. Three different standard mixtures of porcelain bodies were prepared which composed of (kaolin, flint and potash feldspar). The FLGW is added to the porcelain samples at different ratios of (0, 5 and 10) wt.% as a partial replacement of potash feldspar. The samples were prepared using semi-dry process and then sintered at different temperatures ranged of (925–1250)°C. Sintering behavior, physical and mechanical properties of the prepared porcelain bodies were measured. The results showed the possibility of using the FLGW as a fluxing agent for the production of porcelain bodies. Increasing of sintering temperature leads to enhance the physical and mechanical properties of porcelain bodies. Addition of FLGW as a partial replacement of potash feldspar in the porcelain composition batch has beneficial effect on lowering the sintering temperature of porcelain bodies, consequently of accelerating the densification rates. The physical and mechanical properties of porcelain bodies reduced when added of high amount of FLGW up to 10 wt%. This is related to the composition of FLGW that contents of different materials with the presence of impurities in considerable amounts.