Inhomogeneous Size Distribution Research Articles

Numerical simulation on thermal properties of closed-cell metal foams with different cell size distributions and cell shapes

In this study, the effect of cell structure on the thermal properties of closed-cell foam metals are studied numerically. To do this, a novel modeling procedure is proposed to generate the FEM foam models with different cell structures. The cell size distribution and cell shape in the established models can be controlled by the modeling parameters applied in the modeling process. Two structural parameters termed as characteristic diameter Dch and characteristic shape anisotropy αch are then introduced to describe the cell size inhomogeneity and cell shape irregularity in the established models. The steady-state heat transfer simulation is carried out to calculate the effective thermal conductivity of foam models. It can be concluded from the simulation results that relative density is not the only factor that influences the thermal properties of closed-cell metal foams. Both the increase of Dch and αch could also induce a reduction in the normalized thermal conductivity. It indicates that, at a given relative density, the foams with the inhomogeneous cell size distribution and irregular cell shape are inclined to have a degraded thermal conductivity. Finally, the underlying mechanism governing the heat transfer behavior is also discussed.

Mechanical properties and microstructure of 9Cr-ODS-CLF-1 steel

A kind of oxide dispersion strengthened (ODS) steel with addition of 0.3 % Y2O3 and 0.3 % Ti was manufactured via mechanical alloying (MA) process from CLF-1 steel raw powder that was prepared by Ar gas atomization. This 10 kg ingot of 9Cr-ODS-CLF-1 steel was obtained by hot isostatic pressing (HIP) and subsequent forging. The as-HIPed and forged 9Cr-ODS-CLF-1 steel exhibits high Vicker hardness to 384 Hv which is much higher than that of CLF-1 steel (224 Hv). The ultimate tensile strength (UTS) is about 1100 MPa with elongation of 7 % at room temperature (RT). After 90 min tempering at 1013 K, the RT elongation increased to 11 % and the ultimate tensile strength decreased to 670 MPa. The creep results showed that the minimum strain rate for 9Cr-ODS-CLF-1 steel as received and 1013 K tempered state tested at 873 K under 160 MPa were low as 1.6 × 10-8 /s and 8.42 × 10-9 /s, respectively. Typical small dispersion particles were observed in the matrix. The grains showed inhomogeneous size distribution for both the as received and the 1013 K tempering state. The method of mechanical alloying combined with HIP proved to be an effective way to strengthen CLF-1 steel in large scale.

Significant differences in NaNbO3 ceramics fabricated using Nb2O5 precursors with various crystal structures

NaNbO3 (NN)-based solid solutions show potential applications in energy storage capacitors, strain actuators, and electrocaloric cooling devices. However, NN ceramics with distinct structures, which are prepared using various Nb2O5 precursors, have not been studied. In this work, two types of Nb2O5 precursors were used, including coexisting orthorhombic and monoclinic phases (denoted as OM), and single orthorhombic phase (denoted as O). Phase structure, grain morphology, sintering characteristics, ferroelectric performance, dielectric properties, and thermal-expansion properties were systematically investigated. Rietveld refinement of XRD data revealed that synthesized and sintered samples showed different phase structures. The content of ferroelectric phase (Q phase, space group P21ma) was 82.7% in synthesized NN-OM, whereas it was only 73.2% in synthesized NN-O; it was 33.8% in sintered NN-OM, while it was 18.6% in sintered NN-O. Raman spectra verified that the Q phase in NN-OM was more than that in NN-O. Curie temperature (Tc) of NN-OM was 363 °C, whereas Tc of NN-O was only 352 °C. Furthermore, compared with NN-O, NN-OM showed an inhomogeneous grain size distribution, lower optimum sintering temperature, higher phase transition temperature, stronger ferroelectric performance, and larger thermal-expansion displacement. Therefore, crystal structure of Nb2O5 has a great influence on the structure and performances of NN ceramics.

ULTRAFINE CONTROL OF Cu NANOPARTICLES AND THEIR ANTIBIOTIC EFFECT ON E. coli

Metallic nanoparticles have attracted intense interest for the potential applications in biocompatibility due to the reduced particle size. However, the methods to produce metallic nanoparticles usually produce an inhomogeneous size distribution. In this work, Cu nanoparticles were generated using a gas-aggregation cluster source technique, employing a specially designed quadrupole mass filter to control the size of the nanoparticles with a mass resolution (m/[Formula: see text]m) of 5. Transmission electron microscopic (TEM) analysis was used to confirm the size control of our technique. The generally high angular electronic scattering analysis revealed the spherical shapes of the Cu nanoparticles. We used beams of these nanoparticles to prepare nano-granular films on a Si substrate. Their antibacterial effect of the modified materials on Escherichia coli was assessed by means of a bacterial adhesion test. Our results may not only reveal the cluster technique to produce the uniform metallic nanoparticles, but also form the basis of antibacterial applications.

Effect of the injection pressure and orifice diameter on the spray characteristics of biodiesel

The purpose of this study was to analyze the influence of the injection pressure and orifice diameter on the spray characteristics of soybean biodiesel. The macroscopic spray characteristics of the spray tip penetration (STP) and spray cone angle (SCA) were tested with a high-speed camera system. The microscopic spray characteristics, such as the statistical size distribution, Sauter mean diameter (SMD), representative diameters and dispersion boundary, were obtained using a Malvern laser particle size analyzer (PSA). The test results showed that with an increasing injection pressure, the STP and the SCA of the biodiesel increased, but the curves of size-volume distribution and cumulative volume distribution of the atomized droplets shifted to smaller diameters. The SMD and representative diameters decreased, and the dispersion boundary was reduced. Moreover, with a decreasing orifice diameter, longer STP and smaller SCA values were observed. Similarly, the size distribution curves of the atomized biodiesel droplets shifted to smaller diameters. The SMD and representative diameters were reduced, and the relative size range of the atomized biodiesel droplets was enlarged. Higher injection pressures and smaller orifice diameters improved the biodiesel atomization; however, the smaller orifice diameters caused an inhomogeneous size distribution of the atomized biodiesel droplets.

Printability and microstructural evolution of Ti-5553 alloy fabricated by modulated laser powder bed fusion

In this research, the printability of Ti-5553 alloy is assessed using a modulated laser powder bed fusion method. Cylindrical samples were printed with a wide range of volumetric energy density (VED). Density evaluation was practiced by the Archimedes method and X-ray computed tomography (XCT). Surface roughness analysis and hardness mapping were further used to characterize the as-built samples. In addition, the microstructure was studied using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. It was observed that low and high VED values resulted in an increase in the level of porosity. The highest relative density of 99.92% and surface roughness of < 12 μm were achieved while using the VED of 112 J/mm3, resulting in a uniform hardness distribution equal to 295 ± 10 HV. In addition, the characterization by electron microscopy revealed evidence for the presence of ω phase in the sample with the highest density. It was also observed that the use of rather high VEDs gave rise to the in situ precipitation hardening due to nucleation of α-Ti needles in the β-Ti phase matrix. However, due to the inhomogeneous size distribution and volume fraction of the α-Ti needles along the building direction, a non-uniform hardness was obtained when high VEDs were applied.

Fabrication of polystyrene-encapsulated magnetic iron oxide nanoparticles via batch and microfluidic-assisted production

The magnetic properties of nanoparticles make them ideal for use in various applications, especially in biomedical applications. Herein, we describe the fabrication of iron oxide nanoparticles encapsulated in polystyrene (PS) using two methods: a conventional batch and microfluidic synthesis. In particular, we present a simple synthesis method of magnetic composite nanoparticles, based on the use of a microfluidic elongational flow method in a continuous-flow apparatus where magnetite particles are embedded in a polystyrene matrix. Compared to conventional batch synthesis, microfluidics-based synthesis enables precise reaction control, enhanced mixing and rapid chemical reactions, allowing flow synthesis of particles in a controllable, sustainable, and cost-saving manner that is attractive to industry. The composite particles show a high encapsulation of magnetite nanoparticles, but with an inhomogeneous size distribution; instead, the sample obtained with microfluidic approach shows a homogenous composite particle size distribution although the magnetite content is lower compared to the miniemulsion batch methods.

Influence of phase transformation kinetics on the microstructure and mechanical properties of near β titanium alloy

The influences of up-quenching aging (UQA) and step-quenching aging (SQA) on the microstructure development and mechanical properties of near β-Ti alloy Ti-5Al-3Mo-3V-2Cr-2Zr-1Nb-1Fe have been comparatively studied. The results showed that a large number of fine α precipitates were uniformly formed in UQA sample via ω-assisted nucleation, resulting in a higher aging hardening effect. Whereas under SQA treatment, the α precipitates had lower number density and became coarser in addition to inhomogeneous size distribution, in which plenty of α precipitates with large aspect ratio (>50) could be observed. With increasing the aging temperature from 480 °C to 650 °C, the number density of α precipitates with large aspect ratio was gradually reduced, and the hardness interval between UQA and SQA samples was decreased from 90 HV to 20 HV. When aged at high temperature (600 °C), a large number of ultrafine α precipitates were obtained in the UQA sample within 30 min, the number density, thickness and length of α precipitates were ~20 ppt/μm2, 40 nm and 180 nm, respectively, resulting in very high peak hardness (473 HV), but a rapid over-aging occurred due to the ripeness of α precipitates. The SQA treatment showed no evident over-aging tendency, and could yield a good combination of ultimate tensile strength (1284 MPa) and elongation (8%) with the existence of multiscale α precipitates.

Potentials with small‐angle neutron scattering technique for understanding structure–property relation of 3D‐printed materials

Carbon fiber (CF)‐embedded acrylonitrile butadiene styrene polymer composites printed on the large‐scale printer at Oak Ridge National Laboratory were investigated by small‐angle neutron scattering to correlate the microstructure of the composites with their mechanical strength. The microstructure of the polymer domains and the alignment of CF were characterized across the interfaces between layers of the hot‐melt extruded material and were compared with CF‐free ABS. The small‐angle neutron scattering data show that the CF‐containing material displays strong anisotropic scatterings suggesting molecular alignment along the printing direction that is not present in the CF‐free ABS. Scattering data analysis across the interfacial layer revealed enhanced molecular alignment along the printing direction near the boundaries and inhomogeneous size distribution of polymer domains upon the addition of CF. We attribute the compromised strength across interfacial layers from CF‐containing material to this inhomogeneous size distribution which prevents effective lateral interaction between layers. POLYM. ENG. SCI., 59:E65–E70, 2019. © 2018 Society of Plastics Engineers

Microstructure Evolution and Mechanical Properties of Keyhole Repair Welds in AA 2219-T851 Using Refill Friction Stir Spot Welding

The search for a suitable friction-based keyhole repair technique that fulfills the requirements for high-quality repair welds has become an important research topic, especially for aerospace applications. In order to provide and analyze an universal keyhole repair method for lightweight metals, refill friction stir spot welding is applied to through-hole repairs in 3- and 6-mm-thick sheets of precipitate hardening AA 2219-T851. Keyholes with a diameter of 7.5 mm were repair welded achieving a defect-free microstructure. The correlation between the microstructural evolution imposed by the repair process and the resulting mechanical properties is shown. A comprehensive analysis of the precipitate evolution in peak-aged AA 2219 during RFSSW is presented. Thermal cycle measurements revealed high heating rates and peak temperatures of up to 520 °C in the weld center. The thermal cycle caused mainly dissolution and minor equilibrium phase formation in the stirred zone. In the HAZ, overaging of the strengthening precipitates dominates with minor dissolution and equilibrium phase formation only in the direct proximity of the SZ. Microstructural analysis revealed typical weld zone formation with inhomogeneous grain size distribution in the SZ. The resulting mechanical properties are dominated by an inhomogeneous hardness distribution with lowest hardness in the TMAZ at 5 mm from the center of the weld. During tensile loading main yielding and the final fracture occur in the area of lowest strength. Tensile testing showed yield strength of 40 to 46% and UTS of 28 to 25% below BM values in 3- and 6-mm-thick sheets, respectively. The sheet thickness and post-weld natural aging were found to influence the mechanical properties of the weld significantly.

Survival of aerosol particles in a puff with spatially inhomogeneous size spectrum

Aerosol particles released from emission sources undergo various atmospheric and aerosol processes before they become a part of the background aerosols. Coagulation and dispersion, the two important processes that governs evolution of particle characteristics in a puff with an inhomogeneous size distribution of particles in space is considered in this study. This specific case consists of an initial Gaussian aerosol packet in which larger particles are preferentially segregated to farther distances from the centre of the packet. The coagulation-dispersion equation is solved using Jaffe approximation technique for obtaining essential results such as survival fraction, that is, fraction of particles surviving due to the simultaneous action of coagulation and dispersion. Analytical results are developed for the temporal variations of the number concentration, mean size and the standard deviation. The asymptotic results yield the final characteristics of the spectra of the particles which form a part of the background aerosols. These quantities are useful for defining the "effective aerosol source terms" in the general dynamic equations for background aerosols, long-range transport of aerosols, and geo-engineering applications. The results are further discussed.

Preparation of dual-targeted pH-sensitive DOX prodrug-microbubble complex and drug release experiment in vitro

Objective To prepare dual-targeted pH-sensitive DOX prodrug-microbubble complex and explore the characterization of complex with ultrasound as well as drug release in vitro. Methods Dual-targeted ligands, cRGD and folate were conjugated with heparin using carbodiimide method, and then the dual-targeted pH-sensitive DOX prodrug was synthesized by coupling DOX via a pH-sensitive hydrazone bond. The prodrug was combined with microbubbles to prepare complex by biotin-avidin system. The characterization of complex with/without ultrasound was investigated for size, morphology and drug loaded capacity.In vitro drug release manner of complex with/without at different pH was analyzed. Results DOX content of the prodrug determined by UV Spectrophotometry was about 18.9%. Dynamic laser light scattering analysis(DLS), corresponding to transmission electron microscope(TEM) findings, revealed its inhomogeneous size distribution [mean size (159.7±24.5)nm and (1 089.0±174.9)nm]. However, the complex was dispersed into uniform fragment after ultrasound irradiation[mean size (155.9±29.8)nm, polymer dispersity index(PDI) 0.22, Zeta potential -(20.6±3.4)mV]. The cumulative release rate of DOX from both complex and complex with ultrasound at pH 5.0 were much faster than that at pH 7.4, displaying a pH-triggered release manner. Conclusions Dual-targeted pH-sensitive DOX prodrug-microbubble complex displays excellent drug release activity in acid environment. Uniform fragment and smaller particle size of complex could be achieved via ultrasound irradiation, promoting DOX accumulation within tumor tissue and facilitating in vivo antitumor ability. Key words: Sonication; Doxorubicin; Microbubbles; Targeted therapy

Importance of filter’s microstructure in dynamic filtration modeling of gasoline particulate filters (GPFs): Inhomogeneous porosity and pore size distribution

The state-of-the-art multiscale modeling of gasoline particulate filter (GPF) including channel scale, wall scale, and pore scale is described. The microstructures of two GPFs were experimentally characterized. The pore size distributions of the GPFs were determined by mercury porosimetry. The porosity was measured by X-ray computed tomography (CT) and found to be inhomogeneous across the substrate wall. The significance of pore size distribution with respect to filtration performance was analyzed. The predictions of filtration efficiency were improved by including the pore size distribution in the filtration model. A dynamic heterogeneous multiscale filtration (HMF) model was utilized to simulate particulate filtration on a single channel particulate filter with realistic particulate emissions from a spark-ignition direct-injection (SIDI) gasoline engine. The dynamic evolution of filter’s microstructure and macroscopic filtration characteristics including mass- and number-based filtration efficiencies and pressure drop were predicted and discussed. The microstructure of the GPF substrate including inhomogeneous porosity and pore size distribution is found to significantly influence local particulate deposition inside the substrate and macroscopic filtration performance and is recommended to be resolved in the filtration model to simulate and evaluate the filtration performance of GPFs.

Structural and magnetic properties of praseodymium substituted barium-based spinel ferrites

In this research work BaPrxFe2-xO4 (x=0.0, 0.025, 0.05, 0.075, 0.10) spinel ferrites have been synthesized successfully by sol-gel technique. X-ray diffraction analysis confirmed the fcc spinel phase of the synthesized samples. All the samples showed inhomogeneous grain size distribution observed through scanning electron microscopy (SEM).Temperature dependence normalized AC susceptibility and Curie temperature studies revealed that BaFe2O4 exhibited multidomain (MD) structure with high Curie temperature. On the other hand, multidomain to single domain (SD) transitions occurred when the praseodymium is substituted into barium spinel ferrites. Narrow loops showed the soft nature of ferrites and it was confirmed from magnetic properties of the prepared samples. Decreasing trend of saturation magnetization and remanence was observed with the substitution of praseodymium contents. Coercivity and anisotropy constant both enhanced with the praseodymium concentration. The above-mentioned parameters revealed that the synthesized spinel ferrites might be useful for the of high-density magnetic recording applications.

Advanced Synchrotron Radiation and Neutron Scattering Techniques for Microstructural Characterization in Industrial Research

The rapid development of new materials and their application in an extremely wide variety of research and technological fields has lead to the request of increasingly sophisticated characterization methods. In particular residual stress measurements by neutron diffraction, small angle scattering of X-rays and neutrons, as well as 3D imaging techniques with spatial resolution at the micron or even sub-micron scale, like micro-and nano-computerized tomography, have gained a great relevance in recent years.Residual stresses are autobalancing stresses existing in a free body not submitted to any external surface force. Several manufacturing processes, as well as thermal and mechanical treatments, leave residual stresses within the components. Bragg diffraction of X-rays and neutrons can be used to determine residual elastic strains (and then residual stresses by knowing the material elastic constants) in a non-destructive way. Small Angle Scattering of neutrons or X-rays, complementary to Transmission Electron Microscopy, allows the determination of structural features such as volume fraction, specific surface and size distribution of inhomogeneities embedded in a matrix, in a huge variety of materials of industrial interest. X-ray microtomography is similar to conventional Computed Tomography employed in Medicine, allowing 3D imaging of the investigated samples, but with a much higher spatial resolution, down to the sub-micron scale. Some examples of applications of the experimental techniques mentioned above are described and discussed.

Minority carrier lifetime evaluation of periphery edge region in high-performance multicrystalline ingot produced by seed-assisted directional solidification

A high-performance multicrystalline silicon (mc-Si) ingot was produced by seed-assisted directional solidification, and the minority carrier lifetime of the periphery edge region was evaluated. The defects and impurities in the periphery edge region of the silicon wafers were systematically studied with photoluminescence (PL) imaging, minority carrier lifetime mapping, and Fourier transform infrared (FTIR) spectroscopy. Their relationships with the minority carrier lifetime were investigated. The concentration of substitutional carbon, interstitial oxygen, and dislocation clusters is not directly correlated with the low minority carrier lifetime of the edge zone of the mc-Si ingot. Inhomogeneous grain size distribution and contamination with iron impurities were demonstrated to be the main factors affecting the low minority carrier lifetime. By controlling the impurities and improving the grain size distribution, a modified furnace was designed and a higher-quality mc-Si ingot was manufactured.

Influence of sintering temperature on morphology and electrochemical performance of LSCF/GDC composite films as efficient cathode for SOFC

Functional composite cathode films of 56:44wt. % La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)/Ce0.9Gd0.1O2-δ (GDC) films with two different microstructures denoted as coral and columnar were coated on a dense GDC electrolyte by electrostatic spray deposition (ESD) technique. The sintering temperature (Ts) was varied on the ESD films from 800 to 1100°C in air to investigate the influence of sintering conditions on the microstructure, crystalline phases and electrode performances. The amount of porosity, grain growth and electrochemical performance were monitored for both microstructures by combining scanning electron microscope, x-ray diffraction and electrochemical impedance spectroscopies. The microstructures showed marked differences at the micro and nano-scales. The films with lower deposition temperature (columnar film, 300°C) were observed to have accelerated and uncontrolled grain growth and inhomogeneous size distribution at elevated Ts than films with higher deposition temperature (coral film, 350°C). Regardless of the microstructure, as low as 0.05±0.01Ωcm2 at 650°C were measured for the films sintered at low Ts (800-900°C). The differences in resistance and activation energy values were evidenced at high Ts (≥1000°C). The electrochemical processes are discussed in terms of resistance, capacitance and frequency distribution. This study reveals that ESD processing parameters play a critical role in sintering behavior and electrode performances of composite cathode films, mainly at high Ts (≥1000°C).

Revealing the role of strain rate during multi-pass compression in an advanced polycrystalline nickel base superalloy

In the single-pass hot compression of polycrystalline nickel base superalloy, inhomogeneous grain size distribution and grain growth frequently occur. For comparison, a multi-pass compression approach is employed to investigate the effect of strain rate on the flow stress and grain size evolution. By means of imposing different strain rates, the results show that the finest grain size corresponds to the second-pass strain rate of 0.1s−1, while the coarsest grain size arises from a combination of the first-pass strain rate of 0.001s−1 and the second-pass strain rate of 0.01s−1, respectively. A bimodal grain size distribution easily forms under the second-pass strain rate of 0.001s−1. The microscopic analysis discloses the critical roles of dynamic recrystallization (DRX) nucleation rate together with static recrystallization (SRX) in controlling the grain size development. The experimental results provide new insights to optimize the forging process of nickel base superalloy.

Surface Roughening Behavior of 6063 Aluminum Alloy during Bulging by Spun Tubes.

Severe surface roughening during the hydroforming of aluminum alloy parts can produce surface defects that severely restrict their application in the automobile and aerospace industry. To understand the relation between strain, grain size and surface roughness under biaxial stress conditions, hydro-bulging tests of aluminum alloy tubes were carried out, and the tubes with different grain sizes were prepared by a spinning and annealing process. The surface roughness was measured by a laser scanning confocal microscope to evaluate the surface roughening macroscopical behavior, and the corresponding microstructures were observed using electron back-scattered diffraction (EBSD) to reveal the roughening microscopic behavior. The results obtained show that the surface roughness increased with both strain and grain size under biaxial stress. No surface defects were observed on the surface when the grain size was less than 105 μm if the strain was less than 18%, or when the grain size was between 130 and 175 μm if the strain was less than 15.88% and 7.15%, respectively. The surface roughening microscopic behavior was identified as an inhomogeneous grain size distribution, which became more pronounced with increasing grain size and resulted in greater local deformation. Concentrated grain orientation also results in severe inhomogeneous deformation during plastics deformation, and serious surface roughening.

Photoluminescence and time-resolved photoluminescence studies of lateral carriers transfer among InAs/GaAs quantum dots

We report on the lateral transfer and thermal escape of carriers in InAs quantum dots (QDs) grown on a GaAs substrate by solid source molecular beam epitaxy by mean of photoluminescence (PL) and time-resolved PL measurements. The temperature-dependent PL spectra are discussed in terms of the inhomogeneous size distribution of the QDs and the carrier tunneling process from small to large QDs. The dependence of the photoluminescence decay time on the emission-wavelength is attributed to lateral carriers’ transfer within QDs with an interdot carrier tunneling time of 910 ps under low excitation conditions.