Increase In Average Grain Size Research Articles

Effect of Li1+ ion on the physico-chemical properties cation distribution of sol-gel synthesized Ni-Zn spinel ferrite nanoparticles

This study presents the synthesis and comprehensive analysis of polycrystalline LixNi0.6Zn0.4-2xFe2+xO4 (with x values of 0.00, 0.01, 0.03, 0.05, 0.07, 0.09) ferrites, with lithium (Li) concentrations ranging from x = 0.00 to 0.09, utilizing the sol-gel auto-combustion method followed by sintering at 800 °C for 8 h. A nuanced examination of the lattice constants obtained from the X-ray diffraction patterns revealed a slight decrement from 8.386 to 8.357 Å, exhibiting a linear pattern across the Li concentration spectrum. The crystallite sizes, as determined by the Scherrer formula, fluctuated between 31 and 40 nm, while Field Emission Scanning Electron Microscopy indicated an increase in average grain size from 146 to 186 nm due to nanoparticle agglomeration. High-Resolution Transmission Electron Microscopy analysis of nanoparticles yielded an average grain size of ∼69 nm and an interplanar spacing of approximately 0.1521 nm. Magnetic characterization revealed a decrease in saturation magnetization from 87 to 70 emu/g with increasing Li content, with the lowest Ms observed for the x = 0.09 sample, indicating the material's soft magnetic nature. Raman and Fourier-transform infrared spectroscopy confirmed the retention of the conventional spinel structure, characterized by both tetrahedral and octahedral iron coordination, and illuminated the impact of co-existing iron phases on the structural anomalies observed. These findings contribute valuable insights into the effects of lithium substitution on the structural, morphological, and magnetic properties of Ni-Zn ferrites, underscoring their potential for various technological applications.

Effect of Nb content on the mechanical properties of Nbx(MoTaW)(1-x) (x = 0.4, 0.55, and 0.7) refractory multicomponent alloys

The MoNbTaW refractory multicomponent alloy (RMCA) retains good yield strength up to 1873K, but limited plasticity and high density at room temperature impede its utility in practical applications. Thus, a unique alloy design approach based on composition modification was used to improve these properties. Among the four constituent elements of the MoNbTaW alloy, Nb has good plasticity and lower density; hence a series of alloys with varying Nb content, namely Nbx(MoTaW)(1-x) with x = 0.4, 0.55, and 0.7 (designated as Nb0.4, Nb0.55, and Nb0.7 in this manuscript), were processed using vacuum arc melting. X-ray diffraction results showed that all the alloys formed as single-phase with the body-centered cubic crystal structure. The microstructures of these RMCAs are dendritic in nature with segregation of elements that decreased with heat treatment. The hardness values showed a decrease as the Nb content increased. The compressive yield strength values are 1251, 1055, and 945 MPa, and those of fractured strain are 10, 22, and 33 % for Nb0.4(MoTaW)0.6, Nb0.55(MoTaW)0.45, and Nb0.7(MoTaW)0.3 respectively. The increase in plastic strain and toughness is due to the increment in the Nb concentration, which is directly interpreted as an enhancement in degree of plasticity. The average grain sizes of Nb0.4, Nb0.55, and Nb0.7 RMCAs are measured to be 86 μm, 106 μm and 145 μm respectively. It was observed that 36 % of the grains are above 100 μm for Nb0.4 alloy, whereas this fraction is increased to 49 % and 60 % for Nb0.55 and Nb0.7 alloys respectively, which indicates an increase in average grain size as well as fraction of coarser grains as the Nb content increases. Hence, the improvement in plasticity is attributed to the increase in the average grain size and broader grain distribution. Fracture surface analysis of all the compositions showed quasi-cleavage behavior. This study demonstrates that increasing the Nb concentration in the MoNbTaW RMCA enhances plasticity while decreasing density. In comparison to conventional niobium alloys like C103 and FS-85, the alloys of the present study had higher yield strength at the temperatures where the tests were carried out. The specific yield strength values of these alloys are found to be higher than commercially available Nb alloys.

Efficiently tuning the electrical performance of PBTTT-C14 thin film via in situ controllable multiple precursors (Al2O3:ZnO) vapor phase infiltration

Conjugated polymer-based organic/inorganic hybrid materials become the current research frontier and show great potential to integrate flexible polymers and rigid solid materials, which have been widely used in the field of various flexible electronics and optical devices. In this study, based on the multiple vapor phase infiltration (VPI) process, various precursor molecules (diethylzinc DEZ, trimethylaluminum TMA, H2O) are applied for the in situ modification of PBTTT-C14 films. The conductivity of the PBTTT-C14/Al2O3:ZnO (AZO) film is significantly enhanced, and the maximum value of conductivity is 1.16 S cm−1, which is eight orders of magnitude higher than the undoped PBTTT-C14 thin film. Here, the change of morphologies and crystalline states are analyzed via SEM, AFM, and XRD. And the chemical changes during the VPI process of PBTTT-C14 are characterized through Raman, XPS, and UV–vis. During the AZO VPI process, the formation of new ZnS matrix in the polymer subsurface can generate new additional electron conduction pathways through the crosslinking of polymer chains with inorganic materials, and the addition of Al2O3 can bring about the increase of average grain size of ZnO crystals, which is also benefit to the conductivity increase of PBTTT-C14 thin film. Generally, the synergistic effect between the inorganic and polymer constituents results in the significantly enhancement of the conductivity of PBTTT-C14/AZO thin films.

Hot deformation behavior and extrusion temperature-dependent microstructure, texture and mechanical properties of Mg–1Mn alloy

Mg–1Mn alloy, extruded at a low temperature in our published protocol, contributed to the intensified basal texture and extremely refined microstructure with spheroidal nanoscale precipitates dispersing throughout the matrix and along the grain boundaries, consequently resulting in the excellent mechanical properties where the alloy exhibited a tensile yield strength of 204.3 MPa and a ductility of 38.8% at room temperature. Therefore, Mg–1Mn alloy was recommended as one of the potential materials for structural applications. In the present investigation, hot deformation behavior through constitutive analysis and extrusion temperature-dependent microstructure, texture and mechanical properties of as-extruded Mg–1Mn alloy were investigated, aiming at revealing how extrusion temperature affected microstructure, texture, and mechanical properties of as-extruded Mg–1Mn alloy. X-ray diffraction patterns demonstrated that phase components of the experimental alloys consisted of the α-Mg matrix and Mn precipitates. Optical microscopy images indicated a significant increase in average grain size of the alloys as the extrusion temperature increasing from 250 °C to 400 °C. Scanning electron microscopy graphics revealed that coarsened particles identified as Mn precipitates by EDS were observed within the matrix when extrusion temperature reached 400 °C. Inverse pole figure maps of the experimental samples subjected to different extrusion temperatures in the present work exhibited the typical basal texture, suggesting that basal slip was activated hardly during the tensile stress applied along the extrusion direction. Consequently, extrusion temperature displayed the significant impact on microstructure, texture, and mechanical properties of as-extruded Mg–1Mn alloy. The alloy extruded at both 250 °C and 300 °C exhibited the strong basal texture and refined microstructure with spheroidal nanoscale precipitates dispersing within the matrix and along the grain boundaries, which contributed to their excellent comprehensive mechanical properties. The alloy extruded at 400 °C possessed the typical basal texture and coarsened microstructure, leading to the extremely poor mechanical properties. Simultaneously, the constitutive model of the Arrhenius equation based on Zener-Hollomon parameters was also established in the present investigation. Therefore, optimizing the extrusion temperature to regulate the microstructure, grain orientation distribution, and morphology of precipitates was considered as one of the effective approaches for achieving the excellent mechanical properties of Mg alloys.

Tuning dielectric performance in novel Na1/2Er1/2Cu3Ti4O12 ceramics: The interplay of sintering temperature, grain size, and grain boundary resistance

The synthesis of novel Na1/2Er1/2Cu3Ti4O12 (NECTO) ceramics using conventional solid-state methods and their characterization as well as their dielectric properties were investigated at various temperatures of sintering. SEM results revealed an increase in average grain size with sintering temperature. The sintered NECTO sample at 1080 °C exhibited good frequency stability and a higher dielectric constant (ε′) of about 6 × 103 at 1 kHz. It is found that the sintering temperature correlates with the dielectric constant, and it agrees with the IBLC model. Additionally, the sample displayed a dielectric loss (tanδ) of less than 0.08 throughout a wide range of frequencies. Particularly, the sintered sample at 1060 °C for 10 h had a significantly low tanδ of 0.06 and exhibited a ε′ of roughly 3.19 × 103 at 1 kHz. A significant decrease in tanδ with increased Rgb was observed, suggesting that reduced grain boundary resistance could minimize the dielectric loss. Moreover, optimizing the sintering temperature enhanced the temperature stability of NECTO ceramics.

Phase-field simulation for evolution of iron-rich phase during solidification of Al–Si–Fe alloys

Iron is a common impurity element in Al–Si alloys. The existence of Fe promotes the formation of needle-like iron-rich phase, which has an adverse effect on the macroscopic mechanical properties. In this study, the effects of casting temperature, Fe content and melt ultrasonic treatment on the morphology of β-Al9Fe2Si2 were investigated by phase-field simulation and experiment. The results show that when the casting temperature is close to the liquidus temperature, the grain size of the precipitated phase will be refined. The increase of iron content in the alloy will promote the increase of average grain size and volume fraction of iron-rich phase by inhibiting the growth of α-Al grains. In addition, the elevation of both casting temperature and Fe content promotes the transformation of the β-Al9Fe2Si2 from short rod-like to needle-like with large scale. The melt ultrasound inhibits the transformation to β-Al9Fe2Si2 by promoting the nucleation and growth of α-Al8Fe2Si. Melt ultrasound, casting temperature and iron content together cause the change of needle-like iron-rich phase morphology.

Mechanism of iron grains aggregation and growth in metalized pellet under the alternating magnetic fields

The direct reduction-magnetic separation method is highly efficient for producing metallic iron powder from low-grade complex ore resources. However, the limitation lies in the small average size of iron grains, which impedes the subsequent separation between metallic iron and gangue minerals. To address this, a novel method utilizing induction heating was introduced to stimulate the aggregation and growth of iron grains. Our study systematically investigated the growth kinetics behavior of iron grains under alternating magnetic fields. Additionally, we compared the impact of induction heating versus conventional heating on iron grain growth and delved into the mechanism through which the magnetic effect enhances the aggregation and migration of iron grains. The results indicate that iron grains can effectively aggregate and migrate to the edges of cracks or pellet surface under alternating magnetic fields, realizing the increase of average iron grain size and the pre-separation of metallic iron from gangue minerals. Specifically, the average iron grain size increased from 12.95 μm to 36.58 μm when induction heating temperature at 1300 °C for 100 min. Additionally, the total iron grade of concentrate reached 94.60% with ball milling 30 min and magnetic field intensity of 750 Gs. Finally, the growth model of iron grains under alternating magnetic fields was established and the mechanism of magnetic effect on promoting iron grains growth was revealed.

Optimization of switching charge and recoverable energy density mediated by structural transformation in Sr-substituted BaNiO3 perovskites.

Because of their distinctive characteristics, ferroelectric perovskites are considered among the most potent and auspicious candidates for energy storage and pulsed power devices. But their energy storage properties and switching capabilities need to be further enhanced which can be done by substitutions of appropriate cations. Hence, a series of lead-free Ba1-xSrxNiO3 (x = 0.00, 0.33, 0.67, and 1.00) ceramics was fabricated using a sol-gel auto combustion technique. Rietveld's refinement of X-ray diffraction plots verified the complete development of the required hexagonal perovskite structure. Scanning electron microscopy images revealed a gradual increase in average grain sizes and agglomeration with the increase in Sr-content. Moreover, the existence of all the constituent elements exactly in proportion to their stoichiometric ratios was verified by energy dispersive X-ray spectroscopy. The characteristic parameters of ferroelectric materials such as ferroelectric response, electrical conductivity, and switching charge density were also determined. The P-E loops indicated that with the increase in Sr-content, the coercive field, remanent polarization, and maximum polarization all decreased gradually, but the recoverable energy density (Wrec) increased as the loops became slimmer. The maximum value of Wrec was found in the Ba0.33Sr0.67NiO3 sample. Moreover, SrNiO3 exhibited minimum energy loss with the highest efficiency of ∼47.21%. The existence of a current barrier in all the samples was proved from the low leakage current values (∼10-7 A). In addition, the pure SrNiO3 showed a low electrical conductivity and minimum value of switching charge density. All these findings make SrNiO3 a promising candidate for fast switching and energy storage applications.

Local heterogeneities and order-disorder: An approach to tailor BaTi1-xZrxO3 ceramics properties

Zirconium-doped Barium Titanate with the formula, BaTi1-xZrxO3 (BZT) for 0 ≤ x ≤ 0.08 had been prepared by the modified solid-state reaction route. X-ray diffraction patterns (XRD) and structural refinement showed the formation of single and double phases for pure and Zr-substituted barium titanate, respectively. Pure barium titanate (BT) was found in the tetragonal phase. BZT-3 and BZT-5 had a mixture of tetragonal and orthorhombic phases. A mixture of orthorhombic and rhombohedral phases was present in BZT-8. The Raman analysis confirmed the existence of two oxygen octahedra of Ti and Zr for Zr-doped BT. The FESEM micrograph exhibited an increase in average grain size with Zr content. The temperature-dependent dielectric studies showed single-phase transitions for BT, two-phase transitions for BZT-3 and BZT-5, and three-phase transitions for BZT-8. XPS analysis confirmed the presence of undercoordinated Ti3+ions. The maximum dielectric constant of 5731 was obtained for BZT-3, which decreased linearly afterward. The maximum remanent polarization = 8.287 μC/cm2 was found for BZT-3. The energy storage efficiency ≥ 50.10 % makes all the compositions suitable for high energy density capacitors. Due to the presence of 90.63 % of the orthorhombic phase in BZT-5, the highest d33 = 164 pC/N was obtained. The UV–visible spectroscopy showed the signature of p-d and d-d transitions present in the ceramics due to disordering. The direct optical bandgap increased with the rise in Zr content.

Microstructure-crystallographic texture and substructure evolution in unpeened and laser shock peened HSLA steel upon ratcheting deformation

ABSTRACT Uniaxial ratcheting behaviours associated with microstructural development of unpeened and laser shock peened ASTM A 588 Grade D High Strength Low Alloy (HSLA) steel were studied in this investigation. The mechanism of plastic deformation and crystallographic texture evolution during ratcheting was also studied. For this, the primary experimental works involved were stress-controlled ratcheting fatigue tests (on unpeened/laser-peened specimens) at room temperature. Followed by this, microstructure and texture evolution on the surfaces and/or cross sections of the deformed specimens, using electron back scattered diffraction (EBSD) were studied in detail. Additionally, the substructural evolution of some selected samples was also studied using transmission electron microscopy (TEM). The results indicated that the average grain size of all the unpeened ratcheted specimens was marginally reduced after fatigue tests. The laser-peened specimen, however, showed a marginal increase in average grain size after ratcheting. Continuous dynamic recovery and recrystallisation (CDRR) during ratcheting was thought to be the cause of the observed reduction in average grain size in unpeened specimens, whereas continuous dynamic recrystallisation (CDRX) was believed to be the controlling factor for marginal accretion of grain size in laser-peened specimens. The plastic deformation of investigated steel was qualitatively explained by the observed dislocation patterns and their evolution.

Optimization of dielectric phenomenon in 0.8[(1-x)SrCoO2.29 + xCr2FeO4] + 0.2PZT tri-phase composites

Composite materials are emerging and have potential to revolutionize the modern technology. In this work, a series of tri-phase composite materials having the chemical formula; 0.8[(1-x) SrCoO2.29+xCr2FeO4] + 0.2PZT, is synthesized to explore their energy storage capability. In this series, SrCoO2.29 and Cr2FeO4 ceramics are synthesized by using a sol-gel auto-combustion process while PZT is prepared by the solid-state method. The XRD analysis confirmed the formation of cubic crystal structure of the SrCoO2.29 and Cr2FeO4 and the rhombohedral phase of PZT. The SEM images exhibited an increase in average grain size with the incorporation and increasing contents of Cr2FeO4. The presence of all constituting elements with the exact stoichiometric ratio is validated through EDX analysis. Wide-range frequency-dependent dielectric behavior showed a dramatic fall in dielectric constant with increasing frequency. A same frequency dependent behaviour of ε'' and tanδ is witnessed as that of ε'. The investigation of electric modulus reveals that in the low-frequency region it possesses a trivial value which became significantly large with the increase of frequency. The presence of a relaxation peak in the plot of the imaginary part of the electric modulus plays a decisive role to distinguish the small and large range hopping mechanism. The complex impedance analysis revealed different electroactivity of composite material in the different frequency domains which made them viable for advanced energy storage devices working in the vast frequency range.

Quantifying the sensitivity of distributive fluvial systems to changes in sediment supply and lake level using stratigraphic forward modelling

ABSTRACTStratigraphic forward modelling has been used to quantify the sensitivity of sandbody connectivity in a distributive fluvial system to changes in sediment supply and lake level. Recent stratigraphic forward modelling using SedsimX from StrataMod Pty Limited of the Oligocene to Miocene Huesca distributive fluvial system in northern Spain was used as a base‐case for this sensitivity analysis. Based on literature research and initial modelling, a sediment supply sensitivity range of 0.22 to 21.85 km3/kyr and lake‐level sensitivity range of −1000 to 1000 mm/kyr were used. Results show that the stratigraphic architecture of the modelled distributive fluvial system is more sensitive to changes in sediment supply than to changes in lake level. While an increase in the rate of sediment supply results in an increase in preserved average grain size, aggradation rates and sandbody connectivity at the same distance from the apex, the average grain size, aggradation rate and sandbody connectivity all decrease with increasing distance from fan apex. The main difference in the stratigraphic architecture can be found in the proximal zones. Only oversupplied models, with much higher sediment supply than the base‐case, deposited fully amalgamated channelized deposits with laterally continuous, tabular beds with occasional scoured surfaces. Models with base‐case sediment supply contain channelized sandy deposits within a fine‐grained floodplain environment. Models with sediment supply much lower than the base‐case had no deposition in the proximal zone. Lake‐level rise leads to reduced distal erosion of sediments, concentration of silts close to the lake shore, and higher aggradation rates and thicker sandbodies in the proximal zone. The sensitivity analysis highlights that the parameters governing the formation of distributive fluvial systems have different weightings but are ultimately all interconnected and interdependent. This quantitative framework can be used as a predictive tool for subsurface exploration in distributive fluvial systems.

Finite element and experimental analysis of grain refinement caused by dynamic recrystallization during high-speed cutting of nickel-based superalloys

Nickel-based superalloys are subjected to complex mechanical and thermal loads during high-speed cutting, resulting in dynamic recrystallization behavior. The microstructure state is closely related to fatigue performance. In this paper, the Johnson-Mehl-Avrami-Kolmogorov model is used to predict the microstructure evolution of during high-speed cutting of superalloy GH4169. The finite element model of microstructure evolution considering dynamic recrystallization is established by user-defined subroutine on simulation platform. The error of cutting force obtained by experiment and simulation is within 12%. Serrated chips are obtained in high-speed cutting of superalloy GH4169. The typical characteristics of serrated chips such as peak, valley and peak-to-peak distance obtained by simulation are used to compare with the experimental results, and the error is within 20%. The dynamic recrystallization grain size increases as cutting speed increases. The promoting effect of increasing temperature on grain growth is greater than that inhibition effect of increasing strain rate, which leads to the increase of average grain size of machined surface.

Insight into microstructure evolution and mechanical properties of 5 wt% SiC/Al composites by high frequency pulse current treatment

In order to improve the status of stress concentration and anisotropy of the as-rolled SiC/Al composites, high frequency pulse current was employed to modify the microstructure and mechanical property. Results show that the skin effect makes the current concentrate on the surface zone. The high density current makes the static recrystallization of 35.8% occurred under the condition that the surface temperature is much lower than that of recrystallization temperature of Al alloy, and the grain size is refined from 2.52 μm to 2.06 μm. The obvious recrystallization behavior in the surface area indicates that the non-thermal effect plays a dominant role in the pulse current treatment process. As a contrast, subgrains growth and partial recrystallization occurred in the internal region and transition region under the non-thermal effect, resulting in a slight increase in average grain size to 2.78 μm and 2.75 μm. Nano-indentation results show that the micro-hardness and the indention work recovery rate in the surface area reach 2.09 GPa and 39.8%, respectively, which are 48.2% and 29.2% higher than that of the as-rolled composites, which proves that the mechanical properties have been improved comprehensively compared with as-rolled composites.

Supersolvus Recrystallization and Grain Growth Kinetics for the Fine Tuning of Grain Size in VDM Alloy 780 Forgings

VDM Alloy 780 is a new polycrystalline nickel-based superalloy developed for aeronautical applications. In most of the targeted applications, grain size after forging must be precisely controlled to meet the targeted mechanical properties and in-service life requirements. Grain size in forgings is the direct consequence of the recrystallization and grain growth kinetics which are addressed in this paper at high temperatures, above the solvus temperature of γ′ and η/δ phases. The dynamic and post-dynamic recrystallization kinetics as well as the grain growth kinetics of VDM Alloy 780 are detailed over a range of thermomechanical conditions. Dynamic recrystallization appears to be limited, with only 30 pct recrystallized at quite high strain of 1.7 applied at 1050 °C and 0.01 s−1 for instance, but this is compensated by fast post-dynamic evolution. Within the investigated thermomechanical range, recrystallization is completed with 5 minutes of post-deformation hold in VDM Alloy 780 independent of the prior strain, strain rate and dynamic recrystallization fraction. For a strain as low as 0.08, an isothermal annealing of 30 minutes at 1050 °C generates a homogenous and fully recrystallized microstructure. Capillarity driven grain growth following recrystallization is also relatively slow, for instance an exposure at 1050 °C (50 °C above the solvus temperature) for 2 hours results in an increase in average grain size from 20 to 70 μm. This opens the possibility to fine tune the grain sizes by subsequent heat treatments within a time scale that is compatible with industrial conditions. The high cobalt content (25 pct) is suspected to play a role in the control of microstructure evolution kinetics. It is noteworthy that VDM Alloy 780 is shown here to not undergo the heterogeneous grain growth phenomenon reported in low strain regions for other nickel-based superalloys, which is also an asset for applications requiring strict control of grain sizes and grain size distributions.

Microstructure, mechanical properties, and corrosion performance of additively manufactured CoCrFeMnNi high-entropy alloy before and after heat treatment

Equiatomic CoCrFeMnNi, one of the well-known high-entropy alloys, possesses attractive mechanical properties for many potential applications. In this research, the effects of heat treatment on additively manufactured CoCrFeMnNi materials were studied. A pilot experiment was conducted to select two selective laser melting (SLM) conditions of different laser scanning speeds based on the density and porosity of obtained materials. Thereafter, microstructure, tensile properties, impact fracture, microhardness, and corrosion resistance were investigated for the materials obtained under the two selected SLM conditions, with and without heat treatment. It was discovered that while the texture with a strong <100> alignment was observed in both as-built and heat treated materials, the texture of heat treated materials was stronger. Also, heat treatment drastically improved the ductility of as-built CoCrFeMnNi by 23 – 59% for the selected SLM conditions, while the ultimate tensile strength showed only negligible change. The increase of ductility was believed to result from the release of residual strain and the increase of average grain size after heat treatment. Moreover, heat treatment was able to bring noticeable improvement in energy absorption for the as-built CoCrFeMnNi, reflected by 11 – 16% more energy absorption. Besides, all studied materials showed signs of ductile fracture, but more signs of brittle fracture, such as cleavage facets, were found in the as-built materials as compared with the heat-treated materials. In addition, higher laser scan speed was found to cause moderate reduction in corrosion resistance. Effect of heat treatment was also negative and mild for lower scanning speed case. However, the highest reduction in corrosion resistance was observed after heat treatment of the high laser scanning speed case.

Acoustic Crystallization of 2D Colloidal Crystals.

2D colloidal crystallization provides a simple strategy to produce defined nanostructure arrays over macroscopic areas. Regularity and long-range order of such crystals is essential to ensure functionality, but difficult to achieve in self-assembling systems. Here, a simple loudspeaker setup for the acoustic crystallization of 2D colloidal crystals (ACDC) of polystyrene, microgels, and core-shell particles at liquid interfaces is introduced. This setup anneals an interfacial colloidal monolayer and affords an increase in average grain size by almost two orders of magnitude. The order is characterized via the structural color of the colloidal crystal, the acoustic annealing process is optimized via the frequency and the amplitude of the applied sound wave, and its efficiency is rationalized via the surface coverage-dependent interactions within the interfacial colloidal monolayer. Computer simulations show that multiple rearrangement mechanisms at different length scales, from the local motion around voids to grain boundary movements via consecutive particle rotations around common centers, collude to remove defects. The experimentally simple ACDC process, paired with the demonstrated applicability toward complex particle systems, provides access to highly defined nanostructure arrays for a wide range of research communities.

Effects of Alloying Elements on Solidification Structures and Macrosegregation in Slabs

A Cellular Automaton-Finite Element (CAFE) model and a secondary dendrite arm spacing (SDAS) model are established to study the evolutionary behavior of the macrostructure and the secondary dendrites on a 295 × 2270 mm2 slab cross-section of experimental steel, respectively. The relationship between the element content, SDAS, equiaxed crystal ratio (ECR) and macrosegregation in continuously cast experimental slabs was studied comprehensively. It is found that with the increase in carbon content, the ECR increases at first and then decreases, and the ECR reaches the maximum value when the carbon content is 0.3%. With the increase in carbon content, the SDAS and average grain size of the equiaxed crystal zone increase, whereas the Si and Al content evidently affects the SDAS and average grain size of the equiaxed crystal zone to a greater extent than the Mn content. In addition, the SDAS can be reduced by reducing the content of C and Si within the acceptable range of alloy composition.

Palladium Membrane with High Density of Large-Angle Grain Boundaries to Promote Hydrogen Diffusivity.

A higher density of large-angle grain boundaries in palladium membranes promotes hydrogen diffusion whereas small-angle grain boundaries suppress it. In this paper, the microstructure formation in 10 µm thick palladium membranes is tuned to achieve a submicronic grain size above 100 nm with a high density of large-angle grain boundaries. Moreover, changes in the grain boundaries’ structure is investigated after exposure to hydrogen at 300 and 500 °C. To attain large-angle grain boundaries in Pd, the coating was performed on yttria-stabilized zirconia/porous Crofer 22 APU substrates (intended for use later in an ultracompact membrane reactor). Two techniques of plasma sprayings were used: suspension plasma spraying using liquid nano-sized powder suspension and vacuum plasma spraying using microsized powder as feedstock. By controlling the process parameters in these two techniques, membranes with a comparable density of large-angle grain boundaries could be developed despite the differences in the fabrication methods and feedstocks. Analyses showed that a randomly oriented submicronic structure could be attained with a very similar grain sizes between 100 and 500 nm which could enhance hydrogen permeation. Exposure to hydrogen for 72 h at high temperatures revealed that the samples maintained their large-angle grain boundaries despite the increase in average grain size to around 536 and 720 nm for vacuum plasma spraying and suspension plasma spraying, respectively.

The Effect of Silver Oxide on the Structural and Optical Properties of ZnO: AgO Thin Films

Compounds from ZnO doped with AgO in different ratio (0,3,5,7, and 9)wt.% were prepared.Thin films from the prepared compounds were deposited on a glass substrate using the pulsed laser deposition method. The XRD pattern confirmed the presence of a single-phase hexagonal wurtzite ZnO structure, without the presence of a secondary phase. AFM measurements showed an increase in both average grain size and average surface roughness with increasing concentration content of (AgO).The crystallite size of ZnO of the main peak corresponding to the preferred plane of crystal growth named (100) increases from 17.8 to 22.5nm by increasing of AgO doping ratio from 0 to 9%. The absorbance and transmittance in the wavelength range (350-1100 nm) were used to determine the optical properties. The results showed that the optical energy gap for direct allowed transition (r =0.5 )are (3.21, 3.2,3.15, 3.15, 2.95 ) Ev, respectively. The optical constants were also measured as a function of wavelength. This optical measurements showed the prepared thin film have many applications for solar cell fabrication and sensing devices.