Grain Size Ratio Research Articles

Optimizing design of the microstructure of sol–gel derived BaTiO3 ceramics by artificial neural networks

Modeling and application of artificial neural network (ANN) technique to the formulation design of BaTiO3-based ceramics were carried out. Based on the homogenous experimental design, the results of BaTiO3-based ceramics were analyzed using a three-layer back propagation (BP) network model. Then the influence of sintering temperatures, holding time, donor additives (La2O3, MnO2, Ce2O3) and sintering aids (Al2O3–SiO2–TiO2 (AST)) on the average grain size (da), the degree of grain uniformity given by the ratio of the maximal grain size to the average grain size (dmax/da), and the relative density (Dr) of doped BaTiO3 ceramics system was investigated. The optimized results and experiment data were expressed and analyzed by intuitive graphics. Based on input data and output data, the sintering behavior of BaTiO3 nano-powder was explained well. Furthermore, the fine and uniform microstructure of sol–gel derived BaTiO3 ceramics with da ≤ 3 μm, dmax/da ≤ 1.20, and Dr ≥ 98% was obtained.

The effects of substrate temperature on the structure and properties of ZnO films prepared by pulsed laser deposition

ZnO thin films were prepared by pulsed laser deposition (PLD) on glass substrates with growth temperature from room temperature (RT) to 500 °C. The effects of substrate temperature on the structural and optical properties of ZnO films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission spectra, and RT photoluminescence (PL) measurements. The results showed that crystalline and (0 0 2)-oriented ZnO films were obtained at all substrate temperatures. As the substrate temperature increased from RT to 500 °C, the ratio of grain size in height direction to that in the lateral direction gradually decreased. The same grain size in two directions was obtained at 200 °C, and the size was smallest in all samples, which may result in maximum E g and E 0 of the films. UV emission was observed only in the films grown at 200 °C, which is probably because the stoichiometry of ZnO films was improved at a suitable substrate temperature. It was suggested that the UV emission might be related to the stoichiometry in the ZnO film rather than the grain size of the thin film.

MICROWAVE ABSORPTION AND HIGH-FIELD JOSEPHSON MAGNETIC RESONANCE IN HIGH-Tc SUPERCONDUCTORS

The possibility of high-field Josephson magnetic resonance (HFJMR) in high-T c superconductors (HTSCs) is theoretically demonstrated. The HFJMR is caused by the penetration of Abrikosov vortices into the grains in fields within H c1 ≤H<Hx (where H c1 is the first critical field and Hx is the field corresponding to vortex separation from pinning centers in the grains). The signals from microwave absorption is dependent on the ratio of grain sizes that produces junction, the anisotropy and the intergrain coupling strength. These properties can be used for investigations of HTSC macrostructures and a vortex matter.

Methodology for recovering and analyzing two-point pair correlation functions in polycrystalline materials

The authors introduce methods for obtaining two-point microstructure pair correlation functions and coherence length in polycrystalline material, using a set of oblique section planes around a fixed axis, and these are illustrated for a sample of alloy 304L stainless steel. A particular tessellation of the fundamental zone of Euler angle space is described; individual orientations of the data set are binned into discrete tesserae. Elementary relationships between the two-point pair correlation functions and coherence length and the grain size distribution are explored. A coherence plateau is evident in the statistical data and is shown to correlate with the magnitude of the invariant measure of the tesserae and the ratio of average grain size to scan length.

Grain size effects on the mechanical properties of nanonickel examined by nanoindentation

Pulse-electrodeposited nanonickel was heat-treated to produce grain sizes from nanoscale to microscale. The hardness of individual grains was examined by nanoindentation. The results show that hardness not only depends on the grain size, but also on the ratio of grain size to the indent size. Beside of the conventional Hall–Petch relation different dependencies were found. The hardness scaled with the dislocation density in the range where the indent size was smaller than the grain size, when a critical load was reached in a single grain, evidence for dislocation emission in adjacent grains could be deduced from later pop-ins in the load–displacement curve.

Effects of the film microstructures on CVD diamond radiation detectors

The polycrystalline nature of the films has limited the improvement of CVD diamond radiation detectors. In this work, three CVD diamond films with different microstructures were grown by a hot-filament chemical vapor deposition (HFCVD) technique and were fabricated as CVD diamond radiation detectors. The photocurrents and the pulse height distributions (PHDs) obtained by the detectors were measured by using 5.9 keV 55Fe X-rays. The dark-current of 16.0 nA and the photocurrent of 15.9 nA are achieved at a bias voltage of 100 V. The PHD peak is well separated from the noise and a better energy resolution of 21.2% is obtained due to the high ratio of grain size to the film thickness. The time-dependent photocurrent initially increases rapidly and then levels off due to the ‘polarization’ effect.

Improvement in the non-linear electrical characteristics of the SnO 2·CoO·Ta 2O 5 varistor material with La 2O 3 additive

The effect of La 2O 3 additive on a SnO 2-based varistor material sintered at 1350 °C for 80 min was investigated. It was found that La 2O 3 significantly decreases the grain size and improves the non-linear electrical properties of SnO 2-based varistors. The sample with 1.00 mol% La 2O 3 has the best non-linear electrical property and the highest non-linear coefficient ( α = 23.0) among all the samples. The reason that the grain size decreases with increasing La 2O 3 concentration is explained. The permittivity decrease with increasing La 2O 3 concentration is caused by the ratio of grain size to barrier width. A modified defect barrier model was introduced in which the negatively charged acceptors substituting for Sn ions should be located at the grain boundaries.

Shear-induced pressure changes and seepage phenomena in a deforming porous layer - I

We present a model for flow and seepage in a deforming, shear-dilatant sensitive porous layer that enables estimates of the excess pore fluid pressures and flow rates in both the melt and solid phase to be captured simultaneously as a function of stress rate. Calculations are relevant to crystallizing magma in the solidosity range 0.5–0.8 (50–20 per cent melt), corresponding to a dense region within the solidification front of a crystallizing magma chamber. Composition is expressed only through the viscosity of the fluid phase, making the model generally applicable to a wide range of magma types. A natural scaling emerges that allows results to be presented in non-dimensional form. We show that all length-scales can be expressed as fractions of the layer height H, timescales as fractions of H2(nβ′θ+ 1)/(θk) and pressures as fractions of . Taking as an example the permeability k in the mush of the order of magnitude 10−15 m2 Pa−1 s−1, a layer thickness of tens of metres and a mush strength (θ) in the range 108–1012 Pa, an estimate of the consolidation time for near-incompressible fluids is of the order of 105–109 s. Using mush permeability as a proxy, we show that the greatest maximum excess pore pressures develop consistently in rhyolitic (high-viscosity) magmas at high rates of shear (, implying that during deformation, the mechanical behaviour of basaltic and rhyolitic magmas will differ. Transport parameters of the granular framework including tortuosity and the ratio of grain size to layer thickness (a/H) will also exert a strong effect on the mechanical behaviour of the layer at a given rate of strain. For dilatant materials under shear, flow of melt into the granular layer is implied. Reduction in excess pore pressure sucks melt into the solidification front at a velocity proportional to the strain rate. For tectonic rates (generally 10−14 s−1), melt upwelling (or downwelling, if the layer is on the floor of the chamber) is of the order of cm yr−1. At higher rates of loading comparable with emplacement of some magmatic intrusions (∼10−10 s−1), melt velocities may exceed effects due to instabilities resulting from local changes in density and composition. Such a flow carries particulates with it, and we speculate that these may become trapped in the granular layer depending on their sizes. If on further solidification the segregated grain size distribution of the particulates is frozen in the granular layer, structure formation including layering and grading may result. Finally, as the process settles down to a steady state, the pressure does not continue to decrease. We find no evidence for critical rheological thresholds, and the process is stable until so much shear has been applied that the granular medium fails, but there is no hydraulic failure.

A sandpile experiment and its implications for self-organized criticality and characteristic earthquake

We have performed an experiment in which a conical sandpile was built by slowly dropping sand onto a circular disk through a funnel with a small outlet. Avalanches (sand dropping off the disk) occurred, the size and the number of which were observed. It was seen that the behavior of avalanches (frequency-size distribution) was determined solely by the ratio of grain size to disk size, which is consistent with earlier studies. We categorize the behavior into three types: (1) the self-organized criticality (SOC) type (obeying Gutenberg-Richter’s law), (2) the characteristic earthquake (CE) type where only large avalanches are almost periodically generated, and (3) the transition type. The transition from SOC to CE type drastically occurs when the ratio of grain diameter to disk radius is reduced to about 0.02. The underlying mechanism to cause the transition is considered. Results of simulation by cellular automaton models, an experimental result showing that a conical pile has a stress dip near its center, and a two-dimensional simulation building up a conical pile, all suggest that the transition occurs due to a change in stress profile inside and near the surface of the pile. Although we are unfortunately not able to understand the detailed mechanism at the present stage, it seems very important to further investigate the underlying physics of the transition because it presumably provides us a clue to understand the mechanism of the periodicity of large characteristic earthquakes and may open a way for earthquake prediction.

Flume observations of enhanced fine‐particle deposition to permeable sediment beds

Predictions of the deposition rate of fine particles are integral to the study of the transport of many constituents, including contaminants and organic matter. Generally, fine‐particle deposition rates are assumed to be equivalent to the suspension settling velocity. Deposition rates in excess of settling are considered enhanced. Flume observations of deposition were made using treatments that covered a wide range of flow, particle, and bed conditions. No enhancement was observed to impermeable boundaries. Specific treatments of sand bed experiments demonstrated large enhancements (up to eight times settling). For coarser sediment beds, little to no enhancement was observed. Previously identified mechanisms that could alter deposition rates, such as topography and aggregation, were dismissed using careful flow and particle size distribution measurements. Correlations between drag coefficient and deposition suggest that the mechanisms delivering additional particles to the sediment also reduce the effective drag of the bed on the flow. This is consistent with velocity slip at the sediment‐water interface. Another trend evident in the data is a dependence on the ratio of the bed grain size to particle diameter. Small ratios were associated with large enhancements, consistent with the idea that filtration within the sediment could be retaining delivered particles. In concert, fluid incursions and bed filtration might be capable of increasing the particle flux to the bed. The observation of enhanced deposition to flat sediment beds reinforces the importance of permeable sediments to the transport of particles from the water column to the sediment bed.

ＨＶＯＦ溶射によるＣｒ３Ｃ２‐ＮｉＣｒ皮膜の組織構造と物性との相関性

Cr3C2-25 %NiCr cermet coatings were deposited by HVOF spray process. The carbon content, carbide grain size and carbide content were estimated quantitatively. The mechanism of carbon loss in spraying and the effect of carbide grain size on the properties of sprayed coating were examined. The main conclusions obtained are as follows. (1) Carbon content of Cr3C2-25 %NiCr cermet coating deposited by HVOF spraying was lower than that of the powder. It was found that the carbon loss during particle in-flight is much limited. It can be suggested that the main mechanism of carbon loss is due to the rebound-off of large carbide particles. (2) It was recognized that the grain size and content of carbide in sprayed coating were lower than those in starting powder. (3) With the increase in carbide grain size and decrease in carbide content, the abrasive wear loss of HVOF sprayed coating was increased. Moreover, it was recognized that the erosion rate of HVOF sprayed coating was proportional to the ratio of carbide grain size to carbide content.

Ostwald ripening kinetics of angular grains dispersed in a liquid phase by two-dimensional nucleation and abnormal grain growth

Abstract Based on the fact that the angular shape of solid grains dispersed in the liquid matrix indicates a singular interface, the coarsening kinetics of angular grains was formulated based on 2-dimensional (2-D) nucleation and solved numerically. For comparison, diffusion-controlled coarsening of grains with a spherical shape was also solved numerically. The solutions showed that coarsening by 2-D nucleation induced abnormal grain growth whilst diffusion-controlled coarsening did not. This result agrees with the general experimental observation that the abnormal grain growth in liquid phase sintering takes place exclusively in the system with angular grains. The ratio of the largest grain size to the average increased monotonously with time in coarsening by 2-D nucleation whilst it decreased in diffusion-controlled coarsening. The artificially-added large grain (10 times larger than the average) became the abnormal grain in 2-D nucleation controlled coarsening but did not in diffusion-controlled coarsening.

Two-Way Shape Memory Effect Induced by Bending Deformation in Ductile Cu-Al-Mn Alloys

Martensitic transformation temperatures and the two-way shape memory effect (TWME) in ductile Cu-Al-Mn alloys deformed at room temperature were investigated using differential scanning calorimetry (DSC) and the bending test. The M s and A f temperatures were found to increase slightly with increasing degree of pre-deformation, while the M f and A s temperatures decreased. The TWME is strongly influenced by the M s temperature and the grain size of the specimens, i.e., the highest degree of TWME is always obtained in the specimens with M s -100°C and the TWME increases with increasing ratio of grain size to specimen width, where the maximum value of TWME = 3.2% was obtained in the present study. In situ observation of the surface relief at several temperatures on the deformed specimens was also performed and it was found that some restricted martensite variants grow and shrink with temperature change without the typical self-accommodation microstructure in the specimens with large TWME.

Observation of .GAMMA..RAR..ALPHA. Transformation in Ultralow-carbon Steel under a High Temperature Optical Microscope.

The basic composition of IF steel is Fe-ultralow-carbon (<0.02 mass%). There is little research on the transformation behavior and microstructures of ultralow-carbon steel compared to low-carbon steels, and the details, for instance, transformation mechanism and the ratio of grain sizes of γ and α, remain unclear. Therefore, in situ observation of the γ→α transformation in an Fe-0.004%C steel was performed at a cooling rate of 0.5-18 ° C/s under a high-temperature optical microscope. The main microstructure of ferrite was αq, and with an increase in the cooling rate, the fraction of Widmanstatten ferrite-like structure and ferrite having a severely ragged interface increased. The growth rate of αq was 1x10-4 - 9x10-4 m/s which increased with the cooling rate. The growth rate of α qdecreased to about half when the amount of carbon increased to 0.01%. The ratio of γ grain size to α grain size was about 1.2, and this value is considerably smaller than the values reported for the low-carbon steels. αqcrossed γ grains frequently and some αqgrains were larger than γ grains. Usually the curvature of the αq/ γ interface did not change at the int αq rsection of the boundaries of αqand γ. This shows that αq/γ interfaces are usually incoherent in ultralow-carbon steels. Transformation temperature was in the single-phase region of α. Therefore, the γ→αq transformation observed in the present research is thought to be massive transformation. The terminology of mechanisms of γ→α transformation in ultralow-carbon steels and the microstructures of generated a was discussed.

The ‘size effect’ on the stress–strain, fatigue and fracture properties of thin metallic foils

In this investigation a microtensile machine in combination with a non-contacting laser-optical speckle correlation sensor to determine strain with high resolution was used to study the stress-strain behavior of thin metallic foils of Cu and Al with varying thickness ranging between 10 and up to 250 μm. The grain sizes varied between 2 and up to 250 μm. A size effect was detected resulting in an influence mainly on the fracture strain. This effect will be explained on the basis of texture differences, the number of activated gliding systems as a dependence on the ratio of grain size to foil thickness. To support these experimental findings the fracture topography has also been investigated. In addition, the fatigue crack propagation properties of the above mentioned Cu foils were studied as function of thickness. Using a specially designed fatigue testing set-up it was feasible to determine crack growth curves from free-standing foils. Depending on thickness, an unexpected crack growth behavior was detected. Using the ECCI technique it was feasible to study the interaction of the global dislocation arrangement with the crack tip.

Snow texture: a comparison of empirical versus simulated texture index for Alpine snow

AbstractThe texture of snow has a great impact on the mechanical and thermal properties of a snowpack. The texture index (TI) is a new concept to quantify the texture of snow at the micro- and mesoscale, a scale at which the properties of snow layers are responsible for the stability of a snowpack. It is calculated by taking the ratio of mean grain-size (mm) of snow to density (kg m−3) of snow in a given layer. It combines a microstructural with a mesostructural parameter. An empirically derived TI is compared with a simulated TI for laboratory experimental snow and natural snow profiles. TheTI was calculated throughout the development of three temperature-gradient snow experiments from laboratory measurements of grain-size and density. In a one-dimensional finite-element snowpack model (SNOWPACK), the development of the mean grain-size and density of these snow samples was simulated. It can be shown that the measured TI can be predicted by the modelled TI. Furthermore, three natural snow profiles from the Weissfluhjoch (Switzerland) test-field are compared with their simulations in terms of TI. This comparison reveals shortcomings in the measurement of fundamental parameters. It also shows the dependency of a good physical model on quantitative process descriptions at the microscale TheTI can be estimated using the force signal of the SnowMicroPen, a new high-resolution snow micropenetrometer. It is suggested that more accurate classical measurements combined with penetrometer measurements in the immediate vicinity of the snow profile will allow better verification of SNOWPACK simulations.

INITIAL MOTION OF STREAMBEDS COMPOSED OF COARSE UNIFORM SEDIMENTS.

Results of an experimental study of the initial motion of coarse uniform sediments are presented in this paper. The experiments were conducted in an 8 m long, 0·3 m wide by 0·3 m deep tilting flume. Natural sediments were used and they ranged in size from 1 mm to 14 mm. The purpose of the experiments was to determine flow conditions associated with the initiation of bed sediment motion. To eliminate the subjectivity in defining the beginning of streambed movement, the concept of critical-bed state is linked to the intensity of sediment motion. The experiments reveal that critical-bed shear-stress for sediment motion depends not only on the grain size, but also on the bed slope. The latter fact is explained by the effect of relative depth (depth to grain-size ratio) on overall flow resistance. It is also shown that the value of critical dimensionless bed shear-stress is not constant for rough turbulent flow, as is usually assumed. The same conclusion follows from the measurements of turbulence characteristics near the surface of the bed. A revised Shields diagram relating critical stress, grain Reynolds number and bed slope is derived for different intensities of sediment motion. Finally, a diagram relating critical flow depth, bed slope and grain size is presented in a form suitable for use by design engineers.

Initial motion of streambeds composed of coarse uniform sediments

Results of an experimental study of the initial motion of coarse uniform sediments are presented in this paper. The experiments were conducted in an 8 m long, 0·3 m wide by 0·3 m deep tilting flume. Natural sediments were used and they ranged in size from 1 mm to 14 mm. The purpose of the experiments was to determine flow conditions associated with the initiation of bed sediment motion. To eliminate the subjectivity in defining the beginning of streambed movement, the concept of critical-bed state is linked to the intensity of sediment motion. The experiments reveal that critical-bed shear-stress for sediment motion depends not only on the grain size, but also on the bed slope. The latter fact is explained by the effect of relative depth (depth to grain-size ratio) on overall flow resistance. It is also shown that the value of critical dimensionless bed shear-stress is not constant for rough turbulent flow, as is usually assumed. The same conclusion follows from the measurements of turbulence characteristics near the surface of the bed. A revised Shields diagram relating critical stress, grain Reynolds number and bed slope is derived for different intensities of sediment motion. Finally, a diagram relating critical flow depth, bed slope and grain size is presented in a form suitable for use by design engineers.

Measurement of macrotexture by automated crystal orientation mapping: an alternative to X-ray diffraction

Automated crystal orientation mapping (ACOM) with digital beam scan in the SEM enables crystal orientation mapping and quantitative texture analysis on large specimen areas of half a square centimetre wide or more, without sacrificing accuracy of orientation measurement or spatial resolution, provided that program facilities for dynamic focusing of the beam, dynamic system calibration, and automatic flat fielding for background correction are available. At present, the speed of ACOM exceeds 25 000 orientations per hour with cubic and hexagonal crystal symmetry. The orientation density function has been calculated using the data from ACOM measurement by series expansion under the assumption of triclinic sample symmetry and various spreads of the Gaussian function. ACOM competes well in speed and in results with X-ray diffraction, but is a more universal instrument owing to the additional facilities of SEM. Grain statistics are similar with both techniques since they depend on the ratio of average grain size to measured area. The advantages and limitations of macrotexture determination by ACOM are discussed.

Constrained Film Sintering of Nanocrystalline TiO2

The sintering of thin, nanocrystalline TiO2 films either 140 or 65 nm thick is characterized and compared with the sintering of bulk material. Grain size, pore size distribution, and density data are obtained. Observation of the microstructural evolution during sintering suggests that grain growth, as well as pore growth, at low density can be attributed to differential sintering. A continuum mechanical model for the intermediate stage is useful until the grain size becomes one‐half the film thickness. From then on, the ratio of grain size to film thickness affects the degree by which both densification and grain growth decrease, as compared with the continuum computation results.