Microstructural Units Research Articles

Approaches to quantification of microstructure for model lipid systems

AbstractSemisolid fat samples with different solid fat contents and microstructures were prepared by crystallization of mixtures of model lipid systems containing high‐melting and lowmelting lipids and analyzed for microstructural properties. Microstructure images were acquired by confocal scanning light microscopy and showed fat crystals or fat crystal flocs combined with their surrounding continuous phase to constitute microstructural units and a microstructural network that was formed through their interaction. Fat crystal flocs and their centroids, microstructure units, and their interface boundaries were identified by image analysis. Several methods to quantify microstructure were compared. A new concept was introduced: the microstructure density, defined as the number of microstructural units per unit volume of the system. Also, the Richardson plot and particle counting methods (PCM) were used to find the fractal dimension of the crystal network. The Euler characteristic and nearest neighbor features of the microstructure were obtained as well by use of custom‐developed programs. The different metrics of semisolid lipid microstructure were compared in terms of their physical meaning, means of acquisition, and consistency. The results showed that the quantitative microstructure parameters obtained from different approaches, except the fractal dimesion determined by the PCM, can identify both differences and similarities of microstructural characteristics in the model lipid systems studied in this work.

Micro-structural study of the GeS 2–In 2S 3–KCl glassy system by Raman scattering

Room temperature Raman spectra of samples on three serials within the GeS 2–In 2S 3–KCl glassy system have been investigated systematically. According to XRD patterns and Raman spectra of several pseudo-binary systems, the Cl atoms, which was added into the GeS 2–In 2S 3 glasses through KCl, was considered to be leading to the breaking of In–In bonds among the S 3In–InS 3 ethane-like units and the forming of InS 4− x Cl x , InS 6− x Cl x mixed polyhedra. Considering the effect of K + ions upon mixed anion units (InS 4− x Cl x and InS 6− x Cl x ) and the corresponding micro-structural model, the Raman spectral evolution of the GeS 2–In 2S 3–KCl glasses can be elucidated successfully. The microstructure of the GeS 2–In 2S 3–KCl glasses was considered to be that the potassium atoms, which exist in the form of chlorine atoms as its nearest neighbor, are homogeneously dispersed in the glassy net formed by the micro-structural units such as InS 4, InS 6, InS 4− x Cl x , InS 6− x Cl x , GeS 4 polyhedra and S 3In(Ge)–In(Ge)S 3 ethane-like units.

Shock propagation through alumina observed at the mesoscale

The shock response of 88% and 99.9% pure aluminas, chosen since they had been tested previously, was simulated at the mesoscale. Microstructures were investigated using electron microscopy and then digitized for use in simulation. These microstructural units were stacked to recover larger-scale structures generated randomly. These extended the length ranges in the simulations from the micrometer to the continuum scales. Modeling emphasized the inhomogeneity of the flow at this length scale and phenomena such as precursor decay were accentuated in the material with the greater impurities. The bulk composite behavior could be recovered from the properties of the individual phases by adopting simple expressions for the shock parameters. These behaviors include the profile of the stress histories and quantitative prediction of the Hugoniot elastic limits recovered using information derived purely on constituents.

3327 インデンテーション試験によるタービンロータ鋼の材質劣化解析(S18-2 結晶塑性解析,S18 材料の強度と組織)

Advanced high Cr ferritic steel have a complex lath martensitic structure consisting of several microstructural units, i,e., in the order of their size, fine lath, block and/or packet including several laths, and prior austenite grain which is the largest unit. In addition, precipitation, solid-solution and dispersion strengthening contribute to their strength. However, it is by no means easy to separate the contributions of such strengthening factors and quantitatively understand them because of extremely fine and complicated microstructure. In this study, the instrumented indentation test was carried out under a wide variety of maximum indentation loads using the interrupted creep specimens to clarify the contributions of block to their strength and/or material degradation.

The Raman coupling coefficients of calcium and sodium silicate melts in high-frequency region - SiOT model study

The Raman coupling coefficient (CC), which was defined by Shuker and Gammon, of silicate melt in high-frequency region, is still an untouched subject but the key parameter for quantitatively processing the Raman spectra (RS) to achieve the abundance of microstructural units. In this paper, we present the results of a newly constructed model - SiOT model (Wu et al) about the Raman coupling coefficients of calcium and sodium silicate melts, especially in the high-frequency region. This new model combines classical MD simulation with decomposition of simulated configurations and vibrational analysis including Wilson's GF matrix method, electro-optical parameter method (EOPM) and bond polarizability model (BPM). The displacement dependence of the cluster polarizability through the combination of EOPM and BPM connotes the description of the frequency dependence of CC. This allows us to make a direct comparison for the first time between the calculated VDOS (vibrational density of states) and RS within the entire frequency range. A strong conclusion was given that the partial VDOS, RS and CC are all the intrinsic properties of respective Qi species, and the only variable inducing the change in total VDOS, RS and CC is the change of microstructure, i.e. the distribution of the Qi.

Measuring elastic properties and anisotropy of microstructural units of laminate composite materials by microacoustical technique

The paper is devoted to application of focused ultrasonic beams for measuring bulk elastic properties in advanced fiber composite materials, such as carbon fiber-reinforced composite (CFRC) laminates. Long-focus convergent beam of 50 MHz ultrasound frequencies provides the exceptional means of measuring elastic properties of microstructural units in composite materials with intricate microstructure as well as their integral properties. The microacoustical measurements reveal high anisotropy of CFR-laminate layers: sonic velocity across plies was found to be equal 3.1 km/s; in ply plane across fiber packing—7.0 km/s and along fibers—9.0–9.8 km/s.

A micromechanical approach to fatigue in small notches*

ABSTRACTThe present work shows the application to small notches of a micromechanical model which describes the growth of a short crack across the steep stress gradient generated at the root of a notch. The model, based on the theory of distributed dislocations, takes into account the interaction between short cracks and material barriers such as grain boundaries. The term ‘small notches’ refers in this paper to stress raisers the size of which is of the same order as the characteristic microstructural unit of the material. Typical examples are superficial scratches, corrosion pits, inclusions or pores. Comparisons between predicted fatigue limits and experimental results reported in the literature for different materials containing small artificial defects are shown and discussed.

Synthesis of Poly(alcohol)s by Hydroboration/Oxidation of Poly(methylallene) Prepared by π-Allylnickel-Catalyzed Living Coordination Polymerization

The π-allylnickel-catalyzed living coordination polymerization of methylallene gave polymers with predictable molecular weight and narrow molecular weight distribution in high yields. The polymers possessing various microstructural units (i.e., the ratio of the 1,2- and the 2,3-polymerizations), produced by varying the nature of the catalyst and the solvents, were subjected to the hydroboration with borane reagents such as borane tetrahydrofuran complex (BH3•THF) and 9-borabicyclo[3.3.1]nonane (9-BBN). Subsequent oxidation gave poly(alcohol)s whose hydroxy-content could be varied by the borane reagents used. For example, the quantitative conversion of the double bonds in poly(methylallene) into the hydroxy group was attained by the hydroboration using an excess amount of BH3•THF. Thermal properties of poly(alcohol)s were found to be dependent upon the microstructure and the hydroxy-content of the polymers.

Raman scattering coefficients of symmetrical stretching modes of microstructural units in sodium silicate melts

Quantitative analysis of Raman spectra of vitreous or molten silicate is always one of the key subjects in some fields, e.g. materials science, geological physi cs, etc. But there are many difficulties with this analysis, one of which is the determination of Raman scattering coefficient. Not long ago, we developed a new method for the calculation of Raman spectrum of amorphous silicate. Essentiall y, this method combines the molecular dynamics simulation with wilson's GF matri x method, electro_optical parameter method and bond polarizability model. With t his theoretical method, we have studied the Raman scattering coefficients of sym metrical stretching modes of Qi in sodium silicate melts, and concluded th at these coefficients are independent of composition. Meanwhile, the five values of the coefficients are also given as follows: S0=１, S1=0514, S2=0 242, S3=0090 and S4=0015 In order to apply these quantities to experiments, the Raman spectrum of sodium disilicate melt has been measured and its high_frequency envelope has been deconvolved into three Gaussian bands. Fina lly, the molar fractions of Qi were achieved by dividing the area fraction s of the three Gaussian bands by corresponding scattering coefficients. Addition ally, combining the results of theoretical calculation and quantitative analysis of experimental spectra, we found that the intensities of anti_symmetrical stre tching modes of Q0 and Q2 in sodium silicate melts are so strong tha t they cannot be neglected in the deconvolution process.

Modelling and simulation of microchannel catalytic WGS reactor for an automotive fuel processor

The water-gas shift (WGS) is one of the major steps for H2 production from gaseous, liquid and solid hydrocarbons. It is used to produce hydrogen for ammonia synthesis, to adjust the hydrogen-to-carbon monoxide ratio of synthesis gas, to detoxify gases. The WGS reactor is widely used as a part of fuel processors which produce hydrogen-rich stream from hydrocarbon-based fuels in a multi-step process. The WGS unit is placed downstream the fuel reformer in order to increase overall efficiency of hydrogen production and to lower CO content in reformate. Fuel processors stand for considerable option for fuelling PEM fuel cells for both portable and stationary applications. Micro-structured reactors are used with benefits of process miniaturization, intensification and higher heat and mass transfer rates compared with conventional reactors. Micro-structured reactor systems are essential for processes where potential for considerable heat transfer exists as well as for kinetic studies of highly exothermic reactions at near-isothermal conditions. Modelling and simulation of a microchannel reactor for the WGS reaction is presented. The mathematical models concern a single reaction channel with porous layer of catalyst deposited on the metallic wall of the microstructure unit. Simplified one-phase and more sophisticated two-phase models, with separate mass and energy balances for gas and solid phase at different levels of complexity, were developed. The models were implemented into gPROMS process modelling software. The models were used for an estimation of parameters in a kinetic expression using experimental data obtained with a new WGS catalyst. The simulations provide detailed information about the composition and temperature distribution in gas phase and solid catalyst inside the channel.

Image analysis of exfoliation fracture in cold drawn steel

This work studies the anisotropic fracture behavior of cold drawn prestressing steels in the form of exfoliation fracture consisting of oriented and enlarged cleavage, its orientation being parallel to the wire axis (cold drawing direction) and with river patterns which are detectable in such a direction. Using a computer-assisted image analysis technique, a geometric relationship was found between this special cleavage and the conventional cleavage topography, which indicates that the fracture micromechanisms in both cases are also similar and allows a definition of the critical fracture unit in the drawn material as the pearlite colony more than the prior austenite grain. Thus the slender pearlitic colonies become the actual microstructural fracture units and determine the size of the enlarged cleavage facets characteristics of the exfoliation fracture in notched samples of heavily drawn steels.

Charpy-impact-toughness prediction using an “effective” grain size for thermomechanically controlled rolled microalloyed steels

Thermomechanically controlled rolling of steel plate can involve substantial straining in the intercritical temperature region, which may result in the final ferrite grains not fully recrystallizing, and, hence, the presence of low-angle grain boundaries. It is shown in this article that a Nb-microalloyed thermomechanically controlled rolled (TMCR) steel can contain a high proportion of low-angle grain boundaries (the extent depending on the thermomechanically controlled rolling schedule) and that during toughness testing, the crack front ignores boundaries with less than a 12 deg misorientation. Thus, the average microstructural unit experienced by the crack front (i.e., the cleavage facet) is significantly larger than the average metallographic, two-dimensional grain size. Consequently, use of the metallographic grain size gives a poor prediction of the impact transition temperature (ITT) and fracture stress for these steels. It is also shown that the micromechanism of crack initiation and propagation involves grain-boundary carbides and groups of closely aligned grains that act as single “effective” grains.

Predictability of Charpy impact toughness in thermomechanically control rolled (TMCR) microalloyed steels

A number of empirical equations, based primarily on average metallographic grain size and carbide thickness, exist to predict the Charpy impact transition temperature in steels. Some of these commonly used equations, successful for normalised steels, have been shown in this paper to be inadequate for predicting the transition temperature for thermomechanically control rolled (TMCR) microalloyed steels. Thermomechanical control rolling can produce clusters of small grains with low angle grain boundaries, i.e., the steel shows mesotexture. The cleavage facet size in TMCR steels has been found to be significantly larger than the optical grain size and it was also observed that individual cleavage facets can be comprised of multiple grains. In contrast, it was observed for a heat treated steel that the facet size matches the optical grain size and that individual facets consist of single grains. It is concluded that in TMCR steels, the average microstructural unit experienced by the crack front is larger than the optical grain size because mesotexture causes groups of closely orientated grains to be treated as single 'effective' grains. This paper shows that the 50% and 27 J impact transition temperatures can be predicted for TMCR steels using the existing equations if mesotexture and grain boundary carbide size are taken into account.

Influence of microstructural features on water, ion diffusion and transport in clay soils

The presence, distribution, and sizes of pore spaces, together with the continuity between them, and the interactions established therein are examined in terms of: (a) mechanisms associated with wetting and water uptake, (b) the role of soil composition on the development of microstructural units (MUs), and (c) the contribution of MUs to the macrostructural behaviour of a clay soil using viscometer measurements. A key element in the production of microstructure and distribution of pore spaces is the nature of the soil fractions comprising the clay soil. The influence of microstructure on the wetting of clay soils and water uptake performance is discussed in terms of hydration processes and film boundary transport. Viscometer measurements were used to assess soil composition and formational environments on soil microstructure.

Analysis of different acicular ferrite microstructures in low-carbon steels by electron backscattered diffraction. Study of their toughness behavior

Acicular ferrite formation, promoted by the intragranular nucleation of ferrite plates, is well known to be beneficial for achieving a good combination of mechanical properties. However, the set of microstructures that can be obtained during the subsequent development of the transformation from the primary plates generated at particles can be quite complex and depends on a certain number of variables: steel composition, temperature range, prior austenite grain size, and particle density. In the present work, acicular ferrite microstructures have been produced by isothermal treatments in three different steels with different active particle types and densities. The morphology of the obtained intragranular microstructures has been found to depend on the steel composition, the prior austenite grain size, and the density of particles able to promote intragranular nucleation. Electron backscattered diffraction (EBSD) techniques have been used to define the microstructural unit controlling toughness in these types of microstructures.

SHEAR WAVE IN GLUTIN AS A SOFT MATTER

This paper focuses on the function between the internal friction and frequency in soft matters. It attempts to prove that the shear wave can interact with microstructure units of certain sizes in soft matters. The specimen used in our experiment is glutin. Using the apparatus1 developed by ourselves, we get the frequency spectrum of glutin, and point out that the spectrum is an inherent physical property of the substance.

Effect of Additives on Self-Assembling Behavior of Nafion in Aqueous Media

The dynamic light scattering technique is employed to study the self-assembling behavior of Nafion in dilute aqueous solutions and in water-based mixture solvents. The mixture solvents contain either salt or a small amount of glycerol, which is often necessary for the fabrication of the electrode−membrane assembly. Two kinds of aggregates are found in Nafion aqueous solutions: (1) an intrinsic aggregate (∼150 nm) due to the hydrophobic interaction of fluorocarbon backbone, which is found to be always present in aqueous solutions; (2) a larger, secondary aggregate, which can be suppressed by the addition of salt or a small amount of glycerol. This secondary/higher level aggregation may arise from the electrostatic attraction through the nonionized ion pairs, which are believed to facilitate the formation of large ion clusters and provide the ion connection between the ion clusters. We discuss the structures of Nafion aggregates based on the rodlike microstructure units and propose a microgel-type aggregation model.

Gypsum morphological analysis and modeling

When plaster is put in water, a network of needles is spontaneously formed. The morphology of the plaster microstructure have been studied in order to understand precisely its role with respect to its physical properties. Three microstructures of plaster were prepared from different hydration conditions, to obtain three crystal sizes at a given level of porosity. We propose a morphological characterization and modeling of the plaster microstructure by means of simple tools of mathematical morphology. From the use of a two parameters random model of microstructure, the Boolean model, contact properties between the microstructural units made of gypsum needles are estimated, and bounds of the elastic behavior of the plaster are compared to measurements.

Comparison between Cooling Rate Dependence of Macroscopic and Microscopic Quantities in Simulated Aluminium Glass

Constant-pressure molecular dynamics simulations and an analysis of the local atomic structures have been performed to study the cooling rate dependence of some macroscopic and microscopic quantities in aluminium glass. Macroscopic quantities, enthalpy and density, see an observable but small dependence on the cooling rate. Icosahedral ordering units exhibit strong cooling rate dependence, which is responsible for the dependence of the enthalpy and the density on the cooling rate; while the almost independence of some microstructural units such as the 1541, 1431 and 1421 pairs of the cooling rate may lead to a small dependence of the enthalpy and the density on the cooling rate.

Different Cooling Rate Dependences of Different Microstructure Units in Aluminium Glass by Molecular Dynamics Simulation

Constant-pressure molecular dynamics simulation and the pair analysis technique have been performed to study the microstructural evolution of aluminium during rapid solidification. The microstructure characteristics of icosahedral ordering increase with decrease of the cooling rate, whereas the microstructure unit characteristics of hcp crystalline structure decrease. There are two kinds of microstructure units which are similar to those in the fcc crystal containing interstitialcies. These two kinds of microscopic units are nearly independent of the cooling rate. The microscopic structural unit characteristics of fcc crystalline structure do not depend on the cooling rate either. These results may help us understand the microstructure of glass and its stability.