Role Of Grain Size Research Articles

The role of grain size on the thermal instability of nanostructured metal oxides used in gas sensor applications and approaches for grain-size stabilization

This review examines the influence of grain size on the thermal stability of nanostructured metal oxides by studying their structural parameters. The main consideration was focused on the behavior of SnO2, the most studied and used metal oxide in the field of gas sensor design. It has been shown that a decrease of the grain size was accompanied by a deterioration of the structural stability of the gas sensing material; a change of grain size in the gas sensing material could occur during annealing and exploitation. The study provides an analysis of the reasons for the changes in gas sensor properties during thermal treatment. The effectiveness of different approaches used for stability improvement of metal-oxide structures were considered. In particular, various approaches such as preliminary high-temperature annealing of as-synthesized powders, optimization of the processes of synthesis and deposition, the use of 1-D structures, and metal-oxide doping with various additives were analyzed.

Effect of microrelief on the optical characteristics of light Cr-Zr copper alloys bombarded by ions of deuterium plasma

The effect of the structure and size of grains on changes in the microrelief and optical characteristics of specimens of mirrors made of copper alloys with substantially differing grain size upon bombardment by ions of deuterium plasma are studied. Based on a comprehensive study of the structural features of the surface layers of specimens of mirrors made of light copper-chromium alloys, a conclusion is drawn as to the determining role of grain size in their radiation properties.

Bismuth-film electrodes for Sn2+ Sensing: The Roles of Grain Size, Preferred Orientation Ratio, and Surface Roughness

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Effect of pH on the Grain Size Dependence of Magnesium Corrosion

Prior works show that grain size can play a role in the corrosion of a metal; however, such works are nominally executed in a single electrolyte/environment at a single pH. In this work, the anodic and cathodic reaction kinetics of pure Mg specimens with grain sizes ranging from approximately 8 μm to 590 μm were compared as a function of pH in 0.1 mol dm−3 sodium chloride (NaCl) electrolytes using anodic polarization experiments and an in situ scanning vibrating electrode technique (SVET). Anodic polarization experiments showed that grain size is important in determining overall electrochemical response, but the environment dictates the form of the grain size vs. corrosion rate relationship (i.e., pH is the overall controlling factor). Consequently, the role of grain size upon corrosion cannot be fully assessed unless a variation in environment is simultaneously studied. For example, the anodic reaction, which dictates active corrosion, also dictates passivation, so the corrosion rate vs. grain size relationship has been shown to “flip” depending on pH. Further, SVET analysis of unpolarized Mg immersed in 0.1 mol dm−3 NaCl electrolyte at neutral pH showed that breakdown of passivity of cast Mg occurred after ~1 h immersion, giving filiform-like corrosion tracks. The front edges of these corrosion features were revealed as intense local anodes, while the remainder of the dark-corroded Mg surface, left behind as the anodes traversed the surface, became cathodically activated. In contrast, grain-refined Mg samples were significantly less susceptible to localized corrosion, and breakdown was not observed for immersion periods of up to 24 h.

Simplified Transient Hot-Wire Method for Effective Thermal Conductivity Measurement in Geo Materials: Microstructure and Saturation Effect

The thermal conductivity measurement by a simplified transient hot-wire technique is applied to geomaterials in order to show the relationships which can exist between effective thermal conductivity, texture, and moisture of the materials. After a validation of the used &#x201c;one hot-wire&#x201d; technique in water, toluene, and glass-bead assemblages, the investigations were performed (1) in glass-bead assemblages of different diameters in dried, water, and acetone-saturated states in order to observe the role of grain sizes and saturation on the effective thermal conductivity, (2) in a compacted earth brick at different moisture states, and (3) in a lime-hemp concrete during 110 days following its manufacture. The lime-hemp concrete allows the measurements during the setting, desiccation and carbonation steps. The recorded <svg style="vertical-align:-2.21957pt;width:57.025002px;" id="M1" height="13.5625" version="1.1" viewBox="0 0 57.025002 13.5625" width="57.025002" xmlns="http://www.w3.org/2000/svg"> <g transform="matrix(1.25,0,0,-1.25,0,13.5625)"> <g transform="translate(72,-61.15)"> <text transform="matrix(1,0,0,-1,-71.95,63.41)"> <tspan style="font-size: 12.50px; " x="0" y="0">Δ</tspan> <tspan style="font-size: 12.50px; " x="9.0271664" y="0">𝑇</tspan> <tspan style="font-size: 12.50px; " x="15.903816" y="0">/</tspan> <tspan style="font-size: 12.50px; " x="21.455149" y="0">l</tspan> <tspan style="font-size: 12.50px; " x="24.930983" y="0">n</tspan> <tspan style="font-size: 12.50px; " x="33.270481" y="0">(</tspan> <tspan style="font-size: 12.50px; " x="37.433983" y="0">𝑡</tspan> <tspan style="font-size: 12.50px; " x="41.34742" y="0">)</tspan> </text> </g> </g> </svg> diagrams allow the calculation of one effective thermal conductivity in the continuous and homogeneous fluids and two effective thermal conductivities in the heterogeneous solids. The first one measured in the short time acquisitions (&#x3c;1&#x2009;s) mainly depends on the contact between the wire and grains and thus microtexture and hydrated state of the material. The second one, measured for longer time acquisitions, characterizes the mean effective thermal conductivity of the material.

Role of grain size in superconducting boron-doped nanocrystalline diamond thin films grown by CVD

The grain size dependence of the superconducting transition, the normal state resistivity, and the insulating behavior at high magnetic fields are studied on a series of boron-doped nanocrystalline diamond (B:NCD) thin films with different grain sizes. The systematic change of the grain size is achieved by varying the methane-to-hydrogen ratio (C/H ratio) for the growth of different B:NCD films. Even though a fixed trimethylboron- (TMB) to-methane gas ratio is supposed to induce the identical boron-doping level in all the B:NCD films, the boron concentration and the carrier density are found to be a decreasing function of the grain size. Another consequence of the increase in grain size is the decreasing grain boundary density. These two concurrent consequences of the chemical vapor deposition mode of B:NCD are responsible for the grain size dependence of the critical temperature ${T}_{C}$, the localization radius ${a}_{H}$ at the boron site, the normal state resistivity ${\ensuremath{\rho}}_{\mathrm{norm}}$, the Hall mobility ${\ensuremath{\mu}}_{H}$, the Ioffe-Regel product ${k}_{F}$$l$, the ${H}_{C}$${}_{2}$-$T$ phase boundary, and the coherence length ${\ensuremath{\xi}}_{GL}$.

Comprehensive evaluation of heavy metal contamination in surface and core sediments of Taihu Lake, the third largest freshwater lake in China

The spatial and temporal variations of Fe, K, Co, V, Cr, Cu, Ni, Zn, and Pb were determined in the sediments of Taihu Lake, the third largest freshwater lake in China and categorized into natural origin (Fe, K, Co, and V) and human contamination (Cr, Cu, Ni, Zn, and Pb) groups by principal component analysis. Most of the metals were positively correlated with the clay content ( 16 μm fraction, indicating the dominant role of grain size in regulating metals concentrations. Geochemical normalization and enrichment factors (EFs) were introduced to reduce the confounding of variable grain size and to quantify anthropogenic contributions. Higher EF values for Cr, Cu, Ni, and Zn occurred in the north Zhushan, Meiliang, and Gonghu Bays, indicating a high level of human contamination from the northern cities, such as Wuxi and Changzhou. Higher EF values of Pb were also present in the southwest and east lake areas, denoting the existence of additional anthropogenic sources. Chrome, Cu, Ni, Zn, and Pb showed increasing EF values in the top layers of sediment cores, indicating enhancing contamination since 1970s with rapid economy development in the catchment. These results indicate that geochemical normalization is a necessary and effective method in quantifying heavy metals contamination, and that historic sediment should be used as background values in calculating EFs. Potential risks of the heavy metals were assessed linking the consensus-based sediment quality guidelines and human contamination. Concentrations of Ni and Cr are greater than the threshold effect concentration (TEC) values, even in the sediments before 1970s, due to higher background concentrations in terrestrial parent materials. Concentrations of Ni and Cr are generally lower than the probable effect concentration (PEC) values, and concentrations of Cu and Zn are below the TEC values in the open lake areas. Whereas, concentrations of Ni and Cr are surpassing the PEC values and Cu and Zn are surpassing the TEC values in the north bays due to the high level of human contamination, where they were with EFs over 1.2, denoting higher potential eco-risks.

Sintering of Hydroxyapatite Ceramic Produced by Wet Chemical Method

In the present work, densification of synthesised hydroxyapatite (HA) bioceramic prepared via chemical precipitation method was investigated. HA samples was prepared by compaction at 200 MPa and sintered at temperatures ranging from 800°C to 1400°C. The results revealed that the HA phase was stable for up to sintering temperature of 1250°C. However, decomposition of HA was observed in samples sintered at 1300°C with the formation of tetra-calcium phosphate (TTCP) and CaO. Samples sintered above 1400°C were found to melt into glassy phases. The bulk density increases with increasing temperature and attained a maximum value of 3.14 gcm-3 at 1150°C whereas maximum hardness value of 6.64 GPa was measured in HA sintered at 1050°C. These results are discussed in terms of the role of grain size.

Physical basis of the Thellier–Thellier and related paleointensity methods

Émile and Odette Thellier produced the first reliable determinations of paleointensity following an experimental protocol used earlier by Johann Koenigsberger. Although Koenigsberger did groundbreaking work on thermoremanent magnetization (TRM), it was the Thelliers who formulated the fundamental idea of partial TRMs as building blocks for TRM. In his 1938 doctoral thesis and a series of short notes, Émile Thellier minutely examined the data on TRM and partial TRM, ultimately establishing for bricks and other baked clays his laws of pTRM reciprocity, independence and additivity. In 1946 he speculated that blocking represents “…immobilization of elementary magnetic moments below a temperature Θ … Θ will vary at each point in the body, perhaps with the dimensions and the shape of the crystalline grains … One can thus explain thermoremanence by the progressive fixing, in the course of cooling, of moments which find themselves held fast when they pass through their individual temperature Θ.” Thellier thus established the physical basis of TRM blocking and recognized the essential role of grain size and shape. In 1949 Louis Néel quantified these concepts in terms of the properties of single-domain grains. Today the Thellier–Thellier method remains the benchmark of reliable paleointensity data. The challenge has been the non-ideality of real geological and archeological materials: TRM carriers larger than single-domain size and physicochemical alteration during heating. The Thelliers avoided these problems by using bricks and pottery previously fired under conditions similar to those in laboratory heatings, eschewing volcanic and other rocks. But despite their problems, we have to deal with the material nature provides. This paper provides insights into the physics underlying the Thellier–Thellier method and check procedures that detect non-ideal behavior, as well as reviewing recent advances in paleointensity methodology.

Fatigue Threshold R-Curve Behavior of Grain Bridging Ceramics: Role of Grain Size and Grain-Boundary Adhesion

To better understand the role of grain size and grain-boundary adhesion on the fatigue threshold R-curve behavior of grain bridging ceramics, a study was conducted on the fatigue threshold behavior of 99.5% pure polycrystalline alumina with two different microstructures (fine and coarse) and in two different environments (moist air and dry N2). The fine-grained microstructure showed higher fatigue thresholds at short crack sizes, while the coarse-grained microstructure demonstrated higher fatigue thresholds at long crack sizes. The former effect lead to slightly higher calculated fatigue strengths and was attributed to the crack stalling process that leads to earlier elastic bridge formation in that microstructure. The latter effect is attributed to toughening that is dominated by frictional and mechanical interlocking bridges at longer crack sizes where the larger grains are able to give more bridging. By testing the coarse microstructure in a dry environment, a higher K0 was achieved for the glassy grain boundaries giving a higher R-curve at short crack sizes and higher calculated fatigue strengths.

Compositional and microstructural effects in composite electrolytes for fuel cells

Composite ionic conductors were produced by combination of alkaline carbonates with various ceramic oxides, including ceria, zirconia and alumina. The adopted mechano-thermal processing routes originated materials with the same nominal composition but with significantly different microstructures. The electrical performance of these composites, studied by impedance spectroscopy, showed the relevance of the mixed carbonate phase on the transport properties, but also unexpected composite effects. The role of grain size on the electrical performance could not be isolated from the possible influence of alkaline metal rich interfacial layers (ceramic/carbonate) consisting of nanosized 1D crystals. Modest electrode impedances in open air experiments are coherent with the coexistence of various charge carriers. The known interaction of major composite constituents and minor secondary phases with water might explain the presence of additional charge carriers. Copyright © 2011 John Wiley & Sons, Ltd.

The effect of microstructure on hardness and toughness of low carbon welded steel using inert gas welding

The heat affected zone (HAZ), has a great influence on the properties of welded joints since it can alter the microstructure and residual stresses. In this paper, the effect of welding parameters and heat input on the HAZ and grain growth has been investigated. The role of grain size on hardness and toughness of low carbon steel has also been studied.It was observed that, at high heat input, coarse grains appear in the HAZ which results in lower hardness values in this zone. For example raising the voltage from 20 to 30V decreased the grain size number from 12.4 to 9.8 and hardness decreased from 160 to 148 HBN. High heat input and low cooling rates produced fine austenite grains, resulting in the formation of fine grained polygonal ferrites at ambient temperature.

Characterization of Fatigue Fracture in Ni-20 Pct Cr Alloys Using White Light Interference Microscopy and Scanning Probe Microscopy

Nanostructured and ultra–fine-grained metals and alloys are becoming of engineering interest. However, little is known about the influence of grain refinement on fatigue crack behavior. In this study, fatigue crack growth behavior and the key microstructural features controlling the fatigue fracture in nanocrystalline and ultra–fine-grain nickel alloys, processed using different techniques, were investigated. White light interference microscopy as well as the combination of atomic force microscopy (AFM) and ultrasonic force microscopy (UFM) were used to characterize the fractured surfaces of the metals. The role of grain size on the fatigue crack growth resistance and the effect of fracture surface roughness on the crack growth rate were evaluated. The combination of AFM and UFM is presented as a complementary tool to scanning electron microscopy in the fractography of metals.

Penetration of nearby supernova dust in the inner solar system

We investigate the method by which nearby supernovae – within a few tens of pc of the solar system – can penetrate the solar system and deposit live radioactivities on earth. The radioactive isotopic signatures that could potentially leave an observable geological imprint are in the form of refractory metals; consequently, it is likely they would arrive in the form of supernova-produced dust grains. Such grains can penetrate into the solar system more easily than the bulk supernova plasma, which gets stalled and deflected near the solar system due to the solar wind plasma pressure. We therefore examine the motion of charged grains as they decouple from the supernova plasma and are influenced by the solar magnetic, radiation, and gravitational fields. We characterize the dust trajectories with analytical approximations which display the roles of grain size, initial velocity, and surface voltage. These results are verified with full numerical simulations for wide ranges of dust properties. We find that supernova dust grains traverse the inner solar system nearly undeflected, if the incoming grain velocity – which we take to be that of the incident supernova remnant – is comparable to the solar wind speeds and much larger than the escape velocity at 1 AU. Consequently, the dust penetration to 1 AU has essentially 100% transmission probability and the dust capture onto the earth should have a geometric cross section. Our results cast in a new light the terrestrial deposition of radioisotopes from nearby supernovae in the geological past. For explosions beyond ∼10 pc from earth, dust grains can still deliver supernova ejecta to earth, and thus the amount of supernova material deposited is set by the efficiency of dust condensation and survival in supernovae. Turning the problem around, we use observations of live 60Fe in both deep-ocean and lunar samples to infer a conservative lower bound iron condensation efficiency of M dust,Fe/ M tot,Fe ≳ 4 × 10 −4 for the supernova which apparently produced these species 2–3 Myr ago.

Organic facies of the Oligocene lacustrine system in the Cenozoic Taubaté basin, Southern Brazil

Abstract A quantitative study of palynofacies and organic facies was carried out in the Cenozoic sedimentary succession of the Taubate basin. The palaeoenvironmental distributions of particulate organic components were examined in relation to various potential controlling factors (lithology, depositional environment, and stratigraphic sequence). About 30 samples were analyzed from a single borehole drilled in Sao Paulo State. This involved rigorous kerogen counts supported by 30 TOC and sulphur, 20 Rock-Eval pyrolysis and 20 biochemistry analyses. In the studied area the Oligocene deposits are approximately 600 m thick. Data was obtained by counting 300 to 500 kerogen particles per sample, and then recalculating the percentages of the different constituent groups (phytoclast, palynomorph, and amorphous organic matter — AOM). The kerogen assemblage is palynomorph-dominated (> 70%), consisting mainly of freshwater lacustrine algae ( Pediastrum and Botryococcus ). Non-opaque phytoclasts predominate in most of the kerogen samples. However, significant variations in the proportion of biostructured and non-biostructured brown phytoclasts occur in some intervals. The fluorescent AOM content occurs in some levels and is composed of two main components: an intensively fluorescing structureless organic matter, which also has high lipid and protein content indicating a probable bacterial origin for the organic matter (microbial mats); and terrestrially-derived amorphous organic matter, which has been reworked to a different extent exhibiting a high content of carbohydrates. Comparison of the mean kerogen assemblages from different lithologies revealed that the finer-grained lithologies generally have higher palynomorph percentages, whereas coarser-grained lithologies present higher percentages of phytoclasts, emphasizing the important role of grain size in organic-matter distribution. The TOC content is generally less than 10%, but reaches as high as 44% in some intervals, due mainly to the presence of coaly seams. The T max , Spore Coloration Index, and spectral fluorescence measurement values obtained from these samples indicate a low maturity stage. The integration of these results, together with the organic facies parameters, indicate that the analyzed sedimentary section represents a variation from a freshwater lacustrine environment with an oxidant regime to a restricted saline, lacustrine environment with a dysoxic–anoxic regime. There was an excellent correlation between the optical and geochemical parameters.

Coupled effects of grain size distributions and crystallographic textures on the plastic behaviour of IF steels

Micro–macro scale transition theories were developed to model the inelastic behaviour of polycrystals starting from the local behaviour of the grains. The anisotropy of the plastic behaviour of polycrystalline metals was essentially explained by taking into account the crystallographic textures. Issues like plastic heterogeneities due to grain size dispersion, involving the Hall–Petch mechanism at the grain scale, were often not taken into account, and, only the role of a mean grain size was investigated in the literature. Here, both sources of plastic heterogeneities are studied using: (i) experimental data from EBSD measurements and tensile tests, and, (ii) a self-consistent model devoted to elastic–viscoplastic heterogeneous materials. The results of the model are applied to two different industrial IF steels with similar global orientation distributions functions but different mean grain sizes and grain size distributions. The coupled role of grain size distributions and crystallographic textures on the overall tensile behaviour, local stresses and strains, stored energy and overall plastic anisotropy (Lankford coefficients) is deeply analyzed by considering different other possible correlations between crystallographic orientations and grain sizes from the measured data.

Thermal conductivity measurement in clay dominant consolidated material by Transient Hot-Wire method.

The transient hot-wire (THW) technique is widely us ed for measurements of the thermal-conductivity of most fluids and some attempts have also been carried out for simultaneous measurements of the thermal-diffus ivity with the same hot wire. This technique was also tried to determine thermal prope rties of soils by the mean of probes which can be considered as wire with some assumptions. The purpose of this paper is to validate the thermal conductivity measurement by th e THW technique in geomaterials, composed of compacted sand + clay mineral that can be used for earth construction (Compacted Earth Brick). The thermal transfer behaviors are mainly governed by the texture and moisture of the geomaterials. Thus the investigations were performed (1) in media made of glass beads of different diameters in dry and saturated state in order to observe the role of grain sizes and saturation stat e on the wire temperature (Δt) measurements and (2) in the compacted clay-geomaterial at different moisture states. The Δt / ln(t) diagrams allow the calculation of two the rmal conductivities. The first one, measured in the short time acquisition (< 1s), char acterizes the microtexture of the material and its hydrated state. The second one, me asured for longer time acquisitions, characterizes the mean thermal conductivity of the material.

Processing and evaluation of 15Cr-15Mo nickel base superalloy

A Nickel base solid solution strengthened alloy has been made with a nominal chemical composition of 15Cr-15Mo (balance Ni) through vacuum melting route and was characterized in hot worked and heat-treated conditions. Processing parameters have been optimized to get the desired microstructure and mechanical properties. The alloy has shown very good mechanical properties at elevated temperatures as well as at cryogenic temperatures. Role of solution treatment temperature and correspondingly role of grain size on mechanical properties at different temperatures has also been evaluated and reported. Heat treatment cycle for application of alloy upto 700°C has been optimized. Properties of the alloy have been compared with similar class of alloys.

Direct Evidence for Effects of Grain Structure on Reversible Compressive Deposition Stresses in Polycrystalline Gold Films

A component of the compressive stress that develops during deposition of polycrystalline thin films reversibly changes during interruptions of growth. The mechanism responsible for this phenomenon has been the subject of much recent speculation and experimental work. In this Letter, we have varied the in-plane grain size of columnar polycrystalline gold films with a fixed thickness, by varying their thermal history. Without a vacuum break, the stress in these films was then measured in situ during growth and during interruptions in growth. Homoepitaxial gold films were similarly characterized as part of this study. The inverse of the in-plane grain size and the corresponding reversible stress change were found to be proportional, with zero reversible stress change observed for infinite grain size (homoepitaxial films). These results demonstrate a clear role of grain size in the reversible changes in gold films.

Structural and magnetic properties of Mg_{0.8-x}M_{0.2}Ni_xFe_2O_4 (M = Zn, Mn) ferrite powders

Structural and magnetic properties of Mg_{0.8-x}M_{0.2}Ni_xFe_2O_4 (M = Zn, Mn; x = 0, 0.2, 0.4, 0.6, 0.8) ferrite powders, prepared by solid state reaction method, were studied. The variations of lattice parameter, X-ray density, crystallite size, saturation magnetization, effective number of Bohr magneton, and coercivity with Ni content were investigated. The role of grain size was found to be crucial in the behavior of coercivity.