Effect Of Chemical Heterogeneity Research Articles

Abnormal martensitic transformation and morphology induced by chemical heterogeneity in additively manufactured maraging steel

We report on the effect of chemical heterogeneity on martensitic transformation in a maraging steel produced through laser-based directed energy deposition. Unlike conventional maraging steels with lath martensitic microstructures, the maraging steel exhibited an abnormal morphology, which was refined and elongated in the building direction. The growth direction of the abnormal lath martensite did not occur along the habit plane, while the lath martensite morphology corresponded to the cellular dendritic microstructure of the maraging steel. Among the elements partitioned to the interdendritic region, Ni played a major role in the reduction of the martensitic transformation start temperature (Ms temperature), thereby interfering with the martensitic transformation across the interdendritic region. The interdendritic region acted as a new domain boundary of martensitic transformation, where incomplete martensitic transformation in the region resulted in the retention of austenite.

Dynamics of competition model between two plants based on stoichiometry.

The dynamics of two-plant competitive models have been widely studied, while the effect of chemical heterogeneity on competitive plants is rarely explored. In this study, a model that explicitly incorporates light and total phosphorus in the system is formulated to characterize the impacts of limited carbon and phosphorus on the dynamics of the two-plant competition system. The dissipativity, existence and stability of boundary equilibria and coexistence equilibrium are proved, when the two plants compete for light equally. Our simulations indicate that, with equal competition for light ($ b_{12} = b_{21} $) and a fixed total phosphorus in the system ($ T $), plants can coexist with moderate light intensity ($ K $). A higher $ K $ tends to favor the plant with a lower phosphorus loss rate ($ d_1 $ vs $ d_2 $). When $ K $ is held constant, a moderate level of $ T $ leads to the dominance of the plant with a lower phosphorus loss rate ($ d_1 $ vs $ d_2 $). At high $ T $ levels, both plants can coexist. Moreover, our numerical analysis also shows that, when the competition for light is not equal, the low level of total phosphorus in the system may lead the model to be unstable and have more types of bistability compared with the two-dimensional Lotka-Volterra competition model.

Chemical-element-distribution-mediated deformation partitioning and its control mechanical behavior in high-entropy alloys

• Effect of chemical heterogeneities on plasticity and strength is studied using atomic simulations in high-entropy alloys. • Elemental anisotropy/difference factor is proposed, and then used to evaluate the short range order and predict the HEA properties. • Elemental anisotropy factor for optimal high performance is accurately estimated by machine learning. • By a machine learning approach coupled with MD simulations, elemental anisotropy ranges from 2.9 to 3. The chemical element distributions always strongly affect the deformation mechanisms and mechanical properties of alloying materials. However, the detailed atomic origin still remains unknown in high-entropy alloys (HEAs) with a stable random solid solution. Here, considering the effect of elemental fluctuation distribution, the deformation behavior and mechanical response of the widely-studied equimolar random CoCrFeMnNi HEA are investigated by atomic simulations combined with machine learning and micro-pillar compression experiments. The elemental anisotropy factor is proposed, and then used to evaluate the chemical element distribution. The experimental and simulation results show that the local variations of chemical compositions exist and play a critical role in the deformation partitioning and mechanical properties. The high strength and good plasticity of HEAs are obtained via tuning the chemical element distributions, and the optimal elemental anisotropy factor ranges from 2.9 to 3 using machine learning. This trend can be attributed to the cooperative mechanisms depending on the local variational composition: massive partial dislocation multiplication at an initial stage of plastic deformation, and the inhibition of localized shear banding via the nucleation of deformation twinning at a later stage. Using the new insights gained here, it would be possible to create new metallic alloys with superior properties through thermal-mechanical treatment to tailoring the chemical element distribution.

Effects of nanoscale chemical heterogeneity on the wear, corrosion, and tribocorrosion resistance of Zr-based thin film metallic glasses

The effects of nanoscale chemical heterogeneity on the wear, corrosion, and tribocorrosion resistance of ZrCuNiAl thin film metallic glasses were investigated by examining samples of similar global composition but with either homogenous or heterogeneous local composition. Unlike the homogenous sample, the heterogeneous sample exhibited local compositional fluctuations of Zr-rich (~52.8 at.%) and Zr-lean (~51.7 at.%) regions separated by ~413.0 ± 64.7 nm. Dry scratch wear study showed that the homogenous samples exhibited lower wear rates and friction coefficients than their heterogenous counterparts due to their higher hardness and lower stiffness, as measured from nanoindentation tests. Corrosion resistance of both samples was studied through potentiodynamic polarization and Mott-Schottky analysis in 0.6 M NaCl aqueous solution under room temperature. It was found that the heterogeneous samples exhibited higher pitting resistance than their homogenous counterparts by forming a protective passive layer with lower defect density. Finally, the effects of chemical heterogeneity on the tribocorrosion rate and repassivation kinetics of both samples were discussed based on their differences in mechanical and electrochemical properties measured.

Influence of chemical heterogeneity and microstructure on the corrosion resistance of biodegradable WE43 magnesium alloys.

Magnesium-yttrium-rare earth element alloys such as WE43 are potential candidates for future bioabsorbable orthopedic implant materials due to their biocompatibility, mechanical properties similar to human bone, and the ability to completely degrade in vivo. Unfortunately, the high corrosion rate of WE43 Mg alloys in physiological environments and subsequent loss of structural integrity limit the wide applications of these materials. In this study, the effect of chemical heterogeneity and microstructure on the corrosion resistance of two alloys with different metallurgical states was investigated: cast (as in traditional preparation) and as-deposited produced by magnetron sputtering. The corrosion behavior was studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests in blood bank buffered saline solution. It was found that the as-deposited alloy showed more than one order of magnitude reduction in corrosion current density compared to the cast alloy, owing to the elimination of micro-galvanic coupling between the Mg matrix and the precipitates. The microstructure and formation mechanism of corrosion products formed on both alloys were discussed based on immersion tests and direct measurements of X-ray photoelectron spectrometry (XPS) and cross-sectional transmission electron microscopy (TEM) analysis.

Dynamics of Water Monolayers Confined by Chemically Heterogeneous Surfaces: Observation of Surface-Induced Anisotropic Diffusion.

Water present in confining geometries plays key roles in many systems of scientific and technological relevance. Prominent examples are living cells and nanofluidic devices. Despite its importance, a complete understanding of the dynamics of water in nanoscale confinement remains elusive. In this work, we use molecular dynamics (MD) simulation to investigate the diffusive dynamics of water monolayers confined in chemically heterogeneous silica slit pores. The effect of chemical heterogeneity is systematically investigated through the fraction fSiOH of randomly distributed surface sites that possess hydroxyl functional groups. Partial hydroxylation results in heterogeneous surfaces comprising nanoscale hydrophobic and hydrophilic regions. We find that the in-plane diffusivity of water increases monotonically with fSiOH; at low surface hydroxylation (fSiOH ≤ 50%), slow water dynamics arise due to the formation of icelike structures in the hydrophobic regions, while at fSiOH ≥ 75%, surface-water H-bonds in the hydrophilic regions result in faster dynamics. We show that surface patterning with ordered hydrophobic and hydrophilic "stripes" can be used to induce one-dimensional diffusion, with water diffusing through the slit pore preferentially along the direction of the hydrophilic surface patterns.

Effect of chemical heterogeneity on photoluminescence of graphite oxide treated with S-/N-containing modifiers

Graphite oxide (GO) obtained using Hummers method was modified by hydrothermal treatment either with sulfanilic acid or polystyrene (3-ammonium) sulfonate at 100°C or 85°C, respectively. Both modifiers contain sulfur in the oxidized forms and nitrogen in the reduced forms. The materials were characterized using FTIR, XPS, thermal analysis, potentiometric titration and SEM. Their photoluminescent properties and their alteration with an addition of Ag+ were also measured. As a result of these modifications nitrogen was introduced to the graphene layers as amines, imides, amides, and sulfur as sulfones and sulfonic acids. Moreover, the presence of polyaniline was detected. This significantly affected the polarity, acid–base character, and conductivity of the materials. Apparently carboxylic groups of GO were involved in the surface reactions. The modified GOs lost their layered structure and the modifications resulted in the high degree of structural and chemical heterogeneity. Photoluminescence in visible light was recorded and linked to the presence of heteroatoms. For the polystyrene (3-ammonium) sulfonate modified sample addition of Ag+ quenched the photoluminescence at low wavelength showing sensitivity as a possible optical detector. No apparent effect was found for the sulfanilic acid modified sample.

Effect of Chemical Heterogeneity on Linear Adsorbed Solute Dispersion in fixed Bed

The paper aims at investigating the importance of including chemical heterogeneity in fixed bed as it has been found to induce additional dispersion. A discrete chemical heterogeneity distribution has been considered in the one-dimensional advective-dispersive equation. The partial differential equation was solved using finite volumes method based on the Adam-Bashforth algorithm. Increased dispersion was estimated comparing breakthrough curves second order moments keeping identical hydrodynamic properties as well as medium global capacity. In the objective to prove the presence of chemical heterogeneity effect, we study in the first the transport in homogeneous and chemically heterogeneous medium without hydrodynamic dispersion. Then effect of medium capacity on linear adsorbed solute dispersion into chemically heterogeneous at constant bed length and at the same chemical heterogeneity distribution was investigated. After that, different distributions were considered at different bed lengths too. Effect of chemical heterogeneity was found has nonregular behavior with the medium size but depending on the distribution type though a constant mean value of the distribution. As a result, dispersion increase due to chemical heterogeneity witch depends essentially on the column size and on the nature of heterogeneity distribution causing dependence of the breakpoint time on both.

Elemental Mercury Capture from Flue Gas by Magnetic Mn–Fe Spinel: Effect of Chemical Heterogeneity

A stoichiometric nanosized Mn–Fe spinel (Fe2.2Mn0.8O4) was synthesized using a coprecipitation method. After the thermal treatment at 400 °C under air, chemical heterogeneity deriving from the oxidation kinetic difference between Fe2+ and Mn2+/Mn3+ was observed in (Fe2.2Mn0.8)1-δO4. XPS and TEM analyses both pointed a Mn enrichment (especially Mn4+ cation) on the particle’s surface. Furthermore, the percent of cation vacancy on the surface increased obviously due to the enrichment of Mn4+ cation on the surface. As a result, the capacity of (Fe2.2Mn0.8)1-δO4-400 for elemental mercury capture was generally much better than those of MnOx/γ-Fe2O3, (Fe2.2Mn0.8)1-δO4-200 and Fe2.2Mn0.8O4. Furthermore, the saturation magnetization of (Fe2.2Mn0.8)1-δO4 obviously increased after the thermal treatment under air at 400 °C, which made it easier to separate the sorbent and adsorbed mercury from the fly ash for recycling, regeneration, and safe disposal of the adsorbed mercury. Therefore, (Fe2.2Mn0.8)1-δO4-400 may be a promising sorbent for elemental mercury capture.

Highly Ordered Selective Adsorption of Methyl Orange on Heterogeneous Surfaces in Aqueous Solutions

Abstract The effect of chemical heterogeneity on the adsorption of Methyl Orange (MO) in aqueous solutions was investigated by atomic force microscopy (AFM). On hydrophilic mica, a small number of disordered islands of Methyl Orange were formed. However, after deposition of self-assembled monolayers (SAMs) of octadecyltrichlorosilane (OTS) on mica, MO molecules adsorbed extensively and selectively on the hydrophobic OTS SAMs. Most importantly, the MO molecules on hydrophobic domains were highly ordered and almost perpendicular to the OTS surface.

Generalized isobaric–isothermal ensemble: application to capillary condensation and cavitation in heterogeneous nanopores

The influence of pore size and chemical heterogeneity on the adsorption/desorption hysteresis loop of a Lennard–Jones fluid confined within simple models of heterogeneous cylindrical nanopores is investigated. The thermodynamic pressure, or grand potential density, is calculated by a new method which was previously developed for mesopores (a few nanometers) to allow the introduction of chemical heterogeneity and further improved in this work for micropores (down to molecular diameters). The efficiency of the algorithm is first verified on simple cases. Secondly, we focus on the pore size effect. It is shown to have a weak influence on the capillary condensation phenomenon which always occurs around the same value of the thermodynamic pressure. On the other hand, the desorption pressure (corresponding to the liquid fracture or cavitation threshold) exhibits a linear dependence on the inverse pore radius. Finally, the effect of chemical heterogeneity, which is characterized by the relative amplitude (<40%) and wavelength (<4 nm), is investigated. It is shown to strongly influence the desorption branch of the hysteresis loop. As expected, liquid fracture is favoured by large amplitude heterogeneity. However, for a given amplitude, atomic-scale heterogeneity has a minor influence, whereas the longest wavelengths considered (4 nm) destabilize the confined liquid. It is proposed to correlate this with the typical size of the bubble critical nucleus.

The effect of chemical heterogeneity on the properties of statistical copolymers: the conductivity of poly(aniline‐co‐2‐bromoaniline)

AbstractChemical heterogeneity can influence the properties of statistical copolymers. It is shown that any integral property of a copolymer will depend on the chemical heterogeneity if such a property is a non‐linear function of copolymer composition. This is illustrated by means of the conductivity of copolymers of aniline and 2‐bromoaniline. The monomer reactivity ratios of this monomer pair are rA (aniline) = 0.94 and rB (2‐bromoaniline) = 0.31. The dependence of conductivity on the copolymer composition is non‐linear. Consequently, the conductivity depends on the compositional distribution, ie on the extent of chemical heterogeneity. Heterogeneous high‐conversion copolymers have lower conductivity than corresponding relatively homogeneous low‐conversion copolymers. The change in the average copolymer composition with increasing conversion is demonstrated for a copolymerization mixture containing 30 mol% aniline. The conductivity decreases at the same time as the chemical heterogeneity of the copolymer develops. The change in the average copolymer composition alone cannot explain the observed conductivity decrease. The conductivity is dependent not only on average composition but also on the chemical composition distribution. Copyright © 2004 Society of Chemical Industry

Trends in aquatic macrophyte species turnover in Northern Ireland — which factors determine the spatial distribution of local species turnover?

ABSTRACTAim The study examined qualitative predictions of ecological theories in relation to the spatial distribution of species turnover of aquatic macrophytes, through the following parameters: (1) distance between lakes (2) chemical conditions of the lakes (3) chemical differences between the lakes, and (4) the lake size.Location 562 lakes dispersed throughout Northern Ireland were analysed.Methods To obtain species turnover estimates independent of richness, the average distance between focal lakes and their five nearest neighbours in ordination space (DCA) was standardized by the species richness in a Generalized Additive Model (GAM). The relationships between species turnover and ecological (chemical condition, chemical difference, distance between lakes, and lake‐size) and geographical parameters (latitude, longitude, and altitude) were analysed using GAM.Results The results indicate that the pattern in species turnover is a combination of the chemical conditions and the distance between the lakes, including the interaction term. The effects of chemical heterogeneity and lake size parameters were both positive but weak. In general, increased distance and decreased ionic concentration contribute to increased turnover. The influence of distance on species turnover is strongest at low and high altitude, and at mid‐elevation the species turnover is mainly driven by the chemical conditions. Towards the north there is an increasing influence of distance, whereas in the south the chemical conditions have their strongest influence.Conclusions There is a need for components from several established ecological theories to explain the spatial trends in species turnover within Northern Ireland. Central theories in this particular study are the population/metapopulation dynamics, the continuum concept, and the species‐pool concept.

Laser alloying of zinc with aluminum: solidification behavior

Laser alloyed tracks were produced by blowing aluminum powder into melt pools generated in zinc substrates. Analysis of the microstructures revealed a structural and compositional stratification related with a deficient aluminum redistribution in the liquid. The effect of chemical heterogeneity on solidification mechanisms was modeled. The composition gradients and the solidification undercooling were shown to strongly influence the geometry of the solidification front. A reasonable agreement was obtained between experimental and predicted characteristic dimensions of the microstructures, in particular, the radii of the dendrite tips observed experimentally were comparable to the calculated ones.

Possible effects of chemical heterogeneity in higher land plant cuticles on the preservation of its ultrastructure upon fossilization

Morphologically well preserved fossilized cuticles of Symplocos hallensis of Eocene age from Geiseltal (Germany) and isolated cuticles from its “extant relative” Symplocos paniculata have been studied in order to determine the possible impact of diagenetic processes on the structure and chemical composition of higher plant cuticles. Both samples were studied by means of transmission electron microscopy, ultrahistochemical staining reactions, and extraction, and chemical degradation methods in combination with gas chromatography-mass spectrometry and Curie-point pyrolysis-gas chromatography/mass spectrometry. Diagenesis apparently induced several significant changes in the cuticle of S. hallensis. There were considerable differences in leaf anatomy and fine structure between the two species. A cuticle proper could not be detected in S. hallensis but ultrastructural observations permit the inference that it could have disintegrated as first part of the cuticular membrane during diagenesis. Furthermore, the fossil species S. hallensis contained, apart from the resistant biopolymer cutan, “cutin-derived” material with non-saponifiable intermolecular linkages instead of the saponifiable biopolyester cutin present in S. paniculata. The “cutin-derived” material could either have been biosynthesized by the plant itself or be the result of diagenetically induced reactions of reactive groups, such as epoxide, originally present in the cutin. It is speculated that the absence the cuticle proper in S. hallensis is related to its very specific chemical composition which is different from that of the cuticular layer.

A contribution to the study of the effects of chemical heterogeneity on the ultimate properties of copolymer blends

Blends of statistical copolymers of styrene and 2-methoxyethyl methacrylate differing in their chemical heterogeneity were subjected to slow stress-strain experiments. The chemical heterogeneity of blends was chosen so as to be comparable with the chemical heterogeneity of the common high-conversion random copolymers. No pronounced influence of chemical heterogeneity on the copolymer properties under investigation could be observed, if the variance of chemical composition wasD(w)<10−2.

Effects of Chemical Heterogeneity in Copolymers on Some Physical Properties

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffects of Chemical Heterogeneity in Copolymers on Some Physical PropertiesLawrence E. NielsenCite this: J. Am. Chem. Soc. 1953, 75, 6, 1435–1439Publication Date (Print):March 1, 1953Publication History Published online1 May 2002Published inissue 1 March 1953https://doi.org/10.1021/ja01102a047RIGHTS & PERMISSIONSArticle Views98Altmetric-Citations55LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (582 KB) Get e-Alerts Get e-Alerts