The Experts below are selected from a list of 7374 Experts worldwide ranked by ideXlab platform
Kenneth J. Klabunde - One of the best experts on this subject based on the ideXlab platform.
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Near infrared reflectance properties of Metal oxide nanoparticles
The Journal of Physical Chemistry C, 2007Co-Authors: P. Jeevanandam, R. S. Mulukutla, M. Phillips, S. Chaudhuri, And L. E. Erickson, Kenneth J. KlabundeAbstract:Powders of Nanocrystalline Metal oxides were compared with common macrocrystalline powders and minerals for their ability to reflect near-infrared light (NIR) (750−2500 nm). The Nanocrystalline Metal oxides were found to possess higher NIR reflectance values (∼15−20%) and this can be attributed to their smaller crystallite sizes coupled with smaller mean aggregate sizes in accordance with the Kubelka−Munk theory.
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adsorption of thiophenes out of hydrocarbons using Metal impregnated Nanocrystalline aluminum oxide
Microporous and Mesoporous Materials, 2005Co-Authors: P. Jeevanandam, Kenneth J. Klabunde, S H TetzlerAbstract:Abstract Adsorption of thiophene and its derivatives was carried out using silver impregnated Nanocrystalline Metal oxides, with special emphasis on aluminum oxide. A modified Nanocrystalline aluminum oxide was prepared by an impregnation method and characterized. The adsorption experiments were carried out for thiophene, benzothiophene, dibenzothiophene and 4,6-dimethyl dibenzothiophene. Incorporation of soft Lewis acid sites such as silver ion is necessary for the adsorption of thiophene related molecules. The modified adsorbent was found to retain its adsorption characteristics even after compaction and it can be used for adsorption again after regeneration by heating at modest temperatures. The adsorption properties of the silver impregnated aluminum oxide (prepared by aerogel procedure) (Ag-AP-Al 2 O 3 ) were compared with several other high surface area materials (>200 m 2 /g). Detailed characterization studies showed that the active site in Ag-AP-Al 2 O 3 is the Ag + ion coordinated to carbonate. Metallic silver nanoparticles do not appear to be effective in thiophene adsorption.
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Nanocrystalline Metal oxides as destructive adsorbents for organophosphorus compounds at ambient temperatures
Chemistry: A European Journal, 2002Co-Authors: Shyamala Rajagopalan, Shawn Decker, Olga Koper, Kenneth J. KlabundeAbstract:Nanocrystals of magnesium oxide react with organophosphorus compounds at room temperature by dissociative chemisorption, which we term "destructive adsorption". This process involves cleavage of P-O and P-F bonds (but not P-C bonds) and immobilization of the resultant molecular fragments. These ultrafine powders have unusual crystalline shapes and possess high surface concentrations of reactive edge/corner and defect sites, and thereby display higher surface reactivity, normalized for surface area, than typical polycrystalline material. This high surface reactivity coupled with high surface area allows their use for effective decontamination of chemical warfare agents and related toxic substances. Herein data is presented for paraoxon, diisopropylfluorophosphate (DFP), and (CH3CH2O)2P(O)CH2-SC6H5 (DEPTMP). Solid-state NMR and IR spectroscopy indicate that all OR and F groups dissociate; this leaves bound -PO4, -F, and -OR groups for paraoxon, DFP, and DEPTMP, respectively. For paraoxon, it was shown that one monolayer reacts. For DEPTMP, the OR groups dissociate, but not the P-CH2SC6H5 group. The Nanocrystalline MgO reacts much faster and in higher capacity than typical activated carbon samples, which physisorb but do not destructively adsorb these phosphorous compounds.
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Nanocrystalline Metal oxides as unique chemical reagents sorbents
ChemInform, 2002Co-Authors: Erik Lucas, Corrie L. Carnes, Shawn Decker, Abbas Khaleel, Adam Seitz, Shawn Fultz, Aldo Ponce, Kenneth J. KlabundeAbstract:A new family of porous inorganic solids based on Nanocrystalline Metal oxides is discussed. These materials, made up of 4–7 nm MgO, CaO, Al2O3, ZnO, and others, exhibit unparalleled destructive adsorption properties for acid gases, polar organics, and even chemical/biological warfare agents. These unique sorption properties are due to nanocrystal shape, polar surfaces, and high surface areas. Free-flowing powders or consolidated pellets are effective, and pore structure can be controlled by consolidation pressures. Chemical properties can be adjusted by choice of Metal oxide as well as by incorporating other oxides as monolayer films.
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Unique Chemical Reactivities of Nanocrystalline Metal Oxides toward Hydrogen Sulfide
Chemistry of Materials, 2002Co-Authors: Corrie L. Carnes, Kenneth J. KlabundeAbstract:Nanocrystalline Metal oxides prepared through sol−gel or aerogel syntheses were allowed to react with hydrogen sulfide and compared with microcrystalline commercially available Metal oxides. The Nanocrystalline Metal oxides were found to be considerably more reactive than the commercial samples, as a result of their higher surface areas as well as higher intrinsic reactivities. In some cases, nearly stoichiometric solid−gas reactions took place at selected elevated temperatures, and the oxides exhibited a general reactivity trend of CaO > ZnO > Al2O3 > MgO. At lower temperatures (25−100 °C), the trend was ZnO > CaO > Al2O3 ≈ MgO. Core/shell particles, where a thin layer of Fe2O3 was deposited on Nanocrystalline CaO, yielded the best results, thus demonstrating another example of transition Metal oxide catalysis in solid−gas reactions.
Christopher A Schuh - One of the best experts on this subject based on the ideXlab platform.
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tension compression strength asymmetry in a simulated Nanocrystalline Metal
Physical Review B, 2004Co-Authors: Alan C Lund, T G Nieh, Christopher A SchuhAbstract:We explore asymmetries in the plastic deformation of idealized Nanocrystalline nickel through static molecular simulations. We find that both the yield and flow stresses of these materials are higher in compression than in tension. This result is discussed in the context of earlier work on Metallic glasses, and it is suggested that very similar atomic-level mechanisms control yield in both of these materials classes.
Avinash M. Dongare - One of the best experts on this subject based on the ideXlab platform.
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Strengthening Behavior and Tension–Compression Strength–Asymmetry in Nanocrystalline Metal–Ceramic Composites
Journal of Engineering Materials and Technology, 2012Co-Authors: Avinash M. Dongare, Bruce Lamattina, A. M. RajendranAbstract:Metal–ceramic composites are an emerging class of materials for use in the next-generation high technology applications due to their ability to sustain plastic deformation and resist failure in extreme mechanical environments. Large scale molecular dynamics simulations are used to investigate the performance of Nanocrystalline Metal–matrix composites (MMCs) formed by the reinforcement of the Nanocrystalline Al matrix with a random distribution of nanoscale ceramic particles. The interatomic interactions are defined by the newly developed angular-dependent embedded atom method (A-EAM) by combining the embedded atom method (EAM) potential for Al with the Stillinger–Weber (SW) potential for Si in one functional form. The molecular dynamics (MD) simulations are aimed to investigate the strengthening behavior and the tension–compression strength asymmetry of these composites as a function of volume fraction of the reinforcing Si phase. MD simulations suggest that the strength of the nanocomposite increases linearly with an increase in the volume fraction of Si in the Al-rich region, whereas the increase is very sharp in the Si-rich region. The higher strength of the nanocomposite is attributed to the reduced sliding/rotation between the Al/Si and the Si/Si grains as compared to the pure Nanocrystalline Metal.
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tension compression asymmetry in Nanocrystalline cu high strain rate vs quasi static deformation
Computational Materials Science, 2010Co-Authors: Avinash M. Dongare, Bruce Lamattina, A. M. Rajendran, M A Zikry, D W BrennerAbstract:Abstract Large-scale molecular dynamics (MD) simulations are used to understand the yield behavior of Nanocrystalline Ni and Cu with grain sizes ⩽10 nm at high strain rates. The calculated flow stress values at a strain rate of 109 s−1 suggest an asymmetry in the strength values in tension and compression with the Nanocrystalline Metal being stronger in compression than in tension. This tension–compression strength asymmetry is observed to decrease with a decrease in grain size of the Nanocrystalline Metal up to a grain size of 4 nm, after which, a further decrease in grain size results in an increase in the strength asymmetry. The effect of strain rate on the yield behavior of Nanocrystalline Metals as obtained from MD simulations is discussed and compared with that reported in the literature obtained by molecular statics simulations for quasi-static loading conditions.
M. Taher A. Saif - One of the best experts on this subject based on the ideXlab platform.
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Effect of microstructural heterogeneity on the mechanical behavior of Nanocrystalline Metal films
Journal of Materials Research, 2011Co-Authors: Jagannathan Rajagopalan, M. Taher A. SaifAbstract:Conventionally, mean grain size is considered the most critical microstructural parameter in determining the mechanical behavior of pure Metals. By systematically controlling the distribution of grain orientations in aluminum films, we show that microstructural heterogeneity alone induces large variation in the mechanical behavior of Nanocrystalline Metal films. Aluminum films with relatively homogeneous microstructure (all grains with identical out-of-plane orientation) show substantially less early Bauschinger effect compared to films with heterogeneous microstructure, irrespective of film thickness or grain size. On the other hand, the films with homogeneous microstructure show relatively higher yield stresses. A direct correspondence is found between the nonuniformity of plastic deformation and early Bauschinger effect, which confirms the critical role of microstructural heterogeneity.
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In situ TEM study of microplasticity and Bauschinger effect in Nanocrystalline Metals
Acta Materialia, 2010Co-Authors: Jagannathan Rajagopalan, Christian Rentenberger, H. Peter Karnthaler, Gerhard Dehm, M. Taher A. SaifAbstract:In situ transmission electron microscopy straining experiments with concurrent macroscopic stress–strain measurements were performed to study the effect of microstructural heterogeneity on the deformation behavior of Nanocrystalline Metal films. In microstructurally heterogeneous gold films (mean grain size dm = 70 nm) comprising randomly oriented grains, dislocation activity is confined to relatively larger grains, with smaller grains deforming elastically, even at applied strains approaching 1.2%. This extended microplasticity leads to build-up of internal stresses, inducing a large Bauschinger effect during unloading. Microstructurally heterogeneous aluminum films (dm = 140 nm) also show similar behavior. In contrast, microstructurally homogeneous aluminum films comprising mainly two grain families, both favorably oriented for dislocation glide, show limited microplastic deformation and minimal Bauschinger effect despite having a comparable mean grain size (dm = 120 nm). A simple model is proposed to describe these observations. Overall, our results emphasize the need to consider both microstructural size and heterogeneity in modeling the mechanical behavior of Nanocrystalline Metals.
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On plastic strain recovery in freestanding Nanocrystalline Metal thin films
Scripta Materialia, 2008Co-Authors: Jagannathan Rajagopalan, Jong H. Han, M. Taher A. SaifAbstract:Abstract In a recent article [J. Rajagopalan, J.H. Han, M.T.A. Saif, Science 315 (2007) 1831–1834], we have reported substantial (50–100%) plastic strain recovery in freestanding Nanocrystalline Metal films (grain size 50–65 nm) after unloading. The strain recovery was time dependent and thermally activated. Here we model the time evolution of this strain recovery in terms of a thermally activated dislocation propagation mechanism. The model predicts an activation volume of ≈42b3 for the strain recovery process in aluminum.
D W Brenner - One of the best experts on this subject based on the ideXlab platform.
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tension compression asymmetry in Nanocrystalline cu high strain rate vs quasi static deformation
Computational Materials Science, 2010Co-Authors: Avinash M. Dongare, Bruce Lamattina, A. M. Rajendran, M A Zikry, D W BrennerAbstract:Abstract Large-scale molecular dynamics (MD) simulations are used to understand the yield behavior of Nanocrystalline Ni and Cu with grain sizes ⩽10 nm at high strain rates. The calculated flow stress values at a strain rate of 109 s−1 suggest an asymmetry in the strength values in tension and compression with the Nanocrystalline Metal being stronger in compression than in tension. This tension–compression strength asymmetry is observed to decrease with a decrease in grain size of the Nanocrystalline Metal up to a grain size of 4 nm, after which, a further decrease in grain size results in an increase in the strength asymmetry. The effect of strain rate on the yield behavior of Nanocrystalline Metals as obtained from MD simulations is discussed and compared with that reported in the literature obtained by molecular statics simulations for quasi-static loading conditions.
