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Title: SYNTHETIC STRATEGIES FOR ANISOTROPIC AND SHAPE-SELECTIVE NANOMATERIALS

Authors:
Publication Date:
Research Org.:
SRS
Sponsoring Org.:
USDOE
OSTI Identifier:
1424598
Report Number(s):
SRNL-STI-2017-00109
DOE Contract Number:
DE-AC09-08SR22470
Resource Type:
Book
Country of Publication:
United States
Language:
English

Citation Formats

Murph, S. SYNTHETIC STRATEGIES FOR ANISOTROPIC AND SHAPE-SELECTIVE NANOMATERIALS. United States: N. p., 2017. Web.
Murph, S. SYNTHETIC STRATEGIES FOR ANISOTROPIC AND SHAPE-SELECTIVE NANOMATERIALS. United States.
Murph, S. Wed . "SYNTHETIC STRATEGIES FOR ANISOTROPIC AND SHAPE-SELECTIVE NANOMATERIALS". United States. doi:. https://www.osti.gov/servlets/purl/1424598.
@article{osti_1424598,
title = {SYNTHETIC STRATEGIES FOR ANISOTROPIC AND SHAPE-SELECTIVE NANOMATERIALS},
author = {Murph, S.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Feb 22 00:00:00 EST 2017},
month = {Wed Feb 22 00:00:00 EST 2017}
}

Book:
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  • Boron nitride (BN) is a synthetic binary compound located between III and V group elements in the Periodic Table. However, its properties, in terms of polymorphism and mechanical characteristics, are rather close to those of carbon compared with other III-V compounds, such as gallium nitride. BN crystallizes into a layered or a tetrahedrally linked structure, like those of graphite and diamond, respectively, depending on the conditions of its preparation, especially the pressure applied. Such correspondence between BN and carbon readily can be understood from their isoelectronic structures [1, 2]. On the other hand, in contrast to graphite, layered BN ismore » transparent and is an insulator. This material has attracted great interest because, similar to carbon, it exists in various polymorphic forms exhibiting very different properties; however, these forms do not correspond strictly to those of carbon. Crystallographically, BN is classified into four polymorphic forms: Hexagonal BN (h-BN) (Figure 1(b)); rhombohedral BN (r-BN); cubic BN (c-BN); and wurtzite BN (w-BN). BN does not occur in nature. In 1842, Balmain [3] obtained BN as a reaction product between molten boric oxide and potassium cyanide under atmospheric pressure. Thereafter, many methods for its synthesis were reported. h-BN and r-BN are formed under ambient pressure. c-BN is synthesized from h-BN under high pressure at high temperature while w-BN is prepared from h-BN under high pressure at room temperature [1]. Each BN layer consists of stacks of hexagonal plate-like units of boron and nitrogen atoms linked by SP{sup 2} hybridized orbits and held together mainly by Van der Waals force (Fig 1(b)). The hexagonal polymorph has two-layered repeating units: AA'AA'... that differ from those in graphite: ABAB... (Figure 1(a)). Within the layers of h-BN there is coincidence between the same phases of the hexagons, although the boron atoms and nitrogen atoms are alternatively located along the c-axis. The rhombohedral system consists of three-layered units: ABCABC..., whose honeycomb layers are arranged in a shifted phase, like as those of graphite. Reflecting its weak interlayer bond, the h-BN can be cleaved easily along its layers, and hence, is widely used as a lubricant material. The material is stable up to a high temperature of 2300 C before decomposition sets in [2] does not fuse a nitrogen atmosphere of 1 atm, and thus, is applicable as a refractory material. Besides having such properties, similar to those of graphite, the material is transparent, and acts as a good electric insulator, especially at high temperatures (10{sup 6} {Omega}m at 1000 C) [1]. c-BN and w-BN are tetrahedrally linked BN. The former has a cubic sphalerite-type structure, and the latter has a hexagonal wurtzite-type structure. c-BN is the second hardest known material (the hardest is diamond), the so-called white diamond. It is used mainly for grinding and cutting industrial ferrous materials because it does not react with molten iron, nickel, and related alloys at high temperatures whereas diamond does [1]. It displays the second highest thermal conductivity (6-9 W/cm.deg) after diamond. This chapter focuses principally upon information about h-BN nanomaterials, mainly BN nanotubes (BNNTs), porous BN, mono- and few-layer-BN sheets. There are good reviews book chapters about c-BN in [1, 4-6].« less
  • The direct synthesis of nanostructures using wet chemical reduction methods has had a major impact on catalysis and materials design. However, no mechanism has yet been reported that explicitly provides growth parameters for shapes and sizes as a function of desired metals, making it difficult to directly synthesize shaped particles from specific metals. There have been reports in the literature using this method to obtain core-shell, porous cage-like and irregular structures, however only one report proposing a mechanism of the displacement process exists, which does not explain surface and bulk morphology changes as a function of reaction condition. Here, wemore » demonstrate the use of small angle x-ray scattering (SAXS), and microscopy to study the Ag-to-Pt displacement process of nanoparticles, nanowires and nanoplates at known intervals throughout the reaction. Obtaining a fundamental understanding of the displacement process will allow us to tune composition, morphology, and thus electronic properties of novel materials.« less
  • Among the broad portfolio of preparations for nanoscale materials, spontaneous galvanic displacement (SGD) is emerging as an important technology because it is capable of creating functional nanomaterials that cannot be obtained through other routes and may be used to thrift precious metals used in a broad range of applications including catalysis. With advances resulting from increased understanding of the SGD process, materials that significantly improve efficiency and potentially enable widespread adoption of next generation technologies can be synthesized. In this work, PtAg nanotubes synthesized via displacement of Ag nanowires by Pt were used as a model system to elucidate themore » fundamental mechanisms of SGD. Furthermore, characterization by X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), and atom probe tomography (APT) indicates nanotubes are formed as Ag is oxidized first from the surface and then from the center of the nanowire, with Pt deposition forming a rough, heterogeneous surface on the PtAg nanotube.« less