Thermodynamic Stability and Ultrasmall‐Size Effect of Nanodiamonds

Wang, Chengxin; Chen, Jian; Yang, Guowei; Xu, Ning

doi:10.1002/ange.200501495

Cited by 7 publications

(6 citation statements)

References 34 publications

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“…These results 20,21 have been confirmed by other groups. − X-ray diffraction and TEM studies 24,25 showed that NDPs ( d ∼ 5 nm) under thermal treatment at temperatures below 1973 K convert into spherical onion-like particles, having nearly the same size as the starting nanodiamond particles. At higher temperatures (∼2273 K), notably larger size hollow polyhedral particles are formed as the main product.…”

Section: Introductionsupporting

confidence: 54%

“…Unlike theoretical studies, the experimental work on interconversions of different nanoscale forms of carbon was carried out thus far mostly on diamond and onions. − It involved either thermal stability studies of different size fractions or stability of the nanoparticles under high-energy electron 28 or laser 30 irradiation and did not particularly focus on size-dependent phase stability of these carbon forms.…”

Section: Introductionmentioning

confidence: 99%

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Size-Dependent Phase Transition of Diamond to Graphite at High Pressures

et al. 2007

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Size-dependent phase transition of nanosize diamond particles (NDPs) to graphite was found in the course of studies of high pressure high temperature (HPHT) induced transformations of NDPs at 8 GPa and in the temperature range of 873−1623 K. Analysis of the products of HPHT treatment of powder NDPs (with the mean size of 4.5 nm) by X-ray diffraction (XRD), scanning (SEM) and transmission electron (TEM) microscopies, and Raman spectroscopy have shown that at 8 GPa the increase of the treatment temperature results in a gradual enlargement of NDPs. According to XRD data, the temperature increase from 873 to 1473 K at the treatment time of 60 s gives rise to NDP mean size enlargement from initial 4.5 to 8.8 nm. However, the largest NDPs can reach the sizes of 13.5−14.0 nm at 1473 K, as measured directly from TEM images. At 1623 K, size-dependent phase transition of diamond to graphite has been observed. By applying the Arrenius equation to the particle mean size versus treatment temperature plot, activation energy for the diamond solid phase growth at 8 GPa was calculated to be 112 ± 8 kJ/mol. The critical size of NDP corresponding to the point of phase transition at 8 GPa and 1623 K was estimated to be ∼18 nm. The likely effect of the size-dependent diamond-to-graphite phase transition on the process of diamond synthesis and, in particular, the problem of formation of critical seeds for crystal growth of macroscale diamond are discussed in the paper.

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Section: Introductionsupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Size-Dependent Phase Transition of Diamond to Graphite at High Pressures

et al. 2007

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“…A key aspect of this argument, independent of the specifics of the model, is that for a small-diameter wire a capillary pressure (or so-called Young-Laplace pressure) ΔP ≈ 2γ/r (where r is the radius) can be sufficiently high to allow the diamond phase to exist in the inner core while the outer shell with less equivalent pressure takes on the graphitic phase. Depending on the specific surface and interface energy parameters, within a thick nanotube-like shell of an interior radius around 10-25 nm, or for even smaller dimensions occurring at a defective spot of the nanotube wall, the equivalent pressure could reach the order of 1~5 GPa [17]. Similar phenomena were observed experimentally in diamond nucleation inside carbon onion high curvature enclosures [18].…”

Section: Status Of Effortsupporting

confidence: 66%

Diamond Nanowire for UV Detection

Xu¹,

Kim²,

Hsu³

et al. 2010

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“…These observations were rationalized by surface energy measurements to yield phase diagrams comprising enthalpy as a function surface area (particle size), which revealed cross overs in stability below about 200 nm [139,140]. The oxides ZrO 2 [141] and Al 2 O 3 [142] also exhibit similar particle size-dependent phase stability, as does carbon for which nanodiamonds are more stable than graphite [143]. Molecular simulations have played a key role in predicting phase stability switch-overs for these inorganic oxides and in rationalizing observed experimental data, for example, see surface energy calculations on Al 2 O 3 [144].…”

Section: Phase Stability and Transitions At The Nanoscalementioning

confidence: 99%

Polymorphic phase transitions: Macroscopic theory and molecular simulation

Anwar

Zahn

2017

Advanced Drug Delivery Reviews

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Transformations in the solid state are of considerable interest, both for fundamental reasons and because they underpin important technological applications. The interest spans a wide spectrum of disciplines and application domains. For pharmaceuticals, a common issue is unexpected polymorphic transformation of the drug or excipient during processing or on storage, which can result in product failure. A more ambitious goal is that of exploiting the advantages of metastable polymorphs (e.g. higher solubility and dissolution rate) while ensuring their stability with respect to solid state transformation. To address these issues and to advance technology, there is an urgent need for significant insights that can only come from a detailed molecular level understanding of the involved processes. Whilst experimental approaches at best yield time- and space-averaged structural information, molecular simulation offers unprecedented, time-resolved molecular-level resolution of the processes taking place. This review aims to provide a comprehensive and critical account of state-of-the-art methods for modelling polymorph stability and transitions between solid phases. This is flanked by revisiting the associated macroscopic theoretical framework for phase transitions, including their classification, proposed molecular mechanisms, and kinetics. The simulation methods are presented in tutorial form, focusing on their application to phase transition phenomena. We describe molecular simulation studies for crystal structure prediction and polymorph screening, phase coexistence and phase diagrams, simulations of crystal-crystal transitions of various types (displacive/martensitic, reconstructive and diffusive), effects of defects, and phase stability and transitions at the nanoscale. Our selection of literature is intended to illustrate significant insights, concepts and understanding, as well as the current scope of using molecular simulations for understanding polymorphic transitions in an accessible way, rather than claiming completeness. With exciting prospects in both simulation methods development and enhancements in computer hardware, we are on the verge of accessing an unprecedented capability for designing and developing dosage forms and drug delivery systems in silico, including tackling challenges in polymorph control on a rational basis.

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Thermodynamic Stability and Ultrasmall‐Size Effect of Nanodiamonds

Cited by 7 publications

References 34 publications

Size-Dependent Phase Transition of Diamond to Graphite at High Pressures

Size-Dependent Phase Transition of Diamond to Graphite at High Pressures

Diamond Nanowire for UV Detection

Polymorphic phase transitions: Macroscopic theory and molecular simulation

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