Surface and bulk melting of small metal clusters

Chang, J.; Johnson, Erik

doi:10.1080/14786430500228663

Cited by 44 publications

(40 citation statements)

References 34 publications

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“…More realistic assumptions are either the formation of a liquid or liquid-like layer at temperatures significantly below the melting temperature or a continuous process of melting starting at the surface. Thermodynamic calculations support these models [34–35]. Sakai [34] concludes that the phenomenon of a liquid-like surface layer is, at least for the example of lead, restricted to particles larger than a critical size in the range of 4 nm; otherwise, the particles melt all at once.…”

Section: Reviewmentioning

confidence: 97%

Surface energy of nanoparticles – influence of particle size and structure

Vollath¹,

Fischer²,

Holec³

2018

Beilstein J. Nanotechnol.

160

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The surface energy, particularly for nanoparticles, is one of the most important quantities in understanding the thermodynamics of particles. Therefore, it is astonishing that there is still great uncertainty about its value. The uncertainty increases if one questions its dependence on particle size. Different approaches, such as classical thermodynamics calculations, molecular dynamics simulations, and ab initio calculations, exist to predict this quantity. Generally, considerations based on classical thermodynamics lead to the prediction of decreasing values of the surface energy with decreasing particle size. This phenomenon is caused by the reduced number of next neighbors of surface atoms with decreasing particle size, a phenomenon that is partly compensated by the reduction of the binding energy between the atoms with decreasing particle size. Furthermore, this compensating effect may be expected by the formation of a disordered or quasi-liquid layer at the surface. The atomistic approach, based either on molecular dynamics simulations or ab initio calculations, generally leads to values with an opposite tendency. However, it is shown that this result is based on an insufficient definition of the particle size. A more realistic definition of the particle size is possible only by a detailed analysis of the electronic structure obtained from initio calculations. Except for minor variations caused by changes in the structure, only a minor dependence of the surface energy on the particle size is found. The main conclusion of this work is that surface energy values for the equivalent bulk materials should be used if detailed data for nanoparticles are not available.

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Section: Reviewmentioning

confidence: 97%

Surface energy of nanoparticles – influence of particle size and structure

Vollath¹,

Fischer²,

Holec³

2018

Beilstein J. Nanotechnol.

160

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“…29͒ and ZrO 2 . 30 Additionally, Chang and Johnson 31 show that for very small particles a perfect structure is thermodynamically impossible. Their study shows an increasing disorder from the center to the surface of particles.…”

Section: Discussionmentioning

confidence: 99%

Structure and grain growth of TiO2 nanoparticles investigated by electron and x-ray diffractions and Ta181 perturbed angular correlations

Schlabach

Szabó

Vollath

et al. 2006

Journal of Applied Physics

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Bare and coated TiO 2 nanoparticles with particle sizes d Ͻ 5 nm have been synthesized in a microwave plasma process. Structural properties of these materials have been investigated by transmission electron microscopy, x-ray diffraction, and perturbed angular correlation ͑PAC͒ measurements of the electric quadrupole interaction ͑QI͒ at the probe nucleus 181 Ta on the metal site of TiO 2 at temperatures 290ഛ T ഛ 1450 K. The electron diffraction of the uncoated nanoparticles in the as-synthesized state reflects long range order in the Ti sublattice. Depending on the particles size, either the anatase or the rutile phase of TiO 2 was found. Anatase appears to be the stable form of nanocrystalline TiO 2 below d ϳ 10 nm. The PAC spectra of these nanocrystalline oxides are characterized by a broad distribution of strong quadrupole interactions, indicating a strongly disordered oxygen environment of the metal sites. Upon annealing, the grain size grows from d Ͻ 5 nm after synthesis to d Ͼ 100 nm after 1300 K. PAC spectra taken in the same temperature range show that with increasing temperature, the initially disordered state transforms to well-ordered rutile TiO 2 . The data suggest a critical grain size of d ϳ 10 nm for the onset of the ordering process. The spectra of coarse-grained TiO 2 are reached at a particle size d ജ 30 nm. In n-TiO 2 coated with Al 2 O 3 and ZrO 2 both the cores and the coatings were found to grow with increasing temperature; the cores of the coated particles, however, grow much less than those of the noncoated particles. The PAC method was used to investigate the QI in both TiO 2 cores and in the ZrO 2 coating of n-TiO 2 / ZrO 2 at different temperatures. These data suggest that although the coated particles grow with temperature, the ordering process is obstructed, possibly by a solid state reaction between the TiO 2 kernels and the coatings.

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“…The lower density of nanoparticles than in conventional material is in agreement with the literature, which indicated that in the case of nanoparticles, there is a reduction in the material density caused by high contribution of surface layers, which are less densely packed than the bulk. 33 The XRD analysis was conducted on GoHAP, commercial HAp (NanoXIM), and a plate from a pig's shank bone (Figure 2). The XRD results confirmed that the material is a pure well crystalline hexagonal HAp with nano-sized particles.…”

Section: Nanoparticles Characterizationmentioning

confidence: 99%

Highly biocompatible, nanocrystalline hydroxyapatite synthesized in a solvothermal process driven by high energy density microwave radiation

Smolen

Chudoba²,

Malka³

et al. 2013

IJN

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Abstract:A microwave, solvothermal synthesis of highly biocompatible hydroxyapatite (HAp) nanopowder was developed. The process was conducted in a microwave radiation field having a high energy density of 5 W/mL and over a time less than 2 minutes. The sample measurements included: powder X-ray diffraction, density, specific surface area, and chemical composition. The morphology and structure were investigated by scanning electron microscopy as well as transmission electron microscopy (TEM). The thermal behavior analysis was conducted using a simultaneous thermal analysis technique coupled with quadruple mass spectrometry. Additionally, Fourier transform infrared spectroscopy tests of heated samples were performed. A degradation test and a biocompatibility study in vitro using human osteoblast cells were also conducted. The developed method enables the synthesis of pure, fully crystalline hexagonal HAp nanopowder with a specific surface area close to 240 m 2 /g and a Ca/P molar ratio equal to 1.57. TEM measurements showed that this method results in particles with an average grain size below 6 nm. A 28-day degradation test conducted according to the ISO standard indicated a 22% loss of initial weight and a calcium ion concentration at 200 µmol/dm 3 in the tris(hydroxymethyl)aminomethane hydrochloride test solution. The cytocompatibility of the obtained material was confirmed in a culture of human bone derived cells, both in an indirect test using the material extract, and in direct contact. A quantitative analysis was based on the 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide. Viability assay as well as on DNA content measurements in the PicoGreen test.Indirect observations were performed at one point in time according to the ISO standard for in vitro cytotoxicity (ie, after 24 hours of cell exposure to the extracts). The direct contact tests were completed at three time points: after 24 hours, on day 7, and on day 14 of a culture in an osteogenic medium. All of the tests revealed good tolerance of cells toward the material; this was also shown by means of live/dead fluorescent staining. Both quantitative results and morphological observations revealed much better cell tolerance toward the obtained HAp compared to commercially available HAp NanoXIM, which was used as a reference material.

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Surface and bulk melting of small metal clusters

Cited by 44 publications

References 34 publications

Surface energy of nanoparticles – influence of particle size and structure

Surface energy of nanoparticles – influence of particle size and structure

Structure and grain growth of TiO2 nanoparticles investigated by electron and x-ray diffractions and Ta181 perturbed angular correlations

Highly biocompatible, nanocrystalline hydroxyapatite synthesized in a solvothermal process driven by high energy density microwave radiation

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