Metal Nanopowders

Production, Characterization, and Energetic Applications

Alexander A. Gromov, Ulrich Teipel

• Publisher: Wiley-VCH
• Year: 2014
• Print ISBN: 9783527333615
• eBook ISBN: 9783527680719
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Industrial & Technical Chemistry

Written with both postgraduate students and researchers in academia and industry in mind, this reference covers the chemistry behind metal nanopowders, including production, characterization, oxidation and combustion. The contributions from renowned international scientists working in the field detail applications in technologies, scale-up processes and safety aspects surrounding their handling and storage.

1

Estimation of Thermodynamic Data of Metallic Nanoparticles Based on Bulk Values

Dieter Vollath and Franz Dieter Fischer

1.1 Introduction

It is a well-accepted fact: the temperature of phase transformation is particle-size dependent. In general, this dependency is described as

1.1

In Equation 1.1, the quantities

and

stand for the transformation temperature of nanoparticles and the bulk material, respectively, d for the particle diameter, and α is a constant value depending on the entropy of transformation and the difference of the surface energy in both phases [1]. The same description, as proved for phase transformations, was found to be valid for the enthalpy of phase transformations. As typical examples, experimental results obtained for aluminum particles were given by Eckert [2], for tin particles by Lai et al. [3], or by Suresh and Mayo [4, 5] on yttrium-doped zirconia particles.

The range of particle sizes where Equation 1.1 is valid is limited. In the case of larger particles, Coombes [6] has shown that these have a surface layer of about 3 nm, where melting starts. As long as this surface layer dominates the behavior of the particles, Equation 1.1 cannot be applied. The existence of such a surface layer was also shown by Chang and Johnson [7] by theoretical considerations, concluding that this surface layer is less ordered than the center of the particles. As it was shown by Kaptay [8], the thickness of this premelting layer can be estimated by the rules of classical thermodynamics. Therefore, the assumption of a surface layer where melting starts is well justified. Now, one may ask if there is also a lower limit of particle sizes, below which Equation 1.1 is not applicable. Experimental results suggest this. Figure 1.1 displays the melting temperature of gold nanoparticles according to Castro et al. [9]. In this graph, the melting temperature is plotted versus the inverse particle size. According to Equation 1.1, one has to expect a linear relation.

Figure 1.1 Experimental data for the melting temperature of gold nanoparticles, according to Castro et al. [9], together with linear fits plotted versus the inverse particle size. This graph shows clearly two separated ranges of the melting temperature: at larger particles, a range following Equation 1.1 (Range I) and a second range with particle-size-independent temperature (Range II).

The experimental data of Castro et al. may be separated into two ranges: Range I, which follows Equation 1.1 and a separated Range II, which is far off from the expected value. A linear fit of the experimental data in both ranges delivers an intersection at an inverse particle size of 0.62 nm⁻¹, which is equivalent to a particle size of 1.6 nm. Obviously, for particle sizes below this intersection, Equation 1.1 is no longer valid. Such a phenomenon or similar ones are quit...

Table of contents

• Cover
• Related Titles
• Title Page
• Copyright
• Foreword
• List of Contributors
• Introduction
• Chapter 1: Estimation of Thermodynamic Data of Metallic Nanoparticles Based on Bulk Values
• Chapter 2: Numerical Simulation of Individual Metallic Nanoparticles
• Chapter 3: Electroexplosive Nanometals
• Chapter 4: Metal Nanopowders Production
• Chapter 5: Characterization of Metallic Nanoparticle Agglomerates
• Chapter 6: Passivation of Metal Nanopowders
• Chapter 7: Safety Aspects of Metal Nanopowders
• Chapter 8: Reaction of Aluminum Powders with Liquid Water and Steam
• Chapter 9: Nanosized Cobalt Catalysts for Hydrogen Storage Systems Based on Ammonia Borane and Sodium Borohydride
• Chapter 10: Reactive and Metastable Nanomaterials Prepared by Mechanical Milling
• Chapter 11: Characterizing Metal Particle Combustion In Situ: Non-equilibrium Diagnostics
• Chapter 12: Characterization and Combustion of Aluminum Nanopowders in Energetic Systems
• Index
• End User License Agreement