8 research outputs found
Advances in scalable gas-phase manufacturing and processing of nanostructured solids: A review
Although the gas-phase production of nanostructured solids has already been carried out in industry for decades, only in recent years has research interest in this topic begun to increase. Nevertheless, despite the remarkable scientific progress made recently, many long-established processes are still used in industry. Scientific advancements can potentially lead to the improvement of existing industrial processes, but also to the development of completely new routes. This paper aims to review state-of-the-art synthesis and processing technologies, as well as the recent developments in academic research. Flame reactors that produce inorganic nanoparticles on industrial- and lab-scales are described, alongside a detailed overview of the different systems used for the production of carbon nanotubes and graphene. We discuss the problems of agglomeration and mixing of nanoparticles, which are strongly related to synthesis and processing. Finally, we focus on two promising processing techniques, namely nanoparticle fluidization and atomic layer deposition
Improved thermal energy storage of nanoencapsulated phase change materials by atomic layer deposition
Renewable energy has become of great interest over the past years in order to mitigate
Global Warming. One of the actions gaining attention is the enhancement of the thermal
energy storage capacity of Concentrated Solar Power plants. The addition of
nanoencapsulated phase change materials (core-shell nanoparticles) to the already used
materials has been proposed for that purpose, due to the possibility of increasing
thermal storage through the contribution of both core latent heat and sensible heat. In
this work, Atomic Layer Deposition has been used to synthesise SiO2 and Al2O3
nanoscale coatings on tin nanoparticles. The multi-encapsulated phase change materials
have been characterised in terms of chemical composition, crystalline structure, particle
size, thermal stability and thermal storage capacity. Sn@Al2O3 nanoparticles present the
best thermal behaviour as they show the lowest reduction in the phase change enthalpy
over 100 cycles due to the oxidation barrier of the coating. Moreover, the specific heat
of both nanoparticles and solar salt-based nanofluids is increased, making the
nanoencapsulated phase change material suitable for thermal energy storage
applications
Controlled Growth of Palladium Nanoparticles on Graphene Nanoplatelets via Scalable Atmospheric Pressure Atomic Layer Deposition
We
demonstrate the deposition of crystalline palladium nanoparticles
on graphene nanoplatelets (Pd/graphene) via atmospheric pressure atomic
layer deposition (ALD) carried out in a fluidized bed reactor. The
nucleation and growth of Pd nanoparticles on the inert graphene surface
was enabled by applying an ozone pretreatment step, without significantly
affecting the graphene crystalline structure. Uniform nucleation on
both basal planes and edges of the graphene was obtained. The Pd loading
and dispersion as well as the average particle size could be controlled
by varying the number of ALD cycles. By analyzing the evolution of
the particle size distribution and spatial density, we obtained insights
into the nucleation and growth of Pd ALD on graphene. Furthermore,
by shortening the pretreatment time, selective growth of Pd nanoparticles
on the edges of the graphene was achieved. The Pd/graphene fabricated
with our method showed a significantly lower level of impurities compared
to the Pd/graphene synthesized by wet chemistry routes. Our approach
provides a 100% solvent-free, controllable and scalable process for
producing the bulk quantities of Pd/graphene required for practical
applications in, for example, catalysis
Numerical analysis of mechanical reliability of multi-coated phase change materials
Nanoencapsulated phase change materials (nePCMs) are nowadays under research for thermal energy storage purposes. NePCMs are composed of a phase change core surrounded by a shell that confines the core when molten. One of the main concerns of nePCMs when subjected to thermal processes is the mechanical failure of the passivation shell initially present in commercial metallic nanoparticles. In order to overcome this issue, multi-coated nePCMs, based on the synthesis of an additional coating by atomic layer deposition, appear to be as a candidate solution. With the objective of studying the influence of the composition and thickness of the additional nePCM shells on their probability of failure, a numerical tool combining a thermomechanical finite element model with phase change and Monte Carlo algorithms is developed. This tool also allows including the uncertainty of material and geometrical properties into the numerical analysis to account for their influence in the mechanical performance of nePCMs. In the present work, the mechanical reliability of SiO2 and Al2O3 coatings on Sn@SnOx nanoparticles is assessed by considering both deterministic and probabilistic failure criteria and Al2O3 coatings appear to have a better mechanical performance than their SiO2 counterparts
Numerical Modeling of the Mechanical Reliability of Multicoated Nanoencapsulated Phase-Change Materials with Improved Thermal Performance
Nanoencapsulated phase-change materials (nePCMs) are investigated for enhancing thermal energy storage. However, the shell of these nanocapsules may fail due to stress developed during thermal processes, leading to melting enthalpy loss. To overcome this problem, SiO2 and Al2O3 coatings on Sn nanoparticles are synthesized by atomic layer deposition (ALD). To study the influence of shell thickness and composition on the probability of failure (POF) of nePCM shells in single- and multicoated nePCMs, a probabilistic numerical tool combining Monte Carlo techniques and a thermomechanical finite-element model with phase change are used. The uncertainties of the material and geometrical properties of nePCMs are included in the analysis. Both deterministic and probabilistic failure criteria are taken into account to consider the effect of dispersion on tensile strength. The results indicate that multicoated nePCMs enhance thermomechanical performance in relation to their single-coated counterparts. Both the numerical simulations and experiments confirm that the POF of nePCM shells and melting enthalpy loss in multicoated nePCMs lower with shell thickness. The results after 50 ALD cycles indicate that Al2O3 coatings exhibit better performance because a POF of 1.66% is obtained with 1.1% enthalpy loss, while the POF for SiO2 is 72.38% with 3.5% enthalpy loss
Improving heat transfer of stabilised thermal oil-based tin nanofluids using biosurfactant and molecular layer deposition
The development of advanced heat transfer fluids (HTF) with enhanced heat transfer properties has been identified as a key target to increase the efficiency of industrial processes. In this work, heat transfer performance improvements of a novel nanofluid, consisting of metallic nanoparticles dispersed in a commercial thermal oil, were investigated. Nanofluids combining tin nanoparticles (1 mass %) with Therminol 66 (TH66) were synthesised using the two step-method and experimentally analysed. The effectiveness of biosurfactant addition and nanoparticle polyethylene terephthalate (PET) nanocoating for high temperature nanofluid stabilisation were independently investigated. The PET nanoscale coatings were grown by molecular layer deposition, which has been used for the first time in this field. The thermal conductivity, dynamic viscosity and specific heat capacity of the stable, oil-based nanofluids were characterised at high temperatures, and the results were compared and in good agreement with models found in the relevant literature. Finally, the heat transfer performance of the nanofluids with respect to their base fluids was evaluated, employing empirical values for the thermophysical properties of the involved materials. In this way, increments of the heat transfer coefficients up to 9.3% at 140 °C, relevant to industrial applications were obtained