A large thermal hysteresis between melting and solidification temperature on nanoscale Pb particles embedded in amorphous sio2 matrix prepared by sputtering

Kim, Byung-Geol

doi:10.1007/bf03026084

Cited by 4 publications

(4 citation statements)

References 25 publications

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“…The melting of Sn cores was observed at 228.3 C, while freezing occurred only at 98.3 C. Such large thermal hysteresis (undercooling) in tin melting/freezing (~130 C) could be related to antifreezing properties of PVP shell [26] or due to the small size of the high-purity Sn particles. Similar thermal hysteresis was reported in the literature for 5 nm Pb particles in SiO 2 matrix [27]. Authors interpreted the large undercooling of Pb particles as a heterogeneous nucleation process in the nearly impurity-free fine particles.…”

Section: Thermal Energy Storagesupporting

confidence: 87%

Nanofluids with encapsulated tin nanoparticles for advanced heat transfer and thermal energy storage

Cingarapu

Singh

Timofeeva

et al. 2013

Int. J. Energy Res.

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SUMMARY Novel high‐temperature heat transfer fluids (HTFs) with incorporated phase change nanomaterials were synthesized and tested for heat transfer and thermal energy storage. The advanced thermal properties were achieved by preparing a nanofluid consisting of core/shell silica encapsulated tin (Sn/SiO2) nanoparticles dispersed in a synthetic HTF Therminol 66 (TH66) at loadings up to 5 vol%. Tin nanoparticles were synthesized by modified polyole reduction method followed by sol–gel silica encapsulation process. The measured increase in thermal conductivity of the nanofluid (~13% at 5 vol%) was in agreement with Maxwell's effective medium theory. Latent heat of phase change during melting of Sn core added ~11% increase to the volumetric thermal energy storage of the nanofluid when cycled in between 100°C and 270°C. The value could be further improved if thermal cycling is conducted in a narrower temperature range. The experimental results demonstrated dual functionality of the engineered nanofluids as desired for Concentrated Solar Power systems. Viscosity and stability of the nanofluids as well as thermal stability of core/shell nanomaterials) were investigated in a wide temperature range to obtain a perspective on any additional pumping power requirements for the nanofluid over the base fluid. Copyright © 2013 John Wiley & Sons, Ltd.

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Section: Thermal Energy Storagesupporting

confidence: 87%

Nanofluids with encapsulated tin nanoparticles for advanced heat transfer and thermal energy storage

Cingarapu

Singh

Timofeeva

et al. 2013

Int. J. Energy Res.

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“…They reported that these materials showed a high field superconductivity. Kim [29] prepared a sputtered film of the SiO2/Pb system, and obtained the granular microstructure, where Pb particles are homogeneously embedded in an amorphous SiO2 matrix, and measured the melting points and solidification temperatures of fine Pb particles, and reported that anomalously large thermal hysteresis was observed.…”

Section: Introductionmentioning

confidence: 99%

Anomalous electric conductivity for insoluble SiO2/Pb films prepared by sputtering

Kim

2000

Metals and Materials

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Dual phase sputtered films of an insoluble SiO2/Pb system were prepared by sputtering and their electric conductivity mechanisms were investigated. The microstructure of the sputtered films consisted of an amorphous SiO2 phase and a crystalline fcc Pb phase. The homogeneous granular structure, where Pb particles of 5-20 nm in diameter were embedded homogeneously in a SiO2 matrix, was observed in the Pb content of 64~71 vol.%, and the inhomogeneous granular structure, where fine and coarse Pb particles coexisted, was observed in the Pb content of 78-92 vol.%. Dissolution of Si or O into the Pb phase was not detected. The sputtered films showed a great diversity in TCR signs and inclinations according to Pb content. As Pb content decreased, the positive TCR slope decreased and changed into a negative TCR from Pb 64 vol.%. This is because as Pb content decreased, the percolation cluster composed of Pb particles, which makes metallic electric conductivity possible, diminished gradually, and electric channels disappeared finally, changing into other electric conductivity mechanisms induced from the tunneling effect of electrons. Sputtered films were conductors with high electric resistivity when they had homogeneous granular structures. This is probably due to the fabrication method, which makes atomic level control during film preparation possible. It seems that because the movement of electrons was obstructed by fine Pb particles dispersed in an insulator SiO2 matrix and lattice defects introduced during sputtering, the mean free path length of electron was reduced drastically. Also the significantly reduced cross section area in the links of channel where the contact regions of particles that form percolation clusters also generates high resistivity. The percolation limit for this system was Pb 67 vol.%. There was an inverse relationship between 9-,93 and TCR, which corresponds to Mooji's empirical rule, but TCR was still positive when 9293>2 ~f2m at certain compositions. It seems that this result is also due to the unique hybrid microstructure of these films. The electric conductivity mechanism of sputtered films was investigated using the power law of percolation electric conductivity and a result of p=4.1 was obtained. A composite cell effective-medium theory was applied to explain this result, and it was found that the sputtered films consisted of composite cells (A and B type). This coincided well with the microstructures observed by TEM.

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“…A phenomenon that frequently takes place in nePCMs and that needs to be considered, is the supercooling of the nuclei material, meaning that their crystallisation takes place at a temperature inferior to that of the melting 37,38 . This difference between the melting and crystallisation points is probably due to the purity and small size of the nuclei, that favours homogeneous crystallisation taking place.…”

Section: Metallic Nanoencapsulated Pcms (Nepcms)mentioning

confidence: 99%

“…This type of crystallisation requires of more energy than heterogeneous one (when several nucleation spots are present), so it occurs at a temperature lower than that of the melting. The extent of that difference varies according to the material and size of the nuclei, ranging from a few degrees up to more than one hundred 38 . Although this peculiarity can be seen as a disadvantage when we think of pure thermal energy storage, since the energy will be released at a lower temperature than that was stored, causing loses, it can be of use in other several applications such as thermal barriers or air conditioning.…”

Section: Metallic Nanoencapsulated Pcms (Nepcms)mentioning

confidence: 99%

Development of nanofluidst based on nanoencapsulated phase change materials

Argilés¹

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A large thermal hysteresis between melting and solidification temperature on nanoscale Pb particles embedded in amorphous sio2 matrix prepared by sputtering

Cited by 4 publications

References 25 publications

Nanofluids with encapsulated tin nanoparticles for advanced heat transfer and thermal energy storage

Nanofluids with encapsulated tin nanoparticles for advanced heat transfer and thermal energy storage

Anomalous electric conductivity for insoluble SiO2/Pb films prepared by sputtering

Development of nanofluidst based on nanoencapsulated phase change materials

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