| 1. |
- Manchili, Swathi Kiranmayee, 1987, et al.
(author)
-
Effect of Nanopowder Addition on the Sintering of Water-Atomized Iron Powder
- 2020
-
In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 51:9, s. 4890-4901
-
Journal article (peer-reviewed)abstract
- A promising method of improving the densification of powder metallurgical steel components is to blend nanopowder with the otherwise typically used micrometre-sized powder. The higher surface-to-volume ratio of nanopowder is hypothesized to accelerate the sintering process and increase the inter-particle contact area between the powder particles. This is supposed to enhance the material transport and improve the densification. In the present investigation, water-atomized iron powder (− 45 μm) was mixed separately with pure iron and low-carbon steel nanopowder, each at a ratio of 95 to 5 pct. These powder mixes were compacted at different pressures (400, 600 and 800 MPa) and then sintered at 1350 °C in a pure hydrogen atmosphere. The sintering behavior of the powder blend compacts was compared to that of the compact with micrometre-sized powder only. Densification commenced at much lower temperatures in the presence of nanopowder. To understand this, sintering at intermittent temperatures such as 500 °C and 700 °C was conducted. The fracture surface revealed that the nanopowder was sintered at between 500 °C and 700 °C, which in turn contributed to the densification of the powder mix at the lower temperature range. Based on the sintering experiments, an attempt was made to calculate the activation energy and identify the associated sinter mechanism using two different approaches. It was shown that the first approach yielded values in agreement with the grain-boundary diffusion mechanism. As the nanopowder content increased, there was an increase in linear shrinkage during sintering.
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| 2. |
- Chen, Shujing, et al.
(author)
-
Manufacturing Graphene-Encapsulated Copper Particles by Chemical Vapor Deposition in a Cold Wall Reactor
- 2019
-
In: ChemistryOpen. - : Wiley. - 2191-1363. ; 8:1, s. 58-63
-
Journal article (peer-reviewed)abstract
- Functional fillers, such as Ag, are commonly employed for effectively improving the thermal or electrical conductivity in polymer composites. However, a disadvantage of such a strategy is that the cost and performance cannot be balanced simultaneously. Therefore, the drive to find a material with both a cost efficient fabrication process and excellent performance attracts intense research interest. In this work, inspired by the core-shell structure, we developed a facile manufacturing method to prepare graphene-encapsulated Cu nanoparticles (GCPs) through utilizing an improved chemical vapor deposition (CVD) system with a cold wall reactor. The obtained GCPs could retain their spherical shape and exhibited an outstanding thermal stability up to 179 degrees C. Owing to the superior thermal conductivity of graphene and excellent oxidation resistance of GCPs, the produced GCPs are practically used in a thermally conductive adhesive (TCA), which commonly consists of Ag as the functional filler. Measurement shows a substantial 74.6 % improvement by partial replacement of Ag with GCPs.
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| 3. |
- Fazi, Andrea, 1992, et al.
(author)
-
Multiple growth of graphene from a pre-dissolved carbon source
- 2020
-
In: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 31:34, s. 345601-
-
Journal article (peer-reviewed)abstract
- Mono- to few-layer graphene materials are successfully synthesized multiple times using Cu-Ni alloy as a catalyst after a single-chemical vapor deposition (CVD) process. The multiple synthesis is realized by extracting carbon source pre-dissolved in the catalyst substrate. Firstly, graphene is grown by the CVD method on Cu-Ni catalyst substrates. Secondly, the same Cu-Nicatalyst foils are annealed, in absence of any external carbon precursor, to grow graphene using the carbon atoms pre-dissolved in the catalyst during the CVD process. This annealing process is repeated to synthesize graphene successfully until carbon is exhausted in the Cu-Ni foils. After the CVD growth and each annealing growth process, the as-grown graphene is removed using a bubbling transfer method. A wide range of characterizations are performed to examine the quality of the obtained graphene material and to monitor the carbon concentration in the catalyst substrates. Results show that graphene from each annealing growth process possesses a similar quality, which confirmed the good reproducibility of the method. This technique brings great freedom to graphene growth and applications, and it could be also used for other 2D material synthesis.
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| 4. |
- Fu, Yifeng, 1984, et al.
(author)
-
Graphene related materials for thermal management
- 2020
-
In: 2D Materials. - : IOP Publishing. - 2053-1583. ; 7:1
-
Journal article (peer-reviewed)abstract
- Almost 15 years have gone ever since the discovery of graphene as a single atom layer. Numerous papers have been published to demonstrate its high electron mobility, excellent thermal and mechanical as well as optical properties. We have recently seen more and more applications towards using graphene in commercial products. This paper is an attempt to review and summarize the current status of the research of the thermal properties of graphene and other 2D based materials including the manufacturing and characterization techniques and their applications, especially in electronics and power modules. It is obvious from the review that graphene has penetrated the market and gets more and more applications in commercial electronics thermal management context. In the paper, we also made a critical analysis of how mature the manufacturing processes are; what are the accuracies and challenges with the various characterization techniques and what are the remaining questions and issues left before we see further more applications in this exciting and fascinating field.
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| 5. |
- Guo, Sihua, et al.
(author)
-
Toward ultrahigh thermal conductivity graphene films
- 2023
-
In: 2D Materials. - : IOP Publishing. - 2053-1583. ; 10:1
-
Journal article (peer-reviewed)abstract
- With increasing demands of high-performance and functionality, electronics devices generate a great amount of heat. Thus, efficient heat dissipation is crucially needed. Owing to its extremely good thermal conductivity, graphene is an interesting candidate for this purpose. In this paper, a two-step temperature-annealing process to fabricate ultrahigh thermal conductive graphene assembled films (GFs) is proposed. The thermal conductivity of the obtained GFs was as high as 3826 +/- 47 W m(-1) K-1. Extending the time of high-temperature annealing significantly improved the thermal performance of the GF. Structural analyses confirmed that the high thermal conductivity is caused by the large grain size, defect-free stacking, and high flatness, which are beneficial for phonon transmission in the carbon lattice. The turbostratic stacking degree decreased with increasing heat treatment time. However, the increase in the grain size after long heat treatment had a more pronounced effect on the phonon transfer of the GF than that of turbostratic stacking. The developed GFs show great potential for efficient thermal management in electronics devices.
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| 6. |
- Liu, Ya, 1991, et al.
(author)
-
Surface modification of graphene for use as a structural Fortifier in water-borne epoxy coatings
- 2019
-
In: Coatings. - : MDPI AG. - 2079-6412. ; 9:11
-
Journal article (peer-reviewed)abstract
- Graphene, the typical two-dimensional sp2 hybridized carbon allotrope, is widely used as a filler for improving the mechanical performance of polymers. However, its superhydrophobic surface makes it a big challenge to obtain stable graphene dispersions, especially in water-borne systems. On the contrary, graphene oxide (GO) shows excellent dispersibility in water, but strong oxidants and acids destroy its structure and degrade its mechanical properties. This largely limits its application in water-borne coatings. In this work, graphene from mechanical exfoliation was surface modified by p-aminophenol derived diazonium salt to achieve a homogenous dispersion. Moreover, the hydroxyl groups in p-aminophenol are able to combine with epoxy resins during the curing process to improve mechanical performance of the final coatings. The result shows that functionalized graphene shows a lower coefficient of friction and better abrasion resistance compared to GO.
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| 7. |
- Liu, Ya, 1991, et al.
(author)
-
Thermally Conductive and Electrically Insulating PVP/Boron Nitride Composite Films for Heat Spreader
- 2019
-
In: Proceedings - 2019 IMAPS Nordic Conference on Microelectronics Packaging, NORDPAC 2019. ; , s. 1-5
-
Conference paper (peer-reviewed)abstract
- Thermally conductive materials with electrically insulating properties have been extensively investigated for thermal management of electronic devices. The combined properties of high thermal conductivity, structural stability, corrosion resistance and electric resistivity make hexagonal boron nitride (h-BN) a promising candidate for this purpose. Theoretical studies have revealed that h-BN has a high in-plane thermal conductivity up to 400-800 W m-1 K-1 at room temperature. However, it is still a big challenge to achieve high thermally conductive h-BN thick films that are commercially feasible due to its poor mechanical properties. On the other hand, many polymers exhibit advantages for flexibility. Thus, combining the merits of polymer and the high thermal conductivity of h-BN particles is considered as a promising solution for this issue. In this work, orientated PVP/h-BN films were prepared by electrospinning and a subsequent mechanical pressing process. With the optimized h-BN loading, a PVP/h-BN composite film with up to 22 W m-1 K-1 and 0.485 W m-1 K-1 for in-plane and through-plane thermal conductivity can be achieved, respectively. We believe this work can help accelerate the development of h-BN for thermal management applications.
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| 8. |
- Liu, Ya, 1991, et al.
(author)
-
Thermally Conductive and Electrically Insulating PVP/Boron Nitride Composite Films for Heat Spreader
- 2019
-
In: Advancing Microelectronics. - 2222-8748. ; 2019:NOR, s. 1-5
-
Journal article (peer-reviewed)abstract
- Thermally conductive materials with electrically insulating properties have been extensively investigated for thermal management of electronic devices. The combined properties of high thermal conductivity, structural stability, corrosion resistance and electric resistivity make hexagonal boron nitride (h-BN) a promising candidate for this purpose. Theoretical studies have revealed that h-BN has a high in-plane thermal conductivity up to 400 - 800 W m−1 K−1 at room temperature. However, it is still a big challenge to achieve high thermally conductive h-BN thick films that are commercially feasible due to its poor mechanical properties. On the other hand, many polymers exhibit advantages for flexibility. Thus, combining the merits of polymer and the high thermal conductivity of h-BN particles is considered as a promising solution for this issue. In this work, orientated PVP/h-BN films were prepared by electrospinning and a subsequent mechanical pressing process. With the optimized h-BN loading, a PVP/h-BN composite film with up to 22 W m-1 K-1 and 0.485 W m-1 K-1 for in-plane and through-plane thermal conductivity can be achieved, respectively. We believe this work can help accelerate the development of h-BN for thermal management applications.
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| 9. |
- Long, Xu, et al.
(author)
-
Mechanical behaviour of sintered silver nanoparticles reinforced by SiC microparticles
- 2019
-
In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 744, s. 406-414
-
Journal article (peer-reviewed)abstract
- SiC microparticles with various weight ratios (0.0, 0.5, 1.0 and 1.5 wt%) are incorporated into sintered silver nanoparticles (AgNP) as one of the promising packaging materials for high-power electronic devices. Mechanical properties and constitutive behaviour of sintered AgNP reinforced by SiC microparticles are investigated based on nanoindentation experiment and analytical approach. Nanoindentations were performed in the manner of continuous stiffness measurement for a maximum penetration depth of 2000 nm at a strain rate of 0.05 s−1. Particularly, a Berkovich indenter is utilized to evaluate the values of Young's modulus and hardness, and a spherical indenter is utilized to describe the constitutive behaviour. For sintered AgNP with 0.5 wt% SiC, the morphology exhibits uniformly compact microstructures to enable optimizing the heat conductivity, the yield strength and hardening capacity of sintered AgNP material is enhanced. To describe the constitutive behaviour, an analytical approach is proposed to simulate the indentation behaviour. The parameters in the modified power-law model are determined by fitting the average indentation responses. The developed correlation between microstructure and macroscopic properties facilitates the design of AgNP paste morphology and improves the mechanical properties of sintered AgNP in electronics packaging.
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| 10. |
- Lu, Xiuzhen, et al.
(author)
-
The influence of sintering process on thermal properties of nano-silver paste
- 2018
-
In: 2018 19TH INTERNATIONAL CONFERENCE ON ELECTRONIC PACKAGING TECHNOLOGY (ICEPT). - 9781538663868 - 9781538663868 ; , s. 1157-1160
-
Conference paper (peer-reviewed)abstract
- Nano-silver paste with low sintering temperature and high operation temperature was introduced to the application of bonding materials for GaN and SiC devices. Thermal properties are critical issues for die attach materials due to the heat dissipation requirements of high power devices. The influence of sintering process parameters for nano-silver paste on the thermal properties was investigated. The thermal conductivity of sintered nano-silver paste increased with the increase of sintering temperature and sintering time because of the dense structure due to high temperature and long sintering time. To improve the thermal property, Ag coated micro-SiC particles were used as an alternative to partly replace pure nano-Ag particles. The results demonstrate that the SiC particles can reduce the voids and improve the density of the sintered silver structure. Moreover, the addition of SiC particles can also contribute to the increase of thermal diffusivity. As a result, the thermal conductivity of sintered silver paste with 1.5 wt.% Ag coated SiC particles was two times as compared to that without SiC particles with the same Ag concentration.
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| 11. |
- Manchili, Swathi Kiranmayee, 1987, et al.
(author)
-
Surface analysis of iron and steel nanopowder
- 2018
-
In: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 50:11, s. 1083-1088-10886
-
Journal article (peer-reviewed)abstract
- High sinter density is desired in powder metallurgy components as the requirement for performance is increasing day‐by‐day. One of the promising ways to achieve improved densification during sintering is through the addition of nanopowder to the conventional micrometer sized metal powder. It is well known that the surface chemistry of the powder has a decisive effect on sintering and consequently the properties of the components produced. Extensive research has hence been conducted to elucidate the surface chemistry and its influence on sintering for powder used in conventional powder metallurgy. Nanopowder, owing to high surface to volume ratio, can contribute to the activation of sintering at lower temperatures and enhance the sinter density. In this context, the surface chemistry of the nanopowder is also expected to exhibit substantial influence on sintering. The present investigation is aimed at establishing a methodology to study the surface chemistry and oxide thickness of nanopowder. For this purpose, iron nanopowder of 3 different size fractions: 35 to 45, 40 to 60, and 60 to 80 nm with core‐shell structure were studied. Different approaches were adopted to evaluate the shell thickness of the iron nanoparticles. The methodology was developed and tried on low alloy steel nanopowder to measure oxide thickness. X‐ray photoelectron spectroscopy, thermogravimetry, and high‐resolution scanning electron microscopy techniques were used to study the nanopowder. Results from different core‐shell models for iron nanopowder were found to be consistent except in the case where depth profiling was taken into account. The results were in agreement with the values obtained from thermogavimetry‐surface area correlation.
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| 12. |
- Shi, Yuqing, et al.
(author)
-
Fabrication and characterization of graphene based film
- 2017
-
In: 2017 IMAPS Nordic Conference on Microelectronics Packaging, NordPac 2017, Goteborg, Sweden, 18-20 June 2017. - 9781538630556 ; , s. 162-166
-
Conference paper (peer-reviewed)abstract
- Large area, freestanding graphene papers fabricated from 2D graphene nanosheets with optimized microstructure, graphene sheet alignment and superior properties have a wide range of functional applications. In this paper, we propose a novel approach to fabricate graphene film by Electro-spray deposition (ESD), which is considered as the preparation for a roll-to-roll industrial production of the further. Expanded graphite, as the raw materials, was dispersed into N-Methyl-2-pyrrolidone (NMP) which is used as the feeding solution for ESD. It is also shown that high-shear mixing and high ultra-sonication of graphite powder in NMP solvent result in large-scale exfoliation, giving good dispersions of graphene nanosheets. The fabrication of the film with different thicknesses is based on ESD onto the surface of a heated aluminum foil at around 140°C. Brunauer-Emmett-Teller method is used to test the surface area of raw material, which has been reported to reach 1200 m2/g. Raman spectroscopy and scanning electron microscope (SEM) are used to characterize the microstructure and morphology of the film, contributing to the optimization of electrospray's parameters. Joule heating was utilized to quantify thermal conductivity of the film.
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| 13. |
- Wang, Nan, 1988, et al.
(author)
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Improved Interfacial Bonding Strength and Reliability of Functionalized Graphene Oxide for Cement Reinforcement Applications
- 2020
-
In: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 26:29, s. 6561-6568
-
Journal article (peer-reviewed)abstract
- Poor bonding strength between nanomaterials and cement composites inevitably lead to the failure of reinforcement. Herein, a novel functionalization method for the fabrication of functionalized graphene oxide (FGO), which is capable of forming highly reliable covalent bonds with cement hydration products, and therefore, suitable for use as an efficient reinforcing agent for cement composites, is discussed. The bonding strength between cement and aggregates was improved more than 21 times with the reinforcement of FGO. The fabricated FGO also demonstrated many important features, including high reliability in cement pastes, good dispersibility, and efficient structural refinement of cement hydration products. With the incorporation of FGO, cement mortar samples demonstrated up to 40 % increased early and ultimate strength. Such results make the fast demolding and manufacture of light constructions become highly possible, and show strong advantages on improving productivity, saving cost, and reducing CO2 emissions in practical applications.
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| 14. |
- Zehri, Abdelhafid, 1989
(author)
-
Characterization of Multifunctional Nanomaterials for Electronics Thermal Management and Sintering Applications
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- The science of manipulating materials at their nanoscale level is nowadays allowing endless possibilities to disrupt the current limitations on the conventional production processes and products. In electronics, the need for more capable thermal management strategies led to the exploration of advanced approaches and focus on new materials and allowed to push further the thermal dissipation capabilities of each generation of products. In this thesis, we investigate different thermal management concepts and propose new solutions based on carbon and metallic nanomaterials, while we explore the possibility to combine the size effect with the composition effect of the nanoscale materials. Due to their high surface to volume ratio, nanoscale particles show different thermodynamics properties that led to their potential implementation in electronics fabrication processes. More specifically, silver nanoparticles (Ag NPs) have been under focus in recent years for applications to replace lead-free solder and contribute to energy saving. Due to a poor trade-off between the process parameters, the production costs, and the reliability of the silver related application, different strategies are being suggested to optimize its applications. In this present study, we investigate multiple sintering parameters of Ag NPs and use the nanoscale effect in a hybrid approach for the sintering of microscopic powder. The results of the sintering parameters are correlated to the density of the samples and their properties in terms of thermal and electrical conductivity. While the sintering of Ag NPs occurs at low temperatures and allows to obtain relatively high densities, the thermal and electrical properties are still limited and the increase in the temperature and fraction of the NPs higher than 400 degrees and 2wt.% has a much- pronounced effect to improve the physical properties of the samples. The sintering of Ag NPs was also explored in this thesis to propose a novel approach to use graphene foam as a heat sink. While graphene is known for its outstanding physical, chemical, and mechanical properties, its integration as a practical solution in electronics is still missing. The use of Ag NPs in this work allowed to successfully attach the 3D graphene foam on its substrate and further improve both its mechanical and thermal properties by coating the graphene with Ag NPs. Also, the integration of Ag NPs as a die-attach for the 3D porous structure allowed its further use as a container for Phase Change Materials (PCM). Different amounts of PCM were introduced in the lightweight foam and the junction temperature of the hot spot was correlated to the power and the presence of the PCM. We found that graphene foam presents a real advantage for its use in thermal dissipation strategies. 2D graphene material is developed herein as a coating for micro-and nanoscale particles. Using Chemical Vapor Deposition (CVD) and Arc Discharge (AD) methods, we introduce the possibility to produce graphene coating on copper particles for application in thermal management. In addition, we explore the possibility to introduce a doping effect on the coated NPs to further study its effect on the thermal performances of NPs. The morphology and the composition of the coating were investigated and correlated with the bottom-up production process of CVD and AD. The thermal conductivity and chemical stability of the produced particles were studied for their use as fillers in thermally conductive pastes and additives water-based nanofluids. The thermal properties of the different systems were linked to the fraction of the additives and nanofillers. The graphene-coated particles were found to have a multifunctional effect. In both micro-and nanoscale particles, the graphene coating was found to act as a corrosion resistance that stabilizes the metallic core of the particles. The graphene coating also was found to act as a carbon source to reduce the microparticles in a bimodal powder at high temperatures. Finally, the encapsulation of the nanoscale powder allowed to observe a melting point depression related to the composition of the core of the nanoparticles and their nanoscale size. In an effort to combine the size effect of the nanoparticles and their compositions, different alloyed nanoparticles were produced using AC. The morphology, the composition, and their sintering properties were compared to highlight their composition effect. The produced nanopowders were also used as a sintering aid in the spark plasma sintering approach (SPS) and the results show a positive contribution of the nanopowders in the reduction of the sintering temperature and the densification of the samples. An additional effect is also reported and arises from the possibility to use those particles to fine-tune the chemical composition of the bimodal particles.
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| 15. |
- Zehri, Abdelhafid, 1989, et al.
(author)
-
Exploring Graphene Coated Copper Nanoparticles as a multifunctional Nanofiller for Micro-Scaled Copper Paste
- 2021
-
In: 2021 23rd European Microelectronics and Packaging Conference and Exhibition, EMPC 2021.
-
Conference paper (peer-reviewed)abstract
- The current development of the electronics system requires capabilities beyond conventional heat transfer approaches. New solutions based on advanced materials are being developed to tackle the current challenges in the development of electronics systems and the nanoscale 2D materials such as graphene are at the centre of the effort to exploit the intrinsic properties of carbon nanomaterials. In this work, we introduce a new concept of graphene-coated copper nanoparticles (G-CuNPs) and explore their multifunctional potential applications in metallic based paste used in electronics. The nanoscale powder was found to present a core/shell structure with the copper particle at its core and a disordered multilayer graphene structure continuously coating its surface. The composition of the particles was analysed, and the presence of the coating was found to provide oxidation protection for the metallic core. Thermogravimetric analysis (TGA) showed an additional role of the G-CuNPs with a reduction effect without the use of an additional reducing agent. Furthermore, due to the combined effect of the size of the particles and the oxidation-free metallic core, Differential Scanning Calorimetry (DSC) analysis revealed a melting depression at temperatures as low as 155 °C. Finally, the mechanical properties of the nanocoating were investigated and the results showed an enhanced ductility at the surface of the particles due to the presence of the multi-layered graphene structure, which might be exploited for powder flow and lubrication effect.
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| 16. |
- Zehri, Abdelhafid, 1989, et al.
(author)
-
Graphene-coated copper nanoparticles for thermal conductivity enhancement in water-based nanofluid
- 2019
-
In: 2019 22nd European Microelectronics and Packaging Conference and Exhibition, EMPC 2019.
-
Conference paper (peer-reviewed)abstract
- The integration of metallic nanoparticlcs (NPs) in nanofluids was found to enhance the thermal properties of the mixture and affect the rheological properties of the base liquid. However, due to their size and electrochemical properties, the added metallic nanoparticlcs have a limited contribution to the thermal transport and their stability hinders further development of such an approach in thermal management. We investigated in this work the effect of the presence of graphene as a coating layer of on copper nanoparticles dispersed in water as a water-based graphene coated copper nanofluid. Electronics microscopy was deployed to investigate the presence and the number of layers of graphene around the metallic nanoparticles. The observed particles were found to have a spherical morphology with a full coating of several layers. The elemental characterization of the NPs showed the presence of graphitic structure confirming the nature of the coating. The thermal properties of the fluid were estimated versus loading fraction of graphene coated nanoparticles and temperature using a hot disk method. An increase of up to 17% was recorded at a concentration of 0.1 w.% at 45deg C. Dynamic Light Scattering and zeta potential were used to investigate the electrochemical properties of the produced nanoparticles. The particles were found to present weak surface charges corresponding to a zeta potential of 6mV that promoted the segregation of the NPs. The rheological properties of the resulted fluids were investigated using viscometer. The NFs were found to have a Newtonian behaviour.
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| 17. |
- Zehri, Abdelhafid, 1989, et al.
(author)
-
Graphene Fibres: Towards high mechanical, thermal and electrical properties state of art
- 2016
-
In: IMAPS Nordic Annual Conference 2016, Tonsberg, Norway, 5-7 June 2016. - 9781510827226
-
Conference paper (peer-reviewed)abstract
- Nowadays, tremendous efforts are made to enhance the thermal conductivity of materials and answer to demands for fast heat dissipation in various applications such as wearable electronics, photovoltaic energy conversion and advanced structural materials mounted on high power electronics. The main difficulty comes very often from the ability to simultaneously produce superior thermal, electrical and high mechanical properties. For this matter, graphene which owned the nickname of miracle material has attracted all the attention to exploit its outstanding properties at an industriel scale and the field of graphene fibre turned to be a very promising approach to produce a high quality 3D graphene material. In this review paper, we propose to summarize briefly the different advances and attemps made up to now in order the assemble graphene into macroscopic three-dimensional structures and apply the unique properties of its two-dimensional individuels in practical applications.
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| 18. |
- Zehri, Abdelhafid, 1989, et al.
(author)
-
Graphene Oxide and Nitrogen-Doped Graphene Coated Copper Nanoparticles in Water-Based Nanofluids for Thermal Management in Electronics
- 2022
-
In: JOURNAL OF NANOFLUIDS. - : American Scientific Publishers. - 2169-432X .- 2169-4338. ; 11:1, s. 125-134
-
Journal article (peer-reviewed)abstract
- Graphene oxide (GO) and nitrogen-doped graphene (NG) coated copper nanoparticles (NPs) have been developed in this work and investigated as nanofiller for water as Heat Transfer Fluids (HTFs). The morphology and composition of the coating were characterized to confirm the presence of functional groups and the nitrogen-doping of the graphene coating. Different fractions of the two types of coated nanoparticles NPs between 0.1 and 10 wt.% were dispersed in water. The thermal conductivity of the dispersions was evaluated at temperatures between 20 and 50 degrees C. A positive correlation between the thermal conductivity of the HTFs and the fraction and temperature are observed as a result of the increase of the solid phase contribution into the heat transfer. At a concentration of 0.5 wt.%, the thermal conductivity of the NG-CuNPs nanofluid reached its maximum increase of 78%, compared to a 13% increase in the case of GO-CuNPs. However, due to the poor stability of the NG-CuNPs, further increase of the solid phase did not result in any additional improvement. In contrast, the thermal conductivity of the GO-based dispersion resulted in a 103% enhancement at 10 wt.% at a temperature of 50 degrees C.
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| 19. |
- Zehri, Abdelhafid, 1989, et al.
(author)
-
High porosity and light weight graphene foam heat sink and phase change material container for thermal management
- 2020
-
In: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 31:42
-
Journal article (peer-reviewed)abstract
- During the last decade, graphene foam emerged as a promising high porosity 3-dimensional (3D) structure for various applications. More specifically, it has attracted significant interest as a solution for thermal management in electronics. In this study, we investigate the possibility to use such porous materials as a heat sink and a container for a phase change material (PCM). Graphene foam (GF) was produced using chemical vapor deposition (CVD) process and attached to a thermal test chip using sintered silver nanoparticles (Ag NPs). The thermal conductivity of the graphene foam reached 1.3 W m(-1)K(-1), while the addition of Ag as a graphene foam silver composite (GF/Ag) enhanced further its effective thermal conductivity by 54%. Comparatively to nickel foam, GF and GF/Ag showed lower junction temperatures thanks to higher effective thermal conductivity and a better contact. A finite element model was developed to simulate the fluid flow through the foam structure model and showed a positive and a non-negligible contributions of the secondary microchannel within the graphene foam. A ratio of 15 times was found between the convective heat flux within the primary and secondary microchannel. Our paper successfully demonstrates the possibility of using such 3D porous material as a PCM container and heat sink and highlight the advantage of using the carbon-based high porosity material to take advantage of its additional secondary porosity.
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| 20. |
- Zehri, Abdelhafid, 1989, et al.
(author)
-
Low-Temperature Sintering Bimodal Micro Copper-Nano Silver for Electrical Power Devices
- 2018
-
In: 2018 7th Electronic System-Integration Technology Conference (ESTC). - 9781538668146
-
Conference paper (peer-reviewed)abstract
- Copper is generally considered as an electronic packaging material due to its good electrical, thermal properties and relatively low cost. However, copper needs high processing temperature, which negatively affects the electronics reliability. In this paper, silver nanoparticles sintering is evaluated for the propose to decrease the processing temperature of copper. Different fractions of silver nanoparticles were mixed with 10 ×m Cu powder and sintered at temperatures of 250°C, 300°C, 400°C and 500°C, under low pressures 4MPa and 8MPa, and a high pressure of 100MPa for comparison. Densities from 45% to 94% of the density of bulk Cu have been achieved while the thermal and electrical conductivities have been evaluated and reached a value of around 270W/m.K and 1.41×106 S/m.
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| 21. |
- Zehri, Abdelhafid, 1989
(author)
-
Manufacturing and characterization of nanomaterials for low-temperature sintering and electronics thermal management applications
- 2020
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Licentiate thesis (other academic/artistic)abstract
- Nanotechnology is expected to have a significant impact on the long-term development within and across many disciplines. While offering potential improvements in energy efficiency and reduced energy and materials consumption, nanomaterials are at the centre of the cutting-edge technologies and sustainable manufacturing processes era with near half of the products in the next period of 10 years expected to embed nanoscale solutions. The condensed substance of nanosized dimension has shown excellent properties that offer new possibilities due to their surface area to volume ratio. The non-negligible surface energy was proven to induce melting temperature depression, low sintering activation energy and high electronic density that contributes to thermal transport. In this work, we investigate the possibility to take advantage of the advanced nanoscale properties as a sintering aid for low-temperature manufacturing and as thermal dissipation materials for electronics cooling. By combining the high surface energy of the nanomaterial with the tailoring of the local chemical composition, an extra degree of freedom is expected to enable further tuning of their physical and chemical properties. Furthermore, due to the chemical stability of the carbon-based materials and their outstanding physical properties, graphene is explored as a nanoscale coating for nanoparticles and applied herein as a potential nanofiller for nanofluids cooling approach. An additional effort is made to use the graphene/metal composite at a microscale level as high porosity material for heat dissipation. In this thesis, a novel approach for nanoscale materials production was exploited to manufacture multi-elements alloyed iron nanoparticle. Using spark erosion, low carbon steel nanopowder was produced in order to tune the chemical composition of the nanoparticles in order to combine size effect with composition effect and tailor their performances. A melting depression recorder, while the sintering behaviour of the powder indicated an early activation of the diffusion at temperatures higher than 150°C. The results allow such materials to be used as a sintering aid and lower the sintering temperature of iron powders. Secondly, graphene-coated copper nanoparticles were developed as additives for nanofluids. The nanocomposite fillers of the copper core with multilayers graphene shell were added to water as the base-fluid. The presence of the graphene coating acted as oxidation protection for the metallic particles. Besides, it was found that the presence of the graphene as a local coating on the spherical metallic nanoparticles resulted in a proportional increase in the thermal conductivity of the fluid as the temperature and the concentration of the nanoparticles increased. Such an approach was found promising in the use of graphene-coated nanoparticles as fillers for nanofluids with good heat dissipation. Finally, graphene has been used as a three-dimensional (3D) foam structure with sintered silver nanoparticles. The sintering of the metallic particles allowed a pressure-free attachment of the high porosity and lightweight material on the back of a chip as a heat sink. The thermal properties of the graphene foam were investigated and found to reach a thermal conductivity of 319 W/mK. The addition of a layer of coating of silver on the 3D graphene foam material improved further its thermal properties with a 54% enhancement in its effective thermal conductivity. The high porosity fraction was later gradually filled with paraffin as a phase change material. As a result, the maximum temperature of the chip was proportionally lowered and delayed. Most importantly, a CFD model was developed to study the contribution of the secondary microchannels in the heat dissipation process and revealed a positive and non-negligible effect of the additional microporosity present in the case of the graphene foam structure.
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| 22. |
- Zhang, Q., et al.
(author)
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Mechanical property and reliability of bimodal nano-silver paste with Ag-coated SiC particles
- 2019
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In: Soldering and Surface Mount Technology. - 1758-6836 .- 0954-0911. ; 31:4, s. 193-202
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Journal article (peer-reviewed)abstract
- © 2019, Emerald Publishing Limited. Purpose: This study aims to develop a bimodal nano-silver paste with improved mechanical property and reliability. Silicon carbide (SiC) particles coated with Ag were introduced in nano-silver paste to improve bonding strength between SiC and Ag particles and enhance high-temperature stability of bimodal nano-silver paste. The effect of sintering parameters such as sintering temperature, sintering time and the proportion of SiC particles on mechanical property and reliability of sintered bimodal nano-silver structure were investigated. Design/methodology/approach: Sandwich structures consist of dummy chips and copper substrates with nickel and silver coating bonded by nano-silver paste were designed for shear testing. Shear strength testing was conducted to study the influence of SiC particles proportions on the mechanical property of sintered nano-silver joints. The reliability of the bimodal nano-silver paste was evaluated experimentally by means of shear test for samples subjected to thermal aging test at 150°C and humidity and temperature testing at 85°C and 85 per cent RH, respectively. Findings: Shear strength was enhanced obviously with the increase of sintering temperature and sintering time. The maximum shear strength was achieved for nano-silver paste sintered at 260°C for 10 min. There was a negative correlation between the proportion of SiC particles and shear strength. After thermal aging testing and humidity and temperature testing for 240 h, the shear strength decreased a little. High-temperature stability and high-hydrothermal stability were improved by the addition of SiC particles. Originality/value: Submicron-scale SiC particles coated with Ag were used as alternative materials to replace part of nano-silver particles to prepare bimodal nano-silver paste due to its high thermal conductivity and excellent mechanical property.
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