S. Vaucher

Bio: S. Vaucher is an academic researcher from Swiss Federal Laboratories for Materials Science and Technology. The author has contributed to research in topics: Microwave & Diamond. The author has an hindex of 13, co-authored 39 publications receiving 538 citations. Previous affiliations of S. Vaucher include Nagoya Institute of Technology.

On the thermal and chemical stability of diamond during processing of Al/diamond composites by liquid metal infiltration (squeeze casting)

Abstract: Aiming at assessing the feasibility of Al/diamond composites, the present study deals with the thermal stability of different diamond grades under environmental conditions which are characteristic for the selected pressurized liquid melt infiltration technique (squeeze casting). The influence of both the diamond grade, i.e., synthetic and natural, mono- and polycrystalline diamond and the particle size is investigated. The critical parameters with respect to thermal degradation of diamond have been identified. It is shown that as a consequence of their peculiar process history, “micron-grade” diamond powders are particularly susceptible to thermal degradation in the presence of oxygen and that such degradation is most effectively prevented by using hydrogen-containing atmospheres such as forming gas. It is outlined why nanosized diamond powders and polycrystalline diamond powders are not a suitable “reinforcing phase” for Al/diamond composites. Eventually, it is shown that under the conditions prescribed, the liquid metal infiltration technique is principally viable for the processing of sound Al/diamond composites.

Heat transport across the metal–diamond interface

Abstract: Thermal conductivity of the aluminium–diamond (Al–diamond) composites, prepared by the gas pressure infiltration method, is measured by steady state technique. A detailed theoretical investigation on the heat conduction mechanism across the Al–diamond interface is presented. It was confirmed that both electrons and phonons actively take part in the flow of heat at the interface. In the Al side, electrons of Al couple with the phonons and carry the heat up to the interface. This electron–phonon pair which predominantly carries heat in the Al, breaks down at the Al–diamond interface. The coupling between phonons of both Al and diamond takes place at the interface which eventually leads the heat conduction across the interface to the diamond. The phonon–phonon coupling across the interface is discussed by scattering mediated acoustic mismatch model (SMAMM). It is shown that for Al–diamond composite, the implementation of the SMAMM yields an interface thermal resistance (ITR) value of 4.44 × 10 − 9 m 2 K/W, which is in fairly good agreement with values derived from experimental thermal conductivity values of this composite implemented in the Hasselman–Johnson (HJ) mean field scheme.

Internal stresses and voids in SiC particle reinforced aluminum composites for heat sink applications

Abstract: Metal-matrix composites (MMC) are being developed for power electronic IGBT modules, where the heat generated by the high power densities has to be dissipated from the chips into a heat sink. As a means of increasing long term stability a base plate material is needed with a good thermal conductivity (TC) combined with a low coefficient of thermal expansion (CTE) matching the ceramic insulator. SiC particle reinforced aluminum (AlSiC) offers the high TC of a metal with the low CTE of a ceramic. Internal stresses are generated at the matrix-particle interfaces due to the CTE mismatch between the constituents of the MMC during changing temperatures. Neutron and synchrotron diffraction was performed to evaluate the micro stresses during thermal cycling. The changes in void volume fraction, caused by plastic matrix deformation, are visualized by synchrotron tomography. The silicon content in the matrix connecting the particles to a network of hybrid reinforcement contributes essentially to the long term stability by an interpenetrating composite architecture.

Reinforcement architectures and thermal fatigue in diamond particle-reinforced aluminum

Abstract: Aluminum reinforced by 60 vol.% diamond particles has been investigated as a potential heat sink material for high power electronics. Diamond (CD) is used as reinforcement contributing its high thermal conductivity (TC ≈ 1000 W mK −1 ) and low coefficient thermal expansion (CTE ≈ 1 ppm K −1 ). An Al matrix enables shaping and joining of the composite components. Interface bonding is improved by limited carbide formation induced by heat treatment and even more by SiC coating of diamond particles. An AlSi7 matrix forms an interpenetrating composite three-dimensional (3D) network of diamond particles linked by Si bridges percolated by a ductile α-Al matrix. Internal stresses are generated during temperature changes due to the CTE mismatch of the constituents. The stress evolution was determined in situ by neutron diffraction during thermal cycling between room temperature and 350 °C (soldering temperature). Tensile stresses build up in the Al/CD composites: during cooling

In situ synchrotron radiation monitoring of phase transitions during microwave heating of Al-Cu-Fe alloys

Abstract: The effect of rapid microwave heating has so far been evaluated mainly by comparing the state of materials before and after microwave exposure Yet, further progress critically depends on the ability to follow the evolution of materials during ultrafast heating in real time We describe the first in situ time-resolved monitoring of solid-state phase transitions during microwave heating of metallic powders using wide-angle synchrotron radiation diffraction Single-phase Al–Cu–Fe quasicrystal powders were obtained by microwave heating of nanocrystalline alloy precursors at 650 °C in <20 s

Recent Progress on Ferroelectric Polymer-Based Nanocomposites for High Energy Density Capacitors: Synthesis, Dielectric Properties, and Future Aspects.

Abstract: Dielectric polymer nanocomposites are rapidly emerging as novel materials for a number of advanced engineering applications. In this Review, we present a comprehensive review of the use of ferroelectric polymers, especially PVDF and PVDF-based copolymers/blends as potential components in dielectric nanocomposite materials for high energy density capacitor applications. Various parameters like dielectric constant, dielectric loss, breakdown strength, energy density, and flexibility of the polymer nanocomposites have been thoroughly investigated. Fillers with different shapes have been found to cause significant variation in the physical and electrical properties. Generally, one-dimensional and two-dimensional nanofillers with large aspect ratios provide enhanced flexibility versus zero-dimensional fillers. Surface modification of nanomaterials as well as polymers adds flavor to the dielectric properties of the resulting nanocomposites. Nowadays, three-phase nanocomposites with either combination of fillers...

Electrodynamics Of Continuous Media

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Review on Microwave-Matter Interaction Fundamentals and Efficient Microwave-Associated Heating Strategies

Abstract: Microwave heating is rapidly emerging as an effective and efficient tool in various technological and scientific fields. A comprehensive understanding of the fundamentals of microwave-matter interactions is the precondition for better utilization of microwave technology. However, microwave heating is usually only known as dielectric heating, and the contribution of the magnetic field component of microwaves is often ignored, which, in fact, contributes greatly to microwave heating of some aqueous electrolyte solutions, magnetic dielectric materials and certain conductive powder materials, etc. This paper focuses on this point and presents a careful review of microwave heating mechanisms in a comprehensive manner. Moreover, in addition to the acknowledged conventional microwave heating mechanisms, the special interaction mechanisms between microwave and metal-based materials are attracting increasing interest for a variety of metallurgical, plasma and discharge applications, and therefore are reviewed particularly regarding the aspects of the reflection, heating and discharge effects. Finally, several distinct strategies to improve microwave energy utilization efficiencies are proposed and discussed with the aim of tackling the energy-efficiency-related issues arising from the application of microwave heating. This work can present a strategic guideline for the developed understanding and utilization of the microwave heating technology.