Ludovic Charpentier

Continuous Feed Physical Vapor Transport Toward High Purity and Long Boule Growth of SiC

A new reactor concept for the growth of silicon carbide bulk crystals and/or thick epitaxial layers is presented. A coupled approach involving process modeling and numerical simulation and experimental results and characterization was used. This new process combines both high-temperature chemical vapor deposition (HTCVD) for continuous feeding of the polycrystalline source and physical vapor transport (PVT) for single-crystal growth. A special crucible design was built to perform both steps simultaneously. For the feeding step (HTCVD), tetramethylsilane diluted in argon was used. The typical growth rate obtained by the continuous feed PVT process is 100 μm/h at 1900°C. The growth of thick epitaxial layers is demonstrated with a pure two-dimensional growth regime.

Concentrated Solar Energy to Study High Temperature Materials for Space and Energy

In this paper, the concentrated solar energy is used as a source of high temperatures to study the physical and chemical behaviors and intrinsic properties of refractory materials. The atmospheres surrounding the materials have to be simulated in experimental reactors to characterize the materials in real environments. Several application fields are concerned such as the aerospace and the energy fields: examples of results will be given for the heat shield of the Solar Probe Plus mission (NASA) for the SiC/SiC material that can be used as cladding materials for next nuclear reactor (gas-cooled fast reactor-GFR, Generation IV) and for new advanced materials for solar absorbers in concentration solar power (CSP) plant. Two different facilities-REHPTS and MEDIASE-implemented at the focus of two different solar furnaces of the PROMES-CNRS laboratory-5 kW and 1 MW-are presented together with some experimental results on the behavior of high temperature materials.

Behavior at high temperature of metallic liners (Ta, Nb) used in the sandwich cladding material of the GFR

The Gas-cooled Fast-Reactor (GFR) is one of the system developed in the frame of the 4th generation of nuclear plants. The helium coolant may contain some residual oxidizing impurities that can oxidize the cladding material. A sandwich material with a metallic layer (Ta or Nb) inserted between two sheets of SiC/SiC composite is a promising cladding system of the nuclear fuel to support mechanical strengths, to retain fission products without blocking the neutrons. Nevertheless SiC may support active oxidation with production of gaseous SiO and CO and sublimation in accidental conditions for temperatures above 2000 K, so the aim of the following study is to firstly investigate the oxidation resistance of the metallic liner in extreme conditions, alone and then covered by the SiC/SiC composite. The High Pressure and Temperature Solar Reactor (REHPTS) was implemented at the focus of the 6 kW Odeillo solar furnace in order to reproduce in helium atmosphere the sudden and huge temperature increase that can occur in the case of a nuclear accident. XRD and SEM enabled to observe that the high temperature exposure favored the (211) preferential orientation of tantalum and that the amorphization of niobium occurs above 1500 K. Such changes may impact the properties of the cladding elements. Some sandwich materials made of one plate of metal covered with a SiC/SiC composite were also tested and a carburation of the metallic plates at 2200 K was observed.