Marilyne Roumanie

Semiconductors as silicon carbide are used for particle—here fast neutrons—detection because of their wide bandgap and efficiency with thermal and radiation resistance. The behavior of SiC diodes is better documented in harsh environments, but there is a lack of knowledge regarding their industrial integration. To reach a higher technology readiness level, the present work proposes for the detector conception an assembly made by Additive Manufacturing and sealed with Field Assisted Sintering Technologies. The design relies on a coaxial shape of insulating parts in alumina made by using the digital layer process and electrodes, core, and shell made of copper alloys using the layer powder bed fusion process. The overall shape of the parts is conical, which allows for self-centering, locking, and pressure of the electrode on the SiC diode. The electrodes are designed with an origami-type structure, which allows for controlled deformation and ensures electrical continuity. The housing is sealed using transient liquid phase bonding of borosilicate glass applied by screen printing. After sealing, detectors were investigated with x-ray tomography and electrical behavior. Finally, the detector was exposed to a fast neutron flux and successfully detected it.

The Silres H62C methyl-phenyl-vinyl-hydrogen polysiloxane is a promising candidate as a SiC precursor for 3D printing based on photopolymerization reaction. An in-depth nuclear magnetic resonance spectroscopy analysis allowed us to determine its structure and quantify its functional groups. The polysiloxane was found to have a highly branched ladder-like structure, with 21.9, 31.4 and 46.7% of mono-, di- and tri-functional silicon atoms. The polysiloxane cross-links from 180 °C using hydrosilylation between silyl groups (8.4% of the total functional groups) and vinyl groups (12.0%) and contains a non-negligible ethoxy content (2.4%), allowing cross-linking through a hydrolyze/condensation mechanism. After converting the polymer into ceramic and thus releasing mainly hydrogen and methane, the ceramic yield was 72.5%. An X-ray diffraction analysis on the cross-linked and pyrolyzed polysiloxane showed that the ceramic is amorphous at temperatures up to 1200 °C and starts to crystallize from 1200 °C, leading into 3C-SiC carbon-rich ceramic at 1700 °C in an argon atmosphere.

A new coating based on polymer-derived ceramics (PDC), oxides and refractory ceramic with a thickness of around 50 µm has been developed to improve the resistance corrosion of stainless steel substrate against molten aluminum alloy in a thermal energy storage (TES) system designed to run at high temperature (up to 600 °C). These coatings implemented by straightforward methods, like tape casting or paintbrush, were coated on planar and cylindrical stainless-steel substrates, pyrolyzed at 700 °C before being plunged for 600 and 1200 h in molten AlSi₁₂ at 700 °C. The stainless-steel substrate appears healthy without intermetallic compounds, characteristic of molten aluminum alloy corrosion. The protective coating against AlSi₁₂ corrosion shows excellent performance and appears interesting for TES applications.

Metal 3D printing based on the photopolymerization reaction (Digital Light Processing—DLP) of an organic matrix in which metal particles are embedded is a developing technology. This technology requires a step of resin removal and densification by sintering to obtain a metal part. This process has been applied to copper. Photocurable formulations with a high loading rate of copper powder of 60 vol.% were developed and suitable for DLP printing with thicknesses > 25 µm. Debinding and sintering cycles were investigated on specimens fast cured by gamma irradiation to save materials and time. A debinding in air at 400 °C and sintering in hydrogen lead to a C content of 0.018 wt.%, similar to the raw copper powder and slightly higher oxygen content. The low thermal conductivity of 250 W·m⁻¹·K⁻¹ highlighted the harmful effect of phosphorus from the powder and photoinitiators such as BAPO. The C and O contents and the thermal conductivity measured on copper parts printed by DLP confirm the results obtained on specimens cured by gamma irradiation.

A commercially available methylphenylvinylhydrogen polysiloxane preceramic polymer was cross-linked and pyrolyzed in argon in order to study if this compound could be used as an organic precursor for the manufacture of silicon carbide parts by photopolymerisation-based three-dimensional printing. X-Ray diffraction experiments and transmission electron microscopy observations showed that the pyrolyzed material was constituted by an interconnected polycrystalline network made of faulted/twinned β-SiC grains surrounded by an amorphous and porous second phase mainly constituted (at least 80 at%) of carbon. The free carbon residual content was estimated to be around 17.2 wt%. Additional efforts are then required to be able to use such a preceramic polymer to manufacture SiC parts by photopolymerisation-based three-dimensional printing.

This work describes the formation of submicrometer pore arrays using nanoimprint lithography and photoelectrochemical etching of n-type silicon in a hydrofluoric acid electrolyte. This work highlights more specifically the link between silicon resistivity and pore geometry. A properly chosen silicon resistivity is shown to ensure a stable pore growth and to limit damages in pore walls due to electrical breakdown and photogenerated carrier diffusion. Well ordered pore arrays with a depth up to 20μm20μm and a period of 1μm1μm , 750nm750nm , and 500nm500nm have been fabricated using silicon wafers with resistivities of 0.76, 0.35, and 0.15Ωcm0.15Ωcm , respectively.