Rapid pressureless sintering of zirconia ceramics with percolative graphene-like networks
Abstract
Natural cellulose nanofibers (CNF) have emerged as alternatives to synthetic carbon nanofillers in ceramic matrix composites (CMC). They offer homogeneous dispersion and can graphitize in situ during pressure-assisted spark plasma sintering (SPS) into a 3D electrically percolating graphene-like network within a highly refined ceramic matrix. Unlike graphene, they are not prone to anisotropic alignment under pressure. However, translating this concept from pressure-assisted to pressureless SPS (pSPS) remains challenging. The absence of external pressure may limit stress-assisted in situ graphitization of CNF. Here, we investigate the effect of pSPS heating rate (5–750 °C/min) on densification, microstructural evolution, graphitization, and electrical properties in CNF-containing zirconia matrix. Raman spectroscopy confirmed graphitization of CNF within dense zirconia, irrespective of heating rate. The resulting graphitic phase acted as a diffusion barrier, slightly reducing density by 2-4% while refining the grain size from 200 to 155 nm. High heating rates promoted spatial organization of graphitized CNF into an intergranular, few-layer graphene-like network. This is attributed to the heating-rate-driven evolution of thermal von Mises stresses, from 23-100 MPa, which activate graphitization under pressureless sintering conditions. Consequently, electrical percolation was achieved at ≥100 °C/min, yielding DC conductivities of 5-15 S/m. These findings establish a critical link among transient thermal stress, in situ CNF graphitization, and electrical percolation, thereby providing a pressureless, rapid-sintering strategy for CMCs fabrication.
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BibTeX
@article{bhootpur2026rapid,
title = {{Rapid pressureless sintering of zirconia ceramics with percolative graphene-like networks}},
author = {Nikhil Bhootpur and Charles Manière and Sandra Drev and Marjeta Maček Kržmanc and Tadej Rojac and Aljaž Iveković and Bernd Wicklein and Andraž Kocjan},
journal = {Carbon},
year = {2026},
month = sep,
doi = {10.1016/j.carbon.2026.122140},
url = {https://hal.science/hal-05763191v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Rapid pressureless sintering of zirconia ceramics with percolative graphene-like networks
AU - Nikhil Bhootpur
AU - Charles Manière
AU - Sandra Drev
AU - Marjeta Maček Kržmanc
AU - Tadej Rojac
AU - Aljaž Iveković
AU - Bernd Wicklein
AU - Andraž Kocjan
PY - 2026
DA - 2026/09/21
JO - Carbon
DO - 10.1016/j.carbon.2026.122140
UR - https://hal.science/hal-05763191v1
AB - Natural cellulose nanofibers (CNF) have emerged as alternatives to synthetic carbon nanofillers in ceramic matrix composites (CMC). They offer homogeneous dispersion and can graphitize in situ during pressure-assisted spark plasma sintering (SPS) into a 3D electrically percolating graphene-like network within a highly refined ceramic matrix. Unlike graphene, they are not prone to anisotropic alignment under pressure. However, translating this concept from pressure-assisted to pressureless SPS (pSPS) remains challenging. The absence of external pressure may limit stress-assisted in situ graphitization of CNF. Here, we investigate the effect of pSPS heating rate (5–750 °C/min) on densification, microstructural evolution, graphitization, and electrical properties in CNF-containing zirconia matrix. Raman spectroscopy confirmed graphitization of CNF within dense zirconia, irrespective of heating rate. The resulting graphitic phase acted as a diffusion barrier, slightly reducing density by 2-4% while refining the grain size from 200 to 155 nm. High heating rates promoted spatial organization of graphitized CNF into an intergranular, few-layer graphene-like network. This is attributed to the heating-rate-driven evolution of thermal von Mises stresses, from 23-100 MPa, which activate graphitization under pressureless sintering conditions. Consequently, electrical percolation was achieved at ≥100 °C/min, yielding DC conductivities of 5-15 S/m. These findings establish a critical link among transient thermal stress, in situ CNF graphitization, and electrical percolation, thereby providing a pressureless, rapid-sintering strategy for CMCs fabrication.
SN - 0008-6223
ER -