No abstract

No abstract

No abstract

No abstract

No abstract

Densification kinetics by spark plasma sintering (SPS) and hot pressing (HP) have been compared, under isothermal conditions and with heating rates of 20°C/min. Careful calibration of sample temperature has been carried out to obtain comparable results. In all cases, densification kinetics did not exhibit significant differences, ruling out any influence of the SPS current. The stress exponent n and the activation energy Q of the Norton law describing deformation at high temperature of the powder particles have been determined by isothermal experiments at different stresses and temperatures, respectively. The values obtained, n = 1.9 ± 0.3 and Q = 308 ± 20 kJ/mol for SPS, n = 1.5 ± 0.3 and Q = 276 ± 40 kJ/mol for HP, come close in both techniques. Using these values, anisothermal densification kinetics at heating rates of 20°C/ min and 100°C/min, typical of the SPS, could be analytically reproduced, using literature models. The activation parameters suggest that *Text only Click here to download Text only: monchoux_article_version2.docx Click here to view linked References 2 SPS densification kinetics occurs by dislocation climb controlled by Al bulk diffusion, that is, by classical metallurgical mechanisms.

No abstract

Within the context of emergent researches linked to graphene, it is well known that h-BN nanosheets (BNNSs), also referred as 2D BN, are considered as the best candidate for replacing SiO2 as dielectric support or capping layers for graphene. As a consequence, the development of a novel alternative source for highly crystallized h-BN crystals, suitable for a further exfoliation, is a prime scientific issue. This paper proposes a promising approach to synthesize pure and well-crystallized h-BN flakes, which can be easily exfoliated into BNNSs. This new accessible production process represents a relevant alternative source of supply in response to the increasing need of high quality BNNSs. The synthesis strategy to prepare pure h-BN is based on a unique combination of the Polymer Derived Ceramics (PDCs) route with the Spark Plasma Sintering (SPS) process. Through a multi-scale chemical and structural investigation, it is clearly shown that obtained flakes are large (up to 30 μm), defect-free and well crystallized, which are key-characteristics for a subsequent exfoliation into relevant BNNSs.