Études sur le carbure de bore iii. domaine d'existence de la phase carbure de bore

Bouchacourt, M.; Thévenot, F.; Ruste, J.

doi:10.1016/0022-5088(78)90126-1

Cited by 31 publications

(8 citation statements)

References 18 publications

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“…The composites consisted of two phases, B 4 C and SiC (β-type). It is known that boron carbide has a wide non-stoichiometric range (9-20 at%C), 8) and the lattice parameters depend on the composition. 9,10) The lattice parameters of boron carbide in the B 4 C-SiC composites were in agreement with those of stoichiometric B 4 C (i.e., a = 0.561 nm and c = 1.209 nm in hexagonal expression).…”

Section: Methodsmentioning

confidence: 99%

Characterization of Directionally Solidified B<SUB>4</SUB>C-SiC Composites Prepared by a Floating Zone Method

2002

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Directionally solidified B 4 C-SiC composites were prepared by a Floating Zone method. The lamellar texture was observed at 53 mol%SiC. The c-axis of B 4 C phase was tilted 20 • to the growth direction. The (102) plane and [121] direction of the B 4 C phase were parallel to the (311) plane and [121] direction of the SiC phase, respectively. The thermal conductivity of the composite parallel to the growth direction (κ ) was about twice as great as that of monolithic B 4 C. The anisotropy of electrical conductivity and thermal conductivity were explained by a mixing law using the values of B 4 C and SiC. The mass gain due to oxidation was about 1/3 to 1/5 less than that of monolithic B 4 C at 1023 K. The surface perpendicular to the growth direction showed slightly better oxidation resistance than that parallel to the growth direction. The microhardness of the composite was almost the same as that of B 4 C.

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Section: Methodsmentioning

confidence: 99%

Characterization of Directionally Solidified B<SUB>4</SUB>C-SiC Composites Prepared by a Floating Zone Method

2002

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“…1,2 In the literature, there is a general agreement about the existence of solid solubility of carbon with the stable phase B x C, and a large range extending from 8 to 20 at %C. 3 So, Aselage et al 2 have established an abacus that relates the cell parameters to the B/C atomic ratio in the boron carbide.…”

Section: Introductionmentioning

confidence: 99%

“…Several authors emphasized the effect of the boron carbide stoichiometry on its hardness. Bouchacourt et al have demonstrated that, for measured B/C ratios >4 (i.e., for stoichiometries ranging between B 8.9 C:10.1 wt% of C to B 4 C:20 wt% of C), the rise of carbon in the B x C phase involved an increase in the values of Vickers hardness from 29 to 38 GPa. This trend was also observed by Niihara et al on boron carbide coatings elaborated by Chemical Vapor Deposition for B/C ratios > 4.…”

Section: Introductionmentioning

confidence: 99%

Influence of chemical composition on mechanical properties of spark plasma sintered boron carbide monoliths

et al. 2018

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Fully dense boron carbide monoliths exhibiting fine microstructure (i.e., submicrometric grain size) are sintered by Spark Plasma Sintering. Two different commercial powder batches, exhibiting different stoichiometries (i.e., B/C ratio and oxygen content) and various amounts of secondary phases (i.e., boric acid and free carbon), are used. Their chemical composition is well‐defined by coupling different methods (Transmission Electron Microscopy associated with XRD analyses, and Instrumental Gas Analysis), and are correlated with their mechanical properties, characterized from meso‐ to macro‐scopic scales by nano‐indentation and ultrasonic pulse echography. The presence of secondary phases (graphite and boric acid) is evidenced in various proportions in each powder batch. If the boric acid disappears during sintering, the graphite remains. However, for the considered amounts of graphite (lower than 1 wt%), the low variations in graphite content have no significant effect on hardness and elasticity values. At the opposite, the presence of oxygen in boron carbide lattice, leading to a boron oxycarbide phase, induces a decrease in both hardness and elasticity properties.

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“…Confirmed by several independent experiments [16,28], boron carbide is stable as a single-phase solid solution over a broad composition range. Even though a lot of B-C phase diagrams has been suggested from time to time in the literature [16,[29][30][31][32], they have been being argued among the community. It is however generally accepted that the single-phase region of boron carbide extends from 8 to 20 at.% C approximately.…”

Section: Boron Carbidementioning

confidence: 99%

First-principles study of configurational disorder in icosahedral boron-rich solids

Ektarawong¹

2015

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This thesis is a theoretical study of configurationally disordered icosahedral boronrich solids, in particular boron carbides, using density functional theory and alloy theory. The goal is to resolve discrepancies, regarding the properties of boron carbides, between experiments and previous theoretical calculations which have been a controversial issue in the field of icosahedral boron-rich solids. For instance, B 13 C 2 is observed experimentally to be a semiconductor, meanwhile electronic band structure calculations reveal a metallic character of B 13 C 2 due to its electron deficiency. In B 4 C, on the other hand, the experimentally observed band gap is unexpectedly smaller, not the usual larger, than that of standard DFT calculations. Another example is given by the existence of a small structural distortion in B 4 C, as predicted in theoretical calculations, which reduces the crystal symmetry from the experimentally observed rhombohedral (R3m) to the based-centered monoclinic (Cm). Since boron carbide is stable as a single-phase over a broad composition range (∼8-20 at.% C), substitution of boron and carbon atoms for one another is conceivable. For this reason, the discrepancies have been speculated in the literature, without a proof, to originate from configurational disorder induced by substitutional defects. However, owing to its complex atomic structure, represented by 12-atom icosahedra and 3-atom intericosahedral chains, a practical alloy theory method for direct calculations of the properties of the relevant configurations of disordered boron carbides, as well as for a thermodynamic assessment of their stability has been missing.In this thesis, a new approach, the superatom-special quasirandom structure (SA-SQS), has been developed. The approach allows one to model configurational disorder in boron carbide, induced by high concentrations of low-energy B/C substitutional defects. B 13 C 2 and B 4 C are the two stoichiometries, mainly considered in this study, as they are of particular importance and have been in focus in the literature. The results demonstrate that, from thermodynamic considerations, both B 13 C 2 and B 4 C configurationally disorder at high temperature. In the case of B 13 C 2 , the configurational disorder splits off some valence states into the band gap that in turn compensates the electron deficiency in ordered B 13 C 2 , thus resulting in a semiconducting character. As for B 4 C, the configurational disorder eliminates the monoclinic distortion, thus resulting in the restoration of the higher rhombohedral symmetry. Configurational disorder can also account for an exceliii iv lent agreement on elastic moduli of boron carbide between theory and experiment. Thus, several of the previous discrepancies between theory and experiments are resolved.Inspired by attempts to enhance the mechanical properties of boron suboxide by fabricating boron suboxide-boron carbide composites, as recently suggested in the literature, the SA-SQS approach is used for modeling mixtures of boron sub...

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Études sur le carbure de bore iii. domaine d'existence de la phase carbure de bore

Cited by 31 publications

References 18 publications

Characterization of Directionally Solidified B<SUB>4</SUB>C-SiC Composites Prepared by a Floating Zone Method

Characterization of Directionally Solidified B<SUB>4</SUB>C-SiC Composites Prepared by a Floating Zone Method

Influence of chemical composition on mechanical properties of spark plasma sintered boron carbide monoliths

First-principles study of configurational disorder in icosahedral boron-rich solids

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