System Molybdenum-Boron and Some Properties of The Molybdenum-Borides

Steinitz, Robert; Binder, I.; Moskowitz, D.

doi:10.1007/bf03397758

Cited by 30 publications

(42 citation statements)

References 7 publications

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“…16,20,37 The RS A was evidently ∼153 meV/atom lower in enthalpy than that of the AlB 2 -type structure at ambient pressure. This suggests that MoB 2 is beyond the upper stable limit of hexagonal 4d transition metal diborides, for which the boron-deficient compound MoB 2-x (0 < x < 1) with AlB 2 -type structure can be easily obtained.…”

Section: Resultsmentioning

confidence: 94%

Structural Modifications and Mechanical Properties of Molybdenum Borides from First Principles

et al. 2010

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On the basis of the evolutionary methodology for crystal structure prediction, we have clarified the longstanding debates on the ground state structures of technically important molybdenum borides: MoB 2 , Mo 2 B 5 , and MoB 4 . The earlier proposed rhombohedral structure for Mo 2 B 5 and WB 4 -type structure for MoB 4 are ruled out. Instead, two novel hexagonal P6 3 /mmc structures are proposed. Moreover, the yet synthesized MoB 3 was found to adopt the intriguing rhombohedral R3 j m structure and was suggested to be experimentally synthesizable by the calculation of convex hull. Density of states calculation revealed that the strong covalent bonding between Mo and B atoms is the driving force for the high bulk and shear modulus as well as small Poisson's ratio of the studied borides. The hardness calculations suggest that these borides are all hard materials, among which MoB 3 exhibits the largest Vickers hardness of 31.8 GPa, exceeding the hardness of R-SiO 2 (30.6 GPa) and -Si 3 N 4 (30.3 GPa).

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Section: Resultsmentioning

confidence: 94%

Structural Modifications and Mechanical Properties of Molybdenum Borides from First Principles

et al. 2010

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“…The powder X‐ray diffraction patterns (PXRD) of the CeMo 2 B 5 sample annealed at different temperatures are depicted in Figure . Since the as‐cast sample obtained after arc‐melting [micrograph is shown in inset (a) to Figure ] as well as those annealed at 1770 K contained exclusively binary CeB 4 , MoB, CeB 6 or an unidentified phase, one can conclude that the targeted ternary compound is not forming congruently (i.e. directly from the melt).…”

Section: Resultsmentioning

confidence: 99%

CeMo₂B₅: A New Type of Arrangement of Puckered Boron Hexagonal Rings

et al. 2019

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REMo 2 B 5 (RE = Ce, Pr, Nd) and CeW 2 B 5 have been synthesized by arc melting with further annealing at 1300°C. CeMo 2 B 5 crystallizes in a new structure type with space group Pnma, a = 11.0298(2) Å, b = 3.12080(5) Å, c = 9.9594(2) Å, Z = 4. Its structural arrangement reveals puckered [B 6 ]-hexagonal rings, trigonal-prismatic-and empty pyramidal-tetrahedralslabs. The structure can be related to the derivatives of AlB 2 and CrB prototypes. The boron atoms form a two-dimensional network of corrugated ribbons, each composed of four edgelinked [B 6 ] rings infinitely extending along the b-axis. CeMo 2 B 5[a]

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“…18 The thermal expansion coefficients of MoB 2 and Mo 2 B 5 are 7.7 × 10 −6 K −1 and 8.6-9.9 × 10 −6 K −1 , respectively, 30 which are much larger than that of B 4 C. Therefore, when cracks propagate to the independently distributed MoB 2 /Mo 2 B 5 phase, intergranular fracture occurs ( Figure 6A). 21,31 In this process, the residual stress is formed, leading to the unstable bonding in the interior of the molybdenum borides. MoB 2 /Mo 2 B 5 is formed by the in situ reaction in the process of reactive hot pressing.…”

Section: Toughening Mechanism Analysismentioning

confidence: 99%

“…In addition, Mo 2 B 5 is unstable and it can transform into MoB 2 at high temperature. 21,31 In this process, the residual stress is formed, leading to the unstable bonding in the interior of the molybdenum borides. Hence, the cracks prefer to extend along the relatively weaker interior of MoB 2 / Mo 2 B 5 grains rather than the boundary of MoB 2 /Mo 2 B 5 and B 4 C. As crack propagates to the interlocking structure of MoB 2 /Mo 2 B 5 -SiC, the phenomenon of crack bridging occurs ( Figure 6B).…”

Section: Toughening Mechanism Analysismentioning

confidence: 99%

Preparation of B₄C composites toughened by MoB₂/Mo₂B₅‐SiC interlocking structure via reactive hot pressing

Wang

Li²,

Xing

et al. 2019

Int J Applied Ceramic Tech

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B 4 C composites toughened by MoB 2 /Mo 2 B 5 -SiC interlocking structure were prepared via reactive hot pressing with B 4 C and MoSi 2 as raw materials. The phase composition, microstructure, and mechanical properties of the fabricated B 4 C composites were studied. The crack propagation and fracture surface were observed, and the toughening mechanism was analyzed. The results indicate that the interlocking structure of MoB 2 /Mo 2 B 5 -SiC is formed in the obtained B 4 C composites. The relative density, flexural strength, and fracture toughness of the B 4 C composites reach 99.3%, 480 MPa, and 5.2 MPa·m 1/2 , respectively, when the MoSi 2 content is 30 wt%.The hardness is 33 GPa when the MoSi 2 content is 20 wt%. The special laminar fracture of the interlocking structure of MoB 2 /Mo 2 B 5 -SiC elongates the crack extending path and thus consumes more energy of crack extension. The phenomena of crack bridging and branching and the special laminar fracture of the interlocking structure have a synergistic effect on promoting the overall fracture toughness. K E Y W O R D SB 4 C composites, hot pressing, interlocking structure, MoSi 2

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System Molybdenum-Boron and Some Properties of The Molybdenum-Borides

Cited by 30 publications

References 7 publications

Structural Modifications and Mechanical Properties of Molybdenum Borides from First Principles

Structural Modifications and Mechanical Properties of Molybdenum Borides from First Principles

CeMo₂B₅: A New Type of Arrangement of Puckered Boron Hexagonal Rings

Preparation of B₄C composites toughened by MoB₂/Mo₂B₅‐SiC interlocking structure via reactive hot pressing

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System Molybdenum-Boron and Some Properties of The Molybdenum-Borides

Cited by 30 publications

References 7 publications

Structural Modifications and Mechanical Properties of Molybdenum Borides from First Principles

Structural Modifications and Mechanical Properties of Molybdenum Borides from First Principles

CeMo2B5: A New Type of Arrangement of Puckered Boron Hexagonal Rings

Preparation of B4C composites toughened by MoB2/Mo2B5‐SiC interlocking structure via reactive hot pressing

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Product

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About

CeMo₂B₅: A New Type of Arrangement of Puckered Boron Hexagonal Rings

Preparation of B₄C composites toughened by MoB₂/Mo₂B₅‐SiC interlocking structure via reactive hot pressing