Thermal expansion of α-boron and some boron-rich pnictides

Abstract

Thermal expansion of α-rhombohedral boron (α-B12) and two isostructural boron-rich pnictides (B12P2 and B12As2) has been studied between 298 and 1280 K by high-temperature synchrotron X-ray diffraction. For all studied phases no temperature-induced phase transitions have been observed. The observed temperature dependencies of the lattice parameters and unit cell volumes were found to be quasi-linear. Variation of the thermal expansion coefficients in the group of boron-rich pnictides (B13N2 -B12P2 -B12As2) was analyzed.

Phase Composition, Structure and Properties of the Spark Plasma Sintered Ceramics Obtained from the Al12Mg17-B-Si Powder Mixtures

“…It was found that with an increase in the Al 12 Mg 17 -B powder content in the initial powder mixture, the hardness of sintered materials increases. This is due to the formation of compounds based on B 12 icosahedrons (AlB 12 , B 4 Si, B 6 Si) with high hardness [ 3 , 4 , 5 ]. At a content of 70 wt% of Al 12 Mg 17 -B powder in the initial mixture, the hardness of the composite reaches 21.24 ± 1.22 GPa.…”

“…Higher borides belong to the group of compounds based on B 12 icosahedrons. The main compounds based on B 12 icosahedrons are AlB 12 , B 12 C 3 (B 4 C), B 12 Si 3 , B 12 Si 2 (B 4 Si and B 6 Si), and B 12 O 2 (B 6 O) [ 3 , 4 , 5 , 6 , 7 , 8 ]. These compounds exhibit excellent properties at relatively low densities, have extremely high melting points due to the strong bonds of intra- and interclusters B 12 [ 4 ].…”

“…The main compounds based on B 12 icosahedrons are AlB 12 , B 12 C 3 (B 4 C), B 12 Si 3 , B 12 Si 2 (B 4 Si and B 6 Si), and B 12 O 2 (B 6 O) [ 3 , 4 , 5 , 6 , 7 , 8 ]. These compounds exhibit excellent properties at relatively low densities, have extremely high melting points due to the strong bonds of intra- and interclusters B 12 [ 4 ]. Thus, in [ 5 ], the obtained higher aluminum dodecaborides (AlB 12 ) demonstrated excellent hardness from 20 to 30 GPa, and in combination with titanium carbide, the hardness of the AlB 12 + 20% TiC composite reached 40 GPa at indentation fracture resistance of 5.2 MPa m 1/2 .…”

Coupling of lattice dynamics and configurational disorder in metal deficient Al1−δB2 from first-principles

“…54 For α-B, we get a ¼ 5:07 in the QHA at 298 K, while experiments show a ¼ 5:0623(3) Å. 55 The overestimation for fcc-Al and α-B is 0.49% and 0.15%, respectively. For stoichiometric AlB 2 , the overestimation is, on average, 0.50% for a and 1.64% for c. Meanwhile, for the isostructural diboride TiB 2 , a similar comparison between experiments and theory on the quasiharmonic level using GGA yields an overestimation of only 0.40% and 0.39% for the a and c lattice parameters, respectively.…”

Rapid liquid phase–assisted ultrahigh-temperature sintering of high-entropy ceramic composites

“…However, mechanical properties of the composites, such as the hardness, show no pronounced improvement even as the mass ratio of boron carbide or other additives is substantially increased under conventional sintering scenarios, which might be owing to the entrapped porosity present in additives (24,25). Other factors such as the inconsistency of the thermal expansion coefficients of the matrix and additive components can further exacerbate the interface mismatches between the diboride and additive phases (26)(27)(28), compromising the mechanical properties of the composites.…”