Stability and electrical properties of MoSi₂‐ and WSi₂‐oxide electroconductive composites

Abstract

MoSi 2 -and WSi 2 -based electroconductive ceramic composites were fabricated using 40-80 vol% fine-and coarse-Al 2 O 3 , and ZrO 2 particles (refractory oxides) after sintering in argon. Their chemical and thermal stability was tested between 1400°C-1600°C for up to 48 hours. X-ray diffraction analysis showed the formation of secondary 5-3 metal silicide (Mo 5 Si 3 , W 5 Si 3 ) and silica phases on the grain boundaries and surface. The fraction of the W 5 Si 3 (11.4-38.8 vol%) was significantly higher than that of the Mo 5 Si 3 (3.3-7.3 vol%) in the composites after annealing at 1400°C for 48 hours. The rates of grain growth in the composites (0.013-0.023 lm/h) were highly decreased by a grain-boundary pinning effect.This effect was relatively better with the addition of the coarse-grained oxides due to their more homogeneous distribution throughout the microstructure. The 20-80 vol% MoSi 2 -Al 2 O 3 (fine-grained) composite exhibited an electrical conductivity of 8.8 S/cm at 900°C. At the 60 vol% silicide content, MoSi 2 -Al 2 O 3 (coarse-grained) and WSi 2 -Al 2 O 3 (fine-grained) showed higher electrical conductivity (126-128 S/cm) at 900°C. The density, porosity level, particle distribution, intrinsic conductivity of silicide phase, particle size, and fraction of the secondary 5-3 silicide phase highly influenced their electrical properties.

Fabrication and Thermoelectric Characterization of Transition Metal Silicide-Based Composite Thermocouples

“…However, the XRD pattern of the ZrSi 2 -Al 2 O 3 composite showed a different trend, since zirconium monosilicide (ZrSi) and silicon (Si) phases were identified as secondary phases after sintering. The secondary phase formation was found to be related to the interaction of metal silicides with alumina, as well as their reaction with environmental sources such as residual oxygen entrapped in pores or starting silicide powders [15,16,17,18]. In the case of the ZrSi 2 -Al 2 O 3 system, it may be also correlated to the possible presence of residual zirconium monosilicide (ZrSi) phase in the starting powder and its relatively low melting point (~1500–1520 °C) compared to that of ZrSi 2 (1620 °C) [19].…”

“…It is known from the authors’ previous studies [15,21] that these metal silicides have random morphology with 4.2–6.4 µm average particle size, whereas alumina particles have equiaxed morphology and an average size of 0.4 µm. Therefore, the agglomeration of large (silicide) and small (alumina) grains was evident in certain regions for all composite microstructures.…”

Mechanical and electrical properties of 3Y‐TZP/TiSi2 composites sintered at different temperatures

“…They found that the room temperature and high‐temperature fracture toughness can reach 6.46 and 21.881 MPa m 0.5 , respectively. Yakaboylu et al 13,14 . studied the stability and electrical properties of MoSi 2 and WSi 2 with 40–80 vol.% fine and coarse Al 2 O 3 , and ZrO 2 particles.…”

“…They found that the room temperature and high-temperature fracture toughness can reach 6.46 and 21.881 MPa m 0.5 , respectively. Yakaboylu et al 13,14 studied the stability and electrical properties of MoSi 2 and WSi 2 with 40-80 vol.% fine and coarse Al 2 O 3 , and ZrO 2 particles. Then they reported the phase stability, microstructural evolution, oxidation kinetics, and electrical properties of TaSi 2 and NbSi 2 with the addition of 40-70 vol.% Al 2 O 3 and ZrO 2 particles for future hightemperature applications in advanced sensing and the high-temperature electrical conductivities of these composites at 900 • C ranged from 5.3 to 111.3 S/cm.…”