Thermal Conductivity and Mechanical Property of Si₃N₄ Ceramics Sintered with CeF₃/LaF₃ Additives

Abstract

In this paper, rare-earth fluorides were used as sintering additives instead of rare-earth oxides, the influence of the type and the amount of the fluoride on the thermal conductivity, hardness and strength of Si3N4 ceramics was studied. Results show that the thermal conductivity of a sample sintered with CeF3 is nearly 10% higher than that of the sample sintered with Ce2O3, while the samples sintered with LaF3 increases further 15% as comparing with the samples sintered with CeF3. The strength of the samples changes reversely. These results express that the thermal conductivity of Si3N4 ceramics can be improved by using rare-earth fluoride additives instead of the oxides, and the type of rare-earth fluorides has a significant impact on the properties of Si3N4 ceramics.

Enhanced thermal conductivity in Si3N4 ceramic with the addition of Y2Si4N6C

“…However, this positive effect was possibly weakened by the thermal unstability of MgSiN 2 , due to the fact that the decomposition of MgSiN 2 starts at ~1400°C while the sintering temperature of the MgSiN 2 ‐doped Si 3 N 4 ceramics is usually 1900°C . Besides, the use of rare‐earth fluorides instead of the corresponding rare‐earth oxides as additives could enhance the thermal conductivity of Si 3 N 4 ceramic as well . This was because the rare‐earth fluorides reacted with SiO 2 impurity to form rare‐earth oxides and volatile SiF 4 (g), resulting in a decreased oxygen concentration in liquid phase .…”

“…27,28 This was because the rare-earth fluorides reacted with SiO 2 impurity to form rare-earth oxides and volatile SiF 4 (g), resulting in a decreased oxygen concentration in liquid phase. 27 Unfortunately, fluoride additives are generally toxic to the biological system, 29 which limits the mass production of these Si 3 N 4 materials. Therefore, more suitable and effective auxiliaries are still necessarily required to improve the thermal conductivity of Si 3 N 4 ceramic.…”

“…Besides, the use of rare‐earth fluorides instead of the corresponding rare‐earth oxides as additives could enhance the thermal conductivity of Si 3 N 4 ceramic as well . This was because the rare‐earth fluorides reacted with SiO 2 impurity to form rare‐earth oxides and volatile SiF 4 (g), resulting in a decreased oxygen concentration in liquid phase . Unfortunately, fluoride additives are generally toxic to the biological system, which limits the mass production of these Si 3 N 4 materials.…”

Effect of β-Si₃N₄ Powder on Thermal Conductivity of Silicon Nitride Ceramics

“…Compared with conventional techniques, this method could develop unique Si 3 N 4 with graded mechanical properties and have the possibility of getting complete densification [14]. Processing parameters to get high-thermal-conductivity silicon nitrides were systematically studied in previous work [15,16,17] and are therefore continued in this study.…”