Effect of particle size and oxygen content of Si on processing, microstructure and thermal conductivity of sintered reaction bonded Si3N4

Characterization of the Si3N4/Si3N4 joints fabricated using particles modified braze

“…In order to produce Si 3 N 4 components with large size or complex shape, joining becomes a feasible approach. Among the joining methods [2][3][4][5][6], the active brazing method is considered as one of the most promising techniques for joining Si 3 N 4 ceramics to themselves or to metals. Most of the focus on active brazing of Si 3 N 4 ceramic has been directed toward the use of commercial filler alloys based on Ag-Cu eutectic, containing about 2-4 wt% Ti, which readily formed a strong joint [7,8].…”

Enhanced thermal conductivity in Si3N4 ceramic with the addition of Y2Si4N6C

“…Therefore, the replacement of Y 2 O 3 by Y 2 Si 4 N 6 C probably led to an increase in nitrogen/oxygen ratio in the liquid secondary phase during the sintering of Si 3 N 4 ceramic. As previously reported, during the sintering of Y 2 O 3 ‐doped Si 3 N 4 ceramics, Y 2 O 3 would react with SiO 2 and Si 3 N 4 to form Y‐Si‐O‐N liquid phase, and several oxynitride crystalline phases would precipitate from the liquid phase after cooling down. With the increasing N/O ratio in Y‐Si‐O‐N liquid phase, the composition of the precipitated crystalline phase generally changed in the order of Y 5 Si 3 O 12 N (equivalent to 10Y 2 O 3 ∙9SiO 2 ∙Si 3 N 4 , apatite) → YSiO 2 N (2Y 2 O 3 ∙SiO 2 ∙Si 3 N 4 , wallastonite) → Y 2 Si 3 O 3 N 4 (Y 2 O 3 ∙Si 3 N 4 , melilite).…”

“…It is well known that the weight loss of Si 3 N 4 ceramic occurred during sintering was attributed to many factors, including the decomposition of Si 3 N 4 , the evaporation of secondary phases, and the interaction between SiO 2 impurity and Si 3 N 4 . Among them, the last factor was widely recognized to be crucial to the weight loss and the corresponding reaction was given as follows:…”

“…The lattice oxygen content can be reduced through the usage of high‐purity Si 3 N 4 or Si raw materials, effective sintering aids and high‐temperature sintering/annealing with long soaking time. Consequently, high thermal conductivities of 90‐177 W m −1 K −1 have been successfully achieved in the recent studies . However, most of the Si 3 N 4 ceramics with thermal conductivities of ≥120 W m −1 K −1 have been prepared by complicated processes or extended heat‐treatment at high temperature, which induced low reliability and high cost.…”

“…The usage of efficient sintering additives was proved to be a desirable solution for this purpose. The most commonly used sintering aids in high thermal conductive Si 3 N 4 ceramics were rare‐earth oxides (like Y 2 O 3 , Yb 2 O 3 ) and magnesium compounds (MgO, MgSiN 2 ) . These additives would react with the inherent SiO 2 coating of Si 3 N 4 or Si powder, and Si 3 N 4 to form intergranular phases with low melting points, and then promote the densification of Si 3 N 4 ceramics via a solution‐reprecipitation mechanism.…”