Sintered reaction-bonded silicon nitrides with high thermal conductivity: The effect of the starting Si powder and Si3N4 diluents

Effects of yttria and magnesia on densification and thermal conductivity of sintered reaction‐bonded silicon nitrides

“…However, little attention had been paid to its thermal conduction property and it was not classified as a high thermal conductivity ceramic such as AlN and SiC. Recent studies have shown that thermal conductivity of silicon nitride ceramic could be drastically improved through minimizing impurity content and tailoring microstructure when prepared by a sintering of reaction‐bonded silicon nitride (SRBSN) method . By the SRBSN method, a silicon nitride ceramic attained a record‐high thermal conductivity of 177 Wm −1 K −1 , while it possessed a fracture toughness as high as 11.2 MPa·m 1/2 .…”

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).…”

“…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.…”

“…Consequently, high thermal conductivities of 90-177 W m À1 K À1 have been successfully achieved in the recent studies. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] However, most of the Si 3 N 4 ceramics with thermal conductivities of ≥120 W m À1 K À1 have been prepared by complicated processes or extended heat-treatment at high temperature, which induced low reliability and high cost.…”