Thermodynamic descriptions of the light rare‐earth elements in silicon carbide ceramics

Abstract

The Y3Si2C2 coating on the silicon carbide (SiC) powders is reported to improve the sintering process, but the relatively high sintering temperature (1600°C) restricts the engineering application. A series of thermodynamic descriptions for the SiC with light rare‐earth elements are desired to develop potential SiC‐RE3Si2C2 core‐shell structures as sintering aids with lower temperatures. Coupling the CALPHAD (CALculation of PHAse Diagram) approach and first‐principles calculations, we have investigated the RE‐Si‐C (RE = La, Ce and Pr) systems. In the SiC‐RE3Si2C2 core‐shell structures, the RE3Si2C2 phases can react with SiC via ternary eutectic reactions at 810°C, 747°C, and 1148°C respectively. The predicted thermal behaviors of the Pr3Si2C2 phase were further confirmed by our key experiments. Therefore, our database can be used to predict promising sintering aids and guide the subsequent processes.

Low‐temperature Pr3Si2C2‐assisted liquid‐phase sintering of SiC with improved thermal conductivity

“…No Pr 3 Si 2 C 2 phase was detected in the specimens after sintering. This can be explained by the fact that, according to the calculated Pr–Si–C phase diagram (Figure 4), Pr 3 Si 2 C 2 melts at the temperature of ∼1217°C, resulting in the formation of thermodynamically more stable Si–C and Pr–C phases 28 . The Pr–C phase could be oxidized by the oxygen present on the surface of SiC to form Pr–C–O and/or Pr–O phases, as shown in Figure 3.…”

“…On the other hand, Pr 3 Si 2 C 2 is a relatively stable compound. Furthermore, Pr 3 Si 2 C 2 melts at the temperature around 1217°C 28 . This indicates that it might be possible to obtain a near fully dense SiC ceramic material at a temperature under 1500°C when Pr 3 Si 2 C 2 is used as the sintering additive.…”

“…Therefore, the aim of this study was to develop a novel sintering additive for SiC, which can facilitate the consolidation of SiC at low temperatures. In our recent theoretical work, a series of light rare‐earth silicon carbides (RE 3 Si 2 C 2 , where RE = La, Ce, and Pr) were predicted as potential sintering additives for liquid‐phase sintering of SiC ceramics 28 . This was concluded based on the fact that according to the calculated phase diagram of RE–Si–C system, RE 3 Si 2 C 2 can form a liquid phase via ternary eutectic reactions between RE 3 Si 2 C 2 and SiC at 810°C (La 3 Si 2 C 2 ), 747°C (Ce 3 Si 2 C 2 ), and 1148°C (Pr 3 Si 2 C 2 ), respectively 28 .…”

Development of robust surfaces for harsh service environments from the perspective of phase formation and transformation

“…The successful development of Y 3 Si 2 C 2 as a sintering aid has stimulated the exploration for more efficient aids based on rare earth (RE)-containing metallic compounds, RE 3 Si 2 C 2 (RE = La-Nd, Sm and Gd-Tm) [97] . Xu et al [98,99] further compared the effectiveness of Dy, Pr and La incorporated sintering aids on lowering the densification temperature of SiC by examining the vertical sections of RE-SiC using the CALPHAD [96,98,99] with permissions from Elsevier and John Wiley & Sons.…”

“…Temperature of the reaction between RE 3 Si 2 C 2 and SiC at which the liquid phase starts to form is labelled in each diagram. Figure reproduced from Refs [96,98,99]. with permissions from Elsevier and John Wiley & Sons.…”