Thermal and mechanical properties of Si3N4 ceramics obtained via two-step sintering. Issue 13 (1st July 2022)

• Record Type: Journal Article
• Authors: Wang, Yuelong; Tian, Jianjun; Wu, Haoyang; Jia, Baorui; Li, Xingyu; Zhang, Yiming; Zhang, Zhirui; Qu, Xuanhui; Qin, Mingli
• Is Part Of: Ceramics international. Volume 48:Issue 13(2022)
• Page Start: 18294
• Page End: 18301
• Publication Date: 2022-07-01
• Subjects: Silicon nitride -- Two-step sintering -- Secondary phase -- Oxygen content -- Thermal conductivity; Ceramics -- Periodicals; Céramique industrielle -- Périodiques; Ceramics; Periodicals; Electronic journals; 666
• DOI: 10.1016/j.ceramint.2022.03.088
• Languages: English
• ISSNs: 0272-8842

Abstract

Abstract: Si3 N4 ceramics were prepared using novel two-step sintering method by mixing α -Si3 N4 as raw material with nanoscale Y2 O3 –MgO via Y(NO3 )3 and Mg(NO3 )2 solutions. Si3 N4 composite powders with in situ uniformly distributed Y2 O3 –MgO were obtained through solid–liquid (SL) mixing route. Two-step sintering method consisted of pre-deoxidization at low temperature via volatilization of in situ-formed MgSiO3 and densification at high temperature. Variations in O, Y, and Mg contents in Si3 N4 –Y2 O3 –MgO during first sintering step are discussed. O and Mg contents decreased with increasing temperature because SiO2 on Si3 N4 surface reacted with MgO to form low-melting-point MgSiO3 compound, which is prone to volatilize at high temperature. By contrast, Y content hardly changed due to high-temperature stability of Y–Si–O–N quaternary compound. In the second sintering step, skeleton body was densified, and the formation of Y2 Si3 O3 N4 secondary phase occurred simultaneously. Two-step sintered Si3 N4 ceramics had lower total oxygen content (1.85 wt%) than one-step sintered Si3 N4 ceramics (2.51 wt%). Therefore, flexural strength (812 MPa), thermal conductivity (92.1 W/m·K), and fracture toughness (7.6 MPa⋅m 1/2 ) of Si3 N4 ceramics prepared via two-step sintering increased by 28.7%, 16.9%, and 31.6%, respectively, compared with those of one-step sintered Si3 N4 ceramics.