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Design, thermal shock resistance of dense BaO‐Al 2 O 3 ‐SiO 2 glass/Si 3 N 4 ‐barium feldspar coating for porous Si 3 N 4 ceramic
Author(s) -
Tong Zongwei,
Liu Zhengdao,
Yu Huijun,
Zhang Baojie,
Li Xiaolei,
Su Dong,
Ji Huiming
Publication year - 2021
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17724
Subject(s) - materials science , thermal expansion , thermal shock , sintering , coating , composite material , dielectric , silicon nitride , ceramic , silicon , monoclinic crystal system , mineralogy , metallurgy , crystal structure , layer (electronics) , crystallography , optoelectronics , chemistry
Silicon nitride‐monoclinic barium feldspar (Si 3 N 4 ‐m‐BAS) composite possesses great dielectric properties, low density, and low thermal expansion coefficient (CTE). Preparing dense Si 3 N 4 ‐m‐BAS coating on porous Si 3 N 4 ceramic is an effective strategy to improve its water resistance and ensure its dielectric performances. However, this promising coating has not been reported yet, because the synthesis of m‐BAS is difficult, and the densification of Si 3 N 4 ‐BAS composite requires very high temperature. Here, the BaO‐Al 2 O 3 ‐SiO 2 glass/Si 3 N 4 ‐BAS coating was first fabricated by a manual spray method and pressureless sintering at 1450°C. Combining the influence of Si 4+ on the crystal phase composition of BAS and the volume expansion effect of silicon in N 2 , an effective coating structure design scheme was proposed. By changing the content of silicon powder, the CTE and horizontal shrinkage of the coating during sintering were controlled. Besides, the prepared coatings exhibited low water absorption and high bonding strength. During the thermal shock tests, SiO 2 produced by the oxidation of Si 3 N 4 healed the cracks in the coating, thus delaying the degradation of the properties. The coating prepared in this work is expected to be applied to radome in extreme service environments.