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Cold sintering and microwave dielectric properties of dense HBO 2 ‐ II ceramics
Author(s) -
Hong Wen Bin,
Li Lei,
Yan Han,
Chen Xiang Ming
Publication year - 2019
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.16450
Subject(s) - relative density , sintering , ceramic , materials science , relative permittivity , dielectric , analytical chemistry (journal) , dissolution , phase (matter) , permittivity , composite material , mineralogy , chemistry , chromatography , organic chemistry , optoelectronics
HBO 2 ‐ II ceramics were prepared by cold sintering with 10wt% dehydrated ethanol as the transient liquid phase. When the processing temperature is 30°C, the relative density of the mechanically robust HBO 2 ‐ II ceramics increases from 77.5% to 84.5% with increasing the uniaxial pressure from 200 to 500 MP a. It changes less than 0.2% for higher pressure up to 700 MP a. Under a constant uniaxial pressure of 500 MP a, the relative density further increases to 94.7% for the processing temperature of 120°C. HBO 2 ‐I is observed as the secondary phase when the processing temperature is 150°C. In comparison, the compacts prepared in the absence of ethanol are fragile, and the relative densities are 78.5%‐84.5% for the processing temperatures of 30‐120°C and uniaxial pressure of 500 MP a. It is indicated that ethanol promotes the densification significantly through the dissolution‐precipitation mechanism. The permittivity increases with increasing the processing temperature, while the Qf value decreases. The optimal properties with the relative density of 94.7%, ε r = 4.21, Qf = 47 500 GH z, and τ f = −70.0 ppm/°C were obtained in the single‐phase HBO 2 ‐ II ceramics cold sintered at 120°C under 500 MP a for 10 minutes. The relative density and Qf value are significantly higher than those of the HBO 2 ‐ II ceramic prepared by sintering the H 3 BO 3 compact at 180°C for 2 hours (70.3% and 32 700 GH z, respectively). The results indicate that the nonaqueous solvent can also be used as the transient liquid phase for cold sintering, so that more materials that are unstable or insoluble in water can be densified by this method.