Preparation and sealing effects of Mg–Al–Si–Ba–O-based glass-ceramic coatings on NTC thermistors

Abstract

Herein, Mg–Al–Si–Ba–O-based glass ceramics were studied as potential candidates to protect Mn–Co–Ni–O-based negative temperature coefficient (NTC) thermistors at high temperatures such as 900 °C. The ceramics were prepared in three glass formulations (1#: 15MgO–15Al2O3-44.7SiO2–25BaO, 2#: 17MgO–17Al2O3–41SiO2–25BaO and 3#: 17MgO–17Al2O3–41SiO2–20BaO–5Y2O3 (in mol%)) and their glass-transition temperatures (Tg) were determined using the differential scanning calorimetry (DSC) method. Scanning electronic microscopy (SEM) and X-ray diffraction (XRD) were used to characterize the parent glasses and glass-ceramic coatings. The sealing effects of the glass ceramics were examined by conducting an insulation test. The glass-ceramic sealing structures were subjected to 1000 thermal shock cycles at temperatures varying from room temperature to 900 °C. Notably, the sealing structure of glass-ceramic coating 1# was compact at a Tg of 760.9 °C. The glass-ceramic coatings effectively maintained the NTC properties of the sensitive ceramics in all three formulations. Interestingly, the glass-ceramic coating 3# containing Y2O3 demonstrated an increase in electrical resistance. Both the NTC thermistors coated with 1# and 2# glass formulations successfully passed 1000 thermal shock cycles without visible failures, and their resistance change ratios were well below the requisite 20%.