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

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 ?. The ceramics were prepared in three glass formulations (1#: 15MgO-15Al(2)O(3)-44.7SiO(2)-25BaO, 2#: 17MgO-17Al(2)O3-41SiO(2)-25BaO and 3#: 17MgO-17Al(2)O3-41SiO(2)-20BaO-5Y(2)O3 (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?. Notably, the sealing structure of glass-ceramic coating 1# was compact at a Tg of 760.9 ?. 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%.