Preparation and effects of glass-coatings on BaTiO3-based PTC thermistors

Glasses in the Na2O–K2O–K2SiF6–ZnO–Al2O3–B2O3–SiO2 system were investigated as potential intermediate temperature sealing materials to protect BaTiO3-based positive temperature coefficient (PTC) thermistors. The influence of compositional changes on the crystallization tendency and sintering behavior of the glass was reported. Additionally, the electrical properties of PTC thermistors with glass-coatings were compared with those without glass-coatings. The results showed that the formulation (in wt%), 3.1Na2O–9.4K2O–10.6K2SiF6–4.3ZnO–4.3Al2O3–20.3B2O3–48SiO2 (G2), performed better on thermal properties, had a good glass formability within a relatively wide range of sintering temperature and was compatible with the PTC thermistors (no cracks or pinholes). Furthermore, the glass layer did not affect the characteristics of the PTC thermistors too much.