High-solid content, low viscosity and long-term stability Mn–Co–Ni–O ceramic slurry for the fabrication of free-standing ultrathin NTC sheets

Abstract

This study systematically investigated the relationships between Mn–Co–Ni–O ceramic slurry formulations and their volatility, rheology and stability, as well as the electrical properties of free-standing ultrathin sheets made from them. A ceramic slurry with a high solid content of 90%, viscosity <12,000 mPa s, and 720 h long-term stability was successfully obtained by optimizing a spherical clusters powder and organic carrier. The powder was formed by secondary aggregation, which reinforced the wettability of its surfaces. Such spherical clusters ensure that the powders created for ceramic slurry are compact and have good fluidity features microscopically. The optimal formula of the organic carrier system contained three components: 90 wt% organic solvent, 5 wt% ethyl cellulose and 5 wt% Span85. Meanwhile, an organic solvent was made with terpineol, butyldiglycol, 2-(2-butoxyethoxy) ethyl acetate at a ratio of 70:10:20. Mn–Co–Ni–O free-standing ultrathin sheets were prepared by a screen printing method using this slurry, which had a resistivity of 278.25 Ω cm at 25 °C, thermal constant of 3404.3 K, activation energy of 0.29 eV, and temperature coefficient of resistance of −3.83%/K. Furthermore, the response time of a small thermal sensor based on this sheet reached 32 ms. Such Mn–Co–Ni–O free-standing ultrathin sheets with excellent negative temperature coefficient characteristics are promising candidates for fast response temperature measurement.