Resonant acoustic-mixing technology as a novel method for production of negative-temperature coefficient thermistors

The 0.1 mol% B₂O₃-added NiMn₂O₄, Ni_0.5Co_0.5Cu_0.3Mn_1.7O₄ and 0.1 mol% B₂O₃-added Ni_0.5Co_0.5Cu_0.3Mn_1.7O₄ negative-temperature coefficient thermistors (NTC) prepared by Resonant Acoustic-Mixing (RAM) technology were compared with samples produced by the traditional ball-milling technique. The metal oxide powders were weighed and mixed by a resonant acoustic mixer (LabRAM 1, Resodyn Acoustic Mixers) at 15 and 40 g acceleration for 20 min and 2 h. To prepare the other group of samples, the metal oxide powders were mixed by ball milling for 6 h. The B₂O₃ addition was chosen in order to reduce processing time by eliminating calcination step. For further comparison, the Ni_0.5Co_0.5Cu_0.3Mn_1.7O₄ samples without B₂O₃ addition were calcinated at 900 °C for 2 h and sintered at 1100 °C for 5 h, whereas the sintering process at 1100 °C for 5 h without calcination was applied for the 0.1 mol% B₂O₃-added NiMn₂O₄ and 0.1 mol% B₂O₃-added Ni_0.5Co_0.5Cu_0.3Mn_1.7O₄ samples. To the best of our knowledge, RAM was applied to produce NTC thermistors for the first time in this study. The best electrical resistivity and material constant results were obtained as 79.5 Ω cm and 3180 K for the 0.1 mol% B₂O₃-added Ni_0.5Co_0.5Cu_0.3Mn_1.7O₄ (B8RAM) sample after 40 g 20 min RAM process followed by the sintering at 1100 °C without calcination. This study will be the lead to guide future studies into the cost-effective fast fabrication of negative-temperature coefficient thermistors by resonant acoustic mixing technology due to reduction of manufacturing costs by reducing processing time.