Thermal cycling properties of a lead-free positive temperature coefficient thermistor in the Ba0.97(Bi0.5Na0.5)0.03TiO3 system

• Published in: Journal of the Korean Physical Society 2016, 68(1), , pp.121-125
• Main Authors: Choi, Hyoung-Seuk, Choi, Soon-Mok, Choi, Duck-Kyun
• Format: Article
• Language: English
• Subjects: Mathematical and Computational Physics; Particle and Nuclear Physics; Physics; Physics and Astronomy; Theoretical; 물리학
• ISSN: 0374-4884; 1976-8524
• DOI: 10.3938/jkps.68.121

A Pb-free PTC (positive temperature coefficient thermistor) heater was developed in the Ba 0.97 (Bi 0.5 Na 0.5 ) 0.03 TiO 3 system especially for automotive part applications. The reliability was verified by using a thermal cycling test designed on the basis of the result from a quality function deployment (QFD) analysis. We compared the thermal cycling test results from the newly-developed Pb-free PTC heaters with the results from PTC heaters currently on the market, namely, PTC heaters containing Pb. Life prediction and stress-strength relationships were analyzed together with a thermal diffusivity evaluation. We discuss the potential failure mechanisms during the thermal cycling test, focusing on the fact that electrical degradation in PTC materials is closely related to mechanical degradation due to the internal stress in the materials that comes from repeated phase changes. Different grain size distributions on the sintered bulks were considered to a key factor for explaining the different results of the reliability tests between the new Pb-free PTC heaters developed in this study and the commercial PTC heaters containing Pb.