Process for preparing a PTC thermistor

Details Process for preparing a PTC thermistor Process for preparing a PTC thermistor

1988-04-29

1991-01-01

Derrington, James

Plastic and nonmetallic article shaping or treating: processes

Including step of generating heat by friction

264 66, C04B 3564

Patent

active

049816330

ABSTRACT:
A process for preparing a positive temperature coefficient thermistor is disclosed. This thermistor is comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material, and it has a room-temperature resistivity of less than 5,000 ohm-centimeters, an undegraded resistivity of at least about 1,000,000 ohm-centimeters, a degraded resistivity of at least about 900,000 ohm-centimeters, a ratio between its undegraded resistivity and its room-temperature resistivity of at least about 1,000, and a ratio between its undegraded resistivity and its degraded resistivity not exceeding 2.0.
The process of this invention is comprised of the steps of sequentially: (1) providing a powder composition comprised of at least about 60 weight percent of undoped, crystalline, ferroelectric material; (2) fabricating the powder composition into a shaped powder compact; (3) sintering said powder compact by subjecting it to a temperature of from about 1150 to about 1450 degrees centigrade for at least about 1 hour, thereby forming a consolidated, sintered body; (4) reducing said sintered body by subjecting it to a temperature of from about 700 to about 1,400 degrees centigrade for at least about 30 minutes while maintaining said sintered body under a reducing atmosphere comprised of hydrogen; and (5) halogenating said reduced, sintered body by subjecting it to a source of halogen while maintaining it in a closed container at a temperature of from about 700 to about 1200 degrees centigrade for at least about 5 minutes.

REFERENCES:
"Instabilities in PTC Resistors", B. M. Kulwicki (Proceedings of the 6th IEEE International Symposium on Applications of Ferroelectrics, Bethlehem, Pa., Jun. 1986), pp. 656-664.
"PTC Materials Technology, 1955-1980", Bernard M. Kulwicki (Advances in Ceramics, vol. 1, Grain Boundary Phenomena in Electronic Ceramics, publ. by American Ceramic Society, Columbus, OH, 1981), pp. 138-155.
"The PTC Effect of Barium Titanate", J. Daniels, K. H. Hardtl & R. Wernicke (Philips Technical Review, vol. 38, No. 3, 1978/79), pp. 73-82.
"Oxidation Phenomena in Semiconducting BaTiO.sub.3 ", Ichiro Ueda and Seiji Ikegami (Journal of the Physical Society of Japan, vol. 20, No. 4, Apr. 1965), pp. 546-552.
"Halogen Treatment of Barium Titanate Semiconductors", G. H. Yonker (Mat. Res. Bulletin, vol. 2, Pergamon Press, Inc.), pp. 401-407.
"The Effect of Firing Atmosphere on the PTCR Effect in Barium Titanate", Christopher S. Best (Abstract of B.S., Alfred University, 1984).

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