Electrical properties of thermally sprayed Ni- and Ni20Cr-based resistors

Five laboratories were asked to deposit Ni and Ni20Cr powders to obtain resistors; we studied their electrical properties in the temperature range 20-500 C and interpreted the results in the light of their microstructure. Resistors sprayed from Ni powders consist of NiOx "islands" embedded in a Ni matrix. The temperature dependence of resistance (TCR) is in perfect agreement with that of pure Ni, indicating that the matrix detections. the electrical transport. Annealing at temperatures from 200 to 400C results in an irreversible decrease of resistance. A multiphase microstructure is observed in resistors prepared from 80Ni20Cr powders. The major phase in these resistors is a NiCr alloy but with a Ni:Cr ratio larger than 80:20. Minor amounts of metal oxides are also detected. The TCR in these samples spans from 180 ppm/C to 2830 ppm/C, and is attributed to different degree of oxidation and segregation of the metals in the alloy.