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 400C 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