| Popis: |
The electrical resistivities of typical AWG20-Class3 and AWG18-Class27 Ni-coated Cu wires were monitored at 400 ºC for times up to 5500 hours; the resistivities increased by 6.9% and 2.3%, respectively. Microstructural analysis of the thermally aged wires revealed evidence of Ni-Cu interdiffusion. Diffusion experiments were performed on Ni-Cu metal foils in the range 400 to 600 ºC; Ni-Cu compositional profiles across the Ni-Cu interface were collected by energy dispersive X-ray spectrometry. Ni-Cu interdiffusivities determined by the Boltzmann-Matano method were typically 2.5×10-17 m2s-1;calculated activation energies for Ni-Cu interdiffusion were between 79.4 and 89.8 kJ•mol-1. Analysis of the available Ni-Cu interdiffusion data suggested a dependence on grain size of the Cu foils used. A concentric-circle, diffusion-resistivity model was developed. Using the experimentally determined Ni-Cu interdiffusion data, it was possible to accurately predict the resistivity of a Ni-coated Cu wire at 400 ºC as a function of time. It is predicted that the resistivity of the AWG20-Class3 wire would increase by 10% after annealing for 48,000 hours at 400 ºC; in contrast, heating an AWG18-Class27 wire for a much longer time of 140,000 hours would incur the same increase in its resistivity. Low temperature co-fired ceramics (LTCC) with a formulation of 11ZnO-10MoO3 (NSZM) were prepared with additions of 0.5 to 2.0 wt% B2O3 via the mixed oxide route. The NSZM samples were sintered at 850-950ºC to over 96% of theoretical density with co-existence of both ZnMoO4 and Zn3Mo2O9 phases. With increasing the addition of B2O3 to NSZM the relative permittivity, dielectric strength and thermal conductivity increased. NSZM prepared with 1.0 wt% B2O3 exhibited a relative permittivity of 11.1, dielectric strength of 17.6 kV•mm-1, linear thermal expansion of 4.7 ppm•K-1and thermal conductivity of 1.3 W•m-1•K-1. The LTCC material is a possible candidate for insulating applications because of its low dielectric constant and adequate dielectric strength. LTCC insulation films were applied to Ni disc substrates by dip coating; the suspensions contained 5 to 20 vol% NSZM ceramic powders, 1.0 wt% B2O3, a polyvinyl butyral (PVB) based binder system, plus solvents and organic additives. A microstructural study of the LTCC films revealed that the insulation thickness varied from 4.3 to 47.3 µm with the ceramic content of starting suspension. The dielectric strength of these films was in the range 24.2 to 43.7 kV•mm-1. These results showed that dip coating is a promising method for applying the LTCC insulation to Ni-based metal substrates. LTCC-insulated wires were manufactured by withdrawing Ni-coated Cu conductors from the suspension, containing 15 vol% ceramic powders, followed by co-firing at 500 ºC. The LTCC-coated wire exhibited an insulation thickness of 40.3 µm and a breakdown voltage of 798 V. These results suggest that the LTCC-coated wire is a possible candidate for use in high temperature machine windings. |
