Brazed Joint Between Copper and Silver

Reflected Brightfield Illumination

Electrical resistance is related to the reflectivity of the metal: the higher the
reflectivity the lower the electrical resistance for an opaque material, such as a
metal. In this case the darker gray intermetalic that has grown in the brazing
compound has resulted in a higher resistance path. Under electrical load that
results in much higher temperatures for the contact metals. In this case the
the contacts were encased in a plastic that began to char, to crack, and to finally
fail, leading to the loss of the equipment, a Load Tap Changer attached to a large
Transformer.