What should be filled in the outer splice of a conductor to prevent oxidation?

Zinc Chromate is a corrosion-inhibiting compound that effectively protects metal surfaces from oxidation. When applied to the outer splice of a conductor, it serves as a barrier that prevents moisture and air from coming into contact with the underlying metal, which can lead to oxidation and deterioration over time. This is particularly important in the context of electrical conductors, where oxidation can significantly affect conductivity and lead to operational failures.

The other materials mentioned do not provide the same protective benefits against oxidation. While aluminum and copper are commonly used as conductors themselves, they do not have properties that inherently prevent oxidation when used in splicing applications. Sodium, on the other hand, is highly reactive and unsuitable for protecting metal surfaces in this context. Thus, Zinc Chromate is the most effective choice for preventing oxidation in the outer splice of a conductor.