Seals for high temperature reactive material devices

A high-temperature device, comprising:

• a container comprising an internal cavity, wherein the internal cavity comprises a reactive material, and wherein the reactive material is maintained at a temperature of at least about 200° C.;
• a seal that seals the internal cavity of the container from an environment external to the container, wherein the seal comprises a ceramic component, and wherein the seal is exposed to both the reactive material and the environment external to the container;
• a conductor that extends from the environment external to the container through the seal to the internal cavity of the container;
• and
• a metal sleeve coupled to the conductor and to the ceramic component, wherein the metal sleeve is coupled to the ceramic component by a braze joint comprising a braze, and wherein the braze is formed of a material that is substantially unreactive to air and prevents diffusion of air into the container when the reactive material is maintained at the temperature of at least about 200° C. for a time period of at least about 1 day.