top annular volume between grooves 20 and the top of the conductor an expansion joint 28 made of for example of a ceramic felt and the like or other thin material can be disposed between the seal material 26 and the conductor 12 as shown in fig1 a and 1 b the seal material 26 can be a castable ceramic such as aluminosilicates calcium aluminates or other materials a shown in fig1 a conducting filler 32 can be used in the bottom annulus as will as an inconel or other support ring 34 shown in fig1 a near the top part of the annulus the expansion joint 28 at the top of the electrode is a compliant expansion material and selected to protect the seal material 26 upon heat up and operation of the electrode for example at about 960 u00b0 c in an aluminum electrolysis cell in fig1 b conducting filler 32 fills most of the annulus simplifying construction fig1 b and 1 c show protrusion 30 on the top surface of conductor 12 below the grooves 20 these protrusions can simply be for example weld build ups on the conductor surface usually about 3 to 6 weld build ups fig2 a to 2 f which are steps as well as figures schematically illustrate one of many possible processes of making the inert anode electrode form 10 as shown in fig2 a a smooth surfaced mandrel 17 is placed inside.