Why are fused silica and inconel used for dilatometer construction?

Because of our coefficient of thermal expansion which is low. So they don't perturb the measure (or little). They have furthermore a CTE. That of Fused silica is around 0.5/0.6 µm/m.K. For measuring the low CTE of a material, it is necessary to make a first measure on an etalon sample of fused silica in goal of know the elongation of the sample holder.

I'm not sure of my english but I hope I've answered to your question. Bye

Gabriel