A heater comprising a conduit made of corundum (e.g. synthetic sapphire) and having a wall forming a closed cross-section with an interior surface, and an exterior surface. At least one of the interior and exterior surfaces may have a roughened portion comprising inclusions and corresponding protrusions formed substantially continuously therethroughout. An electrically resistive coating may extend substantially continuously over, in, and around the inclusions and protrusions of at least a part of the roughened portion to form a conformal cross-section having a thickness selected to promote bending thereof to accommodate annular expansion and contraction occurring in response to a differential in the coefficients of expansion between the electrically resistive coating and the conduit.