@Keith: Ceradyne’s Ceralloy 147 is described in their brochure as an excellent insulator, 10^16 ohm resistance in the sintered version and is touted as superior to alumina in various measures of durability. Also Wikipedia states that silicon nitride is used as an insulator in integrated circuits. Links to Ceradyne’s spec sheets and brochure PDF’s don’t work from these posts, but here’s a link to their brochure section.
