Ductile long range ordered alloys having high critical ordering temperatures exist in the (V,M)(Fe,Ni,Co)/sub 3/ system having the composition comprising by weight 20.6 to 22.6% V, 14 to 50% Fe, 0 to 64% Co, and 0 to 40% Ni, and 0.4 to 1.4% M, where M is a metal selected from the group consisting of Ti, Zr, Hf, and their mixtures. These modified alloys have an electron density no greater than 8.00 and exhibit marked increases at elevated temperature in ductility and other mechanical properties over previously known ordered alloys.

A catalytic cartridge internally heated is utilized as a SO/sub 3/ decomposer for thermochemical hydrogen production. The cartridge has two embodiments, a cross-flow cartridge and an axial flow cartridge. In the cross-flow cartridge, SO/sub 3/ gas is flowed through a chamber and incident normally to a catalyst coated tube extending through the chamber, the catalyst coated tube being internally heated. In the axial-flow cartridge, SO/sub 3/ gas is flowed through the annular space between concentric inner and outer cylindrical walls, the inner cylindrical wall being coated by a catalyst and being internally heated. The modular cartridge decomposer provides high thermal efficiency, high conversion efficiency, and increased safety.