Abstract: An iron-silicon compound powder whose predominant phases are Fe.sub.5 Si.sub.3, Fe.sub.2 Si and Fe.sub.3 Si, which is useful as a radar absorbing material (RAM) in corrosive and oxidizing atmospheres and when used with corrosive or oxidizing binders is formed by a diffusion process. The powder is made in a process that includes blending magnetic materials such as carbonyl iron, iron cobalt, and/or nickel and very pure silicon powders with an activator, such as a halide salt, and then heating the mixture between 1350.degree. F. and 1600.degree. F. in an inert atmosphere. The result is then ground until it passes through a 200 mesh screen. The powder so formed usually is then heated in air. This forms a thin protective shell about each particle of the powder after which the powder can be combined with a suitable binder to form a RAM coating capable of operating at high temperatures which is relatively unaffected by corrosive atmospheres.