Abstract: This invention pertains to an article that emits infrared radiation for a period of about 15 minutes or more, depending on the size and shape, and to a process for preparing the article. The article includes, in a preferred embodiment, a combustible aerogel or other nanocellular substrate with iron metal impregnant formed by thermal decomposition of iron pentacarbonyl deposited on and in the substrate in an amount of at least about 5% or at least about 20% of the weight of the substrate, depending on the substrate. The impregnant reacts exothermically on contact with air or an oxygen-containing gas and imparts sufficient energy to the substrate to cause it to burn for about 30 seconds to about 30 minutes depending on size and shape, thereby emitting infrared radiation. The process pertains to deposition of the impregnant on and in the substrate by flowing a carrier gas saturated with the impregnant precursor over and through the substrate.