The impact initiated reaction response of a Ta + Bi2O3 thermite powder mixture encapsulated in two different maraging steel geometric structures was investigated. Experiments were performed on the Ta + Bi2O3 mixture initially compressed to similar to 40% theoretical maximum density in a hollow cylinder and 9-Cell linear cellular alloy (LCA) structure, both of equivalent relative solid density. The powder filled structures were impacted against a rigid high-strength anvil over the velocity range of 60-204 m s(-1). Reactions were observed in the powder mixture at velocities as low as 60 m s(-1) in the 9-Cell LCA structure, and at 105 m s(-1) for the hollow cylinder geometry. Three dimensional simulations of the powder filled structures impacting a rigid anvil were carried out at velocities near the reaction threshold conditions. Continuous measurements of pressure and strain were recorded in the simulation at several locations within the powder filler and solid walls of the maraging steel LCA structures. Comparison of calculated results with experimental findings suggested that reaction of the powder filler in both encapsulating geometries occurred at late times as a result of an activated microstructure and elevated temperatures. (C) 2014 Elsevier B.V. All rights reserved.