A model for the film growth in samples with two moving reaction frontiers - an application and extension of the unreacted-core model

A mathematical expression for the film thickness in a flat sample, reacting with a fluid, as a function of reaction time is derived. The formulation i s based on a gas-solid reaction similar to the unreacted core shrinking mod el and takes into account two moving reaction frontiers, one due to the shr inking unreacted core, and one due to the changing thickness of the samples as a result of combustion. The equation of motion for the two reaction bou ndaries is solved exactly for flat samples applying a Lambert W function. T he model for the flat samples is compared with experimental results. (C) 20 00 Elsevier Science Ltd. All rights reserved.