We adopted the verified absolute-reaction theory which originates from the quantum chemistry approach as well as the boundary perturbation technique to capture the unusual experimental results by Dabhade et al.: Nanocrystalline titanium powders were found to exhibit lower activation energy for viscous flow and higher (coefficient of) viscosity as compared to micron sized titanium powders when nanocrystalline Ti (micron and nano) powders were expected to exhibit viscous flow during sintering. We also illustrate some formulations which can help us calculate the temperature-dependent viscosity of flowing Ti powders in micro- and nanodomains. (C) 2016 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.