An improved method for the matrix dissolution extraction of nanoparticles from microalloyed steel

The chemical extraction of niobium and titanium carbonitride precipitates from microalloyed steels was studied. Steel samples and chemically synthesized reference nanoparticles were subjected to commonly used extraction protocols, and conditions were systematically varied. High acid concentrations led to particle etching with losses above 10%; long extraction times and small etchant volumes led to the formation of dense SiOx networks that engulfed the extracted particles. The addition of surfactants was found to reduce agglomeration and limit etching. We developed an optimized extraction protocol that can extract and retain particles with diameters below 10 nm with reduced etching and negligible network formation. The resulting particle dispersions are suitable both for efficient electron microscopy of large particle numbers in a single run and colloidal analysis of large numbers of particles in dispersion.