Multiscale investigation of olivine (0 1 0) face dissolution from a surface control perspective

The surface reaction of olivine materials is critical for their extensive applications in the global cycle of elements, future CO₂ sequestration and fuel production. Here, we investigate a pristine (0 1 0) surface dissolved in flow-through cells with acidic solutions at surface control regime. The multiscale surface topography changes during dissolution are firstly measured by a combination of ex-situ vertical scanning interferometry and in-situ atomic force microscopy (AFM). The deduced dissolution rate maps and rate spectra from surface topography vary temporally and spatially, wherein the average rate is higher at initial stages and reaches to a constant value, about 6.6 ± 1 × 10⁻⁸ mol m⁻² s⁻¹, after 100 h reaction accompanied with the formation of crystallographically controlled pits. Furthermore, in-situ AFM shows that the average height of steps on the pit walls is equal to 1/2b and Raman spectra prevails that the (0 1 0) surface is favorably dissolved layer by layer at Mg2 glide plane with SiO₄⁴⁻ distortion. This work reveals that at far from equilibrium conditions with constant Gibbs free energy, surface reactivity is better defined by rate ranges rather than a single mean rate. This superior method is powerful to quantify surface reaction variabilities in multiscale range and understand the geochemical cycles.