Following the evolution of the system in Fig. , one can observe that as the solution progresses from 0 s (pre-mixing) to 10 s (post-mixing) and beyond, the evolution of the scattering curves clearly reflects the formation of struvite. In terms of the magnitude of changes in the intensity, the most obvious ones are associated with the evolution of the Porod interfaces for q < 0.5 nm -1 (the 1st term in Eq. 2). Therefore, we first consider the evolution of the fit parameters I 0 and D shown in Fig. (from fitting with Eq. 2, Fig. ). We also prompt that the 10 s frame marks the onset of the appearance of the diffraction peaks of struvite (Fig. , Fig. ). The diffraction peaks fully develop throughout 20 s to 40 s frames, and simultaneously the low-q Porod interface intensity (Fig. ) and the associated parameter I 0 increase (Fig. ), which is consistent with increasing specific surfaces due to the nucleation of new crystals. Therefore, we associate the evolution of Porod interfaces predominantly with the growth of crystalline solids. The value of D remains constant at ~3.5 through the reaction, indicating atomically rough surfaces, a fact we previously observed for other crystal systems in solution (with a value of D = 4 for ideal smooth Porod interfaces).