Total scattering X-ray diffraction patterns were collected at beamline i15-1 at the Diamond Light Source using an X-ray energy of 76.7 keV (λ = 0.161669 Å). Initial calibration measurements were performed on a silicon standard. In situ measurements were carried out using a heated steel sample holder with openings for the X-ray beam to pass through the sample. The capillary was positioned so that the beam passed through it close to the base, so that any solid formed during the reaction would not precipitate out of the path of the beam. Once the capillary was loaded, heating was started with a fast ramp, then scattering detection and temperature measurements proceeded at a rate of one scan per minute. Two separate thermocouples measured the temperature of the capillary and of the sample holder. The experimental setup of the hydrothermal cell is shown in Figure .