The effect of additives on the hydration of CaSO4·0.5H2O: A synchrotron X-ray diffraction study

To modulate the rate of hydration calcium sulfate hemihydrate (HH) to dihydrate for industrial applications, additives (both accelerants and retardants) are added HH. Here we explore in detail kinetics mechanism HH presence accelerators K 2 SO 4 or ZnSO , also when a retardant (citric acid tartaric acid) is added. Retardants tend lower maximum temperature reaction increase time needed reach 50% hydration, yet total conversion percentage similar that an accelerant The process found involve heterogenous nucleation regardless nature additive. More soluble act mainly though increasing crystal growth, while less species have more significant effect on nucleation. • In situ X-ray diffraction was used probe dihydrate. retardants investigated. Reaction mechanisms be complex. Standard proxy methods industry not representative actual processes underway.