Abstract: An important problem for the CaSO4/CaSO4・1/2H2O
Chemical heat pump (CHP) is that the material is deactivated through
repetitive reaction between hydration and dehydration in which the
crystal phase of the material is transformed from III-CaSO4 to
II-CaSO4. We investigated suppression on the phase change by adding
a sulfated compound. The most effective material was MgSO4. MgSO4
doping increased the durability of CaSO4 in the actual CHP repetitive
cycle of hydration/dehydration to 3.6 times that of undoped CaSO4.
The MgSO4-doped CaSO4 showed a higher phase transition
temperature and activation energy for crystal transformation from
III-CaSO4 to II-CaSO4. MgSO4 doping decreased the crystal lattice
size of CaSO4・1/2H2O and II-CaSO4 to smaller than that of undoped
CaSO4. Modification of the crystal structure is considered to be related
to the durability change in CaSO4 resulting from MgSO4 doping.