Thermal investigations on abalone nacre

In order to investigate thermally induced changes in microstructure and phase composition, heat treatments of the nacreous layer of the abalone shell were carried out. According to thermoanalysis, 4,1 mass % of organic matrix was decomposed in two major steps between 240 degrees C and 460 degrees C. After the first mass loss, fracture surfaces as well as cross-sections revealed the development of pores inside the aragonite platelets, confirming the existence of organic material within the platelets. Upon further heating, the phase transformation of aragonite to calcite at about 435 degrees C took place simultaneously with the second mass loss and was accompanied by the development of larger pores at the grain boundaries.