Chemical Composition And Thermodynamic Analysis Of Nacreous Layer From Rerna Viridis As Natural Bioporcelain

In this paper, nacreous layer of Perna viridis (PV) from Beihai city's sea area is studied emphatically, at the same time nacreous layer of Pinctada martensii (PM) , synthetic aragonite in liquid and cavernous aragonite are analyzed to compare with PV nacre. Basic structure and chemical composition of PV nacre are examined by X-ray diffraction and FTIR spectra. Finally, phase transformation from nacreous aragonite to calcite is studied preliminarily by using DSC. Three peaks in DSC curve of untreated PV nacre are concerned and explained clearly.Main conclusions of this research are drawn as follows:(1) The results of XRD indicate that there are similar structures between PV nacreous and prismatic layers. Compared with the synthetic aragonite, there are some differences between them. The organic matrix contained by them plays an important role.(2) The temperature of phase transformation from PV nacreous layer to calcite is detected in 380℃. The phase transformation is a gradual thermodynamic process. No phase transformation is found from PV nacreous layer to calcite under 380 ℃ monitored by FTIR spectra. So it is the best way to eliminate the organic matrix heated under 380℃.(3) As ground time prolongs, synthetic aragonite in liquid and cavernous aragonite monitored by DSC show some regularity in phase transformation from PV nacreous layer to calcite under intensive vibrating mill. At the beginning, it is observed that the phase transformation is endothermic; With time changes, the phase transformation becomes exothermal. The conclusion is initially deduced that the mechanical force results in increasing internal stress, decreasing the crystallite size. Then the crystal latter is distorted, and excess enthalpy is stored.(4) On the experimental data of XRD, FTIR, TG/DTA, the three peaks in DSC curve of untreated PV nacre can be finally understood . The excess enthalpy stored in...