Phase evolution during the low temperature formation of stoichiometric hydroxyapatite-gypsum composites

Phase evolution during the low temperature formation of calcium-deficient hydroxyapatite–gypsum composites

“…Based on these findings, it could be concluded that the previously observed delay in the growth kinetics of gypsum was attributed to the decrease in the pH of the medium to values below those obtained during the hydration of POP and its conversion to gypsum. A similar trend was previously observed in composite mixtures containing synthetic stoichiometric HAp (S-SH) and gypsum precursors, where a buffering effect was observed as a result of the slower dissolution of the S-SH powders into these solutions [23]. Release of calcium and phosphate ions from the relatively more soluble S-CH, compared to S-SH, is therefore considered the main cause of the delay of the growth kinetics of gypsum in the current system.…”

“…5, in contrast to a maximum of 10.8 after 6 h with SHAp precursors. This could be attributed to the presence of lower concentration of TetCP in the CDS precursors' mixture, compared to that in the SHAp precursors' mixture [23]. This was followed by a decrease in the solution pH achieving a value of 9.1 after 24 h; marked as area IV in Fig.…”

“…This trend was previously shown in systems containing POP and stoiciometric HAp precursors, where delayed growth peaks were observed in samples containing a majority of POP; S10 and S25, indicating a delayed conversion of POP into gypsum as a result of the presence of calcium phosphate precursors. The presence of two growth peaks in samples containing 50 wt% of the calcium phosphate precursors; CDS, CDH and the previously shown SHAp samples [23], indicates the presence of competing reactions where growth of CDS; CDH or SHAp phases is competing with the growth of gypsum phase.…”

“…In contrast, S-CH75 showed a delayed growth peak with a decrease in its intensity after 2.2 h. As was discussed above, the delay in the growth peak of gypsum due to the addition of S-CH could be related to the participation of S-CH in the dissolution/re-precipitation mechanism of gypsum deposition. In a concurrent study, the presence of a synthetic stoichiometric HAp was shown to decrease the intensity of the growth peaks without affecting its time of appearance [23]. Results in Fig.…”

Bio-calcium sulfate preparation from duck eggshell via chemical reaction process

“…a binder for building material, bone graft materials, periodontal disease treatment, endodontic lesions, alveolar bone loss, maxillary sinus augmentation, filler for plastic, rubber, coating, and construction materials, desiccant, coagulant, and catalysts [1,2,3]. In general, calcium sulfate compounds in the form of γ-or β-anhydrite (the nearly anhydrous) namely anhydrous calcium sulfate, calcium sulfate hemihydrate or plaster of Paris, and gypsum (CaSO 4 .2H 2 O) are the most abundant sulfate mineral in nature [4].…”