Alpha-tricalcium phosphate hydrolysis to octacalcium phosphate: effect of sodium polyacrylate.
Alpha-Tricalcium phosphate (alpha-TCP) hydrolysis into octacalcium phosphate (OCP) has been investigated in phosphoric acid solution at different concentrations of sodium polyacrylate (NaPA). The hydrolysis process has been followed by powder X-ray diffraction, infrared absorption and scanning electron microscopy analyses. In the absence of the polyelectrolyte, alpha-TCP undergoes a complete transformation into OCP in 24 h. The presence of polyacrylate in solution inhibits the hydrolysis so that a NaPA concentration of 0.5 microm is sufficient to lengthen the time required to complete the hydrolysis to 4 days. The variation of Ca2+ concentration in the soaking solution suggests that the transformation occurs through alpha-TCP dissolution followed by OCP precipitation. The delayed OCP nucleation and growth in the presence of polyacrylate implies a preferential adsorption of the polyelectrolyte on the growing OCP crystals, which induces an anisotropic reduction of the coherence lengths of the perfect crystalline domains.
Bigi
A
A
Department of Chemistry G Ciamcian, University of Bologna, Italy. bigi@ciam.unibo.it
Boanini
E
E
Botter
R
R
Panzavolta
S
S
Rubini
K
K
D000180:Acrylic Resins / Q000494:pharmacology*; D000327:Adsorption; D016880:Anisotropy; D018786:Bone Substitutes / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002130:Calcium Phosphates / Q000494:pharmacology*; D003461:Crystallography; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry; D013997:Time Factors; D014961:X-Ray Diffraction
D000180:Acrylic Resins; D018786:Bone Substitutes; D002130:Calcium Phosphates; C485828:alpha-tricalcium phosphate; C485830:tetracalcium phosphate; C022045:octacalcium phosphate; C006903:carbopol 940; C485838:calcium phosphate, monobasic, anhydrous; C020243:calcium phosphate; C485829:calcium phosphate, dibasic, anhydrous; D002118:Calcium