Résumé:
The calcic phosphates represent a complex family. Their conditions of crystallisation and inhibition were studied
at various pH values. Phosphate precipitates obtained from artificial urine in the pH range (6.5; 7; 8) were
identified using FTIR and XRD. At pH = 6.5 brushite accompanied by carbonated amorphous phosphate
complexes precipitated while at pH = 7, the coexistence of brushite, struvite and amorphous phosphate complexes
carbonated were observed. On the other hand carbapatite and struvite were formed exclusively at pH = 8. The
complete disappearance of brushite crystals was obtained after addition of 1mM of citrate ion at pH = 6.5 to
artificial urine. Its effect on struvite was more important at pH=7 as at this pH value inhibition was complete.
Total inhibition of brushite was only observed for a concentration of citrate ion of 4 mM. At lower concentrations
inhibition was partial. At the same pH, pentahydrated octocalcic phosphates (POP) and amorphous carbonated
calcium phosphates (ACCP) were formed as identified by FTIR spectroscopy. In the presence of aluminium ion,
the inhibition of brushite growth and aggregation increased. In fact at a concentration of 0.05 mM the formation
of bushite crystals was halted but ACC P persisted. The addition of up to a concentration of 1 mM of ion
aluminium resulted in total inhibition and crystalline transformation of the ACCP into withlockite. On the other
hand, the effect of ferric ion was less important than that of aluminium ion at pH = 6.5. However, inhibition was
total with a concentration of 0.1 mM ferric ion where ACCP and POP were the only compounds formed. The
total disappearance of the crystalline forms was attained with a ferric ion concentration of 0.5 mM, while
amorphous carbonated calcium phosphate and the carbapatite precipitated. For the iron III ion, total disappearance
of brushite was reached at 0.25 mM, only the ACCP and POP were present. The inhibition effect of citrate,
aluminium, and ferric ions on the aggregation and size of struvite crystals was significant at pH=8 but inhibition
and transformation of this crystalline species were not complete.
