Surface properties of alkaline earth apatites

摘要: Summary In contrast to other investigations of double layer systems, dissolution and ion exchange processes were found play a more important role in this work. Both from an experimental interpretative vantage point statement has been corroborated. Experimental data obtained exclusively by electrophoretic measurements because the high solubility synthesized apatites prohibited direct determination adsorption density p.d. ions. The observed magnitude e.m. solutions constant ionic strength (∼10−2 M) given electrolyte concentration was increase reverse order as alkaline earth apatites: CaFA>CaHA>SrHA>BaA. Thermodynamic arguments suggest that on these apatites, which may be classed tri-ionic crystals (three distinct lattice ions), is characterized existence series p.z.c.'s lying line equilibrium “solution” surface. latter constructed plotting three mutually perpendicular axes (activity) species. absence specific adsorption, di-ionic are single p.z.c. but continuous shift produced such solids likened predicted curve for apatites. multiple verified experimentally. As many independent established hydroxyapatites calcium strontium. Only procedure prevented observation points. Table 5 . TABLE POINTS OF ZERO CHARGE ALKALINE EARTH APATITIES Solid I II b III c CaFA pF=4.63 pCa=4.38 pHPO4≃5.22 CaHA pH=7.15 pH=7.0 pHPO4=4.19 pHPO4=4.48 SrHA pH=8.00 pH=9.80 pSr=4.19 pHPO4=4.0 pHPO4≃4.4 BaA pH=8.57 pH=11.88 pH=3.43 Experimentally determined addition K2HPO4 suspensions CaHA, BaA. KOH suspensions. By extrapolation. On applying suitable corrections retardation orientation Smoluchowski equation zeta potential cyclindrical-shaped apatite particles calculated. With few exceptions ξ never exceeded value 40 mV over hundred-fold range surface charge calculated vary about − 2 +2 μC cm−2. fluoride special controlling behavior those ions not An explanation findings must take into account reactions involving at least monolayer solid