Electrochemical processes of nucleation and growth of calcium phosphate on titanium supported by real-time quartz crystal microbalance measurements and X-ray photoelectron spectroscopy analysis

Noam Eliaz, William Kopelovitch, Larisa Burstein, Equo Kobayashi, Takao Hanawa

Research output: Contribution to journalArticlepeer-review

Abstract

Real-time, in situ electrochemical quartz crystal microbalance (EQCM) measurements are conducted to better understand the electrocrystallization of calcium phosphates (CaP) on CP-Ti. X-ray photoelectron spectroscopy is used to identify the exact phase deposited, so that reliable estimation of the electrochemical processes involved is made. Analysis of the integrated intensity of the oxygen shake-up peaks, in combination with the determination of Ca/P and O/Ca atomic ratios, enables to determine unambiguously that the octacalcium phosphate (OCP) is formed. Its role as a precursor to hydroxy-apatite (HAp) is discussed. After an incubation period, the process by which OCP is formed follows a Faradaic behavior. The incubation time may be related to the need for local increase of pH before precipitation from solution can occur. The standard enthalpy of activation is ∼40 kJ/mol, which excludes diffusion-controlled processes from being rate determining. The OCP deposit has thickness ≈ 0.61 μm, apparent density ≈ 0.95 g/cm3, 63.6% porosity, and deposition rate of 23.5 ng/(cm2 s) or 15 nm/min. The low-equivalent weight value of 20.5 g/equiv, and the associated remarkably high number of electrons transferred in the reaction n ≈ 24, indicates that most of the current is consumed either by electrolysis of water or by a complex set of parasitic reactions. The low-solubility product allows precipitation of CaP even at relatively low concentrations of calcium and phosphate/hydrogen phosphate ions. It is shown that HAp most likely forms via transformation of precursor phases, such as OCP, rather than directly.

Original languageEnglish
Pages (from-to)270-280
Number of pages11
JournalJournal of Biomedical Materials Research - Part A
Volume89
Issue number1
DOIs
StatePublished - Apr 2009

Keywords

  • Calcium phosphate
  • Electrodeposi-tion
  • Quartz crystal microbalance
  • Titanium
  • XPS

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