Microstructure of hydroxyapatite- and octacalcium phosphate-coatings formed on magnesium by a hydrothermal treatment at various pH values

Masanari Tomozawa, Sachiko Hiromoto

Research output: Contribution to journalArticlepeer-review

107 Citations (Scopus)

Abstract

Hydroxyapatite (HAp) coatings with and without octacalcium phosphate (OCP) were uniformly formed on pure magnesium by a hydrothermal treatment using a Ca-EDTA solution. The crystal structure, crystallographic orientation and lattice images were investigated using transmission electron microscopy (TEM) and high-resolution TEM. It was demonstrated that the crystal phase and microstructure of the calcium phosphate-coatings can vary with the pH of the treatment solution. In a weak acid treatment solution, a dual-layer structure was formed: an outer coarse layer consisting of plate-like OCP crystals and an inner dense layer consisting primarily of HAp crystals. One piece of the OCP plate corresponded to a single OCP crystal growing parallel to the (1 0 0) OCP. In a weak alkali treatment solution, a dual-layer structure was also formed: an outer coarse layer consisting of rod-like HAp crystals and an inner dense layer consisting of HAp crystals. One piece of the HAp rod corresponded to a single HAp crystal growing along [0 0 2]HAp. In a strong alkali treatment solution, needle-like HAp crystals were formed. No defect was observed in the lattice image of the OCP and HAp. The corrosion current density of pure magnesium in a 3.5 wt.% NaCl solution decreased with the HAp coating more significantly than the OCP + HAp coating. It is revealed that the degree of protection afforded by calcium phosphate-coatings varies with their crystal phase and microstructure.

Original languageEnglish
Pages (from-to)355-363
Number of pages9
JournalActa Materialia
Volume59
Issue number1
DOIs
Publication statusPublished - 2011 Jan
Externally publishedYes

Keywords

  • Bioabsorbable metals
  • Corrosion-resistant coatings
  • Hydrothermal treatment
  • Hydroxyapatite
  • Magnesium

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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