Effect of ph of coating solution on adhesion strength of hydroxyapatite and octacalcium phosphate coatings on az31 magnesium alloy

Tuyet Thi Anh Ngo, Sachiko Hiromoto, Phong Ngoc Nguyen, San Thi Pham

Research output: Chapter in Book/Report/Conference proceedingConference contribution

1 Citation (Scopus)

Abstract

Hydroxyapatite (HAp) and octacalcium phosphate (OCP) coatings were formed on a Mg- 3Al-Zn (AZ31) alloy with a chemical solution deposition method using a Ca-EDTA solution at various pH levels. The adhesion strength of the coatings was examined using the pull-off method. The microstructures of HAp and OCP coatings were measured X-ray diffraction (XRD). The morphology and composition of the surface and cross section of the samples before and after the adhesion test were characterized using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and a 3D profilometer. The results showed that plate-like OCP crystals grew from a continuous OCP layer on the surface of the AZ31 substrate in the case of a pH 6.3 coating solution. At pH values of 7.5 and 8.6, the HAp coating showed a two-layer structure with a HAp rod-like outer layer and a HAp continuous inner layer. Regardless of the pH of the coating solutions, a very thin Mg(OH)2 intermediate layer was formed between OCP or HAp coating and substrate. The highest adhesion strength of the coatings was 6.7±0.5 MPa, achieved at a coating solution pH value of 7.5. A part of Mg(OH)2 layer remained on the substrate, indicating that the delamination occurred in the Mg(OH)2 intermediate layer. The primary particles in the inner layer formed at pH 7.5 was smaller than those at pH 8.6. This result indicates that the initial corrosion of substrate AZ31 at pH 7.5 was more rapidly than that at pH 8.6, presumably leading to the formation of mixed layer of Mg(OH)2 and calcium phosphate. Further investigation is necessary to understand the better adhesion strength at pH 7.5 than that at pH 8.6. This good adhesion could be due to the flawless and rod-like uniform crystal, which had the densest and finest structure on the surface.

Original languageEnglish
Title of host publicationPhysical Properties and Application of Advanced Materials
EditorsKenji Matsuda, Pham Mai Khanh, Dang Quoc Khanh, Le Van Lich
PublisherTrans Tech Publications Ltd
Pages156-164
Number of pages9
ISBN (Print)9783035714586
Publication statusPublished - 2020
Externally publishedYes
Event13th International Conference on the Physical Properties and Application of Advanced Materials, ICPMAT 2018 - Hanoi, Viet Nam
Duration: 2018 Sep 42018 Sep 7

Publication series

NameMaterials Science Forum
Volume985 MSF
ISSN (Print)0255-5476
ISSN (Electronic)1662-9752

Conference

Conference13th International Conference on the Physical Properties and Application of Advanced Materials, ICPMAT 2018
CountryViet Nam
CityHanoi
Period18/9/418/9/7

Keywords

  • Adhesion
  • Biodegradable implants
  • Calcium phosphate coatings
  • Delamination
  • Magnesium alloy

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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  • Cite this

    Thi Anh Ngo, T., Hiromoto, S., Ngoc Nguyen, P., & Pham, S. T. (2020). Effect of ph of coating solution on adhesion strength of hydroxyapatite and octacalcium phosphate coatings on az31 magnesium alloy. In K. Matsuda, P. Mai Khanh, D. Q. Khanh, & L. V. Lich (Eds.), Physical Properties and Application of Advanced Materials (pp. 156-164). (Materials Science Forum; Vol. 985 MSF). Trans Tech Publications Ltd.