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Deposition of phosphate coatings on titanium within scaffold structure

Trybuś B., Zieliński A., Beutner R., Seramak T., Scharnweber D.

Acta of Bioengineering and Biomechanics

2017

Vol. 19, no. 2

65--72

Purpose. Existing knowledge about the appearance, thickness, and chemical composition of 37 phosphate coatings on titanium inside porous structures is insufficient. Such knowledge is 38 important for the design and fabrication of porous implants. 39 Methods. Metallic scaffolds were fabricated by selective laser melting of 316L stainless steel 40 powder. Phosphate coatings were deposited on Ti sensors placed either outside the scaffolds 41 or in the holes in the scaffolds. The electrochemically-assisted cathodic deposition of 42 phosphate coatings was performed under galvanostatic conditions in an electrolyte containing 43 the calcium and phosphate ions. The phosphate deposits were microscopically investigated; 44 this included the performance of mass weight measurements and chemical analyses of the content of Ca2+ and PO4 2‒ 45 ions after the dissolution of deposits. 46 Results. The thicknesses of the calcium phosphate coatings were about 140 and 200 nm for 47 isolated titanium sensors and 170 and 300 nm for titanium sensors placed inside pores. 48 Deposition of calcium phosphate occurred inside the pores up to 150 mm below the scaffold 49 surface. The deposits were rich in Ca, with a Ca/P ratio ranging between 2 and 2.5. 50 Conclusions. Calcium phosphate coatings can be successfully deposited on a Ti surface 51 inside a model scaffold. An increase in cathodic current results in an increase in coating 52 thickness. Any decrease in the cathodic current inside the porous structure is slight. The 53 calcium phosphate inside the pores has a much higher Ca/P ratio than that of stoichiometric 54 HAp, likely due to a gradual increase in Ca fraction with distance from the surface.

Elektrochemiczna ocena jakości powłok fosforanowych

Flis J.

Ochrona przed Korozją

2007

nr 4

111-115

Wykonano pomiary impedancyjne w roztworach Na2HPO4 o stężeniach 5ź10-4 - 0,1 M na stali i na elektroosadzonym Zn oraz Zn-12% Ni przed i po fosforanowaniu. Do elektrochemicznej oceny powłok fosforanowych wybrano 0,005 M Na2HPO4 ze względu na małą agresywność i silne zróżnicowanie elektrochemicznego zachowania materiałów fosforanowanych i niefosforanowanych. Badania mikroskopowe na zarysowanych powłokach po zanurzeniu do tego roztworu wykazały powstawanie osadów fosforanów na odsłoniętej powierzchni Zn i w mniejszym stopniu na Zn-12% Ni, ale nie na stali. Wskazuje to na możliwość zaleczania istniejących porów podczas pomiarów. Zaproponowano ocenę porowatości powłok na podstawie pomiarów impedancyjnych po odsłanianiu powierzchni metalicznego podłoża poprzez sukcesywne zarysowanie.

Impedance measurements were performed in Na2HPO4 solutions at concentrations from 5ź10-4 to 0.1 M on steel and on electrodeposited Zn and Zn-12% Ni before and after phosphating. A 0.005 M Na2HPO4 solution was selected for the electrochemical evaluation of phosphate coatings owing to its low aggressiveness and strong differentiation of the electrochemical behaviour of phosphated and unphosphated materials. A microscopic examination of the scratched coatings following exposure to the solution showed the formation of phosphate deposits on the bare surface of Zn and to a lesser extent on Zn-12% Ni, but not on steel. This indicates that during measurements a healing of the existing pores can take place. It was proposed to assess the porosity of the coatings on the basis of impedance measurements after exposing the bare surface of a metal substrate by successive scratching.