About Prof. Dr.-Ing. habil. Siegfried Steinhäuser

Institute of Materials Science and Engineering, Chemnitz University of Technology, Chemnitz, Germany

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Strontium-Substituted Hydroxyapatite Coatings on Titanium by Electrodeposition Technique

For the first time, strontium hydrogen phosphate (SrHPO4) was electrocrystallized on titanium substrate by means of electrochemical deposition technique, and converted to strontium hydroxyapatite (Sr10(PO4)6(OH)2) to improve implant adhesion and bone mineralization. Brushite (calcium phosphate dihydrate CaHPO4·2H2O) and strontium hydrogen phosphate were co-electrocrystallized on titanium substrate. With increasing SrCl2 and decreasing CaCl2 in the solution, Sr concentration in the coating was increased. Calcium substitution by strontium ranged from 0 to 100 atomic percent, thus having significant effect on layer thickness, morphology, and composition. Layers containing brushite and strontium hydrogen phosphate were converted to calcium hydroxyapatite and strontium hydroxyapatite. Strontium hydroxyapatite was formed in the case of 100 percent SrCl2 substituting CaCl2. Surface morphology, chemical composition, and phase identification of the coatings were studied by scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDXS) and by X-ray diffractometry (XRD). Effects of the varying Sr substitution on the microstructure and properties are discussed.


    

Phosphate coatings against frictional corrosion at shafthub press-fit connections and as transmission element for forces and moments in press-fit connections

Fig. 1: The active principle of the formation of conversion coatings

Phosphating baths are mostly developed for microcrystalline single-phase coatings which can be precipitated with high reproducibility. The titanium phosphate pretreatment of steel promotes the formation of hopeite. This reaction leads to a deceleration of the covering process of the free surface and consequently to an increase in the amount of iron containing phosphophyllite. The different alloys and structures of the steel types is the reason for different rates of the pickling attack. Multiphase phosphate coatings containing phosphophyllite show improved tribological properties compared to zinc calcium phosphate coatings. This can be seen especially on the significantly decreased stick-slip inclination. The use of manganese phosphate coatings is to be preferred for many press-fit connections because they can be reproducibly precipitated, guarantee a higher torque transmission und successfully prevent tribo-oxidation.