Potentiodynamic Polarisation Test Of Mg Znn-N-Zn-Xca Alloys

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(a) (b)

(a) (b)

3. 1 Potentiodynamic polarization test of Mg-Zn-RE and Mg-Zn-RE-xCa alloys

Potentiodynamic polarization test in Kokubo solution was carried out to evaluate the bio-degradation behavior of Mg-Zn-RE and Mg-Zn-RE-xCa alloys. The results (Fig. 1) revealed that the corrosion potential, Ecorr of Mg-Zn-RE alloy was -1841 mV, which was more negative compared with the Mg-Zn-RE-0.5Ca. This phenomenon indicates that the cathodic reaction was more difficult in quaternary alloys compared to the ternary
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6) shows that the kind of the corrosion products formed on the surface of Mg-Zn-RE and Mg-Zn-RE-xCa alloys were similar but their quantities were different. The very strong and sharp peak at 3704 cm-1 is identified as the O-H stretching which confirm the formation of Mg(OH)2. The Mg(OH)2 has a hexagonal crystal structure and easily undergoes basal cleavage, caused by formation of crack on the corrosion product layer [5,7-8]. It can be also observed that the absorbance of the spectra from the Mg(OH)2 was significantly lower in Mg-Zn-RE-0.5Ca alloy which led to lesser cracks compared to the other alloys. The broad adsorption band from 3664 to 3215 cm-1 is attributed to the vibration of water molecules. The band at 3448 cm-1 is also attributed to water vibration. Phosphate group (PO43−) was detected around 1170–1047 cm−1 for the v3 mode and 560 cm−1 for the v2 mode. This kind of phosphate is more similar to biological apatite and could be more suitable for bone replacement materials [1,5]. The weak bands at 2934 cm−1 could be attributed to phosphate groups. A band at 889 cm−1 assigned to v2 vibration mode of carbonated groups which consistent with the spectra for apatite composition. The FTIR result is an agreement with the XRD analysis result which revealed that the formation of large amount of corrosion products on the surface of the quaternary alloy with higher Ca

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