For the development of Mg-0.6Ca-0,8 wt.% Zn Alloys theprotocol of Zumdick et al. was used 10. Raw material (99.95% Mg) was melted in a low-alloysteel crucible under Argon with addition of Calcium and Zink in form ofgranules. The cast was heated to 750°C and was then slagged of at 730°C.
The alloyswere casted into a mold at 720°C. The exact composition of the alloys weremeasured via spark spectrometer.For the purpose of the immersion test samples were cut wet toa 10 mm x 10 mm x 1mm dimension and were mounted on a non-conductibletwo-component-plastic. Afterwards the samples were grinded with a SIC-Paper (up to 2400 grit), polished and mounted on analuminum cylinder.The immersion test were maintained in artificial saliva basedon the recipe of Klimek et al. 21 with 0.
330 g/LKH2PO4, 0.340 g/L Na2HPO4, 0.160 g/L NaSCN, 0.580 g/L NaCl, 0.128g CaCl2,0.160 g/L NH4Cl, 0.030 g/L Glucose, 0.002 g/L Ascorbic, modified with 0.
2g Ureaand 2.7g Mucin. The solution was heated to 37°C and constantly magneticallystirred. During the corrosion process, the developing H2 wasmeasured at specific time points in a burette. Assuming 1 Mol of H2 matches1 Mol of Mg the amount of developed H2 can be easily read out .
ThepH-value of artificial saliva was kept constantly between 6.8 and 7.6 by addingphosphoric acid and potassium hydroxide.Mg-0.6Ca-0.8wt.
% Zn Alloys were either immersed 10 days into artificial saliva (AS) or 10days into Hank’s salt solution (HS), serving both as control groups. After 5days the electrolyte was renewed due to cloudy liquid changes. For the testgroup (AS/HS) samples were firstly immersed into artificial saliva. 5 dayslater they were transferred into Hank’s’ solution for 5 more days simulatingwound closure, since the alloy would no longer be in contact with artificial saliva,but rather serum. Each experiment was repeated at least 3 times. The content ofHank’s solution is displayed in Table 1.
Its pH-value was kept constantlybetween 7.0-7.5 by adding phosphoric acid and potassium hydroxide. NaCl KCl Na2HPO4 KH2PO4 MgSO4 * 7H2O CaCl2 Glucose Phenol red NaHCO3 8000 400 38 60 200 140 1000 10 350 Table 1: Content of Hank’s solution in mg/l.22 Corrosion rates were calculated via determining thecurve’s incline.
Zeiss Ultra 55 scanning electron microscopy with Oxford EDX(Carl Zeiss AG, Oberkochen, Germany) were used for the characterization of themicrostructure and corrosion mechanism after 10 days.Quantitative data are presented as average plus thestandard deviation. Statistical analysis was performed via SAS 9.4 (PROCGLIMMIX, SAS 9.4, SAS Institute Inc.,Cary, USA).
Kolmogorov-Smirnov was used to assess normality. Eitherstudent’s t-test or one-way analysis of variance was further used to assesssignificance. In order to check for multiple comparison Hochberg’s method wasused as a post hoc test. A p-value below < 0.05 was determined assignificant and is indicated by an asterisk.
Further details are received belowthe figures.