For the development of Mg-0.6Ca-0,8 wt.% Zn Alloys the
protocol of Zumdick et al. was used 10. Raw material (99.95% Mg) was melted in a low-alloy
steel crucible under Argon with addition of Calcium and Zink in form of
granules. The cast was heated to 750°C and was then slagged of at 730°C. The alloys
were casted into a mold at 720°C. The exact composition of the alloys were
measured via spark spectrometer.
For the purpose of the immersion test samples were cut wet to
a 10 mm x 10 mm x 1mm dimension and were mounted on a non-conductible
two-component-plastic. Afterwards the samples were grinded with a SIC-Paper (up to 2400 grit), polished and mounted on an
The immersion test were maintained in artificial saliva based
on the recipe of Klimek et al. 21 with 0.330 g/L
KH2PO4, 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 Urea
and 2.7g Mucin. The solution was heated to 37°C and constantly magnetically
stirred. During the corrosion process, the developing H2 was
measured at specific time points in a burette. Assuming 1 Mol of H2 matches
1 Mol of Mg the amount of developed H2 can be easily read out . The
pH-value of artificial saliva was kept constantly between 6.8 and 7.6 by adding
phosphoric acid and potassium hydroxide.
wt.% Zn Alloys were either immersed 10 days into artificial saliva (AS) or 10
days into Hank’s salt solution (HS), serving both as control groups. After 5
days the electrolyte was renewed due to cloudy liquid changes. For the test
group (AS/HS) samples were firstly immersed into artificial saliva. 5 days
later they were transferred into Hank’s’ solution for 5 more days simulating
wound 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 of
Hank’s solution is displayed in Table 1. Its pH-value was kept constantly
between 7.0-7.5 by adding phosphoric acid and potassium hydroxide.
MgSO4 * 7H2O
Table 1: Content of Hank’s solution in mg/l.22
Corrosion rates were calculated via determining the
curve’s incline. Zeiss Ultra 55 scanning electron microscopy with Oxford EDX
(Carl Zeiss AG, Oberkochen, Germany) were used for the characterization of the
microstructure and corrosion mechanism after 10 days.
Quantitative data are presented as average plus the
standard deviation. Statistical analysis was performed via SAS 9.4 (PROC
GLIMMIX, SAS 9.4, SAS Institute Inc.,
Cary, USA). Kolmogorov-Smirnov was used to assess normality. Either
student’s t-test or one-way analysis of variance was further used to assess
significance. In order to check for multiple comparison Hochberg’s method was
used as a post hoc test. A p-value below < 0.05 was determined as significant and is indicated by an asterisk. Further details are received below the figures.