# Spinning of Endless Bioactive Silicate Glass Fibres for Fibre Reinforcement Applications
## 3 Results
### Glass Degradation and Storage
#### 3.3.2 Determination of the Ion Concentration  
In addition to the pH values, the ion concentrations of the solutions were also determined by ICP-OES. In case of SBF determining the change of Si-Ions-concentration over time was possible. For the other ions was it impossible to measure the concentrations, as the SBF includes many different salts.  
The concentration of Si\({}^{4+}\) ions as a function of time can be seen in Figure 5 and increased for all glasses as the dissolution time progresses. Glass 1-06 showed the highest Si\({}^{4+}\) concentration of all glasses after 14 days. Thereafter, the concentration of Si\({}^{4+}\) ions decreased sharply. Glass 13-93 also showed a maximum after 14 days with a subsequent decrease in concentration. At this point, the fibres of these two glasses were almost completely dissolved. This suggests the formation of a precipitate in the form of poorly soluble compounds in both glasses. For glass 18-06, the maximum Si\({}^{4+}\) ion concentration was determined after a storage period of 28 days. From this point on, a precipitate could be seen at the bottom of the tubes used to store the fibres.  
By analysing the deionized water, the concentration of silicon, potassium, calcium and magnesium ions could be measured. For glass 18-06, the concentration of the various ions as a function of storage time is shown in Figure 6.  
The silicon content dropped to a minimum after 28 days of storage. The concentration of calcium ions also decreased at this time. Thereafter, the concentration of Si\({}^{4+}\) and Ca\({}^{2+}\) ions increased again and reached another minimum after 56 days. These results were not expected, as the glass fibres should simply dissolve during storage and the concentration of the various ions should slowly increase. A possible explanation for the low measured values is the formation of poorly soluble compounds. Glass 18-06 contains very little magnesium (cf. Table 3) and the contents dissolved in the water are below the detection limit.  
Figure 5: Concentration of silicon ions in SBF in relation to time.  
The concentration of the different ions for glass 1-06 in dependence of the storage time can be seen in Figure 7.  
The concentration of silicon ions increased up to a maximum at a storage period of 14 days. Thereafter, the Si\({}^{4+}\) ion concentration decreased again. The Ca\({}^{2+}\) and K\({}^{+}\) ion concentrations also increased up to the storage period of 14 days and then decreased again. The reduction of the ion concentrations can also be attributed here to the formation of poorly soluble compounds. Only the concentration of magnesium ions increased very slowly and continuously.  
Figure 8 shows the concentration of the various ions as a function of the storage time for glass 13-93.  
The concentration of silicon ions increased as the storage period progresses and reached a maximum after 14 days. After that, the concentration dropped sharply again. The concentration of calcium ions also increased and reached a maximum after 2 days. Thereafter, the ion concentration decreased. The concentration of potassium ions increased and slowly decreased after 4 days. Furthermore, the concentration of magnesium ions increased slowly and decreased slowly after 2 days. The increase in ion concentrations  
Figure 6: Ion concentration in deionised H\({}_{2}\)O in relation to time for glass 18-06.  
Figure 7: Ion concentration in deionised H\({}_{2}\)O in relation to time for glass 1-06.  
can be explained by the complete dissolution of the fibres after 2 days and the associated release of ions. The further increase in ion concentrations of silicon and calcium ions can be attributed to minimal remnants of undissolved fibres, which were no longer visible to the naked eye and were filtered off prior to analysis of the eluates. The decrease may be due to the formation of poorly soluble salts.