Which of the following statements describes why ion exchange of 99% SiO2 - 1% B2O3 in a salt bath of molten postassium chloride (KCl) is not an effective way to increase the surface strength of the glass sample?
The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.
The glass is composed of only 1% B2O3, which is not a large enough proportion of B2O3 to undergo ion exchange, and therefore does not increase the surface strength of the sample effectively.
The potassium ion is smaller than B2O3, so when ion exchange takes place the surface is actually being weakened instead of strengthened.
The sample described above is composed of SiO2 and B2O3. Neither of these components are network modifiers, so ion exchange does not take place to strengthen the surface of the glass.
The surfaces of the glass sample are not cooled quickly enough to create a high internal strain energy that leads to strong surfaces.
In which of the following ways would you change the glass sample to make the ion exchange more efficient?
Change the composition of the glass to increase the proportion of B2O3.
Change the composition of the glass to add Na2O, Li2O, or MgO.
Change the composition of the glass to add CaO.
Change the composition of the salt bath (KCl) to an ion smaller than potassium, such as sodium chloride (NaCl).
To evaluate the given statements and determine why ion exchange of 99% SiO2 - 1% B2O3 in a salt bath of molten potassium chloride (KCl) is not an effective way to increase the surface strength of the glass sample, we need to examine each statement individually:
1. The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.
This statement suggests that ion exchange can strengthen the surface, but air-cooling and water-quenching are more effective methods. Therefore, ion exchange may not be the most efficient approach for surface strengthening.
2. The glass is composed of only 1% B2O3, which is not a large enough proportion of B2O3 to undergo ion exchange, and therefore does not increase the surface strength of the sample effectively.
This statement suggests that the low proportion of B2O3 in the glass composition prevents effective ion exchange. Increasing the percentage of B2O3 may potentially enhance the efficiency of the ion exchange process.
3. The potassium ion is smaller than B2O3, so when ion exchange takes place, the surface is actually being weakened instead of strengthened.
This statement highlights that the size difference between potassium ions and B2O3 may lead to a weakening effect during the ion exchange process. This implies that ion exchange may not be suitable for surface strengthening in this case.
4. The sample described above is composed of SiO2 and B2O3. Neither of these components are network modifiers, so ion exchange does not take place to strengthen the surface of the glass.
This statement suggests that neither SiO2 nor B2O3 exhibit network modifier properties, which are necessary for the occurrence of ion exchange. Consequently, ion exchange may not effectively strengthen the glass surface in this composition.
5. The surfaces of the glass sample are not cooled quickly enough to create a high internal strain energy that leads to strong surfaces.
This statement suggests that the cooling rate of the glass surfaces is crucial for creating a high internal strain energy, which contributes to strong surfaces. However, ion exchange may not be directly related to the cooling rate and internal strain energy.
Based on the information provided, the most accurate reason for the ion exchange not effectively strengthening the glass surface is likely statement 4. The glass composition lacks network modifiers required for ion exchange to occur. Therefore, changing the glass composition to incorporate network modifiers would be the best way to make the ion exchange more efficient. Among the given options, changing the composition of the glass to add Na2O, Li2O, or MgO (option 2) would introduce network modifiers and enable the ion exchange process to take place more effectively.