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?
a)The ion exchange works correctly, however both air-cooling and water-quenching are more efficient ways to induce a surface strengthening effect.
b)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.
c)The potassium ion is smaller than B2O3, so when ion exchange takes place the surface is actually being weakened instead of strengthened.
d)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.
e)The surfaces of the glass sample are not cooled quickly enough to create a high internal strain energy that leads to strong surfaces.
The correct statement is:
c) The potassium ion is smaller than B2O3, so when ion exchange takes place the surface is actually being weakened instead of strengthened.
Explanation:
Ion exchange is a process where ions in a solid material are replaced with ions from a solution, resulting in a change in the properties of the material. In the case of glass, ion exchange can potentially increase the surface strength by replacing the alkali ions near the surface with larger ions, creating a compressive stress layer that improves the mechanical properties.
In the given scenario, the glass sample is composed of 99% SiO2 and 1% B2O3. However, the statement mentions that the ion exchange is performed in a salt bath of molten potassium chloride (KCl). The potassium ion (K+) is smaller in size compared to the boron ion (B2O3), which means that during ion exchange, the smaller potassium ions replace the larger B2O3 ions near the surface. This results in a weakening effect rather than strengthening the surface.
Therefore, statement c) correctly explains 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.