A glass of composition 85% SiO2 - 15% K2O is to be surface strengthened by ion exchange. To this end, two identical specimens approximately the size and shape of credit cards are soaked for the same amount of time at 850∘C. Sample A is soaked in NaCl and sample B is soaked in KCl. From the list below, select the statements that are true.
The yield strength of Sample A will decrease while the yield strength of Sample B will increase.
The yield strength of Sample A will increase while the yield strength of Sample B will decrease.
The yield strength of both Samples A and B will increase.
The yield strength of both Samples A and B will decrease.
The yield strength of Sample A will decrease. There will be no change in the yield strength of Sample B.
What do you think?
It's e, the last one.
To determine the effect of ion exchange on the yield strength of the glass samples, we need to consider the ions involved and their behavior during the process.
In the given scenario, Sample A is soaked in NaCl, which contains sodium ions (Na+), and Sample B is soaked in KCl, which contains potassium ions (K+). These ions will replace some of the original ions (Si4+ and K+) on the glass surface through ion exchange.
The yield strength of a material is the maximum amount of stress it can withstand before permanent deformation occurs. In this case, we are interested in how the ion exchange process will affect the yield strength of the glass samples.
When sodium ions (Na+) replace potassium ions (K+), the size of the ions participating in the bonding with the glass network changes. This change in ionic size can potentially weaken the bond strength between the glass atoms, leading to a decrease in yield strength. Therefore, statement 1, "The yield strength of Sample A will decrease," is true.
Similarly, when potassium ions (K+) replace some of the original ions (Si4+) on the glass surface, the bond strength between the glass atoms can be strengthened due to the larger ionic size of potassium ions compared to silicon ions. This strengthening of the bond can lead to an increase in yield strength. Therefore, statement 2, "There will be no change in the yield strength of Sample B," is false.
Considering the explanations above, the correct selection from the list is:
1. The yield strength of Sample A will decrease.
2. There will be no change in the yield strength of Sample B.