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.

1.The yield strength of Sample A will decrease while the yield strength of Sample B will increase.
2.The yield strength of Sample A will increase while the yield strength of Sample B will decrease.
3.The yield strength of both Samples A and B will increase.
4.The yield strength of both Samples A and B will decrease.
5.The yield strength of Sample A will decrease. There will be no change in the yield strength of Sample B.

it's number 5

To determine the true statements, let's consider the ion exchange process and its effects on the glass specimens:

1. The ion exchange process involves replacing one type of ion in the glass with another ion. In this case, Sample A is soaked in NaCl, while Sample B is soaked in KCl.

2. Sodium ions (Na+) from NaCl have a larger ionic radius compared to potassium ions (K+) from KCl. Therefore, during the ion exchange process, the larger sodium ions will diffuse into the glass, replacing some of the smaller silicon ions (Si4+) in the network structure.

3. The replacement of silicon ions with sodium ions in Sample A leads to an increase in the volume fraction of non-bridging oxygen (NBO) bonds in the glass network. This change weakens the glass structure and reduces its yield strength. Therefore, statement 1 is true - the yield strength of Sample A will decrease.

4. On the other hand, potassium ions (K+) from KCl are smaller and have a stronger bonding with oxygen compared to sodium ions. The replacement of silicon ions with potassium ions in Sample B results in a decrease in the volume fraction of NBO bonds and strengthens the glass structure. Therefore, statement 2 is true - the yield strength of Sample B will increase.

Based on this explanation, the correct statements are:

1. The yield strength of Sample A will decrease while the yield strength of Sample B will increase.
5. The yield strength of Sample A will decrease. There will be no change in the yield strength of Sample B.