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.

In which of the following ways would you change the glass sample to make the ion exchange more efficient?

a) Change the composition of the glass to increase the proportion of B2O3.
b) Change the composition of the glass to add Na2O, Li2O, or MgO.
c) Change the composition of the glass to add CaO.
d) Change the composition of the salt bath (KCl) to an ion smaller than potassium, such as sodium chloride (NaCl).
e) Lower the temperature of the salt bath to cool the sample more quickly.

a) option d

The answer for the first question is 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."

The answer for the second question is b

"Change the composition of the glass to add Na2O, Li2O, or MgO"

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To determine the correct answers, let's analyze the given information for each question:

Question 1: Which of the following statements describes 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?

a) The statement suggests that ion exchange can work correctly, but air-cooling and water-quenching are more efficient ways to strengthen the glass surface. However, it does not explain why the ion exchange in the given situation is ineffective. Therefore, this answer is incorrect.

b) This statement correctly states that the glass sample composed of only 1% B2O3 is not sufficient in proportion to undergo effective ion exchange. As a result, the surface strength of the sample is not increased effectively. Therefore, this answer is correct.

c) The statement incorrectly suggests that the potassium ion is smaller than B2O3, weakening the surface during ion exchange. In reality, the smaller ion will usually cause more compression to the surface, increasing the surface strength. Therefore, this answer is incorrect.

d) This statement states that ion exchange does not take place in the glass composed of SiO2 and B2O3 since they are not network modifiers. This is incorrect since boron (B2O3) can undergo ion exchange and strengthen the glass surface. Therefore, this answer is incorrect.

e) This statement claims that the glass sample's surfaces are not cooled quickly enough to create high internal strain energy, resulting in strong surfaces. However, this does not explain why ion exchange is ineffective in the given situation. Therefore, this answer is incorrect.

Therefore, the correct answer to the first question is (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 effectively increase the surface strength of the sample.

Question 2: In which of the following ways would you change the glass sample to make the ion exchange more efficient?

a) This answer suggests changing the composition of the glass to increase the proportion of B2O3. Since increasing the amount of boron (B2O3) would provide a larger proportion for ion exchange, this answer is correct.

b) This answer suggests changing the composition of the glass to add Na2O, Li2O, or MgO. These additives, known as network modifiers, can enhance the effectiveness of ion exchange and strengthen the glass surface. Therefore, this answer is correct.

c) This answer suggests changing the composition of the glass to add CaO. While CaO can modify the glass network, it is not as effective as the additives mentioned in option (b). Therefore, this answer is not as ideal as option (b).

d) This answer suggests changing the composition of the salt bath (KCl) to an ion smaller than potassium, such as sodium chloride (NaCl). While changing the salt bath can modify the ion exchange kinetics, it does not directly change the glass composition to improve the effectiveness of ion exchange. Therefore, this answer is not as relevant as options (a) and (b).

e) This answer suggests lowering the temperature of the salt bath to cool the sample more quickly. While faster cooling can create higher internal strain energy and potentially strengthen the glass surface, it does not directly enhance the efficiency of ion exchange. Therefore, this answer is not as suitable as options (a) and (b).

Therefore, the correct answers to the second question are (a) and (b): Change the composition of the glass to increase the proportion of B2O3 and Change the composition of the glass to add Na2O, Li2O, or MgO.