4. Calculate the fraction of the appropriate Qn units for the following glasses.

Question

4. Calculate the fraction of the appropriate Qn units for the following glasses. Indicate which types of units are present. Calculate the number of NBO per tetrahedra for the same glasses. (a) 25 K20-75 SiO2 (b) 35 K20-65 SiO2 (c) 40 K20-60 SiO2 5. Sketch the effect of alkali oxide concentration on the relative theoretical concentrations of Qn units in alkali silicate glasses 6. Please simply explain what the borate anomaly is? 7. Please simply explain why vitreous silica has much higher glass transformation temperature than vitreous boric oxide. 8. Phosphate glass has tetrahedra as basic building block. However, it doesn't have high glass transformation temperature as vitreous silicate glass does. Please simply explain this phenomenon.

Explanation / Answer

Ques 4)

We can calculate Qn for given classes by using following formulae:

For alkali silicate, with mole % (x) of R2O from 0-33%

a) 25 K2O -75 SiO2

Q4 = 100-3x = 100-3X25 = 25

Q3 = 2x = 2 X 25 = 50

NBO / tetrahedron = 2x / 100-x = 50 / 100-50 = 1

b) 35 K2O -65 SiO2

Q3 = 200- 4x = 200-4(35) = 60

Q2 = 3x-100 = 3X35 -100 = 5

NBO / tetrahedron = 3x-100 / 100-x = 5 / 100-35 = 0.07

c) 40 K2O - 60 SiO2

Q3 = 200- 4x = 200-4(40) = 40

Q2 = 3x-100 = 3X40 -100 = 20

NBO / tetrahedron = 3x-100 / 100-x = 20 / 100-40 = 0.33

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