Exercises
111
Exercise 3.9 – Ionic conductivity-activity relationship of glass
modifier in oxide-based glasses
1. In (SiO 2 ) 1− α (Na 2 O) α -type glasses, identify the glass former and the glass
modifier. Give two examples of glasses that involve other formers and
modifiers.
2. What is the difference between glass former and modifier in terms of the
metal-oxygen bond?
3. Give the coordination indices for silicon and oxygen in these solids.
4. Consider the following electrochemical chain:
(Hg,Na) 1 / (SiO 2 ) 1− α (Na 2 O) α / (Hg,Na) 2
(Hg,Na) denotes an amalgam of mercury and sodium. Given that the electrical conductivity in (SiO 2 ) 1−α (Na 2 O) α is purely cationic,
a. write the expression for the potential difference ΔE measured between
the terminals of the chain as a function of molar fraction x Na of sodium
in the amalgam,
b. determine its value at 200 °C for x
a nd x
2 10
1 0
( )
( )
Na
Na
1
3
2
5
#
=
=
−
−
.
5. Consider a cell where the initial amount of amalgam is 10
−2
mol in compartments 1 and 2. What current I in mA must pass through the chain in 1 min
for the potential difference between the idle terminals to be zero. Neglect
any variation in the amount of amalgam.
6. The impedance diagram (Nyquist) relative to the volume properties of the
glass (SiO 2 ) 1−α (Na 2 O) α is a semi-circle passing through the origin. How does
this diagram change once the glass is completely crystallized by thermal
treatment?
Exercise 3.10 – Electrochemical coloration
A single crystal of potassium bromide KBr is placed in an atmosphere where
the bromine (Br 2 ) partial pressure is 10
−10
bar, independent of temperature.
The dominant intrinsic disorder in KBr is Schottky disorder. The equilibrium
constant K S for defect formation and the ionic diffusion coefficients are given
by the following expressions:
111
Exercise 3.9 – Ionic conductivity-activity relationship of glass
modifier in oxide-based glasses
1. In (SiO 2 ) 1− α (Na 2 O) α -type glasses, identify the glass former and the glass
modifier. Give two examples of glasses that involve other formers and
modifiers.
2. What is the difference between glass former and modifier in terms of the
metal-oxygen bond?
3. Give the coordination indices for silicon and oxygen in these solids.
4. Consider the following electrochemical chain:
(Hg,Na) 1 / (SiO 2 ) 1− α (Na 2 O) α / (Hg,Na) 2
(Hg,Na) denotes an amalgam of mercury and sodium. Given that the electrical conductivity in (SiO 2 ) 1−α (Na 2 O) α is purely cationic,
a. write the expression for the potential difference ΔE measured between
the terminals of the chain as a function of molar fraction x Na of sodium
in the amalgam,
b. determine its value at 200 °C for x
a nd x
2 10
1 0
( )
( )
Na
Na
1
3
2
5
#
=
=
−
−
.
5. Consider a cell where the initial amount of amalgam is 10
−2
mol in compartments 1 and 2. What current I in mA must pass through the chain in 1 min
for the potential difference between the idle terminals to be zero. Neglect
any variation in the amount of amalgam.
6. The impedance diagram (Nyquist) relative to the volume properties of the
glass (SiO 2 ) 1−α (Na 2 O) α is a semi-circle passing through the origin. How does
this diagram change once the glass is completely crystallized by thermal
treatment?
Exercise 3.10 – Electrochemical coloration
A single crystal of potassium bromide KBr is placed in an atmosphere where
the bromine (Br 2 ) partial pressure is 10
−10
bar, independent of temperature.
The dominant intrinsic disorder in KBr is Schottky disorder. The equilibrium
constant K S for defect formation and the ionic diffusion coefficients are given
by the following expressions: