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MATE50002 Degradation: MOCK PAPER 2
Question 1
Answer all parts (a) to (e)
(a) Draw a Qn unit for a silicate-based glass, where n is the maximum number of bridging
oxygen bonds.
[2 marks]
(b) Explain why sodium is added into the commercial glass making process. Describe its
effect on the Q structure and how the mechanism for corrosion of silicate glass can be
used to make scratch resistant glass.
[6 marks]
(c) Explain why silicate glass is transparent.
[4 marks]
(d) Draw a Qn unit for borate units within a silicate glass, and explain how borate and
silicate can be combined and used for nuclear waste encapsulation.
[8 marks]
3 Please turn over
MATE50002 Degradation: MOCK PAPER 2
Question 2
Answer all parts (a) to (e)
The Pourbaix diagrams for Ni and Pt are provided in figures 1 and 2 respectively. Figure 3 is the
free energy diagram for hydrogen evolution at the equilibrium potential on a range of metals.
Figure 1: Pourbaix diagrams for Ni; the dashed
lines demarcate the stability of water.
Figure 2: Pourbaix diagrams for Pt; the dashed
lines demarcate the stability of water.
Figure 3: Free energy diagram for H2 evolution at the equilibrium potential.
(a) Explain on the basis of Figures 1-3, why Pt is a better choice than Ni as a catalyst for H2
evolution in a proton exchange membrane electrolyser (pH=0).
[5 marks]
4 End of Paper
MATE50002 Degradation: MOCK PAPER 2
(b) Explain which catalyst you would choose for H2 evolution in an electrolyser with an OH-
conducting membrane, operating at a pH 14.
[3 marks]
(c) Explain the limitations of using Pourbaix diagrams for predicting stability.
[1 mark]
(d) Pd has similar catalytic properties to Pt. However, it has a greater tendency to form a
bulk hydride. Describe the implication this could have on the use of Pd as a H2
evolution catalyst.
[1 mark]
(e) A corroded antique statue made from a Pt-Ni alloy was found in an archaeological dig.
It was encased in mildly acidic, Cl- containing soil. It is covered with pits. Explain, using
a figure, the type of corrosion that may have taken place.