Page 183 - CW E-Magazine (3-12-2024)

Special Report

side. Painting in a manner similar to base. The anode base has recessed holes electrolyser stack arranged in parallel
that employed for diaphragm cells with a copper washer or facing so that where leakage in a single cell had taken
protects the external surfaces of these the copper anode stud makes a good place due to ring corrosion making that
materials(7). electrical contact. It is covered with cell in operative consequently leading
an ethylene-propylene-diene (EPDM) to production loss.
Cell components blanket to prevent the anolyte from
The anode material in all three seeping to the copper base. However, The anode should preferably be
chlor-alkali technologies is a titanium because of aging of the blanket or poor made from Titanium grade 23 called
substrate, in the form of a mesh or a assembly, the anolyte can seep through as Ti-6Al-4V-Eli. This alloy is struc-
louvered structure, coated with RuO and corrode the copper facing orthe turally α-β wrought alloy. Eli stands
2
+TiO + IrO or SnO . The coated washer, resulting in poor contact and for extra low interstitial. This alloy
2
2
2
titanium mesh is welded to a titanium higher ohmic drop. This is called ring has excellent corrosion resistance as
copper bar with a copper stud thread at corrosion. This is generally prevented by it helps in forming a passive and tena-
one end to fix the anode to the anode good housekeeping. Figure-2 shows the cious oxide film which is highly
resistant to aggressive chloride ions.
It has good tensile strength, and very
good fatigue strength and can easily be
moulded, cut into small strands, coils,
and wires. The chemical composition
of 6Al-4V-Eli is titanium (Ti) 88.9-91%;
aluminium (Al) 5.5-6.5%; vanadium
(V) 3.5-4.5%; iron (Fe) ≤0.25%; and
carbon (C) ≤0.08%.

Comparison of Critical Pitting Tem-
perature (CPT) for two anode materials
commonly used, viz. Commercially
Produced Ti (CP-Ti) & Ti grade 23
(Ti-6Al-4V-Eli) is shown in Figure-3.
It can be seen that the CPT for CP-Ti
o
Fig. 2: Electrolyser stack in parallel showing leakage in a single cell rendering that cell to be is only 83 C whereas the same for Ti-
o
non-functional. 6Al-4V-Eli is 96 C. Pit coalescence
after attaining CPT causes large leak-
age of brine. Figure-4 depicts the picture
of such a pit. Pin hole pitting also take
place in the Ti anode as the CPT is
attained in the process leading to leakage
of chlorine. Such pin holes initiated

Fig. 4: Pit coalescence after attaining CPT
Fig. 3: Comparison of CPT for two best anode material CP-Ti & Ti grade 23. causing large leakage of brine.

Chemical Weekly December 3, 2024 183

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