Page 76 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Positive plate
Consist of many perforated steel tubes which contains nickel hydroxide (Ni(OH)4). To increase the conductivity
of Ni(OH)4 pure nickel flakes are added. Steel tube is about 15mm diameter and 100mm in length contain nearly
300 such layers. Tubes are then compressed in a nickel plated steel frame, this forms positive plate.
Negative plate
Consist of many rectangular perforated steel pocket into which powered iron oxide is filled. To increase the
conductivity small amount mercury is added to pocket. These pockets are clamped in a steel grid, which forms
the negative plate. Negative plate is always one more in number than positive plate.

Electrolyte
Electrolyte is potassium hydroxide (KOH) of specific gravity 1.22.
pecific gravity is constant during discharging and charging. Ell
always kept sealed to avoid the hydroxide combine with carbon
dioxide, which decreases the capacity of the cell. For increasing
capacity of the cell, small quantity of lithium hydroxide (LiOH) is
added to the electrolyte.
Container
Container consist of a steel box The inside and top of the cell cover
is given a thick layer of insulating compound to avoid short circuiting
as it is made of steel container is air tight and a small hole is provided
in the vent plug which allows the gases to escape.

Separator

Separator is made of perforated hard rubber.
These are placed in between the plates to avoid short circuiting
Operation
Chemical changes:
The molecules of electrolyte (KOH) dissociate in to K+ and OH- ions
During discharging

When the cell is fully charged the positive plate is of nickel hydroxide(Ni(OH)4) and the negative plate is of
iron(Fe). When the cell is discharged a current flows from positive plate to negative plate outside the cell and from
negative plate to positive plate inside the cell. The current through the electrolyte breaks it in to potassium ions
Ni(OH)4 and hydroxide ions(OH-). The K+ ions move towards +ve plate (anode)and reduce Ni(OH)4 and The
OH- ions move towards -ve plate (cathode Fe)

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CITS : Power - Electrician & Wireman - Lesson 13-19 CITS : Power - Electrician & Wireman - Lesson 13-19