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Abstract

In Chloride Alcad Nickel-Cadmium pocket-plate flooded cells, iron oxide and PVA are used as expanders in the cadmium negative plate to prevent crystal growth, thus retaining capacity. The use of these expanders in the negative electrode has two advantages, They increase the efficiency of the cadmium electrode and are cheap to buy commercially. Unfortunately, the iron-oxide may find its way to the positive plate where it acts as a poison and reduce the capacity of the plate. It is desirable, therefore, to find alternative expanders and to study the basic mechanism of inhibition of crystal growth in the battery electrodes.

Alternative expanders investigated included TiO2 (not formatted correctly, read the pdf), and Mg(OH)2 and these showed extremely promising results when incorporated in the negative cadmium electrode, particularly magnesium hydroxide. The capacities obtained were almost as good as the iron-oxide incorporated electrode but the amount of magnesium hydroxide added to the electrode was less than 1/10 (not formatted correctly, read the pdf) that of the iron-oxide.

Mechanistic studies showed that iron underwent dissolution but the amount was very minute, The use of a planar-microelectrode in conjunction with linear sweep voltammetry, limiting current measurements, a.c, impedance and potential step techniques was found to be a cheap and efficient means bf organic expander assessment, The major function of PVA appeared to be to increase the surface area/porosity of the electrode by acting in a number of ways and may be a means of improving the active material utilisation

a-Fe203 (not formatted correctly, read the pdf), probably provides nucleation centres or spaces for cadmium hydroxide and acts in combination with the organic material in increasing the surface area for cadmium hydroxide formation. This makes the cadmium hydroxide film thinner and therefore much easier to reduce.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science > QD Chemistry
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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