Page 155 - Battery Reference Book

Mercury-indium-bismuth and mercury-cadmium primary batteries
ereury-zinc primary batteries specified. Rest periods are not required as in the case
of carbon-zinc batteries.
Mercury batteries have an appreciably higher energy- Mercuric oxide batteries are available with two for-
to-weight ratio than carbon-zinc batteries, resulting mulations designed for different field usage. In general,
from the high energy density of the materials used the 1.35 V cells (that is, 100% mercuric oxide depolar-
in their construction. Thus mercury batteries are only ization) or batteries using these cells are recommended
one-third the size of conventional dry batteries of the for voltage reference sources (that is. high degree of
same capacity. voltage stability) and for use in applications where
Characteristics and features of the mercuric oxide higher than normal temperatures may be encountered
electrochemical system include the following: (and for instrumentation and scientific applications).
The 1.4V cells (mixture of manganese dioxide and
1. Long life. mercuric oxide depolarization) or batteries using these
2. High capacity-to-volume ratio, resulting in sev- cells are used for all other commercial applications.
eral times the capacity of alkaline manganese and The 1.4V cells or batteries should be used for long-
carbon-zinc cells in the same volume, or propor- term continuous low-drain applications if a very flat
tionally reduced volume for the same capacity. voltage characteristic is not needed.
3. Flat discharge characteristic. Although Union Carbide and Mallory are two of the
4. Higher sustained voltage under load. major producers of mercury-zinc cells and batteries,
5. Relatively constant ampere hour capacity. there are, of course, other important producers such
6. LOW and substantially constant internal impedance. as Ever Keady (Berec) (UK), Crompton-Parkinson
7. No recuperation required, therefore the same (Hawker Siddeley) (UK) and Varta (West Germany).
capacity is obtained in either intermittent or Table 8.1 gives the type numbers of equivalent cells
continuous usage. that meet a given International Electrochemical Com-
8. Good high-temperature characteristics. mission (IEC) designation as produced by Union Car-
9. High resistance to shock, vibration and accel- bide. Mallory, Ever Ready (Berec) and Varta. In many
eration. instances equivalent cells are available from more than
10. Electrically welded or pressure intercell connec- one manufacturer. In such instances comparative cost
tions. quotations would be of interest to the intending pur-
11. Single or double steel case encapsulation. chaser.
12. Chemical balance - all the zinc is converted at the The performance characteristics of a 675 size mer-
end of the battery's life. cury-zinc primary button cell are Listed in Table 8.2.
13. Automatic vent.
14. Resistance to vacuum and pressure.
15. Resistance to corrosive atmospheres and high 8.2 Mercury-indium-bismuth an
relative humidity. mercury-cadmium primary batteries
The ampere halur capacity of mercury cells and bat- Mercury-indium-bismuth and mercury-cadmium
teries is relatitely unchanged with variation of dis- batteries are available from some manufacturers (q.
charge scheduk and, to some extent, with variation Crompton-Parkinson). These are alkaline systems
of discharge current. They have a relatively flat dis- recommended for applications where high reliability
charge charactierisfic (see Figure 8.1; compare this in particularly onerous long-term storage and use
with Figure 6.11 for alkaline manganese types). The conditions is a prime requirement.
mercury system withstands both continuous and inter- For example, the particular advantage of mer-
mittent discharge with relatively constant ampere hour cury-cadmium is that it will show good performance
output and this allows the capacity rating to be at low temperatures even below -20°C where most

1.4
-
-
> 1.2
m
01
s 1.Q
0.8
0 10 20 30 40 50
Discharge time (h)
Figure 8.1 Typical voltage discharge characteristics of mercury-zinc cells under continuous load conditions at 21 "C. At 1.25V, equivalent
current drains for the resistances are: 15 S2, 83 mA; 25 I;t, 50 mA; 32 Q,40 mA; 42 S2, 30 mA 50 a, 25 mA; 60 Q, 20 mA (Courtesy of Union
Carbide)