July 1959 Popular Electronics
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Scott, prepare to load the promethium batteries into the
chamber." OK, I made up the promethium batteries
part, but you might not have suspected it. Back in the mid to late 1950s,
atomic batteries were seriously thought to potentially (no pun intended)
be a futuristic source of energy storage and generation. The concept
worked by having beta particles from promethium decay impinge on silicon
photodetectors, and having that be the source of power. That's almost
as Rube Goldbergish as having a gasoline engine drive an electric generator
to power a motor for automotive locomotion. Oh, wait, that describes
the Chevy Volt.
Note that in 1959, nickel cadmium (NiCad) batteries
were just coming into commercial use, and the author envisions a day
when they might be used for portable power tools and flashlights. At
least he was right about that one.
See the 1957 edition of Time
magazine with an article titled, "Science:
New Atomic Battery
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Recent Developments in Battery Design
Atomic batteries, fuel cells, and other new battery types hold
great promise for the future
by Saunder Harris, WINXL
soldiers at a front-line observation post crouch behind a strange-looking
device that looks like a spotlight: As they wait in the darkness, instead
of straining their eyes to discern enemy movements, their attention
is riveted to the spotlightlike device. Capable of spotting a single
enemy soldier a half-mile away in total darkness, this is the Army's
new "Silent Sentry" mobile radar set.
. Operation of the fuel cell. Electron flow
from hydrogen electrode to oxygen electrode provides electric current.
who did much of the research on the
fuel cell, Dr. Karl Kordesch, examines an electrode used in the
and mercury batteries such as these
are already on the market.
. Exploded view of mercury battery (courtesy
National Carbon Company)
. Comparison of discharge curves of mercury
cell and carbon-zinc cell. It is readily seen that the mercury cell
enjoys a much longer useful service life.
. Typical simple rectifier circuit employed
to reactivate rechargeable batteries.
. Promethium cell composed of center layer
of promethium and phosphor with outer layers made up of photocells.
Under battle conditions quiet operation of the Silent Sentry could be
a matter of life or death; therefore, a noiseless source of power for
the unit is essential. Obviously, here is a job tailor-made for batteries.
But which type should be used? Of a whole parade of new batteries, the
Army has chosen one of the newest-the little-known fuel cell-to power
the Silent Sentry.
The fuel cell is only one of the new battery
types which are today proving their worth. Already on the commercial
market are the tiny, power-packed mercury cell and the rechargeable
nickel-cadmium battery. Before long, the fuel cell, too, will be available
to private citizens. And the most fascinating development in batteries
- the amazing promethium cell which is powered by energy from the atom
itself - is now being tested and refined in research laboratories in
Let's examine these "wonder" batteries. First,
since it's one of the newest, we'll take a look at the fuel cell, the
power source of the Silent Sentry. Fuel Cell
The most interesting characteristic of the fuel cell is that, unlike
conventional batteries, it never becomes exhausted. Since it produces
electrical current from the electrochemical reaction which takes place
when oxygen and hydrogen are combined, the fuel cell itself remains
usable as long as the "fuel" - oxygen and hydrogen - is supplied.
Operation of the fuel cell is diagrammed in Fig. 1. Oxygen and
hydrogen enter the cell through two hollow carbon electrodes. Since
these electrodes are porous, the gases rapidly diffuse to the outer
surface of the electrodes where they come into contact with the electrolyte,
a solution of potassium hydroxide. The chemical reaction which takes
place releases electrons from the hydrogen electrode which flow through
the external circuit and are returned at the oxygen electrode. It is
this flow of electrons which provides the electric current. Water, a
by-product of the reaction, is passed from the cell in the hydrogen
One fuel cell can produce only about one volt. Any required
voltage may be attained, however, by simply connecting the cells together
in series. As with ordinary dry cells, the amount of current which can
be drawn from a fuel cell is a function of its physical size. Thus,
by varying the number and size of the cells, many variations of voltage
and current can be obtained. Fuel cells have been operating eight hours
a day, five days a week, for over a year with no sign of deterioration.
It is very possible that the fuel cell will be the practical
means of putting both nuclear energy and solar energy to use. At present,
one of the big difficulties involved in using the energy of the sun
is in storing its power for future use. Now, during the sunlight hours,
the sun's energy could be used to decompose water, producing both hydrogen
and oxygen for later use in fuel cells. In the same manner, where nuclear
reactors are used as heat sources in steam generating plants, the nuclear
energy decomposes water. Instead of this being a disadvantage, as it
has been, this process can now be the means of producing the necessary
hydrogen and oxygen for fuel cell operation. Mercury
. Wherever long life and lots of punch must be jammed
into a small package, the mercury battery has come into wide use. This
battery was developed primarily for hearing aids and other ultra-miniature
An exploded view of a typical mercury battery is
shown in Fig. 2. The materials used in its construction are high-purity
zinc powder for the anode, mercuric oxide and carbon for the cathode,
and potassium hydroxide as the electrolyte. The mercury cell develops
an open-circuit voltage of approximately 1.35 volts.
3 illustrates the difference in performance between the mercury cell
and the standard carbon-zinc cell. It can be readily seen that the voltage
of the mercury cell remains constant over a longer period of time than
does the carbon-zinc cell.
For general use, the mercury battery
is very expensive. The size "D" mercury battery (flashlight size) costs
about $2.50 as compared with a price of 20 cents for an ordinary carbon-zinc
"D" cell. This high cost is due to the expensive materials used in construction.
Mercury batteries became financially practical only when devices such
as hearing aids were designed to use them. Nickel-Cadmium
. Along with other dry cells, the mercury battery suffers
from one big disadvantage. It cannot be recharged. However, rechargeable
nickelcadmium batteries are just coming into popular use today in rechargeable
flashlights, radios and electric razors. Tomorrow they may be used to
power TV sets, portable electric drills, and perhaps even your car.
After conventional dry cells have been used awhile, the action
of the cell is gradually choked off by a gas which is developed in the
cell. In the nickel-cadmium battery, the recharging process converts
this gas back into a liquid, thus reactivating the cell. Recharging
is accomplished by plugging the battery unit into the house power line.
Figure 4 shows a typical half-wave rectifying circuit used for this
purpose. In most cases, the rectifier is built into the same unit as
Nickel-cadmium cells can't give you something for
nothing, however. Rechargeable cells cost more, and give less energy
per charge than an ordinary carbon-zinc cell. For example, a nickel-cadmium
flashlight cell costs about $2.75 as against 20 cents for a comparable
carbon-zinc cell. But it can be charged over and over.
more expensive than the nickelcadmium battery is its highly refined
"cousin," the silver-cadmium battery. This battery enjoys all the advantages
of the nickel-cadmium design, and, in addition. offers higher output
at one-half to onethird its size and weight. Since the silvercadmium
battery is quite costly, its greatest application so far has been in
rockets. missiles, and satellites. Atomic Batteries
Much misleading publicity has surrounded the atomic battery. In spite
of newspaper reports which would lead you to believe that an atomicpowered
radio is just around the corner this is not the case. As one battery
engineer put it, "there are a great many problems to be solved before
atomic batteries are brought out of the laboratories and put into your
One objection to the atomic battery i its potential danger.
How would you like to have a little package of radioactivity around
the house where it might be broken into by youngsters with a yen for
experiments? Another objection is cost; at this time, the material which
goes into such batteries is extremely expensive, The batteries we have
working for us now do a good job at reasonable cost and the idea of
replacing them with atomic batteries might be novel but cannot be considered
practical at present .
However, laboratory research continues
on the atomic battery. Radioactive promethium - promethium is a by-product
of uranium fission - is the power source. It is valuable because it
emits large amounts of beta rays (actually electrons) over its 2 1/2-year
half-life. These beta rays can be tapped as a source of power. Alpha
a gamma rays are emitted only in small quantities.
The actual size of the promethium and its shielding is about that of
a penny Figure 5 shows a typical promethium cell in cross section. The
center layer is a mixture of promethium and phosphor. Small photocells
compose the outer layers. When the promethium gives off beta rays, they
strike the phosphor with great force. The phosphor then lights up in
much the manner as your TV screen does when the electron stream of the
cathode-ray tube hits it. This light is then converted to electrical
energy by the two outer layers of photocells.
Output of the
promethium cell is small actually less than one-millionth of the electrical
power used by a 40-watt bulb. It does give off power, though, and the
power comes from atomic radiation. Considering its early stage of development,
the promethium cell shows great promise.
Any discussion of batteries
must necessarily lead us back to the fact that the carbon-zinc cell
is still battery king of the present. And in the distant future, when
you send one of the kids down to the Lunar Hardware on the Moon to pick
up a battery for your flashlight, chances are you will end up with our
old friend, the carbon-zinc cell.