Mercuric oxide cathode

The HgO is usually mixed with a conductive carbon powder, like graphite, to improve the electrical conductivity of the cathode. Mercuric oxide forms Hg as it is... 

Batteries. Many batteries intended for household use contain mercury or mercury compounds. In the form of red mercuric oxide [21908-53-2] mercury is the cathode material in the mercury—cadmium, mercury—indium—bismuth, and mercury—zinc batteries. In all other mercury batteries, the mercury is amalgamated with the zinc [7440-66-6] anode to deter corrosion and inhibit hydrogen build-up that can cause cell mpture and fire. Discarded batteries represent a primary source of mercury for release into the environment. This industry has been under intense pressure to reduce the amounts of mercury in batteries. Although battery sales have increased greatly, the battery industry has aimounced that reduction in mercury content of batteries has been made and further reductions are expected (3). In fact, by 1992, the battery industry had lowered the mercury content of batteries to 0.025 wt % (3). Use of mercury in film pack batteries for instant cameras was reportedly discontinued in 1988 (3). 

Miniature zinc—mercuric oxide batteries have a zinc anode and a cathode containing mercuric oxide... 

Some battery-producing companies prefer purchasing pure, nonamalgamated zinc powder to apply their own proprietary corrosion protection system. The general trend is to keep the anodes of all the consumer cells mercury-free (usually indicated by a "green label) and to make them disposable with the regular household trash. The exceptions to this rule are those cells where this makes no sense, such as cells with a mercuric oxide cathode. 

Mercury batteries (cells) consist of a zinc anode and a mercuric oxide cathode. These cells produce a steady 1.3 volts throughout the cells hfetime. 

William Cruickshank in 1787 and Adair Crawford in 1790 independently detected strontium in the mineral strontianite, small quantities of which are associated with calcium and barium minerals. They determined that the strontianite was an entirely new mineral and was different from baryta and other barium minerals known at the time. In 1808, Sir Humphry Davy isolated strontium by electrolysis of a mixture of moist strontium hydroxide or chloride with mercuric oxide, using a mercury cathode. The element was named after the town Strontian in Scotland where the mineral strontianite was found. 

Mercury cells, like dry cells, have a zinc anode and a use a mercuric oxide (HgO) cathode. The electrolyte is potassium hydroxide, KOH. These small, flat, metallic cells are widely used in watches, calculators, cameras, hearing aids, and other applications where small size is a premium. The reactions in the mercury cell are ... 

This system, commonly known as the mercury cell , is based on an amalgamated zinc anode, a concentrated aqueous potassium hydroxide electrolyte - saturated with zincate ion by zinc oxide - and a mercuric oxide/graphite cathode ... 

The most obvious advantages of the oxygen cathode are that it has low weight and infinite capacity. Consequently, prototype D-size cells based on the zinc-air system have been shown to have twice the overall practical capacity of zinc-mercuric oxide cells (and 10 times that of a standard Leclanchd cell) when subjected to a continuous current drain of 250 mA. In the larger industrial cells, energy densities of up to 200 Wh/kg and specific capacities of 150 Ah/dm3 may be obtained. On the other hand, a catalytic surface must be provided for efficient charge transfer at the oxygen cathode, and by its nature the electrode is susceptible to concentration polarization. 

Mercury batteries with cathodes of a mixture of mercuric oxide and manganese dioxide have a voltage of 1.4 V and a more sloping discharge curve. 

A third primary dry cell is the zinc-mercuric oxide cell depicted in Figure 17.7. It is commonly given the shape of a small button and is used in automatic cameras, hearing aids, digital calculators, and quartz-electric watches. This battery has an anode that is a mixture of mercury and zinc and a steel cathode in contact with solid mercury(II) oxide (HgO). The electrolyte is a 45% KOH solution that saturates an absorbent material. The anode half-reaction is the same as that in an alkaline dry cell,... 

Amalgams with the alkali metals are readily formed by plunging the latter into warmed mercury. They are of interest in that by using a mercury cathode, Sir Humphry Davy in 1807 was able to isolate both potassium and sodium by electrolysis of potash and soda (p. 144). Mercury is used to-day in the commercial manufacture of caustic soda and hydrochloric acid by the electrolysis of brine. It is used also as the raw material for the preparation of mercuric oxide, vermilion, mercurous and mercuric chloride, fulminate and other derivatives. The oxide is of special historical interest as it led 170 years ago to the discovery of oxygen (p. 21)... 

Essentially the same constituents as alkaline manganese cells, except that mercuric oxide has replaced manganese dioxide. Silver may be present in the cathode. Mercury cells are being phased out wherever feasible. 

Over the years, several different battery technologies have been tried. Including mercury-zinc, rechargeable silver-modified-mercuric-oxide-zinc, rechargeable nickel-cadmium, radioactive plutonium or promethium, and lithium with a variety of different cathodes. Lithium-cupric-sulfide and... 

It is also normal to use the highest grade of manganese dioxide (inevitably more expensive) but in all respects the performance of such batteries is superior to the Leclanch cell. In the small (0.02—0.2 A h) button cells, the cathode active material is more commonly mercuric oxide + graphite or silver oxide + graphite pressed into pellets and the electrolyte is again aqueous potassium hydroxide (Fig. 10.19). The cell reactions are... 

Reactions (1.3) and (1.4) will actually proceed only when the two electrodes are connected outside the cell containing them. Electrons then flow from the zinc anode (the negative pole of the cell) to the mercuric oxide cathode (the positive pole). The cell is said to undergo discharge while producing current. Within the cell, the hydroxyl ions (OH ) produced by reaction (1.4) at the cathode are transferred (migrate) to the anode, where they participate in reaction (1.3). The ions and electrons together yield a closed electrical circuit. 

Inorganic mercury is now employed in the chlor-alkali industry (where chlorine is produced by electrolysis of sodium chloride using a mercury cathode) and in the production of electric batteries, mercury vapor lamps and electrical relays with liquid contacts. It is also used in paint manufacture and as a catalyst, in the form of mercuric chloride (HgCl2), in the manufacture of vinyl chloride, urethane plastics and acetaldehyde. Elemental mercury is universally used in chemical and physical laboratories and in thermometers and barometers. Mercury is still used in the form of mercuric oxide (HgO) as a catalyst in Kjeldahl procedures for deterjnining total nitrogen in soils and plant tissues and it may find its way into laboratory drains from this source [63]. 

Some types of zinc/mercuric oxide cells exhibit open-circuit voltages between 1.40 and 1.55 V. These cells contain a small percentage of manganese dioxide in the cathode and are used where voltage stability is not of major importance for the application. 

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