Another remarkable property of mercury: the ability to dissolve other metals, forming solid or liquid solutions – amalgams. Some of them, for example amalgams of silver and cadmium, are chemically inert and solid at the temperature of the human body, but they are easily softened by heating. Of them, dental fillings are made.
Amalgam thallium, hardening only at -60 ° C, is used in special designs of low-temperature thermometers.
The old mirrors were covered not with a thin layer of silver, as is done now, but with an amalgam containing 70% of tin and 30% of mercury. In the past, amalgamation was the most important technological process when extracting gold from ores. In the XX century, it could not stand competition and ceded to a more perfect process – cyanidation. However, the old process finds application now, mainly when extracting gold, finely impregnated in ore.
Some metals, in particular iron, cobalt, nickel, practically do not lend themselves to amalgamation. This allows the liquid metal to be transported in containers of simple steel. In addition to iron and its analogues, tantalum, silicon, rhenium, tungsten, vanadium, beryllium, titanium, manganese and molybdenum are not amalgamated, that is, almost all the metals used for alloying steel . This means that mercury is also not afraid of alloyed steel.
But sodium, for example, is easily amalgamated. Amalgam sodium is easily decomposed by water. These two circumstances have played and continue to play a very important role in the chlorine industry.
In the production of chlorine and sodium hydroxide by electrolysis of common salt, cathodes of metallic mercury are used. To get a ton of caustic soda you need from 125 to 400 g of element number 80. Today, the chlorine industry is one of the most massive consumers of metallic mercury.
It is obtained by the interaction of the metal with mercury (when the surface of the metal is wetted with mercury) at ordinary temperatures or by heating, by electrolytic separation of the metal or cationic complex on the mercury cathode, or by other methods. Many metals form stable compounds with mercury (mercurides).
Amalgam is used in the gilding of metal products, in the manufacture of mirrors, as well as in fluorescent lamps, including compact energy-saving fluorescent lamps and induction lamps. Amalgams of alkali metals and zinc in chemistry are used as reducing agents. Amalgam is used in the electrolytic production of rare metals, the extraction of certain metals from ores (see Amalgamation). Amalgam is used in cold welding in microelectronics. Still in many countries, silver amalgam is used in dentistry as a material for dental fillings.