Amalgam (chemistry)

An amalgam (Greek μαλακός malakos, soft ' with alpha privative, ie the "non- Softening ."; Etymology by other Arab al malagma, emollient ointment ') is in chemistry, an alloy of mercury. When amalgam in the broader sense are often not ( easily ) reversible mixing other substances referred to, usually the alloy of several metals. In a figurative sense are called amalgam mixtures of different concepts, ideas, cultures or traditions.

Since many metals are soluble in mercury (an exception is, for example, iron), there are many amalgams. Amalgams with a very large proportion of mercury are often at room temperature - as the mercury itself - liquid, with smaller mercury levels they are fixed.

In classic alchemy, the amalgamation of mercury with other metals is often compared to the physical union. As alchemical lexeme is mlat. amalgama occupied since the 13th century.

Natural amalgams

There are several known naturally occurring amalgams and recognized by the IMA as an independent minerals:

• With Lead: Lead amalgam ( Pb2Hg )
• With Copper: Belendorffit ( Cu7Hg6 ) Kolymit ( Cu7Hg6 )
• Palladium: Potarit ( PdHg )
• With silver: Eugenit ( Ag11Hg2 ) Luanheit ( Ag3Hg ) Moschellandsbergit ( Ag2Hg3 ) Paraschachnerit (AG1, 2Hg0, 8) Schachnerit (AG1, 1Hg0, 9)

Technical amalgams and their use

Dental amalgam

In dentistry is an alloy of mercury with other metals, such as silver, copper, indium, tin and zinc, widely used as a dental filling material. A connection with serious health complaints could not be substantiated. A mercury pollution is minimal given, but not in the measurable range.

Sodium amalgam

A technically important reduction in the organic and inorganic chemistry and in a large scale produced amalgam is sodium amalgam, which is formed as an intermediate in the chlor-alkali electrolysis. It is decomposed with water to form caustic soda, hydrogen and mercury which is recycled to the electrolysis circuit.

Ammonium amalgam

Since the alkali metals form amalgams, for example in the electrolysis of solutions of alkali metal ions with mercury electrodes have been tried to produce an ammonium salt or ammonia amalgam ( the ammonium often behaves like the alkali metal ions ); Ammonium amalgam decomposes to form mercury, ammonia and hydrogen.

Gold amalgam

For gold production is still partially used mercury. This makes the gold, which is present in small flakes mixed with rock, a first liquid amalgam, which flows by its higher density of the lighter rock residues. To obtain pure gold therefrom, the amalgam is heated to evaporate the mercury; This process is also known as fuming. This produces highly toxic mercury vapors.

Gold amalgams are also used in the electroless gold plating, the so-called fire gilding. This gold amalgam is applied or coated onto a metallic object and by the action of heat, the mercury is vaporized.

Aluminum amalgam

Aluminum amalgam is used as the reducing agent.

Thallium amalgam

Thallium amalgam is used because of its low freezing point of -58 degrees Celsius as a thermometer for liquid cryogenic thermometers.

Other

Tin amalgam formed until the mid-19th century, the reflective coating of mirrors.

Amalgam can be used as a substitute for the otherwise technically necessary liquid mercury in CFLs. By the use of amalgam to the light flux over a wider temperature range remains almost constant. This advantage is made ​​especially for use in enclosed fixtures, Globe enclosures and outdoor use. A disadvantage is the low initial light output immediately after power, as the mercury evaporates at higher temperatures from the amalgam.

Amalgam sample

Mercury salts are highly toxic, in contrast to metallic mercury and amalgam due to their water solubility. They are facing the so-called amalgam sample: the nitric acid solution is added to a copper sheet - leaving a not a wipe-clean, silvery amalgam stain:

The mercury forms with the copper sheet metal, an alloy, the copper amalgam. Silver salts would form similar spots; However, the resulting silver is wiped off. Thus ultimately silver salts of mercury salts are distinguishable.

Amalgam process

In the chlor-alkali electrolysis for large-scale production of chlorine, caustic soda and hydrogen gas is used in the amalgam process mercury as the cathode, so that the salt water deposits from forming by reducing sodium than amalgam. The sodium amalgam migrates to the amalgam decomposer where it reacts with water to form salt- free sodium hydroxide, hydrogen gas and mercury. This electrolysis process has the advantage that it is salt- free sodium hydroxide supplies ( caustic soda), but is ecologically unacceptable, because to be deprived of the products mercury residues ( post-purification, detoxification, for example, activated carbon filters).