Nitro

Amalgame
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        Reprezinta un caz aparte de aliaje ale metelelor cu mercurul. Ele pot
fi constituite din solutii lichide, solutii solide, compusi intermetalici sau
amestecuri eterogene de compusi intermetalici in solutii de Hg.
        Amalgamele se produc prin simplu contact al metalelor cu mercurul la
rece:
        -metale alcaline
        -alcalino-pamintoase
        -Aur, Argint, Platina, Cupru

sau la anumite temperaturi:
        -Aluminiu
        -Paladiu

Formarea lor are loc cu degajare de caldura, mai ales a celor cu metalele
alcaline. In numeroase cazuri, in cadrul unui sistem M-Hg rezulta o suita de
compusi intermetalici.
  Ex:
  --
In cazul amalgamului de Na, au fost identificati compusii :
        NaHg6, NaHg4, Na3Hg2
        NaHg, Na5Hg2, Na3Hg
        Na7Hg8, NaHg2;
Amalgamele cu continut mic de metal strain sunt lichide, air cele cu
continut mare sunt solide, uneori cristalizate. Prin incalzire, amalgamele se
descompun in elemente, iar cele ale metalelor alcaline sau cu Al sunt usor
alterabile in aer sau in apa.
        Depuse pe suprafata metalelor rezistente fata de agenti chimici,
acestea devin active. Al descompune apa la rece cu degajare de O2, explicatia
fiind datorata faptului ca amalgamele indeparteaza pelicula protectoare si
aderenta de oxid.
        Amalgamele de Plutoniu sunt piroforice.

    Mercurul este elementul chimic aflat pe cea de-a 80-a poziţie în tabloul lui Mendeleev, cu simbolul Hg (din latinescul hydroargentum, argint lichid). Acesta este singurul metal din tabelul periodic al elementelor care este lichid la temperatura camerei ( luand tem,peratura camerei drept 20 de grade Celsius. Cesiul se topeste in jurul a 25 de grade iar galiul la 38 de grade), punctul de fuziune fiind -38 grade Celsius.Mercurul este un elemenmt cu densitate foarte mare( aproximativ 13,5 grame/ centimetru cub). Mercurul metalic se intrebuinteaza la fabricarea termometrelor, barometrelor, aerometrelor . Sarurile mercurului se folosesc in laboratoare si in medicina. De exemplu HgCl2 ( clorura mercuroasa) se foloseste ca desinfectant extern atunci cand alcoolul nu se poate folosi iar apa oxigenata sau rivanolul nu asigura o asepsie destul de temenica( de exemplu la recoltarea sangelui pentru determinarea alcoolemiei). Tot clorura mercuroasa se foloseste in laboratoarele de anatomie patologica ca si fixator la prepararea unor lame cu materie de analizat la microscop. Fulminatul de mercur se intrebuinteaza la fabricarea explozibililor(in special a capselor detonante) dar are dezavantajul; de a improsca cu picaturi de mercur metalic la momentul exploziei. Oxidul de mercur ( rosu, HgO) se intrebuinteaza la prepararea unor vopsele pentru protejarea metalelor. Clorura mercuroasa se mai intrebuinteaza la fabricarea fetrului pentru palarii. Calomelul se intrebuinteaza la electrozi pentru electroliza si electrodializa.

Utilizare:
Pe linga utilizarile in instalatiile electrochimice de laborator  (polarografia ) si in termometre, se foloseste pe scara larga in industria  chimica la fabricarea NaOH in electrizoare cu catod de mercur, iar in idustria  extractiva la separarea aurului si argintului prin amalgamare.
Amalgamele de Na se folosesc ca agenti reducatori in chimie, iar cele  de zinc si alte metale pentru plombe in stomatologie.
De asemenea joaca rolul de agent termic in reactoarele nucleare.  Sarurile sale se utilizeaza in farmacie, iar “fulminatul de mercur” la  detonarea explozivilor. Mai este folosit in pompele de difuzie cu mercur, care  permit obtinerea unui vid inaintat de ordinul a 10e-10 torr, in lampile de  iluminat etc.

ENG: Mercury
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Mercury is the only common metal liquid at ordinary temperatures. Mercury is sometimes called quicksilver. It rarely occurs free in nature and is found mainly in cinnabar ore (HgS) in Spain and Italy. It is a heavy, silvery-white liquid metal. It is a rather poor conductor of heat as compared with other metals but is a fair conductor of electricity. It alloys easily with many metals, such as gold, silver, and tin. These alloys are called amalgams. Its ease in amalgamating with gold is made use of in the recovery of gold from its ores.

The most important salts are mercuric chloride HgC1₂ (corrosive sublimate – a violent poison), mercurous chloride Hg₂Cl₂ (calomel, occasionally still used in medicine), mercury fulminate (Hg(ONC)₂, a detonator used in explosives), and mercuric sulphide (HgS, vermillion, a high-grade paint pigment).

Organic mercury compounds are important – and dangerous. Methyl mercury is a lethal pollutant found in rivers and lakes. The main source of pollution is industrial wastes settling to the river and lake bottoms.

As mercury is a very volatile element, dangerous levels are readily attained in air. Mercury vapour should not exceed 0.1 mg m^-3 in air. Air saturated with the vapour at 20°C contains mercury in a concentration far greater than that limit. The danger increases at higher temperatures. It is therefore important that mercury be handled with care. Containers of mercury should be securely covered and spillage should be avoided. Mercury should only be handled under in a well-ventilated area. If you are in possession of any mercury you are advised to contact a properly qualified chemist or public health laboratory for its safe disposal.

Small amounts of mercury spillage can be cleaned up by addition of sulphur powder. The resulting mixture should be disposed of carefully.

The physical appearance of mercury is well known because of its use in many thermometers. It was common to demonstrate the formation of mercury in the laboratory by heating mercury sulphide (cinnabar, HgS) but this is strongly discouraged today because of the toxicity of mercury vapours. Don’t do it! However, this method forms the basis of commercial extraction. The prepared cinnabar ore is heated in a current of air and the mercury vapour condensed.

HgS + O₂ (600°C) → Hg (l) + SO₂ (g)

The crude mercury is then washed with nitric acid and treated with air in order to remove impurities as oxides or into solution. Further purification is achieved by distillation at reduced pressure.