Iridium is the most corrosion resistant metal, but why is it not the most chemically stable

Corrosion resistance and HE chemical stability are two different concepts.

Corrosion resistance description It is difficult to react directly with acid and alkali [that is, temperature, pressure, or after the catalyst is added, the reaction can occur].

The chemical properties are stable, which means that they do not react with other substances under general conditions (for example, noble gases, the reaction conditions are very harsh).

Iridium. 1.Elements: Periodic group VIII platinum elements, symbol IR, atomic number 77, atomic weight, peripheral electron shell configuration 5d76s2, first ionization energy electron volts.

2.Physical properties: Silvery-white metallic, hard and brittle.

During thermal processing, as long as it is not annealed, it can be expanded into filaments and thin sheets; Once annealed, it loses its ductility and becomes hard and brittle. Density grams of cubic centimeters. Melting point 2410+-40c

Boiling point 4130cFace-centered cubic crystals.

3.Chemical properties: The chemical properties are very stable, insoluble in acids, slightly soluble in aqua regia; Slightly attacked by molten sodium hydroxide, potassium hydroxide and sodium dichromate. There is a strong tendency to form complexes. The main valence is +2, +4, +6

4.History: Iridium, derived from iris, means "goddess of the rainbow".In 1803, it was discovered by the Englishman Tennant.

5.Application: Pure iridium is used exclusively in aircraft spark plugs.

It is mostly used to make scientific instruments, thermocouples, resistance wires, etc. It is used as an alloy to enhance the hardness of other metals. It is an alloy formed with platinum (10% IR and 90% PT), which is often used to make international standard meters because of its very small expansion coefficient.

Iridium can resist corrosion, which has a lot to do with the surface oxide film.

Modulus of bulk elasticity: GPA 320.

Enthalpy of atomization: kj mol @25 628.

Heat capacity: j (mol· k).

Thermal conductivity: w (m·k) 147.

Electrical conductivity: 10-6 (cm·

Heat of melting: (kJ mol).

Heat of vaporization: (kJ mol).

In fact, under certain conditions, there are very few liquids that can corrode iridium, but it does not mean that there are none, here are two examples:

1. The chemical properties of iridium are very stable. is the most corrosion-resistant metalIridium is extremely chemically stable to acids and is insoluble in acids, and only the spongy iridium slowly dissolves in aqua regiaIf it is iridium in a dense state, even boiling aqua regia cannot corrode iridium; Slightly attacked by molten sodium hydroxide, potassium hydroxide and sodium dichromate. Ordinary corrosives cannot corrode iridium.

There is a strong tendency to form coordination compounds. The main valence is +2, +4, +6

2. In fact, for ordinary iridium, at least at atmospheric pressure, among all acids, alkalis, and salts, only boiling magic acid can slowly corrode it.

Therefore, iridium metal cannot withstand the corrosion of 155 boiling magic acid for a long time.

Iridium has extremely high chemical stability to acids, insoluble in acids, only spongy iridium will slowly dissolve in hot aqua regia, if it is iridium in a dense state, even if it is boiling aqua regia, it cannot be corroded; However, in a closed reactor under high temperature pressure, iridium is significantly corroded in aqua regia above 250°C. The mixed acid, which consists of 20 parts concentrated hydrochloric acid and 1 part concentrated nitric acid, is about 20 times more corrosive to iridium than aqua regia at the above temperature and pressure, so it is commonly used as a reagent for the digestion of metal iridium in chemical analysis.

1.It is the only metal that can withstand 150 degrees of pressurized aqua regia, and the use temperature can reach 200 degrees, other metals, tantalum can not be used above 150 degrees, and ruthenium and rhodium will be significantly corroded at about 140 degrees. Chromium begins to corrode at temperatures above atmospheric boiling.

2.The only metal with a corrosion rate of less than 190 years in 37% oxygenated hydrochloric acid.

3.It is one of the two metals that can be boiled at 338 degrees in concentrated sulfuric acid without corrosion (the other metal is ruthenium).

4.It is the only metal that is completely corrosion-free in a high concentration of phosphoric acid at 400 degrees.

5.It is the only metal that is completely corrosion-free in a 360 degree, 25MPa pressurized 5% H2SO4 + 5% HCl + 1% H2O2 high corrosive solution. (Under this working condition, even the corrosion rate of platinum is as high as more than 1mm per year).

In fact, of all the acids, bases, and salts, at least at atmospheric temperatures, only boiling magic acid can slowly corrode iridium.

1) Metal iridium is usually a silvery-white solid, with a melting point of 2410, high density and hardness, and good ductility at high temperatures.

2) From the inscription, it can be seen that the iridium metal is chemically resistant to reeds at room temperature, and can be heated with O2 when heated in air

Reaction is a property that is manifested in chemical changes, and it belongs to chemical properties, so the answer is: (1) silvery-white solid, melting point 2410, high density and hardness, and good ductility at high temperature; (2) The chemical properties are inactive at room temperature, and it can react with Lu Mu O2 when heated in the air