Vanadium (V) — refractory metal (melting point=1915 °C), chemically quite inert. The standard conditions on the hardness scale of metals the vanadium is in the middle position. The hardness of vanadium is much smaller than, for example, titanium and chromium, but higher than copper and aluminum.
Vanadium can be dissolved only in hot concentrated sulfuric or nitric acid, Aqua Regia. It is the chemical resistance provided this metal widely used. Alloy of vanadium and Nickel, having mechanical properties of steel far exceeds the vanadium in chemical resistance.
Pure vanadium is got from vanadium oxide with calcium:
Vanadium exhibits a wide variety of oxidation States from +2 to +5. The highest oxide of V2O5 is the substance of yellow-orange color. The corresponding acid exists only in solution.
Vanadium reacts with hot alkali:
and form the vanadium salts of the acid - Vanadate.
Even greater use is ferrovanadium is an alloy of vanadium with iron. The vanadium in such alloy contains up to 30 %.
Vanadium is relatively cheap and can easily replace steel in the creation of corrosion-resistant products. Even a small (1%) vanadium content in steel increases its elasticity is about two times!
Chrome(Cr) is a silvery white metal, hard and refractory (tm.p.=1890 °C). At room temperature it is not oxidized in the air. Chrome metal resistant to oxidation even at elevated temperatures, but in the powder form (in the form of small chips) - burns in air at 300 °C and forms green chrome oxide (III) Cr2Î3.
Ferrochromium (contains about 60 % chromium) and pure chrome are used as additives to steel: formed alloy — chromium steel has a high hardness and resistant to oxidation. The most popular brand of stainless steel contains 18% chromium and 6% Nickel. This steel is used in chemical and petrochemical industries, as well as for the manufacture of household appliances. Alloys of chromium and nickel — nichrome, not only corrosion resistant, but also has high electrical resistance. They are used to get the spiral filament electric heaters. Many products coated with a thin (0.1 µm) layer of chromium metal is chrome plated. The chrome adds a beautiful appearance and protects from corrosion.
The name "chrome" (from Greek "chromium" — "color", "paint") emphasizes the diversity of color of salts of this metal. Thus, in aqueous solutions of chromium compounds (II) are of sky blue color, chromium (III) purple or green, chromium (VI) — orange or yellow. If chromium compounds (II) have the basic properties, the compounds of trivalent chromium are amphoteri.
Sulfide chromium is the chemical formula of(Cr2S3). But sometimes properties of the obtained compounds strongly depend on what chemical reaction use when it is received. Here, an example, any attempt to get a sulfide of chromium Cr2S3 from water solution is doomed to failure: the resulting substance is easily decomposed with water with precipitation of chromium hydroxide Cr(OH)3 and the release of large amounts of hydrogen sulfide:
However, if in the quartz tube place a few grams of powder of anhydrous chromium chloride, over which pass a dry hydrogen sulphide, gradually raising the temperature to 600 °C, is formed of chromium sulfide Cr2S3 in the form of black crystals with a metallic sheen:
2CrCl3+3H2S +t°→ Cr2S3+6HCl.
This compound is inert not only to water but also to dilute acids.