Vanadium, Niobium, Tantalum, and Protactinium

Zirconium occurs in nature principally as the mineral zircon, ZrSi04. Zircon crystals are found in a variety of colors —white, blue, green, and red —and because of its beauty and hardness the mineral is used as a semiprecious stone. The principal oxidation state of zirconium is +4 the states +2 and +3 are represented by only a few compounds. [Pg.659]

Hafnium is closely similar to zirconium, and natural zirconium minerals usually contain a few percent of hafnium. The element was not discovered until 1923, and it has found little use. [Pg.659]

Thorium is found in nature as the mineral thorite, Th02, and in mona-zite sand, which consists of thorium phosphate mixed with the phosphates of the lanthanons (Section 18-7). The principal use of thorium is in the manufacture of gas mantles, which are made by saturating cloth fabric with thorium nitrate, Th(NOa)4, and cerium nitrate, Ce(N03)4. When the treated cloth is burned, there remains a residue of thorium dioxide and cerium dioxide, Th02 and Ce02, which has the property of exhibiting a brilliant white luminescence when it is heated to a high temperature. Thorium dioxide is also used in the manufacture of laboratory crucibles, for use at temperatures as high as 2300°C. [Pg.659]

Vanadium is the most important element of group Va. It finds extensive use in the manufacture of special steels. Vanadium steel is tough and strong, and is used in automobile crank shafts and for similar purposes. The principal ores of vanadium are vanadinite, Pb5(V04)3Cl, and carno-tite, K(U02)V04-IH20. The latter mineral is also important as an ore of uranium. [Pg.659]

The chemistry of vanadium is very complex. The element forms compounds representing the oxidation states +2, +3, +4, and +5. The hydroxides of bipositive and terpositive vanadium are basic, and those of the higher oxidation states are amphiprotic. The compounds of vanadium [Pg.659]

Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...