An elementary metal (symbol V), vanadium is widely distributed, and is a pale-gray metal with a silvery luster. Its specific gravity is 6.02, and it melts at 1780°C. It does not oxidize in the air and is not attacked by hydrochloric or dilute sulfuric acid. It dissolves with a blue color in solutions of nitric acid. It is marketed as 99.5% pure, in cast ingots, machined ingots, and buttons. The as-cast metal has a tensile strength of 372 MPa, yield strength of 310 MPa, and elongation of 12%. Annealed sheet has a tensile strength of 537 MPa, yield strength of 455 MPa, and elongation of 20%, and the cold-rolled sheet has a tensile strength of 827 MPa with elongation of 2%. Vanadium metal is expensive, but is used for special purposes such as for springs of high flexural strength and corrosion resistance.
Commercially important as an oxidation catalyst, vanadium also is used in the production of ceramics and as a colorizing agent. Studies have demonstrated the biological occurrence of vanadium, especially in marine species; in mammals, vanadium has a pronounced effect on heart muscle contraction and renal function.
Fabrication Hot Working
Since vanadium oxidizes rapidly at hot-working temperatures, forming a molten oxide, it must be protected during heating. This is most easily accomplished by heating in an inert-gas atmosphere. Other common practices have been found less suitable.
Vanadium ingots up to 152 mm in size have been successfully hot-worked, but the degree of contamination is a modifying factor. Generally, the procedures used in working alloy steels apply.
In view of the difficulties involved in heating the metal, reheating is generally avoided and the starting temperature is a function of the amount of hot work to be accomplished and of the desired finishing temperature. Starting temperatures can range as high as 1260°C and the finishing temperatures is limited by the beginning of recrystallization. Straightening is performed between 371 and 427°C but not at room temperature.
Vanadium has excellent cold-working properties, provided its surfaces are uncontaminated. They are therefore machined clean by removing between 0.50 to 1 mm.
Strip can be readily made from hot-rolled sections 31 x 152 mm in cross section, and 0.25 mm material has been produced without and 0.03 mm with intermediate annealing. Where incipient cracking is observed, vacuum annealing at 899°C becomes necessary.
Extrusion is one of the most suitable fabricating methods for vanadium, since warm extrusion followed by cold rolling or drawing avoids hot working with the troublesome heating step. At temperatures below 538°C, tube blanks 50.8 mm outside diameter x 6.4 mm wall thickness have been produced from hot-rolled and turned bars as well as from ingots.
Wires can be drawn from 9.5-mm-diameter stock down to 0.025 mm, especially after copper plating. Reductions are usually 10% per pass.
In machining, vanadium resembles the more difficult stainless steels. Low speeds with light to moderate feed are used and very light finishing cuts at higher speeds are possible.
Welding is not difficult but contamination of the metal must be avoided by shielding from air by means of an inert gas, i.e., argon.
Uses and Applications
The greatest use of vanadium is for alloying. Ferrovanadium, for use in adding to steels, usually contains 30 to 40% vanadium, 3 to 6% carbon, and 8 to 15% silicon, with the balance iron, but may also be had with very low carbon and silicon. Vanadium-boron, for alloying steels, is marketed as a master alloy containing 40 to 45% vanadium, 8% boron, 5% titanium, 2.5% aluminum, and the balance iron, but the alloy may also be had with no titanium. Van-Ad alloy, for adding vanadium to titanium alloys, contains 75% vanadium and the balance titanium. It comes as fine crystals. The vana-dium-columbium alloys containing 20 to 50% columbium, have a tensile strength above 689 MPa at 700°C, 482 MPa at 1000°C, and 275 MPa at 1200°C.
Vanadium salts are used to color pottery and glass and as mordants in dyeing. Red cake, or crystalline vanadium oxide, is a reddish-brown material, containing about 85% vanadium pentoxide, V2O5, and 9% Na2O, used as a catalyst and for making vanadium compounds. Vanadium oxide is also used to produce yellow glass; the pigment known as vanadium-tin yellow is a mixture of vanadium pen-toxide and tin oxide.
Vanadium is used in the cladding of fuel elements in nuclear reactors because it does not alloy with uranium and has good thermal conductivity as well as satisfactory thermal neutron cross section.
Because the metal alloys with both titanium and steel, it has found application in providing a bond in the titanium-cladding of steel. Also, the good corrosion resistance of vanadium offers interesting possibilities for the future; it has excellent resistance to hydrochloric and sul-furic acids and resists aerated salt water very well. But its stability in caustic solutions is only fair and, in nitric acid, inadequate.
Borides, Carbides, and Oxides
Vanadium boride, VB, has a melting point of 2100°C with oxidation at 1000 to 1100°C; density 5.1 g/cm3; Mohs hardness 8 to 9; electrical resistivity 16 Q-cm. It is also formed as VB2.
Vanadium carbide, VC, has a density 5.81 g/cm3 and is silver gray in color. It is chemically very stable; among the cold acids, it is attacked only by HNO3. Below 499°C, Cl2 reacts with VC. It burns in oxygen or air, but is stable to 2500°C in nitrogen. VC is harder than corundum.
Vanadium pentoxide, V2O5, has a melting point of 690°C and is slightly soluble in water. V2O5 is used by the ceramic industry as coloring agents producing various tints of yellow and greenish yellow. Vanadium pentoxide is an excellent flux and small amounts may be helpful in promoting vitrification of ceramic products. Vanadate glasses are relatively fusible when compared with other oxide types.