Applications of Vanadium

By far the largest proportion of the world's production of vanadium is absorbed in the production of ferrovanadium alloy for the manufacture of vanadium steels, which usually contain up to 0.3 per cent, of vanadium. The effect of the addition of vanadium to a steel is to increase its tensile strength enormously, also its hardness, and its resistance to shock and fatigue. A good carbon steel containing about 1.10 per cent, of carbon has an elastic limit of about 30 tons per square inch and an ultimate stress of about 60 tons per square inch. Addition of 0.3 per cent, of vanadium to such a steel raises the elastic limit to 43 tons and the maximum stress to 76 tons per square inch, while addition of 0.6 per cent, of vanadium gives an elastic limit of 65 tons and a maximum stress of 85 tons per square inch. Similar improvement in physical properties takes place with the incorporation of small quantities of vanadium into cast iron. Vanadium steels are admirably suited to situations where they are subject to varying stresses and vibrations. They are used in the construction of transmission shafts, piston rods, axles, bolts, gears, motor-car parts, aeroplane parts, and in tools for punching, shearing, and drawing. The coefficients of thermal expansion of vanadium steels are given by Souder and Hidnert.

It is found that the use of vanadium up to about 1 per cent, with tungsten and molybdenum in the manufacture of high-speed tools again exerts a favourable influence by imparting increased cutting efficiency under heavy working conditions. The presence of a small proportion of vanadium reduces the quantity of tungsten or molybdenum required to impart to the steel definite hardness and toughness. Used in conjunction with other alloying metals, e.g. in nickel steels, cobalt steels, chromium steels, and nickel-chromium steels, it produces equally useful results. These special steels closely resemble the chrome- nickel steels, but have the advantage of greater freedom from surface imperfections. They are employed mainly in automobile construction. Some chromium-vanadium steel which has high resistance imparted by heat treatment is used for armour plate of medium thickness, gun shields, gun tubes, torpedo tubes, etc. The use of vanadium steel for the manufacture of Brinell balls has recently been suggested.

The function of vanadium in steel appears to be twofold: (a) It acts as a "scavenger," removing traces of oxygen and nitrogen, and (b) it effects a more homogeneous distribution of carbon throughout the mass. The vanadium displaces the iron from the iron carbide, Fe₃C, in the steel, producing vanadium carbide, V₄C₃, which does not segregate as readily as cementite or pearlite, with the consequence that the carbon is more evenly distributed throughout the mass and a finegrained structure results. In the case of cast iron, vanadium also assists the retention of the carbon in the combined form.

Vanadium finds application to a limited extent in the manufacture of non-ferrous alloys. The introduction of the metal up to about 0.5 per cent, into brasses which contain from 60 to 70 per cent, of copper and 30 to 40 per cent, of zinc is stated to increase the maximum stress and elongation. Copper-vanadium and aluminium-vanadium alloys are used in aeroplane construction; an aluminium-manganese-vanadium alloy is used for castings, and a copper-vanadium bronze is used in marine work. Addition of vanadium also improves the tensile strength and the elastic limit of copper-aluminium bronzes and of copper-zinc-aluminium bronzes, but not beyond the amount due to its deoxidising properties.

Vanadium compounds function as extremely efficient catalysts in various oxidative reactions of technical importance. They are used in the oxidation of aniline to aniline-black, of naphthalene to phthalic anhydride, of anthracene to anthraquinone, of benzene to maleic acid, of toluene to benzaldehyde and benzoic acid, as well as in the conversion of acetylene into acetaldehyde. Among important inorganic processes in which vanadium catalysts are employed are the oxidation of ammonia to nitric acid and of sulphur dioxide to sulphur trioxide. To prepare the catalyst for these operations, pure alumina, or other inert, porous material of the type of pumice or kieselguhr, may be mixed with about 10 per cent, of ammonium metavanadate or other vanadium salt and compressed into briquettes, which are then strongly heated; the vanadate decomposes and leaves a porous block impregnated with finely divided vanadium pentoxide. Alternatively, ferric chloride, or a soluble salt of another metal, is added to a solution of ammonium metavanadate which has been acidified with hydrochloric acid; the precipitated vanadate is washed, dried, and gently ignited. Recently, complex vanadium silicates have been introduced, particularly to replace platinum in the contact process for the manufacture of sulphuric acid. It is claimed for them that they are closely parallel to the best platinum catalysts with respect to optimum temperature, conversion equilibrium, and activity, and have the advantages of being cheaper and of not becoming poisoned by arsenic or hydrochloric acid. In the laboratory the vanadium catalyst can be prepared by soaking asbestos fibre in a dilute solution of vanadyl sulphate, VOSO₄, which is obtained by reducing a boiling solution of ammonium vanadate with sulphur dioxide at 40° to 50° C.; the solution is made alkaline with ammonia and evaporated almost to dryness; the fibre is then dried and heated to about 500° C. to decompose ammonium salts.

Vanadium salts have also been found to be effective as catalysts in various electrolytic oxidation and reduction processes; for example in the preparation of hypochlorites, the reduction of polynitro-aromatic compounds, and in the sulphonation of aromatic compounds. On being incorporated into a drying oil in the form of a rosinate or linoleate, vanadium accelerates oxidation of the oil even more efficiently than lead or manganese, which are commonly used for the purpose, but not so efficiently as cobalt. The oxidised film is smooth and tough. Vanadium cannot, however, be incorporated into oils to be used for white paints, as the film possesses a brown colour.

On being fired at a red heat with pottery or glass, vanadium compounds impart a fine gold colour with a greenish tinge. Vanadium chlorides and other vanadium compounds are used with potassium ferricyanide in toning bromide prints; the green colour which is produced is attributed to the deposition of yellowish-green vanadium ferrocyanide together with Prussian blue. A solution of vanadium pentoxide in sulphuric acid is used under the name of Mandelin's Reagent in testing for the presence of various alkaloids.

Main article: Vanadium Alloys Vanadium alloys readily with many metals, including aluminium, cobalt, copper, iron, manganese, molybdenum, nickel, platinum, and tin, also with silicon. These alloys have hitherto received scant attention, and little is known in most cases of the systems produced.

Vanadium compounds are poisonous when taken internally. The usual symptoms are paralysis, convulsions, lowering of the body temperature, and feeble pulse. The fatal dose in the case of a rabbit is between 0.00918 and 0.01466 gram. Workmen exposed to fumes of vanadium compounds, especially those engaged on ore-reduction plants, are said to be susceptible to vanadium poisoning, but this has been denied. Vanadium compounds have been shown to possess antiseptic action, and in suitable form to be useful in medicine; they are not, however, at present used in medicine.