Preparation

Scandium and Titanium Subgroups

Metallic scandium was obtained in 1937 by electrolysis of a eutectic mixture of potassium, lithium, and scandium chlorides at 700–800 °C. Especially pure 99% metallic scandium was produced in 1960. Aluminium-scandium alloys are widely used.

Metallic Ti, Zr and Hf preparation has difficulties since the bond energy of these elements with O, N, and C is high. For instance, the reagent required to extract titanium from its various ores can not be carbon, because with titanium the latter gives titanium carbide.

Titanium subgroup elements are mostly produced by metalthermy from chlorides or fluorocomplexes. W. Kroll proved that titanium could be produced by reducing titanium tetrachloride (TiCl₄) with magnesium, calcium, and even sodium in what became known as the Kroll process:

Titanium chloride is obtained at the action of carbon and chlorine on titanium ores:

TiO₂ + 2C + 2Cl₂ = TiCl₄ + 2CO

It is reduced by magnesium:

TiCl₄ + 2Mg = Ti + 2MgCl₂

The product is spongy titanium.

Production of Zr and Hf is the reaction between fluorocomplexes of metals with sodium:

K₂ZrF₆ + 4Na = Zr + 4NaF + 2KCl

In turn, fluorocomplexes are obtained by sintering silicates:

ZrSiO₄ + K₂SiF₆ = K₂ZrF₆ + 2SiO₂

Titanium of very high purity was obtained in small quantities when Anton Eduard van Arkel and Jan Hendrik de Boer discovered the iodide, or crystal bar, process in 1925, by reacting with iodine and decomposing the formed vapors over a hot filament to pure metal.

Zr_(cryst) + 2I_{2 (g)} ZrI_4(cryst)

Equilibrium of this reaction is shifted to the left at high temperature, and to the right at low temperature (S<0). This process is usually called the transport reaction and can be applied to other elements (Si, Bi etc.)

A titanium crystal bar made by the iodide process

The scheme of transport reaction: 1- dusty metal, 2, 4 – current supply, 3 – Zr of very high purity that is heated, 5 - chamber.

Vanadium Subgroup

Production of metallic vanadium, niobium, and tantalum is a complex and difficult process since:

• it is necessary to separate them from various admixtures;

• separation of niuobium and tantalum is an extremely complicated task;

• reduction to the free state requires significant efforts.

The ores of iron that contain vanadium are one of the important sources of vanadium. During processing the ore in the blast furnace the predominating part of vanadium is reduced and included into cast iron. The further treatment of vanadium cast iron to steel gives vanadium slags containing FeVO₄. Annealing of the latter with NaCl gives NaVO₃:

4FeVO₄ + 4NaCl + O₂ = 4NaVO₃ + 2Fe₂O₃ + 2Cl₂

NaVO₃ is isolated by water, transformed to (+ H₂SO₄) + V₂O₅ and reduced by Са or Al:

V₂O₅ + 5Ca = 2V + 5CaO

Ferrovanadium alloy can be produced when the cheap reducing agent ferrosilicon is used:

2V₂O₅ + 5Si(Fe) = 4V(Fe) + 5SiO₂

Especially pure vanadium is produced by thermal decomposition of VI₂ (iodide process, A. E. van Arkel).

The first stage of production of Nb and Ta is concentration of ores. Afterwards they can be transformed to fluorocomplexes K₂[MF₇] (M = Nb, Ta). These coordination compounds are, in turn, separated due to their difference in solubility. And, finally, free elements can be obtained by metallothermy with active metals:

K₂[MF₇] + 5Na = M + 5NaF + 2KF

Uses

Scandium is extracted in only a few mines worldwide due to the low availability and difficulties in the preparation of metallic scandium, which was first done in 1937. Applications for scandium were developed in 1970s. The positive effects of scandium on aluminium alloys were discovered in the 1970s, and its use in such alloys remains the only major application of scandium. High purity scandium is used in electronic engineering, space explorations (resistance to corrosion and thermal stability). Annual production of scandium increases from year to year: 1973 (27 kg), 1985 (100 kg), 1990 (1000 kg.).

Y is used as a component of nuclear reactors and to introduce doping in some metalllic materials (Cr, Mo, W). Sс₂O₃ and Y₂O₃ can be transformed to mangnetic materials. Yttrium was used in the yttrium barium copper oxide (YBa₂Cu₃O₇, aka 'YBCO' or '1-2-3') superconductor developed in 1987. This high temperature superconductor (HTSC) operated at 93 K, notable because this is above liquid nitrogen's boiling point (77.1 K). As the price of liquid nitrogen is lower than that of liquid helium, which has to be used for the metallic superconductors, the operating costs will decrease.