The usually stable at standard conditions crystalline form of metal zirconium and hafnium is of close-packed hexagonal form with a crystal structure as shown in FIG. 1, c). All distances between atoms are equal. At a temperature of 862.degree. C. (1584.degree. F. ) for zirconium and about 1800.degree. C. (3300.degree. F. ) for hafnium the hexagonal crystal form converts to the cubic body centered close-packed form. Since the close-packed structure is isotropic, it means that the physical properties (such as electroconductivity, thermal conductivity, etc. ) of all metals with close-packed crystal structure monocrystal are equal in all directions. It is necessary to say that zirconium and hafnium, as other refractory transition metals, usually are obtained by high temperature reduction of their compounds (halides, oxides or complex halides) where the metal is in a higher state of oxidation. The high temperature of the processes leads to obtaining of the metals in the close-packed crystal modifications which are stable at this temperature and which transform to the close-packed hexagonal structure at cooling.
The electrochemical methods for obtaining refractory transition metals (such as Ti, Zr, Hf) by electrolysis from molten salt baths are very well developed and are usually high temperature methods (over 800.degree. C. =1470.degree. F. ) (U. S. Pat. No. 2,864,749 and U. S. Pat. No. 3,444,050). It was established that the optimal temperature for production of zirconium by molten salts electrolysis is 800-860.degree. C. (M. Steinberg et al. , J. Electrochem. Soc. , 101, 78 (1954). Those skilled in the art know that it is possible to produce the deposit of a metal by introducing one of its derivatives, such as metal halide into a molten salt bath and by subjecting it, in its simplest principle, to the action of a potential of two electrodes linked to the poles of a source of direct current: halogen is released at the anode and the metal is deposited on the cathode. It was shown that the process of electrochemical reduction of polyvalent metals, such as zirconium, is achieved via formation of lower metal halides which however are dissolved in the melt and do not form solid crystalline phases during the process (M. Smirov et al. , Russ. J. Phys. Chem. , 37, 901 (1958); U. S. Pat. No. 4,588,485 to Cohen).
A method of producing metal titanium (the metal of the same group as zirconium) obtained by electrolytic reduction of lower chlorides of titanium (dichloride and trichloride) as initial compounds which could be put into operation was described in U. S. Pat. Nos. 2,734,856 and 2,864,749 4,686,025, but said lower chlorides were dissolved in a melt. The X-ray and metallographic analyses of metals (Ti, Zr, Hf) obtained by electrolysis of molten electrolytes show that the metal is always formed in close-packed hexagonal form (.alpha.-form) and it does not included other phases except small quantity of metal hydride (M. Steinberg et al. , J. Electrochem. Soc. , 101 63-78, (1954); C. Graighead et al. , J. Metals, 4, 1317, (1952).
However, in all these cases the deposited metal is in a close-packed form--a well known usual modification (for example, for zirconium it is .alpha.-modification).
The essence of my invention is that it has now been found that new allotropic modifications of metal zirconium and hafnium unknown before can be obtained by electrochemical reduction of the solid zirconium or hafnium monochlorides and monobromides in their solid crystalline form without dissolving it in the melt. More specifically this process of reduction is the process of electrochemical reduction (electrolysis) in molten inorganic electrolyte consisting of lithium chloride and chlorides of alkali and alkaline earth metals at the temperature of about 450.degree. C. (830.degree. F. ) with an inert anode and a cathode from solid crystalline zirconium monohalide in a basket from an inert metal, such as nickel with electrical contact between the cathode and zirconium monohalide. The basket consists of a lattice, the mesh of which has dimensions, such that it prevents the easy passage of particles of initial solid zirconium or hafnium monohalide and the formed metal without causing clogging.
As a result of such a reduction processes of solid crystalline zirconium or hafnium monohalide, the obtained metal zirconium or hafnium has a novel type of crystal structure unknown before for these metals. The allotropic modification has a crystal structure consisting of doubled layers of metal atoms with decreased distance between close-packed metal atoms in the doubled layers and an increased distance between the atoms in one double layer and the metal atoms in the other double layer which differs in comparison with the usual .alpha.-form of these metals. This new allotropic modification of metal zirconium and hafnium has different chemical and physical properties than usual .alpha.-zirconium and .alpha.-hafnium especially in respect to their density, hardness, catalytic activity, hydrogen adsorption, thermoplastic properties and electroconductivity. It is not surprising, since in accordance to a well known empirical rule: the layered allotropic modification of the same element usually has much higher electroconductivity than the close packed modification. Carbon serves as a good example. Its close packed modification (diamond) is an insulator, and its layered modification (graphite) is a metallic electroconductor. These properties of obtained new allotropic modification of metal zirconium and hafnium may be used for many useful applications: for catalyzing of oxidation/reduction processes with gaseous hydrogen participation, for hydrogen storage, for industrial items fabrication from metal zirconium and hafnium by powder pressing or by process of extrusion, etc.
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