US2946729A - Production of electrolytic zirconium - Google Patents

Description

- chloride and dissolved therein two chlorides United States Patent O 2,945,729 PRODUCTION or ELECTROLYTIC znzcoNIUM Reginald S. Dean, Hyattsville, Md., assignor to Chicago Development Corporation, Riverdale, Md, a corporation of Delaware No Drawing. Filed June 9, 19 58, Ser. No; 740,568 1 Claim. or. 204- 64) This invention relates to the production of electrolytic zirconium. It has for its aim the production of coarsely crystalline zirconium adherent to an inert conducting cathode from a molten bath of alkalinous metal chloride and lower zirconium chlorides. 1

In my copending applications, Serial No. 605,232, filed August 20, 1956; Serial No. 638,901, filed February 8, 1957; and Serial No. 647,206, filed March 20, 1957, now abandoned, I have disclosed the formation of coarsely crystalline intergrowths of pure metals of groups IV-B, V-B and VIB in characteristic form of 'a thin layer of the metal on the cathode growing into a layer of fine crystals in salt and finally into coarse crystal intergrowths of the metal frangibly attached to said salt layer. The inter- 'growths constituting 90% or more of the metal adherent to the cathode. I have disclosed that the formation of these intergrowths is due to their crystallization from 'a supersaturated solution in a w of the metal to be depsoited and free alkalinous metal.

The production of titanium in the form described and by the procedure descr'bed, has been disclosed in the above copending applications.

The ternary system Zr-Cl-Na differs from the analgous titanium system by the existence of a stable compoun ZrCl, which is insoluble in molten alkalinous'chl'oride. This compound metallic character and occurs as small shiny flakes.

The psendobinary system ZrCl-NaCl divides the ternary system into two composition areas, above the line, the melt is in equilibrium with Zr and so behaves analogously to titanium, below the line, the stable "solid phase is ZrCl.

in order to function satisfactorily as an electrolyte, the co position of the single phase liquid must be prevented 'rrom changmg in composition so as to fall below the pseudobinary line ZrCl-NaCl. This is rendered 'difii'cultby reactions not encountered in the case ofjtitaiiium and other metals of groups IV-B, V-B and Vl-B or 'thep'eri- 'odic system. These may be listed as follows: t1 zrclpzrcnzrci Reaction 1 is a general electrolyte reaction driven from melt-of alkalinous metal This reaction goes primarily forms a layered lattice of semiright to left by the volatility of ZrCl and depleting the electrolyte in soluble Zr eventually to the point of uselessness. Reaction 2 occurs at metallic zirconium anode material and also depletes'the electrolyte. I

The result of these two side reactions is that-sooner or later the electrolyte becomes essentially NaCl+ZrCl with alittle dissolved Zr There are several ways of combating these sidemeactions. Reaction 1 is inhibited by conducting the electrolysis under pressure as disclosed in our copending application. I have, however, found it sometimes preferable to drive Reaction 1 from right to left by periodic v 2,946,729 Patented July 26, 19 60 "ice where x is from 2-3.

, Reaction 2 gradually degenerated the anode residue into ZrCl and if the electrolyte is maintained by adding ZrCl-l-ZrCh, this may simply be allowed'to continueand the ZrCl recovered periodically and used to add with the 21-01 which is also recovered from the "cooler parts of the apparatus.

ZrCl is conveniently made by heating .ZrCl and .Zr in molten NaCl underpressure .tor. a long period. For purposes of replenishing the electrolyte, the .product may be added directly to the cell.

ZrCl can also be made electrolytically by passing a direct current through a cell having a particulate anode of Zr and an electrolyte of alkalinous metal chloride and ZrCl For this purpose, a low melting electrolyte like SrCl 65%, NaCl 35% is desirable. Several percent of ZrCL; can bedissolved in'such an electrolyte at 1100? .F, The ZrCl,, is obtained more or less adherent to the cathode in the form of graphitic appearing flakes.

From either product containing ZrCl, it may be .recovered by dissolving the salt in dilute HCl. The after thorough wa'shinganalyze approximately ZrCl.

.Since other metals of the titanium group including hafnium do not form an-analogous compound, the washed flakes contain only zirconium and chlorine. This method may, therefore, be used as a separation from hfin'ium.

It will be recognizedv that ZrCl can also be made by sodium reaction of ZrCl by long heating of ZrCl,; under pressure with the stoichiometric requirement of sodium. tometallic Zr and ZrClhowever, after long heating, ZrCl is formed. It is preferable, however, to accomplish this in two stages, reduction to finely divided Zr in the first stage and then reaction with ZrCl,; by one of the methods above.

The flakes of ZrCl have practically important proper- The anode basketcan be eliminated; it is, however, preferable to maintain it and when its contents Ihave too far become ZrCl simply place this in the reservoir at the bottom of the cell and replace it with Zr to be refined.

Example I In this example, I take an electrolytic cell having an inert atmosphere, a centrally located steel cathode surrounded with a steel anode basket containing comminuted zirconium scrap. I place sodium chloride in the cell and add a mixture of ZrCl and ZrCl in the proportions necessarytoprovide an electrolyte containing 4% dissolved Zr as chloride, average valence 2.1. I find that this electrolyte contains 1.2% free sodium as determined by hydrogen evolution in acidified FeCl I electrolyze at a currentdensity of 200 amps/sq. ft. on the cathode. Anode current density is less than .01 amp/sq. ft. I add ZrCl+ZrCl at regular electrolyte. V

The anode material analyzed intervals to maintain the 7 Percent Tin i' 1.0 Iron 0.3

0.15 Balance substantially zirconium. 1

The cathode product which was coarse crystal intergrowths formed on the cathode surmounting a zirconium plate and a layer of salt with fine crystals of zirconium distributed theretbrough.

After washing with dilute acid, the zirconium crystal intergrowths analyzed Percent 'Iin 10001 Iron .002 0 .005

When melted in an inert atmosphere furnace, the hardness of the zirconium was Vickers 72.

Example I] Example 111 In this example, I make ZrCl for carrying out the pre- Example IV In this example, I make ZrCl from zirconium sponge containing 3% Hf and ZrCl., containing 3% of the weight of Zr as Hf by making the sponge an anode in a cell having an inert atmosphere and a steel cathode surrounded by an anode basket containing the zirconium.

The electrolyte is 65% SrCl NaCl containing 2% Zr as ZrCl The electrolysis is carried on at 1100 F. The current density on the cathode is 400 amperes/ sq. ft. There is deposited on the cathode a loosely adhering deposit of flakes. These flakes are washed with dilute HCl and water and analyze 25.2% C1 corresponding approximately to ZrCl.

The flakes are hafnium free. X-ray studies reveal a layered lattice of Zr and Cl. Measurements of capacity show-the flakes to behave as condensers having a capacity independent of frequency.

Example V Zr+ZrCl 3 ONaCl- 2ZrCl 3 ONaCl This electrolyte when removed from the cooled bomb analyzed 4% soluble zirconium Average valence, 2.2

Sodium equivalent to 6 cc. hydrogen/gram evolved in acified FeCl The ZrCl., pressure of this electrolyte at 850 C. was mm. Hg.

I place this electrolyte in a cell so arranged that the electrolyte is separated from the upper part of the cellby a barrier in a heated zone at 850 C. which has only capillary openings to the top part of the cell which is cool. The top part of the cell is maintained at an argon pressure of 75 mm. to prevent diffusion of ZrCl., into the cooler parts of the cell.

I place in the cell a'centrally located steel cathode and surrounding it in the electrolyte a steel basket containing the crude comminuted zirconium to be refined.

I pass a direct current through the cell with the basket of crude comminuted zirconium as anode.

The current density on the cathode is 500 amperes/sq. ft. and on the anode material less than 1 ampere/sq. ft.

Coarse crystalline zirconium free from ZrCl is deposited adherent to the cathode.

After washing with dilute HCl the cathode product analyzed:

Percent Zr 9999+ O .02 Fe .001 N2 V.' Hf Less than .004

with substantially no other impurities.

The crude zirconium used as anode material analyzed:

Percent 0 1.2 Fe 3 N 0.2 Hf 2.8 Balance substantially zirconium. 7

Example V1 V by heating in a sealed container ZrCl., with Na in the proportions to form ZrCl and NaCl. This product contains about 22% Zr. To produce the electrolyte, it is added to 4 times its weight of NaCl and melted under 2 atmospheres pressure.

The electrolyte analyzes the same as that of Example V and is used in the same way.

What is claimed is:

The method of producing coarsely crystalline zirconium free from ZrCl as a deposit adherent to the cathode which consists in making comminuted zirconium in an annular steel basket an anode in a cell having an inert cathode centrally located with respect to said anode and a molten electrolyte at about 850 C. consisting of sodium chloride in which is dissolved 26% zirconium as chloride, average valence 2.0-2.4 and sodium as determined by hydrogen evolution in acidified ferric salt solution .12.0%, passing a direct current through the cell at a cathode current density of about 500 amperes per sq. ft. and an anode current denslty of less than 1 ampere per sq. ft. and maintaining during the electrolysis a partial pressure of ZrCl.; of about 75 mm. of mercury. i

I References Cited in the tile of this patent UNITED STATES PATENTS In this example, I make the electrolyte of Example