US2874454A - Titanium group metals deposits - Google Patents

Description

Feb. 24, 1959 w. w. GULLETT TITANIUM GROUP METALS DEPOSITS 2 Sheets-Sheet 1 Filed June 20, 1956 SALT LAYER CONTAINING SMALL CRYSTALS S E L m T R m s U 0 T N E M A L F a a s 3 PLATE- CATHODE SALT LAYER CONTAINING SMALL CRYSTALS FILAMENTOUS PARTICLES PLATE CATHODE (IRON ROD) will v INVENTOR Will am ZlZZZZZZ gmwflwgv an 7&4 ATTORNEYS Feb. 24, 1959 w. w. GULLETT 2,874,454

TITANIUM GROUP METALS DEPOSITS Filed June 20, 1956 2 Sheets-Sheet 2 IN VE NTOR BY I A; ATTORNEYS Un td ates 4 Patent TITANIUM GROUP METALS DEPOSITS William Gullett, College Park, Md., assignor to Chicago Development Corporation, Riverdale, Md., a corpo'ration of Delaware Application June 20, 1956, Serial No. 592,543

2 Claims. (Cl. 291-194) This invention relates to deposits of titanium group metals formed in an electrolytic cell having a fused electrolyte having components of alkalinous metal, titanium group metals and chlorine. It has for its object the pro duction of such deposits of a 'new and highly useful character.

I have discovered a new form of titanium group metal deposits formed, in suchfused electrolytes which is characterized by a three part structure, (1) a continuous nonporous plate on the cathode, (2) a. zone ofintimately mixed salt and more or less fine crystals, and (3) bundles of coarse filamentary particles. A deposit of this structure has many important uses particularly as the proportion of the three structural elements listed may be varied. For example, the deposit may be made to consist essentially of the plate simply by interrupting the process before the other two structural elements are formed. In another example the plate and .the fine crys-' tal layer may be made quite thin so that substantially all the metal is recovered in the bundles of coarse filamentary particles.

The structure of thedeposit of my invention has a superficial similarity to certain electrodeposits from aqueous solution such as those, for example, of manganese which' start by the formation of a thin plate of gamma manganese on the cathode, then form a thick plate of alpha manganese and fin'allya dendritic deposit as the time of deposition is extended. This similarity, however, is entirely superficial. The intermediate layer of fine crystals in the structure of my invention'is not a continous electrodeposit but a mass of fine crystals distributedthrough the fused salt electrolyte having a density in grams of metal per unit volume less than the bundles of filamentary particles constituting the outer structural element of the deposit of my invention. 7

In short, the deposit of my invention is not one which is becoming dendritic by decrease in current density. It is possible to make dendritic whiskery deposits of titanium group metals 'byhaving' a low chrrent density. Such deposits are not a part of my invention.

A typical deposit having the'characteristics of my invention is shown in Figure 1. This figure is a cross section of a deposit made from an electrolyte consisting of sodium chloride. 90%, barium chloride 10%, with added titanium dichloride providing about '1% soluble titanium. In preparing this deposit the titanium was maintained in a highly reducedzcondition at the anode and a slightly oxidized condition at the cathode by providing .asoluble titanium anode and a steel cathode and an auxiliary circuit with a foraminous cathodic member between the main anode and cathode and a graphite anodic member near the main cathode. In preparing the deposit of this figure the cathode current density was 150 amps/sq. ft. and the auxiliary circuit amperage was such'as to-maintain the open circuit E. M. F. between-the foraminous auxiliary cathode and the main cathodeat less" than .05 volt. In Figure 1 the deposit is shown at a magnification of 2 /2, and the three structural characteristics of the deposit are clearly shown.

Figure 2 shows a cathode deposit from a different type of electrolyte, namely, one in the single phase liquid in the system titanium-sodium-ehlorine illustrated in the ternary diagram Figure 3 for 850 C. The cathode current density in this instance was 600 amperes/sq. ft.;

Figure 2 shows the structure of the deposit on the cathode at a magnification of 2 /2.

I have found that the thickness of the plate and the extent of the fine crystal zone are determined by the 'initial cathode current density. Lowering the current density after forming the initial plate at high current density does not reduce the extent of the zone of fine crystals- The three part-structure of the deposits :of my inven-- I have illustrated my invention particularly as it relates to titanium, but I wish it understood that my invention with suitable variations which will be clear from.

the examples hereinafter given is applicable to Ti, Zr, Hi and Th. I a

One embodiment of the present invention relates to the production of plates of titanium group metals on. solid metallic objects used as cathodes by utilizing only' the first structural element of my deposit. As previously pointed out, by the use, of high current density on the' cathode and an electrolyte having a suitable composition, a plate is obtained the thickness of which depends on the current density. For the production of articles plated with titanium for decorative or protective purposesI prefer to use an electrolyte having the composition within the cross-hatched phase field of Figure 3. The presence of sodium metal dissolved in this electrolyte can be readily ascertained by analysis. I have found thatif a solution of sodium in sodium chloride is prepared by mixing the components at 850 C. in an inert atmos-.- phere and the melt 'is quenched, a blue solid is obtained. containing metallic sodium in some degree of dispersion.

This blue solid evolves'hydrogen in dilute acid, but-does not reduce an acid solution of ferric sulphate. Since titanous salts reduce ferric sulphate without hydrogenevolution, the hydrogen evolved in acidified ferric sulf' phate, e. g., in a fermentation tube-is a quantitive measure of the sodium contained ina sample of electrolyte quenched from its molten condition.

The same method of analysis for sodium can be aptplied to systems of the other members of the titanium group chlorine and an alkalinous metal.

It is characteristic of the electrolytesm tain sodium according to the above'test. Such electrolytes may be prepared in many ways, such as reduction or a higher chloride of the titanium group metal with sodium at a low temperature as described for titanium in my copending application Serial No. 573,336 filed March 23, 1956, Patent No. 2,817,631 and then the ad.-

trated with sodium as the alkalinous metal and titanium Patented Feb. 24,1959.

7 the systems: alkalinous metal, titanium group metal, chlorine which are particularly suitable for my invention that they con-f as the titanium group metal. The same principles apply to otheralkalinous metals, that is, Na, K, Li, Ca, Ba and Sr and mixtures of alkalinous metals and to other titanium group metals. In general electrolytes suitable for my invention may be made by dissolving higher chlorides of titanium group metals in at least one fused alkalinous metal chloride and adding alkalinous metal. The proposition of titanium group metal in the final composition is from 2-8% and the free alkalinous metal is from 0.56%.

The molecular or atomic species which exist in the molten single phase electrolyte of my invention is not known. It may be noted that the proportion of alkalinous metal which may be dissolved Without precipitation of titanium group metal is larger when the apparent valence of the titanium group metal is higher. The apparent valence of the titanium group metal is determined by the relation of total titanium group metal present to the reducing power for ferric sulphate solution. The apparent valence is always at least 2.

I have described my invention as it applies to titanium group metals. It is also applicable to alloys of these metals with certain other metals. When such alloys are used as anodes, their behavior depends on the anodic current-density. Since the production of the deposit of my invention depends on control of cathode current density, it-follows that anode current density in any given embodiment of my invention is determined by anode surface. When it is desired to produce a pure deposit of titanium group metal according to my invention the anode current density must be low and I prefer to use a particulate anode supported in an iron basket. With such an anode pure titanium group metals may be deposited from alloys containing oxygen, nitrogen, carbon, iron, manganese, chromium aluminum, vanadium, molybdenum or combinations of these alloying metals.

By the use of small anodes the deposits of titanium group metal may be made to contain iron, chromium, manganese, vanadium and molybdenum by using as anodes alloys of the titanium group metals with one or more of these alloying metals.

Example I is 2.5. I make a steel rod /4 inch in diameter a cathode I in this bath, and provide an anode of particulate titanium held in a foraminous iron basket. The anode and cathode are spaced 3 inches apart. Ielectrolyze at 5000 amperes/sq. ft. on the cathode for minutes and obtain a plate .003 inch thick. The plate is continuous, adhcrent and non-porous. It has a Brinell hardness of 87. The plate is surmounted by a layer inch thick of fine crystals dispersed in salt. After diffusing to equilibrium, the composition of the bath is unchanged. I therefore repeat the plating cycle to provide an additional .003 inch thickness to the plate. The current eificiency of the plating is grams per Faraday. The layer of fine crystals does not interfere with the building up of the plate as the crystals are not attached to the plate and are simply displaced by the further deposition of titanium as a plate.v

Example 11 nally used- The efieet n'fsthis is to add'NaCl and Tito the bath without changing the free sodium. The bath is nowready for another plating cycle.

Example III In this example I make an electrolyte by dissolving 231 grams of ZrCl in 1000 grams of LiCl+KCl in eutectic proportions and adding 5.0 grams of sodium to the melt at 600 C. The apparent valence of the zirconium remains 4 so that the melt contains 4% sodium metal and 7.3% Zr. I use this melt to produce a heavy zirconium plate on uranium rods by making a rod the cathode in a cell having the above electrolyte in an inert atmosphere and a particulate, zirconium anode held in a foraminous iron basket. A current density of 6000 amperes/sq. ft. is applied for 5 minutes, and then 10 minutes allowed for diffusion and another plating cycle of 5 minutes applied. This program is continued for 5 plating cycles, at the end of which time the uranium rod is plated with .100 inch of adherent, continuous zirconium metal having a hardness of Brinell. A current etficiency 24 grams per faraday is obtained.

Example IV In this example I prepare an electrolyte within the composition range of the cross-hatched area in Figure 3. Theparticular composition used in this example contained 5% Ti, 64.9% C1, balance Na. This electrolyte is prepared by adding TiCl to fused NaCl and electrolyzing with a particulate titanium anode and an'inert cathode at such a current density that the open circuit voltage of the cell is reversed to the applied voltage. This electrolyte is placed in a steel 'cell with an argon atmosphere. The anode consisted of 4 iron baskets distributed on the periphery of an 8 inch diameter circle and containing particulate impure titanium analyzing .5% oxygen, 3% iron, 1% manganese, .1% nitrogen, balance substantially titanium. The cathode was a /1 inch iron rod which was spaced in the center of the circle formed by the basket anodes. The current density on the cathode was 600 amperes/sq. ft.

After electrolysis for 5' hours, the electrolyte was removed from ,the cell by bottom flow and the drained deposit consisted of a plate .001 inch thick on the cath- I proceed as in Example IV except that I apply an initial current density of 2500 amperes/sq. ft. for 10 minutes and then lower the current density for the remainder of the 5 hour electrolyzing period. The deposit formed has three elements as before but the plate is .005 inch thick and the finely crystalline deposit is 2 inches thick with only an outer layer /2 inch thick of bundles of coarse filamentary particles' The deposit of finev crystals contains 50% salt and has a bulk density of .75. The fine crystals are all finer than 20 mesh. Analysis of all sections of the deposit show it to be 99.99% .ti tanium after washing with dilute hydrochloric acid. The current efliciency was 21 grams per faraday. 1

Example VI I proceed as in Example IV except that instei t Of a particulate anode contained in a basket, I use a rod of titanium-chromium alloy 2 inches in diameter contain ng 4% chrom um, -5.% oxy en ca bo b lance substan ially t n um Th result of th exampl the same as that of Example IV except that all elements of the deposit contain 4% chromium and only traces of other impurities present in the anode. A current efficiency of 18 grams per faraday is obtained.

Example VII In this example I prepare an electrolyte of 87% NaCl, BaCI and 3% TiCI I fuse this at 835 C. in a cylindrical iron pot having a titanium rod anode and a cylindrical cathode surrounding it. Around the anode I place a foraminous iron cylinder and near the bottom of the cathode I place a graphite ring. I connect these two in an auxiliary circuit, the foraminous cylinder being the cathode. I pass 350 amperes through the main circuit which provides a cathode current density of 150 amperes/sq. ft. I pass about amperes through the secondary circuit which is enough to reduce the open circuit voltage between the foraminous cylinder and the main cathode to .02 volt. A deposit is formed on the cathode which consists of a plate adhering to the cathode, a layer of fine crystals distributed in the electrolyte and a layer of bundles of coarse filamentary titanium particles. A current efiiciency of 22 grams per faraday is obtained.

Example VIII I proceed as in Example IV except that I use an electrolyte having a composition of 5% Th, 66.2% C1, balance Na. This electrolyte is prepared by adding ThCl, to fused NaCl and electrolyzing with a particulate Th anode on an inert cathode at such a current density that the open circuit voltage of the cell is reversed to the applied voltage. I use this electrolyte in a cell like that described in Example IV, except that the anode material is impure particulate thorium. I obtain a thorium plate on the cathode .003 inch thick, a layer of fine Th crystal distributed in electrolyte, and 95% of the deposit as bundles of coarse filamentary particles of pure thorium. The current efiiciency is 52 grams thorium per faraday.

What is claimed is:

1. As a new product an article consisting essentially of a conductive metal cathode carrying thereon a laminated deposit composed of an inner layer of a nonporous plate, less than .003 inch thick, of a titaniumgroup metal adherent to said cathode; an intermediate layer, less than .25 inch thick, of small discrete granular crystals of said titanium-group metal dispersed through solidified fused salt; and an outer layer of coarse crys tals of said titanium-group metal frangibly attached to and growing out of saidintermediate layer, said outer layer of coarse crystals constituting the greater part, by weight, of said deposit.

2. The article of claim 1 in which the plate is less than .003 inch thick, the small crystal layer less than .25 inch thick, and the coarse crystals constituting at least of the deposit by weight.

References Cited in the file of this patent UNITED STATES PATENTS 1,527,734 Huggins Feb. 24, 1925 1,566,265 Antisell Dec. 22, 1925 2,734,856 Schultz et al. Feb. 14, 1956 2,765,270 Brenner et al. Oct. 2, 1956 2,786,809 Raynes Mar. 26, 1957 OTHER REFERENCES Journal of The Electrochemical Society, vol. 99, No. 8, August 1952, pages 2230-2240.

Claims (1)

1. AS A NEW PRODUCT AN ARTICLE CONSISTING ESSENTIALLY OF A CONDUCTIVE METAL CATHODE CARRYING THEREON A, LAMINATED DEPOSIT COMPOSED OF AN INNER LAYER OF A NONPOROUS PLATE, LESS THAN .003 INCH, OF A TITANIUMGROUP METAL ADHEREWNT TO SAID CATHODE; AN INTERMEDIATE LAYER, LESS THAN 925INCJ THICK, OF SMALL DISCRETE GRANULAR CRYSTALS OF SAID TITANIUM-GROUP METAL DISPERSED THROUGH SOLIDIFIED FUSED SALT; AND AN OUTER LAYER OF COARSE CRYSTALS OF SAID TITANIUM-GROUP METAL FRANGIBLY ATTACHED TO AND GROWING OUT OF SAID INTERMEDIATE LAYER, SAID OUTER LAYER OAF COARSE CRYSTALS CONSTITUTING THE GREATER PART, BY WEIGHT, OF SAID DEPOSIT.

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