US2901411A - Methods for preparing single phase molten baths of alkalinous chlorides, titanium chlorides, and alkalinous metals - Google Patents

Description

Aug. 25, 1959 w. w. GULLETT 2, METHODS FOR PREPARING SINGLE PHASE MOLTEN BATHS OF ALKALINOUS CHLORIDES, TITANIUM CHLORIDES AND ALKALINOUS METALS Filed May '20, 1957 if: y ,0 O a J;

MOLTEN ELECTROLYTE wamww 2w INVENTOR United States Patent METHODS FOR PREPARING SINGLE PHASE MOLTEN BATHS 0F ALKALINOUS CHLO- RIDES, TITANIUM CHLORIDES, AND AL- KALINOUS METALS William W. Gullett, College Park, Md., assignor to Chicago Development Corporation, Riverdale, Mat, a corporation of Delaware Application May 20, 1957, Serial No. 660,418

1 Claim. (Cl. 20464) This invention relates to methods for preparing single phase molten baths of alkalinous chlorides, titanium chlorides and alkalinous metals. This is a continuation in part of my application, Serial No. 573,336, filed March 23, 1956, now Patent No. 2,817,631.

In these applications, I have disclosed single phase molten compositions having l8% soluble titanium as chloride and .15% alkalinous metal dissolved in molten alkalinous chloride. The average valence of the titanium being 2.052.7. I have disclosed methods of making these compositions, for example, by reaction of sodium reduction with TiCl in the proportions of TiCl +2Na having a little excess Na to produce a product which is dissolved in molten alkalinous chloride to provide the composition of my invention.

It should be understood that the definition of the composition of my invention is based upon analytical methods described in several of my applications and published in a paper entitled The Chemistry of the Reduction of Titanium Chloride in Fused Alkalinous Chlorides by Solutions of Alkalinous Metals, published February 8, 1957, as Contributions to Titanium Metallurgy, No. 3, Chicago Development Corporation, Riverdale, Maryland, February 8, 1957.

The present invention relates to methods of adjusting the average valence and alkalinous metal content of the single phase molten solutions of my invention. It relates especially to the adjustment of valence and alkalinous metal content in such solutions by electrolytic means.

I have found that when single phase compositions of my invention, in which the titanium has an average valence of more than a certain magnitude related to the titanium content, the average valence may be reduced to that magnitude and a corresponding alkalinous metal content by making the single phase composition an electrolyte in a cell having a titanium anode and an inert cathode and passing a current at very low current density on the electrodes.

The following table shows the relationship of average valence to soluble titanium content and dissolved alkalinous metal for a sodium chloride electrolyte.

For other electrolytes e.g. 65 SrCl -35% NaCl, the relationship is different. In this electrolyte, the titanium concentrations and alkalinous metal concentrations are higher for a given valence. A preferred electrolyte of this composition is 8% soluble Ti, 5% alkalinous metal for an average valence of 2.4. Dilution as with the NaCl electrolyte lowers the valence and alkalinous metal content.

It is characteristic of these systems that they may be supersaturated with alkalinous metal (alkali and alkaline earth metals) and that titanium will then crystallize therefrom. My present invention therefore is limited to those conditions of electrolysis Where supersaturation does not take place. The criterion for this is current density, more especially cathode current density. I have found that the cathode current density in the process of my present invention should not exceed 50 amperes per square foot. Anode current density is substantially lower.

Another valuable criterion for insuring that the average valence of the titanium in the bath is lowered without substantial formation of metal is the instantaneous open circuit voltage of the cell. At the start of electrolysis, according to my invention, the open circuit voltage Will be in reverse to the applied voltage. In my invention, I continue electrolysis until the open circuit becomes a few millivolts in the same direction as the applied voltage. Electrolysis is carried on beyond this only to permit the bath to become uniform by diifusion which is indicated by a steady open circuit voltage of about 20 millivolts in the same direction as the applied voltage.

The cell for carrying out the electrolyses of my invention is not critical so long as an inert atmosphere is provided and means for passing a current from a large surface anode to a large surface cathode. A simple and satisfactory cell is shown in the figure. In this figure, the steel cell (a) serves also as cathode, the anode (b) is a steel basket containing particulate titanium, e.g. sponge particles. The connections to anode and cathode are indicated by the conventional symbols; (0) and (d) are argon inlet and outlet respectively to provide an inert atmosphere.

Having now described my invention in its general form, I will now illustrate it by examples.

Example I I react TiCl with Na by adding them to a reactor in small increments in the proportions of TiCl +2.2 Na and maintaining a temperature of 600 C. during the reaction. I add this reaction product to molten NaCl at 850 C. in a cell like that of the figure to obtain a titanium concentration of 5.0% soluble titanium having an average valence of 2.7. I pass a current through the cell at 10 amperes per square foot on the cell surface. The initial instantaneous open circuit is mv. in a direction reverse to the applied voltage. I continue the current for 10 hours after which the instantaneous open circuit voltage of the cell has become substantially zero. Further electrolyses for 4 hours at 5 amperes brings the instantaneous open circuit voltage of the cell to a steady value of 20 mv. in the direction of the applied voltage.

The bath is now a single phase liquid analyzing 5.4% soluble Ti, average valence 2.52, alkalinous metal 1.2% by weight.

Example 11 I proceed as in Example I to obtain the reaction product of TiCl +2.2 Na. I add this to a molten bath of 65% SrCl 35% NaCl at 650 C., to produce a single phase melt containing 8% soluble Ti, average valence 2.85.

I subject this bath to electrolysis as in Example I except that to obtain zero instantaneous open circuit voltage, I pass 10 amperes for 24 hours. I then pass 5 amperes for 4 hours to obtain a steady positive voltage of 10 mv.

The single phase liquid so obtained analyzes 9% soluble titanium, average valence 2.4, 5% dissolved alkalinous metal.

Example 111 I take TiCl and add enough of this material to molten NaCl to provide 1% soluble Ti. The average valence of the melt is 3.0; I electrolyze as in Example I for 20 Hours until the instantaneous open circuit voltage is zero. The resulting bath analyzed 1.45% titanium, average valence 2.05, dissolved sodium .09% by weight.

What is claimed is:

In a process for preparing a single phase molten bath for use as an electrolyte in a process for electrorefining titanium characterized by passing a direct current from crudetitanium anode to an inert cathode in an electrolyte of at least one alkalinous chloride containing 1-8% soluble titanium as chlorides, 0.1-5 dissolved alkalinous metal, the titanium having an average valence from 2.05-2.4, the improvement which consists in establishing the optimum relationship of soluble titanium, dissolved alkalinous metal and average eifective titanium valence for titanium refining by treating a bath of at least one molten alkalinous chloride containing 1-8%"Ti as lower titanium chlorides with an average valence of 2.7-3.0 by passing a direct current from a large-surface titanium anode to an inert cathode at a cathode current density not exceeding 50 amperes per square foot and a substantially lower anode current density untiltthe instantaneous open circuit voltage initially in reverse to the applied voltage is in the same direction as the applied voltage by a steady value not exceeding 20 millivolts whereby to maintain the cathode in its initial condition.

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