US2779672A

US2779672A - Method of treating molten magnesium

Info

Publication number: US2779672A
Application number: US389498A
Authority: US
Inventors: Douglas S Chisholm; William P Saunders
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1953-10-30
Filing date: 1953-10-30
Publication date: 1957-01-29
Anticipated expiration: 1974-01-29

Description

United States P teflm" METHOD OF TREATING MOLTEN MAGNESIUM No Drawing. Application October 30, 1953,. Serial No. 389,498

3 Claims. (Cl. 75-67) The invention relates to methods of treating molten magnesium to improve its purity. It more particularly concerns an improved method of reducing the concentration of metallic contaminants especially iron, aluminum, and manganese.

Much of the currently manufactured magnesium is produced by the electrolysis of magnesium chloride derived from ocean water and inland brines. As a consequence, the magnesium so-obtained contains small amounts of iron, manganese, and aluminum as impurities. For some purposes as in the making of commercial magnesium-base alloys, the presence of the small amounts of manganese and aluminum in the magnesium is notdetrimental since these metals are constituents of many of the commercial magnesium-base alloys. On the other hand iron even in small quantities has a detrimental effect on the resistance to corrosion of magnesium and its alloys. Hence, it is desirable to provide suitable methods of reducing the concentration of this impurityto a negligible level. In some uses of magnesium, as for example, in the making of fine chemicals, the presence of aluminum and manganese as well as iron is highly undesirable becausethese contaminants are oftentimes carried over into the products derived from the magnesium containing these impurities.

Accordingly, it is the principal object of the invention to provide a method of reducing the concentration of metallic impurities particularly iron, aluminum, and manganese in commercial magnesium containing these impurities. Other objects and. advantages will appear as the description of the invention proceeds.

The invention is predicated upon the discovery'that by introducing into a molten body of the magnesium to be purified titanium tetrachloride vapor by passing the titanium tetrachloride through a body of a suitable saline flux underlying the magnesium into the molten magnesium whereby the titanium tetrachloride reacts with the molten magnesium forming a precipitate of metallic titanium in the molten magnesium the precipitated titanium quickly settles out of the molten magnesium carrying metallic impurities with it. The so-treated molten magnesium is then separated from the precipitated titanium as the purified product with a greatly reduced concentration of metallic impurities. The invention then consists of the improved method of purification herein fully described and particularly pointed out in the claims.

In carrying out the invention, the magnesium to be purified is superimposed in the molten state upon a quantity of a molten saline flux having a suflicientdensity to form a molten body below and in contact with the molten magnesium. For this purpose, there may be used the fused chlorides of alkali and alkaline earth metals, e. g. the chlorides of barium, calcium, magnesium, sodium, potassium, and lithium. Adequate density of flux can be obtained by adding more or less barium chloride to those chlorides which alone or in admixture with others are not heavy enough to remain under the molten magnesium. The conventional fluid. magnesium foundry fluxes may be used. An example of such a flux is a mixture of KCl 57 parts, CaClz 28 parts, BaClz 12.5 parts, and CaFz 2.5 parts by weight. This mixture is heavier than magnesium and when molten magnesium will float on it. The flux should be substantially unaffected by the titanium tetrachloride which is to be passed through the flux into the magnesium. This condition is fiulfilled with the aforementioned saline fluxes.

The treatment of the molten magnesium which is superimposed on the saline flux is eflected by introducing titanium tetrachloride into the molten flux body under the molten magnesium as by inserting the open end ofa delivery pipe into the body of the flux and delivering the titanium tetrachloride in the form of vapor through the pipe into the flux. The titanium tetrachloride vapor on leaving the open end of the pipe in the flux rises through it as bubbles and passes into the molten magnesium further rising therein as bubbles until they are absorbed or escape. The rate of introduction of the titanium tetrachloride vapor may be so-regulated that but little, if any, of it escapes from the molten magnesium. The titanium tetrachloride thus introduced into the magnesium reacts with the magnesium, thereby forming magnesium chloride and precipitates metallic titanium in situ at a rate which depends upon the temperature and rate of introduction of the titanium tetrachloride. If the rate of introduction is relatively high some of the vapor will pass all the way through the molten magnesium and become wasted as already indicated. Accordingly, the rate of introduction is regulated so as to avoid undue wastage.

The progress of the purification can be determined by taking samples of the molten metal separated from the precipitated titanium by settling. The samples may be analyzed for one or more of the metals, iron, aluminum or manganese as desired. The amount of titanium tetrachloride required to effect purification of the magnesium is relatively small being generally in the range of about 1 to 3 percent of the weight of the magnesium to be purified. This amount corresponds stoichiometrically to precipitating in situ an amount of metallic titanium equal to about 0.25 to 0.75 percent of the weight of the magnesium. Smaller or larger amounts of titanium tetrachloride may be used. For example as little as 0.5 percent of 1 titanium tetrachloride lowers the iron content of impure magnesium. The amount of titanium tetrachloride to use is greater the higher the concentration of the impurities to be removed.

After introducing the desired amount of titanium tetrachloride into the magnesium through the flux the precipitated titanium so-t'ormed is allowed to settle thereby carrying with it sequestered impurities. Settling is rapid and it takes place to a large extent during the introduction of the titanium tetrachloride so that little, if any, additional time need to be taken to obtain purified magnesium from the supernatant portion of the molten metal mass above the flux. Separation of the treated molten magnesium from the precipitated titanium may be effected by decantation or dipping after sufiicieut settling.

The following examples are illustrative of the practice of the invention.

Example 1 pounds of magnesium produced by the electrolysis of a magnesium chloride cell feed derived from ocean water was melted in a steel crucible and heated to 1400 F. along with 15 pounds of magnesium foundry flux composed of 34 parts of MgCl2, 55 parts of KCl, 9 parts of BaClz, and 2 parts of CaFz by weight together with an additional 2 pounds of BaClz. Most of the flux sank to the bottom of the crucible under the molten magnesium while a thin layer of flux coated and protected the upper surface of the molten magnesium from atmospheric at 3 tack. After standing in the nesium so that the vapor bubbled through the fiux into the molten magnesium above the flux. As the titanium tetrachloride vapor was thus introduced into the molten magnesium through the flux, the vapor reacted with the magnesium forming a precipitate of metallic titanium in situ.

cent state for about minutes to permit the precipitated titanium with the sequestered impurities to settle. The supernatant portion of the settled molten magnesium was sampled and the sample analyzed for iron,'manganese,

aluminum, iron, and titanium with the following results:

Mn 0.027 percent, Al 0.001 percent, Fe 0.002 p'er'centfli less than 0.024 percent.

Example 2 quiescent state for 15 minutes, a sample of the molten metal was taken. Its ana of titanium tetrachloride I The so-treated molten metal was again held in thequies- A melt of magnesium 75 pounds of magnesium derived.

from a similar source to that of Example 2 and brought to a temperature of 1400 F. with a similar amount of the same kind of flux on being held quiescent'for 15 minutes was analyzed. The analyses showed the following: manganese 0.049 percent, iron 0.031 percent, alumi.

' num 0.006 percent, Ti 0.004 percent. 'The melt of magnesium was then treated in similar manner to that of Example 1 with 2.8 percent by weight 'oftitanium tetrachloride; After allowing the so-tre'ated melt tosettle for 15 minutes, the supernatantportion Was sampled and the sample analyzed with the following results: Mn 0.018 percent, Fe 0.002 percent, Al 0.004 percent, Ti less than 0.028 percent.

Example 3 magnesium was then treated with 0.96 percent by weight 1 introduced through the flux into "the metal as in Example 1. The so-trea'ted magnesium was held quiescent for 15 minutes and then a sample was decanted ofi and analyzed for manganese, iron, aluminum, and titanium with the following results: Mn 0.024 percent, Al 0.001 percent, Fe 0.003 percent, Ti less than 0.025 percent.

Among the advantages of. the invention are that certain metallic impurities in magnesium can be reduced in concentration to tolerable limits without adding undesirable contaminants. The magnesiumso-purified-is ideally suited for use in the manufacture of metallic titanium by the reduction of titanium tetrachloride with-the purified magnesium because the so-p'urified magnesium introduces into the titanium no metallic contaminants from the magnesium incidental to its purification. The reaction of the titanium tetrachloride on the magnesium produces magnesium chloride in situ which also serves to flux and purify the magnesium.

We claim: I

' 1. The methodof treatinga moltenbody of magnesium containing at least one of the metals iron, aluminum, and manganese as an impurity which comprises maintaining under and in contact with the body of molten magnesium to be purified a quantity-of a saline flux therefor having a greater density than the said molten magnesium and being inert to titanium tetrachloride, passing titanium tetrachloride vapor into themolten magnesium through the fiux under the molten magnesium in amount sufficient to purify the molten magnesium whereby metallic titanium is precipitated in the molten magnesium sequestering impurities therein, and separating the so-treated molten magnesium from the precipitated titanium.

2. The method according to claim 1 in which the amount of titanium tetrachloride used does not exceed 3 percent by weight of the magnesium.

3. The method according to claim 2 in which the saline flux comprises magnesium chloride.

References :Cited in the file'of this patent UNITED STATES PATENTS 1,847,555 Frary Mar. 1, 1932 2,073,018 Lepp -1 Mar. 9, 1937 2,205,854 Kroll June 25, 1940 2,373,515 Stroup et a1 Apr. 10, 1945 FOREIGN PATENTS 594,152 Great Britain Nov. 4, 1947

Claims

1. THE METHOD OF TREATING A MOLTENBODY OF MAGNESIUM CCONTAINING AT LEAST ONE OF THE METALS IRON, ALUMINUM, AND MANGANESE AS AN IMPURITY WHICH COMPRISES MAINTAINING UNDER AND IN CONTACT WITH THE BODY OF MOLTEN MAGNESIUM TO BE PURIFIED A QUANTITY OF A SALINE FLUX THEREFOR HAVING A GREATER DENSITY THAN THE SAID MOLTEN MAGNESIUM AND BEING INERT TO TITANIUM TETRACHLORIDE, PASSING TITANIUM TETRACHLORIDE VAPOR INTO THE MOLTEN MAGNESIUM THROUGH THE FLUX UNDER THE MOLTEN MAGNESIUM IN AN AMOUNT SUFFICIENT TO PURIFY THE MOLTEN MAGNESIUM WHEREBY METALLIC TITANIUM IS PRECIPITATED IN THE MOLTEN MAGNESIUM SEQUESTERING IMPURITIES THEREIN, AND SEPARATING THE SO-TREATED MOLTEN MAGNESIUM FROM THE PRECIPITATED TITANIUM.