US2066579A - Production of refined magnesium and magnesium alloys - Google Patents

Description

Patented Jan. 5, 1937 UNITED STATES PATENT I OFFICE Georg Schichtel, Austria,

. ration of Delaware No Drawing. Application. January assignor to American Metals Corporation, Pittsburgh, Pa., a corpo- Dobriach-on-Millstattersee,

Magnesium Serial No. 706,558. In Austria, March 30, 1933 Claims.

This invention relates to the production of refined magnesium and magnesium alloys.

One object of the present invention is to provide a simple and commercially practicable 5 process for the production of compact metallic magnesium in a substantially chemically pure state.

Another object of my invention is to enable magnesium and magnesium alloys respectively,

to be recovered, in-a refined state, from waste,

such as for example scrap arising from machine working and casting of magnesium or its alloys,

and thereby not only to obtain a purer product as a result of my improved process, but also to of the recoveries.

The'mechanical properties and. resistance to corrosion of magnesium and its alloys are adversely affected by the presence of impurities, especially extraneous oxides and other compounds (nitrides, carbides, silicides and the like), and also by other foreign substances, such as carbon, even though said impurities be present in very small amounts. I

The present invention aims at enabling magnesium which is technically pure (and its alloys) 1 to be very extensively refined in the simplest manner. The process is also admirably adapted for the elimination of impurities present during the recovery of magnesium by re-melting magnesium scrap (for example from machine work ing and from the foundry). Thus, for example in the case of magnesium dross, from which only 30% of the magnesium content could be recovered, as refined metal, by treatment according to known processes, the present invention en ables up to 90% of the metal originally present to be recovered as metal free from slag.

For this purpose, it was formerly the practice to remelt magnesium scrap high in magnesium,

moved by special after-treatment. In order to.

avoid this necessity, it has been proposed to moisten the metal with only just sufficient of a magnesium chloride melt to efiect a cementation of the foreign substances and to assure the recovery of a metallic melt free from magnesium chloride. With this object the scrap metal was to bemelted at high temperatures, such as 800 C. and over, with small quantites of anhydrous magnesium chloride, corresponding approximately to the amount of impurities present. Moreover, the use of saline melts consisting of ensure great saving by increasing the quantity mixtures of magnesium chloride or carnallite (KMgCla-HiHzO) with inspissating additions, such as oxides (e. g. of magnesium) or fluorides "(of magnesium, calcium, aluminium or other metals) was proposed for the purpose. Subsequently it was proposed to replace these melts by potassium chloride, with additions of fluor spar, .the salts primarily separating out during the cooling of the melt then serving as the thickening media.

This group of processes also includes the proposal to refine magnesium by melting the metal in association with alkali chlorides (especially sodium chloride or potassium chloride) or mixtures of alkali chlorides, having melting points 1 substantially higher than that of magnesium. These conditions are fulfilled by mixtures in which the sodium chloride or potassium chloride predominates. After melting, the whole is left to cool down to a temperature at which the salt, 20 or saline mixture, has solidified to form a crust in which the impurities are occluded, whilst the metal is still fluid.

Another group of processes consists in refinin the metal by melting it in association with addi- 25 tions which lead to the formation of an alloy to a moderate extent. Zinc, for example, is specified as an addition of this kind in United States specification No. 1,698,647, with the qualification that, as an alloying component, this metal exerts 30 a highly unfavorable influence on the magnesium (page 1, lines 41-58). For this reason, the specification recommends that, when magnesium fluoride is used as the main refining agent, a small amount (0.05-0.3%) of metallic calcium 5 should be incorporated According to the present invention, the magnesium, or material containing same, that is to be refined is melted inassociation' with small ad ditions of heavy metals in the form of salt, such 4 as for instance halides, the cations of which do not alloy, at the fusing temperature,'with the molten magnesium to any substantial extent, with or without addition of magnesium halides. As compared with the first group of the aforesaid known 45 processes, the difference exists in relation to the cation; the refining effect obtained in accordance with the invention can only be obtained with heavy metals. From the aforesaid second group of known processes the process of the present invention differs in that, for producing the effects obtained by the invention, the metal must be added in the form of a salt.

The salts which I have found suitable for the purpose are especially chlorides of iron, man- 56 ganese and zinc. Iron (III)--chloride (FeCla) shows a very high vapor pressure even a little above its melting point of 300 C. Zinc chloride boils at a temperature of 730. The very significant refining effect of 'these two salts obviously depends on the fact that vapors are developed from these salts at the working temperature, which become more intimately intermixed with the fused metal to be refined than is the case with a molten flux. On the other hand iron (ID-chloride (FeClz) at the working temperature has a very low vapor pressure and nevertheless exerts a very considerably purifying effect. The salts of manganese, especially manganous chloride, which combine with magnesium to form alloys when introduced in great excess into the fused metallic material, accompanied with overheating of the melt, do not alloy with the molten magnesium to more than a very slight extent, if at all, under the working conditions of the present process; that is to say if only small proportions are used and overheating of the melt is avoided. Manganese chloride is preferably employed in conjunction with chlorides of iron, or zinc chloride, or both. The amount of the additions depends on the quantity and nature of the impurities, 1 to 3 per cent by weight (referred to the total weight of material under treatment) being usually sufilcient.

The melting point of the selected salt or saline mixture should preferably be lower than that of magnesium, but the specific gravity higher than that of the molten metal. If such salts be strewn over the metal during the melting down process, they melt sooner than the metal and envelop it, thereby protecting it against oxidation. This behaviour has a specially advantageous effect in the case of magnesium alloys, their melting points being lower than that of the metal. When the metal is stirred, with a further addition of the salts, after fusion has taken place, the higher specific gravity of the saline melt causes it to subside quickly after absorption of the impurities, so that, after settling, the refined metal can be poured off. Nevertheless the fused metal remains protected against oxidation by a supernatant thin film of the saline melt.

In order to obtain intimate mixing, it is advisable to melt the salts or saline mixtures beforehand, and to crush the melt for use.

Example 1 Two separate portions of magnesium refined by distillation and containing 99.858% of Mg, were treated with 1% of zinc chloride in one case and with 1% of ferric chloride in the other. .The magnesium content increased in both cases to 99.940%, the carbon content sinking from 0.031% to nil and the iron content from 0.061% to 0.026% when zinc chloride was used, and to 0.028% in the case of using ferric chloride. A third portion was melted with a mixture of equal parts of magnesium chloride, zinc chloride and ferric chloride. By employing 1% of this mixture the iron content was reduced to 0.016%, by

employing 3% of the mixture to 0.003%, the carbon content being entirely eliminated in both cases.

Example 2 Contaminated magnesium scrap (and also dross and turnings) was melted downwith 3% of a saline mixture consisting of 30% of ferric chloride, 30% of zinc chloride, 30% of magnesium chloride and 10% of magnesium fluoride, a casting entirely free from slag being obtained. The iron content of the metal remained unaltered, whereas the zinc content, after the treatment, was about 0.04%.

I use the term magnesium in the following claims to include not only crude or technically pure magnesium metal but also magnesium alloys and magnesium waste arising for example from machine working or casting of magnesium or its alloys.

I claim:-

1. The method of producing refined magnesium, which comprises melting impure magnesium with a fluid flux containing as the main purifier at least one halide of the metals selected from the group consisting of iron and zinc, agitating the molten metal with the flux, allowing the metal and the flux to segregate from each other, and separating the metal from the flux.

2. The method of producing refined magnesium, which comprises melting impure magnesium with a fluid flux containing as the main purifier at least one halide of the metals selected from the group consisting of iron and zinc, and further containing a magnesium halide, agitating the molten metal with the flux, allowing the metal and the flux to segregate from each other, and separating the metal from the flux.

3. The method of producing refined magnesium, which comprises melting impure magnesium with a fluid flux containing as the mainpurifier at least one chloride of the metals selected from the group consisting of iron and zinc, agitating the molten metal with the flux, allowing the metal and the flux to segregate from each other, and separating the metal from the flux.

4. The method of producing refined magnesium, which comprises melting impure magnesium with a fluid flux containing as the main purifier at least one chloride of the metals selected from the group consisting of iron and zinc,' and further containing a magnesium halide, agitating the molten metal with the flux, allowing the metal and the flux to segregate from each other, and separating the metal from the flux.

5. The method of producing refined magnesium, which comprises melting impure magnesium with a fluid flux containing equal parts of chloride of iron, zinc chloride and magnesium chloride, and a smaller amount of magnesium fluoride, agitating the molten metal with the flux, allowing the metal and the flux to segregate from each other, and separating the metal from the flux.

GEORG SCHICHTEL.