US2116245A - Preparation of alkaline earth metals - Google Patents

Description

May 3, 1938. ca. N. KmsEBoM 2,116,245

PREPARATION OF ALKALINE EARTH METALS Filed Sept; 15. 1955 Patented May 3, 1938 UNITED ST ATES' PATENT PBEPWTIQN EARTH Gustaf Newton Kirsebom,

land, assignor to Calloy'Limited, land, an English joint- OFFICE Clifton, Bristol,-Eng- London, Engstock company Application September 13, 1935, Serial No. 40,441

In Great Britain September 21, 1934 6' Claims. (CI. 75-07) This invention is for improvements in or relating to the preparation of magnesium.

According to the present invention magnesium is prepared by heating an alloy thereof in a closed ves'selto a temperature above the volatilization temperature of magnesium and condensing the metal vapour given oil.

In its simplest form the invention consists in volatilizing the magnesium in a closed vessel from 1a previously prepared alloy thereof with alumin- At the temperature required, e g. 1200-1300 C. for carrying out the process of the invention,

I aluminium has an extremely destructive efiect upon any of the refractory crucibles or furnace linings employed. If, for example, the aluminium containing the alkaline earth material were simply heated externally in a crucible, the heavy costs entailed-through the disintegration of the crucible may make the process uncommercial.

It is therefore of great importance in carrying out the process oi the invention to employ a method of heating, in which the heat is developedwithin the body of the metal itself and the crucible only becomes heated by conduction from,the hot metal.

. vOne very convenient way in which the inven- Q tion maybe carried into effect is to heat the magnesium al inium alloy in a high frequency electric furnace lined with carbon or other suitable lining material.

For example; in carrying out the process, an

aluminiummagnesium alloy may conveniently be prepared by the process describedinUnited States ,Patent dated 14th November 1933 No. 1,935,245 and such alloy may then be heated in a high frequency furnace without separatingthe alloy from the dross consisting of particles of alloy dispersed in aluminium oxide which is.

It is not, however; necessary to ,prepare an aluminium alloy previously. On the contrary,f metallic aluminium may be melted in a crucible I with calcined magnesite or material containing magnesium oxide in pieces of suflicientsize to overcome the surface tension of, the molten aluminium at a temperature above the volatiliza-' ,tion point of the saidyalkaline earth metal. The aluminium will then reduce the magnesium oxide formed in the reduction process.

. tion temperature of magnesium.

. The process of the invention has the great ad- 15 vantagethat no hydrogen is required to prevent a reverse reaction and no special means are required for evacuating the apparatus before or during the reaction. The small amount of air which is initially contained in the closed chamber 20 in which the reaction is carried out reacts in.the early stages of the process with the first magnesium formed, producing a. small amount of oxide and nitride dust which does not interfere with the subsequent condensation of metal.

In carrying out the distillation the condensing 25 tube may be immersed in an oil bath and the condensed magnesium drops into this oil bath in large pieces, which after cleaning, inay easily melted together, e. g. under a flip: or by other means.

As the vapour pressure, of aluminium at these temperatures is practically nil, magnesium condensed in this way does not even contain traces of (aluminium and is.chemically pure in other I respects. I I

It has sometimes been found useful to charge,

- the crucible first with the calcined magnesite in and the magnesium formedalloys with the alus minium and simultaneously the magnesium will be volatilized and may be condensed in a suitable chamber. In this waythe reaction may be continueduntil' the bulk of the aluminium has been converted to oxide.

,the disc and the sides of the crucible.

pieces and tocover the charge with a disc, preferablyv of graphite, of somewhat smaller diameter than the crucible to allow space for molten metal to trickle down between the periphery of Moltenaluminium or aluminium magnesium alloy is then poured in: The weight of the disc prevents the calcinedmagnesite from floating up to the surface of the molten aluminium and in this way from the start'of the reaction the magnesite.is surrounded by aluminium ensuring thereby a quicker and more thorough reaction between the pieces ofmagnesite and aluminium. After finishing distillation the still molten (residual metal isremoved from the dross by tilting the crucible with the disc in place.

Instead of using pieces of calcined magnesite,

2 I briquettes of calcined magnesite and carbon may be employed.

The reaction between the calcined magnesite and aluminium will then first take place and the briquettes will retain their form but will mainly consist of aluminium, aluminium carbide and aluminium oxide which may be worked up to aluminium. It is also possible instead of carbon to use other materials capable of forming briquettes with magnesite.

In the practical working of the process for the manufacture of magnesium it has been found that magnesium does not suihciently readily distil out of an alloy containing less than 8 per cent magnesium. The distillation may therefore be conveniently carried out in 'such a way that 8 vper cent aluminium-magnesium-alloy is used as starting material along with calcined magnesite, for example, in equal parts by weight. The magnesium will distil of! and this will go on until practically all the magnesium in the magnesite over and above what is required to maintain an 8 per cent alloy will distil over. when the rate of distillation slackens off, the remaining alloy will contain 8 per cent magnesium approximately.

By working with a'series of furnaces it is, therefore, possible on the'hrge scale to use the 8 per cent aluminium-magnesium-alloy left over from one furnace by pouring it into the next furnace along with the necessary fresh aluminium and calcined magnesite in lumps or pieces.

The system is then closed and distillation resumed until the rate of distillation again slackens off when the molten metal remaining in'the furnace and consisting of an aluminium-magneslum-alloy of approximately 8' per cent will be transferred to the next furnace in the series and so on. After the removal of the 8 per cent aluminium-magnesium-alloy from any furnace, the dross will be removed and treated separately for the recovery of aluminium, the furnace then being ready for a new operation.

In carrying out the process on a commercial scale it is not practicable to conduct the condensed magnesium directly into an oil bath owing to the amount of oil volatilized and the danger of explosion, but provided air is kept out of the apparatus during the volatilization stage, it is possible to collect the condensed metal without any serious losses in a chamber.

An arrangement of apparatus which has been found to work satisfactorily in practice is represented by the accompanying drawing in which Fig. 1 shows diagrammatically the arrangement of thewhole apparatus and Fig. 2 shows a modified form of oil seal.

Referring to Fig.1 an ordinary injector furnace iris heated by an oil jet 2. In the furnace a graphite crucible l is placed which is long enough to protrude above the top of the furnace.

The crucible is covered by a graphite lid 4. In

the side of the crucible above the level of the top of the furnace, an opening 0 is made to which the condenser pipe 'I is attached by the graphite and fireclay luting 5. The condenser pipe 1 leads into the top of a hood 8 standing in a shallow bath of oil la. Inside .the hood is a cylindrical receiver 9 in'two parts held't'ogether bythe tray l0 and the ring II. The receiver I stands upon a ring ii to raise it inside the hood. In the side of the hood a narrow tube H is fixed with its centre line in alignment with the centre of the condenser tube 1 and extending outwa'rdfrom the hood in a planev parallel with that of the condenser tube I. The

above the level of the 011 end of this tube is a packing gland I! through which a rod I! passes and extends along to the bend in the condenser pipe I. This rod is sealed with an oil seal at its lower end. In this pipe l4 there is also provided a narrow inlet pipe 16 ,which may be closed with a valve or rubber tube and clip.

In operation, magnesium oxide-containing material e. g. burnt magnesite is placed in the crucible 3 and molten aluminium filled into the crucible about half way. The system is then closed and the crucible heated to a temperature of 1200-1300 C.

The magnesium oxide is reduced and at the temperature of reduction it is volatilized off and condensed in the condenser tube 1. The condenser tube becomes heated by the heat of condensation to a temperature above the melting point of magnesium and the metal then melts and runs down dropping into the receiver 9. From time to time the rod I5 is moved to make sure that there has been no building up of condensed magnesium in the condenser tube 1 which may cause a blockage in the system. At the end of the run the furnace is shut down and as it cools, a reduced pressure is created in the hood I. Enough air is allowed to enter through the inlet IE to avoid oil being sucked up into the I When the metal in .the receiver has cooled sufficiently the hood is removed and the tray III and the ring II are knocked off the receiver 9 which is then broken apart.

Instead of the-oil tray the hood is closed with a disc 20 which is clamped to the bottom of the hood 8 by means of wedges 23 passing through eye-pieces 2| which latter are welded on to the through slots in the periphery of the disc 20. The hood I in this case is provided with a side tube It bent in the form of a U and dipping down into a small oil bath it.

While the apparatus above described employs an oil fired furnace, it is, of course, preferable to employ a high frequency furnace for the reasons already set out.

The metal obtainedas 'above described con- II, a slightly modified formof oil lock is shown in Fig. 2. In this case sides of the hood 8 and pass sists of large globules and prills separated by films of magnesium oxide and nitride. By simple melting under a flux such as carnallite a solid ingot of high purity may be produced.

I claim:'-

1. A process for preparing metallic magnesium which comprises heating magnesium oxide at a temperature above the boiling point of magnesium with an aluminium-magnesium alloy containing about 8% of magnesium and condensing the metal vapour given off.

2. A process for preparing metallic magnesium which comprises heating together magnesium oxide with excess of aluminium by first charging pieces of magnesium oxide into a crucible and covering the said; pieces with a loosely fitting graphite cover and pouring molten aluminium into the crucible and'thereafter heating the molten aluminium and magnesium oxide above the volatilization temperature of magnesium.

3. A process as claimed in claim '2 wherein there is employedinstead of pieces 01' magnesium aluminium in a closed vessel above the boiling point of but below that of aluminium, the magnesium oxide being in pieces of suiflcient size to overcome the surface tension of the molten aluminium and the amount or aluminium belngsuflicient to form an alloy with the reduced magnesium; (b) condensing the magnesium vapour formed.

15 the reduction process is carried out at a temperature Just above the boiling point pi magnesium 6. A process for preparing metallic magnesium which comprises forming an alloy of magnesi with aluminium by heating together magnesi oxide with excess of aluminium at a temperature above the boiling point oi magnesium whereby volatilization is effected simultaneously with the regeneration of the aluminium-magnesium alloy, and'heating the aluminium-magnesium alloy in a closed vessel to a temperature above the boiling point of magnesium and condensing the metal a vapour given ofl. I 5. A process as claimed in claim 4 wherein ops'rsr' zmsmaom;

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