US2867527A - Process of simultaneously producing calcium metal and a silicon-aluminum alloy - Google Patents

Description

' process under vacuum from lime.

United States PatentC PROCESS OF SIMULTANEOUS LY PRODUCING CALCIUNI METAL AND A SILICON-ALUMI- NUNI ALLOY Jean Lucien Andricux and Etienne Bonnier, Grenoble, France No Drawing. Application September 20, 1956 Serial No. 610,902

Claims priority, application France October 5, 1955 3 Claims. (CI. 75-67) The present invention relates to the simultaneous prep+ aration of calcium metal and a silicon-aluminum alloy.

Calcium metal is generally obtained by an electrolytic process from calcium chloride or by an aluminothermic Silicon-aluminum al-, loy is generally prepared by an electrothermic process.

The above processes of manufacture of calcium all give defective yields, the electrolytic process owing to the metal losses, in particular, by dissolving in the bath, and the aluminothermic process owing to the necessary form: ing of a slag of lime aluminatef It is possible, by distillation under vacuum, to separate the constituents of metal alloys, as far as these constituents form a true solution at the temperature of the operation and have sufficiently different vapor pressures.

It is known that the presence of strong intermetallic affinities limits the yield of such separations by distillation.

.It is known, also, that in the case of strong inter: metallic afiinities impeding the separation of the constituents of an alloy, it is'possible to displace favorably the equilibrium of dissociation of the definite compounds by introducing a third element presenting for one of the constituents a greater affinity than that which it reveals, at the temperature in question, for the other.

As regard the AlCa and SiCa alloys, the vapor pressures of aluminum and silicon are substantially lower at any temperature than that of calcium. This would allow to foresee a possible separation of the calcium from the other elements of these alloys. However, each of these systems, AlCa and SiCa, presents, besides definite compounds which are unstable at a temperature above 1000 (3., compounds stable at a higher temperature, which are respectively CaAl and CaSi. Theheat of formation of these definite compounds ishigh and shows the strength of the afiinities between A1 and Ca on the one hand and Si and Ca on the other hand. This situation limits the abovefconsidered possibilities of separating Ca from Al and Si to only the elements which are free in the alloy.

At last the Al-Si system presents no compounds but, only, in the liquid state, a continuous zone of solution of 0 to 100% of each of the constituents. Then it is not possible to think of an effectual displacing of equilibrium of Ca from Al or Si by the addition of one or the other of the metals Al or Si used alone.

The present invention allows one to overcome these diificulties. It comprises heating at a temperature of from 1300" to 1400 C. under a reduced pressure of from 0.1 to 1 micron of mercury a mixture of two alloys (aluminum-calcium alloy and silicon-calcium alloy) in judiciously calculated proportions and collecting the calcium metal which distills on a cooled condenser; der the conditions which will be indicated further, the non-vaporized molten residue is then composed of a silicon-aluminum alloy containing very little calcium.

It is preferred to use as raw material, on the one hand,

2,867,527 en e Ji 6 2 the aluminum-calcium alloys which are obtained by the process of aluminothermic reduction of lime at normal pressure and whose calcium content can reach 25% in weight and, on the other hand, the electrothermic siliconcalcium alloys whose content is near 30 to 33% calcium.

These latter alloys may be obtained, for example, by reduction of silica by carbon and calcium carbide or, also, by reduction of lime by silicon-aluminum alloys.

'But it is possible in order to improve the production of calcium metal to start with alloys richer in calcium, such as those which it is possible to obtain by the electrolytic method from lime aluminates and silicates.

Anyway, it is thus possible to extract with an excellent yield the calcium contained in the alloys of this metal with aluminum and silicon. i I I The operation may be carried out as follows.

The charge, suitably crushed to the size grain of wheat, is intimately mixed and placed in a refractory crucible which is introduced into a distillation furnace. The pressurebeing reduced to a pressure of 0.1 to 1 micron of mercury, the furnace is filled with argon from which nitrogen has been carefully cleared and the argon is then removed from the furnace. One proceeds afterwards to the heating while maintaining the reducedpressure in order to ensure the removal of gas fromthe metallic mass, chiefly from the AlCa alloy. wiinjs'iemperature of 1320 to 1350 C. has beeiire'achedgfbr an interior pressure of about 0.3 to 0.1 micron of mercury, this state is maintained during a time determined ac; cording to the weight of the mass to be treated and to the superficial dimensions of-the liquid metallic bath. For example, when a refractory crucible containing a mass of 50 g. of mixture is used, one hour is enough to carry out the operation, The heating is afterwards stopped and, when the furnace is sufliciently cool, argon is in-, troduced until an interior pressure equal to the outer pressure is obtained. The furnace can then be opened and the condenser removed. The condenser retains the calcium deposited according to the basaltic structure peculiar to distilled calcium.

The weight of metal collected. on the condenser, its calcium content, the. weight of molten residnereinaining in the crucible and it calcium contentallow one to calculate the yield of calcium. Under the indicated conditions, it is between 95 and generallyabout 97%. t

' The metal collected on the condenser always contains a little aluminum in proportions comparable'with those present in aluminothermic-produced calcium obtained under vacuum. The silicon content on the other hand is veryllowas indicated by the examples given hereafter. The contamination of the calcium by aluminum increases with the temperature employed and. may be minimized by a lowering of the temperature but this lowers the yield of calcium.

According to economic conditions, it is possible to vary within great limits the relative ratios of the AlCa and Si-Ca alloys so as to extract as much calcium metal as possible from the less expensive raw material.

The advantage presented by the process according to the invention are as follows:

(1) A great part of the extracted calcium comes from electrothermic silicon-calcium alloy easy to obtain and generally less expensive than the aluminum-calcium alloy.

(2) The aluminothermic reduction of lime at ordinary pressure and the further distillation under reduced pressure of the obtained alloy are more economical than the operation of aluminothermic reduction of lime under reduced pressure because the yield of the operation carried out on the aluminum-calcium alloy under reduced pressure is near 100% and is not limited by the formation of slag which in the aluminothermic process. of reducing lime retains nearly 60% of the introduced calcium and aluminum. The aluminothermic reduction of lime with a low yield is carried out in a rudimentary apparatus as large as desired. It is, on the other hand, very expensive and often impossible to build large furnaces with a much reduced pressure.

(3) The residue of the operation is a silicon-aluminum alloy of high commercial value, utilizable for the preparation of light foundry alloys of the Alpax type, whereas the aluminocalcic slag collected in the process of direct reduction under vacuum of lime by aluminum is, on the one hand, a worthless residue and, on the other hand, a hindrance to carrying out the process, in particular, on account of the destruction of the working crucibles.

,In order that the invention may be more clearly understood, two examples of carrying out the process according to the invention are given below.

Example 1 The composition and the origin of the basic raw materials are as follows:

(1) Aluminothermic aluminum-calcium alloy with a Ca metal content of 17.0i0.3%.

(2) Electrothermic silicon-calcium alloy with a Ca metal content of 30.5:0.5%.

Composition of the charge- Al-Ca alloy 64% Si-Ca alloy 36% Weight of the charge 50 g. Distillation temperature 1320 C. Distillation pressure 0.20 micron of mercury. Time required for the distillation 1 hour.

The weights and compositions of the obtained products were as follows:

1. Condensate of calcium g 10.5

Contents in elements other than calcium- Si percent 0.17

A1 do 1.60

2. Residue of silicon-aluminum alloy g 38.5 a-eo entf this alloyCa percent 1.12

The content of aluminum in the so densate of calcium can be lowered by increasing the proportio Yield of calm of silicon-calcium alloy in the charge as in the followf ing example.

4 Weight and composition of the obtained products 1. Condensate of calcium 10 g. Contents in elements other than Ca Si "percent; 0.53 A1 do 1.1 2. Residue of silicon-aluminum alloy g 38 ,Ca content of this alloy Ca "percent" 5.20

Yield of calcium do 84 By increasing still more the silicon-calcium alloy rato in the charge, the aluminum content of the distilled calcium lowers still more but its silicon content increases and the extraction rate lowers. For instance, if the charge is composed of 13% Al'-Ca alloy and 87% Si-Ca alloy, the obtained calcium contains 1.75% Si and 0.93% Al and the yield ofcalcium is lowered to 69%.

The composition of the silicon-aluminum alloy obtained as residue of the distillation depends, of course, on the proportions of the AlCa and Si-Ca alloys in the charge.

The invention is not limited to the preferred embodiment but may be otherwise embodied or practiced within the scope of the following claims.

We claim: v

1. A process of simultaneously producing calcium metal and a silicon-aluminum alloy,.which comprises v heating a mixture of aluminum-calcium alloy and silicon calcium alloy in an inert atmosphere at a temperature of 13001400 C. at a pressure of 0.1 to 1 micron of 2. A process according to claim 1, wherein the aluminum-calcium alloy employed is produced by the alumi nothermic reduction of lime 'at normal pressure and contains up to 25% by weight of calcium.

3. A process according to claim 1,. wherein the silicon-calcium alloy employed is produced by the reduction of silica by carbon and calcium carbide and contains about 30% by weight of silicon.

References Cited in the file of this patent UNITED STATES PATENTS 1,607,245 Duhme Nov. 16, 1926 1,728,942 Marden Sept. 24, 1929 2,194,965 Andrieux Mar. 29, 1940 7.298 Dean .4 Dec. 23, 1941 2,362,147 Mondolfo Nov. 7, 1944 2,425,705 Tetu Aug. 12, 1947 2,464,767 Pidgeon et al. Mar. 15, 1949 2,513,339 Loevenstein July'4, 1950 2,684,898 Barton, July 27, 1954 FOREIGN PATENTS 2,270,060 Great Britain May 5, 1927

Claims (1)

1. A PROCESS OF SIMULTANEOUSLY PRODUCING CALCIUM METAL AND A SILICON-ALUMINUM ALLOY, WHICH COMPRISES HEATING A MIXTURE OF ALUMINUM-CALCIUM ALLOY AND SILICONCALCIUM ALLOY IN AN INERT ATMOSPHERE AT A TEMPERATURE OF 1300-1400* C. AT A PRESSURE OF 0.1 TO 1 MICRON OF MERCURY TO DISTILL OFF CALCIUM AND PRODUCE A MOLTEN RESIDUE OF SILICON-ALUMINUM ALLOY, CONDENSING AND RECOVERING THE CALCIUM, AND RECOVERING THE SILICON-ALUMINUM ALLOY.