High purity aluminum

An ounce

Aluminum is available as a metal and compounds with purities ranging from 99% to 99,9999% (ACS grade to ultrahigh purity) in the form of films, sputtering targets and nanopowders.

Elemental or metallic forms include pellets, rods, wires and granules for evaporation purposes. High purity (99,999%) alumina (Al2O3) powder is available in the form of powders and dense pellets for applications such as optical coatings and thin films.

High purity (99,9999%) aluminum (Al) sputtering targets are available in soluble forms, including chlorides, nitrates and acetates. These compounds are also prepared as solutions at certain stoichiometries.

Aluminum can be synthesized in ultrahigh purity (99,999 +%) for laboratory standards, advanced electronic thin film deposition using sputtering targets and evaporation materials, metallurgical and optical materials and other high technology applications.

Organometallic aluminum compounds are soluble in organic or nonaqueous solvents.

Aluminum ingot

The purest aluminum with a purity of> 99,999% is produced with the help of three-layer electrolysis. In order to clarify the technical effort, we have included the original description of the patent DE4329732C1 below. This process is to be used for the ingot as well as for the fine wire products.

The invention relates to a method and apparatus for refining aluminum in a three-layer melt-flow electrolysis cell, wherein the addition of the metal to be refined takes place via a forehearth containing a liquid anode alloy.

Usually, in the three-layer electrolysis, a furnace with a forehearth is used. This serves to charge the electrolysis cell, wherein the supply of the pure aluminum to be refined takes place in liquid form over the preform formed as a siphon into the lower layer of the electrolytic metal, the so-called anode metal. About 30% of copper is added to the anode metal to increase the density, and because of the constant supply of fresh aluminum material, an uneven alloy distribution in the electrolytic furnace is observed.

In addition to the anode metal, the three-layer electrolysis consists of a middle layer of a molten electrolyte and the product "pure aluminum" above that, which is the top layer in contact with the graphite cathodes.

The electrolysis is operated with direct current, with the anodic power supply at the bottom of the furnace and the cathodic supply via graphite electrodes. Due to the electrochemical Potentionalverhältnisse essentially only aluminum is anodically dissolved or cathodically deposited. Due to the low diffusion rate, there is no automatic mixing of the supplied liquid pure aluminum with the anode alloy, so that has been mechanically pumped to achieve a concentration balance between the various components of the anode metal.

By a manual or mechanical pumping there is a risk that waves occur at the interfaces of the three layers, leading in extreme cases by local short circuits to contamination of the cathode with the anode metal. Furthermore, it is disadvantageous that hitherto, in order to improve the miscibility, the pure aluminum to be refined has been melted in a separate furnace and then mixed with the anode metal via the forehearth. The known procedure could also be carried out only intermittently, since it always had to wait until the added pure aluminum was distributed by mechanical pumping in the forehearth.

Object of the present invention is to avoid the disadvantages mentioned and to provide a method and apparatus that allow a continuous supply of pure aluminum in particulate form in the Elektrolysemetall, shorts are avoided and impurities are removed continuously.

This object is achieved by the features specified in the main claim. Further preferred embodiments of the invention can be taken from the features of claims 2 to 15.

The essential idea of ​​the invention is that a portion of the electrolysis is passed through the forehearth in the anode metal. This results in the combination of the current flow with the magnetic field of the furnace, a force that leads to a metal movement in the forehearth. This movement is sufficient with a corresponding flow of current to cause melting and mixing of the introduced in the forehearth pure aluminum.

The current supplied to the forehearth via the 9 electrode is about 1 to 20%; preferably 10 to 15%, of the total flow of the electrolytic cell. From numerous experiments it has been found that a current from 1,5 to 7,5 kA can be introduced into the forehearth via the 9 electrode, preferably 3 to 6 kA being sufficient to allow good dissolution also of lumpy aluminum in the forehearth.

The adjustment of the current flowing through the electrode 9 can be carried out, for example, by the following parameters:

• 1. Change in the conductivity of the nipple material, the ramming mass or the carbon electrode
• 2. Change of the cross-section of the 9 electrode or the surface active in the anode metal
• 3. Turn on or off individual power supply to the cathode or anode
• 4. Change of material combination graphite / copper / synthetic resin binder.
• 5. Change in the thickness of the ramming compound 19.

On the basis of experiments, it has proven to be particularly effective to use the material of the 9 electrode made of double-impregnated electrographite. However, it is also possible with graphite or carbon to introduce sufficient power into the anode metal.

The limits for the current supplied via the 9 electrode are defined by the following boundary conditions:

At less than 1%, the anode metal effective force is insufficient to achieve sufficient mixing. At more than 20% of the total current current densities occur, which must be limited in terms of a sufficient life upwards.

In a preferred embodiment, the 9 electrode has a protective cover intended to prevent burnup. It consists of a ceramic material which is gas-tight and resistant to an aluminum-copper-anode alloy; For example, nitride-bonded silicon carbide can be used. A mixture of silicon carbide and silicon powder, which has been annealed under nitrogen, has proved to be particularly favorable.

From time to time, it is important that the underside of the 9 electrode be cleaned of dross from the charred aluminum pieces. The electrode 9 should therefore protrude from the bottom of the protective cover, whereby a vertical adjustment relative to the protective cover allows stripping or cleaning. Furthermore, the conductivity of the electrode 9 must be adjustable in order to effect the desired stirring or mixing in the anode metal.

Due to the inventive design of the three-layer electrolysis, it is possible that an automatic addition of pure aluminum takes place in lumpy form, the operation can proceed fully automatically by simple control engineering measures.

On the previously required mechanical stirrer can be omitted; Due to the materials used and the structural design of the 9 electrode, a long service life is guaranteed. As a result, the operating times of the electrode according to the invention have been significantly extended.

In the 10 electrolytic cell, a lining of magnesite 1 and an anode bottom of carbon 2 can be seen. The power supply is anodic via the anode rail 3 steel and cathodic graphite cathode 7, which are suspended from a corresponding cathode rail. Inside the electrolysis cell is the refining aluminum or 4 anode metal, which is covered at the top by a molten electrolyte 5.

The anode metal 4 extends into the forehearth 8, which is attached to improve the flow conditions obliquely to the electrolytic furnace.

The anode 3 is connected to the 11 anodes and the 9 electrode. Lateral aluminum in the direction of the 9 can be added to the side of the 12 electrode.

The purified aluminum settles as ultrapure aluminum at the electrolyte / cathode interface. From the cathode compartment it can be withdrawn in a known manner.

With the method according to the invention can be kept constant in an advantageous manner, the bath level in the three-layer electrolysis cell, with such great accuracy that even small fluctuations by continuous addition of pure aluminum, preferably in particulate form, can be compensated. This has the surprising advantage that the degree of purity in the method according to the invention can be substantially improved, since no impurities are absorbed by the lining of the electrolytic cell. In the case of three-layer electrolysis, this is particularly important because the impurities of the respective layer are deposited on the walls of the cell so that, when the bath level fluctuates, there is a risk that the impurity will be absorbed again into the already cleaned aluminum layers.

In Fig. 2 the inventive structure of an electrode 9 is shown in more detail. One recognizes the electrode material 13 and the cladding 14, which is separated from the electrode material 17 by a gap 13, which contributes to the isolation of the cladding.

The 9 electrode also consists of the electrode nipple 18 and a thin ramming layer 19, which surrounds the electrode nipple 18 inside the sleeve-shaped electrode.

At the electrode nipple 18 in the upper part of the further 14 cladding is attached, which is pressed over a screw 20 and a cover 21 against an annular disc 22. Between the envelope 14 and the nipple 18 is a sealing material 23, so that a gas-tight termination of the electrode is secured to the ambient air out. The washer 22 presses against the stop blocks 24 of the nipple 18.

To improve the bearing surface on the forehearth 8 a wall support 25 is provided. At the same time, it also fulfills sealing functions and serves as a fastener for the overlay of the 21 cover.

In order to minimize the resistance in the 9 electrode, the distance between the low point 15 of the 9 electrode and the lower edge 16 of the 14 cladding must be kept within certain limits. An adjustment possibility is given by the mechanical connection of the nipple 18 over the screws 26, 27, 28 with the electrode rod 29. Preferably, the distance between the lower edge 16 and the low point 15 is between 20 and 30 cm.