Aluminum based anodes and process for preparing the same

Inactive Publication Date: 2012-08-02
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AI-Extracted Technical Summary

Problems solved by technology

However, the use of such anodes is limited due to the corrosion of the anode, which occurs mainly at open circuit voltage and at low current density by reaction of the aluminum anode (Al-anode) with the electrolyte.
Such corros...
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Disclosed is a method for preparing an aluminum-based anode, including at least one alloying element, prepared using solid solution heat treatment, in addition to plastic deformation, artificial aging, or a combination thereof.

Application Domain

Cell electrodes

Technology Topic

Alloy elementAnode +3


  • Experimental program(5)


Example 1
Corrosion Rate after SSHT Before Decomposition
[0011]1.5 kg of Al—Mg 2.5% alloy was smelted from 1.462 kg of aluminum (purity 99.99%) and 0.038 kg of magnesium (purity 99.999%) in a graphite crucible in an induction furnace under a protective atmosphere. Magnesium and other alloying elements were wrapped up in Aluminum foil and plunged into already melted Al. The melt was poured out into a steel mould of 150×15×260 size. Before casting the melt was vigorously stirred by graphite rod. The same procedure (besides the alloy's composition) was used for smelting of all the mentioned below Al base alloys.
[0012]Casting stress relief annealing was carried out at 350° C. for two hours, cooled down to room temperature and then the strips were rolled in a duo rolling mill to a thickness of 3.5 mm. This annealing procedure is optional and may be performed to reduce internal stress and to homogenize the structure. SSHT of the strips was carried out in an electric batch type furnace with circulating air. The strips were heated up to 415° C., maintained at this temperature for four hours and quenched in water to room temperature. A rolling duo mill having a roll diameter of 300 mm was used for rolling the ingots with different rates of deformation.
[0013]The test samples had a size of 30 mm diameter and 2.5 mm of thickness. Aluminum samples were machined directly from the ingots while alloy samples were machined from the strips and later subjected to solid solution heat treatment, and optionally an artificial aging process. The artificial aging process was carried out in a batch furnace at 150-200° C., depending on alloy composition, under an air atmosphere (the specific temperatures used during the artificial aging process for each alloy are presented in Table III below).
[0014]The corrosion value, coulombic efficiency and polarization tests were carried out in electrochemical half-cells in 4M KOH at 50° C. The corrosion value at OCV and coulombic efficiency in galvanostatic experiments were measured by weight loss. Here and further all the potentials were measured vs. Hg/HgO reference electrode with IR drop correction. Before each test the sample's working surface was polished by the SiC abrasive paper grit 600, followed by a fine alumina suspension AP-A polishing.
[0015]The corrosion rate at OCV for Al and Al based alloys after solid solution heat treatment is as follows:
TABLE I Corrosion rate Alloy composition SSHT (° C.) (mg/cm2 · min) Al 99.99 — 0.81 Al 99.9 — 0.92 Al—Mg 2.5% 415 0.52 Al—Mg 3.8% 415 0.51 Al—Mg 6% 415 0.63 Al—Mg 2.7%—Si 0.7% 415 0.83 Al—Mg 2.1%—Ge 0.6%—Ga 415 0.85 0.3% Al—Si 1.2% 560 0.82
[0016]As shown in Table I, performing solid solution heat treatment for Al—Mg alloys having an Mg content of less than 4% results in a significant decrease in the corrosion rate in comparison to pure Al, as well as other Al based alloys. It was further found that the corrosion products of Al—Mg alloys having up to 4% Mg completely dissolve in an alkaline solution, and therefore, the working (corroded) surface of these alloys is smooth and clean. In contrast, it was found that the other alloys, including the Al—Mg alloy with 6% Mg, form a porous layer of corroded product on the working surface of anode. This porous layer can notably increase the anodic polarization, as will be shown below. Additionally, the corroded products may migrate into the electrolyte to form a very fine suspension, further disrupting the efficiency of the anode.


Example 2
Corrosion Rate after Artificial Aging
[0017]The alloys prepared according to the procedure detailed above were additionally subjected to artificial aging. The corrosion rate .vs. the time of aging of the various alloys is shown below in Table II.
TABLE II Aging Time of aging/Corrosion Alloy composition (° C.) rate (h/(mg/cm2min)) Al—Mg 2.5% 150 90/0.47; 175/0.4; 220/0.42 Al—Mg 3.0% 150 170/0.38; Al—Mg 4.5%—Ga 0.5% 150 90/0.58; 190/0.52 Al—Mg 6% 150 90/0.60; 175/0.49 Al—Mg 2.7%—Si 0.7% 160 90/0.77; 175/0.63 Al—Mg 2.1—Ge 0.6—Ga 160 90/0.71; 175/0.59 0.3 Al—Si 1.2% 190 90/0.79; 175/0.65


Example 3
Comparison Between Corrosion Rates when Using Artificial Aging and Plastic Deformation
[0018]1.5 kg of an Al—Mg 3.4% alloy was prepared according to the procedure described in Example 1. The ingot of size 150×15×260 mm was rolled to the strips having thickness 4.5 mm. The solid solution heat treatment for these strips was carried out as follows: heating up to 415° C., maintaining at this temperature for 4 hours and quenching in water at room temperature. After quenching the strips were rolled from the thickness of 4 mm to 1.1-1.2 mm and then some samples (Group A) were electrochemically tested and some of them (Group B) were subjected to aging process at 150° C., before electrochemical testing.
[0019]The results show that the average corrosion rate for Group A samples was 0.33 mg/cm2·min The results of the corrosion test for samples of Group B are summarized in Table III
TABLE III Time of aging, h 0 67.5 133.5 200 263 Corrosion rate, mg/cm2/min 0.34 0.34 0.33 0.32 0.34
[0020]From comparing the results presented in Examples 2 and 3 (Group A), it can be concluded that solid solution heat treatment+plastic deformation by rolling of the Al—Mg alloy, having supersaturated solid solution structure, results in notably lower corrosion rate as compare to the solid solution heat treatment+aging (see Table II). It should be also emphasized that a plastic deformation by rolling is much less time and labor consuming compared to the low temperature, long time aging process. Further, the rolling also provides the flattening of the strips, which are deformed after the solid solution heat treatment. By comparing the results of Group A (including plastic deformation with no artificial aging) and Group B (including both plastic deformation and artificial aging) it is concluded that once plastic deformation is performed, the additional artificial aging process does not change the corrosion rate.


Temperature40.0 ~ 50.0°C
Fraction0.02 ~ 0.04fraction
Fraction0.005 ~ 0.1fraction

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