Title of Invention

"AN IMPROVED PROCESS FOR THE PROLUCTION OF ALUMINIUM DRY CELL."

Abstract

An improved process for the production of aluminum dry cells which comprises: a) preparation of standard size aluminum metal shell, b) characterised in that lining the inside of the said aluminum shell with an ionically permeable material such as herein described and lining the bottom with an insulating paper, c) filling a cathode mix having the following composition range: Composition dry mix; weight percent MnO2 60 to 70 Carbon black 8 to 10 CaC12 0 to 22 A1CI3 0 to 11 (NH4)2Cr2O7 0 to 0.1 < Percent by weight of dry mix Water 18 to 20 inside the permeable lining with a graphite/carbon rod, having metal cap, in the centre of the said shell, d) covering the top of the said cathode mix by a cardboard through which the said graphite/carbon rod passes, e) sealing the said shell at the top with wax.

Full Text

This invention relates to an improved process for production of aluminium dry cell. The invention can be used to produce aluminium dry cells for use in flash lights, electronic equipment such as transistor radios, tape players, millimeters, clocks, toys. The art and technology of production of zinc dry cells is well established. It consists of zinc metal shell as galvanic anode and MnO as cathode separated by permeable 2 starch layer or paper. Controlled oxidation of zinc is accomplished according to reaction as given below ++ Zn —> Zn + 2e and the oxidant MnO aided by the electrolytes like 2 ammonium chloride mixed with MnO provides the electrical 2 energy. Zinc metal shell anode accounts for 30% of the total raw material for manufacture of of zinc dry cells. For a thousand million pieces approximately 12000 ton of zinc metal are required. It would be advantageous to use commonly available commercially pure aluminium metal shells galvanic anodes as aluminium is not only cheaper but also much superior to zinc, both on coulombic and energy basis. The excellent storability, formability, abundant availability and rather inexpensive virtues are additional advantages. On a coulombic basis 9.0 gm. of aluminium is equivalent to 33.0 gin. of zinc and the Gibb's free energy released per mole of electrons exchanged is 161.0 kJ and 73.3 kJ for aluminium and zinc respectively. A number of patents have been taken throughout the world for production of aluminium dry cells but none so far with commonly available commercially pure aluminium. The problems of using aluminium as a galvanic anode are due to its reactive nature towards alkali or acid alike and its passivation characteristic in neutral medium. On dissolution of the passive film Aluminium, (standard electrode potential (SEP) -1.67 V) is very active and prone to self corrosion in aqueous medium. Previous developments require specially developed duplex/composite alloys or aluminium alloyed with zinc, tin, antimony, bismuth to inhibit the self corrosion. Simultaneously some inhibiting agents like chromates and dichromates, chromium chloride or salts of ethylene diamine tetra acetic acid (EDTA) and activating agents like chlorides of mercury, sodium were included in the electrolyte mix to enhance the life of the aluminium dry cells. G. S. Lozier and R. Glicksman in their U. S. patent no. 2874079 disclosed use of anodes with duplex layer, having an outer layer comprising an alloy with composition 95.5% Al, 3% Mg, 1% Zn and 0.5% Mg; and an internal layer of super purity aluminium which comprised of 70% by weight of duplex product. The cathode was an organic oxidizing agent in which the oxidizing properties were due to positively charged halogen atoms. The electrolyte was hydrated aluminium chloride and chromic chloride which also contained other metal chlorides but their purpose is not clarified. the open circuit voltage (OCV) of the cell was 1.5V and discharge life of 350 minutes to 0.9V. J. J. Stokes Jr. in his U. S. patents nos. 2796456 and 3307976 used duplex aluminium alloy container the inner part constituting 70% of the anode was ultra pure aluminium and the outer layer constituting 30% of the anode was alloyed with a metal such that the outer layer was less anodic than the inner layer. The bulk electrolyte aluminium chloride contained chromium chloride and or ammonium chromate as inhibiting agent ammonium chloride was added to achieve the best results. The capacity of these cells was between 790 and 795 minutes discharge time (to 0.9 V) and an average shelf life of less than three years (retaining 75% of the initial value). J. Foucry in his U. S. patent no. 3415688 used super purity aluminium shell as anode and electrolyte was ammonium chloride containing mercuric chloride as accelerator and salts of ethylene diamine tetra acetic acid (EDTA) or ethanolamine prepared by neutralizing fluoboric acid as complexing agent. The cathode was a very porous graphite rod charged with PbO deposited by electrolysis. Michel Angelo, V. Debanathan, B. A. Shenoi, P. L. Joseph and V. Subramaniam in their Indian patent no. 106324 used aluminium metal with electrolyte manganese chloride containing mercuric chloride or aluminum amalgamated with mercury when the electrolyte contained no mercuric chloride. The electrolyte also contained complexing agents like citrates, tartrates or EDTA. The OCV of cells with mercuric chloride in the electrolyte was 1.7 to 1.9 V; and those with no mercuric chloride in the electrolyte was 1.5 V. Data regarding other tests is not documented in the patent. P. L. Joseph, V. Subramaniam, G. Jothinathan, B. A. Shenoi, M. Angelo and V. Debanathan in their Indian patent No. 106324 used Al-Hg alloy anode shells and MnCl with alkyl pyredinium halide. With unamalgamated anode mercuric salt was added to the electrolyte. They also used Al-Hg-Sn alloy for making anode shells. The OCV ranged from 1.5 to 1.8 V. No information regarding other tests are documented. The known process using aluminium anode as mentioned above have the following drawbacks. 1) Pronounced self corrosion when the cell is either idle or active. 2) Requirement of specially developed duplex/composite alloys or super quality aluminium to combat the self corrosion. These are not only costly but also unavailable commercially upsetting the advantages of aluminium dry cells. 3) The use of corrosive and poisonous electrolytes e.g. chlorides of aluminium, manganese, sodium, ammonium, or mercury with different inhibiting agents like salts of chromates dichromates or EDTA. These electrolytes are poisonous and very corrosive to the duplex/composite special alloys, not to speak of the commonly available commercially pure aluminium shells. Successful functioning of a dry cell with aluminium anode is contingent upon: a) High degree of inhibition of self corrosion when the cell is idle and in action. b) Large delivery of current at a practicable operating voltage when the cell is in action. There are two modes of approach to achieve these twin objectives. The first is to use aluminium alloyed with elements like zinc, tin, manganese, indium, gallium, thallium, bismuth followed by special heat treatments or to use duplex/composite alloys. The second is to find out an electrolyte such that, commonly available commercially pure aluminium having 99.9% purity can also be used to produce stable dry cells, comparable to commercially available zinc dry cells. The main object of the present invention is to provide an improved process for the production of aluminium dry cells by overcoming the above mentioned drawbacks. Another objective of the present invention is to provide a process for the production of aluminium dry cell using a novel electrolyte possessing a perfect balance of the inhibiting and activating properties expedient for the purpose. The present is based on our findings that chlorides of alkaline earth metal, such as calcium chloride can be used as the electrolyte due to its excellent balance of inhibiting and activating properties, when the cell is at rest or in action respectively. The appropriate inhibiting property of calcium chloride may be due to the physically adsorbed chloride molecules on the aluminium shell with the positively charged calcium ions disposed towards anode shell. This protects the aluminum shell from self corrosion in all conditions. It has also been found that along with the AEM chlorides complexing agents like 2-Hydroxy propane-1,2,3, tricarboxyllic acid and inhibitors like dichromates of sodium, potassium or ammonium in small proportions below 5% can be added to enhance the inhibiting action to combat corrosion with no adverse effect on the performance of the improved aluminium dry cells. It was also found that other alkaline earth metal chloride chloride can be used along with aluminium chloride in appropriate proportions when consistency of the cathode mix is hard to prevent the cell from corrosion. It was also found that other activators like aluminium fluoride ammonium per chlorate in traces ~ 0.1% have a Beneficial effect on the performance of the cell in terms of continuous current voltage (CCV) and current. The proportion of water has an important bearing on the corrosion behavior and the performance of the cell. Below a certain minimum the activity of the cell is impaired badly where as beyond a certain maximum the corrosion is fast and the cells are punctured. Accordingly the present invention provides an improved process for the production of aluminum dry cells which comprises: a) preparation of standard size aluminum metal shell, b) characterised in that lining the inside of the said aluminum shell with an ionically permeable material such as herein described and lining the bottom with an insulating paper, c) filling a cathode mix having a composition such as herein described, inside the permeable lining with a graphite/carbon rod, having metal cap, in the centre of the said shell, d) covering the top of the said cathode mix by a cardboard through which the said graphite/carbon rod passes, e) sealing the said shell at the top with wax. According to an embodiment of the invention ; The aluminum shell may be made of commercially pure aluminum having purity - 99.9% The manganese dioxide may be of electrolytic grade or any other grade which is battery active or mixture of several grades having battery activity The graphite rod having metal cap can be any other non reacting material having good electrical conductivity such as commonly used for dry cells The insulating paper lining at the bottom may be a strong enough waxed paper The card board covering the cathode mix at the top may be a card board normally used for such purpose The sealing wax may be pitch or any other material used normally for such purpose By the process of present invention aluminum dry cells were produced having properties as given in table 1 below Table 1 (Table Removed) The following examples are given by way of illustration and should not be construed to limit the scope of the invention. Example: 1. Aluminium dry cells (R20 size) were assembled as explained below. i) A thoroughly cleaned aluminum anode shell was insulated at the bottom by placing a waxed card board disc at the bottom. ii) The inner wall of this was lined with an ionically permeable liner ( a filter paper in this case). iii) The cathode mix of the composition: MnO - 69.93%, 2 Carbon black - 9.79%, CaCl - 20.28% with 18% water 2 of the weight of the above three ingredients was pressed inside this liner with the graphite rod in the center. iv) A thick card board disc with a central hole for the graphite rod was then pressed over the cathode mix. v) The whole assembly was then sealed at the top by pouring sealing wax over the card board, vi) Another card board disc was then fixed over the sealing wax so that a gap of one or two mm. remained in between, vii) The metal cap was then fitted on the top of the graphite rod. The OCV and the CCV of the cell were 1.7 and 1,5 V respectively. The initial current with a 4 ohm load was 370 mA. Example: 2. Aluminium dry cells (R20 size) were assembled as explained below. i) A thoroughly cleaned aluminum anode shell was insulated at the bottom by placing a waxed card board disc at the bottom. ii) The inner wall of this was lined with an ionically permeable liner ( a filter paper in this case). iii) The cathode mix of composition: MnO - 69.93%, Carbon 2 black - 9,79%, CaCl - 18.65%, A1C1 - 1.63%, with 18% 2 3 water of the weight of above four ingredients was pressed inside this liner with a graphite rod in the center. iv) A thick card board disc with a central hole for the graphite rod was then pressed over the cathode mix. v) The whole assembly was then sealed at the top by pouring sealing wax over the card board. vi) Another card board disc was then fixed over the sealing wax so that a gap of one or two mm. remained in between. vii) The metal cap was then fitted on the top of the graphite rod. The OCV and the CCV of the cell were 1.7 and 1,5 V respectively. The initial current with a 4 ohm load was 370 mA. Example: 3. Aluminium dry cells (R20 size) were assembled as explained below. i) A thoroughly cleaned aluminum anode shell was insulated at the bottom by placing a waxed card board disc at the bottom. ii) The inner wall of this was lined with an ionically permeable liner ( a filter paper in this case). iii) The cathode mix of composition: MnO - 67.75%, Carbon 2 black - 9.70%, CaCl - 11.05%, A1C1 - 11,05%, and 2 3 (NH ) Cr O - 0.05%, with 19.3% water of the weight 42 27 the five ingredients was pressed inside this liner with the graphite rod in the center. iv) A thick card board disc with a central hole for the grciphite rod was then pressed over the cathode mix. v) The whole assembly was then sealed at the top by pouring sealing wax over the card board. vi) Another card board disc was then fixed over the sealing wax so that a gap of one or two mm. remained in between. vii) The metal cap was then fitted on the top of the graphite rod. The OCV and the CCV of the cell were 1.7 and 1,5 V respectively. The initial current with a 4 ohm load was 370 mA The main advantages of the present invention are: 1) By the process of present invention aluminium dry cells can be produced from commonly available commercially pure aluminium e.g 2S grade where as the existing processes use duplex/composite alloys or super purity aluminium for anode shells which are costly and commercially not available 2) By the process of present invention aluminum dry cells can be produced with electrolytes that are competitively economic ecologically innocent, abundantly available, easy to handle whereas the existing processes used electrolytes which are either too aggressive towards aluminium requiring inhibiting or moderating agents, or too noble requiring activators like mercuric chloride, environmentally hazardous We Claim: 1. An improved process for the production of aluminum dry cells which comprises: a) preparation of standard size aluminum metal shell, b) characterised in that lining the inside of the said aluminum shell with an ionically permeable material such as herein described and lining the bottom with an insulating paper, c) filling a cathode mix having a composition such as herein described, inside the permeable lining with a graphite/carbon rod, having metal cap, in the centre of the said shell, d) covering the top of the said cathode mix by a cardboard through which the said graphite/carbon rod passes, e) sealing the said shell at the top with wax. 2. An improved process as claimed in claim 1 wherein the aluminum shell used is made of commercially pure aluminum having purity 99.9%. 3. An improved process as claimed in any of the previous claims wherein the graphite/carbon rod having metal cap used is of any nonreactive material with the cathode mix having good electrical conductivity and having a composition Mn02 60 to 70 (dry mix wt.%) ,Carbon black 8 to 10 (dry mix wt.%), CaCI2 0 to 22 (dry mix wt.%), A1CI3 0 to 11 (dry mix wt.%), (NH4)2Cr207 0 to 0.1 (dry mix wt.%) and Water 18 to 20%. 4. An improved process as claimed in any of the previous claims wherein the graphite rod having metal cap used for conducting current is a material which does not react with the cathode mix. 5. An improved process as claimed in any of the previous claims wherein the composition of the electrolyte consists of: calcium chloride mixed with other chemicals selected from ammonium chloride, aluminum chloride, aluminum fluoride, ammonium chromate/dichromate or citric acid. 6. an improved process as claimed in any of the previous claims wherein carbon black, acetylene black or graphite powder or charcoal powder or a mixture of any two or all of these is used for the cathode mix, 7. An improved process for the production of aluminum dry cell substantially as herein described with reference to the examples.

Documents:

1809-del-1996-abstract.pdf

1809-del-1996-claims.pdf

1809-del-1996-complete specification (granded).pdf

1809-del-1996-correspondence-others.pdf

1809-del-1996-correspondence-po.pdf

1809-del-1996-description (complete).pdf

1809-del-1996-form-1.pdf

1809-del-1996-form-2.pdf

1809-del-1996-form-4.pdf