CA2119084A1 - Composite for oxidation and corrosion protection of anode nipples - Google Patents

Composite for oxidation and corrosion protection of anode nipples

Info

Publication number
CA2119084A1
CA2119084A1 CA002119084A CA2119084A CA2119084A1 CA 2119084 A1 CA2119084 A1 CA 2119084A1 CA 002119084 A CA002119084 A CA 002119084A CA 2119084 A CA2119084 A CA 2119084A CA 2119084 A1 CA2119084 A1 CA 2119084A1
Authority
CA
Canada
Prior art keywords
composite material
collar
per cent
accordance
dry weight
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Abandoned
Application number
CA002119084A
Other languages
French (fr)
Inventor
Trygve Foosnaes
Knut Bergli
Tormod Naterstad
Audun L. Bosdal
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Norsk Hydro ASA
Original Assignee
Norsk Hydro ASA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Norsk Hydro ASA filed Critical Norsk Hydro ASA
Publication of CA2119084A1 publication Critical patent/CA2119084A1/en
Abandoned legal-status Critical Current

Links

Classifications

    • CCHEMISTRY; METALLURGY
    • C25ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25CPROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
    • C25C3/00Electrolytic production, recovery or refining of metals by electrolysis of melts
    • C25C3/06Electrolytic production, recovery or refining of metals by electrolysis of melts of aluminium
    • C25C3/08Cell construction, e.g. bottoms, walls, cathodes
    • C25C3/12Anodes
    • C25C3/125Anodes based on carbon

Landscapes

  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Prevention Of Electric Corrosion (AREA)
  • Electrolytic Production Of Metals (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Abstract

A B S T R A C T

A composite material for protecting one or more anode hanger nipples against oxidation and corrosion during operation in a Hall-Heroult electrolysis cell, consisting of a base material in the form of a particle aggregate of waste products from anodes consumed in aluminum electrolysis cells, calcium aluminate cement, a catalyst and water. Substances hazardous to health, such as PAH, have been removed. The composite material is characterised in that the particle aggregate can consist of particles between 1 and 2000 µm and make up at least 80 % of the composite material, the cement up to 15 %, the catalyst 0.6 % and the added water approximately 28 % of the solid mass.
The composite material is compressed under pressure to form a collar around the anode hanger nipples and can be prefabricated.

Description

- -`"` 2 1 ~ 4 - ~

The present invention concerns a composite material for protecting one or more anode hanger nipples (hereinafter called nipples) against oxidation and corrosion during operation in a Hall-Heroult aluminium electrolysis cell, consisting of a particle aggregate of waste products from anodes consumed in aluminium electrolysis, calcium aluminate cement, a catalyst and water. Ready-processed and mounted, the composite material forms a protective collar around the nipple.
There are two main different types of composite materials which are used in this context:

For many years it has been normal practice to use petroleum coke and/or waste from consumed anodes as the base material and pitch as the binder for the first type of material for protecting anode hanger nipples against oxidation and corrosion during operation in an electrolysis cell. The disadvantages of this solution are that the pitch contains elements which are hazardous to health, for example PAH (polyaromatic hydrocarbons) which are released through the high temperature in the electrolysis cell, and that the nipples' resistance to aggressive gases i~ relatively low because the collar covers the whole of the nipple only for part of the operating time before it is partly dissolved on account of too weak particle binding and dilation forces which arise between the collar and the nipple.

A combination of the components petroleum coke, graphite, semi-graphite and waste electrode material is used as the base material of the second type, as well as a special cement mixture as the binder and water to trigger the hardening process and to obtain a suitable consistency for the composite material.
The disadvantages of this type of composite materials is that the base material not only consists of waste products from carbon and electrolysis processes but also uses raw materials such as petroleum coke, graphite and semi-graphite, each of which is an element which makes the production of the composite material more expensive.
2 1 ~ 4 EP application no. 269534 describes a coating of the latter type to achieve a composite material with a view to protecting the nipple against oxidation and corrosion. On the basis of the facts of the application, the assumed new features seem to be that 0.01 to 5 ~ antioxidant is added to the composite aggregate in the form of a passivated aluminium powder with particle size less than 0.1 mm and that the calcium aluminate cement should not contain more than 2 ~ contaminated elements.
One disadvantage is that the base material must be a powder, i.e.
particles between 1 and 1000 ~m, which results in a comprehensive and expensive crushing and screening process as well as in more calcium aluminate cement having to be added to enclose the powder particles so that an even, good bond is achieved in the composite. A further condition is that the base material is selected as sta~ed above for the second type of composite material. Together these disadvantages will make the final composite material considerably more expensive. As a catalyst is not added, the result is that the cement will find it difficult to enclos2 all the particles in the powder aggregate on account of the surface tension, which leads to the individual parts of the coating having a weaker bond than those enclosed by cement, and that the dilation forces between the nipple and the collar are different, which can lead to craks in the individual parts of the coating during operation in the electrolysis cell and thereby trigger an attack on the nipples.

The aim of the present invention i9 to improve protection of the anode hanger nipples against oxidation and corrosion during operation in an electrolysis cell beyond that which is known from the above solutions.
A further aim is to eliminate components which are hazardous to health, use waste products from existing processes to avoid waste storage and to produce a cheap product which effectively protects the nipples.
In accordance with the present invention, this has been achieved by means of a composite material as mentioned in the introduction and which is further characterised in that the particle size of ~
~ , ~ 211~0~ -the waste products from consumed anodes can be between 1 and 2000 ~m and make up at least 80 per cent dry weight of the composite material. Furthermore, the composite material consists of up to 15 per cent dry weight calcium aluminate cement and up to 28 per cent dry weight water and 0.6 per cent dry weight catalyst, as defined in claim 1. Moreover, the present invention includes removal of substances hazardous to health, such as PAH, as defined in claim 7.
Other particularly advantageous features of the present invention are defined in claims 2-6.
The present invention will now be described in further detail by means of an example and with reference to the enclosed drawing which shows a perspective sketch of an anode hanger 1 with three nipples which are lowered into three holes in a carbon anode 4, and where each nipple 2 has a collar 3 of compressed composite material added to protect the nipple against oxidation and corrosion. The nipples are fastened, in a manner not de~cribed in further detail, to the carbon with cast iron filled in an annulus between the carbon and nipple. During operation the positive current i9 conducted down through the anode hanger and the nipples, the carbon anode , the oxide/cryolite bath and the liquid aluminium bath to the carbon cathode under high resistance which gives off strong heat and results in a cell temperature of approximately 960 degrees Celsius. The high temperature causes the reaction between the oxide and the cryolite, plu9 other components so that liquid aluminium is produced. During the reaction phase, which takes place continuously, highly aggressive gases are given off which attack, I in particular, the anode hanger nipples and release iron into the bath and aluminium which greatly reduces the quality of the ,~ aluminium. The collar, made either as a prefabricate or stamped when mounted, protects the nipples very well during the whole operating period. This results in higher aluminium purity and higher prices.

As mentioned in the introduction, the composite material consists of a particle aggregate of waste products from anodes consumed ~l in an electrolysir cell, binding material in the ~orm o~ calcium 2~ ~ 90~4 :`

aluminate cement, a catalyst and water. The composite material is compressed and hardened at 60-90 degrees Celsius to a compressive strength of 1 MPa. The collar 3 is preferably prefabricated and mounted in the rodding department, i.e. the department where the carbon anode and the anode hanger are mounted together.

There are a number of different types of calcium aluminate cement on the market for use as a binder in composite material for the protection of anode nipples against oxidation and corrosion.
Undesired elements in the calcium aluminate cement, such as Fe2O3, SiO2, Na2O, Cr2O3 and K2O can vary considerably between various manufacturers but the total should not exceed 7 per cent dry weight in the present invention.

EXAMPL~ ;
60 carbon anode/anode hanger installations were produced for this experiment, of which ~iO had cardboard around the anode hanger nipples. No significant difference (at the 5 % significance level) could be discovered between the installations with and without cardboard. The following formula was used for the composite material:
.,.. ~":.
Waste products from consumed anodes 2 80 i~
Calcium aluminate cement ~ 15 % ;
Catalyst = 0.6 i~
Water approx. 28 ~

20 kg mixtures were produced. The solid matter was mixed well before the water was added. The required quantity of water to be added was measured out (28 %) and the catalyst was dissolved in water before the solid matter was added. The water and the solid matter were mixed well by means of a mortar beater. A mould formed an annulus around the nipple into which the composite material was poured and compressed manually with a hammer and ramming shoe. Subsequently, the collar was hardened at 60-90 degrees Celsius. The anode installations were mounted in 6 electrolysis cells. The collars and the anodes were observed 211~0~4 . .

thoroughly by measuring the gases, temperature and density during operation in the electrolysis cell. The quantity of composite material which was left on the nipples after use in the electrolysis cell covered the whole nipple and the ring coverage was considerably thicker than when traditional composite material i9 used. The iron content of the aluminium metal showed no tendency to change over a 60-day period.

" ' ': ' ~ ':
' ':;:: '

Claims (7)

1. A composite material for protecting one or more anode hanger nipples against oxidation and corrosion during operation in a Hall-Heroult electrolysis cell, consisting of a base material in the form of a particle aggregate of waste products from anodes consumed in aluminium electrolysis and calcium aluminate cement, a catalyst and water, c h a r a c t e r i s e d i n t h a t the particle size of the waste products are between 1 and 2000 µm and represents 80 or more per cent dry weight of the composite material which in addition consists of up to 15 per cent dry weight calcium aluminate cement, up to 28 per cent water of the dry weight of the waste products and cement and up to 0.6 per cent dry weight catalyst.
2. A composite material in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the cement consists of up to 70 per cent weight of alumina.
3. A composite material in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the particle aggregate consists of at least 1 per cent dry weight ash.
4. A composite material in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the composite material is either processed to form a prefabricated collar or is compressed around the anode nipple so that a collar is formed.
5. A composite material in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the collar is hardened at 60-90 degrees Celsius for 60 minutes to a compressive strength of 1 MPa.
6. A composite material in accordance with claim 1, c h a r a c t e r i s e d i n t h a t an inoxidisable, tight intermediate layer, for example of paper material, can
7 be inserted between the collar and the nipple to prevent the collar bursting in the event of a difference of dilation between the anode nipple and the collar.

7. A composite material in accordance with claim 1, c h a r a c t e r i s e d i n t h a t the waste products used in the particle aggregate have had substances hazardous to health, such as PAH components, removed by processing.
CA002119084A 1993-03-17 1994-03-15 Composite for oxidation and corrosion protection of anode nipples Abandoned CA2119084A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO930957A NO930957L (en) 1993-03-17 1993-03-17 Marterial composite for oxidation and corrosion protection of anode nipples
NO930957 1993-03-17

Publications (1)

Publication Number Publication Date
CA2119084A1 true CA2119084A1 (en) 1994-09-18

Family

ID=19895934

Family Applications (1)

Application Number Title Priority Date Filing Date
CA002119084A Abandoned CA2119084A1 (en) 1993-03-17 1994-03-15 Composite for oxidation and corrosion protection of anode nipples

Country Status (8)

Country Link
EP (1) EP0627505A1 (en)
CN (1) CN1092822A (en)
AU (1) AU5769494A (en)
BR (1) BR9401181A (en)
CA (1) CA2119084A1 (en)
NO (1) NO930957L (en)
NZ (1) NZ260060A (en)
ZA (1) ZA941615B (en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103896555B (en) * 2014-03-25 2015-12-09 湖南创元铝业有限公司 Anode steel claw protection ring production method
CN104005056A (en) * 2014-05-28 2014-08-27 沈阳化工大学 Method for preparing electrolytic aluminium carbon anode protective coating

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2606796B1 (en) * 1986-11-14 1989-02-03 Savoie Electrodes Refract PROTECTIVE COATING FOR PRE-COOKED ANODE ROUND
IN169360B (en) * 1987-12-22 1991-09-28 Savoie Electrodes Refract

Also Published As

Publication number Publication date
AU5769494A (en) 1994-09-22
CN1092822A (en) 1994-09-28
NO930957D0 (en) 1993-03-17
NO930957L (en) 1994-09-19
BR9401181A (en) 1994-10-18
ZA941615B (en) 1994-10-12
NZ260060A (en) 1994-12-22
EP0627505A1 (en) 1994-12-07

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Legal Events

Date Code Title Description
FZDE Discontinued