Aluminum manufacturing cells and cathode current collector assemblies for aluminum manufacturing cells

Abstract

The aluminum production cell comprises an elongated cathode current collector bar (7) in contact with the carbonaceous cathode (4), the copper or copper alloy cathode current collector bar (7) being coated on its surface facing the cathode or on its entire circumference with a thin steel protective layer of thickness 0.15 mm to 4 mm which effectively protects the current collector bar from diffusion of aluminum or other reaction products produced at the carbonaceous cathode during operation. The volume ratio of copper or copper alloy to the thin steel protective layer is for example in the range of 400% to 500%. The thin steel protective layer, optionally including a pre-applied thinner conductive non-ferrous undercoat or overcoat, is preferably in direct contact with the ready-to-use carbonaceous cathode without the need for rod machining in cast iron.

Description

[Technical Field]

[0001] This invention relates to aluminum manufacturing cells. and for aluminum manufacturing cells Cathode current collection Body assembly Regarding. [Background technology]

[0002] Aluminum is produced by the Hall-Héroult process, which involves electrolyzing alumina dissolved in a cryolite-based electrolyte at temperatures up to 1000°C. A typical Hall-Héroult cell consists of a steel shell, a refractory insulating lining, and a carbon cathode that holds the liquid metal. The cathode is composed of several cathode blocks, with current collectors embedded at its base to extract the current flowing through the cell.

[0003] Patent Document 1 describes the structure of a current collector rod used in a Hall-Héroult electroreduction cell for manufacturing aluminum. Each current collector rod includes a core made of a relatively highly electrically conductive material (copper or copper alloy) and an outer housing made of a material (usually steel) that is more chemically resistant than the core material. Preferably, the current collector rod is cylindrical, and the diameter of the core is 60-80%, preferably 70%, of the diameter of the current collector rod. This means that the diameter, and therefore the thickness, of the steel housing is at least 20% of the diameter of the copper or copper alloy core. In this example, a copper rod with a diameter of 70 mm is fitted into a steel pipe with an outer diameter of 100 mm and an inner diameter of 70 mm (i.e., the wall thickness of the steel pipe is 15 mm). This corresponds to a relative volume of 96% copper to steel and a relative volume of 104% steel to copper.

[0004] Each current collector rod includes a portion that is cast or bonded to the channel of the cathode block. This typically involves machining the end face of the rod in cast iron to fit with the cathode and its side when the cell is in use.

[0005] Patent Document 2 provides a composite conductor rod with a simpler structure than that of Patent Document 1, in which a large mass body (steel) with lower conductivity is bonded to and supported by a small mass body (copper) with higher conductivity that contacts the carbon cathode, and the relative cross-sectional area of ​​the two conductors of the composite current collector rod optimizes the current and heat flux through the composite. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2001 / 63014 [Patent Document 2] U.S. Patent Application Publication No. 2010 / 00258434 [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide a cathode current collector assembly for Hall-Héroy aluminum manufacturing cells, the assembly comprising an elongated current collector rod made of highly conductive copper or copper alloy, the surface facing the cathode or its entire circumference coated with a protective layer that is more mechanically and chemically resistant than copper or copper alloy, the assembly - It has the advantage of being ready to use immediately, as it does not necessarily require rod processing using cast iron, adhesive, or ramming paste for preparation, and is called a Ready-to-Use Cathode or RuC. - The aluminum and other products generated during the operation of the cell will not have harmful effects from diffusion into the copper or copper alloy underlying the current collector rods, and the aluminum and other products generated during the operation of the cell will not unnecessarily react with the copper or copper alloy underlying it, allowing for long-term operation. -When the cell reaches the end of its service life and is dismantled, the copper and copper alloys can be recovered immediately, so virtually the entire amount of copper and copper alloys that make up the assembly can be recovered. - The significantly reduced size allows for changes in cell design, resulting in longer cell lifespan and lower production costs. [Means for solving the problem]

[0008] The present invention relates to an aluminum manufacturing cell equipped with an elongated cathode current collector rod that contacts a carbonaceous cathode, wherein the elongated cathode current collector is made of highly conductive copper or a copper alloy, with the surface facing the cathode or its entire circumference coated with a thin-film steel protective layer that is more mechanically and chemically resistant than copper or a copper alloy.

[0009] According to the present invention, the thickness of the thin protective steel layer corresponds to the minimum thickness of a layer sufficient to form an effective diffusion barrier to protect the copper or copper alloy of the current collector rod from the diffusion of reaction products generated on the carbonaceous cathode during operation. - The volume ratio of copper or copper alloy to the thin-film steel protective layer is at least 200%, preferably at least 300%, more preferably at least 400%, for example, in the range of 300% to 950% or 400% to 500%, compared to a preferred volume ratio of 96% for the steel tube alone, or only 57% when considering the additional steel sleeve surrounding the copper tube at its ends, as shown in Figure 6 with respect to International Publication No. 2001 / 63014. -The thin-film steel protective layer has a thickness ranging from 0.15 mm to 4 mm. - The protective thin-film steel layer is in direct or indirect contact with the carbonaceous cathode, is self-supporting, and preferably does not require fixing with adhesive or cast iron, eliminating the need for wide slots or covering rods fixed with ramming paste, cast iron, or adhesive.

[0010] Preferably, a protective thin film steel layer, or optionally a thinner conductive nonferrous metal pre-coated on the protective steel layer. lower layer or upper layer However, it comes into direct contact with the walls of the carbonaceous cathode slot.

[0011] Alternatively, though less desirable, a protective thin film steel layer (optionally pre-coated with thinner conductive nonferrous metals) can be used. lower layer or upper layer It may also include) and contacts the carbonaceous cathode through a conductive layer of ramming paste, cast iron or adhesive.

[0012] The protective thin film steel layer can be made of standard steel or alloy steel. Standard steel is an alloy of iron and usually contains a few tenths of a percent of carbon to improve its strength compared to iron. Alloy steel is made of iron, carbon, and other elements such as vanadium, silicon, nickel, manganese, copper, chromium, etc. Preferably, the protective thin layer is made of low-carbon steel, chromium-based steel, nickel-based steel or chromium-nickel-based steel. Other examples include low-carbon manganese-based steel containing various impurities.

[0013] In a preferred embodiment, the thickness of the protective thin film steel layer is preferably from 1.5 mm to 3 mm. The volume ratio of the conductive copper or copper alloy to the protective thin film steel layer is higher than 200%, preferably higher than 300%, more preferably higher than 400%, and is in the range of, for example, 300% to 950% or 400% to 500%.

[0014] The cathode current collecting bar of the RuC cathode having a thin steel protective layer on a copper or copper alloy core or rod can be manufactured by a hot or cold extrusion process, a hot or cold rolling process, a hot or cold drawing process, a hot or cold hammering process, a winding and / or welding process and a shrink fitting process.

[0015] As an example of this manufacturing process, the cathode current collecting bar can have a cylindrical core of a copper or copper alloy rod, and the protective thin film steel layer can be a tube pressed against the copper or copper alloy rod so that the copper or copper alloy core is in complete contact with the protective layer, and when it operates, a uniform pressure of the cathode current collecting bar towards the carbon cathode can be achieved. [[ID=1*]]

[0016] Initially, there may be a gap between the copper or copper alloy and the protective thin film steel layer, and the gap is smaller than the thermal expansion of the copper or copper alloy to achieve the contact pressure between the copper or copper alloy and the protective thin film steel layer, and between the protective thin film steel layer and the carbon cathode.

[0017] In another embodiment, the copper or copper alloy is in the form of a rod with a rectangular or square cross-section, and one side facing the cathode is protected by a protective thin-film steel layer.

[0018] In some embodiments, the protective thin-film steel layer is coated with additional upper and / or lower layers of copper, nickel, and / or chromium, and / or graphite paint or foil layers, the additional upper and / or lower layers preferably having a thickness of 1 μm to 1 mm. The copper layer, nickel layer, and chromium layer may be applied by electrodeposition or other methods.

[0019] If the copper or copper alloy is in the shape of a rectangular bar, the protective thin-film steel layer covers all sides of the rectangular bar or one side of the rectangular bar, and at least partially covers the other two sides of the rectangular bar adjacent to the covered side.

[0020] In the cell according to the present invention, the outer end of the copper or copper alloy current collector rod is preferably as specified in International Publication No. 2016 / 079 6 As described in U.S. Patent No. 05 and U.S. Patent No. 11136682, it is connected to an external current bus by a heavy steel bar. Alternative connections to an external current bus are described in International Publication Nos. 2018 / 019888 and 2018 / 019910.

[0021] Furthermore, in the cell according to the present invention, the copper or copper alloy current collector rods having a thin protective steel layer are usually arranged horizontally, as in conventional cells. However, in a modified example, the current collector rods may include inclined portions, as described in International Publication No. 2018 / 019910, and features can be integrated such that the cell does not require rod processing in cast iron. [Brief explanation of the drawing]

[0022] [Figure 1] This is a schematic cross-sectional view of a Hall-Elouser equipped with a current collector rod according to the present invention. [Figure 2]This is a schematic vertical cross-sectional view passing through a cell cathode, showing a conventional carbon cathode on the left and a carbon cathode with a copper rod protected by a thin-film steel layer according to the present invention on the right. [Figure 3] This photograph shows yellow aluminum bronze after prolonged use without a thin steel layer that provides greater mechanical and chemical resistance. [Figure 4] This figure shows the relative conductivity of copper with diffused aluminum as a function of the aluminum concentration in the copper, relative to the conductivity of pure copper. [Figure 5] This is a schematic diagram of two cathodes, showing how saving the height of carbon above the current collector rod results in a longer cell lifespan. [Figure 6] This is a graph of the voltage of a cathode having a protective layer according to the present invention during a 20-month operating period. [Figure 7] This is a micrograph of a vertical cross-section of a copper rod with a 2 mm protective steel layer after 18 months of operation in Hall-Eroucel. [Figure 8] This graph shows the diffused aluminum concentration at the interface between the copper and the steel protective layer, calculated as a function of the cell operating time on a monthly basis and extrapolated to 100 months. [Modes for carrying out the invention]

[0023] Figure 1 schematically shows a Hall-Héro-aluminum production cell 1 comprising a carbon cathode cell bottom 4, a pool 2 of liquid cathode aluminum on the carbon cathode cell bottom 4, a fluoride-based cryolite-based molten electrolyte 3 containing dissolved alumina on the aluminum pool 2, and multiple anodes 5 suspended in the electrolyte 3. Also shown are the cell cover 6 and the outside of the cell container 8, and carbon CathodeThe cathode current collector rod 7 and anode suspension rod 9 according to the present invention, connected to the cell bottom 4, are also shown. As shown in the figure, the current collector rod 7 is divided into zones. Zone 10 is electrically insulated, and zone 11 is the central zone where the current collector rod 7 is located below the central part of the cell. The molten electrolyte 3 is housed in a crust 12 of frozen electrolyte. A heavy-mass steel rod 18 electrically connected in series to the end of the current collector rod 7 protrudes outside the cell 1 to connect to an external current supply source. As shown in Figure 1, the heavy-mass steel rod 18 carbon Cathode cell bottom Although it is located on the outside of 4, instead, the inner end of the massive steel rod 18 is carbon Cathode cell bottom It's also possible that it penetrates the inside of 4 by a very small distance.

[0024] As shown in the figure, the current collector rod 7 can be divided in the middle so as to leave a gap 7' mainly to compensate for thermal expansion, but such a gap is not essential.

[0025] Zone 10 of the current collector rod is insulated, for example, by wrapping it with an alumina sheet or covering it with an electrically insulating ceramic material.

[0026] The current collector rod 7 is made of a copper or copper alloy core or rod, which for ease of manufacture may have a thin protective steel layer applied along its entire length. However, this thin protective steel layer is not essential in the insulating zone 10, but is essential in the central zone 11, which comes into contact with the carbon cathode to transmit current and protects the copper or copper alloy.

[0027] Figure 2 is a schematic vertical cross-sectional view through the cell cathode. On the left is a conventional carbon cathode 21 using a steel rod 25 machined from cast iron 24. On the right is a carbon cathode 22 in which a copper rod 26 protected by a thin protective steel layer 27 according to the present invention is fitted, and is called a RuC cathode, meaning "ready-to-use cathode". As shown in the figure, the copper rod 26 has a rectangular cross-section, and its side with the thin protective steel layer 27 fits directly into the opposing wall of the rectangular groove of the carbon cathode 22 without the interposition of cast iron.

[0028] RuC cathodes differ in many ways from conventional carbon cathodes because they use a thin protective steel layer on the copper rod.

[0029] a) The importance of the protective layer was demonstrated by testing copper cores with direct contact between copper and carbon without a protective layer. Due to the open-pore structure of the carbon cathodes 21, 22, the liquid bath layer 23 present beneath the liquid metal in the cell diffuses to the carbon current collector rod interface. In the case of conventional cathodes, the interface is cast iron 24, and the heavy-mass conductor rod 25 is made of steel. In the case of RuC cathodes, the interface is a thin protective steel layer 27. At the interface, liquid aluminum is produced by numerous chemical reactions involving liquid Na3AlF6, AlF3, NaF, MgF2, and other species (Reference: Aluminum Smelter Technology, K. Grjotheim and B. Welch ISBN 3-37017-162-6, Aluminum Verlag pp119-124). One known chemical reaction is: 3Na (gas) + AlF3 (solid) -> Al (liquid) + 3NaF (solid).

[0030] Without a thin protective steel layer, the liquid aluminum formed on the surface of the copper rod diffuses into the copper, forming a solid aluminum bronze alloy. Figure 3 is a photograph showing yellow aluminum bronze observed on a copper rod without a protective layer 450 days after the start of cell inspection. Yellow aluminum bronze 28 and pure copper 29 are shown in 70 × 25 mm cross-sectional samples.

[0031] b) As can be observed in Table 01 for copper rods without a protective layer, the diffusion depth after 450 days is important, ranging from 5 mm to 15 mm and even deeper. The content of other metallic elements is also important. Table 01 shows the Al and Si content as a function of the distance to the copper rod surface after 450 days of operation for 10 samples taken around the copper rod.

[0032] [Table 1]

[0033] c) Figure 4 shows the relative conductivity to the conductivity of pure copper as a function of the percentage of other metals, particularly diffused aluminum, due to diffusion. The abbreviation "%IACS" in Figure 4 represents the electrical conductivity of copper with alloy aluminum concentration relative to the International Annealed Copper Standard, which has an electrical conductivity of 100%. The electrical conductivity of copper decreases significantly with increasing concentration of metallic elements, especially aluminum. This is clearly undesirable, as one of the important roles of a copper rod is to reduce the electrical resistance of the cathode.

[0034] d) An advantage of using RuC cathodes compared to conventional carbon cathode solutions 31 is that the height of carbon 34 on the rod 30 can be saved, which by technology leads to an extension of cell life from one year to several years. This height ranges from 5 mm to 150 mm. This is shown in Figure 5. Similar to Figure 2, the copper rod has a rectangular cross-section, and its sides, which have a thin protective steel layer, are fitted in direct contact with the opposing walls of the rectangular groove of the carbon cathode 36 without the interposition of cast iron. When the copper rod is received into the open-end slot of the cathode block 36, as opposed to a round or closed hole as shown, the open end of the copper rod can be protected by a carbonaceous material, concrete, or refractory material 35.

[0035] e) In conventional carbon cathodes 33, if the thickness 32 of the side wings is too small, cracks 31 may occur in the wings. The solution using copper rods, with their smaller dimensions and precise machining, can prevent cracking of the wings. In fact, the steel and cast iron of large-mass steel cathodes have greater thermal expansion than carbon blocks, which leads to mechanical stress and can cause cracks in the carbon cathode. Although copper expands more than carbon cathodes, in the case of RuC cathodes 36, the smaller dimensions of the copper rods allow for wide carbon wings 32' that are not affected by mechanical stress. Furthermore, precise machining of the grooves in the carbon cathodes 36 achieves a precise contact pressure of 2 MPa to 12 MPa at the interface, resulting in low contact electrical resistance. Such pressures reduce electrical contact resistance to 1 / 2 to 1 / 10 compared to conventional carbon cathodes, preventing crack formation. The conventional rod processing method used for cathode 33 involves preheating the cathode, casting cast iron at around 1500°C, allowing it to solidify and shrink at room temperature, and then reheating it in a cell at an operating temperature of around 900°C. This rod processing method does not yield good and accurate electrical contact.

[0036] f) The thin-film steel barrier prevents the diffusion of metal in the copper, thereby avoiding an increase in the rod's volume, which can alter local stress and ultimately lead to cracking of the wing, even in copper rods, and / or avoids eutectic alloys that lower the melting temperature.

[0037] g) When using conventional carbon cathodes, there is also a technique of using a copper insert inside the steel rod, in accordance with International Publication No. 2001 / 063014. However, removing or separating the copper core or insert from the distorted steel current collector rod at the end of its life cycle is costly and makes copper recovery uneconomical. The main reasons for this are that Cu diffuses and welds to the steel, Fe diffuses and welds to the Cu, and the weight ratio of the distorted steel to the copper is too high, making it impossible to recycle as is. The thin thickness of the protective thin film steel layer on the copper rod of the RuC cathode of the present invention is advantageous both during cell operation and at the end of the cell's life cycle. In the RuC cathode, the volume ratio between the protective thin film steel layer and the copper core is small, and in particular, this corresponds to a high weight ratio between the copper core and the protective layer, for example, from 10,000% for a 0.15 mm layer to 600% for a 2.5 mm thick layer. This allows for the complete recovery of the current collector rods from the spent cathode block when the cell lifespan ends, eliminating the need to separate the protective layer from the copper core beforehand, and allowing the current collector rods to be directly introduced into copper recycling. In the copper recycling industry, spent current collector rods can be directly fed into copper refining processes, yielding 99% copper through high-temperature metallurgy, converters, and anode furnaces. Further electrochemical refining of the 99% copper achieves a copper purity of 99.99%. Because copper can be effectively recovered from spent current collector rods, the total cost of ownership can be reduced. Furthermore, the initial amount of copper contained in the RuC cathode remains in the cell production loop over the long term because the value of the recycled copper, slightly reduced by the loss of copper recycled metal, is reused at the end of each cell's lifecycle.

[0038] (Pre-configured for use due to thermal coupling, compared to a large-mass steel cathode current collector rod) The current collector rods for RuC cathodes can be assembled by thermal fitting. Thermal fitting means simply inserting the current collector rod into a precisely machined cavity in a carbon block, without using intermediate retainers as used in all conventional rod manufacturing processes, and with sufficient interference to hold the rod in place. The different thermal expansion behaviors of the current collector rod and the carbon cathode block allow for electrical contact as the temperature rises from room temperature to operating temperature during cell startup. As described, using copper rods surrounded by a thin protective steel layer advantageously avoids conventional rod manufacturing, adhesives, and ramming pastes. The current collector rod is simply inserted into a precisely machined graphite slot with sufficient interference to hold it in place, without the intermediate retainers used in conventional rod manufacturing processes. The thin protective steel layer enables thermal fitting, making the cathode usable without further processes or materials.

[0039] Conventional technology requires the cathode current collector rod to be machined from cast iron during cell starting. Cast iron machining is time-consuming and poses safety and technical risks to the performance and integrity of the carbon cathode block. Furthermore, when using cast iron, the cast iron shrinks during rod machining, increasing the contact area between the rod and the carbon block. In addition, casting cast iron requires a large gap between the current collector rod and the cathode. All of these drawbacks are advantageously avoided with RuC cathodes, although they can be implemented, albeit less favorably, by contacting the carbonaceous cathode via a conductive layer of ramming paste, cast iron, or adhesive.

[0040] The specific conductivity of copper is far higher than that of steel, cast iron, carbon paste, graphite paste, and carbonaceous adhesives used inside cathode blocks.

[0041] At an operating temperature of 1000°C, the ratio of the specific electrical conductivity of copper to steel is 8 to 15. For example, copper has 10 times the conductivity of steel. To obtain the same or equivalent electrical resistance as a steel rod with a copper rod of the same length, the cross-sectional area and volume of the copper rod must be reduced by 10 times.

[0042] For example, a typical cross-section of a conventional steel rod used inside a cathode is 122 x 122 mm. 2(14,884mm 2 ). To replace this with a Cu rod (conductivity 10) and obtain the same electrical resistance with the same rod length, the cross-sectional area must be 1,488 mm². 2 A copper rod of this size would suffice, which would be a copper rod with a height of 70 mm and a thickness of 21.3 mm. The height of the copper rod is only 57% of that of the steel rod, and the width of the copper rod is only 17% of that of the steel rod.

[0043] While the thermal expansion of a copper rod from room temperature to 1000°C is 0.3-0.4 mm, a 122 mm wide steel rod expands to 1.4-1.5 mm, or 4-5 times. This expansion of more than 1 mm in the steel rod places significant stress on the slot radius, leading to cracking of the wing. To prevent this with steel rods, an initial void must be created at room temperature. The overlapping thermal expansion of the steel rod at operating temperature should normally be around 0.1-0.3 mm. In the case of copper rods, this range is achieved by allowing thermal expansion without an initial void or by tight mechanical fitting of the slots (i.e., measuring an initial void on the order of a few micrometers). Tight mechanical fitting is sufficient and is advantageous in ensuring high contact pressure at operating temperature while simultaneously avoiding excessive stress on the cathode material wing. Reducing the wing height also contributes to reducing stress on the cathode material.

[0044] Measurements of the CVD (cathode voltage drop) and cathode resistance of RuC cathodes have demonstrated and confirmed that, even with a contact area 30-50% smaller than that of steel rods, the contact resistance and contact voltage are lower.

[0045] In the RuC cathode of this invention, the problem of thermal expansion difference is minimized by providing a very thin steel protective layer on the copper / copper alloy. Problems with initial voids and poor electrical contact are suppressed, and contact pressure is always guaranteed.

[0046] (The melting point of copper decreases as alloying with elements such as aluminum and silicon progresses.) The thin-film steel barrier of the present invention prevents Cu from alloying with elements such as Al and Si during operation in an electrolytic cell. This prevents melting that could occur without protection. The electrical conductivity and the melting point of Cu (1083°C) decrease due to alloying, as shown in the phase diagram.

[0047] (Reducing thick film protection to a single thin film layer) In conventional Cu rod designs, Cu is protected only by cast iron, but in most cases, Cu components are protected by two thick film layers. The first layer is cast iron derived from the cast iron rod machining, with a typical thickness of 10-30 mm. The second layer is a thick steel layer surrounding the Cu insert, and its thickness varies depending on the shape and design, usually ranging from 10-200 mm. The total thickness of the two layers is 20-200 mm.

[0048] In the novel RuC solution, the barrier is reduced to a single thin-film steel layer (preferably without cast iron), which is sufficient for protection over the cell's lifespan. In the case of RuC, the thickness of the thin-film steel layer is reduced to 1 / 5 to 1 / 20 of that in conventional designs.

[0049] (Example 1) Dimensions: 400 x 450 x 3300 mm 3 A rectangular slot measuring 27 mm in width and 105 mm in depth was machined into a conventional carbonaceous cathode raw material block using a conventional end mill that moves through the bottom surface of the raw material block. Dimensions: 27 × 85 × 1670 mm 3 Two steel-coated copper cathode current collectors, as shown below, with dimensions (width x height x length), were symmetrically inserted into the pre-formed slots of each block, leaving a 150 mm gap in the center of the block, which was then filled with conventional refractory material. If necessary due to slight deformation of the current collectors, a mechanical or hydraulic press was used to push the current collectors into the slots. Different types of coated steel were produced by cold-rolling rectangular copper rods, with coating thicknesses of 1.0 mm, 1.7 mm, 2.0 mm, and 2.5 mm, and the corresponding copper rod cross-sections (width x height) were 25.0 x 83.0 mm. 2 23.6 x 81.6 mm 2 23.0 x 81.0 mm 2, 22.0×80.0 mm 2 , The volume ratios of copper to steel are approximately 9.4, 5.2, 4.5, and 3.3. The outer ends of the current collector bars are then connected via large cross-section steel blocks and connected to the current source of the electrolytic cell.

[0050] (Example 2) The same copper cathode current collector bars as in Example 1 were each coated with a 2 mm thick layer of low-carbon steel. The cross-section of the cathode current collector bar including the 2 mm thick layer of low-carbon steel applied by cold rolling was 30×75×1670 mm 3 (width × height × length). The current collector bar is composed of a copper core with a rectangular cross-section of 26×71 mm 2 (width × height). The steel layer has a radius of 3.4 mm on the outside of the four corners along the length of the rectangle. At the ends of the cathode current collector bar, a 30×75 mm steel plate with a thickness of 3 mm is attached for connection to an external current supply source. The width tolerance of the cathode current collector bar was ±30 μm over the entire length. 2 (width × height). A rectangular slot with a width of 30.07 mm (±30 μm over the entire length), a radius of 4.0 mm, and a depth of 105 mm was machined in a conventional carbonaceous cathode raw material block with dimensions of 400×450×3300 mm

[0051] <00-slot using a conventional end mill that moves through the bottom surface of the raw material block. An initial nominal gap of 0.07 mm was provided between the cathode current collector bar and the machined slot. Two cathode current collector bars according to the present invention with dimensions of 30×75×1670 mm 3 (width × height × length) were symmetrically inserted into the formed slot, leaving a 150 mm gap in the central part of the block, and filled with a conventional refractory. If necessary due to slight deformation of the current collector bar, the current collector bar was pushed into the slot using a mechanical or hydraulic press. 3 (width × height × length) were symmetrically inserted into the formed slot, leaving a 150 mm gap in the central part of the block, and filled with a conventional refractory. If necessary due to slight deformation of the current collector bar, the current collector bar was pushed into the slot using a mechanical or hydraulic press. (width × height × length) were symmetrically inserted into the formed slot, leaving a 150 mm gap in the central part of the block, and filled with a conventional refractory. If necessary due to slight deformation of the current collector bar, the current collector bar was pushed into the slot using a mechanical or hydraulic press.

[0052] The outer ends of the current collector bars are then connected via large cross-section steel blocks and connected to the current source of the electrolytic cell.

[0053] (Example 3) A rectangular slot measuring 27mm in width and 105mm in depth, with dimensions of 400 x 450 x 3300mm. 3 A conventional carbonaceous cathode raw material block was processed using a conventional end mill that moves through the bottom surface of the raw material block. Dimensions: 27 x 85 x 1670 mm 3 Two steel-clad cathode current collectors according to the present invention, with dimensions (width x height x length) as shown below, were symmetrically inserted into a pre-formed slot, leaving a 150 mm gap in the center of the block, which was then filled with conventional refractory material. Where necessary due to slight deformation of the current collectors, a mechanical or hydraulic press was used to push the current collectors into the slot. The current collectors measured 21.4 x 79.4 mm. 2 It consists of a copper core with a rectangular cross-section of (width x height), surrounded by a double layer of graphite foil, each 0.1 mm thick. This intermediate layer is then covered with a 1.7 mm thick layer of low-carbon steel by cold rolling. Finally, the steel layer is coated with layers of nickel (0.4 mm thick) and chromium (0.4 mm thick), and then another layer of graphite foil (0.1 mm thick) is added to obtain the aforementioned overall dimensions. The outer end of the current collector rod is then connected via a large cross-section steel block and connected to the current source of the electrolytic cell.

[0054] (test) The cathode blocks and cathode current collectors of Examples 1 and 2 were mated into aluminum manufacturing cells without rod processing using cast iron, adhesive, or ramming paste, and subjected to long-term testing for at least 20 months. The cells were started with electrical preheating using a full current load of 11.0 kA per cathode (without shunt). The average cathode current density was 0.83 A / cm². During operation, the cells were operated with an average current of 5.5 kA per copper rod on both sides of the cathode. The operating bath temperature ranged from 955°C to 975°C. To test the robustness of the copper rods at higher temperatures, the cells were heated to 1100°C for 10 hours. No effects of high temperature were observed during inspection. The cathodes were graphitized, and the thermal conductivity at 1000°C was close to 100 W / mK. The voltage between the liquid metal and the ends of the current collector rods was measured periodically along with the current. As shown in Figure 6, the electrical resistance remained almost constant for 20 months, close to 40 μΩ.

[0055] Figure 7 is a micrograph of a fracture perpendicular section of a copper rod 40 having a 2.5 mm protective steel layer 41 (Example 1), showing the intermetallic alloy aluminum 42 formed in the protective layer on the carbon cathode side 44 after 18 months of operation in Hall-Eloucester. The 100% pure copper 40 is protected, and no aluminum enrichment is observed after 18 months. The aluminum layer 42 varies depending on the grade of the carbon cathode. In this example, it is 400 microns thick. On the copper core side, a 50 micron layer 45 contains copper diffused into the protective layer. The protective thin film steel layer 41 shows a network of carbides 46.

[0056] Figure 8 shows a graph of the calculated diffused aluminum concentration at the interface between the copper and the thin-film steel protective layer on the copper side for a cell according to the present invention (Example 2), in which a 2 mm thick steel layer is coated on a copper core. This concentration is extrapolated to 100 months as a function of the cell's monthly operating time. As can be seen from this curve, the diffusion of aluminum is significantly reduced, and the diffused aluminum concentration ultimately remains below 1.2% over the entire extrapolated lifespan of the cell.

[0057] (Transformed form) The conditions of the above embodiment can be modified as follows without compromising performance with respect to the cell's operating voltage, lifespan, and protection of the copper layer from unwanted alloying by aluminum.

[0058] Copper current collectors can also have square or circular cross-sections, rather than just rectangular ones.

[0059] The thickness of the steel layer can be varied from 0.15 mm to 4 mm. A thickness of less than 0.15 mm provides insufficient protection. A thickness greater than 4 mm increases the operating potential, leading to problems with copper recovery at the end of the cell's lifespan. Within these two extreme ranges, a steel layer thickness of 1.5 to 3 mm is preferable.

[0060] If an intermediate, underlayer, or top layer of graphite and / or nickel and / or chromium and / or copper is applied, its thickness is preferably 1 μm to 1 mm and should generally be less than the thickness of the steel layer.

[0061] The gap between opposing ends of the current collector rods can be varied as a function of the length of the copper current collector rod, taking into account thermal expansion at the cell operating temperature. [Explanation of symbols]

[0062] 1. Aluminum manufacturing cell 2 Aluminum pools 3 Electrolytes 4 Carbon cathode cell 5 Anodes 6 Cell Cover 7 Cathode current collector rod 8-cell container 9 Anode suspension rods 12 Crust 18 steel rod 24 Cast Iron 25 steel rod 26 copper rod 27 Thin protective layer 28 Yellow aluminum bronze 30 bars 31 Carbon cathode solution 32 Side Wing 33 Carbon cathode 36 Cathode Blocks

Claims

1. An aluminum manufacturing cell comprising an elongated cathode current collector rod in contact with a carbonaceous cathode, wherein the cathode current collector rod is made of highly conductive copper or a copper alloy, and the surface facing the carbonaceous cathode or the entire circumference of the surface is coated with a thin protective steel layer that has higher mechanical and chemical resistance than copper or a copper alloy. The thin protective steel layer is thin, and its thickness corresponds to the minimum thickness of a layer sufficient to form an effective diffusion barrier to protect the copper or copper alloy from the diffusion of reaction products generated on the carbonaceous cathode during operation. The volume ratio of the copper or copper alloy to the thin film protective steel layer is at least 200%. The thin protective steel layer has a thickness of 0.15 mm to 4 mm. The thin protective steel layer is in direct or indirect contact with the carbonaceous cathode. An aluminum manufacturing cell characterized by the following features.

2. The aluminum manufacturing cell according to claim 1, wherein the thin protective steel layer is made of carbon steel or alloy steel.

3. The aluminum manufacturing cell according to claim 2, wherein the thin protective steel layer is made of low-carbon steel, chromium-based steel, nickel-based steel, or chromium-nickel-based steel.

4. The aluminum manufacturing cell according to any one of claims 1 to 3, wherein the thickness of the thin protective steel layer is 1.5 mm to 3 mm.

5. The aluminum manufacturing cell according to any one of claims 1 to 4, wherein the cathode current collector rod has a cylindrical core made of copper or a copper alloy, and the thin film protective steel layer is a tube pressed against the copper or copper alloy core such that the copper or copper alloy core is in complete contact with the thin film protective steel layer, and when operated, it achieves a homogeneous pressure of the cathode current collector rod toward the carbonaceous cathode.

6. An aluminum manufacturing cell according to any one of claims 1 to 5, wherein there is an initial period gap between the copper or copper alloy and the thin film protective steel layer, and this initial period gap is smaller than the thermal expansion of the copper or copper alloy core.

7. The aluminum manufacturing cell according to any one of claims 1 to 4, wherein the copper or copper alloy is in the shape of a rectangular cross-section rod, with one side facing the carbonaceous cathode protected by the thin protective steel layer.

8. The carbonaceous cathode comprises a slot, a) The thin protective steel layer is in direct contact with the wall of the slot of the carbonaceous cathode. Or, b) The aluminum manufacturing cell according to any one of claims 1 to 7, wherein the thin film protective steel layer comprises a conductive non-ferrous upper and / or lower layer that is thinner than the thin film protective steel layer, and the conductive non-ferrous upper and / or lower layer is in direct contact with the wall of the slot of the carbonaceous cathode.

9. The thin film protective steel layer comprises the conductive nonferrous upper layer and / or lower layer, The aluminum manufacturing cell according to claim 8, wherein the conductive non-ferrous upper and / or lower layers are coated with copper, nickel and / or chromium and / or graphite paint or foil layers.

10. The aluminum manufacturing cell according to claim 9, wherein the conductive non-ferrous upper layer and / or lower layer has a thickness of 1 μm to 1 mm.

11. The aluminum manufacturing cell according to any one of claims 1 to 7, wherein the thin film protective steel layer, which includes a pre-coated thinner conductive non-ferrous underlayer or upper layer, is in contact with the carbonaceous cathode via a conductive layer of ramming paste, cast iron, or adhesive.

12. The aluminum manufacturing cell according to claim 1, 2, 3, or 4, wherein the copper or copper alloy is in the shape of a rectangular rod, and the thin protective steel layer covers all sides of the rectangular rod or one side of the rectangular rod, and at least partially covers along two other sides of the rectangular rod adjacent to the covered side.

13. A cathode current collector assembly for an aluminum manufacturing cell, comprising an elongated cathode current collector rod in contact with a carbonaceous cathode, wherein the cathode current collector rod is made of highly conductive copper or a copper alloy, and the surface facing the carbonaceous cathode or the entire circumference of the surface is coated with a thin protective steel layer that has higher mechanical and chemical resistance than copper or a copper alloy. The thin protective steel layer is thin, and its thickness corresponds to the minimum thickness of a layer sufficient to form an effective diffusion barrier to protect the copper or copper alloy from the diffusion of reaction products generated on the carbonaceous cathode during operation. The volume ratio of the copper or copper alloy to the thin film protective steel layer is at least 200%. The thin protective steel layer has a thickness of 0.15 mm to 4 mm. The thin protective steel layer is in direct or indirect contact with the carbonaceous cathode. A cathode current collector assembly for aluminum manufacturing cells, characterized by the following features.

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