JPS59500974A - Cathode element of aluminum reduction electrolyzer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Refractory hard metal (RHM ) is a hard, dense material with a high melting point, and is generally used for many reagent solutions. and low solubility in molten cryolite and most acids and alkalis. It has corrosion resistance.

Refractory hard metals have the characteristics of high electrical conductivity due to their metal structure and the above-mentioned properties. Due to the characteristics of molten salt electrolytic processing, corrosion resistance and electrical conductivity are important issues from an economic point of view. It has been considered to be used as an electrode in

Refractory hard metals have properties that have limited their use. This material is They are usually brittle, have poor thermal shock resistance, and are extremely difficult to manufacture or form into useful products. It costs a lot of money.

Products include hot pressing of granular or powdered materials, chemical Numerous methods including vapor deposition and in-situ reduction of metals with carbon and other reducing agents has been manufactured by. Thermal compression is the most widely used method for producing molded parts. This is one way to This involves filling the mold cavity apparatus with powder, approximately 30 to 8 Heat it to 00℃, apply a pressure of about 2X10Pa, take it out from the mold, and heat it to about 1500℃. This process is performed by heating or sintering in a mold at a temperature of 2,000°C or higher.

Thermal compression is only applicable to simple shapes and may cause mold erosion. productivity is low. Products made by thermal compression can be damaged during handling. This method is expensive in terms of the yield of useful products.

Refractory hard metals include metals from groups ■A, iVB, VB and ■B of the periodic table, especially T There are carbides, ferrides and nitrides of i, VISi and W. Of these, crawling Compounds are of particular interest as electrodes for high-temperature electrolysis because of their electrical conductivity. There is. Among the ferrides, TlB2 is a Hall-He electrolytic cell. Regarding use as a cathode or cathode element for It has been extensively researched.

Hall electrolyzers generally have a shallow bottom, with the floor serving as the cathode and the side walls containing coke and pitch. The anode is formed by pouring the mixture, and the anode is suspended in a molten bath of alumina and cryolite. The cathode is separated from the block by a distance of several centimeters. anode Usually, a mixture of pitch and calcined petroleum coke is pre-calcined to form a monolith of amorphous carbon. Formed as a molded block. The cathode is generally made of prefired pitch or calcined A steel bar made of anthracite or a mixture with coke and placed in a groove at the bottom of the cathode. Iron is cast on site around the electric body.

In operating a Hall electrolyzer, the actual reduction of alumina to aluminum is , only 25 parts of the power consumption is used, and about 40 parts of the current is used. It is consumed by the voltage drop caused by the resistance of the bath. Distance between anode and cathode is usually about 4 to 5α, but if you try to reduce this distance, the floating A discharge occurs from the cathode to the anode via the aluminum droplets.

Aluminum is present in the electrolyzer as a liquid bad, covering the cathode, but the molten aluminum The surface of the carbon cathode is preferentially affected by molten cryolite rather than by minium. Aluminum is not in a static state as it is wetted by water, thus the aluminum forms droplets, Strong electromagnetic force generated by high current density causes irregular movement of molten aluminum Become.

Wetting of a solid surface in contact with two immiscible liquids is achieved by the interfacial free surface of the three interfaces. It can be interpreted as a function of energy, but in this case, the surface of the carbon cathode Due to its low energy, it is not easily wetted by liquid aluminum. Cryolite-a The angle of the aluminum droplet at the aluminum-carbon contact point is In the above formula, α12. α13 and Φ3 are respectively The interface properties of the aluminum-carbon, cryolite-carbon, and cryolite-aluminum interfaces represents energy due to

the surface of the cathode, for example when ceramic is used instead of carbon. When the energy of is high, the contact angle with liquid aluminum is larger, Good wettability to liquid aluminum. This allows liquid aluminum The surface of the bath is smooth and there is less chance of electrical discharge occurring between the electrodes. The distance between the pole and cathode can be reduced, and this also reduces the voltage drop across the bath. It is possible to improve the thermodynamic efficiency of the electrolytic cell by making it smaller. Amorphous carbon generally has small surface rays and lugs, but is extremely durable and can be used for cathodes. However, it is possible to use 1-RO 1 joint for several years, and it is relatively inexpensive. However, it has good moisture resistance and can further reduce the distance between the anode and cathode. The cathode or cathode element, such as the Tjlh stud, has good thermodynamic efficiency and , very cost effective.

In this technical field, we are currently developing cathodes made of refractory materials with high energy. has been done. Granted to Foster on October 27, 1981. U.S. Patent No. 4,297,180 discloses that Ti ・Using a columnar element as a cathode by immersing it in an electrolytic bath 1-1 Electrolysis of metal acids A molten salt electrolyzer is described. ] Kabra filed on May 29, 979 No. 43,242 (later patent) of Kapla, n. describes a Hall electrolytic cell whose bottom is made of TiB2. July 1981 U.S. patent application filed on the 27th by Elnie Jo (L, A, Joo), etc. No. 287,125 describes a sintered body of a refractory hard metal. .

U.S. Patent No. 4.308, issued to Das on December 29, 1981. ．． No. 114 Meishoki describes the operation of a Hall electrolytic cell with a TiB2 cathode. It is. Granted to Foster on December 29, 1981. U.S. Pat. No. 4,308,115 discloses that graphite is coated with Ti1h. The cathode of the Hall electrolyzer is described. Sui announced on December 2, 1981 Yaw opening and horns of 5w1ss Aluminum Patent application No. 81810185.9 describes a TiB2 cathode element for Hall electrolytic cell. child is listed.

Summary of the invention It has been proposed to use titanium dihydride TiB2 as a cathode element in Neel electrolysers. However, this is different from the currently used amorphous carbon and semi-graphite. aphite) shows superior performance than the cathode.

Titanium dihydride (TiB2) can be used with or in place of carbon or semigraphite. However, when used in a Hall electrolytic cell, it can be used as a cathode element in the electrolytic production of aluminum. It has long been known to be useful. Mainly, keep the distance between the anode and cathode the same. By making the layer smaller, the conductivity becomes even better, so the electrolytic cell's current Energy efficiency is improved. When the distance between the anode and cathode (A-C) is reduced, the electrical Savings can be expressed as a figure as follows.

Distance between A-0 Saving rate (@ 38tM drift quasi 1.9cm 20% 1.3z 27th lead 10α 30% The main obstacle when using Ti1h as a cathode in a ball electrolyzer is the thermal shock sensation. The cost of conventional carbonaceous compositions is approximately $13/9 (approximately 0.6 It costs about $55/y (about $25/bond) compared to $0/pound). One example is the high strike rate.

The present inventor has developed a Hall Elu aluminum alloy, which is made of a fire-resistant hard metal and has a substantially mushroom shape. We have completed a new and cost-effective cathode element for umium reduction electrolyzers. This new The shaped cathode element is made by sintering uncompacted refractory hard metal powder without applying pressure. method of forming a plastic mixture of refractory hard metal powder and binder, refractory A hard metal is preformed by applying pressure evenly or in the axial direction, and this preform is Methods of sintering and precursors to form refractory hard metals, e.g. TiO2+B 2O3 and carbon, or TlO2+ temperature above 1200℃ like B4C and C A substance that reacts to form TlB2 is reacted in a mold to create a refractory hard material molded body. It can be manufactured by any of a number of methods, including in-situ methods. can.

An integrally molded element formed in such a shape has a large area where the cathode faces the anode, and The current density of the entire tank can be reduced. This integrally molded element is part of the pamphlet. The baffling effect improves the agitation of the aluminum bath. Maintain a controlled state regardless of the purpose. In addition, this molded element is made of expensive TiB2. Material costs can be kept to a minimum.

Furthermore, a desired void space and a desired molten aluminum accumulation area can be obtained.

This device also reduces the voltage drop during electrolysis and improves current efficiency. can be reduced. Furthermore, the element with is comparable to a solid cylinder of the same height and diameter. In comparison, the heat resistance and bonding properties are better.

Detailed description of the invention When sintering the device in a loosely filled mold, TiB2 powder with the following properties is available. It is for use.

Ti 69.06% B 31.24 Section C2270ppm (1 part per million) 02 3490 ppm N2 150 ppm At0.1% Average particle size 7μ Particle size of 5-15μ 90% Maximum particle size 44μ Refractory hard metal powder, refractory hard metal powder and calcined petroleum coke, charging coke mixtures with carbonaceous particulate materials such as graphite powder and charcoal powder. Can be sintered at 1700-3000°C in an inert atmosphere such as Rougon. can. The most useful refractory hard metals are Ti + Ta and Zr borides. , metals belonging to Groups 1VA, IVB, VB and ■B of the periodic table, especially T 1. Carbides of V+Sr and W can also be used as hydrides and nitrides. .

Elements of the invention also incorporate refractory hardeners in carbon-forming binders such as coal tar pitch. A plastic mixture made by dispersing quality metals or pressurized to form a preform and then sintered. This is where refractory hard metals are formed or formed from refractory hard metal forming reactions on site. Can be done.

The molded device is then baked for 1 to 10 days at a temperature cycle of 700 to 1200°C. to be accomplished. Petroleum pitch that gives a softening point of about 110 to 120°C to the fired compact Impregnating the resin with carbonaceous liquids such as phenol-formaldehyde or It is advantageous to Place the molded body in an autoclave, remove the air, and create a vacuum. Next, high-temperature pitch or other impregnating agent melted at about 150 to 300°C is added, and pressure is applied. Increase the force by 15 x 103 Pa (200 psi). This results in The liquid impregnant penetrates all the voids that it can access. removed from autoclave After that, the resin is cured or the pitch-impregnated molded body is fired again to remove residual carbon. Converts into amorphous carbon. Next, this was heated to 2000 to 300 ml in an inert atmosphere. Heat to 0°C to convert the amorphous carbon matrix to graphite or refractory hard metals. The formation reaction may be accelerated and the particles of the metal may be sintered. In the graphitized molded body, Reimpregnation treatment, recalcination treatment, and regraphitization treatment can be performed.

FIG. 1 shows the basic shape of the cathode element, with the cathode element 10 facing the anode. a fairly flat top surface or flat upper use surface 12, and a cross-sectional area smaller than this use surface. is equipped with a small support stem 14. The support stem is usually embedded in the cathode base 12. The cathode base 12 is made of calcined graphite carbon, amorphous carbon, or SiC. Or graphitic carbon coated with a melt-resistant, refractory hard metal such as SisNa? You can make it from scratch. Mushroom-shaped compacts are usually round, with a circular cross section. However, it can be shaped into other shapes such as square or rectangular to reduce space and electrolytic current. It may be used efficiently. The connection part 20 between the use surface and the stem has stress points. It is curved to reduce the amount of

FIG. 2 shows an alternative configuration in which the stem and part of the head are hollow and have a cavity 18. A cathode element is shown. The cavity 18 is also made of foamed carbon. by a preform of a material with a coefficient of thermal expansion that matches the stem and head, such as It can also be formed by

Example 1 A mushroom-shaped cathode element made of refractory hard metal is first powdered into a mold using a low-density sintering method. filled with TiB2, vibrated to remove voids, sintered, and placed in an argon atmosphere. The temperature is slowly raised to 2100°C inside the chamber, and then cooled to ambient temperature. accomplished. The device had the following dimensions and physical values.

゛Stem diameter 2.98cTn Stem and curved part length: 5.66 tyn Top thickness: 1.46 crn Top diameter 8.69 side Overall height 7.12crn Weight: 334.71 Body volume 126.7cc Apparent density 2.64f/cc The dimensions of a solid cylinder with similar use surfaces are as follows:

Diameter 8.69crn Height 7.12c+++ Volume: 422.00 cc Therefore, while the mushroom-shaped one has a volume of 126.7 cc, the same top surface The volume of the cylindrical body is 422 cc, and the raw material cost is The cost is only 30 cm of a solid cylindrical body.

Example 2 By roughly filling and performing sintering treatment in the same manner as in Example 1, the following dimensions and volume were obtained. A larger element was formed with

Mushroom-shaped element solid cylindrical body Top diameter 10.16cr++ 10.16crn Overall height 11.43c rn11.43cm Stem diameter 3.051:Tn Top thickness 1.46 cm Volume: 188°88cc 926.69cc The mushroom-shaped element has a volume of 20 of a solid cylinder with the same use surface and height, and therefore, compared to a solid cylinder. It is possible to save 80% on raw material costs.

The cathode elements of the present invention are also more durable than those of solid cylinders with the same top diameter and height. TiB2 powder has excellent thermal shock properties compared to coal tar pitch (softening point 11). 0℃) and a weight ratio of 85:15 at a temperature of approximately 160℃. , created a mushroom-shaped element. The ratio of refractory hard metal to binder is 70: by weight. It can be varied in the range of 3o to 98:2. Wet TiB2 sufficiently, After the mixture becomes a smooth plastic mass, it is placed in a mold and preheated to 105°C for about 1. Pressurization was applied at a pressure of 4×10 Pa (2000 psi).

Next, the molded body was taken out from the mold and fired for 6 days at a temperature increase cycle of 720°C. The pinch indasher holding the iB2 particles was carbonized. This is combined with a carbon-forming binder. Petroleum pitch with a softening point of 110 to 120°C is heated under vacuum and 7×10 pa. Impregnation for 2 hours at a temperature of about 240°C with alternating cycles of pressure and It was fired again to increase density and strength and reduce porosity. firing The body was heated to approximately 2,300°C, converting the anthrax matrix to graphite. To this, again Impregnation treatment, re-firing treatment and graphitization treatment can be performed.

A mushroom-shaped cavity was prepared by combining Hβ2 and carbon powder with an M ratio of 90:10. It is injected into a mold with to sinter the mixture of TjB2 and C and graphitize the residual carbon. did. This is then impregnated and re-fired, and then placed in an argon atmosphere. Regraphitization treatment can be performed at a temperature of 2400°C. Obtained mushroom-formed body A mold with an O-shaped cavity is made of Ti1h powder with good electrical and thermal properties. It is injected into the cavity device', heated to 500℃, and heated to about 2×108Pa in the axial direction. Apply pressure, remove from the mold, and heat to approximately 2300℃ in an argon atmosphere. The molded body was sintered.

Example 6 A part of the mold with a mushroom-shaped cavity was filled with 'TiB2 powder, and then T A porous carbon preform with heat and expansion coefficients equivalent to iB2 was inserted into the mold. . After filling the mold with TiB2 powder to enclose the preform, the same process as in Example 1 was carried out. Sintered. The cathode element has a mushroom-shaped cavity with excellent thermal durability. After filling a part of the mold with TiB2 powder, a piece of wood with the desired internal cavity shape is filled. A preform made of aluminum was inserted into the mold. Fill the preform with TiB2 powder in the mold. The mixture was filled in the same manner as in Example 1, and sintered in the same manner as in Example 1. The cathode element thus obtained has , voids are formed by carbonization of the wooden preform, and it has excellent thermal durability. there was. thermally degradable or temporary materials such as thermoplastic or thermosetting polymers. It is also possible to use prepared bodies. Since the walls of the hollow element are thin, they are It had excellent thermal shock resistance.

Example 8 Using similar materials and in a similar manner as in Example 3, a temporary preform is made in the center of the mold. A hollow element was created by arranging the body and molding the preform as a center.

The preform is made of phenol bone formal which starts to decompose at a temperature of about 400°C. Solidification of dehyde plastic molded bodies, wooden molded bodies, and other elements is performed. Although it is stable at high temperatures such as A molded body of a material can be used.

Example 9 After firing the mushroom-shaped element of Example 3 at a temperature of 720°C for 6 days, it was directly placed in a furnace. and heated to 2300℃ to graphitize residual carbon and sinter TiB2. I did it. A strong, homogeneous and excellent cathode element was obtained.

jG-j Submission of translation of written amendment (Article 184-7, Paragraph 1 of the Patent Law) February 1982 - Date Mr. Kazuo Wakasugi, Commissioner of the Patent Office 1. Display of patent application P CT/US 83100852 2. Name of the invention Cathode element of aluminum reduction electrolyzer 3. $j permit application Person Location United States 10171 New York State.

New York, Park Avenue 299 Name Crate Lakes Carbon Corporation Representative Tonopan, Joe Zea Bi.

4 Agent: 105 Telephone (591) 10045, Date of submission of amendment November 7, 1983 6. Appearance of attached documents 1 1. (“First correction”), the upper part with the almost horizontal @ pole pair and the same curve and the almost perpendicular support stand. and a lower part that is the only conductive means on the surface facing the anode. The area of the anode facing surface is approximately the same as that of the lateral area of the support stem. , and the boronization of metals in groups 1VA, IVB, VB and VB of the periodic table. A hole made of a refractory hard metal selected from the group consisting of metals, carbides, and nitrides. ・Monolink cathode element for L-aluminum reduction tank.

2. The upper anode facing surface is larger than the area inside the periphery of the support means. A cathode element according to claim 1, characterized in that:

3. The cathode element according to claim 1, which is made of a refractory hard metal. Child.

4. The cathode element according to claim 1, which is made of TiB2.

5. (First correction) Fill the mold with incompressible refractory hard metal particles. heating the mold to the sintering temperature of the particles in an inert atmosphere without applying pressure; A cathode element according to claim 1, characterized in that it is made by:

6. (First correction) Inject the mixture of refractory hard metal and carbon particles into the mold. The mixture is then filled into a mold, and the filled mold is placed in an inert atmosphere. Compound negative table Sho 59-500974 (6) Made by heating to sintering temperature and sintering without applying external pressure. The cathode element according to claim 1 or 10, characterized in that:

7. The mushroom according to claim 1, which has a shape similar to a mushroom. Cathode element.

8. The device according to claim 1, characterized in that it has a flat and horizontal anode facing surface. Cathode element.

? i! A plastic mass is formed by mixing hard metal and liquid carbon as a binder. , mold the mass to make a cathode element molded body, and heat this molded body at 700 to 1200°C. A composite of carbon and refractory hard metal is produced by firing for 1 to 10 days in a cycle of increasing the temperature to The fired compact is heated to approximately 2000 to 2400°C to graphitize the carbon. 1 ~ Made by forming a cathode element made of graphite and a refractory hard metal composite. The cathode element according to claim 1, characterized in that:

10 Wrap a temporary preform in the shape of a desired cavity inside the element. ・Uni is characterized by being made by filling a mold with refractory hard metal powder. A cathode element according to claim 1.

11.Put the refractory hard metal or metal powder into the mold cavity device, heat and pressurize the powder. to form a preform, and further heat the preform to a sintering temperature. A cathode element according to claim 1, characterized in that it is manufactured.

12 The refractory hard metal is made of TlB2, the powder is put into the mold cavity device, 5 Heated to 00℃, pressurized in the axial direction with a pressure of 2×10”Pa, and further placed in an argon atmosphere. The shade according to claim 11, characterized in that the shade is heated to 230°C in air. i element.

16. The area of the upper part having a flat anode facing surface and the cross section is larger than that of the upper facing surface. It has a small support stem, is shaped into an approximately mushroom shape, and has a maximum particle size of 44μ. Powdered TiB2 is mixed with coal tar pitch with a softening point of 110°C and the weight is 70 = 30 TiB2 is fully wetted by the pitch at a temperature of about 160°C with a ratio of up to 98°2. a step of mixing the element with an electric current; a step of molding the element in a mold; and a step of molding the element in a mold. In a furnace for a period of 1 to 10 days with a cycle of increasing the temperature from 0 to 1200℃. a step of firing, and a step of taking out the element from the furnace and placing it in an autoclave. and alternating cycles of vacuum and pressure of 1 to 15 x 10 Pa at 150 to 300°C. a step of impregnating the element with petroleum pinch having a softening point of 110 to 120° C. , the device is heated in a cycle of heating from 7θO to 1200°C for 1 to 10 days. A firing process and heating the element to 2000 to 3000°C to remove the remaining pitch. A hole characterized in that it is made by a process of graphitizing carbon dioxide. ・Monolithic cathode element for aluminum ε reduction electrolytic cell.

14 (first correction), molding is performed to surround the temporarily placed insert. The claim is characterized in that it is made by forming an internal space in the element. The cathode element according to claim 13.

15. Fill the mold with TiB2 powder with a maximum particle size of 44μ, and fill the mold with argon gas. Place it in a furnace with an atmosphere, raise the temperature to about 2100°C, and then maintain the argon atmosphere. It is made by a method that does not involve pressurization by cooling at an ambient temperature of 1. A cathode element according to claim 1, characterized in that:

16 The ratio of the diameter of the anode facing surface to the diameter of the support stem is 29 to 33. @Pole element according to claim 1, characterized in that:

17 From an upright cylindrical stem with a tilted top having a substantially horizontal and flat anode facing surface The overall shape is roughly mushroom-shaped, and the maximum horizontal dimension of the surface facing the anode is the stem. The horizontal maximum ratio of the stem is 29 to 3.3, and the stem is A hole characterized in that it forms the sole support and conductive means of the top part. ・Integrated cathode element for aluminum electrolytic cells.

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Claims (1)

[Claims] 1. Comprising an upper part having a surface facing the anode and a lower part acting as a support means for the upper part. , characterized in that the area of the @pole and the same plane is larger than the @cross-sectional area of the supporting means. Monolink negative element for Hall L aluminum reduction electrolyzer. 2. The upper anode facing surface is larger than the inner area of the periphery of the support means. A shadow element according to claim 1, characterized in that: 3. The cathode element according to claim 1, which is made of a refractory hard metal. Child. 4. The cathode element according to claim 1, which is made of TiB2. 5. Fill the mold with refractory hard metal powder and place the filled mold in an inert atmosphere. The method of claim 1, wherein the powder is heated to a sintering temperature of the powder. A cathode element according to range 1. 6 Fill the mold with refractory hard metal and carbon powder and fill the mold with a completely inert atmosphere It is characterized by being made by heating the powder at the sintering temperature at A cathode element according to claim 1 or 10. Z. The shade according to claim 1, which has a shape similar to a mushroom. Pole element. 8. Claim 1, characterized in that it has a flat and horizontal anode facing surface. Cathode element as described. 9. Mix a refractory hard metal and liquid carbon as a binder to form a plastic mass, and to form a cathode element molded body.The temperature of this molded body was raised to 700 to 1200°C. A composite of fired carbon and refractory hard metal is formed by firing for 1 to 10 days in a cycle of Then, the fired molded body is heated to about 2000 to 24001: to graphitize the carbon. By forming a cathode element made of a lead/refractory hard metal composite. A cathode element according to claim 1, characterized in that: 10 Wrap a temporary preform with a desired cavity shape inside the element. It is characterized by being made by filling a mold with powder of a refractory hard metal. A cathode element according to claim 1. 11.Put the refractory hard metal powder into the mold cavity device, heat and pressurize the powder. to form a preform, and further heat the preform to a sintering temperature. 2. The cathode element according to claim 1, wherein the cathode element is provided with: 12. The refractory hard metal is TlB2, put the powder into the mold cavity device, Heated to 500'C, pressurized in the axial direction with a pressure of 2 x 10 Pa, and then Claim 11, characterized in that the method is heated to 2301: in a negative atmosphere. Cathode element as described. 13 The area of the upper and lateral surfaces having a flat anode facing surface is larger than that of the upper facing surface. It has a small support stem, is shaped into an approximately mushroom shape, and has a maximum particle size of 44μ. Powder T i B 2 was mixed with coal tar pitch with a softening point of 110°C and a weight of 70: At a temperature of about 160°C in a ratio of 30 to 98:2, TiB2 becomes more abundant than the pitch. a step of mixing in step 1 in which the element is moistened with the liquid; a step of molding the element in a mold; and a step of molding the element in a mold. in a furnace over a period of 1 to 10 days in a cycle of increasing the temperature to 700 to 1200℃. a step of firing the element in the oven, and removing the element from the furnace and placing it in an autoclave. process, vacuum and pressure of 1 to 15 x 10 Pa at 150 to 300°C. In alternating cycles, the element is impregnated with petroleum pitch having a softening point of 110-120°C. 1 to 10 cycles of heating the device to 700 to 1200°C. A step of firing the element over a period of days, and heating the element to 2000 to 3000°C to It is characterized by being made by a process of graphitizing the residual carbon of pitch. Monolithic cathode element for Hall L aluminum reduction electrolyzer. 14. Shape the element to surround the temporarily placed insert. Claim 9 is characterized in that it is created by forming an internal space in the is the cathode element according to item 13. 15 Fill the mold with Ti1h powder with a maximum particle size of 44μ, and fill the mold with argon gas. It was placed in a furnace with an atmospheric atmosphere, and the temperature was raised to approximately 2100°C, and the argon atmosphere was further maintained. The special feature is that it is made by a method that does not involve pressurization by cooling it to ambient temperature. A cathode element according to claim 1, characterized in that: