The invention relates to a large-dimension electrode in ac¬ cordance with the preamble of claim 1.

Such an electrode is described for example in the Interna¬ tional publication WO 02/061181 A2. The known large-dimension electrode is made of a plurality of flat electrode elements which are fixed with a distance in between on the surface of a flat support. A gap between the electrode elements is filled with an electric isolating material. Each electrode element is made of a silicon or silicon carbide substrate which is covered by a layer made of electroconductive dia¬ mond. The known large-dimension electrode demands for a high expenditure in manufacturing. Furthermore, the toughness of the known electrodes is not very high and the handling is complicated.

The DE 199 11 746 Al discloses a method for making an elec- trode being provided with a electroconductive diamond layer. Thereby the layer is made by a CVD-process. When covering in particular substrates having larger dimensions they often go out of shape. Furthermore, the deposited diamond layer is not very homogeneous .

The DE 694 10 576 T2 describes a method for treating waste water by electrolysis with electrodes having a electroconduc¬ tive diamond layer on their surface. The diamond contains a doping which makes it electroconductive. A large-dimension electrode is not described in this document.

It is an object of the present invention to provide a large- dimension electrode which can be manufactured in a simple manner at low cost. According to a further aim of the inven¬ tion there shall be provided a large-dimension electrode hav¬ ing an improved effectiveness. A further aim of the present invention is it to provide an electrode which can be manufac- tured in a variety of 3-dimensional shapes.

This object is solved by the features of claim 1. Embodiments of the invention are described by the features of claims 2 to 24.

According to the present: invention it is provided that the substrates are joined together by a joint which is provided on at least one of their flanges to form a mechanically sta¬ ble electrode body and wherein the joint provides a electric conductivity between the substrates.

When joining the substrates together at their flanges it is advantageously not necessary to provide a support. The pro¬ posed electrode can be manufactured with less effort. The proposed joints can be manufactured such that the diamond layers of adjacent substrates lay side by side. I. e. the proposed electrode exhibits essentially a continuous diamond layer across its entire surface. The effectiveness of the proposed electrode is enhanced. Besides that, by the proposed invention it is possible to provide a large-dimension elec¬ trode which is coated on both opposite surfaces with diamond layers. Thereby the effectiveness of the electrode can be doubled.

According to the present invention a large-dimension electro¬ de can be manufactured by joining plurality of relatively small electrode elements, each electrode element having for example a substrate with a size of 10 cm x 10 cm or like. Such small electrode elements can be manufactured without go¬ ing out of shape. Even if the electrode elements exhibit fol¬ lowing a CVD-process a curvature such an deviation from the original shape of the substrate can be compensated when join- ing the substrate elements. In this case, the large-dimension electrode may have an undulating surface. However, the large- dimension electrode has general a flat shape which can be easily attached to a mounting structure.

According to an embodiment of an invention the diamond and/or the substrates has/have an electrical resistance of less than 100 Ωcm, preferably of less than 0,1 Ωcm. Advantageously the joint between the substrates has in a similar manner an elec¬ trical resistance of less than 100 Ωcm, preferably of less than 0,1 Ωcm. Thereby a sufficient electrical conductivity across the joined substrates is guaranteed. It is in particu¬ lar not necessary to provide a support or the like in order to connect the substrates electrically.

According to a further embodiment the diamond contains a dop¬ ing. The doping can comprise at least one of the following substances: boron, nitrogen. The amount of the doping con¬ tained in the diamond can be in the range of 10 ppm to 3000 ppm, preferably in the range of 100 ppm to 1000 ppm. By the proposed doping the aforementioned electrical resistance of the diamond can be adjusted.

According to further embodiments the joint provides a force locked linkage and/or a metallic continuity of the substra- tes. The force locked linkage may be made by a screw joint, a retrieved joint, a clamped joint, a rebated joint or a push fit fitting. In order to provide a suitable joining surface it is possible that the substrate is not coated with diamond along those flanges which are connected by the joints. Fur¬ thermore the flanges of the substrate may be bent for example m a S-like manner to receive on a bend portion of the flange a portion of an adjacent substrate. Tne flange may also be bent or formed like a groove m which the flange of an adja¬ cent substrate may be inserted.

The metallic continuity of the joined substrates is prefera¬ bly made by a welded joint. The welded joint can be made by diffusion welding, electron beam welding or laser welding. It is also possible to use other suitable welding techniques. Such welding techniques are known to the skilled artisan.

The welded joint is preferably made on the side of the sub- strate which is not covered with a diamond layer. However, it is also possible to provide in particular a welded joint on each side of the substrate along at least one flange thereof. If m particular a welded joint is provided on the side of the substrate which is covered by a diamond layer the joint may be covered by an anti-corrosion layer. The anti-corrosion layer may be a self passivation layer of the metal or may be made of an organic material, in particular of a plastic. Ac¬ cording to a further embodiment the self passivatmg layer can also consist of an anorganic material, in particular a ceramic.

According to a further embodiment the joint can also be a soldered joint. Further the joint may be made by an electro- conductive polymer. Such a polymer may be a resin containing electroconductive particles like carbon fibres and the like. By hardening such a resin the substrates can easily be glued together. The metal is preferably a self passivating metal. Under the term "self passivating metal" there is understood a metal which is passivated on its surface by the formation of an isolating layer by chemical or electrochemical oxidation. The metal may be selected from the following metals: titanium, niobium, tantalum, aluminium, zirconium, steel, steel being coated with a layer which separates the iron of the steel from the atmosphere used in the CVD-process and forms cova- lent bonds to the diamond layer. Suitable layers are for ex- ample layers made of titanium boron nitride or chromium car¬ bide.

The substrate has advantageously a thickness in the range of 0.1 to 20.0 mm. The diamond layer may have a thickness in the range of 2 μm to 200 μm.

According to an advantageous embodiment of the invention the diamond layer is provided on the opposite sides of the sub¬ strate. Thereby the effectiveness of the electrode can be en- hanced remarkably. The substrates may have an angular, pref¬ erably a rectangular, form which makes it easy to manufacture for example large-dimension flat electrodes. However, it is also possible that the substrates have a curved surface. The substrates may be tubes, slabs, rods or plates. Furthermore the substrate may be an expanded metal. It may have one or more apertures. By joining in particular substrates having a curved surface it is possible to manufacture large-dimension electrodes which may have the form of large-dimension tubes or the like.

Embodiments of the invention are now described by way of non- limiting examples with reference to the accompanying drawings in which: Fig. 1 shows a top view of a first electrode,

Fig. 2 shows a schematic sectional view through a joint of the first electrode,

Fig. 3 shows a top view of a second electrode,

Fig. 4 shows a schematic sectional view through a joint of the second electrode,

Fig. 5 shows a schematic sectional view through a joint of a third electrode,

Fig. 6 shows a top view of a fourth electrode,

Fig. 7 shows a perspective view of a fifth electrode,

Fig. 8 shows a SEM-photograph of electrode elements being connected by a welded joint and

Fig. 9 shows a sectional view of the electrode shown in Fig. 8.

The electrodes shown in Fig. 1 to 7 are made of electrode elements 1.1, 1.2, 1.3, ..., l.n. Each electrode elements comprises a substrate 2.1, 2.2, 2.3, ..., 2.n which is pref¬ erably made of titanium or another suitable self passivating metal. Each substrate 2.1, 2.2, 2.3, ..., 2.n is covered on a first surface Sl with a diamond layer 3.1, 3.2, 3.3, ..., 3.n. The diamond layer may be made by CVD. It may have a thickness in the range of 0.1 μm to 200 μm, preferably of 2 μm to 20 μm. The diamond exhibits an electrical conductivity which is created by a doping for example of boron. The amount of the doping contained in the diamond may be in the range of 10 ppm to 3000 ppm, preferably in the range of 100 ppm to 1000 ppm.

As can be seen in particular from Fig. 1 the electrode may be provided along their edges with a fastening structure F which may be made by strips of sheet metal. Such a fastening struc¬ ture F is preferably connected to the electrode by a further joint which may be similar to the joints 4 described above. The further joint for connecting the fastening structure F is preferably also an electric conductive joint. The electrode may be connected to a power supply via the fastening struc¬ ture.

As can be seen in particular from Fig. 2 the substrates 2.1, 2.2, 2.3, ..., 2.n of the electrode elements 1.1, 1.2, 1.3, ..., l.n are connected to each other by a joint 4 which is provided on a second surface S2 which is opposite of the first surface Sl. The joint 4 is provided along the flanges of the substrates 2.1, 2.2, 2.3, ..., 2.n and is made by welding. A small gap 5 between the adjacent diamond layer 3.1, 3.2, 3.3, ...., 3.n is filled and/or covered by an anti- corrosion material 6 which protects the electrode elements 1.1, 1.2, 1.3, ..., l.n against corrosion along the flanges. The anti-corrosion material 6 may be made of silicone, plas¬ tic or other suitable materials.

Fig. 3 and 4 show a second electrode. As can be seen in par- ticular from Fig, 4 the joint 4 is provided on a first side Sl and on the second side S2 on the flanges of the adjacent substrates 2.1, 2.2. In particular the joint 4 on the first side Sl of the substrates 2.1, 2.2 may also be covered by an anti-corrosion material 6 (not shown here) .

Fig. 5 shows a schematic sectional view of a third electrode. Therein each of the electrode elements 1.1, 1.2, 1.3, ..., ■ l.n has a flange 7.1, 7.2, 7.3, ..., 7.n which is bent in a S-like manner. Along the flange there is provided a strip on which the diamond layer 3.1, 3.2, 3.3, .. -, 3.n does not cover the substrate 2.1, 2.2, 2.3, ..., 2.n. The form of the flange 7.1, 7.2, is such that a flat end of an adjacent elec¬ trode element 1.1, 1.2, 1.3, ..., l.n may be positioned on the first surface Sl of the flange 7.1, 7.2, 7.3, ..., 7.n. The flange 7.1, 7.2, 7.3, ..., λn is bent such that when an adjacent electrode element 1.1, 1.2., 1.3, ..., l.n is laying on the bent portion the substrates 2.1, 2.2, 2.3, ..., 2.n are essentially on the same level so that the electrode ex¬ hibits a more or less even surface. The joint 4 may be in this case a force locked linkage provided by a fastening ele¬ ment 8 like a screw, a bold or other like. A gap 5 between the adjacent electrode elements 1.1, 1.2, 1.3, ..., l.n may be filled and/or covered by the anti-corrosion layer 6.

Fig. 6 shows a top view of a forth electrode. Therein the electrode elements 1.1, 1.2, 1.3, ..., l.n are made from ex- pended metal substrates having a plurality of apertures 9. The apertures 9 have in this particular embodiment the form of routes. However, the aperture 9 can have any form like circles, triangular or rectangular forms and the like.

Fig. 7 shows a fifth electrode. Therein the electrode ele¬ ments 1.1, 1.2 are made of tubes having apertures 9. Like in Fig. 6 the substrates 2.1, 2.2, 2.3, ..., 2.n are connected by welded joints 4. Fig. 8 and 9 show SEM-pictures of an electrode which is simi¬ lar to the electrode shown schematically m Fig. 2. Fig. 8 shows a top view on the second surface of two electrode ele- ments 1.1 and 1.2 which are connected by a joint 4 which has been made by welding. The joint has been produced by laser welding with a C02-laser having a power of 5 kW. As an output power there has been used 3 kW and a welding velocity of 3,5 m/mm. As mertgas helium gas has been used. As can be seen in particular from Fig. 9 the welded joint has a depth of around 3 mm and is provided just at the second surface S2 of the first 2.1 and second substrate 2.2.

Although it is not shown in the figures it is clear that also the second surface S2 may be additionally coated with a dia¬ mond layer 3.1, 3.2, 3.3, ..., 3.n. The anti-corrosion layer 6 may be provided on each joint 4, 8. The proposed electrode can have any form.

The electrode proposed according to the present invention can be in particular an anode for a treatment of waste water an the like. Reference list

1.1, ..., 1.n electrode elements 2.1, ..., 2.n substrate 3.1, ..., 3.n diamond layer 4 joint 5 gap 6 anti-corrosion material 7.1, ..., 7.n flange 8 fastening element 9 aperture

51 first surface 52 second surface F fastening structure