Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/075—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound
  • C25B11/081—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of a single catalytic element or catalytic compound the element being a noble metal
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds

Definitions

• the invention relates to electrodes for electrolysis purposes, which contain a metal alloy tantalum, tantalum boride, tantalum carbide or alloys of metals of the iron group individually or in a mixture and are doped on the surface with metals of the platinum group, in particular with rhodium.
• German Offenlegungsschrift 23 46 055 describes electrodes for electrolysis purposes which, in addition to an alloy of tungsten with metals of the iron group tantalum, tantalum boride, tantalum carbide or alloys of tantalum with metals of the iron group, contain individually or in a mixture and on the surface with metals of. Platinum group, especially with rhodium, are doped. If these anodes are used in amalgam cells, small amounts of tungsten can reach the cathode in the event of short circuits with the amalgam cathode, which reduce the hydrogen overvoltage.
• the invention seeks to remedy this.
• the invention as characterized in the claim, solves the problem of creating electrodes when used as anodes in amalgam cells when short circuits occur a reduction in the hydrogen overvoltage at the cathode is definitely avoided.
• the electrodes according to the invention have the further advantage over the known, tungsten-containing electrodes that when used as anodes in chlor-alkali electrolysis at pH ranges from 2 to 4.5, as are usually observed, they give about 50% less chlorate and that the oxygen content in the anodically developed chlorine is about 60% lower.
• the proportion of tantalum, tantalum boride, tantalum carbide or a tantalum alloy in the electrode should be at least 10 percent by weight, preferably 30 to 60 percent by weight, in each case calculated as tantalum, in order to obtain well-adhering, dense, corrosion-resistant layers which provide adequate protection for the electrically conductive carrier guarantee. With tantalum contents of more than 60 percent by weight one obtains extremely stable and stable anodes, such electrodes have somewhat higher overvoltages, so that generally higher tantalum contents should be avoided.
• the metals of the iron group are particularly advantageous as alloy components for the metals niobium or tantalum, since lower overvoltages can be achieved with these elements.
• iron which enables particularly good adhesion when doped with the platinum metals.
• the content of metals of the iron group in the niobium and optionally the tantalum alloy should total less than 10 percent by weight, preferably 0.5 to 5 percent by weight. Higher iron contents deteriorate the corrosion resistance, while too low iron contents do not Ensure sufficient adhesion of the platinum metals and conductivity.
• the electrode contains tantalum in the form of alloys with metals of the iron group, the proportion of iron in the niobium alloy to that in the tantalum alloy is 1: 0.1 to 1: 5.
• Platinum metals can be used for doping the electrodes. Rhodium has proven to be the cheapest metal because, at high anodic current densities, it is superior to all other platinum metals with regard to the adhesive strength on the electrode surface.
• the content of platinum metals should be less than 1.5 g / m electrode surface, preferably 0.25 to 0.75 g / m 2 .
• the electrodes can be used as such or also applied to an electrically conductive carrier.
• Titanium, graphite and in particular titanium-tantalum and titanium-niobium alloys are preferred, since these alloys are particularly corrosion-resistant.
• the tantl or niobium content in the alloys should be at least 10 percent by weight in order to achieve a significant improvement over unalloyed titanium.
• the electrodes can be produced by applying a mixture consisting of a fine-grained alloy of niobium with metals from the iron group and fine-grained tantalum, tantalum carbide, tantalum boride or an alloy from tantalum with metals from the iron group with the aid of a plasma torch on an electrically conductive base and the layer thus applied is then doped on the surface with platinum metals, in particular rhodium.
• the grain size of the metal powder used should be 40 to 100 / um.
• the electrodes can also be produced, for example, by rolling layers of the mixtures described above onto an electrically conductive base or by plating them.
• the layers applied to the electrically conductive carrier should be thicker than 0.1 mm in this process. Layer thicknesses between 0.1 and 0.8 mm are preferably selected.
• the electrodes are impregnated with a 0.1 to 10, in particular 0.5 to 3, percent by weight solution of an inorganic platinum metal compound and then at +600 to + 1200 ° C, preferably +800 to + 900 ° C, under Protective gas atmosphere annealed for about 1 to 10 seconds.
• An aqueous hydrochloric acid rhodium (III) chloride solution with a pH of 0 to 0.5 has proven to be particularly advantageous for the doping.
• this solution and the iron-containing niobium or tantalum alloys a particularly stable doping and clean electrode surfaces are obtained, since the iron chlorides formed sublimate immediately when doping.
• such electrode surfaces that are not contaminated with oxides have particularly low overvoltages on.
• the doping itself must be carried out under a protective gas atmosphere or in a high vacuum in order to avoid oxidation. Argon is preferably used as the protective gas.
• the electrodes can be manufactured using electrically conductive metallic carrier bodies, for example, by first degreasing the carrier body and freeing it from oxides by chemical etching with hydrofluoric or oxalic acid b or ion etching with noble gases at low pressures.
• the layer of an alloy of niobium with metals of the iron group, optionally simultaneously with tantalum or the tantalum compound, is then applied to the oxide-free, electrically conductive supports with the aid of vapor deposition or ion plating processes in a high vacuum.
• the platinum metals are doped into the surface of this layer by ion plating or implantation in a high vacuum.
• the layer of the niobium alloy with metals of the iron group and with tantalum or tantalum compounds, by vapor deposition ion plating or the plasma process can be applied simultaneously with platinum metals. It has proven to be advantageous here if the proportion of metals of subgroup VIII in the layer is 1/10 to 1/100 of the content of the surface.
• a titanium sheet with the dimensions of 30 x 20 x 2 mm is blasted with corundum and one side of the plasma torch with a fine-grain mixture consisting of 50 parts by weight of a lesiaration with 95% by weight of niobium and 5% by weight of 88 s and 50 parts by weight of tantalum, about 0.25 mm thick sighted.
• the finished anode is preferably suitable for the electrolysis of dye waste water, alkali chloride solutions and sulfuric acid.
• the overvoltage in aqueous alkali chloride solution is approximately 30 mV at a load of 2.3 kA / m 2 (anode surface).
• a titanium expanded metal mesh with the dimensions of 240 x 240 mm is degreased and oxides are removed by etching with argon in vacuo. Then a 2,000 ⁇ thick niobium iron layer (with 3 weight percent iron) is applied to the oxide-free surface.
• the surface is then doped with rhodium by ion plating.
• the rhodium content on the electrode is ⁇ 0.34 g / m 2 .
• the electrode can be used as an anode for the electrolysis of alkali chloride solutions and hydrochloric acid. After an operating period of 50 days at a current density of 15 kA / m 2 , there is no increase in the overvoltage. In the event of short circuits with the mercury cathode, there is no reduction in the hydrogen overvoltage.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6023309

Family Applications (1)

Country Status (6)

Families Citing this family (5)

Citations (4)

Family Cites Families (1)

• 1977
  • 1977-11-09 DE DE19772750029 patent/DE2750029A1/de not_active Ceased
• 1978
  • 1978-10-14 EP EP78101152A patent/EP0001778A3/fr not_active Withdrawn
  • 1978-10-14 GB GB7935270A patent/GB2058838B/en not_active Expired
  • 1978-10-14 BE BEBTR33A patent/BE33T1/fr not_active IP Right Cessation
  • 1978-10-30 US US05/955,580 patent/US4212725A/en not_active Expired - Lifetime
• 1979
  • 1979-09-17 FR FR7923304A patent/FR2436195A1/fr active Granted

Patent Citations (4)

Also Published As

Similar Documents

Legal Events