DD257361A3 - ELECTROCHEMICAL CIRCULAR PROCESS FOR THE APPLICATION OF IRON AND ITS ALLOYS - Google Patents

Abstract

The invention includes an electrochemical cycling process for the treatment of iron and its alloys. The etching is carried out with a solution containing ferric chloride. It is used in particular for the production of precisely broken structures. The proposed solution involves a complete or partial regeneration of the iron (III) chloride consumed during the etching process. The method is also suitable for iron alloys and in particular for alloys with nickel and / or cobalt. It works with solutions containing ferric chloride, which also contain chlorides of the alloying constituents. These redemptions are separated after passing through the Aetzmaschine and completed Aetzung again.

Description

incurred pure iron. However, both methods are only suitable for the etching of pure iron materials. In iron alloys, preferably those with nickel and / or cobalt, they are not applicable, since the preferred cathodic deposition of iron over the alloying constituents nickel and cobalt results in a rapid accumulation of these metals in the etching solution, the permissible limit concentration, which is still an edge-sharp Etching results, is reached very soon and the spent etching solution must be replaced. As a result of the cathodic deposition of iron, this limit concentration is reached much sooner than with a conventional regeneration by chlorine gas.

But even in the etching of pure iron, there are a number of disadvantages of these regeneration processes. Thus, a truly continuous operation is not possible because the cathode is able to absorb only a limited amount of the deposited iron without disturbing the electrolysis process. In order to prevent the cathode space from growing, the separated iron must be removed mechanically or chemically after a short period of operation at a short distance between the cathode and the diaphragm. With a larger gap cathode diaphragm, although longer operating times, but due to the greater cell resistance also higher cell voltages and thus losses of electrical energy. Further losses result from the fact that iron chloride also passes through diffusion and migration in the cathode space, so that a portion of the current is consumed for its cathodic reduction. This has a negative effect on current yield. It has been found that the adaptation of the amount of iron ions passing into the cathode space and to be discharged therein to the anodic process is extremely difficult, since diffusion and migration through the diaphragm can not be controlled in any desired manner. Also known is the complex binding of dissolving copper ions in the etching of copper with ferric chloride. It is described in DD-PS 113026, without indicating a regeneration.

The known methods for the regeneration of ferric chloride-containing etching solutions are therefore on the one hand associated with relatively high technical and economic expenses, on the other hand, only partially or not at all suitable for the precise etching of iron alloys.

Object of the invention

The object of the invention is to develop an electromechanical recirculation method for etching and regeneration, which is also suitable for etching iron and alloys of iron, preferably with nickel and / or cobalt, and avoids the disadvantages of the prior art described above.

Explanation of the essence of the invention

From this, the technical task is derived from a method by selecting a structure for thin edges in an accurate edged etching as well as for a subsequent electromechanical regeneration process equally favorable composition of the etching solution in combination with an electromechanical regeneration process, the deposition of metals at the cathode avoids and allows easy process control even in the presence of alloying components such as nickel / cobalt in the etching solution allows to develop. The process according to the invention is characterized in that iron-chloride-containing etching solutions which additionally contain chlorides of the alloy constituents up to a metal content of 110 g / l, preferably up to 60 g / l and a density of 1.40 to 1.53 g / cm ³ at 2OX, preferably 1.46 to 1.51 g / cm ³ , is worked. After passing through the etching machine, these etching solutions are fed to the anode compartments of a bipolar regeneration electrolysis cell, preferably divided by suitable separation systems, with preferably graphite electrodes whose cathode compartments are circulated through by a stationary electrolyte containing hydrochloric acid. In this case, the amount of hydrochloric acid consumed in the overall process is completely, the amount of water required to comply with the density interval of the etching solution completely or partially supplied via the cathode chambers of the regeneration cell. Suitable separation systems in the context of the invention are diaphragms, especially those made of microporous PVC, which are preferably ribbed. The ribbing not only improves the mechanical stability, but also stabilizes the flow supply by forming interference channels. But also cation exchange membranes can be used as separation systems. It has been found that it is possible to achieve a good to very good edge sharpness at a sufficiently high etching speed only within the specified narrow sealing interval. It has surprisingly been found that the iron chloride can be replaced in part by other, derived from the alloy metal chlorides without etch rate and edge sharpness go back in an inadmissible way. In the range of the density and the foreign metal content, which is preferably to be maintained according to the invention, it is also possible, when etching metal foils with a thickness> 50 .mu.m, to achieve high precision with good edge sharpness. In the rest of the invention to be observed range is still a precise etching thinner films (<50 ^ m) possible, while in thicker films a smaller, but still sufficient for many applications edge sharpness is obtained. Depending on the intended use and the required parameters, it is therefore necessary to set and maintain the most favorable composition of the etching solution in the concentration range to be maintained according to the invention.

The inventive combination of the etching process with a bipolar electrolysis cell for the regeneration of the etching solution while adjusting the required density interval by supplying dilution water through the cathode chambers or anode chambers of the regeneration cell, it is possible to set and maintain the respective most favorable etching conditions.

Due to the acidic reaction of the stationary catholyte, the hydrochloric acid, which is supplied completely via the cathode chambers, not only ensures the maintenance of a good electrical conductivity of the catholyte, but also prevents the deposition of iron and alloying metals at the cathode in the current density to be maintained in accordance with the invention. As a result, the use of an optimally dimensioned electrolytic cell using real bipolar electrodes, especially those made of liquid-tight impregnated graphite, even possible. The advantages of a bipolar cell, simple design and low voltage losses can be fully utilized for the process. In addition, thereby an additional enrichment of the alloy components in the anode compartment due to a preferred cathodic deposition of iron is avoided. It is even possible, surprisingly, to slow down the accumulation of the constituents of the alloy in the anolyte which is circulated via the etching machine, in that in the stationary catholyte

accumulate the alloy components during the electrolysis process. It has been found that the catholyte nickel and / or cobalt in relation to the iron accumulate 3 to 5 times compared to the composition of the anolyte. According to a further feature of the invention, the process is first started with a freshly prepared ferric chloride solution, which is conducted over the etching machine and regeneration cell until the content of alloy constituents which is still permissible for the required etching result with simultaneous increase in volume is reached. Thereafter, the exhausted etching solution is completely replaced and the cycle is repeated. But it is also possible to continuously supply the required amount of ferric chloride solution before the etching machine and to separate a part of the exhausted etching solution after the etching machine.

In this case, the enrichment of alloying components in the catholyte has a very advantageous effect since it prolongs the useful life of the etching batch or reduces the amount of fresh iron-III chloride solution to be fed in continuously.

For iron alloys with a low content of foreign metals and / or lower demands on the achievable edge acuity, it is possible to adjust the molar ratio of the metals in the exhausted etching solution to that in the etched alloy. This results in the possibility to run the entire process continuously with an approximately constant composite etching solution without the addition of iron-lll-chiorid.

Again, it is of particular advantage that it is possible by the enrichment of the alloy components in the cathode space to run such a continuous process with a solution composition that still allows a good or sufficient Ätzqualität. Depending on the chosen or required process parameters, the ratio of ferric chloride reached after regeneration in the range between 5: 1 and 40: 1 should be set.

The combined etching and regeneration process is advantageously carried out at temperatures between 30 and 60 ° C. This makes it possible to use PVC as a material for cell components and for the circulation system. Higher temperatures, which are possible in principle, would require the use of special, expensive materials.

The current densities to be maintained during regeneration are between 2 and 15A / dm ² . Lower current densities require too much expenditure for the regeneration line, while higher ones result in excessive specific electrical energy consumption as a result of the increasing cell voltage. The latter is also decisively determined by the distances of the bipolar electrodes from the diaphragms, which are to be chosen as small as possible. However, the cathodic evolution of hydrogen and the resulting stationary gas loading of the catholyte results in an increase of the electrical resistance in the cathode space and thus an increase in the cell voltage. By inventively provided for circulation of the catholyte by the promoting effect of the evolving hydrogen is effectively counteracted. This not only makes it possible to lower the gas content even at a small distance cathode diaphragm, but in guiding the Katolyt cycle over a heat exchanger to be provided can also be a temperature control of the cell, without having to cool the bipolar electrodes themselves. The cooling is advantageously adjusted so that the Joule heat is used to heat the etching or to maintain the working temperature. So z. B. after re-preparation of the etching solution, the cell are operated without cooling until the working temperature in the range of 30 to 60 ⁰ C is reached. By regulating the amount of cooling water, this optimum working temperature can then be maintained.

As already mentioned, according to the invention, hydrochloric acid and water are metered into the cathode circulation, and some of the water is also metered into the anode circulation, if necessary. This leads to an increase in volume of the catholyte, possibly also of the anolyte. It has now proved to be advantageous if a portion of the stationary catholyte is constantly transferred through the pores of the diaphragms into the anode compartment. This is preferably achieved by setting a hydrostatic overpressure in the cathode compartment. This counteracts a transfer of anolyte in the cathode space, which would lead to reduction of yield by cathodic reduction of the iron l chloride already formed. Thus, the required concentrations of metal chlorides and hydrochloric acid can be adjusted in the stationary catholyte. The latter can also be achieved by arranging overflow channels from the cathode compartment to the anode compartment. This variant is to be preferred especially when using cation exchange membrane as a separation system. An increase in volume of the etching solution and / or of the stationary catholyte, depending on the process control, is absorbed by an intermediate container connected as a buffer volume, from which the solutions enriched with alloy constituents can be taken for recycling without impairing the circulation. This prevents that a portion of the etching solution or of the catholyte is already removed by overflow from the circulation before the present invention to be respected or required foreign metal concentration is reached.

From the exhausted etching solutions obtained at the end of the etch-regeneration cycle and / or the alloyed-out, recirculated electrolyte, the metals can be recovered by known methods. One possibility for this is, for example, in a separate metal extraction electrolysis, in which the metals are deposited catodically under known conditions.

embodiments

The principle of the electrochemical circulation process will be described in more detail below with reference to the technological scheme (FIG. 1).

The circulation system consists essentially of a conventional etching system 1, an intermediate container 2 for volume buffering of the etching solution and the regeneration cell 3. The regeneration cell contains anode and Katodenräum, which are separated from each other by a microporous PVC diaphragm. Anode and cathode material are made of graphite. The etching liquid is circulated by a motor pump 4. Output of the anode compartment is a mixer 5 of the possibly formed in excess chlorine can react in turbulent mixing with residual Fe ²⁺ . With the Fe ³ VFe ²⁺ analyzer 6, the current strength of the regeneration process can be adjusted via a moment analysis of the Fe ³⁺ and Fe ²⁺ . In Katodenkreislauf carried in a mixer or separator 7 by metered addition of water and hydrochloric acid, the maintenance of a certain hydrochloric acid concentration and the deposition of the hydrogen formed at the cathode. By means of a heat exchanger 8 in the cathode circulation, it is possible, if necessary, to temper the cell without having to cool the bipolar electrodes themselves. For a more detailed explanation of the electrochemical circulatory system, some preferred embodiments are given.

Example 1:

In an FeCl ₃ starting solution of 230 g / l Fe ³⁺ (p 2 0 ° C = 1.485 g / cm ³ ), partially resist-coated metal sheets of thickness 250 μm and composition Fe 54%, Ni 28%, Co 18% are conventionally used for the production of molded parts etched. After a certain etching time, an Fe ²⁺ content of 20 g / l is achieved. At this point, the loop system is put into operation with regeneration. The process is controlled by analytical monitoring so that a constant Fe ²⁺ content of 20 g / l is maintained. The density is kept constant by regulating the water transfer from cathode to anode compartment. The current density is 8A / dm ² at a temperature of 5O ⁰ C. After reaching a Ni and Co content of 40g / l, the etching is stopped. Without recycling, a satisfactory etching result would no longer be achieved with a Ni-Co content of 10 g / l.

Example 2:

For the production of molded parts, a partially masked metal sheet of thickness 200 μm and the composition of 58% Fe, 42% Ni in a conventional etching system with a FeCl ₃ solution of 223 g / l Fe ³⁺ (p 2O ⁰ C = 1.447 g / cm ³ etched). At an Fe ²⁺ content of 10 g / L, the recycle electrolytic regeneration system is turned on and kept constant by shaping the electrical values in the regeneration cell while monitoring the Fe ²⁺ value analytically. The density is also kept constant by adding water. At a Ni content of 60 g / L, the etching is stopped.

Example 3:

Sheet material of 30-50 / xm thickness and composition of 58% Fe, 42% Ni, in an aqueous FeCI ₃ solution having an Fe ³⁺ -Gehaltvon218g / I {p20 ° C = 1,462g / cm ³⁾ after partial lacquer coverage usually etched at 5O ⁰ C. At an Fe ²⁺ concentration of 8 g / l, the electrolytic cycle regeneration system is put into operation. By analytical monitoring and corresponding control of the electrolysis current, this Fe ²⁺ value is kept constant. By adding water, the density is kept constant. After a certain time, an etching solution of composition 118 g / l of Fe ³⁺ , 8 g / l of Fe ²⁺ , 92 g / l of Ni ²⁺ sets in. The ratio of Fe ³⁺ + Fe ²⁺ / Ni ²⁺ corresponds to the ratio of Fe: Ni in the etched foil material. With this etching solution, the pending material can now be fully etched continuously without having to add FeCl ₃ . The increase in the volume of liquid due to the density is counteracted by discharging solution from the buffer vessel and supplying this solution to a suitable preparation. An impairment of the circulatory system does not occur.

Example 4:

A metal sheet the thickness of 150 / xm is owned by a usual for the Formteilätzung paint cover in an initially 45% aqueous FeCl ₃ at 5O ⁰ C etched. The metal has the composition Fe 58%, Ni 28%, Co 18%. After a certain etching time, a Fe ²⁺ content in the solution of 15 g / l is achieved, and then the regeneration of the electrolytic cycle is begun with proper control of the density and the Fe ²⁺ and Fe ³⁺ concentrations. Maintaining good etch results, finally, an anolyte of the composition Fe ³⁺ becomes 187.1 g / L, Fe ²⁺ 14.5 g / L, Ni ²⁺ 38.8 g / L, Co ²⁺ 24.9 g / L and a density of 1.52 g / cm ³ reached. The catholyte formed after this time is of composition Fe ³⁺ 0.2g / l, Fe ²⁺ 12.0g / l, Ni ²⁺ 13.2g / l, Co ²⁺ 5.5g / l, HCl 5%.

Claims (2)

, 1. An electrochemical cyclic process for etching iron and its alloys preferably those containing nickel and / or cobalt, containing by means of ferric chloride and chlorides of the alloy constituents etching solutions, which after passing through the etching machine the anode chambers of a suitable separation systems, bipolar regeneration cell are supplied , The cathode chambers are flowed through by a hydrochloric acid contained stationary electrolyte in the circuit, characterized in that the etching solutions have a density of 1.40 to 1.53 g / cm ³ at 2O ⁰ C. 2. An electrochemical circulation process for the etching of iron and its alloys according to claim 1, characterized in that the etching solutions have a density of 1.46 to 1.51 g / cm ³ at 2O ⁰ C. For this 1 page drawing Field of application of the invention The invention relates to an electrochemical circulation process, which is particularly suitable for the etching of iron and its alloys, preferably those with nickel and / or cobalt, by means of iron-l chloride-containing solution. In particular, it serves to produce precisely perforated structures in thin metal sheets and involves mainly the complete or partial regeneration of the ferric chloride consumed in the etching process. Characteristic of the known technical solutions The production of precisely perforated structures in thin metal sheets, which preferably consist of alloys of iron with nickel and / or cobalt, is possible in many applications only by etching. This requires a high edge sharpness, which is characterized by a sufficiently high ratio of depth to side etching. Especially at material thicknesses above 50 ^ m, this criterion is crucial for a quality-appropriate etching. The etchant used is generally an aqueous solution of ferric chloride. The etching process proceeds according to the following equations. For iron or iron contained in the alloys: 2 FeCl ₃ + Fe - »3 FeCl ₂ . (1) For the alloy components contained in the iron alloys Me ^lxl + χ FeCl ₃ - »χ FeCl ₂ + MeCl _x (2) Since χ means the (potential) valence of the metal to be estimated. Me stands for any one or more metals that may be included in the alloys in any limits. Preferably Me represents nickel and / or cobalt; The etching solution consumes in this process and must finally be replaced or regenerated at a ratio of Fe ³ VFe ²⁺ <3 to a fresh solution. The regeneration is done so far by a known method using chlorine gas according to the following equation: 2 FeCl ₂ + Cl ₂ - * 2 FeCl ₃ (3) The metal chlorides MeCI ₂ (here Me = Ni or Co) formed according to equation (2) do not react with Clor, consequently accumulate in the etching solution and are ultimately the reason for the etching solution after repeated repetition of the etching-regeneration cycle ( 3-5 times) must finally be discarded. In this regeneration process, the very high safety effort in storage, transport and handling of the chlorine gas has a very disadvantageous. It has also been proposed (DE-OS 2436567), for etching plate material from alloys whose main component for forming ions having at least two valence states is able to use solutions containing this main constituent in a molar ratio to the other constituents of Included at the beginning. The exhausted etching solutions can be oxidized in a known manner by means of chlorine and the concentration can be maintained by dilution with water. In the case of using iron as the main constituent of the alloy and nickel as a minor constituent, for. For example, etching solutions containing 745 g / l FeCl ₃ · 6H ₂ O and 357 gl NiCl ₂ · 6H ₂ O are used. However, it has been shown that the precision of the edge can not be achieved with these solutions when precisely etching finely divided structures. Such etching solutions are therefore unsuitable for material thicknesses § 50μπι. An electromechanical regeneration process of spent iron-l chloride solutions have hitherto been proposed only for the etching of materials of pure iron (DE-OS 3141949). For this purpose, the exhausted electrolyte is fed to the anode compartment of a regeneration electrolysis cell divided by a diaphragm. Oxidation of Fe ²⁺ to Fe ³⁺ occurs at the graphite ^anode . At the iron cathode, reduction to metallic iron takes place. The iron ions to be discharged pass through diffusion into the cathode space. The cathodic current density should be 20-60 A / dm ² and adjusted so that the katodisch depositing amount of iron corresponds to the gone during the etching process in solution. Also in SU-PS 438729 is all about an electrochemical regeneration process for spent iron-lll-chloride solutions, which in the etching of