Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
  • C25D11/02—Anodisation
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/06—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used
  • C25D11/10—Anodisation of aluminium or alloys based thereon characterised by the electrolytes used containing organic acids

Definitions

• the invention relates to a method for depositing a zinc-nickel alloy from an electrolyte.
• the zinc-nickel alloys usually contain a nickel content of 10 to 16%, because this mass fraction offers the best possible corrosion protection.
• To the zinc-nickel alloys separating out are essentially in the prior art used two different electrolytes. On the one hand, these are the alkaline ones Zinc-nickel alloy baths and, on the other hand, the ammonium-containing, light acidic and chloride-containing baths. However, these baths have significant disadvantages on.
• the alkaline baths have the disadvantage that the separation rates are low, and there are difficulties with coatings from these baths to be deposited directly on cast iron or hardened steel. Another disadvantage is that these electrolytes have high concentrations of highly polluting, complexing Contain substances, which creates problems and high costs in the Cleaning and disposal of the heavily polluted waste water occurs.
• the ammonium-containing, slightly acidic electrolytes have the considerable Disadvantage that the ammonium ions pollute the waste water.
• problems can arise to remove metals from the waste water.
• the Ammonium concentration in the wastewater must be strictly regulated and controlled to meet regulatory requirements. Therefore, when using it of these baths complex and expensive wastewater treatment is carried out, to meet these requirements.
• Baths with a high ammonium content however used especially for the processing of rack and bulk items and needed to deposition a corrosion-technically usable To achieve zinc-nickel alloy on profiled workpieces.
• the present invention was therefore based on the object of specifying a method for the deposition of a zinc-nickel alloy from an electrolyte which enables the alloy to be deposited on metallic workpieces in the widest possible current density range.
• an electrolyte for performing the method is to be specified.
• This object is achieved by a method for the deposition of a zinc-nickel alloy from a zinc-nickel electrolyte, which is characterized in that the electrolyte has at least one aromatic carboxylic acid, its salts and / or its derivatives, or to expand the applicable current density range at least one aliphatic carboxylic acid, its salts and / or its derivatives, or at least one aromatic and / or aliphatic carboxylic acid, its salts and / or its derivatives are added.
• the invention is based on the surprising effect that the addition of at least one aromatic carboxylic acid, its salts and / or its Derivatives or at least one aliphatic carboxylic acid, its salts and / or their derivatives, or at least one aromatic and / or aliphatic carboxylic acid, their salts and / or their derivatives leads to the fact that over a wide Current density range of zinc-nickel alloys from a zinc-nickel electrolyte can be separated. This is also advantageous in that Coating of profiled workpieces possible because of restrictions due to a narrow applicable current density range can.
• the aromatic carboxylic acids or their derivatives are the Electrolytes preferably added as the sodium and / or potassium salt.
• the method according to the invention advantageously means that in the state avoided the disadvantages known in the art.
• the method according to the invention may be due to the addition of an aromatic and / or aliphatic carboxylic acid or their salt and / or one of their derivatives over a wide current density range be worked without the known in the prior art Disadvantages with regard to the deterioration of the layer properties occur. Thereby it is possible to work with geometrically complex workpieces with a coat even, shiny zinc-nickel alloy.
• the aromatic and / or aliphatic carboxylic acid, its salt and / or its Derivative preferably selected so that a shift in the usable Current density range in higher and / or lower ranges is specifically possible.
• the invention advantageously enables that with an ammonium-free Electrolytes can be worked, so that the disadvantages mentioned above Wastewater pollution and the associated costs can be avoided.
• the Advantages of the method according to the invention therefore result in particular from the deposition of a zinc-nickel alloy from a slightly acidic ammonium-free and chloride-containing zinc-nickel electrolytes, so that these Execution is preferred. Examples of such electrolytes can Embodiments are taken.
• the electrolyte as aromatic carboxylic acid nicotinic acid, its salts and / or their derivatives added. It has been shown that the addition of nicotinic acid or the addition of their salts advantageously leads to the Layer properties of the deposited coatings in higher Current density ranges can be significantly improved. Furthermore Burning symptoms reduced. This could be done in trials with one known in the art, slightly acidic, ammonium-free and chloride-containing zinc-nickel alloy bath are impressively shown. So had has surprisingly shown that the addition of nicotinic acid in higher current density ranges leads to that occurring without this addition Cracking and the deliberate chipping of the layer is reduced or even is completely prevented.
• Nicotinic acid or its salts and / or derivatives thereof, can be used in the electrolyte be added in an amount of at least 0.25 to 1 g / l. Preferably the amount is 0.75g / l. Experiments have shown that this amount changes has a particularly advantageous effect on the layer properties.
• the electrolyte as aromatic carboxylic acid salicylic acid, its salts and / or their derivatives added. It has surprisingly been shown that the addition of salicylic acid to an improved layer deposition in leads to low current density ranges. This leads to the otherwise occurring adverse effects and blackening of the alloy layer be prevented.
• the zinc-nickel alloy so deposited is also over the entire current density range demonstrably more uniform. So kick for example fluctuations in the alloy composition in the essential not on what is beneficial to the quality of the deposited Covers affects.
• a salicylic acid derivative for example, acetyl-salicylic acid be used.
• the salicylic acid, its salts and / or their derivatives to the electrolyte in an amount of about 0.5 to 1.5 g / l added. It has proven particularly advantageous to use the electrolyte 1g / l Add salicylic acid, its salts and / or its derivatives.
• the zinc-nickel electrolyte, nicotinic acid and salicylic acid, their salts and / or their derivatives added.
• the addition of both aromatic carboxylic acids or their salts and / or their derivatives to work over a particularly wide current density range can, because the layer properties by the addition of both substances both in low as well as in the high current density range can be improved.
• the Overall effect is better than the respective one by adding both substances separate effects.
• the nicotinic acid and the salicylic acid preferably in an amount of 0.75 g / l and in an amount of 1g / l added.
• the zinc-nickel electrolyte is preferably a slightly acidic ammonium-free and chloride-containing electrolyte.
• additional embodiments of the electrolyte are additionally provided, advantageously, in addition to or instead of already in practice salts of carboxylic acid typically used, such as sodium acetate, at least one further aliphatic carboxylic acid, its salts and / or whose derivatives are added to the electrolyte.
• carboxylic acid typically used such as sodium acetate
• at least one further aliphatic carboxylic acid, its salts and / or whose derivatives are added to the electrolyte.
• the electrolyte as aliphatic Carboxylic acids, their salts and / or their derivatives, preferably aminocarboxylic acids their salts and / or derivatives, particularly preferred Aminoacetic acid, and / or hydroxy (poly) carboxylic acids, their salts and / or Derivatives, particularly preferably 2-hydroxy-propanoic acid, are added. It has shown that specifically the addition of aminoacetic acid or 2-hydroxypropanoic acid, their salts and derivatives, advantageously leads to the fact that especially in bathrooms for rack goods, the layer properties of the deposited coatings can be significantly improved. This effect can especially in bathrooms for rack goods by moving the bathrooms, for example be intensified by moderate flooding.
• the Temperature of the electrolyte during the deposition of the zinc-nickel alloy less than 35 ° C.
• the Lowering the temperature causes the deposited zinc-nickel coating adheres better to the base material and has a lower tendency there is peeling of the layer.
• This effect is completely new and extreme
• the prior art since the prior art has so far been used at temperatures above 38 ° C has also sought to adjust the temperature of the electrolyte due to the Do not cool salt concentrations to below 35 ° C even during breaks in operation to let. Characterized in that according to this training even at lower Temperatures can be worked, costs are saved because less Energy is consumed.
• Electrolyte according to the invention is a slightly acidic, ammonium-free and chloride-containing Electrolyte. This electrolyte is used to make zinc-nickel alloys on one Workpiece deposited, which have a nickel content of 10 to 16%.
• the zinc-nickel electrolyte advantageously contains as aromatic Carboxylic acid nicotinic acid and / or salicylic acid, their salts and / or derivatives.
• aromatic Carboxylic acid nicotinic acid and / or salicylic acid their salts and / or derivatives.
• the properties of the electrolyte deposited zinc-nickel alloy coatings over a wide range Improve current density range. So adding nicotinic acid leads to one Improvement of the layer properties in high current density ranges, so that the deposited layer in this area shows less cracking and also does not have the tendency to flake off quickly.
• Salicylic acid leads to an improvement in the layer properties in low Current density areas so that the deposited layer does not turn black, and also the alloy composition over the entire current density range remains constant.
• the zinc-nickel electrolyte preferably contains both nicotinic acid and Salicylic acid. It preferably has 0.25 to 1 g / l of nicotinic acid, its salts and / or their derivatives and 0.5 to 1.5 g / l salicylic acid, their salts and / or their derivatives.
• the electrolyte according to the invention particularly preferably contains 0.75 g / l nicotinic acid, its salts and / or its derivatives and 1g / l salicylic acid or their salts and / or their derivatives. Such an electrolyte connects in advantageously the positive effects of the individual substances, the Overall effect is better than the sum of the individual effects.
• an electrolyte is provided which enables it to be used over a wide range Current density range is worked.
• the electrolyte according to the invention makes it possible therefore also to provide profiled workpieces with an even coating. This extends the applicability, since the application of different electroplating techniques is possible.
• sodium acetate contains at least one aliphatic and / or aromatic carboxylic acid, their salts and / or their derivatives used, which leads to a particular intensive prevention of the formation of basic nickel compounds, one improved pH correction and more uniform layer compositions leads over the entire current density range.
• the one of such Electrolyte-deposited zinc-nickel alloys are all over Current density range shiny and demonstrably more uniform than zinc-nickel electrolytes, which only contain sodium acetate.
• the zinc-nickel electrolyte preferably contains the salts thereof as the carboxylic acid and / or derivatives of aminocarboxylic acids and / or hydroxy (poly) carboxylic acids or their salts and / or derivatives, especially these preferably aminoacetic acid, and / or 2-hydroxypropanoic acid.
• aliphatic carboxylic acids, their salts and / or derivatives either alone or in combination with other aliphatic and / or aromatic Carboxylic acids whose salts and / or derivatives are used
• Properties of the zinc-nickel alloys deposited from the electrolyte improve significantly over a wide current density range. It has shown, that specifically the addition of aminoacetic acid or 2-hydroxy-propanoic acid, the Salts and derivatives, advantageously leads to, especially in baths for The layer properties of the deposited coatings considerably be improved.
• the basic composition of a standard bath for the deposition of zinc-nickel alloys essentially comprises divalent zinc, divalent Nickel, chloride, boric acid, surfactants and brighteners.
• a typical ammonium-free, weakly acidic, chloride-containing zinc-nickel electrolyte used in practice is composed as follows: zinc chloride 115g / l Nickel chloride (6aq) 143g / l potassium chloride 245g / l boric acid 20g / l Sodium acetate (3aq) 55g / l surfactants 6g / l Saccharin 1.5 g / l Benzal acetone (dissolved in ethyl diglycol) 75 mg / l pH 5.3-5.7
• the surfactants can be anionic or nonionic surfactants, similar to that used in a conventional acidic zinc electrolyte become. So ethoxylated alcohols or nonylphenols are common used. Benzalacetone is added as a gloss additive. As a gloss additive can also aldehydes and ketones, similar to those found in a common acid Zinc electrolytes are used, are added. For example In addition to benzylidene acetone, sodium benzoate etc. can also be used.
• Such a bath can be used to make zinc-nickel alloys on a workpiece are deposited, which have a nickel content of about 12 to 16%.
• the advantage of using such a bath is that it is free of ammonium and also does not have any complexing substances, as is the case with the alkaline zinc-nickel baths is the case.
• Such a bathroom therefore has the evident advantage that there are no substances that pollute the waste water must be removed from these first expensive and complex.
• Has such a bath however, the disadvantage that only in a very limited current density range can be worked. These restrictions are clear with one Hull cell test (2 A, 20min) recognizable. During the Hull cell test systematically records all the current density ranges that are involved in the galvanization of strongly profiled workpieces occur.
• the special shape of the test cell allows the evaluation of the galvanic deposition even in one relatively large current density range.
• a certain current density is established on the cathode plate from the anode, so that the first attempt to shed light on the functioning of the electrolyte in the different current density ranges.
• Using a Hull cell test can thus it can be estimated over which current density ranges an electrolyte works flawlessly.
• Electrolytes were checked using a slightly modified Hull cell to estimate the current density range over which they operate perfectly.
• the Hull cell used here was designed for a volume of 500ml.
• the length of the cathode was 200mm.
• composition of the electrolytes and the test results should in the present table are summarized to give an idea about the to convey extremely positive effects of the present invention.
• the current density ranges derived from the usable or non-usable mm ranges should only give an approximate estimate of the current density ranges in which the electrolyte works properly. However, these values are not to be understood as absolute values in a sense restricting the invention.
• electrolyte Burnings / bubbling Black LCD area mm from the HCD end Estimated current density in A / dm 2 mm from the LCD end Estimated current density in A / dm 2 1.
• the layers deposited by means of the standard bath described above have high internal stresses in high current density ranges, are very brittle and show cracks after some time. The layer also flakes off after some time and is therefore not usable.
• the addition of nicotinic acid and salicylic acid means that it is possible to work over a particularly wide current density range, since the layer properties of the deposited layer are considerably improved by the addition of both substances in both low and high current density ranges. The total effect is better by adding both substances than the respective separate effects.
• the addition of 1 g / l nicotinic acid and 1 g / l salicylic acid enables zinc-nickel layers with good quality properties to be deposited in current density ranges from less than 0.2 to more than 6 A / dm 2 . In these current density ranges, which are very wide compared to the standard bath, the electrolyte works perfectly.
• the method according to the invention can therefore also be used to coat profiled workpieces, and the deposited layer is of higher quality overall due to the demonstrably higher uniformity. Therefore, the galvanization options are expanded by the method according to the invention or by the electrolyte according to the invention, so that drum electroplating is also possible.
• the Hull cell test clearly showed how the inventive addition of nicotinic acid and salicylic acid the usable Current density range improved.
• the cracking and peeling of the layer is greatly reduced in high current density ranges, and also the black one Layer coloration in the low current density range is reduced.
• the deposited layer is significantly more uniform over the entire Current density curve, as could be shown by XRF analysis.
• the above-mentioned zinc-nickel electrolytes can advantageously be further developed by the additional variable use of at least one aliphatic carboxylic acid, its salts and / or derivatives.
• the zinc-nickel electrolytes listed by way of example have proven to be a particularly advantageous further development of a weakly acidic zinc alloy electrolyte for the rack technology because of the very uniform alloy composition over the entire current density range.
• Example 7 zinc chloride 115 g / l Nickel chloride (6aq) 143 g / l potassium chloride 245 g / l boric acid 25 g / l aminoacetic 45 g / l surfactants 6 g / l Saccharin 2.5 g / l brightener 2 g / l pH 5.3-5.7
• Example 8 zinc chloride 115 g / l Nickel chloride (6aq) 143 g / l potassium chloride 245 g / l boric acid 25 g / l 2-hydroxy-propanoic acid 54 g / l surfactants 6 g / l Saccharin 2.5 g / l brightener 2 g / l pH 5.3-5.7
• the temperature of the electrolyte is Deposition below 35 ° C, as this reduces the adhesive properties of the Layer can be improved. This leads to the layer remaining after some time does not peel off what the quality of the method according to the invention the zinc-nickel alloy layers deposited in the electrolyte according to the invention elevated.

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• 2001
  • 2001-09-21 DE DE10146559A patent/DE10146559A1/de not_active Withdrawn
• 2002
  • 2002-09-19 EP EP02020926A patent/EP1295967A3/de not_active Withdrawn
  • 2002-09-19 KR KR1020020057221A patent/KR100556604B1/ko active IP Right Grant
  • 2002-09-20 CN CNB021424853A patent/CN1291068C/zh not_active Expired - Lifetime
  • 2002-09-20 JP JP2002274993A patent/JP4307810B2/ja not_active Expired - Lifetime
  • 2002-09-23 US US10/252,495 patent/US20030085130A1/en not_active Abandoned

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