WO2018178709A1 - Dépôt autocatalytique de couches doubles de nickel-phosphore - Google Patents

Dépôt autocatalytique de couches doubles de nickel-phosphore Download PDF

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Publication number
WO2018178709A1
WO2018178709A1 PCT/GB2018/050866 GB2018050866W WO2018178709A1 WO 2018178709 A1 WO2018178709 A1 WO 2018178709A1 GB 2018050866 W GB2018050866 W GB 2018050866W WO 2018178709 A1 WO2018178709 A1 WO 2018178709A1
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Prior art keywords
plating
range
substrate
fluid
metal
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PCT/GB2018/050866
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English (en)
Inventor
William Little KENNY
Kenneth Charles GAULD
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AJT Engineering Ltd
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Publication of WO2018178709A1 publication Critical patent/WO2018178709A1/fr

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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/1601—Process or apparatus
    • C23C18/1633—Process of electroless plating
    • C23C18/1646—Characteristics of the product obtained
    • C23C18/165—Multilayered product
    • C23C18/1651—Two or more layers only obtained by electroless plating
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
    • C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/32—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron
    • C23C18/34—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents
    • C23C18/36—Coating with nickel, cobalt or mixtures thereof with phosphorus or boron using reducing agents using hypophosphites
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
    • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
    • C23C18/31—Coating with metals
    • C23C18/38—Coating with copper
    • C23C18/40—Coating with copper using reducing agents

Definitions

  • the invention relates to a process for electroless plating of a substrate, and to a plated substrate that can result from such a method.
  • Electroless plating is a widely used technique to deposit a metallic plating onto a substrate, and is often also referred to as chemical or autocatalytic plating.
  • the process involves converting dissolved metal ions to metal in the presence of a chemical reducing agent, the resulting metal becoming deposited onto the surface of a substrate. Examples of electroless plating processes are described in WO 90/00261, WO 03/020443, WO
  • Electroless plating can be used to improve certain properties of a substrate, for example to improve protection against corrosion, improve hardness or wear resistance, impart conducting or magnetic properties to a non-conducting or non-magnetic substrate, or to refurbish worn or mis-machined parts.
  • An advantage of the electroless plating technique over other techniques, such as electroplating methods, is the ability to form a more even deposit on a surface.
  • the present invention relates to a new processing method which results in unexpectedly improved plating performance.
  • the invention is directed to a process for electroless plating of a substrate, comprising;
  • the invention is also directed to a plated substrate that can be obtained by such a process.
  • Electroless plating is often used to improve various characteristics of a substrate, typically a metal substrate. Such features include hardness/wear resistance, corrosion resistance, and also visual appearance such as brightness and lustre.
  • two plating fluids are employed with different concentrations of reducing agent. Fluids with relatively low concentrations of reducing agent are often used to apply a hard, wear-resistant plating to a substrate, whereas fluids with relatively high concentrations of reducing agent are used to apply a corrosion resistant plating. It has now been found that properties of a plated substrate close to or equivalent to the properties expected from applying two separate layers in two separate procedures can actually be achieved using thinner individual coatings than would otherwise be expected.
  • the substrate can be any substrate on which a metallic plating can be applied.
  • they are metals or metal alloys, examples being iron, aluminium, copper, titanium, nickel and magnesium, and alloys of any one or more thereof, and also other alloys such as stainless steel, alloy steels, cast iron, and beryllium alloys, such as beryllium-iron, beryllium-aluminium, beryllium-nickel and beryllium-copper alloys.
  • they may be non-metallic substrates that already have a metallic coating or plating.
  • the first and second plating fluids are typically liquid-phase solutions, usually aqueous solutions, containing dissolved metal or metals which are to be deposited as the plating metal.
  • the plating metals are typically selected from one or more of nickel, cobalt, aluminium, copper and tin. Based on the metal content, the total concentration of metals in each of the first and second plating fluids is typically in the range of from 1 to 600 mM, for example from 10 to 300 mM or from 50 to 150 mM.
  • Other dopant metals can also be present, typically at lower concentrations such as less than 1 mM in each plating fluid, for example at concentrations of 0.01 to 0.5 mM. Examples of dopants include lead, which can act as a stabiliser.
  • the concentration of the dopant in the solution is sufficient to ensure the resulting plating comprises up to 0.2 wt% of the dopant metal such as in a range of from 0.0001 to 0.2 wt%.
  • the dopant metal is present in the plating at less than 0.1 wt%, i.e. in a range of from 0.0001 to less than 0.1wt%.
  • lead is present as a dopant, the resulting plating containing less than 0.1% lead by weight.
  • the total concentration of the one or more first plating metals in the first plating fluid can be the same as or different from the total concentration of the second plating metals in the second plating fluid.
  • typical total concentrations of the one or more first plating metals in the first plating fluid can be in the range of from 60 to 150 mM, for example from 90 to 110 mM.
  • Typical total concentrations of the one or more second plating metals in the second plating fluid can be in the range of from 40 to 130 mM, for example in from 75 to 105 mM.
  • the one or more metals that make up the plating metals in the first plating fluid (i.e. the first plating metals) and second plating fluid (i.e. second plating metals) can comprise a common metal, and in further embodiments all of the first plating metals are the same as the second plating metals. In embodiments there is only a single first plating metal and a single second plating metal.
  • the process of the invention is particularly suited for electroless nickel plating, in which nickel is the major constituent of the first and second plating metals.
  • nickel is the only member of the first and second plating metals.
  • the one or more first plating metals and second plating metals are usually provided in the form of salts that are water-soluble.
  • each salt can be independently selected from a halide (such as chloride, bromide or iodide), sulfate, sulfamate or acetate.
  • Other salts that can be used include nitrate, phosphate, tetrafluorob orate, hexafluorophosphate or oxalate.
  • nitrate salts are avoided
  • the first and second plating fluid can each comprise one or more additional components.
  • One or more chelating agents can be present, to stabilise and maintain solubility of the first and second plating metals to enable more controlled deposition.
  • chelating agents are organic acids or their salts, typically those which comprise more than one carboxyl group, and also those comprising a single carboxyl group and at least one additional -OH group.
  • the number of carbons atoms in the organic acid can be in the range of from 3- 6.
  • Specific examples include citric acid, lactic acid, tartaric acid, succinic acid, malic acid, maleic acid, itaconic acid and gluconic acid, or salts thereof.
  • the organic acid is selected from citric acid, malic acid, itaconic acid, and salts thereof.
  • Other chelating agents include polyamines, typically those comprising 2 to 4 amine groups, such as ethylenediamine and diethylenetriamine; polyethers such as polyethylene glycol, polypropylene glycol and crown ethers, typically those containing from 3 to 8 oxygen atoms, for example from 4 to 6 oxygen atoms; and porphyrins.
  • Salts of the chelating agents typically include those having monovalent or divalent cations, such as alkali metal or alkaline earth metal cations.
  • the chelating agents can be added separately from the salts of the plating metals.
  • any of the first and/or second plating metals can be combined with a chelating agent before addition to the first or second plating fluid.
  • the pH of the first and/or second plating fluids can be controlled. Typically, the pH is maintained at a neutral or slightly acidic value to avoid premature precipitation/deposition of the one or more first and second plating metals, for example by maintaining the pH at a value in the range of from 4 to 7.
  • the first and second plating fluids may be maintained at different pH values.
  • the first plating fluid may be maintained at a value in the range of from 4 to 6, such as from 4.5 to 5.5, or 4.8 to 5.2.
  • the second plating fluid can be maintained at a value in the range of from 5.5 to 7, for example from 6 to 6.6.
  • the pH can be adjusted by one or more pH adjustment agents.
  • the acidity of the fluids can increase during the plating process, so the pH can be maintained or adjusted throughout the process by adding one or more pH adjustment agents to either or both of the first and second plating stages to maintain the pH within the desired range.
  • Agents which raise the pH are typically selected from hydroxides, carbonates and bicarbonates, for example ammonium, alkali metal or alkaline earth metal hydroxides, carbonates and bicarbonates. In one embodiment, ammonium hydroxide is used as the pH adjustment agent. In another embodiment, potassium carbonate is used.
  • Agents which lower the pH can be selected from mineral acids, such as sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, fluoroboric acid, or organic acids, such as carboxylic acids, for example carboxylic acids
  • a composite plating can be achieved by including in the first and/or second plating fluid a composite material. These can be incorporated into the metallic plating, to modify and improve properties such as wear, abrasion resistance or lubricity of the deposit.
  • Composite materials are generally included in the plating fluid as a fine suspension, optionally in the presence of surface active agents which help to stabilise the suspension and control the deposition during the plating process. Examples of composite materials are fluoropolymers such as polytetrafluoroethylene (PTFE), natural or synthetic diamonds, ceramics, chromium carbide, silicon carbide, magnetite and aluminium oxide.
  • PTFE polytetrafluoroethylene
  • the first and/or second plating fluids can comprise one or more additional components, such as one or more stabilisers and/or surfactants.
  • Lead for example in the form of lead acetate, can act as a stabiliser, which can help to avoid indiscriminate and uncontrolled plating.
  • Surfactants such as silicone glycol surfactants, for example polyalkoxylated silicone glycol surfactants, can help to assist the fineness of the grain of the plating metals. They can also help stabilise dispersed composite material that may also be present in the first and/or second plating fluid.
  • Each of the first and second plating media comprises one or more reducing agents.
  • the total concentration of the one or more first reducing agents in the first plating medium is higher than the total concentration of the one or more second reducing agents in the second plating medium.
  • the reducing agent causes reduction of the soluble metal plating ions to metal, which then deposit on the substrate. More than one reducing agent can be used in each of the first and second plating fluids, in which case the concentration of reducing agent refers to the total concentration of reducing agent in the respective fluid.
  • the total concentration of reducing agent in each of the first and second plating fluids is typically in the range of from 50 to 750 mM.
  • the total concentration of the one or more first reducing agents in the first plating fluid is typically, in the range of from 150 to 500 mM, for example from 250 to 350 mM.
  • the total concentration of the one or more second reducing agents in the second plating fluid is typically in the range of from 50 to 300 mM, for example from 150 to 220 mM.
  • the ratio of molar concentrations of the one or more first reducing agents to the one or more first plating metals in the first plating fluid is in the range of from 2 to 4, for example in the range of from to 2.3 to 3.4.
  • the ratio of molar concentrations of the one or more second reducing agents to the one or more second plating metals in the second plating fluid is in the range of from 1.2 to 3.2, for example from 1.7 to 2.7.
  • Examples of reducing agents suitable for use in the present invention include sulfites, nitrites, hydrides, phosphites, hypophosphites and borohydrides, typically provided as salts selected, for example, from alkali metal salts, alkaline earth metal salts, organic "R" salts, where "R” is defined below (such as CH 3 + or C2H 5 + salts), or quaternary ammonium salts of general formula H4- X R X where x is from 0 to 4, and wherein the "R" groups are defined below, for example tetramethylammonium salts.
  • reducing agents include hydrazines, and also boranes and borane adducts such as amine boranes or organoamine boranes of general formula H3- y R y : borane in which y is from 0 to 3, the "R" groups being defined below, an example being dimethylamine borane.
  • the borane is typically BH 3 .
  • Each "R" group referred to above can be selected from C 1-8 alkyl groups, C 3 - 8 cycloalkyl groups, C 3-8 heterocycloalkyl groups, C 3-8 aryl groups and C 3 -8 heteroaryl groups the heterocycloalkyl and heteroaryl groups comprising at least one carbon atom, and having from 1 or 3 heteroatoms, each selected from O, S and N.
  • C 1-8 alkoxy groups can optionally be substituted with one or more groups selected from halide, Ci-4 alkoxy and Ci-4 haloalkoxy groups.
  • C 3-8 cycloalkyl, C 3 -8 heterocycloalkyl, C 3-8 aryl and C 3 -8 heteroaryl groups can optionally be substituted with one or more groups selected from halide, CIA alkyl, Ci-4 haloalkyl, Ci-4 alkoxy groups and Ci-4 haloalkoxy groups.
  • Specific examples of reducing agents that can be used include sodium
  • the first and/or second reducing agents contain phosphorus or boron.
  • Use of phosphorus or boron-containing reducing agents can result in incorporation of phosphorus or boron in the plating on the substrate, which can impart certain advantages to the deposited metal plating. For example, incorporation of increasing amounts of phosphorus into a metal plating, for example a nickel plating, can improve corrosion resistance of the substrate, while at the same time reducing hardness of the plating. Incorporation of boron can also improve hardness.
  • first reducing agent there is only a single first reducing agent, and a single second reducing agent.
  • alkali metal hypophosphites such as sodium hypophosphite, are used as the first and second reducing agents.
  • the first plating on the substrate is a corrosion resistant layer
  • the second plating is for improving the hardness and/or wear characteristics
  • a phosphorus or- boron-containing reducing agent for corrosion resistant layers, for example a hypophosphite or a borohydride.
  • the amount of phosphorus or boron in the resulting plating is typically in the range of from 8-17% by weight, for example 10-13% by weight.
  • Nickel can be the plating metal in such plating layers.
  • phosphorus- or boron- containing reducing agents can be used, for example a hypophosphite or a borohydride.
  • the amount of phosphorus or boron in the resulting plating is typically in the range of from 1-6% by weight, for example from 1-3% by weight.
  • nickel can be the plating metal in such plating layers.
  • the temperature of the two plating treatments can be the same or different. They are typically operated at above ambient temperature, for example in the range of from 60 to 95°C, such as in the range of from 80-93°C.
  • the first plating fluid is maintained at a temperature higher than that of the second plating fluid.
  • the first plating fluid is maintained at a temperature in the range of from 85-91°C.
  • the second plating fluid is maintained at a temperature in the range of from 82-91°C.
  • the first and/or second plating fluid can be agitated during use, and the composition adjusted to ensure sufficient plating metals, reducing agent, other components and properties such as pH are maintained within desired limits.
  • plating takes place in a plating bath, in which plating fluid is removed and analysed. The composition of the plating fluid is then adjusted to ensure the desired characteristics are maintained. The fluid can be filtered before being returned to the main plating bath.
  • this is a continuous process, with plating fluids being recirculated through a recirculation loop that comprises one or more adaptions so that components can be added to adjust the composition, and/or to enable sample to be removed for analysis.
  • analysis is carried out on-line using suitable sensors built into the recirculation loop and/or in the plating bath itself.
  • Steps (i) and (ii) of the process can take place in the same plating bath, optionally with suitable washing and preparation of the plating bath between treatments.
  • the plating is carried out in separate baths, the substrate being removed from one bath after the first treatment and immersed in a second bath optionally after washing and/or rinsing the substrate.
  • Plating thickness for each step can be controlled by known means, for example by the length of time of immersion in the plating fluids, the temperature, the concentration of plating metals and reducing agents, the choice and concentration of chelating agents, and use of other components such as stabilisers.
  • the plated substrate can optionally be heat treated between and/or after the two plating steps. When heating is carried out, it is typically to a temperature in the range of from 150 to 400°C.
  • temperatures above 260°C are often used, typically in the range of from 320 to 370°C, because this can cause crystallisation of the plating metal(s) with additives or dopants in the plating, such as phosphorus or boron from the reducing agent.
  • heat treatment is preferably avoided, particularly in embodiments where the layer incorporates elements such as phosphorus or boron from the reducing agent, since crystallisation of such species can disrupt the uniformity and coverage of the protective plating.
  • the thickness of plating for each stage is typically in the range of from 5 to 125 ⁇ , for example from 6 to 60 ⁇ , or from 10 to 30 ⁇ .
  • the process of the present invention results in a plated substrate with enhanced properties.
  • the substrate comprises a first plating and a second plating, in which the first plating is a metal plating comprising phosphorus and/or boron, and the second plating is a metal plating comprising boron and/or phosphorus, in which the total amount of phosphorus and boron in the first plating is greater than that in the second plating.
  • the total amount of phosphorus and/or boron in the first plating is in the range of from 8 to 17% by weight. In embodiments, the total amount of phosphorus and/or boron in the second plating is in the range of from 1 to 6% by weight.
  • the first and/or second plating metals are selected from one or more of nickel, cobalt, copper, aluminium and tin. In embodiments, all of the first plating metals and second plating metals are the same, and in further embodiments are nickel or predominantly nickel.
  • the first plating is for improving corrosion resistance
  • the second plating is for improving wear resistance and/or hardness
  • the substrate can be as defined above.
  • the second plating is applied on top of or over the first plating, and typically covers the first plating in its entirety.
  • An anodically protected steel plating bath was cleaned and passivated using a 30- 50% v/v nitric acid solution for 4 - 8 hours. The bath was drained, and rinsed to ensure there was no residual nitrate (confirmed by using nitrate test strips).
  • the resulting plating fluid contained 6.0 g/litre (102 mM) nickel and 30 g/litre (283 mM) sodium hyphophosphite monohydrate.
  • the pH was measured, and adjusted where necessary with dilute ammonium hydroxide (50% v/v) or dilute sulfuric acid (10% v/v) to achieve a pH of 4.8.
  • the plating medium was then heated to 88°C, and the steel substrate was then immersed in the plating fluid.
  • the temperature throughout the plating procedure was maintained within a range of 80-90°C.
  • the loading of substrate in the bath was maintained such that the surface area of substrate per litre of plating fluid was in the range of 0.25 - 2.5 dm 2 /litre.
  • the medium was continuously recirculated and filtered using a 1 micron filter at a rate of between 3-7 bath volumes per hour. Recirculation also acted to agitate and mix the solution. Further agitation was achieved by mild bubbling of air. [0063] At regular intervals the plating fluid was analysed for nickel concentration (using EDTA titration), hypophosphite concentration (using thiosulfate titration), and pH.
  • Nickel concentration (as nickel, as opposed to nickel sulfate) was maintained in the range of from 5.4-6.3 g/litre (92-107 mM) by addition of an appropriate amount of a 50/50 vol/vol mixture of (i) the abovementioned first nickel-containing solution and (ii) an alternative hypophosphite solution containing about three times the concentration of sodium hypophosphite present in the abovementioned first hypophosphite solution, and also containing ammonia.
  • Hypophosphite concentration (as sodium hyphophospite monohydrate) was maintained within a range of 27-33 g/litre (255-31 ImM) by addition of a suitable amount of a proprietary solution containing approximately 600 g/litre (5.7 M) sodium hypophosphite monohydrate.
  • the pH was maintained within a range of 4.8-5.2, by adding dilute ammonium hydroxide (50% v/v) or dilute sulfuric acid (10% v/v).
  • a plating rate of 8-15 ⁇ per hour is achievable, usually about 10-13 ⁇ if the initial values of pH, nickel concentration and hypophosphite concentration can be maintained.
  • the process was carried out to achieve a plating thickness of 25 ⁇ .
  • the resulting plating fluid contained 5.4 g/litre (92 mM) nickel and 20 g/litre (189 mM) sodium hyphophosphite monohydrate.
  • the pH was measured, and adjusted where necessary with dilute ammonium hydroxide (50% v/v) or dilute sulfuric acid (10% v/v) to achieve a pH of 6.4.
  • the plating medium was then heated to 85°C, and the steel substrate was then immersed in the medium.
  • the temperature throughout the plating procedure was maintained within a range of 82-91°C.
  • the loading of substrate in the bath was maintained such that the surface area of substrate per litre of plating fluid was in the range of 0.5 - 2.5 dm 2 /litre.
  • Nickel concentration (as nickel, as opposed to nickel sulfamate) was maintained in the range of from 4.6-5.7 g/L (78-97 mM) by addition of an appropriate amount of a 50/50 vol/vol mixture of (i) an alternative nickel disulfamate solution containing a lower concentration of nickel disulfamate than is present in the abovementioned second nickel- containing solution but also containing ammonia, and (ii) an alternative proprietary solution containing sodium hypophosphite (monohydrate) but no ammonia, wherein the concentration of sodium hypophosphite in the alternative proprietary solution is about 3 times the concentration in the abovementioned second hypophosphite solution.
  • Hypophosphite concentration (as sodium hyphophospite monohydrate) was maintained within a range of 18-22 g/litre (170-208 mM) by addition of a suitable amount of proprietary solution containing approximately 600 g/litre (5.7 M) sodium hypophosphite monohydrate.
  • the pH was maintained within a range of 6.0 - 6.6, by adding dilute ammonium hydroxide (50% v/v) or dilute sulfuric acid (10% v/v).
  • HV Vickers Pyramid Number.
  • HK Knoop hardness test. Tests conducted according to method ASTM E384.
  • Example 1 Even though the inner coating of Example 1 is only half that of Comparative Example 1, the corrosion resistance of the plated substrate is still high and only marginally lower than the result of a single, individual coating having twice the thickness.
  • the process of the present invention comprising two plating steps, provides unexpectedly enhanced properties which can enable a substrate to benefit, for example, from improved corrosion resistance and improved hardness/wear characteristics using thinner individual platings without detriment to either property.

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  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
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  • Chemically Coating (AREA)

Abstract

L'invention concerne un procédé de dépôt autocatalytique d'un substrat, consistant : (i) à mettre en contact un substrat avec un premier fluide de dépôt comprenant un ou plusieurs premiers métaux de dépôt en présence d'un ou de plusieurs premiers agents réducteurs en vue de former un premier dépôt sur le substrat ; et (ii) à mettre le substrat en contact avec un second fluide de dépôt comprenant un ou plusieurs seconds métaux de dépôt en présence d'un ou de plusieurs seconds agents réducteurs en vue de former un second dépôt sur le substrat ; la concentration molaire desdits premiers agents réducteurs dans le premier fluide de dépôt étant supérieure à la concentration molaire desdits seconds agents réducteurs dans le second fluide de dépôt, et/ou le rapport molaire desdits premiers agents réducteurs à un ou plusieurs premiers métaux de dépôt dans le premier fluide de dépôt étant supérieur au rapport molaire desdits seconds agents réducteurs à un ou plusieurs seconds métaux de dépôt dans le second fluide de dépôt. L'invention concerne également un substrat déposé qui peut être produit par un tel procédé.
PCT/GB2018/050866 2017-03-30 2018-03-29 Dépôt autocatalytique de couches doubles de nickel-phosphore WO2018178709A1 (fr)

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