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Electroless deposition

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Electroless deposition (ED) or electroless plating is a chemical process by which metals and metal alloys are deposited onto an surfaces.[1][2] The surfaces include plastics, ceramics, and glass, etc. ED-produced films can decorative, anti-corrosive, and conductive. Common applications of ED are for nickel- and silver-containing films/mirrors.[3]

Electroless deposition changes the mechanical, magnetic, internal stress, conductivity, and brightening of the substrate.[1][4] The first industrial application of electroless deposition by the Leonhardt Plating Company electroless deposition has flourished into metallization of plastics.,[1][5][6] textiles,[7] prevention of corrosion,[8] and jewelry.[1] The microelectronics industry including the manufacturing of circuit boards, semi-conductive devices, batteries, and sensors.[1]

Comparison with other methods

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Electroplating is generally cheaper than ED.[9] Unlike ED, electroplating only deposits on other conductive or semi-conductive materials. Requiring an applied current, the instrumentation for electroplating is more complex.[4] Electroless deposition deposits metals onto 2D and 3D structures, whereas other plating methods such as Physical vapor deposition (PVD), Chemical Vapor Deposition (CVD) are limited to 2D surfaces.[10] Electroless deposition is advantageous in comparison to PVD, CVD, and electroplating deposition methods because it can be performed at ambient conditions.[4]

Nickel-plated parts produced by electroless deposition.

History

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The discovery of electroless deposition is attributed to Charles Wurtz who, in 1846, noticed a nickel-phosphorous solution spontaneously formed a black powder. 70 years later François Auguste Roux rediscovered the electroless deposition process and patented it in United States as the 'Process of producing metallic deposits'.[11] Roux deposited nickel-posphorous (Ni-P) electroless deposition onto a substrate but his invention went uncommercialized.[12][11] In 1946 the process was re-discovered by Abner Brenner and Grace E. Riddell while at the U.S. National Bureau of Standards.[11][13][14] They presented their discovery at the 1946 Convention of the American Electroplaters' Society (AES); a year later, at the same conference they proposed the term "electroless" for the process and described optimized bath formulations,[15] that resulted in a patent.[15][16][17] However, neither Abner nor Riddell benefited financially from the filed patent.[18] Deposition of Ni-P was commerciallized by Leonhardt Plating Company in Cincinnati followed by the Kannigen Co. Ltd in Japan, with revolutionary impact.[12][1] The Leonhardt company designed and patented of several deposition baths including plating of metals such as Pt, Sn, Ag, and their alloys.[11][17]

The Tollens' reaction is often used in scientific demonstrations of ED. Tollen's reagent deposits a reflective metallic silver layer on glass, thus its reference as silvering mirrors.[19][20] This reaction was once used to test for aldehydes in a basic solution of silver nitrate.[19]

Preparation and bath

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The ED process can be analyzed as four steps:[1]

  1. Pretreatment or functionalization of the substrate cleans the surface of the substrate to remove any contaminants which affects nanoparticle size and poor plating occurs. Pretreatment determines the porosity of the elemental metal deposition, and the initiation site of elemental deposition.[1][21]
  2. Sensitization is an activator ion that can reduce the active metal in the deposition bath giving catalytic sites for the further deposition ("templation").[1][21]
  3. Activation accelerates the deposition by acting as a catalytic seed on the substrate surface for the final electroless deposition bath metal.[1][21]
  4. Electroless deposition is the process by which metal cation is reduced to elemental metal with a powerful reducing agent.[1][21]
Steps in electroless deposition process

A typical electroless deposition bath consists of many components:

  1. A source of metal cation which is provided by a metal salt (e.g.. Cu2+ from CuSO4 and Ni2+ from NiCl2). The metal salts as their hydrate are first dissolved in the bath.[4] Typical concentrations of metal salt are 30 g/L.[3]
  2. Reducing agent (or reductant), which donates electrons to the metal cation. Common reducing agents include formaldehyde, sodium borohydride, glucose, sodium hypophosphite, [[[hydrogen peroxide]], and ascorbic acid.[1][4]
  3. Other reagents, many in fact, are added to modify the rate of deposition and the nature of the resulting films. Some provide buffering action, others are "stabilizers" to control the rate of deposition. Surfaces are prepared for ED by sensitization", often with a pretreatment of stannous chloride.

Process

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From the perspective of thermodynamics, the process is governed by the Nernst equation: E is the potential of the reaction, E0 is the standard reduction potential of the redox reaction, and Q is the concentration of the products divided by the concentration of the reactants .

The rate of deposition is determined by the kinetics of the autocatalysis, i.e. the efficiency at which the initially deposited islands of metal (or alloy) facilitate the further reduction of the metal salts. In a nickel chloride-sodium hypophosphite bath at 90 °C, the deposition rate is 15 mm/h.[3]

The reducing power of reagents is pH dependent. At pH 0, the E0 of formaldehyde is 0.056 V, but at pH=14 the E0=-1.070.[22] The formaldehyde (pH 14) is a more suitable reducing agent than at pH=0 because of the lower negative standard potential which makes it a powerful reducing agent.[21] The potential dependence on pH is described by the Pourbaix Diagram.

Deposition mechanisms

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Several mechanisms for ED have been discussed.[4][1][12] In the case of nickel hypophosphorous acid, the following summarizes the net equation:

Ni2+ + 2 H2PO−2 + 2 H2O → Ni + H2 + 2 H3PO3

Applications

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Main article: Electroless nickel-phosphorus plating

Mirrors

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Mirrors for furniture, astronomy, and solar collectors, are produced by silvering using ED. A typical precursor is and ammoniacal solution of silver nitrate as the metal source and glucose or hydrazine as the reducing agent.[23]

Catalysts

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Platinum-based catalysts are widely used in fuel cells for hydrogen production, methanol oxidation, and oxygen reduction. Many catalysts have been produced by ED, e.g. from platinum halides and using hydrazine. Platinum salts even moreso than nickel salts are easily reduced in an electrochemical sense, so they are suited for ED.[24]

Metallization of plastics by electroless deposition

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Plastics are typically metallized by nickel-phosphorus, nickel gold, nickel-boron, palladium, copper, and silver.[5] Metallized plastics are used to lower the weight of metal product and minimize the cost associated with the use of precious metals.[25] Electroless nickel plating is used in variety of industries including aviation, construction, textiles, and oil and gas industries.[26]

Electromagnetic interference shielding

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Electromagnetic interference shielding (EMI shielding) refers to the process by which devices are protected from interference from the electromagnetic radiation.[4][27] The interference negatively affects the function of the devices; EMI sources include radiowaves, cell phones, and TV receivers.[4][27] The Federal Aviation Administration and the Federal Communications Commission prohibit the use of cellphones after an airplane is airborne to avoid interference with navigation.[28][29] Elemental Ni, Cu, and Ni/Cu coating on planes absorb noise signals in the 14 Hz to 1 GHz range.[4]

Oil and gas production

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Elemental nickel coating prevents corrosion of the steel tubulars used for drilling.[4] At the core of this industry nickel coats pressure vessels, compressor blades, reactors, turbine blades, and valves.[4]

Schematic of oil rig setup. The steel tubulars are covered with elemental Ni which slows the rate of corrosion. Sections 25, 26, and 27 are examples of where an elemental nickel coating would overlay the steel.

See also

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References

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  1. ^ a b c d e f g h i j k l m Modern electroplating. Milan Paunovic, Mordechay Schlesinger (5 ed.). Hoboken, NJ: Wiley. 2010. ISBN 978-0-470-16778-6. OCLC 792932606.{{cite book}}: CS1 maint: others (link)
  2. ^ "ASM handbook | WorldCat.org". www.worldcat.org. Retrieved 2023-02-24.
  3. ^ a b c Durney, Lawrence J. (2000). "Electrochemical and Chemical Deposition". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a09_125. ISBN 978-3-527-30385-4.
  4. ^ a b c d e f g h i j k G. O. Mallory and J. B. Hajdu, editors (1990): Electroless Plating: Fundamentals and applications. 539 pages. ISBN 9780936569079
  5. ^ a b Viswanathan, B. (1994), "Metallization of Plastics by Electroless Plating", Microwave Materials, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 79–99, doi:10.1007/978-3-662-08740-4_3, ISBN 978-3-662-08742-8, retrieved 2023-02-22
  6. ^ Krulik, G. A. (1976). "Electroless plating of plastics". Journal of Chemical Education. 55 (6): 361. doi:10.1021/ed055p361. ISSN 0021-9584.
  7. ^ Jiang, S. Q.; Newton, E.; Yuen, C. W. M.; Kan, C. W. (2006). "Chemical Silver Plating on Cotton and Polyester Fabrics and its Application on Fabric Design". Textile Research Journal. 76 (1): 57–65. doi:10.1177/0040517506053827. ISSN 0040-5175. S2CID 137801241.
  8. ^ Telegdi, J.; Shaban, A.; Vastag, G. (2018), "Biocorrosion—Steel", Encyclopedia of Interfacial Chemistry, Elsevier, pp. 28–42, doi:10.1016/b978-0-12-409547-2.13591-7, ISBN 978-0-12-809894-3, retrieved 2023-02-22
  9. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 514. ISBN 978-0-08-037941-8.
  10. ^ Siddikali, Palaiam; Sreekanth, P. S. Rama (2022-08-18). "Performance Evaluation of CNT Reinforcement on Electroless Plating on Solid Free-Form-Fabricated PETG Specimens for Prosthetic Limb Application". Polymers. 14 (16): 3366. doi:10.3390/polym14163366. ISSN 2073-4360. PMC 9415912. PMID 36015623.
  11. ^ a b c d Charles R. Shipley Jr. (1984): "Historical highlights of Electroless plating". Plating and Surface Finishing, volume 71, issue 6, pages 24-27. ISSN 0360-3164
  12. ^ a b c Zhang, B. (2016). Amorphous and Nano Alloys Electroless Depositions. Washington State University Pullman.
  13. ^ Ferrar, W. T.; O'Brien, D. F.; Warshawsky, A.; Voycheck, C. L. (1988). "Metalization of lipid vesicles via electroless plating". Journal of the American Chemical Society. 110 (1): 288–289. doi:10.1021/ja00209a046. ISSN 0002-7863.
  14. ^ "Annual Convention of the American Society of Civil Engineers". Scientific American. 64 (23): 352–353. 1891-06-06. doi:10.1038/scientificamerican06061891-352. ISSN 0036-8733.
  15. ^ a b "Reports of committees: Annual Meeting". Proceedings of the American Society of International Law at Its Annual Meeting. 41: 163–165. 1947. doi:10.1017/s0272504500101861. ISSN 0272-5045.
  16. ^ Brenner, A.; Riddell, G.E. (1946). "Nickel plating on steel by chemical reduction". Journal of Research of the National Bureau of Standards. 37 (1): 31. doi:10.6028/jres.037.019. ISSN 0091-0635.
  17. ^ a b "Coalescers". Metal Finishing. 107 (11): 52. 2009. doi:10.1016/s0026-0576(09)80396-6. ISSN 0026-0576.
  18. ^ "Reminiscences of Early Electroless Plating". www.pfonline.com. 6 April 2018. Retrieved 2023-02-16.
  19. ^ a b Benet, William E.; Lewis, Gabriella S.; Yang, Louise Z.; Hughes, D. E. Peter (2011). "The Mechanism of the Reaction of the Tollens Reagent". Journal of Chemical Research. 35 (12): 675–677. doi:10.3184/174751911X13206824040536. ISSN 1747-5198. S2CID 101079977.
  20. ^ Tollens, B. (1882). "Ueber ammon‐alkalische Silberlösung als Reagens auf Aldehyd". Berichte der Deutschen Chemischen Gesellschaft. 15 (2): 1635–1639. doi:10.1002/cber.18820150243. ISSN 0365-9496.
  21. ^ a b c d e Afzali, Arezoo; Mottaghitalab, Vahid; Motlagh, Mahmood Saberi; Haghi, Akbar Khodaparast (2010-07-01). "The electroless plating of Cu-Ni-P alloy onto cotton fabrics". Korean Journal of Chemical Engineering. 27 (4): 1145–1149. doi:10.1007/s11814-010-0221-8. ISSN 1975-7220. S2CID 55179900.
  22. ^ Cotell, C.M.; Sprague, J.A.; Smidt, F.A., eds. (1994), "Electroless Copper Plating", Surface Engineering, ASM International, pp. 311–322, doi:10.31399/asm.hb.v05.a0001265, ISBN 978-1-62708-170-2, OSTI 872041, retrieved 2023-02-23
  23. ^ Schiller, Matthias (2014). "Mirrors". Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–7. doi:10.1002/14356007.a16_641.pub2. ISBN 978-3-527-30673-2.
  24. ^ Chen, Aicheng; Holt-Hindle, Peter (2010). "Platinum-Based Nanostructured Materials: Synthesis, Properties, and Applications". Chemical Reviews. 110 (6): 3767–3804. doi:10.1021/cr9003902.
  25. ^ "Pretreatment for the metallzation of polymers/ plastics". Fraunhofer Institute for Applied Polymer Research. Retrieved 2023-02-15.
  26. ^ Electro-Coating. "Differences & Advantages Between Electroplating & Electroless Plating | Electro-Coating". www.electro-coatings.com. Retrieved 2023-02-24.
  27. ^ a b "What is EMI Shielding and Why is it Important for Your Design?". www.modusadvanced.com. Retrieved 2023-02-22.
  28. ^ "Portable Electronic Devices". www.faa.gov. Retrieved 2023-02-22.
  29. ^ "47 CFR § 22.925 - Prohibition on airborne operation of cellular telephones". LII / Legal Information Institute. Retrieved 2023-02-22.
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