A Research Report On ELECTROLESS Ni PLATING On Mild Steel 69
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A Research Report On
Electroless Nickel Plating
Of Mild Steel
Submitted To
Faculty Of Engg & Tech
University Of Punjab, Lahore
For The Partial Fulfillment Of The Requirements For
The Bachelor Of Science (Engg) In
Metallurgy & Material Science (MMS)
Session 2001 – 2005
Submitted By
Asim Munir 01E810
Muhammad Ali 01E811
M.Junaid Hassan 01E813
Faculty Of Engineering & Technology University Of Punjab
Lahore
Abstract
Electroless deposition (chemical plating) has become an established industrial technique and gained increasing importance at present. By such means not only pure metals but also alloys can be deposited on ferrous and non-ferrous materials to improve their surface characteristics. By using appropriate pee- plate treatment methods, a wide range of plastics and ceramics can also be plated by electroless methods. These processes have particular advantages in the field where galvanic processes can only be used at great expense or where they fail completely.
Electroless Ni plating has undergone a major change over the last decade. As a means of overcoming problems associated with corrosion or abrasive wear and for metallising of non – conductive materials, this is an expanding technology.
In the present research work effect of bath composition, pH of the bath, time & temperature effects on Electroless nickel coating and post heat treatment on low carbon steel (Mild Steel) strip specimen was investigated. The main emphasis was carried out on the thickness of coating affected by immersion time. It was found that coating thickness increase linearly with increase of the time nearly to a min value of 64 microns after 300 minutes of immersion.
The post plating heat treatment or the coated specimen resulted in increase in hardness.
Contents
Chapter No 1 Introduction
Chapter No 2 Fundamentals of Electroless Ni Plating
Chapter No 3 Properties
Chapter No 4 Applications
Chapter No 5 Experimental Work
Chapter No 6 Results & Discussions
Bibliography
ACKNOWLEDGMENT
This research thesis would never been completed but, for the benevolence,
Compassion and mercifulness of the Almighty, omnipresent Allah, Whose
Blessings are yearned by all of us.
We owe heavy debt of gratitude to PROF. DR. Javaid Ahmad
Principle Collage Of Engg & Emerging tech and PROF. Dr. TAQI ZAHID
Butt, DR RAFIQ AHMED & DR ABDUS SALAM Senior Professor
MMS Faculty Of Engg & Tech P.U Lahore For their Kindness, Carefulness,
Encouragement, and for the provision of necessary departmental Facilities.
We wish to express our deep gratitude and sincere thanks to our
Project supervisor Mr Mohsin Ali Raza faculty of Engg & Tech University
Of the Punjab for his patient advice, valuable guidance, encouragement and
Technical discussions during the course of the course of the present research
Work.
Authors
INTRODUCTION
Metal deposition concerns with the development and applications of processes and plants for the deposition of metals. In the main these metals are deposited on the metallic substrates. However, by the appropriate pretreatment methods, a wide range of plastic can also be metallised by using electroless baths.
The great strength of metal deposition lies in its ability to transform a substrate material, which is really suitable for a given task, by coating it with a metal, which is. It thus offers a means for providing a surface, which is adequate for a wide range of duties.
Two of the most important functions of deposited coatings are to provide protection against corrosion and abrasive wear. The corrosion and wear of industrial machinery and plant are major sources of loss in national economy. Not only do they reduce the life of such equipment and increase the amounts of downtime but they also have implications in terms of maintenance costs and expenditure on replacement parts.
The alternative strategy to avoid the use of low cost materials of construction is not only expensive but can also involve materials which are less easy to work.
For these reasons electroless deposition is of industrial importance mainly for copper, nickel and certain nickel base alloys. Of lesser importance is the electroless deposition of cobalt, tin, silver and gold.
As estimated of the market for electroless nickel in the world by Clerault offers a following data for year 1985 to 1987.
Table 1.1 Consumption of Electroless Plating in World
Name of countries / Tonnage per annumWest Germany / 100
United Kingdom / 110
Italy / 60
Benelux / 20
France / 30
USA / 600
For the period 1982 to 1984, the following break down of the market application has been made.
Table 1.2 percentage of Electroless Plating in different industries.
Industry / Break downElectrical, electronics / 23
Oil an gas industry / 15
Machinery / 10
Aerospace / 10
Motor industry / 12
Chemical and foodstuff industry / 10
Textile and printing industry / 10
Others / 10
The high annual rate of market expansion of 15 percent is explained in the following terms.
1. The development, in recent years of electroless nickel formulations with properties superior to so-called “first and second generation” coatings.
2. New thinking in terms of corrosion and wear protection. Protection of materials as apposed to throwing these away is increasingly the watchword.
3. New applications such as coatings of ceramics or glass and shielding against electromagnetic radiation, using electroless nickel and copper.
For all these reasons electroless nickel continues to be a surface coating of increasing importance in industrial applications today.
1.1 BRIEF HISTORY
The history of electroless plating dates back to 1844 when Wurtz found that metallic Nickel powder could be obtained by reduction of its salt with hypophosphite. In 1911 F. Roux registered a patent but it was not used. In 1946 Brenner and Riddle devised an acidic electroless Ni plating process. In 1955 GATC (General American Transport Corporation) developed and patented Kanigen Process as a hot caustic proof linear to transport containers. In this process hypophosphite was used as a reducing agent.
From 1950-1970 other reducing baths were developed using borohydride and hydrazine as substitutes to hypophosphite.
Electroless Nickel composite deposits have also been developed to enhance the desired properties of the electroless Nickel.
1.2 DIFFERENCE BETWEEN ELECTROLESS AND ELECTROPLATING
1.2.1 ELECTROLYTIC PROCESS
The electrolytic deposition of metals is based on the cathodic discharge of metal ions during the electrolysis of metal salt solution; metal ions are reduced to the parent metal at cathode, which acts as an electron source, the anode serving as sink for electrons. The electrons required are produced from an external current source. At the cathode, the over all chemical reactions is:
Me z+ +ze Me
When soluble anodes are used, the reverse process occurs:
Me Me z+ +ze
It is important to note that, in the case of cathodic deposition of metals from aqueous solutions, the better is often not present as a simple hydrated ion, but rather as an ionic complex.
1.2 ELECTROLESS (AUTOCATALYTIC) PROCESS
In the case of electroless deposition processes, the electrons required to bring about the discharged of metal ions are produced by a chemical reaction in solution. Strictly speaking, there fore, there is no such thing as electroless metal deposition and the process should be described as one not requiring external current supply or as a “chemical” deposition method.
According to Gawrilov, all electroless deposition processes can be classified under the following three headings.
1. Deposition by ion exchange are charge exchange (displacement reaction, cementation, immersion plating).
2. Deposition by contacting the metal to be coated, immersed in a solution of metal salt to be deposited, with a second metal.
3. Deposition of metal from solutions containing reducing agents. The chemical reaction can be represented as:
Me1 Me1 z+ + ze
Me2 z+ +ze Me2
In case of ion exchange process the base metal is itself the reducing agent.
The true electroless or “chemical” metal deposition processes are those capable of being used in place of Electro deposited coatings in that they permit a continuous metal deposition. Such deposits form only on certain catalytically active surfaces (auto catalytic deposition). The electrons needed to reduced the metal ions are provided by the reducing agents Rn+ which surrender z electrons, themselves being oxidized to R(n+z). The equations for this are.
R n+ R((n+z)) ze
Me z+ + ze Me
FUNDAMENTAL
OF ELECTROLESS PLATING
2.1 ELECTROLESS NICKEL PLATING
Electro less nickel plating is used to deposit nickel without the use of an electric current. The coating is deposited by an autocatalytic chemical reduction of nickel ions by hypophosphite, aminoborane, or borohydride compounds.
Currently, hot hypophosphite reduced bath are most frequently used to plate steel and other metals, whereas warm alkaline hypophosphite bath are used for plating Nonmetals.
2.2 APPLICATIONS
(1) Electro less nickel is an engineering coating normally used because of excellent corrosion and wear resistance.
(2) Electro less nickel coating are also frequently applied on aluminum to provide a solder able surface and are used with moulds and dies to improve lubricity and part release. Because of those properties, electroless nickel coatings have found many applications including those in petroleum, chemical, plastics, optics, printing, mining, aerospace, nuclear, automotive, electronic, computers, textiles, paper, and food machinery some advantages and limitations of electro less nickel plating are briefly mentioned below:
2.3 ADVANTAGES
· Good resistance to corrosion and wear
· Excellent uniformity
· Solder ability and bras ability
· Low labor costs
2.4 LIMITATIONS
· High chemicals cost
· Brittleness
· poor welding characteristics of nickel phosphorus deposits need to copper strike plate alloys containing significant amount of lead, tin; cadmium, and zinc before electro less nickel can be applied
· Slower plating rate, as compared to electrolytic methods.
Electroless nickel plating is not a new process. Until recently, it's primarily been busy in the electronics industry. The metal finishing industry worldwide is predicting a huge upsurge in the application of electroless coatings. Electro-less Nickel plating is a process that has many advantages over 'electrolytic' processes in an engineering environment. The coating can be used in many fields where a hard, corrosion resistant finish is required. A major advantage of the process is that it is possible to coat the whole surface of an item EVENLY, including internals, unlike electrolytic processes which have difficulty depositing into recessed and internal areas and can result in excessive build-ups on points, corners, etc.
This process can provide significant savings when comparing to a process such as Hard Chrome on a complex shape as the article can be machined to shape prior to coating (with an allowance for the plating thickness) and would not require any post machining to regain the required precise dimensions. To create an internal coating by electrolytic methods requires the use of complex anode arrangements, which are generally costly to produce, and set-up, with these costs being passed on.
It is possible to achieve deposits of electro-less nickel into internal areas where it would be impossible to use electrolytic methods and is cost competitive over the less satisfactory methods.
Example – Injection molding die. Machined to spec with allowance for several microns electro-less nickel. Die is plated and put straight to work – no post plating machining required. The resulting surface has significantly more lubricity than the original steel – so parts release more efficiently. The die is protected from corrosion when stored – resulting in minimal maintenance costs. The die is also protected when in production and subject to water cooling – resulting in less corrosion problems
Other advantages of Electroless Nickel include:
Lubricity - it is able to slide over other metal surfaces without galling.
Hardness - there are various types of solutions giving a variety of as plated harnesses.
Heat treatment increases the hardness to a maximum of approx.70
Rockwell HRc
Corrosion Resistance - dependant upon solution used (Neutral Salt Spray @ 25µm)
Resistant to a wide range of chemicals
Abrasion Resistance - good to excellent dependent upon solution used and hardening
Mould Release - a good non-stick surface in many applications
Additives - such as Teflon or Silicon Carbide can be included into the deposit to further increase the properties such as lubricity and wear resistance
Stainless Steel Alternative - parts can be manufactured from Mild Steel and coated with electroless nickel to provide similar performance to stainless steel at a much lower cost.
2.5 BATH COMPOSITION AND CHHARACTERISTICS
Electro less nickel coatings are produce by the controlled chemical reduction of nickel ions onto a catalytic surface. The deposit itself is catalytic to reduction, and the reaction continues as long as the surface remains in compact with the electro less nickel solution. Because the deposit is applied without an electric current, its thickness is uniform on all area of article in contact with fresh solution.
Electro less nickel solution are blend of different chemicals, each performing an important function. Electroless nickel solution contains:
· A source of nickel, usually nickel sulfate.
· A reducing agent to supply electron for the reduction of nickel.
· Energy (heat)
· Complexing agent (chelators) to control the free nickel available to the reaction.
· Buffering agent to resist the PH changes caused by the hydrogen released during deposition.
· Accelerators (exultant) to help increase the speed of the reaction
· Inhibitors (stabilizers) to help control reduction by products
· The characteristics of an electroless nickel bath and its deposit are determined by the composition of these components.
2.5.1 REDUCING AGENT
A number of different reducing agents have been used in preparing electroless nickel baths, including (a) sodium hypophosphite, (b) aminoboranes (c) sodium borohydride, and (d) hydrazine.