The art of metal plating utilizes the fact that metal ions, usually Ni2+ or Cu2+, can be discharged on the cathode to give well-adhering deposits of metallic nickel, copper, etc.. In a w
Trang 226 Electrodeposition
of Polymers
26.1 Introduction 26-1 26.2 Advantages 26-1 26.3 History 26-2 26.4 Process 26-2 26.5 Equipment 26-3
26.6 Laboratory 5 References 26-5 Bibliography 26-6
26.1 Introduction
The electrodeposition of polymers is an extension of painting techniques into the field of plating and, like plating, is a dip coating process The art of metal plating utilizes the fact that metal ions, usually
Ni2+ or Cu2+, can be discharged on the cathode to give well-adhering deposits of metallic nickel, copper, etc The chemical process of deposition can be described as 1/2 Me2++ 1F (or 96,500 coulombs) of electrons gives 1/2 Me0 In the case of electrodeposition of ionizable polymers, the deposition reaction
is described as R3NH+OH–+ 1F→ R3N + H2O or the conversion of water-dispersed, ammonium-type ions into ammonia-type, water-insoluble polymers known as cathodic deposition Alternatively, a large number of installations utilize the anodic deposition process RCOO–+ H+ less 1F→ RCOOH It should
be mentioned that “R” symbolizes any of the widely used polymers (acrylics, epoxies, alkyds, etc.) The electrodeposition process is defined as the utilization of “synthetic, water dispersed, electrodepos-itable macro-ions.”1
26.2 Advantages
Metal ions, typically 1/2 Ni2+, show an electrical equivalent weight 1/2 Ni2+ equal to approximately 29.5
g, while the polymeric ions typically used for electrodeposition exhibit a gram equivalent weight (GEW)
of approximately 1600 Thus, 1F plates out of 30 g of nickel and deposits 1600 g of macroions If we
George E F Brewer*
George E F Brewer Coating Consultants
* Deceased.
DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
Throwing Power • Maintaining a Steady State • Rupture Voltage Conveyors • Metal Preparation • Tank Enclosures • Dip Tanks •
Water • Bake or Cure Rectifiers • Counterelectrodes • Agitation • Temperature Control • Ultrafilter • Paint Filters • Paint Makeup • Deionized
Trang 327 Electroless Plating
27.1 Introduction 27-1 27.2 Plating Systems 27-2 27.3 Electroless Plating Solutions 27-3
27.4 Practical Applications 27-4 27.5
27.6 Stability of Plating Solutions 27-7 27.7 Electroless Plating 27-7
References 27-11
27.1 Introduction
In electroless plating, metallic coatings are formed as a result of a chemical reaction between the reducing agent present in the solution and metal ions The metallic phase that appears in such reactions may be obtained either in the bulk of the solution or as a precipitate in the form of a film on a solid surface Localization of the chemical process on a particular surface requires that the surface must serve as a catalyst If the catalyst is a reduction product (metal) itself, autocatalysis is ensured, and in this case, it
is possible to deposit a coating, in principle, of unlimited thickness Such autocatalytic reactions constitute the essence of practical processes of electroless plating For this reason, these plating processes are sometimes called autocatalytic
Electroless plating may include metal plating techniques in which the metal is obtained as a result of the decomposition reaction of a particular compound; for example, aluminum coatings are deposited during decomposition of complex aluminum hydrides in organic solvents However, such methods are rare, and their practical significance is not great
In a wider sense, electroless plating also includes other metal deposition processes from solutions in which an external electrical current is not used, such as immersion, and contact plating methods in which another more negative (active) metal is used as a reducing agent However, such methods have a limited application; they are not suitable for metallization of dielectric materials, and the reactions taking place are not catalytic Therefore, they usually are not classified as electroless plating
Electroless plating now is widely used in modifying the surface of various materials, such as noncon-ductors, semiconnoncon-ductors, and metals Among the methods of applying metallic coatings, it is exceeded
in volume only by electroplating techniques, and it is almost equal to vacuum metallization
Electroless plating methods have some advantages over similar electrochemical methods These are as follows:
A Vakelis
Lithuanian Academy of Sciences
DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
Deposition Rate • Solution Life • Reducing Agent Efficiency
Copper Deposition • Nickel Plating • Cobalt, Iron, and Tin Factor • Solution Sensitivity to Activation
Plating • Deposition of Precious Metals • Deposition of Metal
Mechanisms of Autocatalytic Metal Ion Reduction 27-5
Alloys
Trang 427-6 Coatings Technology Handbook, Third Edition
A more versatile explanation of the causes of catalysis in these processes is based on electrochemical reactions It is suggested that reducing agents are anodically oxidized on the catalyst surface and the electrons obtained are transferred to metal ions, which are cathodically reduced The catalytic process comprises two simultaneous and mutually compensating electrochemical reactions In this explanation
of the catalytic process, electrons are the active intermediate product However, electrons are fundamen-tally different from the conversational intermediate products of reactions They may be easily transferred along the catalyst without transfer of the mass, and for this reason, the catalyst reaction, contrary to all other possible mechanisms (which are conventionally called “chemical mechanisms”), occurs not as a result of direct contact between the reactants, or the reactants, or the reactant and an intermediate substance, but because of the exchange of “anonymous” electrons via metal
On the metal surface, when anodic oxidation of the reducer
(27.2) and cathodic reduction of metal ions
(27.3) proceed simultaneously, a steady state in the catalytic system of electroless plating is obtained, in which the rates of both electrochemical reactions are equal, while the metal catalyst acquires a mixed potential
Em The magnitude of this potential is between the equilibrium potentials Ec of the reducer and of the metal The specific value Em depends on the kinetic parameters of these two electrochemical reactions Electrochemical studies of catalytic metal deposition reactions have shown that the electrochemical mechanism is realized practically in all the systems of electroless plating.4,6,7
At the same time, it has become clear that the process is often not so simple It appears that anodic and cathodic reactions occurring simultaneously often do not remain kinetically independent but affect each other For example, copper ion reduction increases along with anodic oxidation of formaldehyde.8
The cathodic reduction of nickel ions and the anodic oxidation of hypophosphite in electroless nickel plating solutions are faster than in the case in which these electrochemical reactions occur separately This interaction of electrochemical reactions probably is related to the changes in the state of the metal–catalyst surface
Electrochemical reactions may also hinder each other: for example, in reducing silver ions by hydrazine from cyanide solutions, their rate is lower than is separate Ag–Ag(1) and redox systems
The electrochemical nature of most of the autocatalytic processes discussed enables us to apply electrochemical methods to their investigation But, they must be applied to the entire system of electroless plating, without separating the anodic and cathodic processes in space One suitable method is based on the measurement of polarization resistance It can provide information on the mechanism of the process and may be used for measuring the metal deposition rate (both in laboratory and in industry).9 The polarization resistance Rp is inversely proportional to the process rate i:
(27.4)
(27.5)
where ba and bc are Tafel equation coefficients (b ≈ 1/αnf), α is the transfer coefficient, n is the number
of electrons taking part in the reaction for one molecule of reactant, and f=F/RT (F= Faraday number)
Red→Ox ne+
Men++ ne
= +
a c
p( a c)
di i
p=
=0
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Trang 527-12 Coatings Technology Handbook, Third Edition
13 G Gawrilov, ChemischelStromläse/Vernickelung Saulgau, Wurt.: Eugen Leuze Verlag, 1974.
14 K M Gorbunova et al., Fiziko-Khimichesklye Osnovy Processa Khimicheskogo Kobaltirovaniya.
Moscow: Nauka, 1974
15 A Molenaar and J J C Coumans, Surface Technol., 16, 265 (1982).
16 Y Okinaka, in Gold Plating Technology, H Reid and W Goldie, Eds Hatch End, Middlesex, England:
Electrochemical Publications, Ltd., 1974, p 82
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Trang 628 The Electrolizing
Thin, Dense, Chromium Process
28.1 General Definition 28-1 28.2 Applications 28-2 28.3
28.4 Solution 28-5 28.5 Properties 28-5
28.1 General Definition
The Electrolizing process uniformly deposits a dense, high chromium, nonmagnetic alloy on the surface
of the basic metal being treated The alloy used in Electrolizing provides an unusual combination of bearing properties: remarkable wear resistance, an extremely low coefficient of friction, smooth sliding properties, excellent antiseizure characteristics, and beneficial corrosion resistance Electrolized parts perform better and last up to 10 times longer than untreated ones
The solution and application processes are carefully monitored at all Electrolizing facilities The result
is a fine-grained chromium coating that is very hard, thin, and dense and has absolute adhesive qualities The Electrolizing process deposits a 99% chromium coating on the basis metallic surfaces, whereas normal conventional chromium plating processes tend to deposit 82 to 88% chromium in most applications Electrolizing calls for the cleaning and removal of the matrix on the basis metal’s surface by multi-cleaning process, using a modified electrocoating process that causes the chromium metallic elements of the solution to bond to the surface porosity of the basis metal It is during this process that the absolute adhesive characteristics and qualities of Electrolizing are generated The Electrolizing coating will not flake, chip, or peel off the basis metal substrate when conventional ASTM bend tests and impact tests are performed Three basic factors are always present after applying Electrolizing to metal surfaces:
• Increased wear (Rockwell surface hardness of 70 to 72 Rc)
• Added lubricity characteristics
• Excellent corrosion resistance
Michael O’Mary
The Armoloy Corporation
DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
General • Specific
Thickness • Adhesion • Corrosion • Wear Resistance (Surface Hardness) • Lubricity • Conformity • Heat Resistance •
Surface Preparation 28-4
Brightness • Hydrogen Embrittlement
Trang 7The Electrolizing Thin, Dense, Chromium Process 28-3
• Automotive
• Business machines
• Cameras and projectors
• Computers
• Cryogenics
• Data processing
• Electronics
• Food processing
• Gauges and measuring equipment
• Medical instruments
• Metalworking
• Molds (plastic and rubber)
• Motor industry
• Nuclear energy
• Pharmaceutical
• Photography (motion and still)
• Refrigeration
• Textile industry
• Transportation
Specifically, Electrolizing is approved and meets the following aerospace, nuclear, and commercial specifications:
• Air Research Company, Garrett, CO
• American Can Company
• AMS 2406
• AMS 2438
• AVCO Lycoming — AMS 2406
• Bell Helicopter
• Bendix Company
Utica, NY, division
Teterboro, NJ, division
Kansas City, MO, division
South Bend, IN, division
• Boeing
BAC 5709 Class II, Class IV
QQC 320
• Cleveland Pneumatic Tool-CPC Specs (Chromium), QQC320
• Colt Industries
Menasco, TX, division
• DuPont
• Fairchild Camera
• Fairchild Republic
• General Dynamics
• General Electric
Lynn, MA
Cincinnati, OH (aircraft)
Wilmington, MA
Wilmington, NC (nuclear)
Fitchburg, MA
• Gillette Company, Boston
• Grumman Aircraft
DK4036_book.fm Page 3 Monday, April 25, 2005 12:18 PM
Trang 829 The Armoloy Chromium Process
29.1 General Definition 29-1 29.2 Applications 29-1 29.3 Surface Preparation 29-2 29.4 Properties 29-2
29.1 General Definition
The Armoloy process is a low temperature, multistate, chromium alloy process of electrocoating based
on a modified chromium plating technology However, instead of the customary chromium plating solutions, the Armoloy process uses a proprietary chemical solution The solution and application process are carefully monitored at all Armoloy facilities The result is a satin finish chromium coating that is very hard, thin, and dense and has absolute adhesive qualities Armoloy deposits a 99% chromium coating o the basis metallic surfaces, whereas conventional chromium plating processes tend to deposit 82 to 88% chromium in most applications
The Armoloy process involves cleaning and removing the matrix on the basis metal’s surface by special proprietary means and using a modified electrocoating process that causes the chromium metallic elements of the solution to permeate the surface porosity of the basis metal It is during this process that the absolute adhesive characteristics and qualities of Armoloy are generated The Armoloy coating actually becomes part of the basis metal itself, and the result is a lasting bond and a continuous, smooth, hard surface The surface will not chip, flake, crack, peel, or separate from the basis metal under conditions
of extreme heat or cold, or when standard ASTM bend tests are involved
Three basic factors are always present after applying Armoloy to metal surfaces:
• Increased wear (70 to 72 Rc surface hardness)
• Added lubricity characteristics (including the ability to utilize Armoloy against Armoloy)
• Excellent corrosion resistance
29.2 Applications
29.2.1 General Applications
All ferrous and most nonferrous materials are suitable for Armoloy application Service life of parts has been increased to 10 times normal life and even higher in certain applications However, basis metals of aluminum, magnesium, and titanium are not good candidates for the Armoloy process
Michael O’Mary
The Armoloy Corporation
DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
General Applications • Specific Applications
Thickness • Adhesion • Corrosion • Wear Resistance • Lubricity •
Embrittlement Conformity • Heat Resistance • Brightness • Hydrogen
Trang 9The Armoloy Chromium Process 29-5
The plating cycle times are very short, and the Armoloy chrome is deposited so rapidly that Armoloy seals the surface porosity of the basis metal before hydrogen ions can invade the surface of the basis metal However, if required, Armoloy can be and will be postplate heat treated to specification
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Trang 1030 Sputtered Thin Film Coatings
30.1 History 30-1 30.2 General Principles of Sputtering 30-1 30.3 Sputter Deposition Sources 30-3
30.4 Other Process Considerations 30-8 30.5 Properties of Sputtered Thin Film Coatings 30-8 30.6 Thin Film Materials 30-9 30.7 Applications for Sputtered Thin Films 30-9
30.8 Additional Resources 30-10 Bibliography 30-10
30.1 History
Sputtering was discovered in 1852 when Grove observed metal deposits at the cathodes of a cold cathode glow discharge Until 1908 it was generally believed that the deposits resulted from evaporation at hot spots on the cathodes However, between 1908 and 1960, experiments with obliquely incident ions and sputtering of single crystals by ion beams tended to support a momentum transfer mechanism rather than evaporation Sputtering was used to coat mirrors as early as 1887, finding other applications such
as coating fabrics and phonograph wax masters in the 1920s and 1930s The subsequent important process improvements of radio frequency (rf) sputtering, allowing the direct deposition of insulators, and mag-netron sputtering, which enables much higher deposition rates with less substrate damage, have evolved more recently These two developments have allowed sputtering to compete effectively with other physical vapor deposition processes such as electron beam and thermal evaporation for the deposition of high quality metal, alloy, and simple organic compound coatings, and to establish its position as one of the more important thin film deposition techniques
30.2 General Principles of Sputtering
Sputtering is a momentum transfer process When a particle strikes a surface, the processes that follows impact depend on the energy of the incident particle, the angle of incidence, the binding energy of surface
In sputtering, the incident particles are usually ions, because they can be accelerated by an applied electrical potential If the kinetic energy with which they strike the surface is less than about 5 eV, they
Brian E Aufderheide
W H Brady Company
DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
Direct Current Diode Sputtering • Triode Sputtering • Radio
Electrical • Magnetic • Optical • Mechanical • Chemical •
Decorative
Frequency Sputtering • Magnetron Sputtering • Beam Sputtering • Reactive Sputtering
atoms, and the mass of the colliding particles (Figure 30.1)