0401227343

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NAME=DEBLEENA SAHA REGD NO = 0401227343

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METAL FINISHING ANDELECTRPOLATING

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TABLE OF CONTENTS

1. INTRODUCTION

2. HISTORY OF ELECTROPLATING

3. PURPOSE OF ELECTROPLATING

4. TREATMENT TECHNOLOGY OFELECTROPLATING

5. ELECTRICAL RELATIONSHIPS

6. ENVIRONMENTAL IMPLICATIONS

7. APPLICATION

8. CONCLUSION

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INTRODUCTION

Electroplating is the application of a metal coating to a

Metallic or other conducting surface by an electrochemicalprocess. The article to be plated (the work) is made thecathode (negative electrode) of an electrolysis cell throughwhich a direct electric current is passed. The article is

immersed in an aqueous solution (the bath) containing therequired metal in an oxidized form, either as an equatedaction or as a complex ion. The anode is usually a bar of themetal being plated. During electrolysis metal is deposited onto the work and metal from the bar dissolves:at cathode Mz+(aq) + ze- M(s)at anode M(s) Mz+(aq) + ze-

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HISTORY OF ELECTROPLATING

Electroplating industry were first established in 1974

but it was not until promulgation of 40 CFR Part 413

on September 7, 1979 that Electroplating CategoricalPretreatment Standards became a reality. The 1979

Standards established specific numerical limitations

for dischargers falling within seven subcategories.

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PURPOSE OF ELECTROPLATING

Appearance Protection Special surface propertiesEngineering or mechanical properties.

Some finishes are purely decorative. Many objects meant to beused indoors, in a dry environment and where danger ofcorrosion is slight, are nevertheless finished with lacquers,

paints and electroplated coatings for purely aesthetic reasons.The very thin layer of gold applied to some articles ofinexpensive jewellery has little or no protective value; it is thereprincipally to attract potential buyer.

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Electroplating

Electro less Plating

Anodizing

Coatings

Chemical Etching and Milling

Printed Circuit Board Manufacturing

TECHNOLOGY OF ELECTROPLATING

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ELECTROPLATING

Electroplating is the production of a thin surface coating of on~ metal uponanother by electrode position. Ferrous or nonferrous basis materials may

be coated by a variety of common (copper, nickel, lead, chromium, brass,bronze, zinc, tin, cadmium, iron, aluminum or combinations thereof) orprecious (gold, silver, platinum, osmium, iridium, palladium, rhodium,indium, ruthenium, or combinations thereof) metals.

ELECTROLESS PLATING

Electroless Plating is the chemical deposition of a metal coating on aworkplece by immersion in an appropriate plating solution. Electricity is notinvolved, therefore uniform deposits are easily obtained. Copper and nickelelectroless plating for printed circuit boards are the most common operations.In electroless nickel plating the source of nickel is a salt, and a reducer is

used to reduce the nickel to its base state. A complexlng agent is used to holdthe metal ion in solution. Immersion plating, which for purposes of thisregulation is considered part of electroless plating, produces a metal depositby chemical displacement.

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ANODIZING

Anodizing is an electrochemical process which converts the metal surfaceto a coating of an insoluble oxide. Aluminum is the most frequently

anodized material. The formation of the oxide occurs when the parts aremade anodic in dilute sulfuric or chromic acid solutions. Anodizingwastewater typically contains the basis material and either chromic orsulfuric acid. When dyeing of anodized coatings occurs, the wastewaterswill contain chromium or other metals from the dye.

COATING

Coatings include chromating, phosphating, metal coloring and passivating.Pollutants associated with these processes enter the wastestream throughrinsing and batch dumping of process baths. The process baths usuallycontain metal salts, acids, bases, and dissolved basis materials. Inchromating, a portion of the base metal is converted to a component of the

protective film formed by the coating solutions containing hexavalentchromium and active organic or inorganic compounds. Phosphate coatingsare formed by the immersion of steel, iron, or zinc plated steel in a dilutesolution of phosphoric acid plus other reagents to condition the surfacesfor cold forming operations.

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Chemical Etching and Milling

Etching and Chemical Milling are processes used to produce specific designconfigurations or surface appearances on parts by controlled dissolution with

chemical reagents or echants. Chemical etching is the same process aschemical milling except the rates and depths of metal removal ere usually muchgreater in chemical milling. The major wastestream constituents are thedissolved basis material and etching solutions.

Printed Circuit Board Manufacturing

Printed Circuit Board Manufacturln involves the formation of a circuit patternof conductive metal (usually copper) on nonconductive board materials suchas plastic or glass.

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ELECTRICAL RELATIONSHIPSMichael Faraday, perhaps the greatest experimental scientist in history,enunciated his laws of electrolysis in 1833, and these laws have remainedunchallenged ever since. They are basic to both the understanding and the

practical use of electrolytic processes. They may be stated as follows:1. The amount of chemical change produced by an electrical current isproportional to the quantity of electricity that passes.2. The amounts of different substances liberated by a given quantity of electricityare inversely proportional to their chemical equivalent weights.Equivalent weight is an older term, but still used widely in analytical andelectochemistry. In redox chemistry it is the molar mass divided by the numberof electrons in the balanced redox half-equation.Mathematically Faraday's laws of electrolys can be expressesed as:QZm/MQ= It= zFnwhere Qis the charged passed, Iis the current passed, tis the time the currentis passed, zis the change in oxidation state, mand Mare the mass and molarmass respectively of oxidised or reduced species, Fis the Faraday constant (96485 C mol-1, the charge of one mole of electrons), and nis the amount of ofsubstance oxidised or reduced.

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ENVIRONMENTAL IMPLICATIONS

In most parts of the world the authorities set acceptance standards forthe discharge of industrial effluent into sewers and water courses. It isusually necessary to obtain the approval of the appropriate authority inthe form of a 'consent to discharge' before a discharge can be made oralterations are made in the concentration or volume of an existing

discharge.There are very few metal finishing plants from which the rinse waterscan be discharged directly to the sewers as the contaminantconcentrations are outside the limits set by local authorities. With themajority of instillations, therefore, effluent treatment is necessary.

There are a number of methods which may be employed to reduce thelevel of contaminant in the effluent discharge and thus simplifysubsequent effluent treatment. In the main these methods rely on goodhousekeeping with a liberal dose of common sense added for goodmeasure.

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APPLICATION

Corrosive resistance

Good appearance

Protective layer

Decorative appeal

finishing

Alloying Conductivity also

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CONCLUSION

In most parts of the world the authorities set acceptance standards for the

discharge of industrial effluent into sewers and water courses. It is usually

necessary to obtain the approval of the appropriate authority in the form of a

'consent to discharge' before a discharge can be made or alterations are made in

the concentration or volume of an existing discharge. So electroplating plays animportant role .

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0401227343