Atotech Basics plating training : ELECTROPLATING TRAINING : WHAT IS ELECTROPLATING ? THE DEPOSITION OF A METALLIC COATING UPON A NEGATIVELY CHARGED CATHODE BY THE PASSING OF AN ELECTRIC CURRENT WHAT IS THE PURPOSE ? TO OBTAIN A METALLIC COATING HAVING CERTAIN PROPERTIES SUCH AS HARDNESS, BRIGHTNESS, CORROSION RESISTANCE AND TO REPRODUCE IDENTICAL FORMS IN ELECTROFORMING. REQUIREMENTS # SOURCE OF DIRECT CURRENT # A PLATING TANK # A SOLUTION CONTAINING THE DISSOLVED SALTS OF THE METAL TO BE PLATED # ANODE ( POSITIVE ELECTRODE ) # A PREPARED OBJECT -CATHODE ( NEGATIVE ELECTRODE ) WHAT IS DIRECT CURRENT ? THE FLOW OF ELECTRONS IN THE SAME DIRECTION BETWEEN POSITIVE AND NEGATIVE ELECTRODES WHAT IS A PLATING SOLUTION ? A CONDUCTING MEDIUM FOR THE MOVEMENT OF METAL IONS IN SOLUTION BETWEEN AN ANODE AND A CATHODE WHAT IS pH ? THE MEASUREMENT OF ACIDITY OR ALKALINITY ON A SCALE FROM 0 TO 14 0 TO 6.9 BEING ACIDIC AND 7.1 TO 14 ALKALINE AND 7.0 BEING NEUTRAL HOW ARE PLATING SOLUTION MAINTAINED ? # CHEMICAL ANALYSIS OF THE CONSTITUENTS # HULL CELL PLATING TESTS # ADDITION OF CHEMICALS # ELIMINATION OF CONTAMINANTS # PERIODIC PURIFICATION # REGULAR INSPECTION OF PARTS FOR DEFECTS # PHYSICAL TESTING WHAT IS A METAL ION ? A METAL ION IS AN ATOM OF A METAL HAVING A POSITIVE ELECTRICAL CHARGE WHAT ARE THE SOURCES OF METAL IONS ? # METAL SALTS IN PLATING SOLUTION # SOLUBLE METAL ANODES WHAT ARE ANODE BAGS ? ANODE BAGS ARE POROUS MEMBRANES PLACED AROUND ANODES TO COLLECT SLUDGE FORMING ON THE DISSOLVING ANODE Basic ELECTROCHEMISTRY CATHODE REACTIONS # Reduction of ions # Draw electrons from the external circuit TYPICAL REACTION Ni++ + 2e = Ni (metal ) 2H+ + 2e = H2 4H2O + 4e = 2H2+ 4(OH) - ANODE REACTIONS # Oxidation of metal to ions # RATE OF CURRENT FLOW Ohm’s Law Amperes = Volts // Ohms I = E // R FARADAY’S LAW Factors / Amperes, Time and Equivalent Weight of Metal / FARADAY’S LAW One ampere flowing for one second represents one coulomb. Faraday’ law states that 96,500 coulombs (one Faraday) will deposit one gram equivalent weight of a metal. Equivalent weight is the atomic weight of the metal divided by it’s valence. FARADAY’S LAW weight of metal deposited 96,500 Coulombs Deposit At. Wt. = grams 96,500 Valence WEIGHT OF NICKEL PLATED KNOWN FACTORS Current = 50 amps Time = 15 mins At. Wt. Ni = 58.7 Valence = 2 CALCULATION X = 13.7 GRAMS CALCULATING THICKNESS FROM WEIGHT Thickness = WT // density X area 1mil = 25. 4 micron EXAMPLE CALCULATING THICKNESS FROM WEIGHT wt = 0.136 grams Density of Ni = 8.9 Area = 4 cm2 ANSWER 1, 5 mils PLATING EFFICIENCY AND TIME OF PLATING % Efficiency=Actual Ni Plated X 100 /Theoretical (Faraday’s Law / FACTORS AFFECTING PLATING CURRENT # Hydrogen Liberation ( cathode) # Oxygen Liberation ( anode ) # Polarization # Concentration Polarization ( Diffusion ) # Hydrogen Overvoltage POLARIZATION E = IR E = Volts( potential difference) R = Resistance( resistance of solution to the flow of current ) E = IR E = Volts I = Current( flow of electricity) E = CURRENT(I) X RESISTANCE(R) Ep = Change in potential difference DUE TO Polarization from resistance CONCENTRATION POLARIZATION # CONCENTRATION OF METAL IONS BUILD ON THE SURFACE OF THE ANODE # CONCENTRATION OF THE METAL IONS DECREASE AT THE SURFACE OF THE CATHODE # CHANGE IN ANODE AND CATHODE FILMS CAUSES POLARIZATION HYDROGEN OVERVOLTAGE POLARIZATION DUE TO EVOLUTION OFHYDROGEN UPON A SPECIFIED ELECTRODE SURFACE OR THE EXCESS POTENTIAL ABOVE THE EQUILIBRIUM POTENTIAL REQUIRED TO EVOLVE HYDROGEN AT THE CURRENT DENSITY SPECIFIED . HYDROGEN OVERVOLTAGE FACTORS : # TYPE OF METAL # SURFACE ROUGHNESS # TYPE OF SOLUTION # CURRENT DENSITY # TEMPERATURE HYDROGEN OVERVOLTAGE (1 ma/cm2 ) Zn - 0,80 Sn-0,80 Cd -0,80 Cu-0,60 Ni-0,40 Ag-0,30 Au-0,15 C-0,11 Pt0,00 CLEANING & PREPLATE PURPOSE FOR CLEANING # TO PROVIDE ADHESION ON THE SUBSEQUENT DEPOSITS # TO OBTAIN A HIGH QUALITY FINISH DEPOSIT # TO OBTAIN THE DESIRED PROPERTIES OF THE DEPOSITS EFFECTS OF IMPROPER CLEANING : # POOR BONDING TO BASE METAL # PEELING OF DEPOSIT # SKIP PLATE # MICRO ROUGHNESS # PITTING # POOR CORROSION RESISTANCE # CONTAMINATED BATHS PRECLEANING OPTIONS : # MECHANICAL CLEANING / WET OR DRY BLASTING / # SOLVENT CLEANING / DEGREASING, EMULSION, DIPHASE / # ALKALINE CLEANING / SPRAY, SOAK, ELECTRO, ULTRASONIC / # ACID CLEANING /SOAK, ELECTRO / HOW CLEANERS WORK : # DISPERSION / S A METHOD WHEREBY SOLID PARTICLES ARE BROKEN DOWN TO SMALL PARTICLES BY THE ACTION OF SURFACTANTS AND OTHER COMPONENTS IN A CLEANER. THE PRINCIPLE IS EFFECTIVE FOR RESIDUE LEFT FROM POLISHING OPERATIONS. # SAPONIFICATION /SAPONIFICATION IS THE CHEMICAL ACTION BY WHICH FATTY ACID, FATTY OIL OR OTHER REACTABLE SOIL IS CONVERTED TO A WATER SOLUBLE COMPOUND, SOAP. ELEVATED TEMPERATURES, CONCENTRATION, AND pH PROMOTES THE SPEED AND COMPLETION OF THE REACTION. EMULSIFICATION IS A CHEMICAL PROCESS BY WHICH SURFACTANTS PENETRATE OILS AND SOILS AND BREAK THEM DOWN TO TINY WATER SOLUBLE GLOBULES DISPERSED AND SUSPENDED IN SOLUTION. TYPE OF CLEANING : # SOLVENT CLEANING / MIXTURES OF SUITABLE SOLVENTS AND SURFACTANTS / # USED IN VAPOR DEGREASING # MINIMAL USE DUE TO HEALTH AND ENVIRONMENTAL CONCERNS .
Posted on: Sun, 04 Aug 2013 23:28:53 +0000