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Electroplating is an electro-depositing process in which an electrode is used to pass an electric current so that the metal adheres to the surface of the object. The purpose of the electroplating is to change the characteristics or size of the surface of the object.
1. 2 plating purpose
A metal plating is deposited on the substrate to change the nature or size of the substrate surface. For example, giving the metal surface gloss and appearance, rust-proof items, to prevent wear; improve electrical conductivity, lubrication, strength, heat resistance, weather resistance; heat treatment of carburizing, nitriding; size or wear parts repair.
1. 3 Various gold plating methods
Electroplating electroless plating
Hot dip plating (hot spray plating)
Plastic plating immersion plating
Diffusion plating (cathode sputtering)
Vacuum plating plating alloy plating
Composite plating (selective plating)
Through-hole plating Pen plating
Electroforming
1.4 Basic knowledge of electroplating
The electroplating is mostly carried out under a solution, and most of them are electroplated in an aqueous solution. About 30 kinds of metals can be electroplated with an aqueous solution such as copper Cu, nickel Ni, chromium Cr, zinc Zn, cadmium. Cd", lead Pb, gold Au, silver Ag, platinum Pt, cobalt Co, manganese Mn, antimony Sb, antimony Bi, mercury Hg, gallium Ga, indium In, gallium, As, Se, Te, Pd, Mn, Re, Rh, Os, Ir, Nb, W, and so on.
Some metals must be plated with non-aqueous solutions such as: lithium, sodium, potassium, rubidium, magnesium, calcium, strontium, barium, aluminum, La, Ti, Zr, Ge, Mo, and the like. The electroplating metals that can be used in aqueous solutions and non-aqueous solutions include: copper, silver, zinc, cadmium, ruthenium, rhodium, manganese, cobalt, nickel, and the like.
It also includes the following items: Solution Properties Substances Reaction Chemical Formula Electrochemical Interface Physical Chemistry Material Properties
1.4.1 Solution
The dissolved substance is called a solute, and the substance that dissolves a solute is called a solute. The solvent is an aqueous solution called an aqueous solution. The amount of solutes dissolved in the solution is the concentration. The maximum amount of dissolved solute in a given amount of solvent is called solubility. The solution that reaches the solubility value is called saturated solution, and the opposite is unsaturated solution. The concentration of the solution, in the production and operation management, uses the easily understood and convenient weight percentage and the usual molar concentration.
1.4.2 reaction of matter
In the electroplating process, there are physical changes and chemical changes, such as grinding, drying and other physical reactions, and the electrolysis process has chemical reactions. We must fully understand the interrelationships and effects of various physical and chemical reactions during the processing.
1.4.3 Chemical Formulas Used for Plating
1. Conversion of temperature: 0°C=5/9(0oF-32) 0oF=1.80°C=32 0K=0°C=273
2. Density: D=M/VM=Quality V=Volume
3. Specific gravity: SG = material density / water density (at 4°C)
4. Baume: (Baume') Be'=145-145/specific gravity=145/145-Be'
For example, a 20% H2SO4 solution has a Be' value of 17 at 20°C. What is the specific gravity of the liquid?
Answer: The specific gravity of this kind of liquid = 145/145-17 = 145-128 = 1.13
5. Moisture ratio of the composition: For example, how much water does NiSO4,7H2O contain?
Answer: NiSO4, 7H2O=280.87 7H2O=126 H2O%=126/280.87*100%=44.9%
6. Ratio: For example, a chrome plating bath contains 400 gal of solution containing 500 lbs of chromic acid. Ask about the same concentration. How much chromic acid is needed for a 100-gallon chrome bath?
400/500=100/XX=125 Answer: 125 pounds of chromic acid are needed.
7. The weight of the solution is converted into volume: For example, 96% H2SO4, specific gravity 1.854 How many milliliters of 96% H2SO4 is required to prepare 1 liter of standard sulfuric acid solution? One liter standard acid solution of sulfuric acid weight=98/2=49 grams 49 grams/((1.8354 grams)/(ml×0.96))=27.82 ml
Answer: Need 27.82ml of 96% H2SO4
8. Neutralization: Example 1. Neutralize 310 ml of NaOH solution with 14.4 ml of a 1 N solution to find the equivalent concentration of NaOH solution: 14.4 ml × 1 N = 10 ml × xN x = 1.44
A: The equivalent concentration of NaOH solution is 1.44N
Example 2, 1.1738N HCl solution and 10ml of 1.1034N NaOH solution, how many milliliters of HCl solution is required? xml×1.1738N=10ml×1.1034N x=9.4ml
Answer: 9.4ml of 1.1738N HCl solution is needed.
9. Faraday's Law
Example 1. Calculate the weight of copper deposition with 5 amps of current for 5 hours. The current discharge rate is 100%.
Deposition weight = (atomic weight / (atomic price × 96500)) × (current × time × current effect) W = (A / (n × 96500)) × (I × T × CE)
W=(63.54/(2×96500))×(5×5×60×60×100%)=31.8g
Answer: 31.8g of copper can be deposited.
Example 2. How much current is required to plate 2.5g nickel in NiSO4 bath in 10 minutes?
Let the current efficiency be 100%, I=((n×96500)/(A))×((W)/(T×CE))
=((2×96500)/(58.69))×((2.5)/(10×60×100%))=13.7A
Answer: 13.7A current is needed
In Example 3, the surface area of ​​the plated part is 1000 cm 2 , and the time required for copper plating 51 m is obtained by passing a current of 15 A in a copper sulfate plating bath and the current efficiency is 100%. Copper density is 8.93g/cm3
t=((n×96500×D)/(A))×((area×d)/(I×CE))=
((2×96500×8.93)/(63.45))×((1000×5×10-4)/(15×100%))
=900 seconds = 15 minutes Answer: The required time is 15 minutes.
In Example 4, the surface area of ​​the plated part is 1.5m2, the average current is 1500A, the average zinc plating thickness is 251m in 15 minutes, the zinc density is 7.14g/m3, the atomic weight of zinc is 65.38, and the current efficiency is required. CE=WAct/WThen×100%
= ((1.5m2 x 251m x 7.14g/m3)/((65.38)/(2 x 96500)) x 1500 x 15 x 60)) x 100% = 59% A: The current efficiency is 59%
Example 5: The acidic tin plating solution is made of continuous copper sheet tin plating. The copper sheet is 0.9m wide. The speed of the copper sheet is 500m/min. The current density is 5000A/m2. The top and bottom sides are to be coated with 0.41m tin thickness, and the current efficiency is 100%. , Tin density 7.31g/cm3, atomic weight 118.7, how many m for plating tank?
Slot length L = ((n × 96500 × D) / (A)) × ((S × d) / (DI × CE)) =
((2×96500×7.31 g/cm3)/(118.7))×((500 m/min×0.41 m)/(5000 A/m2×100%))
=8m Answer: The required length is 8 meters.
Example 6, the use of insoluble anode chrome plating, the current efficiency of 18%, the current 1000A / hour, regardless of take-out losses, how much need to add more CrO3, in order to maintain the concentration of chromium in the bath? Chromium atomic weight 52, oxygen atomic weight 16
W=((A/(n×96500))×(I×t×CE)=((52/(6×96500))×(1000×18%)
WCro3=58.1×CrO3/Cr=58.1×100/52=112g
Answer: Need to add CrO3 112g
Basic knowledge of metal plating
1. 1 plating determination