第五章-电镀与化学镀

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

第五章 电镀与化学镀(Electroplating & Electroless plating)

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Introduction Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath. Usually there is an anode (positively charged electrode), which is the source of the material to be deposited; the electrochemistry which is the mediμm through which metal ions are exchanged and transferred to the substrate to be coated; and a cathode which is the substrate (the negatively charged electrode) to be coated. Plating is done in a plating bath which is usually a nonmetallic tank (usually plastic). The tank is filled with electrolyte which has the metal, to be plated, in ionic form.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

The anode is connected to the positive terminal of the power supply. The anode is usually the metal to be plated (assμming that the metal will corrode in the electrolyte). For ease of operation, the metal is in the form of nuggets and placed in an inert metal basket made out non-corroding metal (such as titaniμm or stainless steel). The cathode is the workpiece, the substrate to be plated. This is connected to the negative terminal of the power supply. The power supply is well regulated to minimize ripples as well to deliver a steady predictable current, under varying loads such as those found in plating tanks.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

As the current is applied, positive metal ions from the solution are attracted to the negatively charged cathode and deposit on the cathode. As a replenishment for these deposited ions, the metal from the anode is dissolved and goes into the solution and balances the ionic potential.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Electrodeposition is an extremely important technology. Covering inexpensive and widely available base materials with plated layers of different metals with superior properties extends their use to applications which otherwise would have been prohibitively expensive. However, it should be noted that electroplating is not a simple dip and dunk process. It is probably one of the most complex unit operations known because of the unusually large nμmber of critical elementary phenomena or process steps which control the overall process.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

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Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Important criteria when selecting coatings.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Hydrogen Embrittlement Definitions: A process resulting in a decrease of the toughness or ductility of a metal due to the presence of atomic hydrogen.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Hydrogen embrittlement has been recognized classically as being of two types. The first known as internal hydrogen embrittlement, occurs when the hydrogen enters molten metal which becomes supersaturated with hydrogen immediately after solidification. The second type, environmental hydrogen embrittlement, results from hydrogen bei

ng absorbed by solid metals.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Electrodeposition and electroless deposition and their associated processing steps including acid pickling and electrocleaning can generate hydrogen which can enter substrates in the atomic form and cause hydrogen embrittlement.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Examples of hydrogen induced damage are: 1. Formation of internal cracks, blisters or voids in steels. 2. Embrittlement (i.e. loss of ductility). 3. High temperature hydrogen attack (i.e. surface decarburation and chemical reaction with hydrogen).

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Structure of commercial copper after heating in hydrogen for 3 hours at 75O℃ (about 250 X).

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Hydrogen blisters in the wall of a steel container.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Vanadiμm wire shattered by cathodic charging with hydrogen.

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Figure 5: Steel sample with no cathodic treatment (x 1).

Steel sample after cathodic treatment (x 1).

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Steel sample with no cathodic treatment (x 3).

Steel sample after cathodic treatment (x 3).

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Steel sample after cathodic treatment than heating at 200°C for five minutes (x 3).

Steel sample after cathodic treatment then heating at 200°C for one hour (x 3).

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

Steel

Electroplating is an electrochemical process by which metal is deposited on a substrate by passing a current through the bath.

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