Properties of the Deposited Materials andor Modified Surfaces

Table 2 shows some of the characteristics of deposits produced in various baths. It also shows a few instances where postplate heat treatment was used to change the stress characteristics of a deposit and some of the changes that additives can make in a deposit.

Table 2 Properties of electrodeposited iron coatings

Basic bath

Additives

Ultimate tensile strength

Elongation, %

Hardness, HV

MPa

ksi

Sulfate

None

572-614

83-89

3.0-3.5

250

NaCl

354

51.4

5.5

200

Boric acid + urea

480-720

Oxalic acid

600-615

NaCl + citric acid(a)

1000-1100

Double sulfate

NaCl + antioxidant

600-700

Chloride

None

421-434

61-63

5.0-18.0

<100

NaCl

448-593

65-86

4.0-18.0

150-530

Glycerol

786-883

114-128

360-380

Sulfate-chloride

Amidopyrine(b)

500-750

Fluoborate

Boric acid

575

Sulfamate

Formic acid(c)

676-1068

98-155

1200-1500

Sulfonate

Antioxidant 15 g/L

650-750

Antioxidant 1.5 g/L

350-400

(a) Properties are for parts stress relieved by heat treatment for 1 h at 250 °C (480 °F).

(b) Properties are for parts stress relieved by heat treatment for 2 h at 200-300 °C (392-572 °F).

(c) Properties are for parts stress relieved by heat treatment for 24 h at 190 °C (374 °F).

Other additives can be used in various combinations with various baths. Organic additives (acetic acid, arginine, dextrin, glycerin, glycine, saccharin, sugar, and thiourea) are grain refiners as a general rule. They induce stress by the inclusion of their breakdown products in the coating. Inorganic additives (manganese chloride and potassium chloride) increase conductivity. A wetting agent (sodium lauryl sulfate) can be used to reduce pitting. The additive characteristics overlap each other and can change with current density, temperature, pH, and concentration.

References cited in this section

3. F. Lowenheim, Electroplating, McGraw-Hill Book Co., 1978, p 333-341

4. S.T. Packman, unpublished data Environmental Considerations

Iron metal does not pose any special waste disposal considerations unless associated radicals are hazardous (Ref 3). In fact, most publicly owned treatment works (POTWs) like to see iron introduced into the sewer system because it acts as a "getter" for the sulfides in the system, thereby reducing the hydrogen sulfide that can form. The only waste treatment required for iron baths is the adjustment of the pH to a value within the operating range specified in a facility's waste disposal permit. The only exception to this rule is the fluoroborate bath, which could introduce fluorides to the waste disposal system. Most POTWs have fluoride limits that have to be considered when designing a waste disposal system. Boron also has limits in some geographical areas. Local permitting agencies can provide detailed information. Compared to other metal finishing operations, iron is very easy to keep in compliance.

Reference cited in this section

3. F. Lowenheim, Electroplating, McGraw-Hill Book Co., 1978, p 333-341 Health and Safety Considerations

As in all metal finishing operations, good judgment should be exercised when operating an iron plating bath. Eye protection, clothing protection, and gloves should be used. Most of the baths are highly corrosive and can have detrimental effects on surrounding equipment. This is especially true of the chloride and fluoroborate baths. High corrosion potentials coupled with current efficiencies in the range of 82 to 87% probably indicate that air emission equipment is necessary. The sulfate, sulfamate, and sulfonate baths are less corrosive and, even though they run at low pH, should require only general ventilation equipment.

Cadmium Plating

Revised by Milton F. Stevenson, Sr., Anoplate Corporation

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