Electroplating 101

A Small Introduction to Plating and Coating

Cadmium Plating

Cadmium is a lustrous, silver-white, ductile, very malleable metal. Its surface has a bluish tinge and the metal is soft enough to be cut with a knife, but it tarnishes in air. It is soluble in acids but not in alkalis. It is similar in many respects to zinc but it forms more complex compounds.


About three-fourths of cadmium is used in Ni-Cd batteries, most of the remaining one-fourth is used mainly for pigments, coatings and plating, and as stabilizers for plastics. Cadium has been used particularly to electroplate steel where a film of cadmium only 0.05 mm thick will provide complete protection against the sea. Cadmium has the ability to absorb neutrons, so it is used as a barrier to control nuclear fission.


Cadmium can mainly be found in the earth's crust. It always occurs in combination with zinc. Cadmium also consists in the industries as an inevitable by-product of zinc, lead and copper extraction. After being applied it enters the environment mainly through the ground, because it is found in manures and pesticides.


Naturally a very large amount of cadmium is released into the environment, about 25,000 tons a year. About half of this cadmium is released into rivers through weathering of rocks and some cadmium is released into air through forest fires and volcanoes. The rest of the cadmium is released through human activities, such as manufacturing.


No cadmium ore is mined for the metal, because more than enough is produced as a byproduct of the smelting of zinc from its ore, sphelerite (ZnS), in which CdS is a significant impurity, making up as much as 3%. Consequently, the main mining areas are those associated with zinc. World production is around 14.000 tonnes per year, the main producing country is Canada, with the USA, Australia, Mexico, JApan and Peru also being the major suppliers.


Taken from Lenntech.com

Cadmium coatings also have good lubricity, easy solderability and other properties that are essential for reliable service life of many engineering components. Cadmium is normally applied by electro-deposition from cyanide or acid solutions in barrels or vats. It can also be applied by mechanical plating, vacuum deposition and metal spraying, but generally only electroplated cadmium is of commercial importance.

Cadmium is a by-product of Zinc production, and it was not until the 1920's that electroplating of cadmium became widely used as a protective coating. Today, the Western World annual consumption of cadmium for coatings is about 1000 tones, which is a relatively small proportion of total cadmium consumption. Over 90 per cent of all Cadmium coatings are deposited by electroplating.


Coating Properties

Cadmium as an electroplated metallic coating has the following advantages:

  • It provides sacrificial protection to the underlying steel (as described under "background")
  • The atmospheric corrosion protection of cadmium is predictable and is proportional to the thickness of the coating. Cadmium electroplating is normally specified with minimum thickness between 5 and 25 microns, depending on the severity of atmosphere. Cadmium has good resistance to rural and marine atmospheres, in alkaline conditions and detergents.
  • It proves an effective barrier to prevent the galvanic/bimetallic reaction between steel and aluminium, such as where aircraft undercarriage and weaponry mechanisms are fixed to aluminium framework.
  • Undercutting of threads on nuts and bolts is not necessary. The coating has a low coefficient of friction, which reduces the tightening torque and allows repetitive dismantling.
  • Cadmium corrosion products have small particle volume and are adherent, so valves and delicate mechanisms will not likely to be jammed with debris.
  • Thin Cadmium coatings are appropriate on threaded components where dimensional tolerances must be maintained.
  • Cadmium can be formed as easily as the substrate.
  • It can easily be soldered without the use of corrosive fluxes, and has a lower electrical contact resistance than zinc coated steel. These are important properties for the electrical and electronics industry.
  • Cadmium can have an attractive polishable silvery finish.
  • The Cadmium plating process can be applied to all ferrous materials, including malleable iron, and to brass and aluminium. The process can enable a high efficiency throwing power, i.e. the recesses are more readily coated with a reasonably even deposit.
  • Cadmium plated steel is readily adhesive-bonded.
  • Chromating directly after electroplating can increase the corrosion resistance of the coating, and greatly extend the coating life by preventing the sacrificial process from commencing until in service.

High Tensile Steels

Most steels are readily electroplated with cadmium and require no heat- treatment, either for stress-relief or for avoidance of embrittlement due to hydrogen entrapped during the process. Base metals of tensile strength above 1100 MPa should not be electroplated with cadmium by conventional methods. Instead, specialised pre-treatment and coating procedures have to be used (Apticote 900L) along with stress-relief and de-embrittlement by way of specific heat-treatment cycles.

Chromate Coatings

After electroplating, and heat-treatment if required, a chromate conversion coating is usually applied, giving the coating its well known iridescent green/brown appearance. A chromate conversion coating adds corrosion resistance, and the protective value increases with the mass of the coating. A thin conversion coating can maintain a bright as-plated finish and does not appreciably affect the electrical conductivity of the surface, nor its solderability. A full chromate conversion coating can double the life of a typical cadmium coating in most atmospheres. Additional protection can be provided by a clear lacquer coating.

Uses

Cadmium coatings are used principally to impart corrosion resistance to steels, and in a great variety of applications which call for other engineering properties of cadmium. The aerospace industries specify cadmium plating to prevent bimetallic corrosion between high tensile steel fasteners and aluminium alloys. Aerospace engineers regard cadmium plating as important for bolts used with engines, major structural members and landing gear, and for fasteners for aluminium sheet. Nevertheless, cadmium is not the widely used "cure for all applications" coating it used to be, primarily due to regulatory actions restricting its use on applications where an alternative coating is not appropriate.

Health Warnings

Cadmium and cadmium electroplated products are safe to deposit, use and handle normally. However, under certain conditions, cadmium can present a health hazard. Effective respiratory equipment and exhaust ventilation must be arranged when welding or otherwise heating cadmium electroplated products over 250 Deg C, as the cadmium oxide fumes produced are highly toxic. Adequate exhaust ventilation must also be arranged when handling cadmium metal in the form of powders or dusts. Routine precautions taken under the UK COSHH regulations will ensure risks are properly controlled.
Taken from Poeton.com

Contact Us

For all quotes, consulting, questions, etc.
Contact: Mike Reeder
E-mail: michaeldreeder@hotmail.com

Phone: 713-645-6921
Fax: 713-645-3583
Mobile: 832-722-6703

Email Request for Quote or drawings to:
michaeldreeder@hotmail.com
Feel free to call my cell phone after normal business hours. We offer 24X365 service when our customers require it. If you have questions about any coating, CALL. We are the coating experts on your team.

If Mike is not available, other points of contact:
Carlos Palma (VP, Operations)
281.797.5706
mailto:carlos.deltaspecialty@yahoo.com

Lisette Rosas (Office Manager)
713.645.6921
rlisette18@hotmail.com

As a metal finishing engineer, I will consult with you on which coating or specification best meets your requirements. If you do not find what you are looking for on this website, please call me. We are always looking for new challenges and will invest in new capabilities as demanded by the market. If we cannot perform the coating process, I will refer you to one of our esteemed competitors who can help you.

Oh yeah, Se habla Espanol! Everybody speaks Spanish here except the Canadian immigrant (our Senior Coatings Chemist).

Mike Reeder
President

Physical Address:
Delta Specialty Coatings LLC
5738 Heiser Street
Houston, TX 77087

Mailing Address:
PO Box 87460
Houston, TX 77287-7460