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topic 35528

What is the difference between Cadmium & Zinc Plating


A discussion started in 2005 but continuing through 2018

2005

Q. What is the difference b/w Cadmium & Zinc Plating? Please explain.

Syed Salman shahid
Purchasing - Karachi, Pakistan


2005

A. Cadmium and zinc are two different elements which have many similar properties but some very different properties. A couple or three decades ago platings of the two metals were used pretty much interchangeably on non-critical hardware because they provide generally similar corrosion protection through the same principle of cathodic protection of steel, and they both provide a nice shiny appearance.

When it was recognized that cadmium is a chronic cumulative poison similar to lead and mercury in its effects, cadmium gradually became restricted to use only on those applications where its unique combination of properties could not be met by zinc plating or a zinc alloy plating. As the pressure to eliminate cadmium grew, cadmium plating continues to be used less and less.

However, cadmium offers a combination of properties which no other metal or alloy can match. If you needed every one of these properties, there could be no substitute; but usually you only need two or three of them. Depending on which two or three you need, various substitutes are possible. Cadmium's properties include: galvanic protection for steel, excellent galvanic compatibility with aluminum, good lubricity (freedom from stick-slip) for consistent torquing of fasteners, freedom from gummy corrosion products, malleability, softness, usefulness at low coating thicknesses, excellent adhesion far superior to paint, and certain specific properties in the nuclear arena. It is very important to not specify cadmium plating indiscriminately because of its health effects--in fact it is prohibited from many applications in many countries. Zinc alloys (zinc-cobalt, zinc-nickel, zinc-iron, and tin-zinc) are the most common substitutes. But it is also very important that substitutions be approved by the responsible engineer, not by substitution at the purchase point, because the two or three properties important to one application may not be the same as for another application. Good luck!

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


2005

A. ZINC IS OFTEN PREFERRED FOR COATING IRON AND STEEL PARTS WHEN PROTECTION FROM EITHER ATMOSPHERIC OR INDOOR CORROSION IS THE PRIMARY OBJECTIVE.

CADMIUM IS SUPERIOR TO ZINC IN MARINE ENVIRONMENT.
EASILY SOLDERED,SILVER LIKE FINISH.
BUT SALTS AND VAPOUR HIGHLY TOXIC.

ajay raina
Ajay Raina
Ludhiana, Punjab, India


thumbs up sign Thanks for adding solderability to the list of cadmium's desirable properties, Ajay. You are right, and I had inadvertently omitted it.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



September 21, 2010

Q. Regarding to the question above, recently I have a client asking to replace the Zinc plated hydraulic hose fittings to Cadmium Plated fittings (the mentioned item is for offshore environment), but then who's also aware of the toxicity of it. Is there any similar alternative for the Cadmium Plated for the fittings mentioned? Or, are the Zinc Plated fittings are sufficient with adequate maintenance, e.g. wrapping them with Denso Tapes?

Kenny Teh
- Selangor, Malaysia

September 21, 2010

A. Hi, Kenny

It's not solely a matter of corrosion resistance, it's the many other properties of cadmium that were mentioned that are probably important to your customer. No material has ALL the properties of any other material (or it would be that other substance rather than being itself). But it is possible that tin-zinc plating will come closest to cadmium for the properties that are needed on hydraulic hose fittings. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey


September 21, 2010

Q. Hi Ted,

Thanks for your reply. My client mention about changing the fittings it's because they have bad experience with zinc plated fittings, they claim that it corrodes in a very short period of time, hence they want something superior, which is why they proposed Cadmium plated fittings. I did consider tin-zinc for this application, but it's quite hard to source it here in my country/neighboring country.

Regards.

Kenny Teh
- Selangor, Malaysia

January 2015

A. Hi again Kenny. If it's solely a matter of corrosion resistance, a heavier plating of zinc is the answer. A heavy layer of zinc will offer greater corrosion resistance than a thin layer of cadmium, even in a salty atmosphere.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



May 13, 2013

Q. I have several cars most of which are vintage Italian. The cars mostly used cadmium on various parts. I'm restoring these cars and found a place that still does cadmium plating ... My question:

Is Cadmium better then zinc as far as lasting longer and corrosion?

Is Cadmium hazardous to handle after the plating process is done and I'm installing my part?

William Hudkins
- Rochester, Indiana, USA


May 14, 2013

A. Hi William. Zinc alloy platings like zinc-nickel, zinc-cobalt, or tin-zinc will offer the corrosion resistance of cadmium without the bio-cumulative issues. The question isn't quite as simple as the potential dangers during handling, which can be ameliorated by wearing gloves. Cadmium should not be specified except where it is life threatening to substitute (certain aerospace applications still remain).

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



October 17, 2013 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. What is the difference between cadmium electroplating and zinc electroplating? Which is more durable?

Renato Hidalgo Jr
- Davao City, Davao del Sur, Philippines

October 18, 2013

A. Hi Renato. Thickness for thickness, which is more corrosion resistant depends on the exact atmosphere -- cadmium is generally better for salty environments, and zinc is generally better for industrial environments. But a thicker layer of a zinc alloy will provide better corrosion resistance than cadmium in every case, and every effort should be made to use zinc or a zinc alloy and to get cadmium out of the environment. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



January 5, 2015

Q. Greetings

I am assembling a cart from aluminum profiles.
I wanted to know which screws are best to use, zinc plated or cadmium plated?
Thank you
Anna

anna kush
- israel nahariya


January 2015

A. Hi Anna. We appended your inquiry to an earlier thread from which you can read that you should not use cadmium plating unless you absolutely have to, and what the special properties of cadmium plating are. Good luck.

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



June 13, 2018

Q. Do you know if there is any issue using mating connectors, one with Black Zinc coating and the mating connector using Cadmium coating on the conductors?

Mike Speer
- Huntsville, Alabama, USA


June 2018

Hi Mike. If the connectors are used indoors in a controlled environment I wouldn't foresee any galvanic corrosion. But asking if there is "any issue" with little situational info offered is difficult. From reading this thread you know that there should be little point in plating half of the connection with toxic cadmium. Good luck.

35528-1

In googling your situation I came across a very interesting paper which other readers might be interested in =>

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



July 13, 2018

Q. Good morning, gents.

ACRONYMS:

CPF = Central Processing Facility

My question is: that in oil & gas CPF, the studbolts are in cadmium but the bidder this time proposes the bright Zinc Plated, what do you think?

Med Med
SONATRACH - Hassi Messaoud Algeria


July 2018

A. Hi Med. This page explains that cadmium is a biocumulative toxin which we should try to remove from use to the extent possible; and the page also lists the important characteristics of cadmium plating which bright zinc plating or other substitutes might lack.

The person responsible for writing the spec can be referred to this page for the discussion … but for a 3rd party, whether it be the bidder or you to me, to overrule the specifier, possibly behind his back, is a dangerous proposition. We may think we know why he specified cadmium, but we may be wrong.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey
Striving to live "Aloha"



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