Hexavalent vs trivalent chrome conversion coating 1

[grayseal]

Do these two coatings offer similar corrosion resistance? The application is fasteners (screws) used on medical exam tables and therefore protection is required to prevent corrosion from exposure to cleaning/disinfecting solutions. Also, since testing per ASTM B117 does not seem appropriate to compare the two methods, what would be an appropriate test?

grayseal

 

[TVP]

It depends on the exact type of chromates, specifically for the trivalent version. If it is a thick film type, then these have similar corrosion resistance as the iridiscent yellow/gold hexavalent chromates. If it is the thin blue trivalent chromate, then these are not as resistant. I don't have any experience with these coatings for the type of use you describe. If it were me, I would contact reputable suppliers of chromate conversion coatings such as MacDermid, Atotech, Dipsol, SurTec, etc.

 

[dik]

from CDC...

Hexavalent chromium (Cr(VI)) compounds are a large group of chemicals with varying chemical properties, uses, and workplace exposures. Their properties include corrosion-resistance, durability, and hardness. Workers may be exposed to airborne Cr(VI) when these compounds are manufactured from other forms of chromium (e.g., the production of chromates from chromite ore); when products containing Cr(VI) are used to manufacture other products (e.g., chromate-containing paints, electroplating); or when products containing other forms of chromium are used in processes that result in the formation of Cr(VI) as a by-product (e.g., welding).

NIOSH considers all Cr(VI) compounds to be occupational carcinogens. Cr(VI) is a well-established carcinogen associated with lung, nasal, and sinus cancer. Some of the industries in which the largest numbers of workers are exposed to high concentrations of airborne Cr(VI) compounds include electroplating, welding, and chromate painting. A hierarchy of controls, including elimination, substitution, engineering controls, administrative controls, and the use of personal protective equipment, should be followed to control workplace exposures. Dermal exposure to Cr(VI) should also be prevented to reduce the risk of skin irritation, corrosion, ulcers, sensitization, and allergic contact dermatitis.

Dik