NationMaster - Encyclopedia: Zinc chromate

Chromate Conversion Coatings are a type of conversion coating used to treat aluminum, zinc, cadmium, copper, silver, magnesium and their alloys. The process uses various toxic chromium compounds which may include hexavalent chromium and is therefore non-compliant with RoHS. The industry is developing less toxic alternatives. General Name, Symbol, Number chromium, Cr, 24 Chemical series transition metals Group, Period, Block 6, 4, d Appearance silvery metallic Atomic mass 51. ... Chromium hexavalent (CrVI) compounds, often called hexavalent chromium, exist in several forms. ... The Restriction of Hazardous Substances Directive (ROHS) became European Law in February 2003. ...

The most common use for chromating is to impart corrosion resistance to zinc, zinc plated steel, and aluminum parts. It is also used as a primer for subsequent coatings and is especially important in the aircraft industry as untreated aluminum is very difficult to pain or glue. Chromated parts retain their electrical conductivity, and the process may be used to add color for decorative or identification purposes. It has been suggested that Corrosive be merged into this article or section. ... A preparatory or primer coating put on materials before painting. ...

Chromate coatings are soft and gelatinous when first applied but harden and become hydrophobic as they age. Curing can be accelerated by heating up to 150° F, but higher temperatures will damage the coating. Thickness is on the order of several μ inches. Hydrophobe (from the Greek (hydros) water and (phobos) fear) in chemistry refers to the physical property of a molecule that is repelled by water. ...

The strength of some chromate coatings is indicated by color, progressing from clear/blue to yellow, gold, olive drab and black. Darker coatings provide more corrosion resistance. Chromate conversion coatings are common on everyday items such as hardware and tools and usually have a distinctive yellow color. Steel parts are usually plated with zinc or cadmium prior to chromating.

Chem film refers to aluminium which has been chromated per Mil-C-5541.

External links

Overview of different chromating processes
yellow and green chromating chemistry on aluminum
MIL-C-5541, Chromate conversion coating specification for aluminum.
MIL-C-17711B, Chromate conversion coating specification for zinc and zinc alloy casting and hot dipped galvanized parts

Categories: Materials stubs | Coatings

Results from FactBites:

Zinc Chromate (3437 words)
	Before a worker is placed in a job with a potential for exposure to zinc chromate, a licensed health care professional should evaluate and document the worker's baseline health status with thorough medical, environmental, and occupational histories, a physical examination, and physiologic and laboratory tests appropriate for the anticipated occupational risks.
	Zinc chromate should be stored in a regulated, marked area that is kept cool, dry, and well-ventilated and in tightly sealed containers that are labeled in accordance with OSHA's Hazard Communication Standard [29 CFR 1910.1200].
	Containers of zinc chromate should be protected from physical damage and should be stored separately from hydrazine, combustible, organic, and other oxidizable materials (such as paper, wood, sulfur, aluminum, and plastics), and strong oxidizers.

More results at FactBites »

COMMENTARY

Share your thoughts, questions and commentary here

Want to know more?
Search encyclopedia, statistics and forums:

Feeds | Contact
The Wikipedia article included on this page is licensed under the GFDL.
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms.

See also GA_googleFillSlot("encyclopedia_square");

External links

See also