ASTM D 6492 Standard Practice for Detection of Hexavalent Chromium on Zinc and Zinc/Aluminum Alloy Coated Steel
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ASTM D 6492 Document Information:
Title
Standard Practice for Detection of Hexavalent Chromium on Zinc and Zinc/Aluminum Alloy Coated Steel
ASTM International
Publication Date:
Dec 10, 1999
Scope:
This practice can be used to detect the presence of hexavalent
chromium on galvanized and
zinc/aluminum alloy coated steel surfaces. Hexavalent chromium-bearing
treatments (passivates) can
be applied to coated steels to prevent storage stain. While passivated
55 % aluminum-zinc alloy
coated steel is commonly painted, passivated galvanized steel is not.
Chrome passivation may
interfere with the successful pretreatment of galvanized steel, as
well as contaminate cleaning and
pretreatment baths on a coil coating line.
The amount of hexavalent chromium that will cause the indicator to
produce a discernible pink color
is in the range of 0.5 parts per million dissolved in the indicator
solution. It is possible that a
coated steel surface that produces a negative result does have
chromium on the surface. If a
material that yields a negative result is suspected of having chromium
on the surface, instrumental
methods should be used. Chrome deposits of 1 mg/ft can be easily
missed by analytical
instruments such as the scanning electron microscope with energy
dispersive x-ray analysis (EDXA)
capability. Auger electron spectroscopy (AES) or electron spectroscopy
for chemical analysis (ESCA)
can identify chemical species present in the levels required for
adequate detection. Stripping the
metallic coating and analyzing for chrome by atomic absorption or
inductively coupled plasma can
also give reliable results in detecting the presence of chrome.
This practice is designed to be a qualitative means of screening
chrome passivated coils from those
which are not chrome passivated.
Some chromium-free passivates are being used commercially. Although
these products will test
negative for hexavalent chromium, they may interfere with cleaning and
pretreating. Chromium
bearing passivates that contain film forming constituents such as
acrylic resins are also being
commercially applied. The reaction of these products to the spot test
will vary. Abrading the
surface with emery paper will improve the likelihood of reliable
detection. This technique is not
recommended for acrylic resin containing passivation treatments.
The values stated in SI units are to be regarded as the standard. The
values given in parentheses
are for information only.
This standard does not purport to address all of the safety concerns,
if any, associated with its
use. It is the responsibility of the user of this standard to
establish appropriate safety and
health practices and determine the applicability of regulatory
limitations prior to use.
Keywords:
- diphenylcarbohydrazide
- hexavalent chromium
- passivate
- passivation
- steel
- zinc
- zinc/aluminum
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