Research method

X-ray absorption
fine structure (XAFS)

Responding to the Restriction of Hazardous
Substances in Electronic Products
Establishment of high-sensitivity nondestructive inspection method for hexavalent chromium

Role of SPring-8

Achievements

Development of a high-sensitivity nondestructive method for measuring the amountof hazardous hexavalent chromium in chromate coatings* used for protecting
electronic products from corrosion
Realization of a high-reliability rapid measurement method replacing theconventional inspection method involving melting
Application of the developed method to satisfy the regulations imposed by the EU(RoHS directive)**R&D facility: Fujitsu Laboratories, Ltd.
*Chromate coatings are used for protecting iron and aluminum from corrosion. Some contain hexavalent chromium (Cr6+) and others containtrivalent chromium (Cr3+). Chromate coatings containing Cr6+ include yellow and black chromates and iridite. Cr6+ is a hazardous substance andcauses diseases such as skin ulcers, nasal septum perforation, and lung cancer, and hence, the use of Cr6+ has started to be regulated. Cr3+, lesshazardous to human bodies than Cr6+, has been studied for use in chromate coatings instead of Cr6+.
**Restriction of Hazardous Substances (RoHS) directive: a standard established by the European Union (EU) to regulate the use of specified
hazardous substances in electric/electronic products, enforced in July 2006. The sale of products that do not conform to the RoHS directive isbanned in the EU. Cr6+ is included in the list of regulated substances.

Chromate treatment
for zinc plating

Chromate coating

Zinc-plated layer

6+

Some chromate coatings contain Crand others contain Cr3+.

BackgroundResults

Measures to abolish the use of Cr6+ are being
increasingly carried out because of the damage tohuman bodies caused by Cr6+ contained in electronic
products and the environmental pollution due tothe disposal of electronic products. Yet there has
been no substantially reliable method of
measuring the amount of Cr6+ through chemicaltreatment. What we need is a nondestructive
analytical method of detecting Cr6+.
In the method of analyzing Cr6+ throughchemical treatment, Cr6+ is extracted by dissolving
a chromate coating in unheated or hot water. In
line with this, the following problems occur. The
valency of Cr6+ changes during extraction, Cr6+reacts with coexisting elements, and precise
analysis is difficult for insoluble coatings. These
result in unsatisfactory reliability.

The SPring-8 XAFS method is appropriate fornondestructively measuring the absolute amountsof trace elements contained in samples. When Cr
compounds were measured by the XAFS method,
Cr6+ and Cr3+ were observed to be clearly separated
in the absorption spectra. We measured andclarified the absolute amount of Cr6+ (contentrate) for various chromate coatings by the XAFSmethod.
Moreover, it has become possible to obtain thedepth distribution of Cr6+ in chromate coatingsfrom the dependence of X-ray injection angle inthe XAFS result. Thus, the technology for directly
analyzing Cr6+ in chromate coatings without chemicaltreatment was improved.

Measurement result for chromate by XAFS

Content rate of Cr6+ in each chromate

The peak at 5.993 keV in the absorption spectrum for each chromate
corresponds to Cr6+. No peak is observed for Cr3+. Thus, the content
rate of Cr6+ can be measured.

The content rate of Cr6+ is calculated from the XAFS spectra inthe figure to the left.

Steel sheet
Yellow chromate (Cr6+)
Black chromate (Cr6+)

Iron and aluminum in electronic components are given a corrosion-proof coating.

6+

Cr3+6+

Iridite (Cr )6+6+

Yellow chromate (Cr )Cr3+Black chromate (Cr )Relative X-ray intensity

Iridite (Cr )X-ray energy (kev)2223