X-ray Diffraction Powder Method
X-ray diffraction is a method which has long been used in industry for
the rapid and accurate identification of crystalline substances.
The method uses x-ray diffraction patterns which act as unique "fingerprints"
for every known crystalline substance. An unknown substance (as little
as a few milligrams of a powdered sample) produces a pattern which is then
compared with standard reference patterns from a file of tens of thousands
of compounds compiled by the National Bureau of Standards, American Society
for Testing Materials, the American Crystallographic Association and the
British Institute of Physics.
EMS has the ICDD diffraction files on computer; it uses PDF-2 data base
on a CD-ROM. This database has accompanying search-match software
where unknown materials are identified using the diffraction pattern and
element matching techniques.
If several substances are present in a mixture, their characteristic patterns
are recorded in the unknown pattern, so that each material present can
be identified. Depending on the material, quantities greater than
one to five percent can be detected with confidence. Since it is the crystal
structure and not the chemical composition which is being analyzed, this
method will distinguish between distinctly different materials which have
identical compositions, for instance, between graphite and diamond (forms
of carbon), quartz and cristobalite (forms of silicon oxide), calcite and
aragonite (calcium carbonate), hematite and magnetite (alpha and gamma
forms of iron oxide).
Where a quantitative analysis of the amount of a known substance in a mixture
is desired, accurate standard mixtures of the substance in question are
prepared and then analyzed along with the unknown mixture. The relative
intensities of the x-ray patterns derived are measured and the weight percentage
of the substances in the mixture computed. An accuracy better than
5% is possible with many substances.
EMS Laboratories has the facilities and expertise necessary to analyze any
crystalline material, in quantities as small as a few milligrams (more is
required for quantitative analysis). In addition, we provide valuable additional
information regarding particle shape and size, composition and crystal habit.
EMS
Laboratories Inc. / 117 West Bellevue Drive / Pasadena CA 91105-2503
Tel.
(626) 568-4065 or (800) 675-5777 Fax (626) 796-5282