Crystal Defects Can be Deadly
PAUL NESDORE, PUBLISHER/EDITOR
Photo by E. Hinchliffe
Crystallography is a fascinating subject and
directly relevant to gases applications, especially with regards to stainless steel. Crystal defects
in stainless steel are a concern for those utilizing such products as electropolished SS, which
is widely used in gases instrumentation and gas
delivery systems. G&I recently approached this
topic in our November 2011 eNewsletter with
the article “Quantitative Means for Measuring
Electropolishing Quality,” by Robert Eiermann,
which discussed the SEM (scanning electron
microscope) examination methodology for
detecting stainless steel defects.
Defects in crystals appear in several forms.
These are usually classified as point defects, line
defects, interfacial defects, and bulk defects.
There are also 3-dimensional defects called
voids (coalesced crystal vacancies) and inclusion stringers, which can trap foreign matter
and alter the characteristics of the material.
Crystals also do not line up nicely, as groups
of crystals within a material can have different
crystal group orientations giving rise to grain
boundaries between these orientations. These
boundaries can trap impurities but can also
mitigate dislocations or shearing. Note that not
all impurities are deleterious. Some are intentionally introduced and then called dopants.
As for gas purity requirements though, defects
can cause contamination, corrosion, and loss
of product. Crystal defects, however, can have
more drastic consequences.
A prime example is the sinking of the Titanic. The Titanic was clad with a steel hull held
together with over three million rivets. The
rivets were made from steel produced with
the only major steel making method at that
time, the open hearth furnace, invented by
Manager, Product & Technology
Swagelok Semiconductor Services Company
Lloyd Brown, Ph. D.
Semiconductor Process Gases R&D Manager
Robert Eiermann, P. E.
President and Chief Engineer
Bulk Specialty Gas Manager
Ralph M. Cohen Consultancy
Dr. Michael P. Fuller
Director of Marketing
Editorial Advisory Board
Manager of Business Development
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J. V. Martinez De Pinillos, Ph. D.
Director, Office of Microelectronics Programs National
Institute of Standards and Technology (NIST)
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Dr. Edward Naranjo
Analytical Chemist/Industrial Scientist
Oxygen Service Company
Kimberly J. Reynolds
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Tiger Optics, LLC
Patrick G. Smith
Vice President and Director of R&D
Senior Staff Scientist, Chromatography
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