Surface World August 2019 Surface World August 2019 | Page 82

PRODUCTS & PROCESSES
Do you need a high-resolution detector in your
coatings X-ray Fluorescence (XRF) analyzer
and when should you consider an upgrade?
Matt Kreiner from Hitachi
High-Tech Analytical
Science talks us through
how to decide if switching
to a high-resolution
detector is right for your
business.
Q: How do I know if
I should switch my XRF
to a newer model with a
high-resolution detector?
With the typical XRF coatings analyzers being
10 years old, it’s possible that when you last
purchased an instrument there were very
limited, if any, options for the detector,
so you chose the instrument with the best
performance and features that fit into your
budget and sample size requirements.
The most common detector around 10 years
ago was a gas-filled proportional counter
(PC) detector. In the last decade, XRF detector
technology has advanced to include
new innovation such as solid state or
semiconductor detectors – PIN diode and
silicon drift detectors (SDD). These new
detectors offer additional benefits for several
of today’s more advanced applications. Even
if you purchased an instrument a few years,
it’s possible your requirements have already
changed or may change in the future, so it’s
worth understanding when it’s time to switch
to a high-resolution solid state detector.
1. When many elements or neighboring
elements are in the sample, including
alloyed plating.
Examples: Cr/Ni/Cu/Zn, ZnNi/Fe.
One of the key features of an SDD is
improved resolution. Much like high-definition
television improves your ability to see features
of a moving picture, the higher the resolution
of an XRF detector, the greater the ability
to see more details in an XRF spectrum.
With EDXRF, the detector is responsible for
differentiating small energy differences to what
80
elements are present. A PC detector
has comparatively poor resolution
and cannot clearly see the series of
characteristic signals from neighboring
elements. An example of this is
with nickel, copper and zinc. These
elements cannot be fully resolved by
a PC detector, so special hardware is
employed sequential analysis. With an
SDD, these elements are seen clearly
and simultaneously. Measurements
can be taken in less time and with
improved accuracy.
2. When coatings are thin (e.g., below 10 uin).
Example: Au/Ni/Cu
Due to the design of solid state detectors,
the background noise is markedly lower than
on a PC detector, making it easier to resolve
the signal from the elements to be measured
from unwanted signal. While that doesn’t
have a significant impact when measuring
thick coatings, it can be critical when
measuring very thin coatings (less than 10
µin). At that range, variations in background
can be the difference between a good
analysis and a non-detect reading. Solid
state detectors have very stable and low
background noise resulting in good sensitivity
to detect and analyze thin coatings.
3. When you need to measure phosphorus
content in electroless nickel plating
and conversion coatings.
Example: NiP/Al, ZnP/Fe
Elements with atomic numbers less than 17
AUGUST 2019
(chlorine) present some challenges for XRF
coatings instruments. These elements do
not travel well through air, and by the time
they travel from the sample surface to the
detector, they have lost much of their signal,
making them harder to analyze than their
more energetic counterparts. The combined
sensitivity, resolution and background of
a solid state detector makes it possible to
directly detect and quantify phosphorus,
even for thin coatings of low-phosphorus
electroless nickel.
Detector choice can be a complicated
subject, and there are many applications
where a PC detector performs very well
and may be preferable to a solid state.
It’s important to choose the right XRF
equipment supplier who will consult with
you and determine the best technology
for your business needs.
Matt Kreiner is a Product Business
Development Manager at Hitachi
High-Tech Analytical Science.
twitter: @surfaceworldmag