Table 1. Comparison of qualitative results to certified elemental concentration.
Ceramic materials often contain elements in the form of
oxides that can have various effects on the
ceramic, including roughness, wettability, wear resistance, color and
conductivity. Manufacturers strive to produce consistent products with a
certain ratio of different metals, and they must closely analyze ceramic
powders to determine the types and amounts of elements in the powder to
maintain that consistency.
The energy dispersive X-ray (EDX) technique permits
non-destructive rapid measurement of a range of elements in ceramic materials.
Manufacturers can use EDX equipment to measure from a qualitative or
quantitative approach. A qualitative approach to analysis is considered
standard-less and uses fundamental parameters to provide elemental content,
which is often a very accurate method for analyzing an unknown sample.
In some cases, however, documentation to
regulations set forth by the International Organization for Standardization
(ISO) is required. For these instances, manufacturers can rely on quantitative
results, where the EDX measures the actual concentration levels of present
elements. This purely empirical approach uses EDX reports to create a
calibration line based on the intensity emitted from each element for a number
Figure 1. Diagram of an EDX spectrometer.
Detection Made Simple
EDX spectroscopy examines samples through interactions between
electromagnetic radiation and matter, analyzing the X-rays emitted by the
matter. A sample is irradiated with X-rays emitted by an X-ray tube, and the
resulting characteristic fluorescent X-rays generated in the sample are
detected. In particular, X-ray fluorescence spectrometers that use
semiconductor detectors are called “energy dispersive” (see Figure 1).
An advantage of EDX
spectrometers is that the systems can perform simultaneous measurements for
many different elements. Systems are also compact, because the distance between
the sample and detector is very small. Using these systems, attenuation of
fluorescent X-rays is small, and, thus, it is possible to measure samples in
air. In addition, these systems do not require time-consuming pretreatment, and
a wide variety of samples can be measured. After analysis, the sample is not radioactive or altered in any way.
EDX’s characterization capabilities are associated with the
fundamental principle that each element of the periodic table has a unique
atomic structure. This allows X-rays that are distinctive of an element’s
atomic structure to be distinguished from each other. EDX can achieve low
limits of detection (LLD) below 10 ppm.
Figure 2. Spectrum of oxides in ceramic powder.
Qualitative EDX Analysis
Qualitative analysis, or
the fundamental parameter (FP) method, measures the constituent elements in
ceramic powders. This method can be used as a screening tool to determine only
the presence of the regulated substances, not necessarily the levels at which
the elements are present.
With an EDX spectrometer, FP software can quantitatively
analyze an unknown sample without the use of standards (see Table 1). The
software uses a library based on spectral comparison from real samples (see
Figure 2), and ceramic manufacturers can easily obtain a virtual comparison by
simply entering the composition of various materials.
Figure 3. Calibration line for SiO2.
Quantitative EDX Analysis
While the FP method is
very accurate in determining elemental concentration, using an empirical method
can often provide additional benefits. For example, an empirical method almost
always provides the user with higher accuracy.
Analysis is often
required to enable ceramic manufacturers to conform to ISO 9000 regulations. In
these cases, quality control procedures are required to be documented. Due to
the complex nature of the FP method, this is not always possible or
straightforward. On the other hand, an empirical method* reports to the
manufacturer a complete set of parameters associated with each quantitative
method. These results are clearly understood by the manufacturer and can be
used for ISO documentation. Figure 3 shows an example of an empirically created
calibration line for silicon dioxide (SiO2
*An example would be
Table 2. Result of repeatability test for R-603.
The samples were measured a number of times (e.g., n = 10)
to determine the precision of the analysis tool. Two values are associated with
a precision measurement. The first is standard deviation, which represents the
absolute precision of the instrument. The second value, the coefficient of
variation, represents the relative precision of the instrument. The results for
R-603 (certified ceramic standard) are shown in Table 2.
It is clear from the results that, in many
cases, fundamental parameters can provide a very accurate method for analyzing
unknown samples. For more detailed and easily documented results, however, a
quantitative approach is recommended, especially when reporting to meet
For more information regarding EDX, contact
Shimadzu Scientific Instrument Inc. at 7102 Riverwood Dr., Columbia, MD 21046;
(800) 477-1227; fax (410) 381-1222; e-mail firstname.lastname@example.org
; or visit www.ssi.shimadzu.com