Ceramic Analysis: It's Elemental
February 1, 2010
Table 1. Comparison of qualitative results to certified elemental concentration.
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 of standards.
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 Shimadzu’s EDX-700/800.
Table 2. Result of repeatability test for R-603.
Repeatability
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 government regulations.
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 rhclifford@shimadzu.com; or visit www.ssi.shimadzu.com.