Introduction to high temperature in-situ SEM EDS analysis

28^th October 2022 | Author: Haithem Mansour

In this blog, I will talk about in-situ SEM EDS analysis, its challenges and solutions, and I will introduce our new product, EDS IR Filter, that makes high temperature EDS analysis in the SEM possible up to 1200 ̊C.

In situ experiments in the SEM give the capability to perform heating and mechanical testing inside the chamber using dedicated heating & tensile stages. Combined with analytical tools like EDS and EBSD, it becomes an even more powerful technique. It helps understand phenomena ranging from precipitation and phase transformation, to diffusion and segregation in a large range of materials like metals, ceramics, composites, and polymers. It allows metallurgists and material scientists to develop new materials with better properties.

The challenge of black body radiation and our solution

EDS is typically used in the SEM at room temperature, but using it at high temperatures comes results in the issue of black body radiation: IR, visible light and even UV. This radiation will severely degrade the EDS detector performance by adding considerable noise. From around 500 ̊C, this noise can make EDS analysis impossible.

Figure 1 shows the degradation in the spectrum quality temperature increases.

Figure 1: Comparison of spectra collected at different temperatures, from room temperature to 500 ̊

As a solution to this, a filter can be used to shield the EDS detector from the black body radiation, but the filter needs to be transparent to X-rays at the same time!

The new Oxford Instruments EDS IR Filter stops black body radiation of the wavelengths encountered up to at least 1200 ̊C. This increases the range of materials and phenomena that can be studied at high temperatures using EDS. The filter is made of a super light material, providing good low-energy sensitivity, and has a novel design which makes it secure and easy to use in a very hot environment!

Figure 2 shows some comparison spectra, firstly between room temperature, and acquisition at 1000 ̊C with the IR Filter, and secondly between room temperature and acquisition at 500 ̊C using conventional EDS without any IR Filter. From these comparisons, you can clearly see the filter is successfully blocking the black body radiation and giving EDS data similar to that seen at room temperature.

Figure 2: Comparison of spectra collected at 1000 ̊C with an IR filter and 500 ̊C without a filter with spectra collected at room temperature.

The need for speed and sensitivity to capture phase transformation and chemical changes 

High temperature in-situ SEM EDS is a great tool to map chemical changes like phase transformation, diffusion, segregation and precipitation. However, these phenomena are dynamic and could be missed if the data acquisition takes too long. In addition, at very high temperatures (>600 ̊C), the detector is likely to be partially retracted to avoid heat damage and so the X-ray count will decrease. So, the solution to this is to use large area sensors EDS detectors with fast electronics to maximise signal, and thus get the best of the in-situ heating experiment and to observe the chemical changes.

Ultim Max EDS detectors have the largest sensors on the market, and together with X4 electronics, they deliver unparalleled speed and sensitivity. This is ideal for challenging experiments like high temperature EDS. For example, in the following application collected using Ultim Max 170 (with an IR Filter) in collaboration with Manchester University, Tescan and NewTec. It shows an automated high temperature EDS analysis in SEM used to observe diffusion and phase transformation in an Fe-Ti alloy. The sample was heated to 850 °C and then cooled to 400 °C. The video shows the direct observation of iron particle diffusion in the matrix and then the titanium alpha to beta phase transformation.

Using Ultim Max detectors with the new EDS IR Filter, you can now run EDS analysis at very high temperatures (<1200°C), this could also be combined with EBSD to study phenomena like phase transformation and precipitation. To find more about this product, follow the link here.

Or sign up for our webinar on 10^th November in which we will discuss our collaboration with Manchester University and NewTec in more detail.

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