Chemical composition and microstructural properties
X-ray diffraction is a technique used to study the chemical composition or microstructural properties of a sample. In situ XRD, or often called non-ambient XRD, adds another dimension: sample changes can be viewed under varying environmental conditions. In principle these environmental conditions can be any physical parameter, but the most common ones with respect to in situ XRD are temperature, gas environment, gas pressure, humidity, strain and electric field. These physical parameters can induce phase transformations, changes in the chemical composition, alter the crystallinity or crystallite size, change the internal stresses and alter the lattice parameters.
In situ XRD for industry and academia
The microstructure properties of materials directly affect the macro-scale properties such as the hardness or strength of a material, or the bio-availability of drugs. For this reason in situ XRD is a key tool to optimize industrial processes in order to get the best quality product. For example, great effort is put into CO2 reduction in the cement industry, which created a need for alternative fuels and rearranging fabrication processes. At the same time production should yield the same quality cement in terms of strength and durability with maximum efficiency. in situ XRD is a major tool to re-optimize such a process.
Alternatively, you can simulate the environment where your sample is being used. Drugs, for example, should have the same quality in humid environments as in dry environments. You can optimize the drug such that the quality stays the same, or optimize storage conditions.
Major recent research themes are the development of Li-ion batteries and CO2 or hydrogen storage. Both are characterized by cyclic operating conditions with cyclic charging / discharging of Li-ion batteries or loading / unloading of gas in storage materials. Behavior of the materials after many cycles can be easily observed using in situ XRD.
On a more fundamental research level, in the development of new (functional) materials, in situ XRD is a major tool for developing phase diagrams or optimizing synthesis processes.
The right solution
The basics of in situ XRD are simple. Instead of having e.g. a sample spinner in your diffractometer a non-ambient chamber can be placed on that same position, with your sample inside. Exchanging sample stages is a fairly simple action with the PreFIX technology, and is a matter of only operating one screw. Non-ambient chambers typically have a window made of X-ray transparent materials such as Kapton, PEEK or graphite.
A wide variety of in situ XRD equipment is available. In terms of temperature there are many different chambers in a total range from -262 °C (11 Kelvin) up to 2300 °C that can be selected. There are chambers that can be evacuated down to a pressure of 10-6 millibar or chambers that can be pressurized up to 100 bar. There is also a chamber available that can handle humidity levels up to 95% relative humidity with temperatures up to 80 °C. In addition, there are devices available that control the electric field and those that can apply strain to the sample.
Is in situ XRD difficult?
It is true that additional control of the environmental parameters of a sample apart from controlling the diffraction experiment, adds a certain degree of complexity to an experiment. Fortunately, non-ambient equipment, together with data collection software have now been organized by PANalytical, so that many instrumental aspects are controlled automatically. Handling of large quantities of data, resulting from an in situ experiment, is automated in HighScore Plus.
Click here to learn more about in situ X-ray diffraction experiments from our partner, Anton Paar GmbH.