Chapter 39: Problem 1

Sample preparation for powder XRD. (a) What mass of powdered sample is required? (b) Does the specimen need to be pure? (c) Does the sample need to be packed tightly into the specimen holder?

Short Answer

Expert verified

The required mass of powdered sample for powder XRD is usually around 2-3 mg. The specimen does not need to be completely pure, but a pure sample provides clearer results. It is crucial to pack the sample tightly into the specimen holder eliminating any air gaps to avoid inaccurate readings.

Step by step solution

Understanding the mass required for powder XRD

Powder XRD requires only a small amount of sample because the X-ray beam that is used can be quite thin. The typical amount of material used is about 2-3 mg. This can vary depending on the specific XRD machine and the size of the sample holder.

Comprehending the importance of purity

While an absolutely pure sample would be ideal for XRD analysis, it is not always necessary. The important thing is that the sample is representative of the specimen as a whole. Contaminants or separate phases within the specimen can complicate the diffraction pattern but they don't automatically invalidate the analysis. However, it's advised to use as pure a sample as realistically possible to get clearer results.

Importance of Packing the Sample Tight

It is important to pack the sample tightly into the specimen holder. This eliminates air gaps which can cause inaccurate readings. However, one must be careful not to crush or damage the sample while packing it. A well-packed sample in the specimen holder helps achieve a smooth surface to minimize diffraction effects from sample topography.

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Sample preparation for powder XRD. (a) What mass of powdered sample is required? (b) Does the specimen need to be pure? (c) Does the sample need to be packed tightly into the specimen holder?

Short Answer

Step by step solution

Understanding the mass required for powder XRD

Comprehending the importance of purity

Importance of Packing the Sample Tight

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