Selecting the Correct X-ray Film
Introduction
Measuring Liquids or loose powders in XRF is normally done using a plastic liquid sample cell with a supporting foil used. Different types of foils can be used for making the liquid cell. The question is which X-ray foil is best for which application???
There are three main areas that need to be taken into consideration when selecting an X-ray foil. These areas are:
1. Degradation Resistance
2. Impurities or contamination of the foil
3. Transmission %
Degradation Resistance
Degradation resistance in general is the resistance to chemical attack, irradiation, thermal softening, brittleness, tearing and stretching. It is important that all degradation tests are completed outside a spectrometer. To complete the degradation test, the user should take a representative liquid of the expected analysis and place in a sample cell for 30 mins. If no degradation is shown, the sample can be measured safely in the spectrometer.
Table 1: Examples of chemicals for Resistance classification
Chemical Classification
Example Chemical
Acids, weak
Citric Acid (0.4g/ml)
Acids, Concentrated
HCL (37%)
Alcohols, aliphatic
E
Table 2: Chemicals vs X-ray Film types.
(+ = Well Resistant) (~ = May cause damage to the film)
Impurities of the Foil
Each foil is comprised of differing impurities. Some foils are cleaner (less impurities) than others making them well suited to trace element analysis. Other foils may contain impurities, but possess better resistance to chemicals and are harder to break.
Table 3: Contamination elements in the X-ray Film
Foil Type
Foil Thickness (um)
Elements present as Contamination
Transmission of Foils
The X-rays transmission through foils is affected by the thickness of the foil as well as its composition. This largely affects the light element analysis in liquids. It is therefore important to know the extent of the transmission of the foil selected for measurement.
Table 4: X-ray Film Transmission using an AUSMON sample, comparing intensities.
Graph 1: X-ray Film Transmission using an AUSMON sample, comparing intensities.
Conclusion
The highest chemical resistant X-ray films are Polyester and Kapton, which are resistant to all chemicals. Every user should however run a degradation test on their analysis samples before completing measurements. The polypropylene is the cleanest of all the X-ray film and the prolene has the highest transmission of all the X-ray films.
If there is any doubt on which foil to use, the operator must test the samples based on the above information to determine which is best to use. It is much better to be safe and test before measurement then to find out you have a problem after measuring.
Scott Gilroy
PANalytical
Measuring Liquids or loose powders in XRF is normally done using a plastic liquid sample cell with a supporting foil used. Different types of foils can be used for making the liquid cell. The question is which X-ray foil is best for which application???
There are three main areas that need to be taken into consideration when selecting an X-ray foil. These areas are:
1. Degradation Resistance
2. Impurities or contamination of the foil
3. Transmission %
Degradation Resistance
Degradation resistance in general is the resistance to chemical attack, irradiation, thermal softening, brittleness, tearing and stretching. It is important that all degradation tests are completed outside a spectrometer. To complete the degradation test, the user should take a representative liquid of the expected analysis and place in a sample cell for 30 mins. If no degradation is shown, the sample can be measured safely in the spectrometer.
Table 1: Examples of chemicals for Resistance classification
Chemical Classification
Example Chemical
Acids, weak
Citric Acid (0.4g/ml)
Acids, Concentrated
HCL (37%)
Alcohols, aliphatic
E
Table 2: Chemicals vs X-ray Film types.
(+ = Well Resistant) (~ = May cause damage to the film)
Impurities of the Foil
Each foil is comprised of differing impurities. Some foils are cleaner (less impurities) than others making them well suited to trace element analysis. Other foils may contain impurities, but possess better resistance to chemicals and are harder to break.
Table 3: Contamination elements in the X-ray Film
Foil Type
Foil Thickness (um)
Elements present as Contamination
Transmission of Foils
The X-rays transmission through foils is affected by the thickness of the foil as well as its composition. This largely affects the light element analysis in liquids. It is therefore important to know the extent of the transmission of the foil selected for measurement.
Table 4: X-ray Film Transmission using an AUSMON sample, comparing intensities.
Graph 1: X-ray Film Transmission using an AUSMON sample, comparing intensities.
Conclusion
The highest chemical resistant X-ray films are Polyester and Kapton, which are resistant to all chemicals. Every user should however run a degradation test on their analysis samples before completing measurements. The polypropylene is the cleanest of all the X-ray film and the prolene has the highest transmission of all the X-ray films.
If there is any doubt on which foil to use, the operator must test the samples based on the above information to determine which is best to use. It is much better to be safe and test before measurement then to find out you have a problem after measuring.
Scott Gilroy
PANalytical