Capillary sample preparation
The X-ray diffraction patterns from samples prepared in capillaries give the highest peak resolution, therefore where possible, samples should be loaded in capillaries for data collection. This form of sample preparation is the most commonly used in User experiments. This section describes how this can be done.
What size capillaries should I use?
It is normally recommended that users use 0.3 mm low X-ray absorption glass capillaries; the angular resolution is optimised by using as small a diameter as possible. Capillary sizes >0.7 mm are not recommended.
How much sample do I need?
For ease of experiment set-up, the length of sample needed in the capillary is usually 15-20 mm (or more), above the base holding the capillary. The beam intercepts the capillary at ~12 mm from the top of the base. It is possible to work with as little as 3-5 mm of sample, if care is taken when positioning the sample so that it is still positioned ~12 mm from the base.
Samples prepared for use with the cryostream and hot-air blowers must be longer, and capillaries used with the flow through cell need to be completely filled.
How do I pack the sample in a capillary?
Hints for loading capillaries are as follows:
The sample should be finely and uniformly ground.
Load only the smallest amount (<1 mm deep) of material into the capillary funnel at any one time - otherwise the sample becomes stuck pretty early on in the capillary.
Vibration is the key to moving the sample down and a good light source behind the capillary is needed to see whether the sample has moved down the capillary and/or is coating the sides of the capillary.
Vibration can be achieved by running a small, fine file across the capillary (while holding the capillary lightly between your fingers); or by 'dropping'/tapping the capillary on a hard surface, e.g. use a narrow tube of at least 15 cm length which the whole capillary will slide through and drop the capillary into the top and let it land on a bench top (this is a repetitive process); or by standing the capillary upright in a beaker or similar container, and placing this in a sonicator; or finally, if you have a vibrating hand-held tool you can hold it to the capillary and get the sample to shuffle down.
To seal the capillary break off the funnel and any excess capillary, and seal it.
What type of capillaries should I use?
Most low- or ambient-temperature experiments will use 'special glass' or 'borosilicate' capillaries', but high-temperature experiments will require 'quartz' capillaries (these can be used up to 1370 K).
Where can I purchase suitable capillaries?
Capillaries can be purchased from Charles Supper or Hilgenberg and standard stock items will take at least two weeks to be delivered. For non-standard thicker-walled quartz capillaries, users will need to contact Hilgenberg directly for pricing and availability. Delivery time might be longer.
What about capillaries at high-pressure?
Capillaries can be pressurised during in situ measurements. It is mandatory that thick wall (0.02-0.05 mm) quartz capillaries are used for experiments where internal capillary pressures above 5 bar are expected. For experiments requiring pressures: 5 – 10 bar, quartz capillaries with a wall thickness of 0.02 mm are required. For experiments requiring pressures: 10 – 20 bar, quartz capillaries with a wall thickness of 0.05 mm are required. These capillaries can be specially ordered from Hilgenberg.
For all high pressure, capillary experiments using either the Norby or flow cell, the maximum pressure allowed is 2 MPa (20 bar). Higher pressures are possible by prior agreement with beamline staff, however sapphire capillaries will be required and the upper pressure limit is capped.
It is mandatory that thick walled quartz capillaries are used for all high-pressure capillary experiments, especially for those that require heating. Pressures of 5 – 10 bar require capillaries with a wall thickness of at least 0.02 mm. 10 – 20 bar experiments require capillaries with a wall thickness of at least 0.05 mm. These can be specially ordered from Hilgenberg.
Please note that for any high-pressure gas experiments above 5 bar with inert gases (at any pressure with flammable gases), there must always be 2 persons present at the beamline to monitor the capillary and ensure that breakages are detected as soon as they occur.