Preparation of samples for XRF using flux and platinum crucible
A method of of preparing samples for XRF using a flux and a platinum crucible includes forming the flux into a free-standing crucible liner. This may be achieved by mixing lithium borate particles with a liquid to form a paste; placing the lithium borate paste onto the inner surface of a mould; and after drying removing from the mould and firing the lithium borate paste to dry the lithium borate to form a free-standing crucible liner. The liner may be placed within a platinum crucible and then a sample placed in the liner. The temperature of the crucible is raised to a sufficient temperature that any oxidation reaction takes place before taking the temperature above the melting temperature of the flux to melt the crucible liner and dissolve the sample into the flux. The crucible can then be cooled and XRF measurements made on the sample.
1. A method of manufacturing a crucible liner, comprising:
mixing lithium borate particles with a liquid to form a paste;
placing the lithium borate paste onto the inner surface of a mould;
drying the lithium borate paste on the inner surface of the mould;
firing the lithium borate paste to form a free-standing crucible liner that maintains its shape and thickness, wherein either
(i) the dried lithium borate paste is removed from the mould before the step of firing the lithium borate paste, or
(ii) the mould is configured to withstand the firing temperature and the dried lithium borate paste is left in the mould during the firing step then the fired crucible liner is removed from the mould.
2. A method according to claim 1 wherein the lithium borate is substantially pure lithium tetraborate.
3. A method according to claim 1 wherein at least 50% of the lithium borate particles have a size less than 100 μm.
4. A method according to claim 1 wherein the mould has at least two parts.
5. A method according to claim 1 wherein the mould is of silicone.
6. A method according to claim 1 wherein the step of drying the lithium borate is carried out at a temperature of 70° C. to 200° C. for at least 5 hours.
7. A method according to claim 1 , wherein the step of firing the lithium borate paste comprises:
igniting the lithium borate in a furnace at a first temperature of 400° C. to 600° C. for a first period of time of 1 to 10 minutes; and
raising the temperature in the furnace to a second temperature of 600° C. to 700° C. for a second period of time of 5 to 20 minutes.
8. A crucible liner configured to be free-standing, the crucible liner having a cup-shaped form and a thicker base than the sidewalls and being made of lithium borate.
9. A crucible liner according to claim 8 wherein the crucible liner has a granular structure of particles joined to make up the cup-shaped form and wherein at least 50% of the particles have a size of less than 100 μm.
10. A crucible liner according to claim 8 wherein the lithium borate liner is substantially pure lithium tetraborate.
11. A method of use of a free-standing crucible liner having a cup-shaped form and being made of lithium borate in an X-ray fluorescence sample preparation method, the method comprising:
placing the lithium borate liner in a platinum crucible;
placing a sample in the lithium borate liner;
raising the temperature of the sample in the crucible to a reaction temperature and oxidising the sample without substantially reacting with the lithium liner; and
raising the temperature of the sample in the crucible to a fusing temperature at which the lithium borate liner acts as a flux and dissolves the oxidised sample.
12. A method according to claim 11 further comprising carrying out X-ray fluorescence measurements on the reacted oxidised sample.