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First: Prepare the sodium polytungstate solution as usual. It is recommended to start with a SPT solution of 2.5 g/ml.This way the viscosity will be not to high to separate tiny particles.
Second: Then transfer a part of the SPT solution (around 20 to 30 %) into a separate container. In this container you will mix the Tungsten Carbide powder (TC powder) with the SPT solution. Be very careful now!
Third: Start to stir the SPT solution and then add very slowly the TC powder into the SPT solution to make a slurry. Again be careful to add the TC powder very slowly! The TC powder must be completely wetted. The idea behind this is, that the TC Powder is at the end of this procedure totally wet and there are NO little lumps or clods in this TC-SPT solution. Avoid any building of clods!
Fourth: Then add the TC-SPT solution (you just prepared) to the SPT solution (you prepared first) very slowly and under constantly stirring the SPT solution. Adjust your desired density by the amount of the TC-SPT solution you put in the SPT solution.
Remember NOT TO ZENTRIFUGE the suspension of SPT and TC, because then TC will separate again from the mixture.
Do not just put Tungsten Carbide into the SPT solution because then the TC particles will settle down.
Sample calculation:
To get a density of 4.0 g/ml of the suspension sodium polytungstate and tungsten carbide you start with a Sodium Polytungstate Solution of the density 2.5 g/ml. For a 100 ml solution = 250g. You add 150g of Tungsten Carbide that gives you 400g of the “SPT”-”TC” suspension = density 4.0. The suspension is at a density of 4.0 stabile. To IMPROVE THE STABILITY you can stir the suspension slowly or run (sparkle, ripple) air bubbles through.
Lithium Metatungstate (LMT) and Lithium Heterotungstate (LST) are the same substance. Lithium Metatungstate contains 110 grams of Sodium Polytungstate!
The analysis was done by The Akademy of Science, Adlershof Germany.
Although the viscosity of LST is lower than that of SPT we do not see any reason for not using sodium polytungstate. Compared to Sodium Polytungstate (SPT), which is marketed in crystaline (powder) form. SPT is almost fully recoverable and can be reused many times.
The disadvantage of LMT/LST is that it is very difficult to adjust the separating agent LST to the required density of 2.85. Only after we heating LST to 30ºC, then it is possible to work for a few hours satisfactorily. (Prof. Dr. W. Buggisch, University of Erlangen - Germany)
Trying to adjust the densities might also be difficult with Lithium Metatungstate! Here an example: The density of a LMT solution can be lowered by adding water, but to increase the same solution is a time consuming evaporation process.
With Sodium Polytungstate the density is easily adjustable by either adding more water to lower the density or adding SPT powder to get back to a higher density.
After all Lithium Metatungstate contains 110 grams of Sodium Polytungstate !
