Rare Earth Existence Form in Rare Earth Tungsten Electrode

In rare earth tungsten electrode, rare earth mainly added in the form of rare earth nitrate. After subsequent doping, drying, reduction processes, rare earth nitrate has be a series of changes and decomposition reactions. Take lanthanum nitrate (La (NO₃) ₃` • 6H<sub>2</sub>O) as example, under inert gas to (La (NO<sub>3</sub>) <sub>3</sub>` • 6H₂O) will produce H₂O, HNO₃, NO, NO₂, and N₂O₅ and other gases. The reaction process and decomposition of cerium nitrate and yttrium nitrate is similar with lanthanum nitrate, but the reaction temperature is different.

To dry the doped powders, the drying temperature can reach 150 ℃. Then the rare earth nitrate will lose crystal water. During reduction, the reduction temperature is generally 400 ~ 1000 ℃. At such a high temperature rare earth nitrate is completely decomposed to produce rare earth oxides.

Analyze XRD of reduction powder found after first reduction there are not diffraction peak of rare earth and clear diffraction peak is WO₂, β-W (W₃O). Indicating that first reduction temperature is lower and the crystal phase of rare-earth is in the low level. Observing the rare earth tungsten powder after second reduction found the diffraction peak mainly α-W, a small amount of β-W, while there has been a significant unknown diffraction peaks. To press and sinter the powder, and then observe its XRD found that the unknown diffraction peak does not disappear. Analyze by PDF card found the peak is similar to rare earth tungstate strongest peak, so it is indicated that the peaks can be rare earth tungstates (La₂WO_6, Ce₂WO₆, Y₂WO₆ and so on.).

Therefore, in the rare earth tungsten electrode, rare earth existence form mainly is LaWO₃, Ce₂WO₆, Y₂WO₆ and other tungstate. Rare earth tungstate after sintered, its calibration peak and relative intensity did not changed significantly, indicating after reduction and sintering the rare earth existence form has not changed.

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