• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.6 no.2
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• pp.129-139
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• 2008

In this study, a sorption experiment of multivalent nuclides such as Eu(III) and Th(IV) relatively stable for redox reactions was carried out for bentonite colloids which had been prepared from the domestic Gyeongju bentonite. The amounts of the nuclides lost by an attachment to bottle walls, by a precipitation, and by a colloid formation were estimated by performing blank tests for the sorption experiments. Sorption coefficients, $K_d's$, reflecting the mass losses were obtained and investigated for the sorption of Eu(III) and Th(IV) onto the bentonite colloids. The net sorption coefficients $K_d's$ considering all the three mass losses were measured as about $10^6-10^7\;mL/g$ and $7{\times}10^6-10^7\;mL/g$ for Eu(III) and Th(IV), respectively, depending on pH. In particular, a precipitation occurred mainly at a pH greater than 5 for Eu(III) and a precipitation and colloid formation significantly occurred at a pH greater than 3 for Th(IV). The precipitation and colloid formation of the multivalent nuclides of Eu(III) and Th(IV) therefore should be considered when $K_d's$ are rightly obtained over the pH range where their precipitation and colloid formation become significant at a given concentration.

• Applied Chemistry for Engineering
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• v.25 no.5
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• pp.455-462
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• 2014

This work investigated the hydrophobic coating of silicate yellow phosphor powder in the form of divalent europium-activated strontium orthosilicate ($Sr_2SiO_4:Eu^{2+}$) by using an atmospheric pressure dielectric barrier discharge (DBD) plasma with argon as a carrier and hexamethyldisiloxane (HMDSO), toluene and n-hexane as precursors. After the plasma treatment of the phosphor powder, the lattice structure of orthosilicate was not altered, as confirmed by an X-ray diffractometer. The coated phosphor powder was characterized by scanning electron microscopy, fluorescence spectrophotometry and contact angle analysis (CAA). The CAA of the phosphor powder coated with the HMDSO precursor revealed that the water contact angle increased from $21.3^{\circ}$ to $139.5^{\circ}$ (max. $148.7^{\circ}$) and the glycerol contact angle from $55^{\circ}$ to $143.5^{\circ}$ (max. $145.3^{\circ}$) as a result of the hydrophobic coating, which indicated that hydrophobic layers were successfully formed on the phosphor powder surfaces. Further surface characterizations were performed by Fourier transform infrared spectroscopy and X-ray photoelectron spectrometry, which also evidenced the formation of hydrophobic coating layers. The phosphor coated with HMDSO exhibited a photoluminescence (PL) enhancement, but the use of toluene or n-hexane somewhat decreased the PL intensity. The results of this work suggest that the DBD plasma may be a viable method for the preparation of hydrophobic coating layer on phosphor powder.