• Proceedings of the Materials Research Society of Korea Conference
• /
• 1994.05a
• /
• pp.26-26
• /
• 1994

• Journal of the Korean Ceramic Society
• /
• v.37 no.8
• /
• pp.799-804
• /
• 2000

Coulometric titration experiments have been done for copper doped cobaltous oxide (Co1-xCux)1-$\delta$ O with various dopant concentrations. We present the obtained experimental data and compare our results to those of previous thermogravimetric investigation. The experimental data are fitted by theoretical calculations based on various defect models. For this modeling, we considered different types fo major defects like copper in substitutional and interstitial lattice sites as well as copper vacancy. We also introduced the copper evaporation effect during titration experiment into our consideration.

• Journal of the Korean Ceramic Society
• /
• v.34 no.7
• /
• pp.722-730
• /
• 1997

The nonstoichiometry (x) of UO2+x and (Er0.06U0.94)O2+x has been in-situ measure against oxygen activity (Po2) at elevated temperatures by a coulometric titration method. From the dependence of the oxygen excess (x) of UO2+x on Po2 at 1000℃, it has been concluded that (2Vo2Oia2Oib)〃〃and (2Vo2Oia2Oib)' clusters are prevailing at low oxygen partial pressure [log(Po2/atm) -10.6] and at high oxygen partial pressure [log(Po2/atm) -10.6], respectively. The nonstoichiometry is found to be reduced with the addition of Er, which is ascribed to the fact that the fixed-valent Er3+ reduces the oxidation capacities of UO2+x. The enthalpy of oxygen incorporation in (Er0.06li0.94)O2+x has been evaluated from the mean valences of U-ion as -180±70 kJ/mole.

• The Korean Journal of Ceramics
• /
• v.4 no.2
• /
• pp.103-113
• /
• 1998

By using a gas-tight electrochemical cell, we can perform high-temperature coulometric titration and measure electronic transport properties to determine the elecronic defect structure of metal oxides. This technique reduces the time and expense required for conventional thermogravimetric measurements. The components of the gas-tight coulometric titration cell are an oxygen sensor, Pt/yttria stabilitized zirconia(YSZ)/Pt, and an encapsulated metal oxide sample. Based on cell design, both transport and thermodynamic measurements can be performed over a wide range of oxygen partial pressure ($pO_2=10^{-35}$ to 1 atm). This paper describes the high-temperature gas-tight electrochemical cells used to determine electronic defect structures and transport properties for pure and doped-oxide systems, such as YSZ, doped and pure ceria $(Ca-CeO_2 \;and\; CeO_2)$, copper oxides and copper-oxide-based ceramic superconductors, transition metal oxides, $SrFeCo_{0.5}O_x,\; and \;BaTiO_2$.

• Journal of the Korean Ceramic Society
• /
• v.31 no.12
• /
• pp.1491-1500
• /
• 1994

Nonstoichiometry($\delta$) and the phase stability region of a ferrite spinel (Mg0.29Fe0.71)3-$\delta$O4 have been investigated by a coulometric titration method as a function of temperature(T) and oxygen partial pressure(Po2). It has been found that the spinel is thermodynamically stable in the ranges -8.0$\leq$log(PO2/atm)$\leq$-2.4, -7.0$\leq$log(PO2/atm)$\leq$-1.7 respectvely at 100$0^{\circ}C$. The nonstoichiometry extends over the ranges of -0.004$\leq$$\delta$$\leq$0.007, -0.008$\leq$$\delta$$\leq$0.006, -0.033$\leq$$\delta$$\leq$0.004 at 100$0^{\circ}C$, 120$0^{\circ}C$, respectvely. The observed PO2-dependence of $\delta$ suggests that the majority ionic defects are cation interstitials in the low PO2 region and cation vacancies in the high PO2 region.

• Journal of the Korean Chemical Society
• /
• v.44 no.6
• /
• pp.581-586
• /
• 2000

Separation and coulometric titration method were applied for the determination of plutonium content in samples of PWR spent fuel. Plutonium was separated on an anion exchange(AG MP-1) column and determined by the controlled-potential coulometric titration. In this study, we discussed some experimental conditions related to the separation and determination of plutonium in PWR spent fuel samples. Average accuracy(recovery of plutonium) for the determination of 0.230∼3.02 mg plutonium standard was 99.36%. Average precision(relative standard deviation, RSD) for the determination of 0.250∼0.450 mg plutonium in PWR spent fuel samples was 0.38%.

• Applied Chemistry for Engineering
• /
• v.2 no.4
• /
• pp.385-392
• /
• 1991

Nonstoichiometry and defect model for $Ni_{1-x}O$ were determined by coulometric titration method. In the temperature range of 1123-1198K and oxygen partial pressure of 0.21-0.1 atm, the nonstoichiometry was found to be proportional to the fourth root of the oxygen partial pressure. This pressure dependence can be explained by the fact that nonstoichiometric $Ni_{1-x}O$ contains singly ionized metal vacancies as the predominant point defects. At T=1173K and $Po_2=0.21atm$, the nonstoichiometry, x was $1.21{\times}10^{-4}$. The standard formation enthalpy of defects in $Ni_{1-x}O$ was found, on the basis of this defect model, to be 0.95 eV. Also the result indicates that both of singly and doubly ionized metal vacancies are simultaneously present at above 1248K.

• The Korean Journal of Ceramics
• /
• v.4 no.2
• /
• pp.78-82
• /
• 1998

The oxygen nonstoichiometry (x) of UO$_{2+x}$ and $(Ce_yU_{1-y})O_{2+x}$ (y=0.05, 0.25) has been measured as a function of oxygen activity (a02) at 100$0^{\circ}C$ by a solid state coulometri titration technique. The results for UO$_{2+x}$ are in a good agreement with literature data and the ao2-dependence of the nonstoichimetry has been well explained with (2:2:2) cluster model. The equilibrium oxygen activity of $(Ce_yU_{1-y})O_{2+x}$ increases with Ce-content (y) for given nonstoichiometry (x), which is ascribed to the fact that Ce is present as Ce$^{3+}\; and\; Ce^{4+}$, and, therefore, the addition of Ce reduces the oxidation capacity of UO$_{2+x}$. From the oxygen activity dependence of x in $(Ce_yU_{1-y})O_{2+x}$ the defect structure of $(Ce_yU_{1-y})O_{2+x}$ is discussed.