Oxygen Isotope Exchange in Nanocrystal Oxide Powders

Abstract

It is shown that investigations of the isotope exchange kinetics in nanocrystalline oxides allows one not only to solve problems connected with determination of process parameters and characteristic scenarios, but also to substantially extend experimental opportunities in analysis of diffusion properties of oxides. A specific behavior of the oxygen isotope exchange was studied in nanocrystalline LaMnO3 and ZrO2:Y2O3 oxides. The former oxide is characterized by very small values of oxygen volume diffusion coefficients, while the latter one is, on the contrary, an ionic conductor. The study was carried out using powdered nanomaterials prepared from original ceramic materials by grinding in planetary mills or by laser evaporation. The study revealed future trends in the use of nanomaterials for analysis of the diffusion kinetics in oxides. It is demonstrated that in this case the sensitivity of traditional isotope methods increases considerably and fundamentally new opportunities are provided for analysis of processes on the "gas phase  solid state" interface as well as for the study of volume diffusion in polycrystals. Considering a strong dependence of the isotope exchange rate on the particle size, it is also topical to conduct studies dealing, along with determination of kinetic parameters of the process, with the use of the obtained data for certification of dimensional characteristics of oxide nanopowders.

Interaction of O2 with LSM–YSZ Composite Materials and Oxygen Spillover Effect

“…It has been shown on lanthanum–strontium cobaltites, but for lanthanum–strontium manganites there are discrepancies in values, connected with the essential difference of diffusion coefficients in volume and on grain boundaries of materials . The value of the diffusion coefficient determined by the IE GPE method is close to the diffusion coefficient at the grain boundaries; and the value determined by the SIMS method is close to the bulk diffusion coefficient …”

“…6 The value of the diffusion coefficient determined by the IE GPE method is close to the diffusion coefficient at the grain boundaries; and the value determined by the SIMS method is close to the bulk diffusion coefficient. 34 The abovementioned results indicate that the oxygen surface exchange rate can be significantly increased due to the TPB between the mixed ionic and electronic conductor, oxygen ionic electrolyte, and the gas phase. The topic of TPB in the electrochemical aspect has been widely covered in the literature, which clearly showed that TPBs were considered the preferred reaction sites.…”

Hydrogen transport property of polymer-derived cobalt cation-doped amorphous silica

“…As listed in Table 3, the i values evaluated for the free Si-OH and the H-bonded Si-OH were in the range of 1.356 to 1.360, and they were also compatible with the abovementioned literature data. 30 The OH/OD conversion behaviour was further assessed using the self-diffusion coefficient of deuterium evaluated according to the procedure reported by Fishman et al 31,32 The following equation based on Fick's second law has been derived in order to estimate the diffusion coefficient for the 18 O and 16 O exchange in oxide-ion conductors: where D [m 2 s −1 ] is the self-diffusion coefficient; r [m] is the particle radius; c [at%] is the 18 O concentration; c0 [at%] is the 18 O concentration of the sample oxide equilibrium to the 18 O atmosphere; Δ [m] is the monolayer thickness; t [s] is the isothermal annealing time.…”

“…For instance, in the case of LaMnO3+δ perovskite, it was found that cðt; rÞ¼ cD eq 1 π 2 n 2 exp D t the surface diffusion coefficient and volume diffusion coeffi-cient were in the order of ∼10 −17 m 2 s −1 and ∼10 −24 m 2 s −1 , respectively. 32 In this modelling expressed in eqn (2), the summation was performed for running indices up to n = 5. This model can be applied for a very fast exchange on the surface of an oxide particle, whereby Δ is around 0.5 nm for typical oxides.…”