Search

The rapid growth of the nuclear industry poses a great challenge for radioactive waste treatment. Volatile radioactive isotopes generated from uranium fission, especially gaseous iodine, attracted great attention due to their environment and health hazards. The widespread species of radioactive iodine are gaseous elemental iodine (I2) and methyl iodide (CH3I). It is difficult to trap the methyl iodide in high humid condition. Activated carbon and derivative materials are widely used as adsorbents to remove volatile iodine. Triethylenediamine (TEDA) is proposed as impregnation via isotope exchange mechanism. In this study, activated carbon fiber (ACF) with high surface area, heat resistant and chemically stable was used as substrate, TEDA-modified viscose-based activated carbon fiber was prepared by hydrothermal reaction. For fiber hydrothermal modified with 5% (mass fraction) TEDA, the surface area and pore volume decrease about 20%. Compared with conventional impregnation, more TEDA impregnation enters into the microporous structure of activated carbon fibers under hydrothermal environment. The gaseous iodine adsorption properties of modified activated carbon fiber were investigated. Static adsorption experiments of elemental iodine and methyl iodide were performed. The adsorption capacity of elemental iodine and methyl iodide increases by 36% and 50% respectively. Methyl iodide adsorption capacity of hydrothermal modified-ACF is 400 mg/g. The dynamic adsorption experiments show that the adsorption performance of modified activated carbon fiber for methyl iodine decreases with the increase of temperature and humidity. The adsorption performance of activated carbon fiber for methyl iodine is greatly affected by environmental humidity. Breakthrough experiment with 5 ppm of gaseous methyl iodide was conducted under high humid conditions (30 ℃, RH 95%), the feed gas flow rate was fixed at 15 L/min for 12 h. Breakthrough curve indicates that hydrothermal modified-ACF has good adsorption performance with respect to methyl iodide. The radioactive CH3131I adsorption experiments under severe conditions were carried out. The removal efficiency of hydrothermal modified-ACF increases from 29.11% to 94.85%. The affinity of methyl iodide is improved by TEDA-modified. The hydrothermal modified-ACF exhibits the high adsorption efficiency of gaseous iodine.

In response to the low separation efficiency of actinide nuclide (An) and fission product (FP) in the separation process of high‐level radioactive waste, as well as the large amount of secondary waste. A novel Ln(1‐x)SrxZrO(3.5‐0.5x) (0 ≤ x ≤1) multiphase ceramic waste form (Nd3+ simulating An3+), which can cure both An and Sr simultaneously, was in‐situ synthesized by sol‐gel spray pyrolysis method. The series of multiphase ceramics are composed of cubic pyrochlore phase Nd2Zr2O7 (NZO) and orthorhombic perovskite phase SrZrO3 (SZO), without any accompanying impurities. The two phases exhibit excellent compatibility, and their content can change regularly with the change of x. Nd and Sr occupy their most stable crystal lattice positions, with low transposition doping levels. The density of the composite ceramics is high, and the measured density is as high as 88 % of the theoretical density. The above experimental results confirm that the new multiphase ceramics can cure An and Sr simultaneously and separately, showing strong adaptability to waste components and high chemical stability. [ABSTRACT FROM AUTHOR]

A series of new Nd(1-x)SrxZrO(3.5–0.5x) (0 ≤ x ≤ 1) multiphase ceramic waste forms, which can simultaneously immobilize An and Sr (with Nd3+ simulating An3+), were synthesized in situ by a sol-spray pyrolysis method. These multiphase ceramics are composed of a cubic pyrochlore phase Nd2Zr2O7(NZO) and an orthogonal perovskite phase SrZrO3(SZO) without any impurities. The content of the two phases can change regularly with the change of x. Nd and Sr can occupy the ceramics' most stable lattice sites. The measured density of multiphase ceramics can reach more than 88% of the theoretical density. At the same time, the leaching rates of target Nd, Sr and Zr elements reached ~ 10−5 g·m−2·d−1, ~ 10−3 g·m−2·d−1, and ~ 10−7 g·m−2·d−1 at 90 ℃ and deionized water for 72 days, respectively, which shows that the multiphase ceramics had strong leaching resistance. The experimental results confirm that the new multiphase ceramics can immobilize An and Sr simultaneously and separately, and they have high chemical stability and strong adaptability to waste components. The multiphase ceramics is expected to be an ideal candidate waste form for An and Sr. [ABSTRACT FROM AUTHOR]

In this study, (Ti1−xWx)3SiC2 (x = 0–0.3) MAX phase ceramics were prepared via a solid-phase reaction synthesis method. The phase and performance effects of W-doping Ti3SiC2 were investigated. The microstructure and homogeneity of samples were characterized by XRD and SEM–EDS. Structural analysis show that when the amount of W is less than 5 mol%, the multi-phase structure of (Ti1−xWx)3SiC2 phase, a small amount of impurity phase TiSi2 and SiC was observed. As the amount of W doping increases, obvious impurity phases appeared. The oxidation behaviors of (Ti1−xWx)3SiC2 solid solution have been investigated at 800 °C in air up to 200 h. The oxidation kinetics of (Ti1−xWx)3SiC2 samples follow parabolic law. Compared to pristine Ti3SiC2, the oxidation resistance of 5 mol% W-doped sample increases by 23.2% at 800 °C. This study shows that Ti3SiC2 can be used for a long time under high temperature environment, and W doping can effectively improve the oxidation resistance of the system. This work provides a reference for the application of (Ti1−xWx)3SiC2 materials in high-temperature environments. [ABSTRACT FROM AUTHOR]

The structure and magnetic properties of the magnetite can be substantial corrected by incorporating foreign cations. In this work, Tb3+ was successfully incorporated into magnetite and superparamagnetic magnetite nanoparticles were obtained, using solvothermal method. The doping of Tb3+ greatly reduces the Mr and Hc values of the magnetite. Due to the doping of high magnetic moment Tb3+, the original magnetic moment of the magnetite is destroyed and magnetic domain are decomposed, resulting in a significant reduction in remanence and magnetic agglomeration. The remarkable effect of Tb3+ doping degaussing will provide new prospects for the application of magnetite materials in the superparamagnetic direction. [ABSTRACT FROM AUTHOR]

Abstract: Electroresistance has become a stimulating research topic because of its potential applications in next‐generation nonvolatile memory technology. Here, an electroresistance‐like behavior of the antiperovskite Mn3GaC compound around the antiferromagnetic–intermediate phase transition is reported. A high sensing current significantly decreases the fraction of the antiferromagnetic phase of higher resistivity relative to the intermediate phase of lower resistivity upon warming, showing a resistivity change up to 50%. Through extensive studies of the resistivity at different sample locations and of the magnetization under applied current, it is unambiguously shown that this electroresistance‐like behavior originates from the local Joule heating of the sample due to high‐resistive lead contacts and not from an intrinsic effect. These findings open an available avenue to explore electroresistance‐like behavior by achieving phase coexistence of a high‐ and low‐resistivity phase under the driving force of local Joule heating. [ABSTRACT FROM AUTHOR]

The PLZT (10/65/35) ceramic powder was synthesized by sol-gel pyrolysis. The samples were analyzed by thermal analysis, X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that a single PLZT crystal can be achieved when the precursors are sintered at 900-1 000 °C. The phase of PLZT ceramics will be changed and decomposed into ZrO2 and Pb0.64 La0.206 Ti0.949 O2.846 when the sintering temperature exceeds 1 100 °C. SEM analyses reveal that the powder samples are nanocrystals. TEM analyses show that the PLZT grains are of spherical and polycrystalline structure. [ABSTRACT FROM AUTHOR]