SPS technique for ionizing radiation source fabrication based on dense cesium-containing core.

The work presents a novel method for fabrication of the high-quality ionizing radiation source (IRS), which is promising to replace unsafe commercial products based on 137CsCl prohibited by IAEA. Spark plasma sintering (SPS) technique has been applied to produce dense ceramic and glass-ceramic matrixes from Cs-containing (˜13.5 wt.%) zeolite yielding in non-dispersible cores sealed in the container of radiation-resistant steel (J93503, US standard). One-stage SPS regimes to provide high-quality product have been optimized: sintering temperature <1000 °C, heating and holging duration 13 and 5 min, respectively, pressure 24.5 MPa. XRD, SEM, EDX, BET, XFS and solid-state MAS NMR 133Cs methods prove exceptional physico-chemical and mechanical characteristics of the obtained materials, namely: density 99.8% from theoretical, compressive strength ˜477 MPa, leaching rate 10-4-10-6 g cm-2 day-1. Results of the investigation can be promising for fabrication of the IRS cores on a large scale as done for similar Russian products RSL, IGI-C, M37C, GID-C.

An alternative approach to kinetic analysis of temperature-programmed reaction data.

To date, kinetic computations have been carried out efficiently for a great variety of physico-chemical processes including crystallization, melting and solid-solid transitions. However, appropriate methods for the kinetic analysis of chemical reactions, especially multi-staged reactions, are currently lacking. Here we report on an alternative way of treating temperature-programmed reaction data using the reduction of iron(iii) oxide as an example. The main principle in the suggested approach is to take into account every stage of the studied process, resulting in a system of kinetic differential equations. Kinetic parameters (activation energy and preexponential factors) are optimized for each of the stages, and cubic splines are used to approximate the conversion functions that reflect changes in reaction-specific surface area throughout the process. The applicability of the suggested method has been tested on temperature-programmed reduction (TPR) data for iron(iii) oxide samples produced from the original Fe2O3 powder by annealing it at 600, 700 and 800 °C. Results of kinetic analysis obtained at different temperature regimes demonstrate the good stability and performance of the method. Peculiarities of iron(iii) oxide reduction have been revealed, depending on the stage and heating rate. The influence of material morphology on the reduction kinetics has been assessed by comparing preexponential factors corresponding to the first reduction stage. This approach allows a comparison of the structural characteristics of the materials based on the kinetic analysis of the TPR data. Using optimized conversion functions, the initial particle size distribution has been reproduced. Theoretically found particle size distribution was found to correlate well with the experimental distribution obtained via laser diffraction.

Interaction of carboxylic acids with chitosan: effect of pK and hydrocarbon chain length.

Sorption of acetic, propionic, butyric, valeric, and isovaleric acid on chitosan and cross-linked chitosan was studied in aqueous solutions and water/ethanol mixtures. Langmuir, Freundlich, and Redlich-Peterson equations were used to fit experimental isotherms of sorption. Correlation between maximum sorption and the pK value of every carboxylic acid was found for sorption on chitosan in aqueous solutions, while sorption in water/ethanol mixtures was mainly determined by structure and the hydrocarbon chain length of the carboxylic acid. Slight molecular-sieves effect was found for carboxylic acids sorption on cross-linked chitosan.