Kitheri Joseph

Bio: Kitheri Joseph is an academic researcher from Indira Gandhi Centre for Atomic Research. The author has contributed to research in topics: Iron phosphate & Glass transition. The author has an hindex of 13, co-authored 29 publications receiving 401 citations. Previous affiliations of Kitheri Joseph include Loughborough University.

Iron phosphate glasses: structure determination and displacement energy thresholds, using a fixed charge potential model

Abstract: Iron phosphate glass is a versatile matrix for the immobilisation of various radioactive elements found in high-level nuclear waste (HLW). Quenched glass structures of iron phosphate glasses with Fe/P ratios of 0.33, 0.67 and 0.75 and with a composition of 40 mol% Fe 2 O 3 and 60 mol% P 2 O 5 , with 4% and 17% Fe 2 + ion concentrations were generated using molecular dynamics and the threshold displacement energies calculated. In the minimum energy structures, we found that in nearly all cases the P atoms were 4-fold coordinated. The potential energy per atom increased with increasing concentration of Fe 2 + ions with similar Fe/P ratio, suggesting that decreasing the Fe 2 + content is a stabilising factor. The average bond distances between Fe 2 + –O, Fe 3 + –O, P–O and O–O were calculated as 2.12, 1.88, 1.5 and 2.5 A respectively. The threshold displacement energy (E d ) was found to be dependent upon the ion specie, less for Fe 2 + ions compared to Fe 3 + ions, and was overall slightly lower than that determined for borosilicate glass.

A versatile monazite–IPG glass–ceramic waste form with simulated HLW: Synthesis and characterization

Abstract: In Ca doped CePO 4 monazite (viz., Ce 0.8 Ca 0.2 PO 4 ) cerium exhibits mixed valence state (+3 and +4) and therefore can accommodate cations of any valence (by converting Ce 3+ to Ce 4+ or vice versa) subject to the size and other restrictions. A simulated waste form prepared based on the versatile monazite phase, Ce 0.8 Ca 0.2 PO 4 , showed higher leaching for Cs and Mo indicating that these elements do not enter the monazite lattice. Iron phosphate glass (IPG) is an alternate glass waste form considered for HLW immobilization. A glass–ceramic composite of crystalline monazite and IPG could have synergistic effects and can improve the leaching resistance. The preparation and characterization of a versatile monazite–IPG glass–ceramic waste form with 20 wt.% simulated HLW oxides and its leaching behavior are reported in this paper. The monazite–IPG glass–ceramic simulated waste form is found to have excellent chemical durability.

A review of the structures of oxide glasses by Raman spectroscopy

Abstract: The family of oxide glasses is very wide and it is continuously developing. The rapid development of advanced and innovative glasses is under progress. Oxide glasses have a variety of applications in articles for daily use as well as in advanced technological fields such as X-ray protection, fibre glasses, optical instruments and lab glassware. Oxide glasses basically consist of network formers, such as borate, silicate, phosphate, borosilicate, borophosphate, and network modifiers such as alkali, alkaline earth and transition metals. In the present review article, Raman spectroscopy results for the structures of borate, silicate, phosphate, borosilicate, borophosphate, aluminosilicate, phosphosilicate, alumino-borosilicate and tellurite glasses are summarized.

Structure of phosphate and iron-phosphate glasses by DFT calculations and FTIR/Raman spectroscopy

Abstract: Phosphate glasses are very promising materials from the application and fundamental point of view. Properties of the glasses are strongly related to the structure which may be modified by various glass constituents. In the paper density functional theory calculations of simple phosphate structural units, chains build of them and iron-phosphate clusters are presented. Influence of a position of the unit in the chain is described. Structural changes of the units due to formation of bonds between non-bridging oxygens and iron atoms in different coordinations are shown. The optimized clusters are used then to calculate theoretical Raman and Fourier transform infrared spectra. The calculated spectra are then compared to the experimental results for an iron-phosphate glass from the pyrophosphate stoichiometry region. Finally the structural features of the glass are described.