[en] Isospecific propylene polymerization behavior of meta- and para-Lewis base (E) functionalized unbridged zirconocenes ([1-(E_n-Ph)-3,4-Me₂C₅H₂]₂ZrCl₂, E = NMe₂, OMe; n = 1 or 2) was investigated under bulk conditions. Catalytic activity of the zirconocenes, and molecular weight and isotacticity of polypropylenes are found to be dependent on the position and number of the Lewis base functional groups in the zirconocenes. All the crude polypropylenes possess a broad molecular weight distribution and multi-melting transitions, indicating an involvement of multi-catalytic active species in the polymerization. The highest [mmmm] value of an isotactic portion of the polypropylenes reached 89%, which is higher than that (85%) from the well-known C₂-symmetric EBIZr (rac-Et(Ind)₂ZrCl₂) catalyst. These results support that the in situ generated, rigid rac-like cation-anion pair through the Lewis acid-base interactions between the functional groups of zirconocenes and methylaluminoxane anion is effective in the formation of isotactic polypropylene under bulk propylene polymerization conditions

[en] The thermal expansion coefficients of zirconolite, both ordered and disordered, and perovskite, were measured by X-ray powder diffraction analysis in the temperature range 25-1200deg C. The principal results are: (1) The mean thermal expansion coefficients (K^-1) of ordered zirconolite are: α_a = (11.35 ± 0.25) x 10^-6; α_b = (8.72 ± 0.22) x 10^-6; α_c = (10.0 ± 0.5) x 10^-6. (2) The mean thermal expansion coefficients (K^-1) of disordered zirconolite are α_parallel = (9.89 ± 0.15) x 10^-6 in the (001) plane and α_{perpendicularto} = (9.37 ± 0.14) x 10^-6 normal to (001). (3) The mean thermal expansion coefficients (K^-1) of perovskite are: α_a = (7.86 ± 0.30) x 10^-6; α_b = (13.46 ± 0.17) x 10^-6, α_c = (16.55 ± 0.26) x 10^-6. (orig.)

[en] Pyrochlore-rich and zirconolite-rich ceramics have been developed for the immobilization of excess weapons Pu. The ceramics are composed of a mixture of pyrochlore, zirconolite, brannerite and rutile. Impurity ions are present in most Pu-waste streams. Most of these impurities can be incorporated into the phases present in the ceramic; however some, such as B and Si, can promote the formation of additional phases. In this work, the impurity ions were classed into sets with supposedly the same valency (2+, 3+, 4+, 5+ and 6+). One set containing Np and Th and another set containing the glass formers (Al, Si, B, Na and K) were also made. These sets of elements were then added to a 'baseline' ceramics of nominal sintered composition, 95 wt.% pyrochlore (Ca_0.89Gd_0.22(Pu or Ce)_0.22U_0.44Hf_0.23Ti₂O₇) and 5 wt.% HF-doped rutile, (Ti_0.9Hf_0.1O₂). A sufficient amount of each of these sets of impurity ions was added so that the primary phases of the baseline ceramic were saturated with them and secondary phases formed. Both Pu/U-doped Ce/U-doped samples were made. The impurity elements were added as nitrates to an alkoxide-route precursor, which was calcined and then ball milled. Pellets were pressed from the powder and sintered in Ar, air or 3.7% H₂ in Ar at about 1350 degrees Celsius for 4 hours. The obtained results are summarized in this work. As a matter of fact, most of the ions can be accommodated in the ceramic, but the partitioning across the different phases in the ceramic is not even. The groups will preferentially move to certain phases or, if sufficient amounts are present, result in the formation of new phases. The conclusion is that all ions of similar size and valency behave in a similar manner unless there are volatility problems

[en] Zirconolite is one of the matrices considered for the confinement of minor actinides in case of deep geological disposal. Its chemical durability has been studied during dissolution under charged particle-induced water radiolysis (He²⁺ and proton external beams) to identify possible effects on dissolution rates and mechanisms. Two experimental geometries have been used to assess the influence of the solid irradiation on one hand and the total deposited energy into water on the other hand. These irradiations have been performed on polycrystalline zirconolite (Ca_0.8Nd_0.2ZrTi_1.8Al_0.2O₇) in pure water or in presence of complexing ions such as F^-. The sample dissolution has been monitored through the release of cations. Under radiolysis, an increase in the Zr, Ti and Nd releases of one order of magnitude has been observed compared to results obtained without radiolysis. The presence of complexing species has induced an additional increase of two orders of magnitude in the Ti and Zr releases. (authors)

[en] The nuclear materials (glasses and ceramics) have been under investigation since decades to account their radiation resistivity, structural and chemical response through ion beam irradiation for the immobilization of HLWs from environment. But ceramics among which titanate based ones, known as SYNROCS, have been reported to be more advantageous over glasses due to their low solubility in water, resistant to radiation damage, high waste loading, high thermal and mechanical stability, and simple processing

[en] The heat treatment conditions are a key factor in fabricating zirconolite ceramics and glass-ceramics following high-temperature melting. An oxide mixture melted at 1450 deg C and subsequently heat-treated at 1200 deg C yielded a glass-ceramic containing crystallized zirconolite-2M. The silica-enriched residual glass represented about 60-70 vol% of the total; the actinide surrogates (Nd, Ce) were equally distributed between the residual glass and the zirconolite crystals. Zirconolite ceramics obtained after melting an oxide mixture at 1600-1700 deg C consisted of zirconolite, perovskite and rutile. Rapid cooling rates (> 100 deg C-min^-1) were obtained by pouring the melt into ingot molds; the resulting zirconolite ceramics were characterized by crystals of zirconolite-2M ranging from 1 to no more than 20 μm. Slow cooling (< 25 deg C.min^-1) produced ceramics with crystals several hundred micrometers long. Despite the microstructural differences, the chemical durability of the zirconolite ceramics was identical. The initial alteration rates r₀ were about two orders of magnitude lower than those measured for the residual aluminosilicate glass of the zirconolite glass-ceramics. Moreover, during long-term leach tests at high S/V ratios to obtain advanced degrees of reaction progress, the alteration rates of all the materials diminished by over 3 to 4 orders of magnitude below r₀. Copyright (2001) Material Research Society

[en] The study of the desorption of Fe"2"+, Cr"3"+, and Zn"2"+ ions in zircon concentrate with HNO_3, HCl, HNO_3 + HCl and H_2O has been conducted. The purpose of this study (1) to obtain that % of desorption, desorption profile and desorption constant of Fe"2"+, Cr"3"+, and Zn"2"+ into HNO_3, HCl, HNO_3 + HCl and H_2O. Subsequently to (2) of this study would predict the speed of desorption constant (k_d_e_s). The research of desorption and constant of desorption were conducted with teflon bomb digester with a variation of contact time. Results of % desorption, desorption rate and desorption constant turns HCl best solvent for the Zn"2"+ ion was obtained that the value of kdes 6.61.10"-"3 minutes"-"1, with a value of kdes on successive ion, i.e Zn"2"+ > Fe"2"+ > Cr"3"+. On the using of HNO_3 solvent the highest of kdes was obtained on Fe"2"+ ions at value of kdes 6.1 x 10"-"3 min"-"1, with the order of Fe"2"+ > Cr"3"+ > Zn"2"+. At the using mixture of HNO_3+HCl was obtained that a value of kdes were similar to solvent of HNO_3 with value of kdes to 3.8 x 10"-"3 min"-"1. While for the solvent H_2O seems only Fe"2"+ which has the highest value of desorption constant (k_d_e_s) 1.04 x 10"-"3 min"-"1. (author)

[en] The purpose of this report is to assess the effects of heavy-ion irradiation on the durability of pyrochlore-rich baseline ceramics and single-phase pyrochlore, zirconolite and brannerite ceramics

[en] Zirconolite (CaZrTi₂O₇) is a proposed ceramic for the disposal of plutonium. Density functional theory with the dispersion correction (DFT-D3) has been used to study the behaviour of the He defect in zirconolite. The lowest energy He interstitial site is located in the 〈0 1 0〉 channels and found to have a migration barrier of 1.46 eV. There was a significant charge state dependence on the binding energies of a He atom to the vacancies, with the neutral 5-fold coordinated Ti having the strongest binding followed by the Ca vacancies. Multiple He interstitials were studied to examine if He bubbles were likely to form in bulk zirconolite. It was found that it was unfavourable for He to cluster at the concentrations studied

[en] Study of defect-formation process in fianite with different defection structure rate under the gamma-rays action is carried out. The preliminary irradiated and non-irradiated fianite crystals adsorption spectra by the different neutron fluences with different stabilizator concentration after irradiation were examined. It is shown, that in the preliminary irradiated crystals a two-stage increase of the 450 and 530 bands intensities has been taken place. The defects accumulation second stage is beginning when gamma-rays dose value decrease with the neutron fluence growth. It is suggested, that the first stage of oxygen vacancies accumulation is caused by pre-radiation vacancies manifestation. The second stage is caused by formation of additional vacancies due to excitons non-radiation decay near initial structures damage. Decrease of the gamma-rays dose - when the vacancies accumulation second stage is beginning - is related with the fianite crystal defection structure increase during the preliminary irradiation fluence growth