Pu Systems Research Articles

Computational study of the interactions of tetravalent actinides (An = Th-Pu) with the α-Fe13 Keggin cluster.

In recent years, evidence has emerged that actinide (An) uptake at the enhanced actinide removal plant (EARP) at the UK's Sellafield nuclear site occurs via An interactions with an α-Fe13 Keggin molecular cluster during ferrihydrite formation. We here study theoretically the substitution of aquo complexes of the actinides Th-Pu onto a Na-decorated α-Fe13 Keggin cluster using DFT at the PBE0 level. The optimised Pu-O and Pu-Fe distances are in good agreement with experiment and Na/An substitutions are significantly favourable energetically, becoming more so across the early 5f series, with the smallest and largest ΔrG° being for Th and Pu at -335.7 kJ mol-1 and -396.0 kJ mol-1 respectively. There is strong correlation between the substitution reaction energy and the ionic radii of the actinides (Δrε0R2 = 0.97 and ΔrG° R2 = 0.91), suggesting that the principal An-Keggin binding mode is ionic. Notwithstanding this result, Mulliken and natural population analyses reveal that covalency increases from Th-Pu in these systems, supported by analysis of the occupied Kohn-Sham molecular orbitals where enhanced An(5f)-O(2p) overlap is observed in the Np and Pu systems. By contrast, quantum theory of atoms in molecules analysis shows that U-Keggin binding is the most covalent among the five actinides, in keeping with previous studies.

Uptake of Ni(II), Eu(III) and Pu(III/IV) by Hardened Cement Paste in the Presence of Proxy Ligands for the Degradation of Polyacrylonitrile

The uptake of 63Ni(II), 152Eu(III) and 242Pu(III/IV) by hardened cement paste (HCP, CEM I) in the degradation stage II (pH ≈ 12.5 [Ca] ≈ 0.02 M) was investigated in the absence and presence of α-hydroxyisobutyric, 3-hydroxybutyric and glutaric acids. These organic ligands were previously identified as proxies for the degradation products of UP2W (a polyacrylonitrile-based material used as filter aid in nuclear power plants) under repository conditions. Sorption experiments were conducted with various ligand concentrations (10−4 M ≤ [L]tot ≤ 0.1 M) and solid-to-liquid ratios (0.5 g⋅dm–3 ≤ S:L ≤ 20 g⋅dm–3). Redox conditions in the Pu systems were buffered with either hydroquinone (HQ, pe + pH ≈ 10) or Sn(II) (pe + pH ≈ 2). Strong sorption is observed for 152Eu(III) and 242Pu(III/IV) in the absence of proxy ligands, with distribution coefficients (log Rd ≈ 2.2–4, with Rd in m3⋅kg–1) in line with data reported in the literature. No differences are observed for sorption experiments with Pu in HQ and Sn(II) systems. Lower Rd values are determined for 63Ni(II) (log Rd,Ni63 ≈ 0-1), consistently with previous studies. In combination with log Rd,Ni determined on the basis of the concentration of stable Ni(II) in pristine HCP and in cement porewater, values of the partition coefficient (α) close to 1 are determined. This suggests that the uptake of 63Ni is possibly driven by isotopic exchange with the complete species inventory of stable Ni present in pristine HCP, including Ni in solid phases and associated with surfaces, e.g., of C-S-H phases. The presence of proxy ligands has a negligible effect on the uptake of 152Eu(III) up to [L]tot = 0.1 M. A slight decrease in the distribution ratios for 63Ni(II) and 242Pu(III/IV) is observed at [L]tot > 10−2 M, although the effect is less evident in the case of plutonium due to the dispersion of the data and the increase of the detection limits with increasing ligand concentrations. Compared to strongly complexing ligands like isosaccharinic acid or gluconate, the investigated proxy ligands show a minor capacity for radionuclide mobilization in cementitious systems, even at high concentrations.

Impact of the degradation leachate of the polyacrylonitrile-based material UP2W on the retention of Ni(II), Eu(III) and Pu(IV) by cement.

The uptake of 63Ni(II), 152Eu(III) and 242Pu(IV) by hardened cement paste (HCP, CEM I) in the degradation stage II (pH ≈ 12.5, [Ca] ≈ 0.02 M) was investigated in the presence of a degradation leachate of UP2W, a polyacrylonitrile-based (PAN) material used as a filter aid in nuclear power plants. The degradation leachate with a concentration of dissolved organic carbon of ∼40 ppm was obtained from the degradation of UP2W in portlandite-buffered solutions for ca. 1100 days. Redox conditions in the Pu systems were buffered with hydroquinone, which defines mildly reducing conditions (pe + pH ≈ 10) where Pu(IV) is the predominant oxidation state. The degradation leachate investigated in this work is moderately sorbed by cement, with distribution ratios (Rd) of (0.35 ± 0.15) m3 kg-1. These values are 30 to 100 times greater than distribution ratios previously reported for proxy ligands of PAN degradation products, i.e., glutaric acid, α-hydroxyisobutyric acid and 3-hydroxybutyric acid. The presence of the degradation leachate induces a moderate decrease in the uptake of 63Ni(II), 152Eu(III) and 242Pu(IV) by cement, as compared to the sorption in the presence of the proxy ligands. Nevertheless, retention in the presence of the degradation leachate remains high for all investigated radionuclides, with Rd(63Ni(II)) ≈ 2 m3 kg-1, Rd(152Eu(III)) ≈ 100 m3 kg-1 and Rd(242Pu(IV)) ≈ 30 m3 kg-1. These observations possibly reflect that the multiple functionalities (-COOH, -OH, amide groups) expected in the macromolecules (10-15 kDa) present in the degradation leachate, can offer further binding/chelating capabilities compared to the small organic proxy ligands with at most bidentate binding.

Synthesis, Characterization of Bio-based Polyol and Assess the Effectiveness of Bio-based Polyurethane Direct-to-metal Coating System

Crude oil is neither a long-lasting energy source nor a raw material source, has a high consumption rate relative to a low regeneration rate and creates massive environmental disorders. Polyurethane is well known and is the most popular film forming material in the coating industry because of its better performance. A coconut oil-based polyol (biobased polyol) was synthesized and acid value, viscosity, reaction water release, oil length, FTIR spectrum, differential scanning calorimetry and colourimetric index were assessed during the synthesis. A series of pigmented wet paint samples were prepared by bio-based polyol and the optimum paint sample was selected among them based on drying time, pencil hardness, dry film thickness, cross hatch test and cylindrical mandrel blending. Two wet PU paint samples, representing commercially available crude oil-based polyols, were prepared to compare in the same aspects with a PU paint sample made with a bio-based polyol (BBP). According to the results, it was proven that bio-based PU paint showed equal magnitudes in film flexibility due to the cylindrical mandrel bending test, film hardness due to the pencil hardness test, substrate adhesion due to the crosshatch test and impact resistance. In some properties, bio-based PU exceeded at least one crude oil-based PU such as gloss, hard drying time and density. Meanwhile, bio-based PU systems must be improved in viscosity and water resistance to compete with artificial PU systems.

Effect of the aramid pulp on the physicochemical, viscoelastic properties and rheokinetics of polyurethanes

This publication highlights the effect of aramid pulp (1 wt.%) on equilibrium swelling, enthalpy reaction, solid viscoelastic properties, and rheokinetics of castor oil (CO) and polyether (PE) polyol blend (50/50 CO/PE) with polymeric isocyanate (pMDI). The CO-pMDI system showed a lower solubility parameter difference (Δδi) than the PE-pMDI and CO/PE-pMDI. Crosslink density values \({v}_{e}\) are higher for CO-pMDI, and when added to aramid pulp, there is a slight increase due to the possible restriction of swollen volume. Regarding the pseudo-solid behavior, AP restricts the macromolecular movement and confers reinforcing characteristics to PU systems. The Prout–Tompkins autocatalytic model satisfactorily described the reactions, resulting in activation energy values Ea within 45 − 54 kJ/mol. However, for the CO/PE blend, the difference between the reactivity of the polyols and the solubility parameter with pMDI results in a two-step reaction kinetics. Aramid pulp practically does not change the reaction mechanism, only the viscosity of the medium. Furthermore, the thermodynamic parameters (ΔS* and ΔH*) indicated that the PU with AP resulted in more ordered complexes. The adequate description of the polymerization reaction and the effect of the aramid pulp allowed for obtaining PU formulations with tunable characteristics for strict composite processing composites.

Studies of Corrosion Resistant Properties of PU Coatings Reinforced with La-Pr-O Nanostructures

This work examines the main parameters to obtain solid solutions of La-Pr-O nanostructures and their incorporation into a poly(urethane) (PU) based on hexamethylene diisocyanate (HDI) (PU-HDI). The effect of obtaining La-Pr-O at different intervals of time was evaluated. Structural results indicated that the alloys, as solid solutions, can be obtained during the first 60 min. These nanostructures were found to have morphologies of agglomerates growing from random and irregular shapes of particles. Once stablished the optimal conditions, 1, 3, and 5 wt.% of La-Pr-O nanostructures were incorporated into PU-HDI through magnetic stirring and deposited onto AISI 1060 carbon steel by spray technique. XRD indicated that the nanostructures were successfully dispersed into PU-HDI with a final reduced crystal size related to the adequate dispersion. The electrochemical findings, such as the displacement in the Ecorr towards to positive direction, an important reduction of the jcorr and polarization resistance, demonstrate that La-Pr-O nanostructures offer an effective strategy to improve barrier properties of PU systems.

Mechanical behavior of particle-reinforced polyurethane composites for load-bearing drives

Two series of polyurethane composites were prepared using NDI- and MDI-based prepolymers and common polyol. NDI-based polyurethane is generally resistant to mechanical wear and rebound-resilient whereas MDI-based PU has cushioning and vibration damping features, and both types can be used as a matrix for load-bearing composites. The objective of this study was to compare the mechanical properties of composites containing 5% vol. of ceramic particles prepared with the use of the mentioned PU systems, and unmodified commercial materials. The effect of various ceramic particles on physical and mechanical properties was studied. The results showed that the mechanical properties changed in comparison to reference materials: E’ improved, and impact strength performed favorably in certain materials. Both the tensile strengths and the elongations at break of the composites were found to decrease with the content of ceramic particles; however, the hardness increased gradually. Since ceramic particles offer better stiffness and hardness, the selected composites could be a viable alternative to the pure commercial PUs available in the industry.

UV-curable self-healing polyurethane coating based on thiol-ene and Diels-Alder double click reactions

Endowing UV-curable coatings with self-healing properties by incorporating dynamic bonds into their cross-linking network is of vital significance. However, in practical applications, self-healing polymers are often plagued with problems such as a high healing temperature and long healing time. To address this challenge, we developed a new type of UV-curable polyurethane coating by the combination of Diels-Alder and thiol-ene click reactions. The Diels-Alder bonds in the polyurethane samples developed in this work furnished perfect mechanical properties and self-healing ability. Self-healing of polyurethane based on Diels-Alder bonds usually occurs at 120 °C. Thiol-ene click reaction is a robust, novel polymerization method, and it improved the structural performance of the polymer with a more homogenous structure being formed than that achieved with traditional UV-curing. Herein, a novel UV-curable self-healing coating, which is referred to as a PU-SH system, was designed by integrating thiol-ene into polyurethane resins containing Diels-Alder bonds. Results of analyses by assorted techniques (including Fourier-transform infrared spectroscopy, different scanning calorimetry, rheology, optical microscopy, and 3D optical interferometric profilometry) strongly indicated that the self-healing ability of the prepared coatings is superior to those of previously studied traditional UV-curing coatings, which are referred to as PU systems. The resultant coatings of the PU-SH system showed a remarkable reduction in the healing temperature from 120 °C for the PU system to 90 ˚C. The rapid scratch-healing properties of the UV-curable coatings, taken together with the moderate healing temperature makes the material attractive for a variety of applications, such as in flexible electronic screens, car paint film, and aircraft interior finishes.

Exploiting thermally-reversible covalent bonds for the controlled release of microencapsulated isocyanate crosslinkers

The paper reports the successful synthesis of microcapsules that incorporate thermally-reversible Diels-Alder or oxime-urethane bonds within the polymer of the microcapsule shell using an interfacial polymerisation technique. The mechanical strength of these microcapsules was found to be dependent on the structure of the thermally-reversible functionality, thus allowing for the design of strong microcapsules that demonstrated excellent stability in one-pot PU formulations. Release of the encapsulated isocyanate crosslinkers using a thermal stimulus demonstrated the potential of this technology for use in the controlled polymerisation of one-pot PU systems.

Predicting Cocrystallization Based on Heterodimer Energies: Part II

Many crystal engineering studies employ urea functionalities for their predictable association into one-dimensional hydrogen bonded chains. Previously, we showed (Cryst. Growth Des., 2015, 15 (10), 5068–5074) that the urea chain motif usually seen in structures of diphenylureas (PUs) with meta-substituents could be disrupted in several cases by cocrystallization with the strong hydrogen bond acceptor triphenylphosphine oxide (TPPO). Computed differences in the urea···urea and urea···TPPO dimer energies of ∼5.3–6 kcal/mol were a reasonably accurate indicator for cocrystallization success. The current study attempts to reassess the limits of this computational approach using a larger set of 16 ortho- and para-substituted PUs. Seven of the 10 PU systems predicted to cocrystallize on the basis of dimer energy calculations were experimentally realized, along with an eighth whose difference in homo/heterodimer energies fell below the threshold. The absence of cocrystallization in two of the predicted systems is...

Polyurethane coatings in twentieth century outdoor painted sculptures. Part II: comparative study of four systems by means of Py-GC/MS

Because PU coatings offer a compromise between aesthetic and performance expectations, unachievable with other types of industrial paints, they are currently recognized as the most appropriate option to coat sculptures intended for an outdoor setting. However, the PU class includes various systems, such as two package solvent-borne, two package water-borne, one package water-borne and fluoropolymer polyurethanes, which possess very different properties. 115 reference samples of PU coatings were investigated by means of Py-GC/MS, in order to outline the differences and the similarities existing, in terms of composition, between the major PU systems used for creating as well as for conserving modern painted outdoor sculptures. The Py-GC/MS study of an extended number of reference samples showed that the composition of equivalent PU systems strongly varies depending on the product line and the manufacturer. Furthermore the comparison of all the produced pyrograms allowed defining characteristic marker compounds helpful to discriminate specific PU paint systems.

Thermodynamic assessment of the Be–Pu and Cd–Pu systems

Thermodynamic assessment of Be–Pu and Cd–Pu systems has been developed with the application of the CALPHAD (Calculation of Phase Diagrams) method, which is established on experimental data including thermodynamic properties and phase equilibria. The Gibbs free energies of the liquid, fcc, hcp, αPu, βPu, γPu, δPu, δ′Pu, and εPu phases were described by the subregular solution model with the Redlich–Kister equation, and those of the intermetallic compounds in the Be–Pu and Cd–Pu binary systems were described by the sublattice model. A set of thermodynamic parameters was derived for describing the Gibbs free energies of solution phases and intermetallic compounds in the Be–Pu and Cd–Pu binary systems. Calculated phase equilibria and thermodynamic parameters are in good agreement with experimental data.

Even–odd effects in prompt emission of spontaneously fissioning even–even Pu isotopes

Abstract The available experimental Y ( A , TKE ) data for 236,238,240,242,244 Pu(SF) together with the Zp model prescription with appropriate parameters allows the investigation of even–odd effects in fragment distributions. The size of the global even–odd effect in Y ( Z ) is decreasing from 244 Pu(SF) to 236 Pu(SF) confirming the general observation of a decrease of the even–odd effect with the fissility parameter. Charge polarizations (Δ Z ) and root-mean squares (rms) as a function of A of 236–244 Pu(SF) were obtained for the first time. In the asymmetric fission region both Δ Z ( A ) and rms ( A ) exhibit oscillations with a periodicity of about 5 mass units due to the even–odd effects. The total average charge deviations 〈 Δ Z 〉 (obtained by averaging Δ Z ( A ) over the experimental Y ( A ) distribution) are of about |0.5| for all studied Pu(SF) systems. The comparison of the calculated Δ Z ( A ) and rms ( A ) of 240 Pu(SF) with those of 239 Pu ( n th , f ) reported by Wahl shows an in-phase oscillation with a higher amplitude in the case of 240 Pu(SF), confirming the higher even–odd effect in the case of SF. As in the previously studied cases ( 233,235 U ( n th , f ) , 239 Pu ( n th , f ) , 252 Cf(SF)) the even–odd effects in the prompt emission of 236–244 Pu(SF) are mainly due to the Z even–odd effects in fragment distributions and charge polarizations and the N even–odd effects in the average neutron separation energies from fragments 〈 Sn 〉 . The size of the global N even–odd effect in 〈 Sn 〉 is decreasing with the fissility parameter, being higher for the Pu(SF) systems compared to the previously studied systems. The prompt neutron multiplicities as a function of Z , ν ( Z ) , exhibit sawtooth shapes with a visible staggering for asymmetric fragmentations. The size of the global Z even–odd effect in ν ( Z ) exhibits a decreasing trend with increasing fissility. The average prompt neutron multiplicities as a function of TKE show an increase of the even–odd effect with increasing TKE, with global effect sizes close to each other (a decrease of the effect for heavier fissioning nuclei is not observed here). The amounts of the global even–odd effect in Y ( Z ) and of the N even–odd effect in 〈 Sn 〉 of 240 Pu(SF) are larger compared to 239 Pu ( n th , f ) . This fact affects the prompt emission leading to a lower Z even–odd effect in the prompt neutron multiplicity of 240 Pu(SF) compared to 239 Pu ( n th , f ) .

Thermodynamic assessments of the Pu–Zn and La–Pu systems

The thermodynamic description of the Pu–Zn and La–Pu systems were obtained using the CALPHAD (Calculation of Phase Diagrams) method on the basis of experimental information for phase equilibria and thermodynamic properties. The Gibbs free energies of the liquid, (εPu), (δ′Pu), (δPu), (γLa) and (βLa) phases were described by the subregular solution model. Seven intermetallic compounds (PuZn2, Pu13Zn58, Pu3Zn22, Pu2Zn17, κ, κ′, and λ) were modeled by the sublattice model. A reasonable agreement between the present calculated results and experimental data has been achieved with a set of optimized parameters.

Study on Thermal and Mechanical Properties of Polyurethane Systems for In-Mould Decoration Ink

In this study, three polyurethane systems A (A450/RD181/L75), B(A450/RD181/N3390) and C(A450/RD181/2104/N3390) for in-mould decoration ink were studied. The results of thermogravimetric analysis showed that introducing rosin modified phenolic resin 2104 (RMPR) and N3390 into PU system A can improve the thermal stability, Moreover, Measurements of gel fraction and swell ratio showed that incorporation of N3390 is benificial for increasing the cross-linking density of PU systems as compared to L75 so as to increase the gel fraction and decrease the swell ratio.The tensile strength of cured PU systems increased following in the order: A<B<C, elongation at break is just the opposite. In addition, it is indicated that incorporation of N3390 is benificial for increasing the cross-linking density of PUs so as to improve the the shore A hardness and decease the water sorption.

The effects of mesoscale confinement in Pu clusters and isolated particles

Calculations of the electronic structure of Pu crystal clusters and isolated particles formed by a finite number of atoms have been performed in terms of the fully relativistic discrete variational (RDV) method, using two types of atomic wave functions incorporated into the RDV code. The density of states results for the central atoms of the finite-size Pu systems as well as the calculated 4f core level energy schemes, for the clusters of different size and structure have been compared to the relevant experimental spectra obtained by synchrotron-radiation-based photoelectron spectroscopy. The robust result of our investigation is the observation of systematic average electronic structure evolution from atomic to bulk behavior through the cluster/nanoparticle regime. The effects of mesoscale confinement established in the present work impose certain limitation for the electronic structure of bulk plutonium and can be useful for the interpretation of Pu photoelectron spectra.

Controlled iodine release from polyurethane sponges for water decontamination

Iodinated polyurethane (IPU) sponges were prepared by immersing sponges in aqueous/organic solutions of iodine or exposing sponges to iodine vapors. Iodine was readily adsorbed into the polymers up to 100% (w/w). The adsorption of iodine on the surface was characterized by XPS and SEM analyses. The iodine loaded IPU sponges were coated with ethylene vinyl acetate (EVA), in order to release iodine in a controlled rate for water decontamination combined with active carbon cartridge, which adsorbs the iodine residues after the microbial inactivation. The EVA coated IPU were incorporated in a water purifier and tested for iodine release to water and for microbial inactivation efficiency according to WQA certification program against P231/EPA for 250l, using 25l a day with flow rate of 6–8min/1l. The antimicrobial activity was also studied against Escherichia coli and MS2 phage. Bacterial results exceeded the minimal requirement for bacterial removal of 6log reduction throughout the entire lifespan. At any testing point, no bacteria was detected in the outlet achieving more than 7.1 to more than 8log reduction as calculated upon the inlet concentration. Virus surrogate, MS2, reduction results varied from 4.11log reduction under tap water, and 5.11log reduction under basic water (pH9) to 1.32 for acidic water (pH5). Controlled and stable iodine release was observed with the EVA coated IPU sponges and was effective in deactivating the bacteria and virus present in the contaminated water and thus, these iodinated PU systems could be used in water purification to provide safe drinking water. These sponges may find applications as disinfectants in medicine.

Thermal stability, curing kinetics and properties of polyurethanes system for in‐mould decoration ink

PurposeThe purpose of this paper is to study thermal stability, curing kinetics and physico‐chemical properties of polyurethanes systems for application in in‐mould decoration (IMD) ink.Design/methodology/approachThe thermal stability of three Polyurethane (Pu) systems A, B, C were evaluated by thermogravimetric analysis (TGA). The kinetic parameters of the curing reaction of Pu system C were calculated using non‐isothermal curing kinetics analysis, including the activation energy Ea, the reaction rate constant K(T), the reaction order n, the initial curing temperature (Ti), the peak temperature (Tp), and the finishing temperature (Tf). Additionally, physico‐chemical properties were also evaluated such as flexibility, impact resistance, pencil hardness, adhesive attraction and solvent resistance.FindingsTGA showed that thermal decomposition temperature T5 (5 wt.% weight loss), T10 (10 wt.% weight loss) and Tend (decomposition termination temperature) of Pu system C was 344°C, 363°C, and 489°C, respectively. T5, T10, Tend increased by 77°C, 61°C, 4°C, respectively, and the char yield at 600°C increased by 25.1 wt.% comparing with Pu system B. Curing kinetics analysis showed that Ea of Pu system C was 62.29 KJ/mol, 65.98 KJ/mol and 65.95 KJ/mol by Kissinger, Flynn‐Wall‐Ozawa and Ozawa method, respectively. The order of the curing reaction (n=0.90) demonstrated that it was a complex reaction. Moreover, Pu system C exhibited good physico‐chemical properties. The results showed that Pu system C was suitable to apply into IMD ink.Research limitations/implicationsThe TGA analysis, curing kinetics analysis and evaluation of physico‐chemical properties provided a simple and practical solution to study suitable resins for IMD ink application.Practical implicationsIMD ink for heat transfer printing technology is highly efficient, relatively low cost, clean and environmentally safe. It has been widely applied into medical and pharmaceutical products, electronic devices, telecommunication equipment, computer parts, appliance panels, automotive parts, etc.Originality/valueIn this paper, the thermal stability and curing kinetics of Pu for IMD ink are reported for the first time. The paper gives very interesting and important information about thermal stability, curing kinetics and properties of Pu coating system for IMD ink application.

Kinetics of UV-curing of waterborne polyurethane acrylate dendrimer

In this study, a dendrimer with 19 sites was modified to form a waterborne oligomer with hydrophilic sites and polyurethane acrylate (PUA) sites. Two PU systems hexamethylene diisocyanate (HDI) and methylene-bis (4-cyclohexylisocyanate) (HMDI) were used; each of them had 5, 9, and 13 PUA sites, respectively. Experimental results revealed that the HDI system was more thermally stable than the HMDI system. The HMDI system, however, exhibited better hardness than the HDI system, even though the final curing conversion of HMDI was low. Additionally, more PUA sites of a dendrimer were associated with greater hardness of the cured resin. In a UV-curing study, simulations revealed that the autocatalysis model could describe the UV-curing mechanism of the PUA-dendrimer system. Both the reaction rate constant k and the final conversion α were highest at a concentration of the photoinitiator of approximately 3 wt% for both HDI and HMDI systems. The reaction rates of both systems were highest when the number of PUA sites was nine. The final conversion of both the systems, however, was optimal when the number of PUA sites was 13. The final conversion in the acrylic reaction increased with temperature up to 80 °C for both the systems, owing to an increase in the ratio of potentially active sites against nonactive sites, according to Arrhenius theory. The rate constant, k, however, was optimal at 60 °C because a higher temperature damaged the photoinitiator. Finally and most importantly, HMDI always had a lower rate constant k and final conversion α than HDI under similar conditions in studies that were conducted to examine the effects of photoinitiator concentration, number of PUA sites, and reaction temperature, revealing that the steric hindrance by the cyclohexane in HMDI negatively influenced its curing kinetics.

Solid-State NMR Study on Actinide Dioxides

ABSTRACTBesides the importance of the actinide dioxide series as a nuclear fuel, the magnetic properties of these compounds at low temperatures are particularly interesting. Their surprisingly varied physical properties at low temperatures stimulate continuing interest for both theory and experiment. Recently, we have performed 17O-NMR studies for the first time on Pu and Amcontaining dioxide systems, (Pu1-xAmx)O2. For the x=0.09 sample, a temperature-dependent NMR line broadening has been observed at low temperatures. By comparing the experimental data with the results of NMR line simulations, we have estimated the effective moment of Am ions to be Peff=1.38 μB. The value suggests the 5f5 (Am4+) state of the Am ion in PuO2. For the x=1 (=AmO2) sample, on the other hand, our 17O-NMR data provide the first microscopic evidence for a phase transition at 8.5 K as a bulk property in this system. A spectrum with a triangular line shape indicates that the internal field is distributed very nearly randomly in the ordered state.