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Acta Mathematica Hungarica
Authors:
M. Asensio
,
J. López Ramos
, and
B. Torrecillas
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Abstract  

It has been established that the coexistence of chemical species structurally different from cerium, is a direct consequence of the time taken for its preparation. Its practical applications, within the scope of purifying uranium, may constitute the most important technological aspect in the process of ionic exchange, to separate141Ce from uranium.

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Abstract  

In the present work Lyocell fibers were subjected to graft copolymerization of poly-N-isopropylacrylamide (pNIPAAm) thermosensitive polymer. The thermal degradation and stability of lyocell/pNIPAAm copolymers gels were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). pNIPAAm/lyocell copolymers are thermally stable and more resistant to temperature than lyocell fibres. Thermal characterization was analyzed as a function of percentage by mass of the pNIPAAm grafted. It has been shown that for pNIPAAm/lyocell copolymers, degradation occurs at higher temperature when increasing the degree of grafting.

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Polymer blends based on an epoxy-amine thermoset and a thermoplastic

Effect of thermoplastic on cure reaction and thermal stability of the system

Journal of Thermal Analysis and Calorimetry
Authors:
J. López
,
M. Rico
,
B. Montero
,
J. Díez
, and
Carmen Ramírez

Abstract  

The effect of thermoplastic modification of an epoxy-amine system on the cure reaction, miscibility and thermal stability of the system was investigated. The cure kinetics showed an autocatalytic behavior. Modifier did not affect either the total reaction heat or the achieved maximum conversion but delayed the kinetics. The model of Horie-Kamal corrected by diffusion factor was used to adjust kinetics in the whole range of conversions. The modified systems showed two glass transitions indicating two separated phases, whose compositions were estimated using the Fox and Couchman equations. Modifier did not affect the thermal and thermooxidative stability of the system.

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Abstract  

The electrophoretic mobility of some radionuclides has been measured to understand its attractive or repulsive tendencies towards other charged species in the medium. In this study, the chemical state of trace concentrations of88Y,103Ru,134Cs, and141Ce in the presence of UO 2 2+ , as a dominant component, in strongly alkaline aqueous solutions (pH>13) was characterized.88Y and141Ce settled almost completely as colloidal species; whereas103Ru,134Cs, and uranium remained as ions. These results closely correlate a procedure for defining both the composition of the water in contact with the fuel and the practical applicability of modified sorbents.

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Abstract  

An effective method to minimize the presence of141Ce in the final hexahydrated uranyl nitrate recovery product has been obtained. This condition is considered as one prepurification stage in the recovery process of residual nonfissioned uranium in the production of99Mo of fission.

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Abstract

Platinum–germanium and platinum–tin catalysts supported on silica, containing different amounts of Sn and Ge, were synthesized using the surface organometallic chemistry on metals technique. The catalysts were characterized using transmission electron microscopy, X-ray photoelectron spectra and X-ray absorption near edge structure and extended X-ray absorption fine structure; and were tested in the liquid-phase selective hydrogenation of furfural. The atomic ratio between the two metals resulted the key factor towards the optimization of the activity and selectivity of the bimetallic catalysts. The bimetallic catalysts were more active than the parent Pt/SiO2 catalyst in the hydrogenation of furfural. These results can be accounted for by considering a new type of active site having an architecture which would favor the hydrogenation of the C=O group is created, allowing an increased activity towards obtaining furfuryl alcohol. All the studied systems allowed to obtain furfuryl alcohol with high selectivity.

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
O. Diaz
,
A. M. G. Figueiredo
,
C. A. Nogueira
,
N. Lopez
,
H. Gonzalez
,
M. V. Manso
,
M. Saiki
, and
M. B. A. Vasconcellos

Summary  

The nonideality of the epithermal neutron flux distribution at a reactor site parameter (α) and the thermal-to-epithermal neutron ratio (ƒ) were determined in three typical irradiation positions of the IEA-R1 reactor of IPEN-CNEN/SP, Sao Paulo, Brazil, using the “Cd-ratio for multimonitor” and “bare bi-isotopic monitor” methods, respectively. This characterization is to be used in the k 0-method of NAA, recently introduced at the IPEN.

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Journal of Thermal Analysis and Calorimetry
Authors:
W. Liu
,
S. Kim
,
J. Lopez
,
B. Hsiao
,
M. Keating
,
I.-H. Lee
,
B. Landes
, and
R. Stein

Abstract  

In this study, the stepwise isothermal crystallization or thermal fractionation of Ziegler—Natta and metallocene based polyethylenes (ZN-PE and m-PE) with two kinds of branch lengths (ethyl and hexyl) and branch compositions were studied using simultaneous synchrotron small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The crystal long period and the invariant were determined by SAXS, and the variations of crystal unit cell parameters and the degree of crystallinity were determined by WAXD. The arithmetic mean length (Ln), the weightedmean length (Lw) and the broadness index (Lw/Ln) of the studied polyethylenes were previously determined by DSC. Results from these studies were interpreted using the model of branch exclusion, which affects the ability of the chain-reentry into the crystal phase. Multiple SAXS peaks and step-change in crystallinity change (WAXD) were seen during heating, which corresponded well with the crystal thickness distribution induced by stepwise crystallization. The effects of the heterogeneity of the 1-olefin branch length and the distribution on the crystal long period and the invariant as well as the degree of crystallinity were discussed.

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