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271.
Mithlesh Kumar R. M. Kadam T. K. Seshagiri V. Natarajan A. G. Page 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(3):633-637
Thermally stimulated luminescence (TSL) and electron paramagnetic resonance (EPR) investigations were carried out on gamma irradiated SrBPO5 samples doped with CeO2 and co-doped with CeO2 and Sm2O3. On gamma-irradiation at room temperature, BO3
2–, O2
– and O– radicals were produced. It was seen that the O– radical ion disappeared in the sample annealed at 500 K. It is proposed that the recombination between trapped electrons and O– radical ions results in transfer of recombination energy to the impurity centre Ce3+ resulting in TSL glow peak at 485 K. In the case of co-doped samples energy transfer occurs between Ce3+ to Sm3+ resulting in increase in the intensity of glow peak at 485 K.The authors are grateful to Dr. V. K. Manchanda, Head, Radiochemistry Division, BARC for his keen interest and encouragement during the course of this work. 相似文献
272.
C. A. Laue D. Gates-Anderson T. E. Fitch 《Journal of Radioanalytical and Nuclear Chemistry》2004,261(3):709-717
This review focuses on dissolution/reaction systems capable of treating uranium metal waste to remove its pyrophoric properties.
The primary emphasis is the review of literature describing analytical and production-scale dissolution methods applied to
either uranium metal or uranium alloys. A brief summary of uranium's corrosion behavior is included since the corrosion resistance
of metals and alloys affects their dissolution behavior. Based on this review, dissolution systems were recommended for subsequent
screening studies designed to identify the best system to treat depleted uranium metal wastes at Lawrence Livermore National
Laboratory (LLNL).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
273.
Xin‐Gui Li Run‐Feng Chen Mei‐Rong Huang Mei‐Fang Zhu Qun Chen 《Journal of polymer science. Part A, Polymer chemistry》2004,42(9):2073-2092
A new series of copolymers was synthesized through the oxidative polymerization of pyrrole (PY) and o‐phenetidine (PHT) with inorganic oxidants in acidic media. The polymerization parameters including the mixing method of the oxidant with the comonomer, the comonomer ratio, the time, the temperature, the oxidant, the organic medium, and the acid were systematically optimized for the synthesis of copolymers with high yields, intrinsic viscosities, and solubility. The resultant copolymers were characterized by elemental analysis, infrared, ultraviolet–visible, solution high‐resolution 1H NMR and solid‐state high‐resolution 13C NMR, circular dichroism spectroscopy, and cyclic voltammetry. The results showed that the PY observed content in the copolymers was much higher than the PY feed content. The regular variation of the polymerization yield, intrinsic viscosity, solubility, macromolecular structure, and electroactivity of the resulting polymers with the comonomer ratio, together with the complete solubility of a PY/PHT (10/90) polymer in highly polar solvents, indicated the formation of real random copolymers containing both PY and PHT units rather than a mixture of two homopolymers. However, the polymers containing more than 59 mol % PY were not homogeneous copolymers consisting of soluble and insoluble parts. A semiquantitative relationship between the polymerization yield or solubility of the copolymers and the polarity index of the organic solvents was examined. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2073–2092, 2004 相似文献
274.
K. Dayananda R. Dhamodharan K. Vijayakumaran T. Rajamannar 《Journal of polymer science. Part A, Polymer chemistry》2004,42(21):5413-5423
A monolayer of covalently anchored, novel, binaphthyl ketone is used as a surface‐confined photochemical radical generator (PRG) for anchoring a variety of polymers to silicon surfaces. The precursor PRG is synthesized by the application of a facile and novel method for the oxidation of sterically hindered benzylic hydrocarbons to carbonyl compounds. Oxidation was carried out with a stoichiometric amount of potassium peroxydisulfate, in the presence of a catalytic amount of copper sulfate in an acetonitrile/water mixture. The PRG synthesized is characterized by 1H NMR, UV, and Fourier transform infrared (FTIR). The covalently attached monolayers are characterized by X‐ray photoelectron spectroscopy, ellipsometry, and water contact angle measurements. The method developed is applicable to the preparation of a monolayer of a variety of polymers on a wide range of substrates carrying surface hydroxyl groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5413–5423, 2004 相似文献
275.
T. Brian Cavitt Brian Phillips Charles E. Hoyle Bo Pan Sukhendu B. Hait Kalyanaraman Viswanathan Sonny Jnsson 《Journal of polymer science. Part A, Polymer chemistry》2004,42(16):4009-4015
Three‐component photoinitiators comprised of an N‐arylphthalimide, a diarylketone, and a tertiary amine were investigated for their initiation efficiency of acrylate polymerization. The use of an electron‐deficient N‐arylphthalimide resulted in a greater acrylate polymerization rate than an electron‐rich N‐arylphthalimide. Triplet energies of each N‐arylphthalimide, determined from their phosphorescence spectra, and the respective rate constants for triplet quenching by the N‐arylphthalimide derivatives (acquired via laser flash photolysis) indicated that an electron–proton transfer from an intermediate radical species to the N‐arylphthalimide (not energy transfer from triplet sensitization) is responsible for generating the initiating radicals under the conditions and species concentrations used for polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4009–4015, 2004 相似文献
276.
Strain hardening of polycarbonate in the glassy state: Influence of temperature and molecular weight
L. E. Govaert T. A. Tervoort 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2041-2049
This study is concerned with the temperature and molecular weight dependence of the strain-hardening behavior of polycarbonate. It is shown that the strain-hardening modulus reduces with increasing temperature and decreasing molecular weight. This result is interpreted in terms of temperature accelerated relaxation of the entanglement network. Moreover, it is shown that frozen-in orientations, induced by homogeneous deformations above the glass transition temperature, lead to anisotropic yield behavior that can be fully rationalized (and modelled) in terms of a superimposed stress contribution of the prestrained network. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2041–2049, 2004 相似文献
277.
Starch belongs to the polyglucan group. This type of polysaccharide shows a broad β-relaxation process in dielectric spectra at low temperatures, which has its molecular origin in orientational motions of sugar rings via glucosidic linkages. This chain dynamic was investigated for α(1,4)-linked starch oligomers with well-defined chain lengths of 2, 3, 4, 6, and 7 anhydroglucose units (AGUs) and for α(1,4)-polyglucans with average degrees of polymerization of 5, 10, 56, 70, and so forth (up to 3000; calculated from the mean molecular weight). The activation energy (Ea) of the segmental chain motion was lowest for dimeric maltose (Ea = 49.4 ± 1.3 kJ/mol), and this was followed by passage through a maximum at a degree of polymerization of 6 (Ea = 60.8 ± 1.8 kJ/mol). Subsequently, Ea leveled off at a value of about 52 ± 1.5 kJ/mol for chains containing more than 100 repeating units. The results were compared with the values of cellulose-like oligomers and polymers bearing a β(1,4)-linkage. Interestingly, the shape of the Ea dependency on the chain length of the molecules was qualitatively the same for both systems, whereas quantitatively the starch-like substances generally showed higher Ea values. Additionally, and for comparison, three cyclodextrins were measured by dielectric relaxation spectroscopy. The ringlike molecules, with 6, 7, and 8 α(1,4)-linked AGUs, showed moderately different types of dielectric spectra. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 188–197, 2004 相似文献
278.
Hiroaki Miyagawa Michael J. Rich Lawrence T. Drzal 《Journal of Polymer Science.Polymer Physics》2004,42(23):4391-4400
The thermophysical and mechanical properties of a nanocomposite material composed of amine‐cured diglycidyl ether of bisphenol A (DGEBA) reinforced with organomontmorillonite clay are reported. The storage modulus at 100 °C, which was above the glass‐transition temperature (Tg), increased approximately 350% with the addition of 10 wt % (6.0 vol %) of clay. Below the Tg, the storage modulus at 30 °C increased 50% relative to the value of unfilled epoxy. It was determined that the Tg linearly increased as a function of clay volume percent. The tensile modulus of epoxy at room temperature increased approximately 50% with the addition of 10 wt % of clay. The reinforcing effect of the organoclay nanoplatelets is discussed with respect to the Tandon–Weng and Halpin–Tsai models. A pseudoinclusion model is proposed to describe the behavior of randomly oriented, uniformly dispersed platelets in nanocomposite materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4391–4400, 2004 相似文献
279.
Raviraj M Kulkarni Dinesh C Bilehal Sharanappa T Nandibewoor 《Analytical sciences》2004,20(4):743-747
The kinetics of oxidation of isoniazid in acidic medium was studied spectrophotometrically. The reaction between QDC and isoniazid in acid medium exhibits (4:1) stoichiometry (QDC:isoniazid). The reaction showed first order kinetics in quinolinium dichromate (QDC) concentration and an order of less than unity in isoniazid (INH) and acid concentrations. The oxidation reaction proceeds via a protonated QDC species, which forms a complex with isoniazid. The latter decomposes in a slow step to give a free radical derived from isoniazid and an intermediate chromium(V), which is followed, by subsequent fast steps to give the products. The reaction constants involved in the mechanism are evaluated. Isoniazid was analyzed by kinetic methods in pure and pharmaceutical formulations. 相似文献
280.
Abbas Shockravi Samad Bavili T Esmael Rostami Ali Yousefi Ali Dehjurian Rahim Tohidi 《Journal of inclusion phenomena and macrocyclic chemistry》2004,49(1-2):163-166
Some new dibenzosulfo, dibenzosulfoxo macrocyclic diamides are synthesized. 相似文献