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Abstract  

Both oxidation and methoxymethylation of the surfaces of a series of MDI (methylene diphenyl isocyanate) and TDI (toluene diisocyanate) polyether and polyester soft segment 1–4 butanediol polyurethanes result in increased thermal stability as measured by TG. Explosive loss of mass above the hard segment melting temperature suggests that the diffusion of the dissociated diisocyanate moiety is hindered at lower temperatures. Thus suppression of the depolycondensation reaction by chemical blockage of the surface may result in a material with an increased service life at use temperatures as thermal stability of a polyurethane may depend upon the low diffusivity of its diisocyanate comonomer. The effect of vacuum, oxygen and water vapor on the kinetics of mass-loss of several of the polyurethanes is presented.

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Abstract  

The use of an electrochemical process for U/Pu partitioning has demonstrated a good performance and is a safe alternative for nuclear facilities. Its great advantages are the lack of introduction of foreign ions into the process and, especially, the minimization of the waste volume generated. For the introduction of electrochemical U/Pu partitioning in the 2nd Pu purification cycle, preliminary studies were carried out with a single mixer-settler unit. Based on the results, an 8-stage electrolytic mixer-settler (M-S MIRELE) was designed. Titanium was MIRELE's housing material (cathode) and platinum the anode, insulated with PTFE. The Pu recovery was higher than 99%, indicating the efficiency of this equipment.

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Abstract  

The use of titanium oxide as a photocatalyst in the degradation of organic complexing agents by ultraviolet radiation is being studied as a possible method for the removal of radioactive ions from solutions of these complexing agents that have been used to decontaminate nuclear facilities. Inorganic absorbers are being increasingly used for the decontamination of radioactive aqueous wastes. Information is presented on two areas of study to incorporate inorganic absorbers into a matrix material in order to provide a granular product suitable for use in a packed bed. Finally, information is reported on the combination of inorganic absorbers with magnetite in order to allow separation of the loaded absorber from the treated liquid waste by use of a magnet.

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Abstract  

The paper is devoted to the utilization of ferrofluid as a separating medium and modifying agent affecting the magnetic properties of solid and liquid materials. The separation tests in a MHS separator have been carried out under laboratory condition. The selectivity of ferrofluid's adsorption to the surface of some materials can be used for enhancing the magnetic susceptibility and influencing the efficiency of separation process. The enhancement of magnetic susceptibility of oil products up to a level sufficient for their magnetic extraction from water is possible by admixing of a definite amount of kerosene-based ferrofluid, which is non-miscible with water. The results point to the fact that the MHS method is suitable for the separation of non-magnetic materials according to their density and the modification of magnetic properties of materials by ferrofluid enhancing their magnetic separability.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Evandro de Queiroz, Augusto Knoechelmann, Eliane de Moraes Medeiros, Cesar de Abreu, and Nelson de Lima Filho

Abstract  

In this work, in addition to the nitrous acid formed by reactive uptake of nitrogen dioxide (NO2) in water, it is proposed to reduce the nitrous ions levels by amino sulfonic acid (HSO3NH2) in a mechanically agitated reactor. To this end, the following parameters were considered: agitation speed, pH, temperature, initial concentration of the reagents and their stoichiometric ratios. It was observed that the nitrous acid conversion (98.54%) was enhanced in acidic medium (pH < 2.5), obeying a first-order reaction in relation to both reagents. A heterogeneous model for nitrogen production was proposed and the kinetics for the gas–liquid process was formulated, where the kinetic rate constants were in the range of 2.62–5.52 m3 kmol−1 s−1 and the gas–liquid mass transfer coefficients were in the range of 0.00502–0.00825 s−1.

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Authors studied the effect of copper nutrition on the yield, kernel weight and raw protein content of winter wheat. Copper was applied in the form of copper tetramine hydroxide that was produced from a clean copper containing waste originating from microelectronical industry. After suitable chemical transformation this waste can be used as an excellent secondary raw material for the preparation of copper fertilizer. The foliar application of copper tetramine hydroxide complex at the phenological phase of tillering significantly increased the yield, kernel weight and raw protein content of winter wheat. The calculated copper doses that gave the maximum yield, raw protein content and kernel weight were 1.04, 1.12 and 0.77 kg ha -1 respectively.

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The importance of the thermal behaviour of glasses is illustrated. Some procedural characteristics for glass preparation upon quenching are discussed to distinguish the positive effects of increasing cooling rate. The basic thermodynamic quantities, kinetic data and procedural parameters are listed. The glass-transformation interval is treated in detail to demonstrate the temperature-dependences of heat capacity, enthalpy an Gibbs energy for as-quenched and annealed glasses, exemplifying processes of thermally stimulated reordering. Particular attention is paid to DTA measurements, which are of use for the determination of characteristic temperatures and to for the distinction of possible types of processes which occur upon reheating. Most common cases are illustrated by a series of hypothetical ΔH vs. T and ΔT dta vs. T plots. Different glass formation coefficients based on the onset temperatures are discussed to confirm the general knowledge that their maxima match with concentration regions close to that of invariant melting of the system.

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Journal of Thermal Analysis and Calorimetry
Authors: F. Mezahi, H. Oudadesse, A. Harabi, A. Lucas-Girot, Y. Le Gal, H. Chaair, and G. Cathelineau

Abstract  

The dissolution kinetic and structural behaviour of natural hydroxyapatite (N-HA) and synthetic hydroxyapatite (S-HA) was studied vs. sintering temperature and using ‘in vitro’ experiments. Obtained results highlight the chemical stability of N-HA. Any structural modification was observed until 1200°C. In the fact S-HA undergoes some modifications. XRD diagrams show the tricalcium phosphate (TCP) phase formation between 800 and 1100°C and tetracalcium phosphate (TetCP) phase formation at 1200°C. The ‘in vitro’ assay shows that the dissolution was occurred more in N-HA than in S-HA. The formed TCP activated the dissolution kinetic and then the precipitation phenomena when a continuous dissolution of TetCP leaded to slow down the kinetic precipitation.

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