Oxidation behavior of Incoloy 800 under simulated supercritical water conditions

For a correct design of supercritical water-cooled reactor (SCWR) components, data regarding the behavior of candidate materials in supercritical water are necessary. Corrosion has been identified as a critical problem because the high temperature and the oxidative nature of supercritical water may accelerate the corrosion kinetics. The goal of this paper is to investigate the oxidation behavior of Incoloy 800 exposed in autoclaves under supercritical water conditions for up to 1440 h. The exposure conditions (thermal deaerated water, temperatures of 723, 773, 823 and 873 K and a pressure of 25 MPa) have been selected as relevant for a supercritical power plant concept. To investigate the structural changes of the oxide films, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX) and electrochemical impedance spectroscopy (EIS) analyses were used. Results show changes in the oxides chemical composition, microstructure and thickness versus testing conditions (pressure, temperature and time). The oxide films are composed of two layers: an outer layer enriched in Fe oxide and an inner layer enriched in Cr and Ni oxides corresponding to small cavities supposedly due to internal oxidation.     

Heterogeneous cationic polymerization of 1,3-dioxolane and 1,3-dioxepane using grafted BF3 on silica

Summary A BF₃ complex has been grafted onto silica and used as initiator to polymerize 1,3-dioxolane and 1,3-dioxepane. Grafting the active centers leads to a decrease of the reaction rate. The molecular weight increases steadily, parallel to the monomer conversion and the polydispersity is rapidly stabilized at a low value. MALDI-TOF mass spectrometry analysis shows that most of the polymer chains are initiated by a proton and lost a CH₂O unit. An exchange process between polymer chains bound to the silica and those remaining in the reactional medium was proposed. Finally, a semi-continuous process was investigated by adding continuously dioxolane during a 100 hours period. Received: 21 February 2001/ Revised version: 2 November 2001/ Accepted: 6 November 2001     

Influence of the chemical structure of transfer agents in coordinated anionic ring‐opening polymerization: application to one‐step functional oligomerization of ε‐caprolactone

Coordinated anionic ring‐opening polymerization of ε‐caprolactone in the presence of alcohols enables functional oligocaprolactones to be obtained easily in a single step. As observed by NMR and Maldi Tof mass spectroscopy, the functionalization of the oligomers, as well as the molecular weight distribution, depend strongly on the chemical structure of the alcohol. Hydroxy telechelic polymers can also be used as transfer agents. Finally, it was found that the chemical nature of the alcohol has a great influence on the kinetics, which suggests a coordination of this moiety on the Lewis site, during all the reaction. Copyright © 2004 Society of Chemical Industry     

Study of dioxolane-dioxepane copolymers through IR and DSC

Summary The composition of the copolymers of 1,3-dioxolane with 1,3-dioxepane was investigated using FT-IR and DSC. The first method produce accurate values for the overall composition, the later allows discriminating between the copolymer and the mixture of homopolymers.     

Study of the cationic photopolymerization kinetics of cyclic acetals

Summary Photocationic polymerization for three cyclic acetals, namely 1,3-dioxolane, 1,3-dioxepane and 1,3,6-trioxocane, respectively, has been studied. Several cationic photo-initiators (diaryliodonium or triarylsulfonium salts, and one arene-metal complex) have been used. Differential scanning photo-calorimetry (DPC) has been employed to record the dependence conversion versus time. DPC thermogrames, in turn, have been utilized to calculate the propagation reaction constants as well as the corresponding activation energies. The values for the propagation constants at 30°C are 1.6·10² L/mol·s for 1,3-dioxolane, using a diaryliodonium salt as photoinitiator, 1.6·10³ L/mol·s for 1,3-dioxepane and 6.1·10³ L/mol·s for 1,3,6-trioxocane, respectively, in the presence of a triarylsulfonium salt as photoinitiator. The activation energies are in the range of 9.6÷19.6 kcal/mole. Received: 19 July 2000/Revised version: 8 November 2001/ Accepted: 8 November 2001