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Very short burn times of nanocomposite, fully dense, stoichiometric 2Al·3CuO thermite particles ignited by electro-static discharge (ESD) observed in earlier experiments are interpreted assuming that the reaction occurs heterogeneously at the Al–CuO interfaces while the initial nanostructure is preserved even after the melting points of various phases present in the particle are exceeded. The heating rate for the ESD-ignited particles is very high, reaching 109 K s−1. The reaction model assumes that the rate of reaction is limited by transport of the reacting species across the growing layer of Al2O3 separating Al and CuO. The model includes the redox reaction steps considered earlier to describe ignition of 2Al·3CuO nanocomposite thermites and adds steps expected at higher temperatures, when further polymorphic phase changes may occur in Al2O3. A realistic distribution of CuO inclusion sizes in the Al matrix is obtained from electron microscopy and used in the model. The model accounts for heat transfer of the nanocomposite particles with surrounding gas and radiative heat losses. It predicts reasonably well the burn times observed for such particles in experiments. It is also found that neglecting polymorphic phase changes in the growing Al2O3 layer and treating it as a single phase with the diffusion-limited growth rate similar to that of transition aluminas (activation energy of ca. 210 kJ mol−1) still leads to adequately predicted combustion temperatures and times for the nanocomposite particles rapidly heated by ESD. The model highlights the importance of preparing powders with fine CuO inclusion sizes in the nanocomposite particles necessary to complete the redox reaction; it is also found that the particle combustion temperatures may vary widely depending on their dimensions. Higher combustion temperatures generally lead to greater reaction rates and, respectively, to the more complete combustion. [ABSTRACT FROM AUTHOR]

Nanocomposite powders with aluminum as a fuel and oxides of molybdenum, copper, bismuth, and iron as oxidizers were prepared by arrested reactive milling. The powders were placed in 0.5-mm-thick layers and ignited by electrostatic discharge (ESD) in air. In different tests, time-resolved light emission was recorded at 568 nm or in the range of 373–641 nm. The amount of material consumed was recorded as well. Time-resolved temperatures were determined. Two distinct ignition regimes were observed. Prompt ignition occurred within 10 µs of the electric discharge, comparable to what had previously been observed for corresponding powder monolayers. This ignition mode was observed for composites with Bi2O3and Fe2O3ignited with a 12-kV discharge, whereas it only occurred at higher spark voltage (20 kV) and energy for CuO and MoO3composites. Delayed ignition, occurring after 0.1–1 ms following the discharge, was observed for all composites with consistently stronger light emission. Analysis of quenched, partially burned particles showed that the original nanostructure was preserved after prompt ignition but not after delayed ignition. It is proposed that prompt ignition represents direct ESD initiation of composite particles rapidly and adiabatically preheated to high temperatures while keeping the nanostructure intact, resulting in a heterogeneous reaction consuming most of the aluminum. Delayed ignition occurs when particles preheated to lower temperatures start oxidizing at much lower rates, leading to cloud combustion, in which thermal interaction between individual aerosolized burning particles is substantial. During this process, the nanostructure may be lost. Temperature measurements show that nanocomposites with CuO and MoO3burned superadiabatically with flame temperatures exceeding thermodynamic predictions. [ABSTRACT FROM PUBLISHER]

Aims: To determine the effect of chlorine on mixed bacterial biofilms on stainless steel (SS) and conveyor belt surfaces. Methods and Results: Biofilms were exposed to pH-adjusted (6·5) and non-pH-adjusted solutions of chlorine (200, 400 and 600 ppm) for either 2, 10 or 20 min and survivors enumerated. There were significant differences in cell death relating to chlorine concentration and exposure time for the cells attached to the SS, with solutions adjusted to pH 6·5 being more effective at reducing numbers. In contrast, on conveyor belt surfaces cell numbers decreased by less than two logs after 20 min regardless of treatment. Conclusions: Chlorine effectiveness is dependent on its concentration, solution pH, exposure time, the nature of the surface and the microbial species present. Significance and Impact of Study: In the interests of food safety it is important that sanitizer users are aware of the conditions that effect their performance. [ABSTRACT FROM AUTHOR]

A pilot plant steam treatment system was developed to reduce L. monocytogenes contamination on exterior surfaces of King Salmon (Oncorhynchus tshawytscha) prior to processing. Numbers of surviving L. monocytogenes cells on the surface were determined using an enrichment-based Most Probable Number (MPN) technique. Inoculated L. monocytogenes cells were not recovered from the surface of salmon after exposure to the steam treatment for 8 sec. A 4-log reduction in L. monocytogenes numbers was obtained. Treated salmon could be processed into a high-yielding, high-quality cold smoked product. An in-plant system was subsequently shown to reduce "naturally" occurring L. monocytogenes numbers and produce a high quality final product. [ABSTRACT FROM AUTHOR]