Analysis of Solid Explosion Products of Mixtures Based on HMX and Peroxide Benzoyl with Aluminum

The explosive transformation of mixtures of HMX and benzoyl peroxide with aluminum was studied. Aluminum oxides formed during initiation of an impact explosion were investigated. An x-ray analysis showed that aluminum is not oxidized during explosion of its mixtures with benzoyl peroxide. An analysis was made of aluminum oxides formed during explosion of HMX mixtures with aluminum hydride and ternary mixtures of aluminum, HMX, and benzoyl peroxide. It was found that the state of aluminum introduced into the composition and the explosion temperature influence the structure of aluminum oxide (Al8/3O4), whose lattice is a derivative of the spinel lattice.     

Performance Evaluation of a Commercial Polyurethane Coating in Marine Environment

A material evaluation study has been carried out to determine corrosion behavior of a commercial polyurethane coating system (Souplethane 5) in the marine environment. The coating system is solvent free, two-component polyurethane protective coating. The performance of the coating on steel and rebar concrete was evaluated by conducting different types of tests which include atmospheric exposure, immersion in 5% sodium chloride solution, exposure to splash zone in seawater, salt fog, sabkha soil burial, and electrochemical tests, which include potentiodynamic polarization and AC impedance measurements. Uncoated, coated, and coated scribed specimens were used in each study. In general, the coating showed good corrosion resistance in marine environment. However, the coated samples, when subjected to break under applied compressive load, showed partial or complete detachment from the substrate, e.g., steel and rebar concrete. This appears to be the major drawback of the coating while applying on steel and concrete structures.     

On the interpretation of vapor pressure measurements on oxide fuel at very-high temperatures for fast reactor safety analysis

Safety analysis of fast reactors requires knowledge of the evaporation behavior and the total vapor pressure of oxide fuel materials in the temperature region from 3000 K upwards. Dynamic vapor pressure measurements on liquid oxide fuels performed in open-evaporation experiments with laser heating techniques imply strong alterations in the composition of the incongruently evaporating fuel surface, since, during evaporation, the depletion in the preferentially evaporating components cannot be resupplied by diffusion from the bulk material. After a short transient evaporation period stationary surface-evaporation is reached with a surface composition which differs greatly from the given fuel composition and depends on the actual evaporation temperature. When this stationary forced-congruent evaporation mode is reached, the gross vapor composition is well-defined and is identical to the bulk composition of the fuel but is quite different from the actual surface composition. In consequence, the total vapor pressure developing in open surface-evaporation of a liquid oxide fuel can substantially deviate from its thermodynamic equation-of-state, in the case of (U_0.80Pu_0.20) mixed oxide by a factor of 2 to 7 depending on the $\text{O}\text{M}$-ratio. Following these thermodynamic calculations direct measurement of the equation-of-state in open-evaporation experiments is practically impossible. Theoretically fitted expressions applicable in reactor safety analysis are presented for the equations-of-state and the vapor pressure equations for open surface-evaporation and also for the heats of evaporation of liquid (U_0.80Pu_0.20)O_1.95…2.00 mixed oxides.     

Corrosion resistance of silicon-infiltrated silicon carbide (SiSiC)

Silicon carbide ceramics have found widespread use due to their high corrosion stability. Both solid state-sintered silicon carbide, which has an extremely high corrosion resistance, and silicon-infiltrated silicon carbide are used for various applications. The latter material contains SiC as well as free silicon, which is less stable. Hence, in the present work, the corrosion behavior of silicon-infiltrated silicon carbide ceramics was investigated in NaOH solutions. Long-term corrosion experiments were conducted, and a method for analyzing the corrosion behavior in short-term experiments was developed. The short-term method is based on the accurate measurement of the corrosion depth by laser scanning microscopy on polished surfaces. The results of both methods were in good agreement. The advantage of the short-term method is that it provides information on changes in corrosion mechanisms and corrosion rates in the initial period and as a function of the impurities present. Preferential corrosion of Si at the interface to SiC was observed. TEM investigations revealed that this enhanced corrosion was caused by the segregation of impurities.     

Hypoxia Suppresses Spontaneous Mineralization and Osteogenic Differentiation of Mesenchymal Stem Cells via IGFBP3 Up-Regulation

Hypoxia has diverse stimulatory effects on human adipose-derived stem cells (ASCs). In the present study, we investigated whether hypoxic culture conditions (2% O₂) suppress spontaneous mineralization and osteogenic differentiation of ASCs. We also investigated signaling pathways and molecular mechanisms involved in this process. We found that hypoxia suppressed spontaneous mineralization and osteogenic differentiation of ASCs, and up-regulated mRNA and protein expression of Insulin-like growth factor binding proteins (IGFBPs) in ASCs. Although treatment with recombinant IGFBPs did not affect osteogenic differentiation of ASCs, siRNA-mediated inhibition of IGFBP3 attenuated hypoxia-suppressed osteogenic differentiation of ASCs. In contrast, overexpression of IGFBP3 via lentiviral vectors inhibited ASC osteogenic differentiation. These results indicate that hypoxia suppresses spontaneous mineralization and osteogenic differentiation of ASCs via intracellular IGFBP3 up-regulation. We determined that reactive oxygen species (ROS) generation followed by activation of the MAPK and PI3K/Akt pathways play pivotal roles in IGFBP3 expression under hypoxia. For example, ROS scavengers and inhibitors for MAPK and PI3K/Akt pathways attenuated the hypoxia-induced IGFBP3 expression. Inhibition of Elk1 and NF-κB through siRNA transfection also led to down-regulation of IGFBP3 mRNA expression. We next addressed the proliferative potential of ASCs with overexpressed IGFBP3, but IGFBP3 overexpression reduced the proliferation of ASCs. In addition, hypoxia reduced the osteogenic differentiation of bone marrow-derived clonal mesenchymal stem cells. Collectively, our results indicate that hypoxia suppresses the osteogenic differentiation of mesenchymal stem cells via IGFBP3 up-regulation.