Application of a gripping system to test a uniaxial graphite fiber-reinforced composite (PMR 15/celion 6000) in tension at 316°C

A gripping system has been developed to test uniaxial, 0° orientation PMR 15/Celion 6000 composites at elevated temperatures. The method involves compression of grit-blasted laminate between grit-blasted metal to give a non-slipping interface for load transfer. Tensile testing at both 316°C and room temperature indicated that deformation was elastic to fracture and that the variation in tensile properties for one laminate is the same as that for several panels. In addition, the tensile properties for uniaxial PMR 15/Celion 6000 are identical at 316°C and room temperature. For nominally 51 volume percent fiber, the elastic modulus is 119.6 GPa, the fracture stress is 1370 MPa, and the strain to fracture is about 1.15 percent. In addition, data are presented which indicate that the gripping system can be used for long term, elevated temperature testing of composite materials.     

Utilizing Terminal Oxidants to Achieve P450‐Catalyzed Oxidation of Methane

Terminal oxidant‐supported P450 reactions alleviate the need for substrate binding to initiate catalysis by chemically generating “compound I.” This allows investigation of the innate substrate range of the enzyme active site. Using iodosylbenzene as the oxidant, CYP153A6, a medium‐chain terminal alkane hydroxylase, exhibits methanol formation in the presence of methane demonstrating that P450‐mediated methane hydroxylation is possible.     

Characterizing Temporal Heterogeneity by Quantifying Nanoscale Fluctuations in Amorphous Fe-Ge Magnetic Films

Equilibrium phase transitions are influenced by fluctuations and often discussed within the framework of the Gibbs free energy, wherein the exchange of energy between system and thermal bath is stationary and all regions of the sample exhibit the same phase. Presence of spatial heterogeneity in the magnetic structures such as pinning centers, domain walls, topological defects, etc. may cause temporal heterogeneity that modifies the nature of the magnetic phase transition. This study reports that interplay of nanoscale thermodynamics with spatio-temporal heterogeneity gives rise to complex phase transition pathways in amorphous Fe_xGe_1-x thin films with temperature and Fe-concentration (x). Coherent resonant soft X-ray scattering experiments that have simultaneous spatial, temporal, and spectral sensitivity show that the origin of helical to paramagnetic phase transition in amorphous Fe-Ge thin films lies in the appearance of enhanced-fluctuation spots deep inside the ordered state. The fluctuations are heterogeneous, starting over a small fraction of the domains that increases and becomes isotropic over the entire film as the temperature increases or the Fe-concentration decreases. The fluctuating-fraction, when normalized to magnetization for different Fe-concentrations, follows a single power law behavior, suggesting that the nature of the transition can be described in terms of the underlying spatio-temporal fluctuations.     

Thermal stability of MxOy-doped zirconia aerogels (M = Y,Yb, Gd,Ce, Ca) studied through 1200°C

The high porosities and low densities of ceramic aerogels offer outstanding insulative performance in applications where weight is a critical factor. The high surface area-to-volume ratios and specific surface areas provide extremely low thermal conductivity, but also contribute to rapid densification of the pore structure at elevated temperatures. This densification diminishes their favorable properties and inhibits use of aerogels in high-temperature applications. This work contributes to a design framework for thermally stable aerogels via the study of dopant chemistry (Y, Yb, Gd, Ca, Ce) in zirconia aerogels. The structural evolution was studied through 1200°C using nitrogen physisorption, scanning electron microscopy, and X-ray diffraction. The role of dopant identity and concentration in thermal stability was elucidated. In the context of the design framework, dopant chemistry is an aggregate for many closely related material properties, each of which may contribute to aerogel structural evolution. To develop a truly predictive design framework for ceramic-based aerogels, systematic and comprehensive evaluation of thermodynamic and kinetic properties must be performed in conjunction with studies on structural evolution.     

The thermal stability of the polymorphs of hexanitrohexaazaisowurtzitane,Part I

Phase transitions in the α-, β-, γ-, and ϵ-polymorphs of 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (HNIW) have been studied as a function of temperature. Described are the results of high temperature equilibrium solvation studies coupled with Fourier transform infrared spectroscopy (FTIR) for the identification of polymorphic conversion. These results are augmented by data in Part II from differential scanning calorimetry (DSC), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and optical hot stage microscopy⁽⁶⁾. The thermodynamic stability order of ϵ > γ > α-hydrate > β is shown, with the epsilon polymorph the most thermodynamically stable phase of HNTW at room temperature. The existence of multiple α-hydrate phases is shown to complicate the determination of the equilibrium P-T phase diagram of HNIW.     

The Solubility of ϵ-CL-20 in Selected Materials

The solubility of the epsilon polymorph of CL-20 was determined in thirteen liquids over the temperature range of ambient to 74°C using high performance liquid chromatography. The experiments included ϵ-CL-20 produced by two different synthesis routes; one lot contained a higher level of polymorphic impurity, the other lot contained a higher level of non-CL-20 impurity.In general, the ϵ-CL-20 was found to be highly soluble in the solvents with carbonyl groups, and relatively insoluble in hydrocarbons and materials containing ether linkages. The amount of phase conversion to γ-CL-20 which occured during the solubility testing was measured using FTIR, and ranged from essentially zero to ∼ 10% conversion. It appears that the presence of β-CL-20 in the virgin ϵ-CL-20 lots will affect the amount of gamma-phase present in the final residue.