Impact resistance and tolerance of interleaved tape laminates

This paper presents and discusses the results of low-velocity impact and compression-after-impact (CAI) tests conducted on interleaved and non-interleaved carbon/epoxy tape laminates. Olefin film interleaves provided a strong interface bond, resulting in a reduction in projected damage area. These interleaves changed the stress distribution under impact and restricted delamination formation at the ply interface. An investigation into the compression behaviour of these laminates revealed a reduction in undamaged strength using olefin interleaves. This was attributed to the lack of lateral support for fibres at the fibre/interleaf interface, allowing fibre microbuckling to occur at a low load. Low modulus copolyamide web interleaves resulted in an increase in damage area and minor changes to CAI strength. Examination of laminate cross-sections revealed that this was due to both the open structure of the interleaf and poor resin/interleaf adhesion. High shear modulus polyethylene interleaves resulted in a significant decrease in damage area at various impact energies, with CAI strength improved compared to the non-interleaved laminates.     

Exposure to aerosolized bacteria and fungi among collectors of commercial, mixed residential, recyclable and compostable waste

Biological hazards associated with the collection of solid and compostable waste have not been well characterized in North America. This is an issue because workers who handle such materials may be exposed to bioaerosols (airborne bacteria and fungi) and dusts resulting in infections or allergic diseases. We conducted a personal sampling campaign for culturable bacteria and fungi in the breathing zones of waste collectors in a variety of typical work settings (scenarios) in the province of Quebec, Canada. Total culturable bacterial and fungal counts were analyzed and compared to ambient environmental levels (background) to determine the degree of incremental exposure among workers. In several scenarios, worker exposure counts were significantly (p < or = 0.05) higher than ambient levels measured upwind, with the highest personal exposures to bacteria observed for urban compostable waste collectors (median = 50,300 Colony Forming Units/m(3) of air (CFU/m(3))). On the other hand, fungal counts collected on an every-other-week cycle were highest among a group of rural compostable waste collectors (median = 101,700 CFU/m(3)). Similar exposures to culturable bacteria and fungi have been reported in European workers who showed such adverse health effects as nausea, diarrhea, upper respiratory tract irritation, and allergy. Therefore, it may be necessary to modify certain work practices in order to minimize exposure. Recommendations include automation of waste and compost collection, use of personal protective equipment including goggles, gloves, and disposable masks, and meticulous personal hygiene.     

Solid-state NMR for the analysis of interface excesses in Li-doped MgAl2O4 nanocrystals

Interface segregation plays a governing role in nanocrystalline ceramics properties due to the relative increase in the interfacial volume fraction. However, due to the complexity of the detection and quantification of interfacial excesses at the nanoscale, the role of ionic dopants or additives on microstructural evolution and thermodynamics can be easily underestimated. In this work, we address the spatial distribution of Li⁺ as a dopant in magnesium aluminate spinel nanoparticles. This is achieved through a novel method for the detection and quantification of Li⁺ across the surface, grain boundary, and bulk (crystal lattice). Based on selective lixiviation combined with chemical analysis, we were able to quantify the amount of Li⁺ forming surface excess, whereas the quantitative solid-state nuclear magnetic resonance technique enabled the quantification of Li⁺ segregated in the grain boundaries and dissolved in the lattice. This comprehensive understanding of the Li⁺ distribution across the nanoparticles makes possible an unprecedented interpretation of coarsening and sintering, with a clear correlation between the microstructure and the Li⁺ distribution. Although the work focuses on MgAl₂O₄, the proposed combination of techniques is expected to have a positive impact on the understanding of other multicomponent nanoscale systems.     

Thermal and viscoelastic property of epoxy–clay and hybrid inorganic–organic epoxy nanocomposites

The properties of nanostructured plastics are determined by complex relationships between the type and size of the nanoreinforcement, the interface and chemical interaction between the nanoreinforcement and the polymeric chain, along with macroscopic processing and microstructural effects. In this article, we investigated the thermal and viscoelastic property enhancement on crosslinked epoxy using two types of nanoreinforcement, namely, organoion exchange clay and polymerizable polyhedral oligomeric silsesquioxane (POSS) macromers. Glass transitions of these nanocomposites were studied using differential scanning calorimetry (DSC). Small-strain stress relaxation under uniaxial deformation was examined to provide insights into the time-dependent viscoelastic behavior of these nanocomposites. Since the size of the POSS macromer is comparable to the distance between molecular junctions, as we increase the amount of POSS macromers, the glass transition temperature T_g as observed by DSC, increases. However, for an epoxy network reinforced with clay, we did not observe any effect on the T_g due to the presence of clay reinforcements. In small-strain stress relaxation experiments, both types of reinforcement provided some enhancement in creep resistance, namely, the characteristic relaxation time, as determined using a stretched exponential relaxation function increased with the addition of reinforcements. However, due to different reinforcement mechanisms, enhancement in the instantaneous modulus was observed for clay-reinforced epoxies, while the instantaneous modulus was not effected in POSS–epoxy nanocomposites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1993–2001, 1999     

Effect of physical refining on selected minor components in vegetable oils

The final quality of vegetable oils is largely determined by the deodorization process. From an organoleptic point of view, oils should be light in color with a bland taste and a good cold and/or oxidative stability. Today, however, more and more attention is paid to the real nutritional quality. Oils should contain low trans fatty acid levels, low polymeric triglycerides, and secondary oxidation products and at the same time being rich in natural antioxidants. In order to comply to these new quality requirements, the deodorization technology has been modified substantially. Mathematical models were established describing the influence of different process parameters (time, temperature, steam, and pressure) on trans fatty acid formation, tocopherol stripping, and production of oxidized and polymeric triacylglycerides during physical refining of soybean oil. Trans fatty acid (TFA) formation was influenced only by time and temperature. No significant influence of pressure or sparging steam could be observed. Models expressing the relative degree of cis/trans-isomerization of linoleic (DI_18:2) and α-linolenic acid (DI_18:3) could be extrapolated to other oils and deodorizer designs. Tocopherol removal was mainly influenced by process temperature and sparging steam. Additionally, tocopherol retention seemed to be dependent on the deodorizer design (steam injection geometry and sparging steam distribution). During physical refining, oxidized and polymerized triacylglycerols were not significantly influenced by any of the investigated process parameters. Industrially, process conditions are adapted to minimize trans fatty acid formation and maximize tocopherol retention. These goals can be achieved in a so-called DUAL TEMP^copy; deodorizer.     

On the chemical interaction of nanoscale lanthanum doped strontium titanates with common scandium and yttrium stabilized electrolyte materials

Chemical interactions between common electrolyte materials and various La doped strontium titanates (LST), which are redox-stable candidates for SOFCs anodes, were thoroughly investigated. The reactions of nanosized reagents were studied by SEM/EDX microscopy and XRD with subsequent Rietveld refinement. It was found that all A-site deficient LSTs promoted a reaction with Sc and Y stabilized zirconia, whilst stoichiometric LST was chemically stable. Detected structural and microstructural changes were solely assigned to high mobility of Ti. Diffusion of Ti into the zirconia structure promoted formation of tetragonal structures with p42/nmc-type space groups. The results indicate that the reduction of oxygen partial pressure during sintering and application of Sc-containing electrolyte material are successful strategies to hinder or even avoid reactivity.     

Analysis of microstructure and microhardness of Zr-2.5Nb processed by High-Pressure Torsion (HPT)

Nanostructured materials have been widely studied due to the improvement of their mechanical properties comparing to those of coarse grain materials. The present work intended to analyze the microstructure and microhardness of Zr-2.5Nb processed by high-pressure torsion (HPT), one of the severe plastic deformation techniques. The deformations were carried out at room temperature using a pressure of 5?GPa and 5 anvil turns. Vickers indentation was used to evaluate the microhardness of the samples. Transmission electron microscopy and X-ray diffraction were used to analyze the microstructure. The results showed a significant refinement from the initial microstructure achieving nanometric grain size around 50?nm and phase transformation α?→?ω?+?β_I induced by shear. The Vickers microhardness values of the material submitted to HPT technique were significantly higher than those of non-deformed material. Also, HPT procedure resulted in a huge grain refinement of the material and in phase transformation.     

Electrophoretic deposition of binary energetic composites

This work utilizes electrophoretic deposition (EPD) as a facile and effective method to deposit binary energetic composites. In particular, micron-scale aluminum and nano-scale copper oxide were co-deposited as a thin film onto a conductive substrate without the use of surfactants. For comparative purposes, films of this energetic mixture were also prepared by drop-casting (DC) the premixed suspension directly onto the substrate, then allowing the liquid to dry. The structure and microscopic features of the two types of films were compared using optical and electron microscopies. The films prepared using EPD had an appreciable density of 2.6 g/cm³, or 51% the theoretical maximum density, which was achieved without any further processing. According to the electron microscopy analysis, the EPD films exhibited much more uniformity in composition and film thickness than those produced by DC. Upon ignition, the EPD films resulted in a smoother and faster combustion event compared to the DC films. The dispersion stability was improved by adding water and decreasing the particle concentration, resulting in dispersions stable for >30 min, an ample amount of time for EPD. Patterned electrodes with fine feature sizes (20 × 0.25 mm) were then combined with EPD to deposit thin films of thermite for flame propagation velocity studies. The fastest velocity (1.7 m/s) was observed for an equivalence ratio of 1.6 ± 0.2 (Al fuel rich composition). This peak value was used to investigate the effect of film mass/thickness on propagation velocity. The deposition mass was varied from 20 to 213 μg/mm², corresponding to a calculated range of film thicknesses from 9.8 to 104 μm. At lower masses, a flame did not propagate, indicating a critical mass (20 μg/mm²) or thickness (9.8 μm). Over the range of thicknesses, in which self-propagating combustion was observed, the flame velocity was found to be independent of sample thickness. The lack of a thickness dependence suggests that under these particular conditions heat losses are negligible, and thus the velocity is predominantly governed by the intrinsic reactivity and heat transfer through the material.     

Sputter deposition of semicrystalline tin dioxide films

Tin dioxide is emerging as an important material for use in copper indium gallium diselenide based solar cells. Amorphous tin dioxide may be used as a glass overlayer for covering the entire device and protecting it against water permeation. Tin dioxide is also a viable semiconductor candidate to replace the wide band gap zinc oxide window layer to improve the long-term device reliability. The film properties required by these two applications are different. Amorphous films have superior water permeation resistance while polycrystalline films generally have better charge carrier transport properties. Thus, it is important to understand how to tune the structure of tin dioxide films between amorphous and polycrystalline. Using X-ray diffraction (XRD) and Hall-effect measurements, we have studied the structure and electrical properties of tin dioxide films deposited by magnetron sputtering as a function of deposition temperature, sputtering power, feed gas composition and film thickness. Films deposited at room temperature are semicrystalline with nanometer size SnO₂ crystals embedded in an amorphous matrix. Film crystallinity increases with deposition temperature. When the films are crystalline, the X-ray diffraction intensity pattern is different than that of the powder diffraction pattern indicating that the films are textured with (101) and (211) directions oriented parallel to the surface normal. This texturing is observed on a variety of substrates including soda-lime glass (SLG), Mo-coated soda-lime glass and (100) silicon. Addition of oxygen to the sputtering gas, argon, increases the crystallinity and changes the orientation of the tin dioxide grains: (110) XRD intensity increases relative to the (101) and (211) diffraction peaks and this effect is observed both on Mo-coated SLG and (100) silicon wafers. Films with resistivities ranging between 8 mΩ cm and 800 mΩ cm could be deposited. The films are n-type with carrier concentrations in the 3 × 10¹⁸ cm^− 3 to 3 × 10²⁰ cm^− 3 range. Carrier concentration decreases when the oxygen concentration in the feed gas is above 5%. Electron mobilities range from 1 to 7 cm²/V s and increase with increasing film thickness, oxygen addition to the feed gas and film crystallinity. Electron mobilities in the 1-3 cm²/V s range can be obtained even in semicrystalline films. Initial deposition rates range from 4 nm/min at low sputtering power to 11 nm/min at higher powers. However, deposition rate decreases with deposition time by as much as 30%.