Thin‐film EXAFS samples have been fabricated using semiconductor‐processing and wet‐chemical etching techniques to eliminate artifacts associated with transmission and fluorescence measurements. Examples include cr...
Thin‐film EXAFS samples have been fabricated using semiconductor‐processing and wet‐chemical etching techniques to eliminate artifacts associated with transmission and fluorescence measurements. Examples include crystalline GexSi1−x alloys, amorphous GaAs and Cu and Au nanocrystals in SiO2. In general, thin films of several microns thickness were first formed on bulk substrates then EXAFS samples were fabricated by separating the thin film and substrate. For transmission measurements, thin films were stacked together to yield the optimum absorption while sample inhomogeneity, non‐uniformity and non‐continuity were readily eliminated. For fluorescence measurements, scattering/diffraction from the substrate was eliminated and stacking the thin films together increased the areal concentration of the absorber. The use of such techniques to fabricate EXAFS samples yielded a significant increase in accessible photo‐electron wave number range and hence more accurate structural parameter determinations.
The introduction of inorganic nanomaterials as additives into polymer matrix systems has resulted in polymer nanostructured materials exhibiting multi-functional, high performance polymer characteristics beyond what t...
详细信息
ISBN:
(纸本)1934551007
The introduction of inorganic nanomaterials as additives into polymer matrix systems has resulted in polymer nanostructured materials exhibiting multi-functional, high performance polymer characteristics beyond what traditional polymer composites possess. Multi-functional features attributable to polymer nanocomposites consist of improved thermal resistance, flame resistance, moisture resistance, decreased permeability, charge dissipation, and chemical resistance. Through control/alteration of the additive at the nanoscale level, one is able to maximize property enhancement of selected polymer systems to meet or exceed the requirements of current military, aerospace, and commercial applications. In this study, Lonza Corporation's PT-15 cyanate ester, a low viscosity, high performance resin system was mixed with Carbon Nanotechnologies' buckytubes to create a new type of cyanate ester-buckytubes nanocomposite. The IKA high shear mixer was used to uniformly disperse the nanoparticles in the resin matrix. Several processing parameters such as mixing speed and mixing duration were examined to produce optimal dispersion of nanoparticles into the resin matrix. Polymer nanocomposites morphological microstructures are characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to determine whether nanoparticles are distributed uniformly within the polymer matrix. Thermogravimetric analysis (TGA) was used to study the thermal stability of these nanocomposites. Differential scanning calorimeter (DSC) was used to determine the Tg of the polymer nanocomposites. Further processing-structure- property relationships of these novel polymer nanocomposites will be discussed.
Magnesium castings are experiencing increased use in the transportation industry because of their high strength to weight ratio, high stiffness, and excellent castability. The casting characteristics allow complicated...
详细信息
The locally wall thinned phenomenon of pipes is simulated as metal loss due to erosion/corrosion. Therefore, fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power p...
详细信息
The locally wall thinned phenomenon of pipes is simulated as metal loss due to erosion/corrosion. Therefore, fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear power plant. In this study, monotonic bending tests without internal pressure are conducted on 1.91-inch diameter Schedule 80 STS370 full-scale carbon steel pipe specimens. We investigated fracture strengths and failure modes of locally wall thinned pipes that welded and unwelded by four point bending test. From test results, we could be divided three types of failure modes.
Substantial R&D activities are presently under way toward the development of advanced pulsed-laser-based production tools and processes that can enable sophisticated yet effective crystallization of Si films for m...
详细信息
We report an observation of low-temperature, athermal, ion-induced decay of infrared-active bond-center hydrogen (BCH) in silicon. Specifically, the infrared intensity of BCH is found to decay monotonically as a funct...
We report an observation of low-temperature, athermal, ion-induced decay of infrared-active bond-center hydrogen (BCH) in silicon. Specifically, the infrared intensity of BCH is found to decay monotonically as a function of ion dose with a decay constant determined by the electronic energy deposited by each ion. Our data indicate that ion-induced decay of BCH results in a different final configuration when compared to the thermal decay process. These findings provide insight into the structure and stability of hydrogen related defects in silicon, and thus have implications for the reliability of state-of-the-art semiconductor devices, radiation damage, and ion-beam characterization studies of hydrogen containing solids.
The pressure dependence of the magnetic transitions in the giant magnetocaloric materials Gd5(SixGe1−x)4 (x=0.125,0.5) has been investigated using x-ray magnetic circular dichroism (XMCD) measurements in a diamond anv...
The pressure dependence of the magnetic transitions in the giant magnetocaloric materials Gd5(SixGe1−x)4 (x=0.125,0.5) has been investigated using x-ray magnetic circular dichroism (XMCD) measurements in a diamond anvil cell (DAC). We found that the most notable features of the x−T phase diagram are also present in the P−T phase diagram. These include a nearly linear increase in Curie temperature, Tc, with increasing both x and P up to 275K, and a discontinuity accompanied by a change in slope, dTc∕d(x,P), at this temperature. However, the results indicate that a similar volume change results in ∼3 times larger increase in Tc with Si doping than with pressure. Si doping, hence, does more to stabilize ferromagnetic interactions than simply uniformly reducing the unit cell volume.
Mechano-active scaffolds were fabricated from very elastic poly(lactide-co-carprolactone) by a gel-pressing method. The scaffolds were seeded with bone marrow stromal cells and the continuous compressive deformation w...
详细信息
Mechano-active scaffolds were fabricated from very elastic poly(lactide-co-carprolactone) by a gel-pressing method. The scaffolds were seeded with bone marrow stromal cells and the continuous compressive deformation was applied to cell-polymer constructs in the chondrogenic media. Then, they were implanted in nude mice subcutaneously to evaluate for the effect of dynamic compression for regeneration of cartilage. From the biochemical analyses, chondrogenic differentiation was sustained and enhanced significantly and chondral extracellular matrix was increased through mechanical stimulation. Histological analyses showed that implants stimulated mechanically formed mature and well-developed cartilaginous tissue, as evidenced by bone marrow derived chondrocytes within lacunae. Consequently, the periodic application of dynamic compression can encourage bone marrow stromal cells to differentiation to chondrogenic lineage and to maintain their phenotypes.
High-purity carbon nanotubes (CNTs) are produced by chemical vapour deposition of camphor, an environment-friendly hydrocarbon. In a small CVD reactor (1-m long and 26- mm wide), CVD of 3 g camphor at 650°C for 1...
In this study, Lonza Corporation's PT-15 cyanate ester (CE), a low viscosity, high performance resin system was used with two types of silicon carbides (SiC): nano-SiC particles and nano-SiC whiskers, as well as m...
详细信息
ISBN:
(纸本)1563478927
In this study, Lonza Corporation's PT-15 cyanate ester (CE), a low viscosity, high performance resin system was used with two types of silicon carbides (SiC): nano-SiC particles and nano-SiC whiskers, as well as multi-wall carbon nanotubes (buckytubes) to create new types of cyanate ester-SiC and cyanate ester-buckytube nanocomposites. High shear mixing techniques were used to uniformly disperse the n-SiC particles, n-SiC whiskers, and buckytubes in the cyanate ester resin matrix. Several processing parameters such as mixing speed and mixing duration were examined to produce optimal uniform dispersions of nanoparticles into the resin matrix. Polymer nanocomposites morphological microstructures were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) to determine whether n-SiC particles/n-SiC whiskers/buckytubes are distributed uniformly within the polymer matrix. Thermogravimetric analysis (TGA) was used to study the thermal stability of these nanocomposites. Differential scanning calorimeter (DSC) was used to determine the Tg of the polymer nanocomposites. All levels of n-SiC particles dispersed well in the CE resin. The 10% n-SiC particle gave the best enhancement of thermal stability. All loadings of n-SiC whisker did not exhibit any thermal stability enhancement to the CE resin. Phase separation was observed for all loading levels of CE-buckytubes specimens. Buckytube failed to disperse uniformly in the PT-15 CE because of processing limitations and fundamental material incompabiltiy. Functionalization of the buckytube is recommended to enhance uniform dispersion in the PT-15 CE resin.
暂无评论