Protonated niobate nanosheets, H1.8Bi0.2CaNaNb3O10 (BCNN), were synthesized using a new organic-free simultaneous ion exchange and exfoliation process from the Aurivillius phase Bi2CaNaNb3O12. Nanosheet/TiO2 composites were prepared by thermal treatment of physical mixtures of commercially available anatase TiO2 and the nanosheet suspension. Methylene blue (MB) dye degradation studies for the composite show a clear correlation between the MB surface adsorption and the degradation rate. The composite exhibits strongly enhanced photocatalytic activity as the calcination temperature increases, suggesting the possibility of charge transfer at the BCNN–TiO2 interface and the existence of Nb5+ and O2−acid–base pairs. Both phenomena are attributed to the processing approach, which includes topochemical dehydration of the BCNN nanosheets during heat treatment.

A potential order-of-magnitude increase in Hall-Petch (H-P)-based strength level for nanoscale grain-size structures is an important enabler of electronic thin film material design applications. Dislocation pileups of smaller lengths in such thin film materials are blocked in a screw orientation at the through-thickness grain boundaries of relatively larger grains. For fully nanopolycrystalline materials, both strength and strain rate sensitivity measurements exhibit complementary H-P reciprocal square root of grain size dependencies. An additional increase in strength level is predicted for transition from a pileup to a single dislocation loop expanding against the grain boundary obstacle. In opposition, disordered grain boundaries are responsible for a reduced H-P stress intensity, kε. And at the limiting high stresses reached at lower-limiting nanoscale grain sizes, reversed H-P dependences are obtained both for the strength and strain rate sensitivity.

Solid-state microcellular foaming (SSMF) process was used to produce porous chemical mechanical polishing (CMP) pads in a variety of pore size and porosity range, using a variety of thermoplastic polyurethane (TPU) resin hardness. By controlling the pore size, porosity, and pad hardness, one is able to manufacture CMP pads that offer tunable pad properties. A brief introduction to the SSMF manufacturing process and thereby, unique microstructures created is first addressed followed by inner layer dielectric (ILD) CMP results, describing the effects of top TPU foam sheet properties, such as hardness, pore size, and porosity on ILD removal rate (RR) and wafer defects. Softer TPU-based porous pads showed significantly lower wafer scratch counts, while only a moderate increase in the ILD RR was seen with increasing resin hardness for similar pore size and porosity pads. Pore size has insignificant influence on wafer defect count but has significant influence on the ILD RR profile. CMP pads made from small pore size foams cause a nonflat RR profile.

This paper presents recent results of foam extrusion of thermoplastic cellulose acetate (CA) using HFO 1234ze as low global warming blowing agent and talc as nucleating agent. Foam extrusion behavior, physical foam properties, and foam morphologies were studied in detail with respect to blowing agent concentration and talc content. Depending on these parameters, thermoplastic CA exhibits excellent foam extrusion performance with good expansion behavior at the die. Talc as nucleating agent results in homogeneous fine foam morphologies with closed cells [i.e., Fig. 3(3)]. Depending on the blowing agent content and talc content, average cell size ranges from 1 to 0.12 mm and foam density ranges between 100 and 400 kg/m3.

We examine the development of stable bimetal interfaces in nanolayered composites in severe plastic deformation. Copper-niobium multilayers of varying layer thicknesses from several micrometers to 10 nanometers (nm) were fabricated via accumulative roll bonding (ARB). Investigation of their 5-parameter character and atomic scale structure finds that when layer thicknesses refine well below one micrometer, the interfaces self-organize to a few interface orientation relationships. With atomic scale and crystal plasticity modeling, we identify that the two controlling factors that determine whether an interface is stable under high strain rolling are orientation stability of the bicrystal and interface formation energy. A figure-of-merit is introduced that not only predicts the development of the prevailing interfaces but also explains why other interfaces did not develop. Through a suite of nanomechanical and bulk test results, we show that ARB composites containing these stable interfaces are found to have exceptional hardness (∼4.5 GPa) and strength (∼2 GPa).

Titanium dioxide (TiO2) and mixed oxides, i.e., mixtures of magnesium oxide and titanium dioxide (MgO–TiO2) with different ratios were synthesized by two methods—flame synthesis and aerogel, for comparison of their properties. The samples were characterized by powder x-ray diffraction (pXRD), energy-dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmet-Teller method of surface area measurements, ultraviolet-visible spectroscopy (UV-vis), and transition electron microscopic analysis. The pXRD patterns of different mixed oxides with different mole ratios revealed that there were formations of different compositions and phases. These mixed oxides were also used as photocatalysts in the UV-vis light to oxidize acetaldehyde, and carbon dioxide (CO2) was measured as a product. The mixed oxides with low content of MgO (∼1–2 mol%) were found to be more UV-active photocatalysts for the degradation of acetaldehyde than the degradation by Degussa P25 and as-synthesized TiO2, the highest by the MgO–TiO2 mixed oxides of 1:50 ratio when comparisons were carried out among the samples prepared by the same method. Furthermore, the mixed oxides prepared by the aerogel method were found to be superior photocatalysts compared with the mixed oxides of equal ratio prepared by flame synthesis. This effect of insulator, MgO, on the photocatalytic activity of semiconductor, TiO2, was found to be interesting and can be applied for other applications as environmentally friendly materials.

Stable, responsive and autofluorescent genipin-crosslinked chitosan–poly(vinyl pyrrolidone) hydrogels have been synthesized. Morphological characterization techniques such as scanning electron microscopy, environmental scanning electron microscopy, and in situ confocal laser scanning microscopy (CLSM), in both reflectance and fluorescence modes, have been compared for their suitability to characterize the network structure of these hydrogels. CLSM is shown to be the optimal technique owing to the facile generation of the three-dimensional porous architecture and extra topographical information while the sample is immersed in the aqueous solution to which it will find application. CLSM is used in both reflectance and fluorescence modes to follow morphology variation as a function of time during swelling. Conveniently, acquisition via reflectance produces images with a higher degree of structural detail than fluorescence, widening the application of this method to characterize hydrogels where addition of a fluorescent probe, which may alter the native structure, is undesired.

Nanosized graphitic carbon provides high selectivity and stability of catalysts. However, the carbon is very light when used as a support, even when loaded with metals. To counteract this problem, carbon/TiO2 core–shell structures were synthesized via chemical vapor deposition (CVD) using a single source precursor to increase its density, while maintaining a high surface area and stability of the materials. The diameter of the carbon/TiO2 spheres could be controlled from 2 μm to 200 nm by varying the flow rate of nitrogen. TEM analysis revealed that a fraction of the spheres exhibited a core–shell structure, with a faint carbon shell surrounding the TiO2 sphere. The density of the carbon/TiO2structures was 0.70 g/mL, which is four times higher than that of pure carbon nanotubes and spheres synthesized by CVD.

Nickel-yttrium nanocrystalline alloys with an as-milled grain size of approximately 6.5 nm were synthesized using high-energy cryogenic mechanical alloying. The microstructural changes due to annealing were characterized using x-ray line broadening, microhardness, focused ion beam channeling contrast imaging, and transmission electron microscopy. Experiments demonstrated that increasing yttrium content led to stabilization of the nanocrystalline grain size at elevated homologous annealing temperatures. Additionally, it was found that inadvertent contamination with nitrogen during the milling process caused the formation of yttrium nitride (YN) precipitates, which, in turn, resulted in an additional nonlinear hardening effect beyond the expected hardening due to grain-size reduction. Results reveal that kinetic pinning by YN particles is effective in retaining a nanostructure to relatively high temperatures.

We report high-resolution transmission electron microscopy (HRTEM) observation of a high density of dislocations with edge components (∼1016 m−2) in nanocrystalline (NC) body-centered cubic (bcc) Mo prepared by high-pressure torsion. We also observed for the first time of the ½<111> and <001> pure edge dislocations in NC Mo. Crystallographic analysis and image simulations reveal that the best way using HRTEM to study dislocations with edge components in bcc systems is to take images along <110> zone axis, from which it is possible to identify ½<111> pure edge dislocations, and edge components of ½<111> and <001> mixed dislocations. The <001> pure edge dislocations can only be identified from <100> zone axis. The high density of dislocations with edge components is believed to play a major role in the reduction of strain rate sensitivity in NC bcc metals and alloys.

TiO2@C core–shell nanostructures with various crystal structures of TiO2-B, anatase, and rutile were successfully synthesized by a simple hydrothermal process and postheat treatments. As-synthesized precursor hydrogen titanate@carbonaceous nanoribbons transformed into TiO2-B@C nanoribbons at 400 °C and further transformed into anatase and rutile TiO2@C nanoribbons at 700 and 800 °C, respectively. The morphology of nanoribbons can be retained up to 800 °C. The transformation temperature (800 °C) from anatase to rutile phase is lower than that of TiO2 nanofibers without carbon layers and anatase TiO2@C nanoparticles. These results show that the carbon shell plays important roles in promoting the phase transition from anatase to rutile phase and protecting the nanoribbon-like morphology. The formation mechanism of the TiO2@C core–shell nanostructures with various crystal structures was discussed.

We have used a hydrogel templating technique followed by the subsequent evaporation of water present to fabricate porous cement and porous PDMS composites, and we have analyzed their sound absorption properties. All experiments were carried out with hydrogel slurries of broad bead size distributions. Porous PDMS and cement composites were produced with porosities of up to 80% and 70%, respectively. Scanning electron microscope analysis shows fibrous domains within the voids created by the hydrogel in the cement samples and open pore network in the PDMS composites of initial hydrogel content higher than 70 vol%. Sound absorption was improved with respect to control nonporous samples in all composites with porosities higher than 60 vol%, where an open pore structure was formed. The porous PDMS and porous cement produced by this method show better sound absorption at 200–400 Hz and 1200–1800 Hz frequency ranges when compared with the sound absorption in the intermediate frequencies range between 400 and 1000 Hz.

Deformation mechanism maps are well established in the field of high temperature creep for materials having conventional coarse grain sizes but they are almost unknown within the field of nanostructured materials. This paper summarizes the background to deformation mechanism mapping, presents simplified examples that may be used to easily construct appropriate maps for any selected condition, demonstrates the potential extension of this approach to other areas such as creep fracture, and then considers the potential limitations associated with using the same approach to predict the deformation mechanisms in true nanostructured materials. Two representative deformation mechanism maps are shown for an ultrafine-grained alloy processed either by equal-channel angular pressing or by high-pressure torsion.

The development and characterization of pressure sensing porous nanocomposites are reported here. A thermoplastic polyurethane (TPU) was chosen as an elastomeric matrix, which was reinforced with multiwall carbon nanotubes (MWNTs) by high shear twin screw extrusion mixing. Porosity was introduced to the composites through the phase separation of a single TPU-carbon-dioxide gas solution. Interactions between MWNT and TPU were elucidated through calorimetry, gravimetric decomposition, conductivity measurements, and microstructure imaging. The piezoresistance (pressure–resistance) behavior of the nanocomposites was investigated and found to be dependent on MWNT concentration and nanocomposite microstructure. Mechanisms of piezoresistance in solid and porous nanocomposites are proposed.

Carbothermal reduction of semiconducting TiO2 into highly conductive titanium oxycarbide (TiOxCy) was investigated. The thermally produced uniform carbon layer on TiO2 (Degussa P25) protects the TiO2 nanoparticles from sintering and, at the same time, supplies the carbon source for doping TiO2 with carbon. At low temperatures (e.g., 700 °C), carbon only substitutes part of the oxide and distorts the TiO2 lattice to form TiO2−xCx with only substitutional carbon. When the carbon-doped TiO2 is annealed at a higher temperature (1100 °C), x-ray diffraction and x-ray photoelectron spectroscopy results showed that TiOxCy, a solid solution of TiO and TiC, was formed, which displays different diffraction peaks and binding energies. It was shown that TiOxCy has much better oxygen revolution reaction activity than TiO2 or TiO2−xCx. Further studies showed that the TiOxCyobtained can be used as a support for metal electrocatalyst, leading to a bifunctional catalyst effective for both oxygen reduction and evolution reactions.

The development of substoichiometric TiO2-based nanostructured materials with high aspect ratios for future proton exchange membrane fuel cells is investigated. Nanostructures were manufactured using atomic layer deposition of TiO2 over both anodic aluminum oxide templates and silicon nanowires. It was observed in this work that nanostructures with aspect ratios of 100:1 can be fabricated using both methods. The conductivity of TiO2 films was enhanced following a postdeposition reducing anneal (at 450 °C in H2). Liquid phase-deposited Pt and plasma-enhanced atomic layer deposition of Pt were both found to be appropriate suited for metallization of TiO2 structures.

We have investigated the microstructure, the quasistatic and high-rate mechanical properties of magnesium (Mg)-based metal-matrix composites (MMCs) reinforced with nanoparticles, also termed as metal-matrix nanocomposites (MMNCs), in this case reinforced with nanoparticles of β-phase silicon carbide (β-SiC) the volume fraction ranging from 5 to 15 vol%. The yield and the ultimate strength increase with reinforcement volume fraction up to 10 vol% nanoparticles. MMCs with micrometer-sized SiC particles have higher yield strength than their MMNC counterparts, whereas the ultimate strength shows the opposing trend, suggesting greater strain hardening in the MMNCs. Transmission electron microscopy shows that the average interparticle distance decreases with increasing SiC vol%. Recrystallization was reported as completed during sintering at 575 °C [R.D. Doherty et al., Mater. Sci. Eng. A, 238, 219 (1997)], but dislocations might be generated due to thermal expansion mismatch of Mg/SiC during cooling. The majority of Mg-grains below 20 nm remain around the nanoparticles. As such a reverse volume fraction effect takes place in 15 vol% nanoparticle-reinforced MMNCs, which off sets the strengthening advantage induced by the nanoparticles.

Metal matrix syntactic foams are promising materials with high energy absorption capability. To study the effects of matrix strength on the quasistatic compressive properties of syntactic foams using SiC hollow particles as reinforcement, matrices of Al-A206 and Mg-AZ91 were used. Because Al-A206 is a heat-treatable alloy, matrix strength can be varied by heat treatment conditions, and foams in as-cast, T4, and T7 conditions were tested in this study. It is shown that the peak strength, plateau strength, and toughness of the foams increase with increasing yield strength of the matrix and that these foams show better performance than other foams on a specific property basis. High strain rate testing of the Mg-AZ91/SiC syntactic foams showed that there was little strain rate dependence of the peak stress under strain rates ranging from 10−3/s to 726/s.