Colloidally stable suspensions are required to fabricate dense samples with uniform microstructure by colloidal processing methods, which necessitate dispersion of ceramic powders in a liquid medium. Aqueous nano ZrO2 suspensions were prepared using polyethylenimine (PEI) as a dispersant. PEI adsorption on nano ZrO2 surfaces was promoted with increasing initial PEI content and suspension pH. Isoelectric point was shifted from pH 7 at 0 wt% PEI to pH 10.4 at 3 wt% PEI. Stable suspensions had mean particle sizes in the range of 100 to 150 nm and sedimentation rates less than0.4 mm/h, as compared to 2–5.5 μm and 10–50 mm/h for unstable suspensions. Samples with 98% relative density were fabricated after sintering at 1300 °C for 4 h from colloidally stable suspensions.

We demonstrate that synchrotron x-ray powder diffraction (XRD) is a powerful technique for studying the structure and self-organization of zinc-oxide nanostructures. Zinc-oxide nanorods were prepared by a solution-growth method that resulted in uniform nanorods with 2-nm diameter and lengths in the range 10–50 nm. These nanorods were structurally characterized by a combination of small-angle and wide-angle synchrotron XRD and transmission electron microscopy (TEM). Small-angle XRD and TEM were used to investigate nanorod self-assembly and the influence of surfactant/precursor ratio on self-assembly. Wide-angle XRD was used to study the evolution of nanorod growth as a function of synthesis time and surfactant/precursor ratio.

We explored the possibility of incorporating carbon nanotubes in a patterned and macroporous silica structure replicated from a thin polystyrene template. A V-shaped thin, vertical channel was constructed and successfully used to assemble 10.06-μm polystyrene spheres into a dense three-dimensionally ordered template of uniform thickness. Infiltration of a single Co/silica precursor sol into the template followed by thermal treatments in vacuum and H2 produced three-dimensionally ordered silica pores with embedded Co nanoparticles. Wormlike carbon nanofilaments of 50–120 nm in diameter were grown on the inner surface of silica pores with plasma-enhanced chemical vapor deposition.

Thin films of SiO2–TiO2 composite oxides with various SiO2:TiO2 compositions were prepared by the sol-gel method, using tetraethylorthosilicate (TEOS) and titanium tetraisopropoxide (TTIP) as precursors. The composition, crystal structure, and chemical bonding configuration of the as-deposited and annealed SiO2–TiO2 thin films were analyzed using Rutherford backscattering spectrometry (RBS), glancing incident angle x-ray diffraction (GIAXRD) and Fourier transform infrared spectroscopy (FTIR), respectively. Optical properties of the films were characterized by spectroscopic ellipsometry and ultraviolet-visible spectrophotometry. The Si/Ti ratios in the SiO2–TiO2 films agree with the TEOS/TTIP molar ratio in the sol-gel precursor. When the TEOS/(TEOS + TTIP) ratio is greater than 40%, the SiO2–TiO2 thin films remain amorphous (without formation of TiO2 crystalline phase) after annealing at temperatures as high as 700 °C. FTIR spectra indicate that the quantity of Si–O–Ti bonding can be maximized when the TEOS:TTIP in the precursor is 80%:20%. The refractive index of the SiO2–TiO2 films increases approximately linearly to the mixing ratio of TTIP/(TEOS + TTIP). However, SiO2-rich films possess higher ultraviolet-visible transmittance than the TiO2-rich films. The modification of microstructure and chemical bonding configuration in the SiO2–TiO2 films by the composition and its influence on the optical properties are discussed.

We studied tensile creep behavior in two silicon nitride ceramics, i.e., 4.8 mol% Lu2O3 (SN48) and 1.2 mol% Lu2O3 (SN12), at 1400–1500 °C under applied stress of 137–300 MPa. Time to failure of SN48 increased with decreasing applied stress and minimum strain rate. The stress–rupture parameter was 10.7 at 1400 °C and 11.4 at 1500 °C. Pore formation was confirmed in a creep-tested specimen of SN48 by transmission electron microscopy. These results suggest that SN48 was fractured by creep rupture. The minimum strain rate of SN12 was almost below the measurement system limitation at temperatures below 1500 °C. Time to failure tended to increase with decreasing applied stress. The stress–rupture parameter was 41 at 1400 °C and 73 at 1500 °C. These results suggest that SN12 was fractured by subcritical crack growth.

W–Si–N films were deposited by reactive sputtering in a Ar + N2 atmosphere from a W target encrusted with different number of Si pieces and followed by a thermal annealing at increasing temperatures up to 900 °C. Three iron-based substrates with different thermal expansion coefficients, in the range of 1.5 × 10−6 to 18 × 10−6 K−1 were used. The chemical composition, structure, residual stress, hardness (H), and Young’s modulus (E) were evaluated after all the annealing steps. The as-deposited film with low N and Si contents was crystalline whereas the one with higher contents was amorphous. After thermal annealing at 900 °C the amorphous film crystallized as body-centered cubic α–W. The crystalline as-deposited film presented the same phase even after annealing. There were no significant changes in the properties of both films up to 800 °C annealing. However, at 900 °C, a strong decrease and increase in the hardness were observed for the crystalline and amorphous films, respectively. It was possible to find a good correlation between the residual stress and the hardness of the films. In several cases, particularly for the amorphous coating, H/E higher than 0.1 was reached, which envisages good tribological behavior. The two methods (curvature and x-ray diffraction) used for calculation of the residual stress of the coatings showed fairly good agreement in the results.

Thin In2O3:Sn (ITO) films prepared by radio-frequency (rf) or direct-current (dc) magnetron-sputtering and in central or peripheral position relative to the target were characterized by x-ray diffractograms and pole figures. The diffractograms were normalized with the powder diffraction intensities of the target. In the normalized diffractograms, a random texture level and preferred orientations can be distinguished. The pole figures are represented by normalized χ-scans that are modeled as a sum of Gaussian curves. The centers of the Gaussian curves are consistent with the prominent orientations of the normalized diffractograms. The textures of the rf-sputtered films in the central and the peripheral position are similar, showing strong contributions from (211)-planes. The texture of dc-sputtered samples is dominated by (400) and (411) planes. In the peripheral sample, the distribution of (400)- and (411)-oriented grains is shifted towards the incidence angle of the particle flux and the frequency of the (222)-grains is suppressed below the random texture level. The results are discussed with reference to a model of incorporation of interstitial oxygen into the growing films.

A new series of 0.4MgF2–0.4BaF2–0.1Ba(PO3)2–0.1Al(PO3)3 glasses highly doped with rare-earth dopants (RE; Nd2O3, Er2O3, and Yb2O3) have been successfully developed for laser applications. Linear refractive index, dispersion properties including Abbe number (ν), dispersion parameter (A′, B′), electronic osciallator energy (Eo), and electronic osciallator strength (Ed) were determined as a function of RE dopants. The refractive index (nD=1.5872 to 1.6047) was found to linearly increase with dopant concentrations irrespective of types of rare earth dopants, while the Abbe number (ν = 65.7 to 68.8) and dispersion parameters including A′ (∼62), B′, Eo (13 ± 0.5 eV), and Ed (19 ± 1 eV) exhibit a concentration independence. It is remarkable that the refractive index of those new glasses increased with increasing RE dopant concentration, while the relatively large Abbe number of those glasses was independent of dopant concentration. The dependence of refractive index (n) on RE cations with high polarizabilities are discussed in terms of molar volume (Vm) and molar refractivity (Rm). Electronic oscillator strengths (Ed), the average electronic energy gap (Eo), and their respective dependence on RE dopant concentration were also investigated using linear refractive index (n) and Abbe number (ν). Those results suggest the present new series of glasses are strong candidates for stable laser hosts with extremely low dispersion.

The one-step synthesis of barium titanate (BaTiO3) nanoparticles was studied by employing a low-pressure spray pyrolysis (LPSP) method. The effects of temperature, pressure, and the addition of urea to the precursor were investigated experimentally. The results were compared with the experimental data of the conventional (atmospheric) spray pyrolysis method. It was shown that the BaTiO3 nanoparticles could be synthesized by the low-pressure method, while only spherical hollow particles with smooth surfaces could be produced by the conventional spray method. The addition of urea greatly improved the crystal growth and particle breakup due to extra heat supplied during the combustion reaction coupled with the evolution of gases. The dispersity of nanoparticles increased with the quantity of urea and with a decrease in pressure. The possible mechanism of the formation of BaTiO3 nanoparticles in the LPSP process was also proposed.

Dimensional analysis and finite element modeling were conducted to examine conical indentation in homogeneous materials and in hard films on soft substrates. In this paper, the solid materials modeled follow the incremental theory of plasticity with a von-Mises yield surface. The validity of the Oliver–Pharr method was examined. It was found that, for hard films on soft substrates, the Oliver–Pharr method is applicable only when the indentation depth is less than 10% of the film thickness. A linear relationship between the ratio of hardness to reduced modulus and the ratio of reversible work to total work was observed for conical indentation in homogeneous materials and in hard films on soft substrates. This relationship can be used to analyze instrumented indentation experiments.

The indentation size effect of pure iron samples with various pre-plastic tensile strains has been experimentally investigated and analyzed. With the increase in the strain, the indentation size effect of iron samples becomes weak, accompanied by the multiplication of the statistically stored dislocations. All of the hardness (H) versus indentation depth (h) curves fit the strain-gradient plasticity model for indentation of Nix and Gao well. Two fitting parameters, the hardness in the limit of infinite depth (H0) and the characteristic length (h*), were obtained for each curve. The hardness (H0) of iron samples can also be estimated as the microhardness (H) at a very large depth, h ≅ 10h*. Both the fitted H0 and the measured H0′ increase linearly with the tensile yield stress σy of iron samples, indicating a dependence of H0 on the statistically stored dislocation density through σy. Furthermore, 1/√h* shows a linear increase with the tensile yield stress σy, which also agrees qualitatively with the general prediction of the Nix and Gao theory. Therefore, our experiments and analysis demonstrate that the strain-gradient plasticity model for indentation of Nix and Gao can interpret the indentation size effect with satisfied precision.

The energy absorption behaviors of mesoporous silica particles immersed in aqueous solutions of ethanol were investigated. Addition of ethanol could significantly lower the infiltration pressure, which has great potential in developing selective protection systems. The ethanol concentration of the confined liquid inside the nanopores was higher than outside.

The interfacial adhesion energy was studied using the four-point bend method for boron carbo-nitride (BCxNy) deposited on dielectric and copper films. Twenty-five nanometer BCxNy films were deposited by chemical vapor deposition at 360 °C and 1 Torr using dimethylamine borane with no coreactant, NH3, or C2H4, producing different composition films, BC0.37N0.15, BC0.11N0.49, BC0.92N0.07, with dielectric constants of 4.1, 4.2, and 3.8, respectively. BCxNy films were deposited on dense and porous dielectrics, and copper. BCxNy films adhered strongly to the dielectric films and the composite beams snapped before debonding, revealing that the critical debond energy Gc exceeded 10 J/m2. The adhesion of BCxNy to oxidized copper increased with carbon content in the film, with the BC0.92N0.07 film beams snapping, and is possibly related to covalent bonding between surface oxygen and carbon in the film.

After this article appeared in the February 2005 issue of Journal of Materials Research, the authors noticed that Eq. (14) was incorrect.

Using analytical and finite element modeling, we studied conical indentation in linear viscoelastic solids with either displacement or load as the independent variable. We examine the relationships between initial unloading slope, contact depth, and viscoelastic properties for various loading conditions such as constant displacement rate, constant loading rate, and constant indentation strain rate. We then discuss whether the Oliver–Pharr method for determining contact depth, originally proposed for indentation in elastic and elastic-plastic solids, is applicable to indentation in viscoelastic solids. We conclude with a few comments about two commonly used experimental procedures for indentation measurements in viscoelastic solids: the “hold-at-peak-load” technique and the constant indentation strain-rate method.

Titanium dioxide nanopowders were synthesized by in-flight oxidation of titanium nitride (TiN) in radio-frequency (rf) induction thermal plasma. The powders were characterized by x-ray diffraction, high-resolution transmission electron microscopy, field emission scanning electron microscopy, Raman spectroscopy, and optical microscopy to reveal the mechanisms of phase selection and particle morphology evolution. The reaction began with surface oxidation of TiN particles, leading to the formation of core-shell composites with oxidized shells and TiN cores, followed by gas-phase condensation of TiO2 nanoparticles. Phase selection of the resultant TiO2 powders was found to largely depend on the oxidation potential of the thermal plasma rather than on the heat transfer itself. Anatase content of the products increased steadily with increasing the O2 input, and TiO2 nanoparticles (∼50 nm) containing ∼90% of anatase were obtained through O2/Ar plasma treatment. Phase-pure rutile nanoparticles (∼50 nm, on average) were also synthesized in H2/Ar plasma injected with O2 as the powder carrier gas.

“Nanoscale Morphology and Indentation of Individual Nacre Tablets from the Gastropod Mollusc Trochus Niloticus” [J. Mater. Res. 20, 2400 (2005)]