Two commercial Si3N4 powders were mixed with Al2O3 and Y2O3 through coprecipitation of the oxides from solutions of nitrates. The samples were characterized by XPS spectroscopy and electrophoretic mobility determinations on the suspensions. Sedimentation tests indicated that an oxylignin-based polyelectrolyte proved effective in the dispersion of the powders. The adsorption of the deflocculant followed Langmuir type isotherms characterized by values of the standard free energy of adsorption in the range typical of physisorption processes. The results of the different characterizations are discussed point by point, and different localizations of the dispersant in the interfacial region of the different samples are proposed.

Novel (Ba,Bi,Nb)-added TiO2 ceramic was previously proved to be potentially useful as a varistor material, and by varying atmosphere compensation the roles of barium and bismuth have been explored. The present work attempted to investigate how the third additive, niobium, operates on varistor characteristics. The content of added niobium is in the range from 0.125 to 1.0 cat. %, while that of the other additives is always maintained at a constant value. The results show that an adequate addition of niobium, 0.25 cat. % Nb, is beneficial to the improvement of varistor characteristics. The variations of varistor behavior are discussed in terms of a point defect model. Two kinds of charge compensation, for the substitutional incorporation of niobium into the titanium rutile lattice, are also used to illustrate the variation. The detailed results and discussions are shown in this paper.

A rapid self-sustaining solid-state precursor route to transition-metal borides, boride solid solutions, and boride composites has been developed. Solid-state metathesis (SSM) reactions between transition-metal chlorides and magnesium boride (MgB2) produce crystalline borides and magnesium chloride. Boride solid solutions are formed using mixed chloride precursors. By using a third precursor, such as NaN3, boride-nitride composites are synthesized. The reaction products are characterized by powder x-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and inductively coupled plasma atomic absorption spectroscopy. These boride reactions become self-propagating when the adiabatic temperature is greater than the melting point of the by-product salt, MgCl2 (mp 987 K).

Small Ag particles were embedded in SiO2 glass thin films by a multi-target sputtering method. The mean diameter of Ag particles in the as-deposited film with 28.0 at. % of Ag was estimated to be 4.4 nm and it was increased to 24.0 nm when the film was heat-treated at 700 °C for 3 h. The diameter was proportional to the cube root of the heat-treatment time, suggesting that the Ag particles grew in the supersaturated solid solution. In the optical absorption spectra of the heat-treated films, the absorption peak due to the surface plasmon resonance of Ag particles was observed about 410 nm. The peak intensity became large and the full width at half maximum of the absorption band was decreased with increasing the diameter of Ag particles.

Powder metallurgy and casting have been used to produce aluminum with 1.3, 4, and 8 vol. % fullerene additions. Fullerene extract was mixed with Al and heat-treated to obtain various levels of dispersion of the fullerenes. Intergranular dispersion of stable fullerenes was accomplished by both powder metallurgy and casting; however, x-ray diffraction indicated the formation of some Al4C3. Homogeneous dispersion did not occur because of limited diffusion in the solid state or limited solubility of fullerene in Al in the liquid state. Enhancements in hardness over that for Al were observed yet were not comparable to precipitation hardened Al alloys since a less homogeneous dispersion was achieved. Interest in Al having fullerene additions is for development of fullerene strengthened materials where fullerenes act as nanosize dispersoids for dispersion strengthening of metals or as a lightweight reinforcement in metal-matrix composites.

A scanning laser crack detection technique has been developed for use in corrosion fatigue testing of fine metallic wires. The technique has been integrated into a computerized data acquisition and control system allowing the unattended operation of extended fatigue tests. The system is capable of detecting cracks with surface lengths as small as 100 μm, with crack opening displacements as low as 1 μm. Detection schemes of light loss and light scattering have been successfully used to monitor crack initiation in air and in 0.9% sodium chloride solution. The present scanning laser system has been used for crack initiation detection in over 50 fatigue experiments and has the potential for use in crack growth monitoring. The method can provide information concerning other surface phenomena in addition to the study of cracks. The technique has potential applications beyond metallic wires, including fibers used in optics and ceramic reinforcement fibers used in structural composites.

Internal damage in metal matrix composite (MMC) under static tensile loading was observed by in situ x-ray computed tomography based on synchrotron radiation (SR-CT). A tensile testing sample stage was developed to investigate the fracture process during the tensile test. Aluminum alloy matrix composites reinforced by long or short SiC fibers were used. The projection images obtained under tensile loading showed good performance of the sample stage, and matrix deformation and breaks of the long SiC fibers could be observed. In the CT images taken at the maximum stress just before failure, debondings of the short SiC fibers to the matrix, many pullouts of the fibers, and matrix cracking could be clearly observed. The in situ SR-CT allowed the observation of generation and growth of such defects under different tensile stress levels. The results from the nondestructive observation revealed that the MMC was broken by propagation of the matrix cracks which might be caused by stress concentration at the ends of the short fibers. A three-dimensional CT image reconstructed from many CT images provided easy understanding of the fiber arrangement, crack shape, and form of the void caused by fiber pullout. In situ SR-CT is a useful method for understanding failure mechanisms in advanced materials.

The fracture behavior of the silicon/Pyrex glass anodic bond was investigated using the methods of linear elastic bimaterial fracture mechanics. Due to the high bond strength, interfacial cracks were invariably observed to kink away from the interface into the more compliant glass under approximately mode I remote tensile loading. Kink angles measured by profilometry increased from 14 to 28°as bonding temperature increased from 300 to 450 °C. A regime of stable cracking accompanied penetration of cracks into the glass, with maximum load and corresponding fracture toughness measurement occurring at a location significantly removed from the interface. Approximately mode I, near-interface, plane-strain fracture toughness values (KIC) measured by rising load testing of chevron-notched and straight-thru-cracked compact-tension specimens increased from 0.63 to 0.68 MPa-m1/2 and 0.66 to 0.75 MPa-m1/2, respectively, as bonding temperature increased from 300 to 450 °C. In addition, XPS measurements revealed a sodium depletion zone of decreasing size and depletion magnitude with increasing bonding temperature over the same range. The near-interface region of the glass also experiences compressive residual stresses which decrease linearly with distance from the interface according to linear elastic computations. These stresses increase in magnitude with increasing bonding temperature due to enhanced differential thermal contraction upon cooling to room temperature. It is proposed that the trends in toughness and in kink angle with bonding temperature can be at least partially accounted for by variation of crack-tip shielding with compressive residual stress magnitude, the effects of interfacial. crack-tip shear stresses induced by the thermal mismatch, and by an increase in Young's modulus of the near-interface glass accompanying sodium depletion.

The model of capillary transport of liquid metals driven by shear stress resulting from the displacement of menisci [J.W. Nowok, Scripta Metal]. Mater. 29, 931 (1993); Acta Metall. Mater. 42, 4025 (1994)] is applicable to liquid-phase sintering of silicate/aluminosilicate glasses. The movement of a liquid phase between adjacent particles is compared with that in capillaries. It appears that the transport property of intergranular melt may be expressed by the viscosity (η) and volume diffusion (D) parameters if mean displacement of menisci is compared with the mean diffusive jump lengths of atoms/molecules (L). This leads to the following relation: (γ/η)Lα = Dcap, where α and Dcap are a specific permeability and volume diffusion coefficient. The use of this model requires the assumption that the diffusing species are also the viscous flow units, and they can be either atoms or structural units. This assumption seems to be applicable for depolymerized silicate melts if the dominant mass transport is initiated by the diffusion of both nonbridging oxygen and silicon atoms.

Local arrangements around Te atoms in TeO2-Li2O glasses with four different Li2O contents (15, 20, 25, and 30 mol %) are observed by Te K EXAFS spectroscopy and x-ray diffraction by making use of synchrotron radiation. EXAFS results based on the two-shell fitting method indicate that interatomic distances of Te-O in axial (ax) sites decrease from 0.208 to 0.197 nm with increasing Li2O contents, while distances between tellurium atom and oxygen atoms in equatorial (eq) sites change slightly from 0.190 to 0.188 nm. Total coordination numbers seem to decrease slightly with increasing Li2O contents. These results suggest the coordination states of tellurium atoms are changed from TeO4 trigonal bipyramids to TeO3+1 polyhedra and TeO3 trigonal pyramids. RDF results also suggest the change of coordination states of tellurium atoms. TeO3+1 polyhedra in glasses are considered to be connected at the vertices with Te-eq Oax-Te or Te-ax Oax-Te linkage as seen in crystalline α-Li2Te2O5.

The deposition of Cu, Zn, Pt, and Co precursor particles from solution onto a flat silicon wafer using a spin coater was studied. Homogeneously distributed monodisperse particles can be obtained. The dependence of particle size and number density on solution concentration and rotation frequency was investigated. Different solvents and support modifications were studied. The particles were analyzed using dark-field microscopy, scanning electron microscopy, and atomic force microscopy.

This paper describes a process for uniformly enhancing the nucleation density of diamond films on silicon (Si) substrates via dc-biased hot filament chemical vapor deposition (HFCVD). The Si substrate was negatively biased and the tungsten (W) filaments were positively biased relative to the grounded stainless steel reactor wall. It was found that by directly applying such a negative bias to the Si substrate in a typical HFCVD process, the enhanced diamond nucleation occurred only along the edges of the Si wafer. This resulted in an extremely nonuniform nucleation pattern. Several modifications were introduced to the design of the substrate holder, including a metal wire-mesh inserted between the filaments and the substrate, in the aim of making the impinging ion flux more uniformly distributed across the substrate surface. With such improved growth system designs, uniform enhancement of diamond nucleation across the substrate surface was realized. In addition, the use of certain metallic wire mesh sizes during biasing also enabled patterned or selective diamond deposition.

To enhance a nucleation rate of diamond particles, hydrogenated amorphous carbon (a-C: H) intermediate layers have been formed by radio frequency plasma chemical vapor deposition (CVD) on silicon substrates prior to diamond deposition by hot filament CVD, and the effect of a-C: H intermediate layers on the nucleation and growth rate of diamond particles is studied by varying the thickness of a-C: H films. It is found that diamond particles are well synthesized on thin a-C: H intermediate layers and the nucleation density and growth rate are decreased with increasing the thickness of a-C: H films. Atomic force microscope observations show that a-C: H intermediate layers with rough surface are more effective than the smooth surface for diamond synthesis. Raman spectroscopy shows that the bonding state of carbon atoms in a-C: H films does not change by varying the thickness of a-C: H films. It is proposed that diamond nucleation is affected by the surface morphology rather than the bonding state of carbon atoms in a-C: H films.

We present experimental data for the c-axis electrical resistivity of SbCl5 intercalated graphite between 20 and 300 K. The data are analyzed together with our previous results for these and other samples [O. E. Andersson et al., J. Mater. Res. 7, 2989 (1992)]. Before the analysis, we correct the experimental data to constant volume, as assumed by theorists. We show that the correction factor is much larger for these materials than for normal metals. Although the original data showed significant nonlinearities with T, the corrected data are linear in T to within the experimental accuracy for low-stage compounds below the intercalate crystallization temperature. We compare our results with several models and conclude that both the temperature dependence, the pressure dependence, and the relative changes in the in-plane and c-axis resistivities associated with intercalate crystallization can be best described by a band conduction model.

The electron cyclotron resonance plasma enhanced chemical vapor deposition (ECR PECVD) method is used to prepare ferroelectric PbTiO3 films. Single-phase perovskite PbTiO3 films with smooth surfaces and fine grain size were successfully fabricated on Pt/Ti/SiO2/Si substrates at low temperatures of 400–500 °C using metal-organic (MO) sources. The chemical compositions, structural phases, surface morphologies, and depth profiles of the PbTiO3 thin films were investigated using EDS, XRD, SEM, RBS, and AES. Variations of those properties with process temperature and gas supply ratio are discussed. When the process temperature was above 450 °C, the stoichiometric perovskite PbTiO3 films could be obtained even though the MO source supply ratio was varied in a wide range if the oxygen supply was sufficient.

Antiferroelectric tin-modified lead zirconate titanate ceramics (PZST), with 42 at. % Sn and 4 at. % Ti, were studied by hot- and cold-stage transmission electron microscopy and selected area electron diffraction techniques. The previously reported tetragonal antiferroelectric state is shown to be an incommensurate orthohombic state. Observations revealed the existence of incommensurate 1/x 〈110〉 superlattice reflections below the temperature of the dielectric maximum. The modulation wavelength for this incommensurate structure was found to be metastably locked-in near and below room temperature. An incommensurate-commensurate orthorhombic antiferroelectric transformation was then observed at lower temperatures. However, an intermediate condition was observed over a relatively wide temperature range which was characterized by an intergrowth of 〈110〉 structural modulations, which was strongly diffuse along the 〈110〉. These structural observations were correlated with dispersion in the dielectric properties in the same temperature range. No previous reports of an incommensurate orthorhombic antiferroelectric state or an incommensurate-commensurate orthorhombic antiferroelectric transformation are known to exist.

The basic building block of the ZnO varistor is the ZnO grain formed as a result of sintering. Nanosized ZnO particles are prepared by carrying out the reaction in the controlled size nanoreactors—the droplets of microemulsions. Chemical doping of the ZnO nanoparticles provides ZnO-based ceramic varistors displaying superior varistor properties. These varistors show a higher value of the nonlinear coefficient, lower leakage current, and higher critical electric field value as compared to those for conventional samples in their log E versus log J curve. The present work has also been aimed at studying the effect of processing variables such as sintering temperature and duration on the microstructure and grain growth of ZnO nanoparticles and ZnO-Bi2O3 ceramics. The activation energy calculated from this data is found to be 175 kJ/mol for pure ZnO. For Bi2O3-doped ZnO, the activation energy is found to decrease considerably (∼148 kJ/mol). All these advantages are due to greater structural homogeneity, smaller particle size, higher surface area, and higher density of the ZnO nanoparticles which are precursors for ZnO varistors, as compared to coarser particles for making varistors.

A stack of five polycarbonate foils, each 1.4 μm thick, was irradiated with 1.3 MeV 4He+ ions to the dose of 1.1 × 1014 cm−2. Ion beam induced polymer degradation, as a function of the particle energy, was studied by UV-VIS and IR spectroscopy of individual foils. In the irradiated foils, a significant reduction of characteristic absorption bands is observed, indicating polymer degradation. Significant increase of the surface polarity, characterized by a polar component of the surface free energy, is also found. Both the degree of the polymer degradation and the surface polarity correlate with the total energy deposited by 4He+ ions in the foils.

ArF excimer laser pulses (193 nm, 20 ns, 150 mJ) have been focused on a hydroxyapatite (HA) target in similar conditions to those normally used for thin film deposition. Fast intensified CCD images of HA laser ablation plumes have been taken in vacuum and under different water vapor pressures ranging from 0.01 mbar to 1 mbar. Images of HA ablation in vacuum have shown a plume freely expanding at a constant velocity of 2.3 × 106 cm/s. HA ablation under a water vapor pressure of 0.01 mbar has revealed an expansion behavior very similar to that of ablation in vacuum. Images taken under a water vapor pressure of 0.1 mbar have shown the formation of a shock structure in the plume. Finally, HA ablation under a water vapor pressure of 1 mbar has revealed the development of some irregularities in the shape of the plume.