The influence of the niobium content on the anatase-to-rutile phase transition in nanopowders of Nb–Ti oxides was studied and the changes in the particle size and microstrain distribution obtained at different temperatures were analyzed. A correlation is found between the initial microstructure in the Ti1 – xNbxO2 (x = 0.03, 0.2) powder and the niobium content. The presence of Nb was found to inhibit the growth of both the anatase and the rutile phases.

The uncertainties inherent to experimental differential scanning calorimetric data are evaluated. A new procedure is developed to perform the kinetic analysis of continuous heating calorimetric data when the heat capacity of the sample changes during the crystallization. The accuracy of isothermal calorimetric data is analyzed in terms of the peak-to-peak noise of the calorimetric signal and base line drift typical of differential scanning calorimetry equipment. Their influence in the evaluation of the kinetic parameter is discussed. An empirical construction of the time-temperature and temperature-heating rate transformation diagrams, grounded on the kinetic parameters, is presented. The method is applied to the kinetic study of the primary crystallization of Te in an amorphous alloy of nominal composition Ga20Te80, obtained by rapid solidification.

We describe the synthesis and characterization of ultrafine TiO2 particles (in both anatase as well as rutile form) produced by a chemical reaction within the aqueous core of a water-in-oil microemulsion. The microemulsion was stabilized and the Ti4+ ions provided by a functionalized surfactant derived from the commercially available Aerosol-OT, i.e., sodium bis (2-ethylhexyl) sulfosuccinate (Na-DEHSS). The Na+ ions in Aerosol-OT were completely replaced by Ti4+ through an ion-exchange reaction in nonaqueous solvents. Ultrafine TiO2 particles were produced by the hydrolysis of the Ti-containing surfactant in the water droplets. The dependence of the size of the precipitated TiO2 · xH2O particles on various structure parameters of the microemulsion was studied in detail.

During the nanoindentation process, the load and depth data are continuously recorded. A single load-displacement curve is thus expected to contain material property information from the whole depth range indented. In the present paper, a new method to obtain the hardness-depth curve has been derived for small depths from the load-displacement curve measured at a large depth, based on the assumption that the elastic properties of the indented material can be obtained from the indentation depth. Using this method, hardness values can be computed for various small depths from a single load-displacement curve. From a series of nanoindentation experiments, it has been proven that the method can be used on both homogeneous and surface-modified materials, such as fused silica, single crystal tungsten, and plasma nitrided steel with and without an iron nitride Fe4N compound layer. Testings on a series of Ni–P films coated on 15 MnB steel also gave fairly good results.

The biaxial stretching behavior of superplastic Y -TZP (yttria -tetragonal zirconia polycrystals) ceramics and Y -TZP/Al2O3 composites in air atmosphere was investigated. Stretching deformation can be made within a limited range. Larger grain size of Y -TZP led to higher applied load needed to obtain the same amount of deformation. However, if some monoclinic phase was present in the materials, which was caused by the over -large grain sizes, defects would occur and thus make deformation easier. Microstructure study of the deformed specimen showed the occurrence of crack -like defects on the outside surface of the stretched disk specimen. Limited grain growth of single phase Y -TZP was obtained while Y -TZP grains in Y -TZP/Al2O3 composites grew extensively after stretching.

A polymeric precursor solution was employed in preparing SrBi2Nb2O9 (SBN) powder and thin films dip coated onto Si(100) substrate. XRD results show that the SBN perovskite phase forms at temperatures as low as 600 °C through an intermediate fluorite phase. This fluorite phase is observed for samples heat-treated at temperatures of 400 and 500 °C. After heat treatment at temperatures ranging from 300 to 800 °C, thin films were shown to be crack free. Grazing incident angle XRD characterization shows the occurrence of the fluorite intermediate phase for films also. The thickness of films, measured by MEV, was in the order of 80–100 nm.

Spray-dried granules were observed by a laser microscopy with the immersion liquid technique. The binder distribution in the granules was analyzed from light intensity profiles of the images. The results showed that a surface layer with a large amount of the binder is formed in the spray-dried granule, and the segregation is influenced by initial binder concentration and size of atomized droplet. A computer simulation for soluble binder segregation during spray drying was conducted by considering simultaneously the solvent evaporation, the relative migration between the liquid and the particles, the diffusion, and drying shrinkage. The simulation coincides with the experimental results. To make uniform granules, reducing the amount of binder, liquid content, size of atomized droplet, and drying rate is favorable.

Ultrasound radiation is used to prepare a composite material made of polymethylacrylate and amorphous iron nanoparticles. Two preparation methods are described, in which the monomer, methylacrylate, is the starting material. The magnetic properties of the composite material are measured and reveal a superparamagnetic behavior.

Annealing of a cold-rolled Fe–3.25%Si sheet having {111} 〈112〉 preferred orientation is performed in a high magnetic field in order to control microstructure orientation. Magnetic field (10 T) was applied in a direction parallel to the rolling direction. Distributions of orientation and misorientation of primary recrystallization grains in the magnetically annealed specimens are characterized with electron backscattering pattern analysis. Magnetic annealing is found to enhance the selection of ?001? axis alignment parallel to the rolling direction in the {hk0} 〈001〉 recrystallization texture and to favor the occurrence of low energy grain boundaries in the recrystallized microstructure. The high frequency of low angle grain boundaries results in the appearance of coarse grains with traces of faint prior grain boundaries, suggesting extensive operation of the mechanism of grain coalescence. As a cause of selective formation of 〈100〉 grains in recrystallization, magnetostriction induced by applying a magnetic field is suggested.

This paper investigates the potentially undesirable noble metal silicide formation reactions that may occur in noble metal electrodes deposited directly on silicon without an intervening diffusion barrier. Metal (90–100 nm)/Si structures of Pt/Si, Rh/Si, Ir/Si, and Ir/Ti/Si were annealed in oxygen or nitrogen ambients at temperatures of 640–700 °C. Metalysilicon reactions and phase formation were studied by Rutherford Backscattering Spectroscopy, x-ray diffraction, and electrical resistance measurements. While complete silicidation was observed in the Rh/Si, Pt/Si, and Ir/Si samples after 640 °C/6 min anneals in nitrogen, some Pt and most of the Ir remained after equivalent anneals in oxygen. More detailed studies of the Ir/Si samples indicated that some Ir is left unsilicided even after a 700 °C/6 min anneal in O2, and that the iridium silicide formed is the semiconducting IrSi1.75. The formation of this silicide can be delayed, but not prevented, with the use of a 5 nm Ti adhesion layer between the Ir and Si.

Based on several experimental observations, Hwang et al. recently proposed “the charged cluster model” [J. Cryst. Growth, 162, 55–68 (1996)] to disentangle the “puzzling thermodynamic paradox” encountered in the gas-activated chemical vapor deposition (CVD) of diamond. Many unusual phenomena observed in the CVD diamond process can be successfully approached by the charged cluster model. However, there are a couple of important subjects still unsolved quantitatively. The first question is connected with the main driving force for this unusual nucleation in the gas phase. The second issue is related to the difference in the thermodynamic stability between graphite and diamond for a nanometer-sized cluster during the growth. In this study, we have theoretically examined the thermodynamic driving forces for the charge-induced nucleation, in general, and have applied this idea to the nucleation of the charged carbon-atom cluster. It was shown that the short-range ion-induced dipole interaction and the ion-solvation electrostatic effect (Born term) were mainly responsible for this unusual nucleation in the gas phase. The theoretical analysis presented in this article is quite generic and, thus, can be applied to any process that involves the charge-induced nucleation.

The quality of hardness H and indentation modulus E* measurements from instrumented indentation is investigated. Load-displacement data from glass and sapphire are obtained by Vickers indentation and converted to H and E* through a series of equations, including those for tip-shape correction. The quality of H and E* is determined by calculating the statistical uncertainty at each step and propagating the uncertainty to the next step. Conventional tip-shape corrections, assuming either constant hardness or constant modulus, introduce significant errors in H and E* when single, continuous correction functions are used. Piecewise correction functions are shown to improve the quality of H and E*. This investigation demonstrates the importance of calculating and propagating uncertainty at each step when converting instrumented indentation load-displacement data to mechanical properties.

A device for spherical indentation using a tip radius of 2 mm and loads up to 10 kN is presented. This facility can be applied, for example, to verify methods for characterizing the behavior of materials exhibiting homogeneous and isotropic constitutive properties. The indentation device can be driven both load- and depth-controlled. The accuracy of measurements is about 1 N for load and 0.2 μm for depth at a total depth of 200 μm. Two materials, an austenitic steel and an aluminum alloy, have been tested and their Young's moduli have been determined. For determining Young's modulus from spherical indentation data, use is made of a so-called Lt method, which had been developed in Ref. 1. Results obtained in this way are compared with corresponding values measured by one-dimensional homogeneous tensile experiments.

During the heat treatment of an anatase nanocrystalline powder at a high temperature, the two processes of anatase-to-rutile (A → R) transformation and grain growth would occur simultaneously and affect each other. With decrease of the original anatase grain size, the A → R transformation temperature range became extended on both sides, which may be partially attributed to the prevention effect of grain growth on this transformation. On the other hand, the grain growth process could be significantly enhanced by the A → R transformation, which can be ascribed to the higher atomic mobility because of the bond breakage during the transformation.

Functionally gradient materials (FGM) were prepared using layers of ZrO2 –3 mol% Y2O3 ceramic and NiCrAlY powders. A fine-grained zirconia powder was chosen to lower the ceramic sintering temperature and achieve simultaneous metal and ceramic densification. Consolidation of FGM's was achieved by a short time field-assisted sintering technique. Sintering was performed either at a constant temperature or in a temperature gradient by using punches made of different materials (i.e., one graphite and one tungsten). A temperature gradient of at least 100 °C was required with a low value of 1200 °C at the metal end and exceeding 1300 °C at the ceramic end. Increasing the number of intermediate layers alleviates some of the cracks formed during sintering due to different coefficients of thermal expansion.

Epitaxially grown Fe3−xO4 films were prepared on MgO(001) substrates by dipping-pyrolysis process using CO–CO2 gas mixtures. The structure and in-plane alignment of these films were examined by x-ray diffraction θ-2θ scans, β scans (pole figures), and asymmetric ω-2θ scans (reciprocal-space maps). The films heattreated at 500 °C and higher in an atmosphere with pCO/pCO2 = 10−4 had a spinel-type structure and were in an epitaxial (cube on cube) relationship with the substrates.

Mixed crystalline tin-titanium phosphates with variable tin-to-titanium molar ratio have been prepared by precipitation of soluble salts of the metal (IV) with phosphoric acid and refluxing the amorphous solids in 17 M H3PO4. The new materials are characterized by chemical textural and thermal analysis and x-ray powder diffraction. The tin-titanium phosphates are solid solutions showing an isomorphic substitution of tin by titanium in the α-tin phosphate lattice and tin substitution in the γ-titanium phosphate lattice. In both cases, the solubility is partial. The coexistence of both saturated phases is observed in samples of composition between the solubility limits.

The sequence of microstructural changes occurring at the wet paste-aggregate interface is documented at an age as early as 5 min using the environmental scanning electron microscope (ESEM). Unlike other microscopic techniques, the ESEM allows pastes of normal water: cement ratio to be observed at early ages without reducing the paste to a powder. Evolution of the paste-aggregate microstructure is followed up to an age of 24 h. The region adjacent to the aggregate surface contains a phase with a morphology referred to as a “sheaf of wheat” morphology. The same interfacial region in a 10-day-old specimen has a microstructure similar to the interfacial transition zone (ITZ) reported in the literature. Variations of the “sheaf of wheat” morphology due to original water-to-cement ratio, mixing energy, incorporation of silica fume, and drying are documented. As revealed by energy dispersive x-ray analysis (EDS), the microstructure contains significant amounts of calcium and silica. These results indicate that the observed morphology is likely to be a calcium silicate hydrate (C-S-H) product that is a precursor to type I C-S-H. A description of the evolution of the observed microstructural features is presented. The “sheaf of wheat” morphology appears to be a general precursor to morphologies commonly seen in mature pastes.

The initial stages of silicate growth on graphite are characterized with atomic force microscopy. The morphological development indicates that decomposition of tetra ethyloxysilane at low pressure produces films of 3 nm clusters located at undercoordinated carbon sites. Clusters eventually cover the surface, at which point a second layer grows. In higher pressure deposition multiple layers of clusters grow simultaneously. A comparison of the oxidation behavior of surfaces with defects completely and incompletely terminated with SiOx shows that edge recession is the primary oxidation mechanism and that the site specificity of SiOx is effective in inhibiting oxidation.

This study investigated the modes of grinding-induced subsurface damage in dental glass-ceramics and the influence of microstructure on strength degradation. A series of micaceous glass-ceramics crystallized from the same glass composition were tested. The diameter of the mica platelets in these glass-ceramics was varied via heat treatment. Grinding was performed using three diamond wheels (with diamond particle size of 40, 100, and 180 µm, respectively) at depth of cut ranging from 5 µm to 100 µm. A bonded- interface technique was employed to examine the machining- induced subsurface damage. Relatively large median and lateral cracks were found in the glass-ceramic with the smallest mica platelets. In contrast, no cracks were found in the material containing large mica platelets. The ground specimens were fractured in four-point flexure to measure strength as a function of grinding conditions and mica platelet sizes. The strength of the ground specimens was reduced to approximately 30% of the strength of the polished specimens for the glass- ceramic containing the smallest mica platelets; that of the glass-ceramic with the intermediate mica platelet size was reduced to 60%. In contrast, virtually no strength loss occurred with the glass-ceramic containing large mica platelets. Microstructure was shown to determine the mode and degree of strength-controlling damage in the machining of these dental glass-ceramics. Polishing after grinding removes subsurface damage and recovers strength for the glass-ceramics containing fine mica crystals.