The spreading kinetics of molten aluminum on ceramic surfaces bearing reactive coatings has been studied through the direct observation of sessile drops, either formed in situ or emplaced at temperature. Analysis of videotapes permitted the assessment of the rate of advance of rapidly spreading droplets. Experimental conditions in this study were chosen to avoid the severe retarding effect of the aluminum oxide film which is typically encountered in aluminum wetting experiments. A variety of reactive coating systems were examined (B, Cu, Ni, Ti, and Ti + B), and the effect of coating amount was assessed. Based upon the experiments of this study, the main effect of the coatings is to drive spreading due to strong exothermic interfacial reactions. The intensity of the interfacial reaction causes the change in free energy per unit area of interface to dominate the rate of movement of the triple line.

10B doped diamond films grown by hot filament chemical vapor deposition were neutron irradiated at moderately high fluence levels. The as-irradiated and annealed samples, along with an unirradiated sample, were analyzed using Raman spectroscopy and x-ray diffraction. It was found that a non-diamond amorphous phase was formed on irradiation. This phase transformed back to diamond on annealing. No graphite formation was observed. A comparison with nanodiamond powder was made. A similarity between irradiated diamond films and nanocrystalline diamond powder is discussed.

Carbon fiber-carbon matrix composites were fabricated using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. The preforms for the infiltration were prepared by stacking 40 layers of carbon cloth in a graphite holder. The preforms were infiltrated with carbon using propylene or methane as a reactant, with hydrogen as a diluent. Composites with porosities as low as 7% have been processed within 8-12 h. The highest deposition rate obtained in the present study was ∼3 μm/h, which is more than an order of magnitude faster than the typical value of 0.1-0.25 μm/h for the isothermal infiltration process.

Nickel is deposited over pristine, surface-treated, and brominated P-100 carbon fibers using cementation and electroplating techniques. The fibers are brominated by bromine vapor for 48 h and then desorbed at 200 °C in air for 12 h. The anodic oxidation treatment is performed by etching fibers electrochemically in a dilute sodium electrolyte for 3 min or by immersing fibers in nitric acid for 72 h. Electroplated-coated fibers show better tensile properties than cementation-coated fibers. Tin-lead alloy composites reinforced by nickel-coated fibers (which are pristine, anodically oxidized, and brominated) are fabricated by squeeze casting. The composites containing coated carbon fibers with bromination or surface treatment have higher tensile and shear strength than the ones containing coated pristine carbon fibers. In addition, the composite containing coated carbon fibers with brominalion shows the best performance in the tensile properties.

Additive-free HIPSN and Y2O3 + Al2O3-doped HPSN are oxidized in air in the temperature range from 1300 to 1500 °C. TEM, SEM, EDS, and XRD are used to analyze the composition and microstructure of the oxide scales in order to determine the oxidation mechanisms. HIPSN exhibits excellent resistance to oxidation in air at temperatures up to 1480 °C due to the formation of a protective silica (cristobalite) scale. No formation of Si2N2O and oxygen-enriched β'-Si3N4 under the silica layer is observed for materials densified without additives. Oxidation rates of additive-containing HPSN are more important due to the formation of a viscous aluminosilicate phase, which easily penetrates along the grain boundaries in the material. Silicon nitride grains in contact with the viscous phase first become enriched in aluminum and oxygen and are then dissolved in the glassy phase. No Si2N2O intermediate layer is formed. The finding of the decisive role of the aluminosilicate in the oxidation process allows one to explain inconsistencies observed in the oxidation kinetics of silicon nitride ceramics. Effects of sintering additives, WC contamination and temperature on the oxidation mechanisms, and structure of oxide scales are discussed.

A study of the temperature and stoichiometry dependence of diamond synthesis in low pressure premixed acetylene-oxygen flames is presented. A specially designed low pressure flat flame operating at 40 Torr is employed to deposit diamond films uniformly over areas of at least 2 cm2. Under optimized conditions of substrate temperatures and flame equivalence ratios, high quality translucent diamond that is well faceted is synthesized exhibiting first-order Raman fullwidths (half maximum) of about 2.5 cm−1. Diamond growth rates under these optimum conditions are approximately 4 μm/h. The film growth rate is found to drop off substantially at high substrate temperatures, with little or no carbon deposited beyond a temperature of 1070 °C. The growth behavior in response to changes in flame equivalence ratio and substrate temperature is discussed in terms of the possible role that oxygen-containing species may have on surface chemistry. The results described here are also used to project a base cost for manufacturing diamond under these process conditions.

Diamond films have been grown by hot filament chemical vapor deposition (CVD) on mirror-polished positively biased Si substrates. Very smooth films a few micrometers thick were obtained in only 30 min. SEM, x-ray diffraction patterns, and Raman were used to characterize the films. Not only diamond but other carbon phases, were also detected. The initial structure showed a high density of defects and large stresses. Structural changes in time were found to occur with films apparently undergoing a phase transformation.

The pressure shifts of the 418 and 379 cm−1 Raman lines of polycrystalline α-Al2O3 ceramic were measured at room temperature to 3190 MPa. A diamond anvil high pressure cell was used in conjunction with a microRaman spectrometer system. Pressures were measured by the ruby fluorescence method. Distilled water was used as the pressure transmitting medium. The pressure dependence of the wave number for the hydrostatic range (to 1585 MPa) was found to be 0.00220 ± 0.00007 cm−1 MPa−1 for the 418 cm−1 Raman line and 0.0011 ± 0.0001 cm−1 MPa−1 for the 379 cm−1 line. Both shifts are based on a linear least squares fit to the data within a 95% confidence interval. Measurements that included the nonhydrostatic regime (to 3190 MPa) gave similar shifts, but with almost twice the uncertainty. Absolute residual stresses in alumina ceramics are in the 200 to 600 MPa range with higher values, 1790 MPa, reported for single-crystal alumina. For the 418 cm−1 Raman line, these values correspond to shifts of 0.4, 1.4, and 3.9 cm−1, respectively. The sensitivity of the microRaman technique is sufficient to detect and measure residual stresses of this magnitude.

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.

Stability of the binary phases in the quaternary system Mo–Ti–Si–C was examined for the combustion synthesis or Self-propagating High-temperature Synthesis (SHS) of MoSi2−TiC composites. Thermochemical calculations were carried out to obtain the adiabatic temperatures and the amounts of molten phases at the adiabatic temperature for the SHS of these composites. MoSi2−20 wt. % TiC and MoSi2−40 wt. % TiC composites were prepared by thermal explosion and SHS modes of combustion from elemental powders. The phase formation was confirmed by x-ray diffraction, and the morphologies were observed under SEM. No general correlation was obtained between the phase formation or product morphology on the one hand, and the adiabatic temperature or the amount of molten phase formed at the adiabatic temperature, on the other. MoSi2−40 wt. % TiC composites obtained by SHS mode of combustion show a highly homogeneous distribution of the two phases with negligible amounts of ternary phases.

Titanium and niobium carbides have been synthesized through self-propagating high-temperature reaction by mechanically alloying the elemental powder mixtures. It is found that this reaction is very similar to the conventional self-propagating high-temperature synthesis (SHS) process, but the ignition of the reaction is identified to be the mechanical collisions instead of heating the materials. Analysis of the products reveals that the final products of the Ti-C system are in good agreement with the equilibrium phase diagram, showing less relation with the alloying process. The decrease of the C content shortens the milling time prior to the SHS reaction of TiC by promoting the intimate mixing of the components, but lowers the heat release of the reaction and makes the propagation of the reaction more slowly. The SHS reaction during the mechanical alloying of the Nb-C system shows little difference, but the decrease of the C content can hardly influence the milling time prior to the reaction. By lowering the heat release of the SHS reaction of NbC, it lowers the reaction propagating rate. Mechanical alloying Nb50C50 and Nb55C45 results in the formation of NbC, while mechanical alloying Nb60C40 results in NbC + Nb instead of NbC + Nb2C according to the phase diagram. It was attributed to the fact that the rapid SHS reaction favors the formation of NbC, but hinders the occurrence of Nb2C phase through slow diffusion between NbC and the residual Nb. The measurement of the lattice parameters of TiC and NbC for different composition affirms the observed results. The particle sizes of obtained TiC and NbC are very fine at around or even less than 1 μm.

An important, somewhat novel procedure for the bulk synthesis of finely divided crystalline BaTiO3 powder has been studied and is applicable to the synthesis of other compounds in the BaO-TiO2 system as well. An aqueous solution of Ba(NO3)2, TiO(NO3)2, and alanine is spray dried. A combustion reaction occurs when heating the product to 300 °C. The reaction converts the spray-dried mixture to BaTiO3. This BaTiO3 powder and its sinterability have been characterized by thermal analysis, XRD, SEM, dielectric, and particle size measurements. The powder resulting from the thermal runaway reaction is finely divided and sinters more readily than the conventionally prepared high purity BaTiO3.

A new method for the synthesis of complex metal oxides, based on hydrodynamic cavitation, was used to prepare pure phase, nanostructured solid-state materials. The continuous process afforded a wide variety of metal oxides in grain sizes of 1-10 nm. Catalysts, ceramics, superconductors, piezoelectrics, and zeolites were prepared by cavitational synthesis. The method enabled the synthesis of fine particles of metals and metal oxides supported on high surface area supports such as silica, and the synthesis of fine particles of cubic zirconia without ion modification.

Aluminum matrix composites and carbon/carbon composites based on vapor grown carbon fiber (VGCF) were fabricated for analysis of thermophysical properties. Due to the highly graphitic nature of VGCF, the resulting composites exhibit values of thermal conductivity that have not been achieved by using any other carbon fibers, and thus represent new materials for thermal management in applications such as packaging for high-power, high-density electronic devices. In the aluminum matrix VGCF composites, a thermal conductivity of 642 W/m-K was obtained by using a VGCF loading of only 36.5 vol.%. For VGCF/C composites, thermal conductivity of 910 W/m-K has been observed, a value which is more than a factor of two higher than that of copper. Based on the observed thermal conductivity of VGCF/Al composites and VGCF/C composites, the room temperature thermal conductivity of VGCF in the composite was calculated to be 1460 W/m-K and 1600 W/m-K, respectively.

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.

Data on phase relations in the system Na2ZnP2O7-Zn2P2O7 reported in the literature are scarce and contradictory. The system was first studied by Berul and Voskresenskaya [Russ. J. Inorg. Mater. (English transl.) 4 (12), 2129 (1968)], who established the existence of a congruently melting intermediate compound, Na8Zn6(P2O7)5. In the paper by Majling et al. [Chem. Zvesti. 28 (3), 294 (1974)], the system Na2ZnP2O7-Zn2P2O7 is considered to be eutectic. The subsolidus phase relations are represented by a mixture of two phases, terminal members of the system. The existence of the above-mentioned compound was not confirmed for this system. In the present work we studied the phase relations in the system Na2ZnP2O7-Zn2P2O7 on samples obtained by solid-state synthesis and glass crystallization. The sequence of crystallization of phases was investigated, and the equilibrium and metastable phase diagrams were constructed for the system.

The primary aim of this present work was to investigate the solubility, microstructure, thermal stability, AlN polytypes, and interfacial reactions in the SiC-AlN system. Alpha SiC particles of different sizes were incorporated into AlN and hot pressed at 2050 °C for 1 to 3 h. XRD, OM, STEM, WDS, and SAD patterns were utilized in analyzing phases, morphology, and distribution of elements. The surface area of SiC particles was found to have substantial effects on the formation of solid solution. Multilayered polytypes, which are usually associated with stacking faults, grew and impeded one another. Additionally, the number of planes between subsequent stacking increased with the increase of either hot-pressing temperature or time. Affinity of oxygen to AlN probably played an essential role in the formation of polytypes and stacking faults.

In this paper, a one-step, combustion synthesis-based process for fabricating Al2O3 fiber-reinforced Ni3Al is described. The process uses relatively low temperatures and pressures, and can be used to prepare relatively large, dense, near-net-shape articles that possess either simple or relatively complicated shapes. This process can be used to incorporate continuous, aligned fibers into the Ni3Al matrix material in such a way that the fibers are not damaged either mechanically (due to relatively small loads applied during the process) or chemically (due to the very short time at which the sample remains at elevated tempertures during the process). (Chopped fibers, as well as equiaxed particles or whiskers, could also be similarly incorporated using this process.) This combustion synthesis process is a relatively simple one-requiring only relatively low temperatures and pressures, as well as relatively low-cost starting materials-which suggests that its scale-up beyond the laboratory scale would be particularly straightforward.

Stoichiometric and 2 wt. % excess lead oxide containing lead magnesium niobate (PMN) ceramics have been prepared by partial oxalate route. Dielectric measurements with frequency showed a typical relaxor behavior for stoichiometric PMN, while PMN with excess PbO shows a scatter in the dielectric curves at all temperatures above Tc. Under the same processing conditions, the dielectric constant (Kmax) decreases drastically from 16,300 to 9500 at 1 KHz for PMN without and with excess PbO, respectively. Microstructure studies revealed a second phase (unreacted PbO) segregated in the grain boundaries for excess PbO samples. A careful analysis of the data on dielectric properties and phases present coupled with microstructural detail indicate that the second phase in the grain boundary has a pronounced effect on the dielectric properties and not the pyrochlore phase.

Highly oriented diamond film was grown on a (100) Si substrate by a bias-enhanced microwave-plasma chemical vapor deposition. The Si surface was carburized at a faster rate by bias treatment than by carburization alone, but the initial carburization stage was indispensable. During the bias treatment, the flat surface was changed to a textured structure on the nanometer scale. The formation of this structure was required for the synthesis of a highly oriented diamond film. Diamond microcrystals formed subsequently were irregular and of a few to a few tens nanometers in size. They then grew to oriented film in the following growth process.