A vacuum infiltration process has been developed to fabricate the aluminum matrix composites reinforced with low volume fraction (<50 vol%) of SiCp. Generally, it is difficult to fabricate low volume fraction particulate composites by traditional infiltration processes because the particles always pack up to about 50 vol% in the preforms or compacts. In this study, the powder compacts were prepared of the well-mixed Ni-coated SiCp and pure aluminum powders and then were packed in quartz tubes. An aluminum alloy (Al–8.7% Si–2.6% Cu) with a composition similar to AA 380.0 was used to infiltrate these compacts. Experimental results showed that the infiltration temperature of 640 °C is favorable for the fabrication of these composites. Infiltration behavior, microstructure, nickel distribution, bending test, and fractography of the composites were investigated.

This paper describes the microstructural characterization, using transmission electron microscopy (TEM), of the solid-state, diffusion-bonded interfaces generated in a SiC whisker-reinforced, aluminum composite. Diffusion bonding was carried out using an aluminum-lithium alloy as the bonding interlayer. Two kinds of bonded interface were studied: those generated between the composite matrix and the metallic interlayer (metallic-metallic) and other ceramic-metallic interfaces formed between the interlayer and the SiC whiskers. The first showed the formation of zones of recrystallization across the original bond interface, and the second generally presented a high degree of continuity without the formation of interface reaction layers between the SiC whiskers and the interlayer. However, the formation of a degradation oxide layer was detected in some of the whisker/interlayer diffusion bonds. Its presence is due to the reaction between the alloying elements of the Al–Li interlayer and the SiO2 layer which surround some of the whiskers of the parent composite.

This study investigates the effects of sintering atmosphere and temperature on the interfacial properties of Cr3C2/Al2O3 composites. Thermodynamic considerations and calculations with computer-assisted methods for the equilibrium compositions in the Al–O–Cr–C system were used to simulate the interfacial reaction in Cr3C2/Al2O3 composite during sintering. The results were in good agreement with the experimental analysis. Cr3C2 is more stable during sintering in a system with carbon due to the lower equilibrium oxygen partial pressure. Controlling CO and O2 gas concentration, Cr3C2 first oxidized, decarbonized, and then transformed to Cr7C3 before reacting with Al2O3. An interfacial reaction between Cr3C2 and Al2O3 was not observed.

This paper reports the formation of a solid solution in the system Bi2O3–TiO2–CuO. This solid solution seems to be isostructural with Bi4Ti3O12, according with the x-ray powder diffraction patterns. Microstructural studies done using scanning electron microscopy show the typical elongated Bi4Ti3O12 grain morphology only in samples with 2 : 2 : y molar ratios of the Bi2O3 : TiO2 : CuO oxides (y = 1, 2, or 3).

Thin films of cubic boron nitride (c-BN) were synthesized using an organometallic precursor trimethylborazine (TMB) which contains both boron and nitrogen in 1 : 1 stoichiometric ratio. The films were deposited at different temperatures ranging from 300 to 500 °C at a pressure of 2 Torr and at 360 W microwave power, using N2 as carrier gas. The deposited films were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM), which reveal the presence of amorphous BN and crystalline c-BN in varying proportions. The x-ray diffraction pattern of the deposited films showed a strongest peak at 2θ = 57.1° where the interplanar distance value, d = 2.06 Å, agreed well with the (111) crystallographic orientation of c-BN phase.

ZrO2–Al2O3 powders were synthesized by spray pyrolysis. These powders were sintered at 1 GPa in the temperature range of 700–1100 °C. The microstructural evolution and densification are reported in this paper. The application of 1 Gpa pressure lowers the crystallization temperature from ∼850 to <700 °C. Similarly, the transformation temperature under 1 GPa pressure for γ → α–Al2O3 reduces from ∼1100 to 700–800 °C range, and that for t → m ZrO2 reduces from ∼1050 to 700–800 °C range. It was possible to obtain highly dense nanocrystalline ZrO2–Al2O3 composite at temperatures as low as 700 °C. The effect of high pressure on nucleation and transformation of phases is discussed.

The structural transformation of anatase TiO2 by high-energy vibrational ball milling was studied in detail by different analytical methods of x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This structural transformation involves both phase transition and nanoparticle formation, and no amorphization was observed. The crystallite size was found to decrease with milling time down to nanometer size ∼13 nm and approaching saturation, accompanied by phase transformation to metastable phases, i.e., TiO2(II), which is a high-pressure phase and TiO2(B), which was identified in ball-milled powder reported for the first time in this paper. These phases eventually started transforming to rutile by further milling.

A method to modify ceramics using a low power microwave plasma torch is described. The size, shape, surface area, and phase of alumina particles were dramatically modified by passage through an atmospheric pressure argon plasma, operated at 1 kW or less power. Specifically, irregularly shaped particles of γ-alumina with an average diameter of 11 μm were converted to smaller (ca. 4 μm) spherical particles primarily consisting of δ- and α- (corundum) phases. Also notable was the finding that modifications of the particles, such as changes in surface area, correlate to applied plasma energy. The plasma torch was operated with an argon flow rate of 5 slpm, power of between 400 and 1000 W, and average particle residence time in the plasma of 0.1 s.

High dielectric and low loss capacitor thin films of Sr2Nb2O7 (SN), Sr2Ta2O7 (ST), and their solid solution Sr2(Nbx, Ta1−x)2O7 (SNT) were investigated using the sol-gel technique. The SN film grows with the (0n0) orientation in the case of heating at over 700 °C. Heat treatment at a lower temperature results in the polycrystal ST-type structure. The SNT at x < 50% also resulted in the ST type. The dielectric constant for the SN film was 45, within 10% variation at ±0.5 MV/cm. Dielectric loss (tan δ) was 0.3–0.5%. The small variation in dielectric constant and the paraelectricity with low loss are suitable for capacitor applications.

The electrical properties of Mn–Zn ferrites undoped and doped with Nb2O5 and V2O5 were investigated by impedance spectroscopy. The observed impedance response corresponded to that of a highly resistive grain boundary component in series with a less resistive bulk component. The presence of Nb5+ and V5+ led to an enhancement in the electrical resistance, especially in grain boundaries, as well as a greater difference in the electrical behavior between bulk and grain boundary components. The different dopant performance of these two components is discussed on the basis of grain boundary structure and chemical data, electrical conductivity, and dielectric dispersion.

Phase-pure perovskite lead titanate with various morphologies has been synthesized by a hydrothermal method at 150 °C. Particle shapes include cubic, tabular, and aggregated platelike shapes. The feedstock concentration greatly influences particle morphology of the hydrothermally derived PbTiO3. At a concentration of 0.05 M, the tabular particles form while cubic particles are produced at 0.1 M. Aggregated plateletlike particles are synthesized at 0.125 M. It was observed that both tabular and cubic particles directly precipitate from the coprecipitated precursor gel. In contrast, the plateletlike shaped intermediate phase appears during the initial stage of reaction at 0.125 M and in situ transforms into perovskite PbTiO3 during further hydrothermal treatment. The intermediate phase preserves its particle shape during transformation and, acting as a template, gives rise to the final tabular PbTiO3 particles. It is demonstrated that only base reagents such KOH and NaOH, which provide a highly basic condition (i.e., pH > 14), promote transformation of the coprecipitated gel into the perovskite PbTiO3. A Hancock and Sharp kinetic analysis in conjunction with microstructural evidence suggests that the formation mechanism is dissolution and recrystallization in which the degree of supersaturation plays an important role in dictating the crystallographic particle phase and morphology of the particles. An experimentally constructed solubility diagram indicates that an excess lead condition is necessary to compensate for loss of lead species and to increase supersaturation to expedite precipitation of PbTiO3 at highly alkaline conditions.

α–Si3N4 whiskers were fabricated first through combustion synthesis (CS) technology. The as-synthesized crystals with [001] as the elongated axis contain a large amount of linear defects including (a + b)-type, (a + b + c)-type, and c-type of dislocations. The growth of α–Si3N4 whiskers is mainly controlled by vapor-condensation (VC) mechanism. Special additive plays an important role in promoting the growth of α–Si3N4 whiskers and suppressing the phase transformation of α–Si3N4 to β–Si3N4.

A composite microstructure, consisting of β-Sialon, O-Sialon, and X-Sialon phases was produced by coating β–Si3N4 particles with amorphous alumina followed by hot pressing and reactive sintering at 1923 K. The particle coating procedure was selected over conventional powder blending in order to promote heterogeneous nucleation of β-Sialon grains on β–Si3N4 particles uniformly. The microstructure, chemistry of the phases, and interphase interfaces of this ceramic were characterized by transmission electron microscopy (TEM) and high-resolution analytical electron microscopy (AEM). Both electron energy-loss spectroscopy (EELS) and energy-dispersive spectroscopy (EDS) x-ray microanalysis in AEM revealed that b-Sialon grains had varying aluminum and oxygen contents. High-resolution electron microscopy (HREM) examination of several interphase interfaces and triple junctions suggests that the amount of glassy phase in the produced ceramic is substantially lower compared to those reported in the literature. This is of importance of high temperature properties. The fracture toughness and wear properties were evaluated at room temperature. Available data indicate that the fracture toughness and wear of β-Sialon composite can be significantly improved by the powder coating technique compared to the conventional powder blending technique.

The influence of the presence of free PbO on densification, the perovskite/pyrochlore phase ratio, and corresponding dielectric properties has been studied for 0.9 PMN–0.1 PT-based ceramics with different added PbO excess. The sintering behavior of PMN-PT-based ceramics was basically controlled by PbO losses. However, the presence of a rich-PbO liquid phase during sintering produced pyrochlore grains, mainly located at the surface of the specimens. The dielectric properties of the PMN-PT-based materials, fabricated with different values of PbO excess, were similar when the secondary phase preferentially located at the surface was removed by polishing prior to electrode deposition. The thickness of the PbO-rich intergranular layers of the four samples with different initial PbO content was mainly independent of the amount of PbO excess because most of the free PbO was eliminated during sintering. Dielectric constant values of approximately 17,000 at 1 kHz and 40 °C were measured.

The microstructure evolution of Pb(Mg1/3Nb2/3)O3 –PbTiO3 (PMN-PT) based ceramics has been investigated to determine the influence of the presence of PbO content in excess of stoichiometric values. The microstructure of the different materials showed a different evolution of secondary phases (free PbO and pyrochlore type) related to the PbO excess. The pyrochlore phase appeared in a layer near the top surface of the specimens. The thickness of the layer and the grain size of this secondary phase increased with the amount of PbO excess. A transmission electron microscopy (TEM) study of the sintered specimens revealed a core-shell structure in more than 30% of grains. The shell of these grains was Ti-rich PMN, and it is related to the presence of a liquid-phase-assisted sintering mechanism.

Starting from elemental powders, simultaneous synthesis and compaction of SiC were conducted at 3 GPa pressure and temperatures in the range 2100–2900 K. The sintered compacts were characterized by x-ray diffraction, microhardness measurements, and microscopic studies. The efficiency of formation of SiC was dependent on the particle size of the silicon powder, crystallinity of the reactant carbon, molar ratio of silicon and carbon, and synthesis temperature and time. Carbon in excess of the stoichiometric amount was required to obtain compacts free from residual silicon. The SiC samples, with a Si: C molar ratio 1: 1.05, prepared at 2100 K for 300 s had a density and hardness of 3.21 g/cm3 (98.8% of theoretical density) and 22 GPa, respectively. The crystal structure of the SiC depended on the synthesis temperature. Pure β–SiC in the temperature range 2100–2500 K, and a mixture of α– and β–SiC above 2500 K were obtained. The β–SiC was highly crystalline and nearly defect-free.

Bulk thermal expansion properties of 19 members of the A2M3O12 family of tungstates and molybdates were determined from room temperature to 800 °C. The observed behavior ranges from strong negative thermal expansion (α = −11 × 10−6 K−1) in Sc2W3O12 to near zero thermal expansion in Al1.68Sc0.02In0.30W3O12.

Mullite-zirconia composites were synthesized by reaction-sintering powder mixtures of α-alumina, amorphous silica, and 3 mol% yttria-stabilized zirconia. It is found that the addition of 3 mol% yttria-zirconia improves sintering and lowers the mullitization temperature. It also suppresses the cristobalite formation and enhances zircon formation between 1300 and 1400 °C. Results further suggest that these effects are consequences of modification of the silicate glass by yttria. Samples containing ≥20 vol% of 3 mol% yttria-zirconia could be sintered at 1500 °C for 2 h to obtain dense composites consisting of mullite and tetragonal zirconia. The microstructural investigations of the sintered samples support the viewpoint that mullite formation is via nucleation and growth from aluminosilicate glass. They also reveal that zirconia can hinder the grain growth of mullite and that the coalescence of zirconia grains is accomplished by grain boundary diffusion.

The simultaneous synthesis and densification of the ternary Ti3SiC2 was investigated by the field-activated, pressure-assisted combustion method. Depending on temperature and time at temperature, relatively pure and nearly fully dense materials can be synthesized by this approach. The optimum conditions to produce this phase were a reaction temperature of 1525 °C and a time at temperature of 2 h. The product contained TiC as a second phase at a level of ≤2 mol%. The resulting ternary phase has typically elongated grains which were about 25 μm in size. Within a range of applied force of 1–4 N, the microhardness of the product was relatively constant, ranging from 6 to 7 GPa. Investigations on the thermal and chemical stabilities of the ternary were also conducted. Vacuum annealing at temperatures of 1600 and 2000 °C resulted in the formation of a surface layer of TiC, while the air annealing at 1000 °C resulted in the formation of TiO2. Oxidation studies on the prepared Ti3SiC2 were made at temperatures ranging from 800 to 1100 °C. The results suggest a two-mechanism process, one dominating in the approximate range of 800–950 °C and the other in the range 950–1100 °C with corresponding activation energies of 137.7 and 312.5 kJ·mol−1. The results are explained in terms of two proposed reactions on the basis of microprobe analyses.

We report on the feasibility of using molybdenum silicide as a conducting barrier for integration of ferroelectric lead zirconate titanate capacitors on Si. Thin films of MoSi2 were deposited by pulsed laser-ablation deposition (PLD). The silicide films showed a structural transition from amorphous to orthorhombic to tetragonal phase as the temperature of deposition was changed from room temperature to 900 °C. The four-probe resistivity and surface roughness of the films decreased with an increase in the deposition temperature and crystallinity of the phase. Ferroelectric (La, Sr)CoO3/Pb(Nb, Zr, Ti)O3/(La, Sr)CoO3 capacitors were grown on Si/poly Si/MoSi2, and Si/poly Si/MoSi2/Pt structures. Transmission electron microscopy (TEM) studies of the MoSi2/LSCO and MoSi2/Pt/LSCO heterostructures indicated the formation of a thin layer of SiO2. In the case of Pt/MoSi2, Pt reacts with the silicide and forms PtSi, consuming the entire platinum layer and, thus, makes it unsuitable as a composite barrier. Electrical testing of the LSCO/PNZT/LSCO capacitors through capacitive coupling showed desirable ferroelectric properties on these substrates.