Journal of the American Ceramic Society

Kalinin, Sergei V.; Shao, Rui; Bonnell, Dawn A.

doi: 10.1111/j.1551-2916.2005.00383.xpmid: N/A

In the last two decades, scanning probe microscopies (SPMs) have become the primary tool for addressing structure and electronic, mechanical, optical, and transport phenomena on the nanometer and atomic scales. Here, we summarize basic principles of SPM as applied for oxide materials characterization and present recent advances in high‐resolution imaging and local property measurements. The use of advanced SPM techniques for solutions of material related problems is illustrated on the examples of grain boundary transport in polycrystalline oxides and ferroelectric domain imaging and manipulation. Future prospects for SPM applications in materials science are discussed.

Krishnamurthy, Ramanathan; Sheldon, Brian W.; Haynes, J. Allen

doi: 10.1111/j.1551-2916.2005.00169.xpmid: N/A

Silicon‐based ceramics are prone to severe oxidation and volatilization problems in the presence of water vapor. To address these issues, mullite has been investigated in recent years as a possible protective coating material. To analyze the stability of such coatings, a multi‐species diffusion model for ionic species is developed. Onsager reciprocity is assumed for the mobility coefficients and the resulting moving boundary problem is solved numerically. The formulation also accounts for substantial Si volatilization away from the outer surface of the coating. This model is used to analyze an initial transient leading to the formation of an internal silica layer, a second transient period that follows this silica formation, and a steady‐state regime that can only be attained if Si diffusion is sufficiently fast.

Araki, Kiyoshi; Halloran, John W.

doi: 10.1111/j.1551-2916.2005.00176.xpmid: N/A

Porous ceramic bodies with interconnected pore channels were fabricated by a novel freeze casting technique using camphene‐based slurries. The pore channels are surrounded by almost fully dense walls and have nearly circular cross‐sections. The pore volume fraction and the channel size were controllable by the solid content in the slurry. The channels are replicas of entangled dendrites of frozen camphene, which sublimed during the freeze‐drying process. This porous structure with entangled pore channels is considered potentially useful in many applications such as implantable bone scaffolds.

Izhevskyi, V. A.; Bressiani, A. H. A.; Bressiani, J. C.

doi: 10.1111/j.1551-2916.2005.00212.xpmid: N/A

A series of silicon carbide‐based ceramics with different sintering additives were liquid‐phase sintered to high densities. Yb2O3 in combination with AlN was used as the additive, instead of the commonly used Y2O3–AlN, to improve the refractoriness of the secondary phase. Thermo‐chemical decomposition of AlN was sufficiently suppressed with the use of nitrogen overpressure and reasonable weight loss was achieved in the different additive containing SiC ceramics without a reactive powder bed. Use of the heavier rare‐earth element modified the liquid phase formed during sintering and reduced the phase transformation controlled grain growth rate, compared with Y2O3 doped materials. It also permitted microstructure tailoring through post‐sintering heat treatments in nitrogen. Materials with self‐reinforced microstructures, formed as a result of anisotropic grain growth, were obtained. Improved fracture toughness (4.5–5 MPa/m1/2) and good flexural strength retention up to 1400°C were also observed.

Fernández‐Jiménez, A.; Palomo, A.; Macphee, D. E.; Lachowski, E. E.

doi: 10.1111/j.1551-2916.2005.00224.xpmid: N/A

Portland cement‐based materials are frequently used for fixing heavy metals but are not very effective for arsenic. Alternatively, alkali activated metakaolin and fly ash systems were tested for arsenic retention by the toxic characteristic leaching procedure and American Nuclear Society 16.1 methods. The influence of Fe and Mn on As leaching rates was assessed. These materials perform well in aggressive environments (pH<3) but the activated metakaolin matrix is less able to retain As than the activated fly ash matrix. The leaching in fly ash matrices occurs in two steps: immediate initial leaching followed by a slow diffusion‐controlled process.

Lambropoulos, John C.; Jacobs, Stephen D.; Gillman, Birgit E.; Stevens, Harrie J.

doi: 10.1111/j.1551-2916.2005.00225.xpmid: N/A

We report a series of microgrinding and polishing experiments on glass–ceramics. Microgrinding includes deterministic microgrinding (two‐body abrasion at fixed infeed rate) and loose abrasive lapping (three‐body abrasion at fixed pressure). We correlate material mechanical properties (Young's modulus, hardness, fracture toughness) and chemical properties (chemical susceptibility or mass loss under chemical attack) with the quality of the resulting surface (surface microroughness and surface grinding‐induced residual stresses). We compare deterministic microgrinding (at fixed infeed) and loose abrasive microgrinding (at fixed pressure) in terms of material removal rates and resulting surface quality.

Kimel, R. Allen; Adair, James H.

doi: 10.1111/j.1551-2916.2005.00226.xpmid: N/A

The objective of this study was to produce well‐dispersed nanosized yttria tetragonally stabilized zirconia (Y‐TZP) powder in aqueous suspension. The Y‐TZP powder was produced by precipitation from homogeneous solution at 200°C under hydrothermal conditions. A homogeneous solution was created through the use of a complexing agent, which subsequently could be used in a dispersion scheme developed for the nanosized Y‐TZP powder. Characterization of the Y‐TZP powder was performed using X‐ray diffraction, Raman spectroscopy, X‐ray fluorescence, and high‐resolution transmission electron microscope. The overall goal of this study is the eventual production of bulk ceramics from well‐dispersed nanosized aqueous ceramic suspensions via wet processing techniques.

Suetsuna, Tomohiro; Ohji, Tatsuki

doi: 10.1111/j.1551-2916.2005.00230.xpmid: N/A

Oxidation behavior of silicon nitride (Si3N4) was investigated in flowing air (2.45 cm/s) containing 10%–50% H2O at a total pressure of 1.8–10 atm at 1300°–1500°C for 100 h. The oxidation of Si3N4 progressed with volatilization of the SiO2 scale; it was more enhanced at a high partial pressure of H2O rather than at high temperature. The total pressure had little effect on the oxidation. In order to avoid the oxidation, Si3N4 substrate was coated with lutetium disilicate (Lu2Si2O7) layer through the intermediate SiO2‐rich phase. While the coating layer well suppressed the oxidation in case of small amount of water vapor, it was not sufficiently effective to suppress the oxidation when the water vapor was rich. SiO2 volatilization was observed between the layer and substrate. The flexural strength of the coated Si3N4 at room temperature was somewhat increased after the oxidation in wet air, while that of the uncoated one was almost unchanged. This increase was attributable to crack healing of the substrate during the oxidation.

Li, Wei; Cheng, Ping; Gu, Mingyuan

doi: 10.1111/j.1551-2916.2005.00233.xpmid: N/A

The influence of surface cleaning, including deionized water, acid, and base cleaning, on the rheological properties of silicon carbide (SiC) aqueous suspensions was investigated. The SiC powders were well dispersed irrespective of the surface treatment. However, the viscosity was affected by the surface cleaning. The experimental results indicated that base cleaning caused a lower viscosity. The reason of the cleaning influence on viscosity was discussed. The influence of SiC oxidative thermal treatment was determined for SiC suspensions. Calcination of SiC powders at 550°C is observed to evidently reduce the viscosity of the SiC slurry. But further increase of the calcination temperature will be deleterious to the rheologic properties. The hydration of amorphous SiO2 on the SiC surface is used to clarify the phenomenon.

Rocha‐Rangel, Enrique; Díaz‐de‐la‐Torre, Sebastián; Umemoto, Minoru; Miyamoto, Hiroki; Balmori‐Ramírez, Heberto

doi: 10.1111/j.1551-2916.2005.00234.xpmid: N/A

Mullite–ZrO2 composites have been fabricated by attrition milling a powder mixture of zircon, alumina, and aluminum metal with MgO or TiO2 as sintering additives, heating at 1100°C to oxidize the aluminum metal, and consolidation by spark plasma sintering (SPS). The influence of the SPS temperature on the formation of mullite, and the density and the mechanical properties of the resulting composites have been studied. For the mullite–zirconia composites without sintering additives, the mullite formation was accomplished at 1540°C. In contrast, for the composites having MgO and TiO2, the formation temperature dropped to 1460°C. The composites without sintering additives were almost fully dense (99.9% relative density) and retained a larger amount of tetragonal zirconia. Those materials attained the best mechanical properties (E=214 GPa and KIC=6 MPa·m1/2). To highlight the advantages of using the SPS technique, the obtained results have been compared with the characteristics of a mullite–zirconia composite prepared by the conventional reaction‐sintering process.