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The paper reviews the wear behaviour of oxide ceramics. Wear maps are considered and consequently mild and severe wear are defined. Since the use of ceramics in engineering applications require operation in the mild wear regime, the paper concentrates on mild wear mechanisms, but also considers factors which control the transition to severe wear. Within the mild wear regime, the formation of tribofilms are discussed and the manner in which dislocation activity leads to the wear transition is considered. The wear of so-called ceramic nanocomposites, for which no time dependent wear transition has yet been observed, is considered and the reasons for enhanced performance discussed. The role of transformation toughening in zirconia ceramics is considered in detail, and reasons for the generally poor wear response of these materials defined. [ABSTRACT FROM AUTHOR]

Structural ceramics, including ultrahigh-temperature ceramics such as zirconium diboride (ZrB2) and hafnium diboride (HfB2), are brittle and sensitive to flaws. As a result, the structural integrity of this ceramic component may be affected seriously. In this paper, a novelty technique namely preoxidation was proposed to overcome this problem. A ZrB2-based composite containing 20 vol% SiC whisker was produced by hot pressing. The composite was preoxidized at temperatures of 800° and 1200°C for various times ranging from 10 to 180 min in air. The flexural strength and microstructure of specimens were investigated systematically under each preoxidation condition. The strength was improved after preoxidation, with a maximum increase of strength (15%) for samples after preoxidizing at 800°C for 180 min. Microstructure analysis suggested that the increase in strength was due to the self-crack-healing behavior of the composite by surface oxide glass, such as B2O3-, SiO2-rich liquids, and borosilicate glass. However, oxide evaporation and formation of gas (i.e., B2O3 and CO) were found to be detrimental to for the crack-healing ability. Oxidation behavior during the preoxidation process followed parabolic-law kinetics. [ABSTRACT FROM AUTHOR]

The red glaze (slip) that characterizes the Terra Sigillata potteries, greatly contributed to their success during the Roman period. This feature can in fact be partially explained by the microstructure (crystalline phases and grain sizes) and the physico-chemistry (compositions) of the ceramics. In this paper, we describe how the technique of synchrotron micro scanning X-raydiffraction could contribute to the understanding of the elaboration process and origins of these ceramics. The small (micron) size of the X-raybeam coupled with the use of a sample scanning stage allows one to spatially resolve the distribution and other characteristics of the constitutive mineral phases. [ABSTRACT FROM AUTHOR]

Abstract: Synthesis of polymer-derived ceramics was explored to build nano-order in a Si–C–N system. The polymeric precursor that leads to the desired ceramic composition was self-assembled using block copolymers as structure-directing agents. This paper summarizes our research in the system polybutadiene-block-poly(ethylene oxide) (PB-b-PEO) with a polysilazane as the ceramic precursor. Microstructures ranging from classic lamellar to cylindrical as well as more complicated morphologies are described, and their evolution is shown to vary sensitively with precursor chemistry, loading and heat-treatment history. The ordered nano-scale structure created in the block copolymer/precursor hybrids can be preserved through the pyrolysis process, thereby leading to ordered nanostructures in the final ceramic. [Copyright &y& Elsevier]

Abstract: The resonant beam technique (RBT) allows the simultaneous determination of the Young''s and the shear modulus. In the present paper this method is extended to materials covering an extremely wide range of porosities from nearly dense to the limit of stability, which is shown for ZrO2-toughened reaction-bonded Al2O3 (RBAO) ceramics as an example. Additional characterisation of the pore structure and the material''s composition was performed to exclude an influence of structural parameters other than porosity. [Copyright &y& Elsevier]

A novel optically transparent ceramic nanocomposite Y2O3–MgO was produced using spark plasma sintering technique. Sintering parameters was optimized to obtain fully dense material while maintaining nanoscale grain size. The sintered nanocomposite has an excellent infrared transmission as a result of small grain size and homogeneous microstructure. Postsinter annealing can significantly improve the transmission. Overly larger grain size severely degrades the transmittance. [ABSTRACT FROM AUTHOR]

Lead zirconate titanate (PZT) ceramics (Zr/Ti = 52/48) have been modified with different quantities of neodymium oxide (Nd2O3). The preparation was carried out via the solid-state-reaction route. The samples were calcined and sintered at 850°C and 1200°C, respectively. The structural evolution and the microstructure were investigated using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM), respectively. The physical properties such as dielectric constants, piezoelectric coefficients, density etc. were also studied. [ABSTRACT FROM AUTHOR]

The microstructure of liquid phase sintered SiC ceramics was characterised by means of high resolution transmission electron microscopy (HRTEM). The SiC ceramics were pressureless sintered with the additions of Al2O3 and Y2O3 at sintering temperatures of 1800 and 1950°C, respectively. At a sintering temperature of 1800°C the microstructure of the SiC ceramics has no crystallised secondary phase and the SiC grains are separated by an intergranular amorphous film. In contrast in the case of the microstructure of SiC ceramics sintered at 1950°C a clean interface without any amorphous layer between the SiC grains was observed. The secondary phase is crystallised into the Y3Al5O12 phase and exhibits a clean interface between the SiC grains. An explanation for the existence or the absence of the intergranular glass films are given by an extended Clarke's model of the force balance of attractive van der Waals forces and repulsive steric forces. The chemical decomposition of the intergranular glass film at elevated temperature was considered. [ABSTRACT FROM AUTHOR]