Preparation Of Dense Ceramics Research Articles

Structural, microstructure and ac impedance spectroscopy investigation of parent and M-doped forsterite Mg1.9M0.1SiO4 (M= Co, Ni and Mn)

Structural, microstructure and electrical properties of un-doped forsterite (Mg2SiO4) and M-doped forsterite (Mg2-xMxSiO4; M = Co, Ni and Mn; x = 0.1) synthesized by sol-gel method were investigated. The X-ray diffraction analysis confirmed the successful formation of single-phase forsterite, which belongs to the orthorhombic symmetry with Pbnm space group. The microstructure results indicated the preparation of dense ceramics and the average grain size was found to have the highest value for Mg1·9Ni0·1SiO4. Impedance spectroscopy investigation revealed the dominance of the grain contribution for all samples in the studied temperature (300–400 °C) and frequency (100–106 Hz) ranges. Furthermore, we found that the doping with transition metals (Co, Ni and Mn) increases the electrical conductivity of the ceramics. For the sample doped with Ni, the electrical conductivity has the highest values with the lowest activation energies for both the conduction and relaxation mechanisms.

Preparation of Dense Ceramics Based on Aluminum–Magnesium Spinel by Forming Solid Solutions in the MgAl2O4–Ga2O3 System

Preparation of Dense Ceramics Based on Aluminum–Magnesium Spinel by Forming Solid Solutions in the MgAl2O4–Ga2O3 System

A Combined Method for Synthesis of Dense Nanoceramics Based on Aluminum Oxide

Abstract—A new technological procedure for preparation of dense ceramics based on aluminum oxide is developed. It features use of a modifying additive and mechanochemical (MCA) activation of the starting material. Use of MCA has a beneficial effect on synthesis of dispersed precursor γ-Al2O3-based powders at 600°C, with the temperature of α-Al2O3 phase formation being reduced from 1200 to 1000°C. MCA is found to affect the relative density of aluminum oxide ceramics sintered at temperatures of 1000–1500°C, the sintering process occurring more intensely in the temperature range of 1000–1300°C. The presence of MgO in the aluminum oxide matrix at a level of 1 to 3 wt % is shown to slow down the growth of α-Al2O3 phase grains owing to the formation of a boundary layer consisting of MgAl2O4 nanocrystallites in the aluminum oxide matrix. A ceramic material prepared on the basis of α-Al2O3 has a mean grain size of ~70 nm, a relative density of 0.98, a microhardness of 25 GPa, and a bending strength of 650 MPa. The proposed combined method is facile and economical and enables us to produce high-density aluminum oxide ceramic with a grain size below 100 nm and high physicochemical characteristics. This ceramic can be used in fabrication of different construction and functional materials.

A Duplex Structure in Dense KSr2Nb5O15 Ferroelectric Ceramics

Dense KSr2Nb5O15 (KSN) ceramics with a duplex structure was successfully prepared using acicular KSN particles as raw materials. It was suggested that the preparation of dense ceramics by adjusting abnormal grain growth was feasible absolutely. The effect of a duplex structure on the electric properties and optical behaviors were investigated. The results indicated that the specimen with the duplex structure had a strong frequency dispersion of dielectric constant. The optical transmittance of the specimens with a duplex structure was higher than that of grain normal distribution, which also gave a new method on the study of the optical ceramics.

Preparation of dense ceramics based on silicon nitride nanopowders

Synthesis of ceramics from silicon nitride nanopowders using hot-pressing and pressure-assisted and microwave (MW) sintering techniques has been studied. Dense ceramics with improved physicomechanical characteristics can be prepared on condition that most of the oxygen in the form of silicon monoxide (contained at 5 – 8 wt.% in the precursor powders) has been removed from the material. In ceramics treated by the three sintering technologies, an extensive grain growth is observed. The microstructure of these materials was more disperse in comparison with that of ceramic prepared from conventional α-Si3N4 powders synthesized in a furnace. This provides a route towards preparing nanopowder-based ceramics with a 25 – 30% increase in strength in comparison to ceramics of the same density prepared from conventional powders.

Some significant advances in sol-gel processing of dense structural ceramics

This review deals with the solution-sol-gel processing of some structural ceramics such as alumina, zirconia, mullite and cordierite and brings out the most significant advances in the preparation of dense ceramics. In the Al2O3 system, seeding of gels with α-Al2O3 and other isostructural seeds led not only to lower crystallization temperature but also enhanced densification with refined microstructure through solid-state epitaxy. This breakthrough of seeding has led to improved abrasive grains with large commercial market. Although highly dense, partially stabilized zirconia ceramics were prepared using monodisperse and spherical or nanophase zirconia sol-gel powders, no commercial applications seem to have been realized thus far. In the Al2O3−SiO2 system, compositionally different sol-gel nanocomposites (diphasic gels) led to enhanced densification of mullite at lower temperatures because of the occurrence of densification and crystallization processes almost simultaneously. Mullite powders derived from the diphasic gel route are a breakthrough and are now commercially marketed by Chichibu Cement Company. Highly dense cordierite was prepared by using three sols, i.e., the compositionally different sol-gel nanocomposites in an analogous manner to that of mullite. Although this process appears to be highly cost-effective, especially for the fabrication of substrates, it has not yet been utilized for commercial applications. The use of sol-gel nanocomposites in the processing of various ceramics is expected to be fully exploited in the future.

Sintering of High‐Purity Magnesia

The effect of calcining temperatures on the sinter ability of high‐purity magnesia powders was investigated. A marked decrease in the density of sintered (fired) compacts occurred when petro‐graphically identifiable periclase was formed in calcining. By employing proper heat‐treatment in calcining the powder, ceramic bodies with zero apparent porosities were obtained at sintering temperatures as low as 1650°C. It is suggested that proper calcinations might also facilitate the preparation of dense ceramics of other oxides.