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Magnesium aluminate has the spinel structure along with good mechanical, chemical, and thermal properties. Magnesium aluminate has a wide range of applications including refractory ceramics, optically transparent ceramic windows, and armors. Its low dielectric permeability and low loss tangent enable its applications for integrated electronic devices, as well. In this paper, MgO and Al2O3 powders were mixed in a one-to-one molar ratio and calcined at temperatures ranging from 1500 to 1800oC to produce phase pure spinel. Thereafter, pellets were crushed and treated in a planetary ball mill for 60 min to obtain a fine powder. All powders were examined for phase composition, crystal structure, and morphology. The obtained results showed that by increasing the temperature, samples with higher density were synthesized. Milling for 1 h led to formation of larger particles, but finer powders after milling. XRPD and Raman spectroscopy showed disorder in the crystal structure after milling.

Single phase MgAl2O4 was made from a one-to-one molar ratio of MgO and Al2O3 powders mixed using ball-milling. Mixtures of MgO and Al2O3 were subsequently treated in planetary ball mill for 30, 60, 90 and 120 minutes in air. The aim of this study was to examine phase composition, microstructure, and densification behavior of sintered specimens. After sintering in dilatometer at 1500°C, the powder was converted to single phase MgAl2O4. The results show that mechanical activation improved the densification behavior of MgAl2O4 sintered specimens, and it reduced the onset temperature for sintering by approx. 100°C. Based on dilatometer data, powders were subsequently densified at 1450°C by hot pressing. Almost аll specimens exhibited full density, while sample activated for 30 minutes showed the fastest densification rate. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 172057, and Grant no. III 45007]

Corundum (α-alumina) is a suiTab. material for usage in various industry fields owing to its chemical stability, electrical and mechanical features. It is known that properties of ceramics could be modified by addition of different oxides, as well as by changing the consolidation parameters. In this respect, alumina was doped with 1 wt.% of Cr2O3, Mn2O3 and NiO, followed by 1 hour of mechanical activation in a high-energy planetary ball mill. A sensitive dilatometer was used for sintering of powder mixtures up to 1400 oC and recording the obtained dilatation. The final density varied between cca. 1.9 and 3.3 g/cm3. Microstructural changes were detected by SEM measurements. Changes in electrical permittivity and loss tangent were associated with the preparation conditions (types of additives, duration of mechanical activation). For a given mixture, the sintering increases the relative permittivity and decreases losses, exhibiting the optimal values of 8.32 and 0.027, respectively, for the sample activated 60 minutes and sintered, with the addition of MnO2. Mechanical measurements indicate significant differences in strength with the addition of different transition metal oxides. Samples with Mn and Ni, activated and sintered, with strength of 121 and 86 MPa, respectively, have a significantly higher tensile strength than the other tested samples, due to their more compact microstructures. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. OI 172057, Grant no. III 45007 and Grant no. III 45019]

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Zirconium carbide ceramics were prepared by carbothermal reduction of ZrO 2 and C that were mixed by high-energy ball milling. Powders were milled for times from 0 to 120 min in air. As milling time increased, the surface area of the powders increased, indicating significant particle size reduction. Milled powders were reacted at 1600 °C and then densified by spark plasma sintering at 2000 °C, which was sufficient to convert the starting powders to zirconium carbide. Unmilled powders did not reach full density. Milled powders reached full density, but ZrO 2 impurities were found for specimens prepared from powders milled for 60 and 120 min. Microstructure analysis showed that grain size was less than 2 µm for ceramics produced from powder milled for 15 min. Based on densification onset temperature and impurity levels, a milling time of 15 min gives the best balance of particle size reduction to promote densification while minimizing impurity levels. [ABSTRACT FROM AUTHOR]