Due to its outstanding electrical characteristics, such as the low temperature expansion coefficient, low dielectric constant and good mechanical properties, cordierite, 2MgO⋅2Al 2 O 3 ⋅ 5SiO 2 , is a very attractive high-temperature ceramic material. In order to accelerate the process of sintering, 2.50 mass% Bi 2 O 3 has been added to the starting mixtures. Liquid phase sintering caused by the presence of bismuth-oxide lowers the temperature of cordierite formation. The mechanical activation of the starting mixtures (0-56 min in vibro-mill) additionally lowers sintering temperatures. The sintering process was performed at 1200, 1300, 1350 and 1400°C, for 2 h. The particle size analysis (PSA) was employed in order to determine the changes in the particle size of the mechanically treated powders. The phase composition of the starting powders and sintered materials was analyzed by the X-ray diffraction method. Furthermore, scanning electron microscopy (SEM) was used in the analysis of the powder morphology.
Cordierite-based ceramic materials are attracting much interest for their various applications in industry, for manufacturing multilayer circuit boards, catalytic converters, filters, thermal insulation, kiln furniture, components of portable electronic devices, etc. In order to reduce production costs and modify cordierite-based materials, mechanical activation can be used. In this study, microstructural and electrical properties of mechanically activated MgO-Al 2 O 3 -SiO 2 system have been analyzed. The mixtures of MgO-Al 2 O 3 -SiO 2 powders were mechanically activated in a planetary ball mill for the time periods from 0 to 160 min. Morphological investigations have been performed on the obtained powders. The effects of activation and two-step sintering process on microstructure were investigated by scanning electron microscopy (SEM). Electrical measurements showed variations of the dielectric constant (ε r ) and loss tangent (tan δ) as a function of time of mechanical treatment.
Due to its characteristics, cordierite, 2MgO?2Al2O3?5SiO2, is a
high-temperature ceramic material of a great scientific interest. Mechanical
activation of the starting mixtures containing 5.00 mass% TiO2 was performed
in a high-energy ball mill for 10 minutes. The compaction pressure varied
from 0.5 to 6tcm-2 (49-588 MPa). The sintering process was performed at
1350?C for four hours in the air atmosphere. The phase composition of the
activated and sintered samples was analyzed using X-ray diffraction. Scanning
electron microscopy was used to analyze the microstructure of both compacted
and sintered samples. The authors have investigated the influence of
compaction pressure on the sintered samples and their electrical properties.
For the development of the Lost Foam refractory coatings with controlled rheologic properties, the influence of the mechanical activation process on the cordierite-based filler's properties change was examined. First of all, the test referred to the change of filler particles' size and shape, as well as to dispersion ability and stability of the coating suspension. Cordierite was obtained by synthesis in a solid state, out of the mass consisting of kaoline, alumina, quartz, sepiolite. For characterization purposes, the following methods were used: X-ray diffraction, differential thermal analysis, SEM and optical microscopy. Mechanical activation of filler was performed in a vibrating mill. The upper boundary of the grain size was 100%-30 x 10-6 m, the times were (min): 15; 30; 60. The new composition of Lost foam refractory coatings has been developed with a change of the coating production process, as well. These newly synthesized coatings proved to be effective in terms of a positive influence on a surface quality, structural and mechanical properties of aluminium castings. Test results may be useful to have the Lost Foam refractory coatings specified together with other process parameters used for the production of castings according to this casting method.
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