Evaluation of alumina slurry dispersion by nuclear magnetic resonance relaxation as a comparison to conventional dispersion evaluation methods.

In this paper, we evaluated the particle dispersion degree of alumina slurry containing a dispersant by solvent nuclear magnetic resonance (NMR) relaxation and compared it with conventional dispersion evaluation methods such as viscosity, particle size, and sedimentation height measurements. The dispersion of slurry was evaluated via numerical analysis of the transverse relaxation time (T2 ). The effect of the changes in different parameters of the experiment in terms of milling time, solid loading, and dispersant amount was investigated by NMR relaxation as well as conventional methods. The results of NMR relaxation measurements revealed that T2 correlates well with other dispersion evaluation methods; thus, it is an efficient technique to evaluate the dispersion of alumina slurry, specifically, when studying the effect of the change in milling time and dispersion amount.

Effects of Y2O3 Additive on Mechanical and Thermal Properties of Cordierite-Mullite Ceramics.

Cordierite is an alumina-magnesia-silica compound widely used as a thermal shock resistant material due to its high thermal shock resistance, low coefficient of thermal expansion (CTE), low dielectric constant, and good electrical insulation. However, its narrow sintering temperature range and low mechanical strength hinder its application in ceramic heaters. Although mullite shows excellent thermal and chemical stability, heat resistance, and mechanical strength, it has the disadvantages of high sintering temperatures (1600-1700 °C) and poor thermal shock resistance. In this study, a composite phase was prepared by mixing cordierite and mullite to expand the narrow sintering temperature range of cordierite and adjust its CTE to be similar to that of Si. Furthermore, Y2O3 was added to reduce the sintering temperature and to increase the mechanical strength. Therefore, the composite showed the highest density of 2.5 g/cm³ at 1380 °C when the ratio of mullite to cordierite was 20 wt%. When 11 wt% Y2O3 was added to this composition, the highest density was 2.8 g/cm³ for a sintering temperature of 1320 °C, and the mechanical strength was relatively good as 180 MPa of 3-points bending strength was comparatively good. The CTE was 2.6×10-6.K-1, which was similar to that of Si.

Dispersion Optimization of Alumina Slurry with Variation of the Dispersant.

Plate-type alumina ceramics are widely applied as the major components in display and semiconductor manufacturing equipment. These materials are mainly produced by a filter casting method. There have been few studies on the dispersion of these slurries. Therefore, various commercial dispersants were compared and evaluated here in an effort to optimize the slurry dispersion, which affects the homogeneity characteristics in the field of alumina manufacturing. In order to optimize the slurry dispersion, three types of water-based dispersants were selected through preliminary experiments and the viscosity, frequency sweep, particle size distribution, and sedimentation height were compared under optimum conditions after optimizing the amounts of these dispersants. The amount of dispersant in each case was optimized for the 5468CF, BYK-194, and BYK-012 dispersants, after which the frequency sweep, particle size distribution, and sedimentation height were compared according to the type of dispersant. The viscosity, frequency sweep and sedimentation height were thus measured, and it was confirmed that BYK-012, 5468CF and BYK-194 all had excellent dispersibility, in that order. As a result, it could be confirmed that the condition under which BYK-012 was added, at 0.9 wt%, led to the best dispersibility. In addition, microstructural changes of sintered body samples according to the type of dispersant used were observed. These observations indicated that the microstructure of BYK-012 at 0.9 wt% with excellent dispersibility led to suppressed grain growth with a finer pore size.

Sintering and Microstructure of BaTiO3 Nano Particles Synthesized by Molten Salt Method.

In order to establish thinner dielectric layers in thick film electronic components such as MLCC (Multilayer ceramic capacitor), BaTiO3 nanoparticles have been utilized. However, studies on the synthesis of nanoparticles smaller than 20 nm, the characteristics of the BaTiO3 powder, and the powder's sintering are lacking. Therefore, this paper aims to synthesize BaTiO3 particles smaller than 20 nm by using the molten salt method and evaluate the microstructure and dielectric properties by varying the sintering temperature from 750 degrees C to 1200 degrees C. Through the molten salt method and by using KOH-KCl mixed salt, 20 nm BaTiO3 powder was synthesized at a low temperature of 150 degrees C. Sintering the pellets formed from the synthesized 20 nm BaTiO3 nano powder led to the observation of an unusual phenomenon where the particles grew to approximate sizes below 850 degrees C where densification progressed. At sintering temperatures above 950 degrees C, particles that expanded into rod shapes were observed and these particles were identified to be unreacted TiO2 based on the results of the EDX (Energy Dispersive X-ray Spectroscopy) analysis and phase analysis results.

Effect of Ca-Al-Si-O common glass on dielectric properties of low-temperature co-fired ceramic materials with different fillers.

High-density integration in single component used for mobile communication is highly demanded with the miniaturization trend in multi-functional light-weighted mobile communication devices. Embedding passive components into multi-layered ceramic chips is also increasingly needed for high integrity. The need for high strength materials to be used in handheld devices has also increased. To this end, many attempts to join different low-temperature co-fired ceramics (LTCC) materials with different dielectric constants have been made, but failed with de-laminations or internal cracks mainly due to difference of thermal expansion coefficients. It is thought that this difference could be minimized with the use of common glass in different LTCC materials. In this study, several candidates of common glass were mixed with various fillers of LTCC to have various dielectric constants in the radio-frequency, and to minimize the mismatch in joining. Ca-Al-Si-O glass was mixed with 1.3MgO-TiO2, cordierite and CaTiO3. Mixtures were tape-cast and sintered to be compared with their micro-structures, dielectric properties and thermo-mechanical characteristics. When 1.3MgO-TiO2 with volumetric ratio of 30% was mixed with Ca-Al-Si-O glass, the measured dielectric constant was 7.9, the quality factor was 3708. With 45 volumetric percent of cordierite, the dielectric constant was 5 and the quality factor was 1052.