Solid State Phenomena Vols. 124-126

Abstract: The characteristics of La0.8Sr0.05Ca0.15CrO3 interconnect material synthesized by modified pechini method, USP, and GNP was investigated. The powder synthesized by Pechini method exhibited somewhat aggregated shape. The precursor synthesized by USP had spherical shape and their particle size decreased somewhat after calcining procedure at 1000oC. In the case of GNP, the precursor formed agglomerated particles. The average particle size of powders synthesized by Pechini method, USP, and GNP were 0.4+m, 0.6+m, and below 10nm, respectively. The La0.8Sr0.05Ca0.15CrO3 powder had a single perovskite phase and orthorhombic structure. After sintering at 1400oC and 1500oC, the relative density of samples synthesized by pechini method was approximately 95% and that of samples synthesized by USP was slightly small. However, that of the samples synthesized by GNP was approximately 92%.

Abstract: For the sealing of solid oxide fuel cells (SOFCs), mid-term (~1,000 h) sealing performance was examined using composite seals prepared with mixtures of a glass and alumino-silicate ceramic fiber. Leak rate could be reduced to < ~0.04 sccm/cm when using a composite seal with 60 vol% glass. Viscosity of the glass at the seal operating temperature of 650
was 2.0×108 dPa·s (log η = 8.3) as estimated by beam-bending method, and found to be suitable for sealing operation.

Abstract: Highly sinterable lithium titanate (Li2TiO3) powder was fabricated by an organic-inorganic solution route. Liquid-type ethylene glycol (EG) was used as an organic carrier for the metal cations. Titanium isopropoxide and lithium nitrate were dissolved in the liquid-type ethylene glycol without any precipitation. The dried precursor gel showed crystalline form at 300 °C and carbon-free Li2TiO3 was observed above 400 °C. The primary particle size of the carbon-free Li2TiO3 was about 100 nm, and the structure of the crystallized powder was porous and agglomerated. The porous powder was ball-milled and easily ground to fine particles. The powder compact was densified to 93% theoretical density (TD) at relatively low sintering temperature of 1100 °C for 2 h. The densifed Li2TiO3 showed a small grain size of 1.2 μm. As well, the grain size was notably increased at 1200 °C and above. After the over grain growth, further densification was no more observed.

Abstract: Effects of MgO coating on electric properties of BaTiO3 have been studied in terms of microstructural development and substitution of Mg ion. MgO coated BaTiO3 particles were prepared by a homogeneous precipitation method and other powders by a conventional mixing method for a parallel study. MgO coated BaTiO3 exhibited homogeneous microstructure compared with mixed samples. XRD analysis revealed that Mg substitution for the Ti site in the MgO mixed sample was much greater than in the coated one. MgO coated BaTiO3 showed higher dielectric constants at the Curie temperature whereas mixed ones had higher dielectric constants at 60
~80
. Electrical properties of MgO mixed and coated BaTiO3 were affected by the diffusion behavior of Mg in BaTiO3 lattice, which was confirmed by leakage currents.

Abstract: Precipitated Calcium Carbonate (PCC) is obtained through three processes; that of calcination, hydration, and carbonation. Thus, changes in each process condition determine the particle size or morphology of the mediums (calcium oxide and calcium hydroxide) as well as the product (PCC). To date, studies concerning precipitated calcium carbonate have mainly focused on the carbonation process, aimed at the manufacturing of PCC. Thus far, few studies on calcination or hydration have been conducted. Calcium hydroxide is regarded as the most important factor during the carbonation process. It is obtained through a hydration process. Therefore, in order to create the valuable PCC studies that center on the hydration process should be carried out. The present study seeks to investigate the effect of the hydration condition, particularly the temperature, on the synthesis characteristics of calcium hydroxide and aragonite PCC. The results show that the particle size of calcium hydroxide changes with variations in the initial hydration temperature. In particular, a higher initial temperature resulted in a larger particle size of the calcium hydroxide used in the synthesis. The particle size and yield of aragonite also increased when calcium hydroxide created at high temperatures was used. However, the water/solid ratio or total amount at the hydration time had no effect on the manufacturing process of aragonite.

Abstract: The oxidation behavior of tantalum diboride (TaB2) powder at high temperature was investigated in order to determine the possibility of the use of advanced high temperature structural materials. Unfortunately, monolithic TaB2 were known to be chemical stability up to high temperatures. To date, there have been few reports regarding the properties of TaB2 ceramics. The samples were oxidized at room temperature to 1273 K for 5 minutes to 25 hours in air. The weight changes were measured to estimate the oxidation resistance. The oxidation of samples oxidized for short oxidation time of 5 minutes started at 873 K, and the weight gain increased with increasing oxidation temperature. On the other hand, at the oxidation time of above 1 hour, a maximum weight gain value at 973 to 1073 K was observed. However, even if the oxidation temperature was increased an additional weight change slightly occurred. The weight gain of the sample oxidized at 1273 K for 5 minutes to 25 hours was about 40 to 20 % of the theoretical oxidation mass change. According to the powder X-ray diffraction date, the oxidized TaB2 sample was changed to Ta2O5 at 873 K. Finally, the TaB2 showed a good oxidation resistance at high temperature, because the surface film of tantalum oxide (Ta2O5) formed by oxidation acted as an oxidation resistant layer.

Abstract: The microwave-assisted combustion synthesis as a route to obtain ultrafine α-alumina and magnesium aluminate composite powders starting from the ammonium aluminum carbonate hydroxide precursor was investigated. The synthetic temperature and the crystallite size of the α- alumina nanocomposite powder were significantly affected by the environmental atmosphere in the microwave assisted combustion. The α-alumina and spinel composite powder was obtained by the microwave-assisted combustion at temperature of 1000°C under H2/N2, but at 1150°C by the normal heat process under air. The rapid transformation from γ- to α-phase was achieved by microwave assisted nucleation at low temperature of 900°C under H2/N2 atmosphere. The least crystallite size of 26.2 nm was obtained under H2/N2 atmosphere at 1000°C for 10 min.

Abstract: This paper describes examines the non-linearity of multilayer ceramic capacitors (MLCC) with new equivalent circuits. The electric charge quantity (Q) was measured as a function of applied voltage (V) under 16 V ac-field to validate the ferroelectricity of MLCC with capacitance of 1 μF. The Q-V curves predicted under ac-field using B2 spice software showed the non-linearity of ferroelectricity in the high ac-field. The Q-V curve predictions were in agreement with the experimental data for the MLCC.

Abstract: The effect of phase transformation and fine particle dispersion on densification behavior of high purity nanocrystalline alumina was investigated. The γ/α phase ratio of the mixture compacts were affected detrimentally by sinterability and phase transformation of α-phase alumina ceramics. The densification was significantly deteriorated with increasing γ-phase owing to faceted pores which are caused by the formation of a colony. The faceted pores were not existed in the α- Al2O3 ceramics with 10% γ-phase. Densification of the 10% γ-phase dispersed α-Al2O3 ceramics was significantly enhanced by rapid transformation of α-alumina. The grain growth was effectively inhibited by a small amount of nanoparticle dispersion for the alumina ceramics. As a result, dense nanostructured alumina can be achieved in the 10% γ-phase dispersed α-Al2O3 ceramics, even sintering at 1400oC for 3 hours.

Abstract: The effect of various environmental conditions on durability of E-glass fiber/vinylester resin composites has been investigated with tensile test specimen of strand type. The durability test method performed by strand type specimen was more convenient and reliable than other conventional test method. The weight gain of E-glass fiber reinforced composites increased with the immersion time in both water and alkali solutions, and the weight gains at 80°C were a little greater than ones at 20°C. The tensile strength decreased with the immersion time in all aqueous solution, and the tensile strength in 80°C of alkaline solution decreased most rapidly. The decrement of tensile strength in various environmental conditions was mainly caused by the degradation of interface and damage of glass fiber surface.