Ik Jin Kim

Low thermal expansion behavior and thermal durability of ZrTiO4–Al2TiO5–Fe2O3 ceramics between 750 and 1400 °C

Abstract The thermal-shock-resistant materials in the system Al 2 TiO 5 –ZrTiO 4 (ZAT) were synthesized by oxide process. The range of ZAT compositions investigated had showed very low thermal expansions of 0.3∼1.3×10 −6 /K compared to 8.29×10 −6 /K of pure ZrTiO 4 and 0.68×10 −6 /K of polycrystalline Al 2 TiO 5 , respectively, compared with the theoretical thermal expansion coefficient for a single crystal of Al 2 TiO 5 , 9.70×10 −6 /K. The composites also had high thermal durability between 750 and 1400° for 100 h. The low thermal expansion and high thermal durability are apparently due to a combination of microcracking caused by the large thermal expansion anisotropy of the crystal axes of the Al 2 TiO 5 phase and the limitation of grain growth Al 2 TiO 5 by the ZrTiO 4 . The microstructural degradation of the composites is presented here analyzed by scanning electron microscopy, X-ray diffraction, and dilatometry.

Hydrophobic partitioning approach to efficient protein separation with magnetic nanoparticles.

A novel approach to the hydrophobic partitioning effect on efficient separation of protein such as BSA was demonstrated by the modification of hydrophobic pockets on the surface of silica-coated magnetic nanoparticles with various alkyl groups at various pH levels. The separation efficiency is strongly reflected and can be attained by controlling the size of the hydrophobic pocket and other factors such as the alkyl chain length, the salt concentration, and the pH levels. Furthermore, the adsorption constant (k(ad)) was calculated for the hydrophobic partitioning interaction between BSA and the hydrophobic pocket size at various pH levels.

Carbon nanotube formation using zeolite template and applications

Carbon nanotubes (CNTs) have attracted intensive interests of researchers for a long time due to their fascinating physical and chemical properties promising for various potential applications, including advanced ceramics, nanoelectronic devices, nanoscale sensors, solar cells, battery electrode, field emitters, etc.. This review summarized the synthetic methods of CNTs, with an emphasis on the chemical vapor deposition (CVD) method, especially catalytic CVD. Although there still are some challenges in the way, with the development of the technology, a hope for widespread applications always exists.

Crack Healing, Reopening and Thermal Expansion Behavior of Al2TiO5 Ceramics at High Temperature

The low thermal expansion (α25-1100oC = 0.05 ~ 1.6 × 10–6/K) of Al2TiO5 ceramics are apparently due to a combination of grain boundary micro cracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. During the reheating run, the individual crystallites expanded at low temperature; thus, the solid volume of the specimen expanded into the micro cracks, where as the macroscopic dimensions remained almost unchanged. As a result, the material expanded very little. The micro cracks closed at higher temperatures. This result is closely related to relatively steeper thermal expansion curves.

Negative Thermal Expansion up to 1000°C of ZrTiO4-Al2TiO5 Ceramics for High-Temperature Applications

High temperature structural ceramics based on Al2TiO5-ZrTiO4 (ZAT) having excellent thermal-shock-resistance were synthesized by a reaction sintering. The ZAT ceramics sintered at 1600oC had a negative thermal expansions up to 1000oC and a much lower thermal expansion coefficient (0.3 ~ 1.3 x 10-6 /K) than that of polycrystalline Al2TiO5 (1.5 x 10-6 /K). These low thermal expansion are apparently due to a combination of microcracking caused by the large thermal expansion anisotropy of the crystal axes of the Al2TiO5 phase. The microstructural degradation of the composites after various thermal treatment for high temperature applications were analyzed by scanning electron microscopy, X-ray diffraction, ultrasonic and dilatometer.

Al2O3–TiO2/ZrO2–SiO2 based porous ceramics from particle-stabilized wet foam

The porous ceramics based on Al2O3–TiO2/ZrO2–SiO2 from particle-stabilized wet foam by direct foaming were discussed. The initial Al2O3–TiO2 suspension was prepared by adding TiO2 suspension to partially hydrophobized colloidal Al2O3 suspension with equimolar amount, to form Al2TiO5 on sintering. The secondary ZrO2–SiO2 suspension was prepared using the equimolar composition, and to obtain ZrSiO4, ZrTiO4, and mullite phases in the sintered samples, the secondary suspension was blended into the initial suspension at 0, 10, 20, 30, and 50 vol%. The wet foam exhibited an air content up to 87%, Laplace pressure from 1.38 to 2.23 mPa, and higher adsorption free energy at the interface of approximately 5.8×108 to 7.5×108 J resulting an outstanding foam stability of 87%. The final suspension was foamed, and the wet foam was sintered from 1400 to 1600 °C for 1 h. The porous ceramics with pore size from 150 to 400 μm on average were obtained. The phase identification was accomplished using X-ray diffraction (XRD), differential thermal analysis (DTA), and thermogravimetric analysis (TGA), and microstructural analysis was performed using field emission scanning electron microscopy (FESEM).

Advanced Engineering Ceramics for Semiconductor Package Technology

Advanced engineering ceramic technology has very remarkable reputation in the high-tech fields such as semiconductor device manufacturing. ZTA (Zirconia Toughened Alumina), ruby and alumina is applied in the manufacturing of the capillaries that demonstrate high strength, fracture toughness and long life. The advantages of the new composite material over the standard ultra-fine grain high-density material have been proven in many applications especially for packages requiring less than 50μm capillary tip diameter. In this work, micro-structural evolution of ceramic composites and its correlation with important criteria in the selection of the suitable capillary material either ZTA composites or high-density ruby ceramics for a specific package applications will be discussed.

Synthesis and Morphological Transformation of NaA Zeolite Crystals at High Temperature

Well-shaped NaA zeolite cubic crystals of a large size of 5-7 ㎛ were synthesized by a hydrothermal method in a mother solution having a 3.55Na₂O:Al₂O₃:1.6SiO₂:593~2000H₂O composition. Thermal treatment of NaA zeolite crystals resulted in the formation of a crystalline phase of NaAlSiO₄-Camegeite between 800 and 900℃. Even at 1000℃, NaAlSiO₄ phase was found as a major product. Environmental Scanning Electron Microscopy (ESEM), High Resolution Transmission Electron Microscopy (HRTEM), X-Ray powder Diffraction (XRD), Fourier Transform Infrared (FT-IR) spectroscopy, and DTA/TGA and BET analyses were used to characterize the initial materials and the obtained products after various heat treatments.

Effect of Cr₂O₃ Content on Densification and Microstructural Evolution of the Al₂O₃-Polycrystalline and Its Correlation with Toughness

The effects of Cr₂O₃ on the microstructural evolution and mechanical properties of Al₂O₃ polycrystalline were investigated. The microstructure of Al₂O₃-Cr₂O₃ composites (ruby) was carefully controlled in order to obtain dense and fine?grained ceramics, thereby improving their properties and reliability with respect to numerous applications related to semiconductor bonding technology. Ruby composites were produced by Ceramic Injection Molding (CIM) technology. Room temperature strength, hardness, Young’s modulus and toughness were determined, as well as surface strengthening induced by thermal treatment and production of a fine-grained homogenous microstructure.

Coating and Intergrowth of NaX Molecular Sieve Films on Porous Ceramic Paper for Membranes

NaX molecular sieve films on ceramic paper prepared by in-situ hydrothermal method were investigated. The NaX zeolite seed crystals of a uniform size of 5 µm were synthesized by hydrothermal method in a mother solution having a composition of 3.5Na2O : Al2O3 : 2.1SiO2 : 500 ~ 1000 H2O. These dip-coated NaX seed crystals on ceramic paper lead to further the thickness (20 ~ 100 µm) of NaX film on the substrate at 90°C for longer 3~7 days in autoclave. Pure zeolite films consisting of a continuous intergrown of 5~ 20 µm NaX crystal have been prepared on the substrates. The zeolite films were characterized by XRD, SEM, BET and XRF.