2017, Vol.27, No.5

Journal of the Korean Crystal Growth and Crystal Technology 2023 KCI Impact Factor : 0.19

pISSN : 1225-1429 / eISSN : 2234-5078
https://journal.kci.go.kr/jkcgct

Aluminum nitride (AlN) powder was successfully synthesized at low temperature via carbothermal reduction and nitridation (CRN) assisted by microwave heating. The synthesis processes of AlN powder were investigated with X-ray diffraction, FE-SEM, FT-IR and TGA/DSC. Aluminum nitrate was used as an oxidizer and aluminum source, urea as fuel, and glucose as carbon source. These starting materials were mixed with D.I water and reacted in a flask at 100 o C for 20 minutes. After the reaction was finished, black foamy intermediate product was formed, which was considered to be an amorphous Al2O3 particles through intermediate product obtained by solution combustion synthesis (SCS) at the results of X-ray diffraction patterns and FT-IR. This intermediate product was nitridated at temperatures of 1300 o C and 1400 o C in N2 atmosphere by a microwave heating furnace and then decarbonated at 600 o C for 2 hours in air. It should be noticed from FE-SEM images that as nitridated particles, identified as AlN from X-ray diffraction patterns, are covered with carbon residues. After decarbonating the nitridated powders, the spherical pure AlN powders were obtained without alumina and their particle sizes were dependent on the nitridating temperature with high temperature of 1400 o C giving large particles of around 70~100 nm.

In this study, TiAl alloy was fabricated by a centrifugal casting method for turbo charge of automotive. Optimum conditions for defectless morphology using various ceramic mold were investigated. The crystal structure, microstructure, and chemical composition of the TiAl prepared by centrifugal casting were studied by X-ray diffractometer (XRD), optical microscopy (OM), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS), microvickers hardness analyzer (HV). Two kinds of dendrite structures were observed with 4-fold and 6-fold symmetries. The FE-SEM, EDS and HV examinations of the as-cast TiAl showed that the thickness of the oxide layer (α-case) was typically less than 50 μm.

In order to prepare porous scaffolds capable of pore control, PMMA powder serving as a pore-forming agent was added to HA powder to synthesize a slurry containing TBA as a solvent. And then, porous HA scaffolds where pillarshaped pore channels interconnected with each other were fabricated by freeze-casting and sintering. The crystal structure of the HA scaffolds according to the addition amount of PMMA powder was measured by XRD and the surface and inner cross section of the scaffolds were analyzed through SEM. It was found that removal of PMMA during sintering affects the internal structure of the scaffolds and the crystallinity of the HA powder. Furthermore, through evaluating the physical and mechanical properties of the scaffolds, it was confirmed that the porosity, pore size and compressive strength can be controlled by controlling the addition amount of the pore-forming agent. It was also found that the HA scaffolds produced in this study were similar in structure and properties to the natural cancellous bone. This suggests that porous HA scaffolds with PMMA can be used as an alternative to autogenous bone for tissue engineering as an artificial bone scaffold.