6H-SiC single crystals were grown by using a resistance heating system. It was recognized that the growth behavior was different according to the different growth temperatures. It was revealed that the temperatures at the source feeding and at the crystal growth position had to be controlled independently. In this report, the effect of growth temperature on the SiC crystal growth was discussed.
Bulk GaN crystals were grown by the basic ammonothermal method. The c-plane GaN templates grown by hydride vapor phase epitaxy were used as seed crystals and sodium metal, amide, and azide were added as a mineralizer.
The growth conditions are at temperatures from 500~600 o C and pressures from 2~3 kbar. The growth rate for the c-axis was increased with increasing the operating pressure. Average dislocation density was measured 1 × 10 5 /cm 2 by the cathodoluminescence measurement. The full-width at half-maximum of the X-ray diffraction rocking curve for (002) reflection was approximately 270 arcsec for Ga face and 80 arcsec for N face.
In this study, it was investigated that characteristic of crack-self-healing of hot-pressed SiC. SiC ceramics was sintered with Al2O3 and Y2O3 sintering additive by hot press. Sintering was performed in hot-press furnace in flowing argon (Ar), holding for 3 hr under 1950 o C and 50 MPa. The sintered SiC was machined into 3-point bending strength specimen of 3 × 4 × 40 mm, and introduced pre-crack by Vickers indentation at 49.6 N. Specimens were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), 3-point bending strength after heat treatment at 1200~1400 o C for 1~10 hr. The best crack-self-healing ability was achieved 770 MPa 3-point bending strength by heat treatment at 1300 o C for 5 hr.
The degradation behaviors of TiN coating layers under thermo-mechanical stress were investigated in terms of comparison of finite element analysis (FEA) and experimental data. The coating specimen was designed to quarter cylinder model, and the pulsed laser ablation was assumed as heat flux condition. The FEA results showed that heat accumulation at the center of the laser-ablated spot occurred and principle stress was concentrated at the lower region of the coating layer. The microstructural observation revealed that surface melting and decrease of the coating thickness occurred in the TiN/Inconel 617 and the interfacial cracks formed in the TiN/Si. The delamination was caused by the mechanical stress from the center to the outside of the ablated spot as the FEA results expected. It was considered that the improvement of the thermal shock resistance was attributed to higher thermal conductivity of Si wafer than that of Inconel 617.
The lanthanum oxide nano-rods were grown on the surface of 3 mol% Yttria Partially Stabilized Zirconia ceramic composite which containing Lanthanum-Strontium Manganate, LaxSryMnzO3 for the purpose of endorsing the antistatic property.
The diameter and the aspect ratio of the nano-rods were greatly changed according to the growing condition. With the optical microscope observation, the nano-rods shining brightly. It was confirmed that the major components of nano-rods is La, and Sr, Mn, Si are minor components by SEM and TEM analyses.
In the present paper, garnet structured Y3Al5O12 : Ce 3+ (YAG : Ce) ceramic phosphor plate (CPP) for high power laser diode (LD) was prepared and optical properties were analyzed. We synthesized monodispersed spherical nano-sized YAG : Ce particles by liquid phase method, fabricated phosphor ceramic plate with the addition of Al2O3. 75 μm and 100 μm thick YAG : Ce CPPs were compared in terms of the factors of conversion efficacy, thermal quenching, luminance and correlated color temperature (CCT). In conclusion, conversion efficacy decreased by 25 % in both samples and 100 μm thick sample provides better optical properties of thermal quenching, maximum light conversion efficacy and maximum luminance value.
AlN single crystals were grown by the PVT (Physical vapor transport) method with position-changable induction coil. And the graphite crucible dimensioned Φ90xH120 was used on processing. The temperature was 1950~2050oC and ambient pressure was 150~1 Torr. And the hot-zone was changed according to times on growing for result comparison.
When hot-zone by coil is located below far enough (> 40 mm) from AlN crystal concentration position, the as-grown crystals physical size is better (300 μm/hr) than another condition, but the condition-reproducibility was very poor. However the closer the distance between hot-zone and AlN growing posion, the smaller the size of as-grown crystal and the rarer the generation of the crystal nuclear, but the crystal growing condition is stable for quality. The best condition for both growth rate and quality is gained when the starting position of hot-zone coil is about 20 mm distance from growing position. For the best growth condition, the position of hot-zone is very sensitive factor and the further more the condition of speed of coil shift also must control.