2022, Vol.32, No.3

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

To improve the crystallinity of GaN, there are researches on surface treatment to control the difference inphysical properties between GaN and heterogeneous substrate. ‘Low-temperature GaN (LT-GaN)’ is one of the ways tosolve the problem and we investigated the relationship between growth temperature and properties of LT-GaN in ourhomemade vertical type HVPE. The LT-GaN nuclei were formed on the sapphire surface at low growth temperatures andthey presented differences in the density and crystallinity depending on the growth temperature. Significantly, the stressrelaxation effect on the epitaxial GaN (epi-GaN) was affected by the crystallinity of LT-GaN. However, the highcrystallinity of LT-GaN exacerbated the crystal quality of epi-GaN because they worked as a catalyst and seed ofpolycrystalline.

In this study, glassy carbon coating was performed on the graphite using a phenolic resin and a curing agent was mixed with ethylene glycol as an additive to form the uniform surface. The phenolic resin was dried and cured under the environments of hot air, then converted into a glassy carbon layer by pyrolysis at 500~1,500°C. FTIR, XRD, SEM analysis, and density/porosity/contact angle measurement were performed for characterization of glassy carbon. The pyrolysis temperature for high-quality glassy carbon was optimized to be about 1,000°C. As the content of the additiveincreased, the effect of reducing surface defects on the coated surface, reduction of porosity, increase of contact angle, andincrease of density were investigated in this study. The method of forming a glassy carbon coating layer through an additive is expected to be applicable to graphite coating and other fields.

Hydroxyapatite (HAp) was synthesized from calcium hydroxide (Ca(OH)2) reacting with phosphoric acid (H3PO4) in aqueous solution. HAp powders were synthesized from extremely high concentration of precursor solutions over 3 M of Ca(OH)2 aqueous suspension using modified process parameters such as phosphoric acid (H3PO4) pouring rate, aging time and post ball milling process. Regardless of phosphoric acid pouring rate, the DCPD (dicalcium phosphate dihydrate) was formed at room temperature and when heated above 700°C, β-TCP (tricalcium phosphate) was synthesized and the amount reached its maximum at 900°C. When the synthesized powder was sintered at 1150°C, β-TCP, a high temperature impurity phase, remained. The single HAp phase without DCPD was obtained from post ball-milled precipitates followed by 3 day aging. For the ball-milled precipitates even without the aging process, the desired single HAp phase without β-TCP could be obtained by heat treatment above 500°C. The post ball milling process provided a convenient route for HAp synthesis.