2021, Vol.31, No.6

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

In this study, Ga2O3/diamond layers were grown on Si substrates to improve the thermal characteristics of Ga2O3 materials. Firstly, diamond thin film was grown on Si substrates by hot-filament chemical vapor deposition. Afterward, Ga2O3 layer was grown in the growth temperature range of from 450~600°C by mist chemical vapor deposition. We found that layer separation happens at the Ga2O3/diamond interface at the growth temperature of 500°C. This is attributed to the different thermal expansion coefficient of the mixture of amorphous and crystalline structures during cooling process. Therefore, this study might contribute to the heat-sink-layer bonded power semiconductor applications by stabilizing thethermal properties at Ga2O3/diamond interface.

In the ceramic industry, a drastic decrease in crystalline formation was found even among the glazes well known for their high crystalline productivity when the ceramic glaze was stored in wet conditions over a period. This study aimedto investigate the reason for decreasing willemite crystals during storage. As the starting materials ZnO, calcined ZnO and frit 3110 are selected; the composition for zinc crystalline glazes was set through a three-component system with thematerials. The firing condition was used from previous studies. The study was observed how wet conditions affected the crystallization of zinc crystalline glazes from a day to 24 weeks. The results were obtained by particle size analysis, XRD,Raman spectroscopy and SEM analysis. The results indicated that ZnO is advantageous in terms of willemite crystalline development and growth; however, Zn(OH)2 cluster, formed by the reaction with water during the storage, caused the decrease in ZnO level in the glaze. The reduction of ZnO in the glaze eventually interfered the willemite development and growth.

This study was started to investigate why autoclave curing (AC) specimen showed an improvement in compressive strength after immersion in water for a long time, although AC specimen did not showed a high initial compressive strengthunlike our expectations. Distilled water and alkaline solutions were used for immersion and three different curing methods were engaged. It was expected that the compressive strength would be improved after immersion in alkaline solutions;however, there was little difference in compressive strength after 21 day immersion because both new crystallites produced by additional geopolymerization and expansion caused by the alkaline aggregate reaction may prevent the additionalimprovement in compressive strength. It was concluded that in order to secure the long-term commonality and underwater stability of the geopolymers, it is desirable aging geopolymers while immersing it underwater for more than 21 days after curing using an autoclave.