Silica is used in shell materials to minimize oxidation and aggregation of nanoparticles. Particularly, porous silica has gained attention because of its performance in adsorption, catalysis, and medical applications. In this study, to investigate the effect of the density of the silica coating layer on the color of the pigment, we arbitrarily change the structure of a silica layer using an etchant. We use NaOH or NH4OH to etch the silica coating layer. First, we synthesize α-FeOOH for a length of 400 nm and coat it with TEOS to fabricate particles with a 50 nm coating layer. The coating thickness is then adjusted to 30–40 nm by etching the silica layer for 5 h. Four different shapes of α-FeOOH with different colors are measured using UV–vis light. From the color changes of the four different shapes of α-FeOOH features during coating or etching, the L* value is observed to increase and brighten the overall color, and the b* value increases to impart a clear yellow color to the pigment. The brightest yellow color was that coated with silica; if the sample is etched with NaOH or NH4OH, the b* value can be controlled to study the yellow colors.

Abstract
 1. 서 론
 2. 실험 방법
  2.1. α-FeOOH 합성(400 nm)
  2.2. α-FeOOH@SiO2 코팅
  2.3. α-FeOOH@SiO2 에칭
 3. 실험 결과
 4. 결 론
 References

• 이나리(한국세라믹기술원 도자세라믹센터) | NaRi Lee (Ceramic Ware Center, Korea Institute of Ceramic Engineering and Technology)
• 유 리(한국세라믹기술원 엔지니어링세라믹센터) | Ri Yu (Engineering Ceramic Center, Korea Institute of Ceramic Engineering and Technology)
• 김유진(한국세라믹기술원 엔지니어링세라믹센터) | YooJin Kim (Engineering Ceramic Center, Korea Institute of Ceramic Engineering and Technology) Corresponding Author