• 한국세라믹학회지
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• 제39권4호
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• pp.420-426
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• 2002

가열가수분해반응에 의하여 제조된 구형의 $ZrO_2$ 겔을 수열결정화시켜 순수한 $ZrO_2$ 분말과 $Y2_O_3$, CaO 등 상안정화제가 도핑된 $ZrO_2$ 분말을 합성하였다. 합성된 $ZrO_2$ 결정분말들은 평균 10nm 크기의 일차 입자들로 구성된 이차입자들이었다. 이차입자의 평균 크기는 $0.4{\mu}m$였고, 수열결정화과정에서 겔의 구형 형상이 그대로 유지되었으며 일차 입자들 사이에는 약한 응집으로 존재하였다. 입자모양, 크기, 상분율, 도핑된 분율 등을 SEM, TEM, XRD, ICP로 연구하였고 구형 겔의 수열결정화기구를 논의하였다.

• 한국세라믹학회지
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• 제24권4호
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• pp.343-348
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• 1987

The effects of salts such as aluminum sulfate as inorganic salt(2-4%), and sodium salts of citrate, tartrate, succinate, potassium tartrate and gelatin as organic salts(0.1%) on the formation of ${\alpha}$-calcium sulfate hemihydrate from by-product gypsum of phosphoric acid process under hydrothermal condition at 123$^{\circ}C$ and 133$^{\circ}C$ were investigated. Aluminum sulfate solution exhibited the catalystic effected on the crystallization of ${\alpha}$-calcium sulfate hemihydrate of which was assumed in the prismatic form, and organic salts solution exhibited little effect on the catalystic action to the crystallization, than inorganic salts. In the acidic solution with sulfuric acid(pH=2), needle like crystal of calcium sulfate hemihydrate was obtained. Hydrothermal process with aluminum sulfate solution also showed certain amounts of impurity removal such as phosphorus penataoxide from calcium sulfate hemihydrate.

• 한국결정성장학회지
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• 제11권1호
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• pp.33-37
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• 2001

$213^{\circ}C$에서 깁사이트와 pseudoboehmite를 출발물질로 하여 산성도를 변화시켜 수열합성법에 의해서 카올리나이트를 합성하였다. 합성된 카올리나이트는 X-선회절 분석기와 적외선 분광광도계를 이용하여 결정화 과정을 조사하였으며 Hinckley 지수를 계산하였다. 산을 이용한 카올리나이트 합성은 출발물질의 용해를 촉진시켜 결정화하였다. 결정화 속도와 적층결함은 음이온의 종류, 산성도와 출발물질에 의존하였다.

• 한국세라믹학회지
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• 제50권6호
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• pp.434-438
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• 2013

Monodispersed 3Y-$ZrO_2$ spherical agglomerates were synthesized by thermal hydrolysis process followed by crystallization processes (hydrothermal treatment and calcination). The crystallization process affected the properties of the final particles, such as the primary particle size, the agglomeration state, and the fraction of $ZrO_2$ monoclinic phase. The hydrothermal treated spherical particles were porous microstructures (weak agglomerates) composed of small primary particles with a size of 14 nm, but the calcined spherical particles had a dense microstructure due to the hard aggregation between primary particles. While the calcined particles had a low green density due to the hard aggregation, hydrothermal treated ones were soft agglomerates and had a deflection point at 50 MPa due to the rearrangement of secondary spherical particles and the filling of the interstices with the primary particles. Finally, the green density of hydrothermally treated $ZrO_2$ particles was 58% at 200 MPa.

• 대한금속재료학회지
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• 제48권6호
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• pp.543-550
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• 2010

This paper investigated the synthesis conditions of nano-sized $TiO_2$ powder in a hydrothermal process at a temperature range of $100{\sim}180^{\circ}C$ considering the precipitation agent, precipitation pH, reaction temperature and time. Titanium hydroxide formed by $NH_4OH$ exhibited a lower crystallization temperature than that by NaOH and formed less aggregated $TiO_2$ particles. As the precipitation pH increased above 8, the shape of the particles changed from spherical to needle form, which appeared to be caused by dissolution and re-precipitation of the titanium hydroxide in an alkali environment.

• 공업화학
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• 제25권6호
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• pp.564-569
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• 2014

지르코니아 나노분말을 수열합성법으로 제조하였으며, 반응온도, 반응시간, 침전제의 종류 및 농도, 전구체의 종류를 실험 변수로 하였고, 각각의 제조된 분말을 X-선 회절(XRD)과 주사전자현미경(FE-SEM)을 통해 입자크기 및 결정상을 측정하였다. 침전제의 농도 증가에 따라 지르코니아 입자크기가 증가하였으며, 입자의 결정화도도 높아졌고, KOH 보다 NaOH 침전제를 사용하였을 경우, 입자 성장 속도가 증가하였다. 이는 입자의 크기 컨트롤에 있어 NaOH를 사용하는 경우보다 KOH를 사용하는 것이 더 효과적이었다. 4 h의 수열반응시간에서는 4 h의 수열반응시간에서는 비정질의 지르코니아 입자가 발견되었지만, 8 h 이상 합성 시, 단사정상의 지르코니아 입자가 생성됨을 확인하였고, 반응시간이 길어짐에 따라 지르코니아 입자의 폭이 소폭으로 줄어들고, 길이는 소폭 늘어남을 확인하였다. 동일한 합성 조건에서 전구체로서 zirconium (IV) acetate, zirconium nitrate, zirconium chloride 중에서 zirconium chloride를 사용하여 합성하였을 경우, 입자의 크기가 가장 작게 형성되었다.

• 한국재료학회지
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• 제34권2호
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• pp.79-84
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• 2024

Thin films of yttria-stabilized zirconia (YSZ) nanoparticles were prepared using a low-temperature deposition and crystallization process involving successive ionic layer adsorption and reaction (SILAR) or SILAR-Air spray Plus (SILAR-A+) methods, coupled with hydrothermal (175 ℃) and furnace (500 ℃) post-annealing. The annealed YSZ films resulted in crystalline products, and their phases of monoclinic, tetragonal, and cubic were categorized through X-ray diffraction analysis. The morphologies of the as-prepared films, fabricated by SILAR and SILAR-A+ processes, including hydrothermal dehydration and annealing, were characterized by the degree of surface cracking using scanning electron microscopy images. Additionally, the thicknesses of the YSZ thin films were compared by removing diffusion layers such as spectator anions and water accumulated during the air spray plus process. Crack-free YSZ thin films were successfully fabricated on glass substrates using the SILAR-A+ method, followed by hydrothermal and furnace annealing, making them suitable for application in solid oxide fuel cells.

• 대한화학회지
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• 제59권3호
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• pp.238-245
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• 2015

The crystallization and morphology change of amorphous titanias by hydrothermal treatment have been investigated. The amorphous titanias were prepared by pure water hydrolysis of two different precursors, titanium tetraisopropoxide (TTIP) and TTIP modified with acetic acid (HOAc) and characterized prior to hydrothermal treatment. In order to avoid complicate situation, the hydrothermal treatment was performed in a single solvent water with and without strong acids at various temperatures. The effects of strong acid, temperature and time were systematically investigated on the transformation of amorphous titania to crystalline TiO₂ under simple hydrothermal condition. Without strong acid the titanias were transformed into only anatase phase nanoparticle regardless of precursor type, temperature and time herein used (up to 250 ℃ and 48 hours). The treatment temperature and time effected only on the crystalline size, not on the crystal phase et al. However, it was clearly revealed that the strong acids such as HNO₃ and HCl catalyzed the formation of rutile phase depending on temperature. HCl was slightly better than HNO₃ in this catalytic activity. The morphology of rutile TiO₂ formed was also a little affected by the type of acid. The precursor modifier, HOAc slightly reduced the catalytic activity of the strong acids in rutile phase formation.

• 한국세라믹학회지
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• 제31권2호
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• pp.117-128
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• 1994

Hematite particles were obtained by hydrothermal reaction of ferric hydroxide in the presence of small amount of citric acid which is acted as crystal growth controller. The effects of hydrothermal reaction condition son the morphology and crystal structure of powder were investigated using X-ray, TEM and FT-IR. Ellipsoidal or rectangular hematite particles were formed in the range of pH 10.75~11.75 as initial basicity of reactants and 3$\times$10-5 ~9$\times$10-5 mol as citric acid content. Crystallization of hematite was inhibited in the range of pH9. 0~10.5 and above citric acid content of $1.5\times$10-4 mol. Hematite particle length and aspect ratio were decreased gradually with increasing of citric acid content. Hematite particles formed at 14$0^{\circ}C$ exhibited particle properties with the length of 0.7 ${\mu}{\textrm}{m}$ and aspect ratio of 8. Hematite particles having a good acicular-type were not obtained above 22$0^{\circ}C$.

• 한국세라믹학회지
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• 제28권1호
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• pp.74-78
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• 1991

Willemite powders which have been prepared by solid state reaction were easy to intermixed impurities, and particle surfaces were demaged in the progress of crushing. The above defacts were easy to accompany non-crystallization for mechanochemical effects and luminescence efficiency was deteriorated. The goal of this study improve each of defacts, and synthesize high purity and fine Mn doped willemite powders by wet and hydrothermal methods without crushing progress. It has been experimentally verified that the single phase Zn1.98Mn0.02SiO4 willemite powders which prepared by hydrothermal synthes is at 220$^{\circ}C$ for 10 hours in 2N KOH solution. The products are like needle and composition is the same with starting composition.