• 한국세라믹학회지
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• 제40권1호
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• pp.18-23
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• 2003

정량의 B$_2$O$_3$/A1/C의 혼합분말을 화학노 대신 고압의 알곤 분위기를 사용하여 SHS 공정으로 B$_4$C-A1$_2$O$_3$ 복합분말을 제조하였다. 2B$_2$O$_3$+4A1+C=B$_4$C-2A1$_2$O$_3$의 반응식에 해당하는 B$_2$O$_3$(-100 메쉬), Al(-200 메쉬), C(-200 메쉬)의 분말을 2시간 건식 볼밀로 혼합한 후, 고온 고압의 SHS 반응기에 넣고 약 10기압의 알곤 분위기에서 점화하여 SHS을 일으켰다. 반응 생성물은 XRD 분석으로 안과 겉이 균일하게 반응이 일어났으며 반응 생성물로 화학노 사용시 동반되는 부산물 AlB$_{12}$C$_2$가 없는 B$_4$C-A1$_2$O$_3$ 복합 분말을 얻었다. 이 복합 분말은 SEM으로 보면 약 0.3~l $mu extrm{m}$ 크기의 결정이 모인 약 60~100$\mu\textrm{m}$ 크기이었다. 그러나 약 15기압을 사용하였을 때는 부분 소결이 일어나 15~25$\mu\textrm{m}$ B$_4$C 분말에 0.1~0.2$\mu\textrm{m}$의 알루미나가 분산되어 있는 고강도의 복합 분말이 생성되었다.

• 한국분말재료학회지
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• 제12권6호
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• pp.422-427
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• 2005

The $Al_2O_3$ with various phases were prepared by simple ex-situ hydrolysis and spark plasma sintering (SPS) process of Al powder. The nano bayerite $(\beta-Al(OH)_3)$ phase was derived by hydrolysis of commercial powder of Al with micrometer size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both nano bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate dense powder compacts with a rapid heating rate of $100^{\circ}C$ per min. under the pressure of 50MPa. After compaction treatment in the temperature ranges from $100^{\circ}C\;to\; 1100^{\circ}C$, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows phase transition of $Al(OH)_3{\to}{\eta}-Al_2O_3{\to}{\theta}-Al_2O_3{\to}\alpha-Al_2O_3$ sequences. On the other hand, the bohemite experiences the phase transition from AlO(OH) to ${\gamma}-Al_2O_3\;at\;350^{\circ}C.$ It shows AlO(OH) ${\gamma}-Al_2O_3{\to}{\delta}-Al_2O_3{\to}{\alpha}-Al_2O_3$ sequences. The ${\gamma}-Al_2O_3$ compacted at $550^{\circ}C$ shows a high surface area $(138m^2/g)$.

• 한국세라믹학회지
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• 제27권3호
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• pp.361-368
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• 1990

The properties of the powder of ZrO2＋3m/o Y2O3 system prepared by co-precipitation method at the pH values of 7, 9, 10 and 11 were investigated. ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Zirconium hydroxide near by Zr(OH)4 structure showed more excellent crystallinity and lower formation temperature of tetragonal ZrO2. In the range of this study, cubic ZrO2 was not formed and stability of tetragonal ZrO2 prepared in the conditiion of pH 7 was most excellent. Average particle sizes and specific surface areas of tetragonal ZrO2 powders, prepared as calcining amorphous zirconium hydroxides at $600^{\circ}C$ for 1h, were 0.6-0.8${\mu}{\textrm}{m}$ and 45-70$m^2$/g, respectively.

• 한국분말재료학회지
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• 제8권3호
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• pp.157-162
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• 2001

An optimum route to fabricate the ferrous alloy dispersed $Al_2O_3$ nanocomposites such as $Al_2O_3$/Fe-Ni and $Al_2O_3$/Fe-Co with sound microstructure and desired properties was investigated. The composites were fabricated by the sintering of powder mixtures of $Al_2O_3$ and nano-sized ferrous alloy, in which the alloy was prepared by solution-chemistry routes using metal nitrates powders and a subsequent hydorgen reduction process. Microstructural observation of reduced powder mixture revealed that the Fe-Ni or Fe-Co alloy particles of about 20 nm in size homogeneously surrounded $Al_2O_3$, forming nanocomposite powder. The sintered $Al_2O_3$/Fe-Ni composite showed the formation of Fe$Al_2O_4$ phase, while the reaction phases were not observed in $Al_2O_3$/Fe-Co composite. Hot-pressed $Al_2O_3$/Fe-Ni composite showed improved mechanical properties and magnetic response. The properties are discussed in terms of microstructural characteristics such as the distribution and size of alloy particles.

• 한국분말재료학회지
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• 제11권1호
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• pp.28-33
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• 2004

In the present study, the focus is on the analysis of carbothermal reduction of the titanium-cobalt-oxygen based oxide powder by solid carbon for the optimizing synthesis process of ultra fined TiC/Co composite powder. The titanium-cobalt-oxygen based oxide powder was prepared by the combination of the spray drying and desalting processes using the titanium dioxide powder and cobalt nitrate as the raw materials. The titanium-cobalt-oxygen based oxide powder was mixed with carbon black, and then this mixture was carbothermally reduced under a flowing argon atmosphere. The changes in the phase structure and thermal gravity of the mixture during carbothermal reduction were analysed using XRD and TGA. The synthesized titanium-cobalt-oxygen based oxide powder has a mixture of $TiO_2$ and $CoTiO_3$. This oxide powder was transformed to a mixed state of titanium car-bide and cobalt by solid carbon through four steps of carbothermal reduction steps with increasing temperature; reduction of $CoTiO_3$ to $TiO_2$ and Co, reduction of $TiO_2$, to the magneli phase($Ti_nO_{2n-1}$, n>3), reduction of the mag-neli phase($Ti_nO_{2n-1}$, n>3) to the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases, and reduction and carburization of the $Ti_nO_{2n-1}$(2$\leq$n$\leq$3) phases to titanium carbide.

• 한국재료학회지
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• 제25권5호
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• pp.215-220
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• 2015

The effect of Al content on the processing of reaction-bonded $Al_2O_3$ (RBAO) ceramics using 40v/o ~ 80v/o Al-Zn-Mg alloy powder was studied in order to improve traditional RBAO ceramic processes that use ~ 40v/o pure Al powder. The influence of high Al content in starting $Al_2O_3$-Al alloy powder mixtures on its particulate characteristics, reaction-bonding, microstructure, physical and mechanical properties was revealed. Starting $Al_2O_3$-Al alloy powder mixtures with 40v/o ~ 80v/o Al alloy powder were milled, reaction-bonded, post-sintered, and characterized. With an increasing Al alloy content, the milling efficiency of Al alloy powder was lowered, resulting in a larger particle size after milling. However, in spite of the larger particle size of Al alloy powder, the oxidation, i.e., reaction-bonding, of the Al alloy was successfully completed via solid and liquid state oxidation, in which the activation energy of the oxidation was nearly the same regardless of Al alloy content. After reaction-bonding and post-sintering at $1600^{\circ}C$, RBAO ceramics from 80v/o Al alloy content showed a relative density of ~97% and a flexural strength of 251 MPa compared to ~ 96% and 353 MPa for RBAO ceramics from 40v/o Al alloy content, respectively. The lower flexural strength at 80v/o Al alloy content was due to the weak spinel phase that formed from Zn, Mg alloying elements in Al.

• 한국세라믹학회지
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• 제29권2호
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• pp.136-142
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• 1992

The effects of cyclic stress, frequency and bias-pressure on densification of Al2O3 powder cyclic compaction are investigated. The effect of frequency was not significant on densification of Al2O3 powder under cyclic compaction. The higher the cyclic stress and the lower the bias pressure, the higher densification was achieved. To obtain a higher densification, cyclic compaction was more efficient than 1 stroke compaction. A densification equation was proposed to describe an cyclic time dependent pressure-volume relation for Al2O3 powder under cyclic compaction. This equation was obtained empirically, based on the pressure-volume equation proposed by Cooper and Eaton, the time dependent densification equation by Kim and Suh and experimental data for Al2O3 powder under cyclic compaction. The agreement between the proposed equation and experimental data for Al2O3 powder under cyclic compaction was very good.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.557-560
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• 2003

The submicron $YBa_2Cu_3O_x$ powder was prepared by the sol-gel method. The particle size is distributed from 0.2 to $1.0\;{\mu}m$, which benefits to eliminate the micro-cracks formed in the $YBa_2Cu_3O_x$ films deposited by electrophoresis. The powder was single phase of $YBa_2Cu_3O_x$ examined by X-ray diffraction. In the sol-gel process the citrate gel was formed from citric acid and nitrate solution of $Y_2O_3$, $Ba(NO_3)O_2$ and CuO. When pH values were adjusted to $6.4{\sim}6.7,\;Ba(NO_3)O_2$ could be dissolved in the citrate solution completely. Appropriate evaporative temperature of the sol-gel formation is discussed. After the heat treatment the transition temperature($T_c$) and critical current density($J_c$) of the $YBa_2Cu_3O_x$ samples made of the submicron powder were measured.

• 한국지하수토양환경학회지:지하수토양환경
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• 제21권2호
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• pp.8-14
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• 2016

We compared the plausible reaction mechanism and quantitative efficiency of highly self-organized TiO₂ nanotube (ntTiO₂) film with TiO₂ powder. Film was fabricated by electrochemical potentiostatic anodization of titanium thin film in an ethylene-glycol electrolyte solution containing 0.3 wt% NH₄F and 2 vol% deionized water. Nanotubes with a pore size of 80-100 nm were formed by anodization at 60 V for 3 h. Humic acid (HA) was degraded through photocatalytic degradation using the ntTiO₂ film. Pseudo first-order rate constants for 0.3 g of ntTiO₂, 0.3 g TiO₂ powder, and 1 g TiO₂ powder were 0.081 min⁻¹, 0.003 min⁻¹, and 0.044 min⁻¹, respectively. HA adsorption on the ntTiO₂ film was minimal while adsorption on the TiO₂ powder was about 20% based on thermogravimetric analysis. Approximately five-fold more normalized OH radicals were generated by the ntTiO₂ film than the TiO₂ powder. These quantitative findings explain why ntTiO₂ film showed superior photocatalytic performance to TiO₂ powder.

• 한국세라믹학회지
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• 제36권7호
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• pp.691-697
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• 1999

TiO2 powder was adsorbed on the surface of mica using the heterocoagulation method in water TiO2 powder was prepared from hydrolysis of titanium-iso propoxide in a mixed solvent of anhydrous ethanol and water. When the molar ratio of water to titanium iso-propoxide was 0.25 monodispersed spherical TiO2 particles were obtained. The prepared TiO2 powder showed anatase phase after heat treatment at 50$0^{\circ}C$ for 2 h and then transformed to rutile phase after heat treatment at 100$0^{\circ}C$ for 2h. The iso-electric points of TiO2 and Mica were pH 3.9 and pH 3.25 respectively which were measured by the Z-potential analysis in water base. The maximum Z-potential difference between two powders was observed in the range of pH 3.6~3.7 TiO2 powder was adsorbed on the surface of mica by heterocoagulation method in pH 3.6~3,7 The properties of prepared TiO2 powder was haracterized by TG-DTA, XRD and SEM The morphology and thermal properties of TiO2-adsorbed mica were examined.