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지르코니아 분말의 치밀화와 소결거동 : I. 가압에 따른 치밀화 응답
박홍채,Frank L. Riley 한국세라믹학회 1992 한국세라믹학회지 Vol.29 No.6
The continuous compaction response of zirconia powders prepared by different processing treatments was investigated. Though the yield point could be or not below 1 MPa, the change of slope was always observed at high pressure range around 60 MPa. Powder compaction was mainly governed by second compaction stage and compaction rate was decreased with increasing forming pressure. Rotary vacuum dried powder favored a high compaction density, whereas freeze dried and calcined powders favored an increase in the pressing efficiency. In order to extract more reliable information about powder compaction, it was necessary to use not only compaction response diagram but also compaction rate diagram.
복합 황산염 수화물의 열분해에 의한 Mg-Al 스피넬의 생성반응
박홍채,오기동 한국세라믹학회 1986 한국세라믹학회지 Vol.23 No.6
The forming reaction processes of magnesium aluminate spinel by a thermal decomposition of sulfate hydrate were studied with DTA, TG. SEM and X-ray powder diffraction methods. The hydrous salt composed of the mixture of the two compounds of $MgSO_4$ $6H_2O$ and ${AL_2}({SO_4})_17H_2O_3$ in which both sulfates were crystalline. On heating the hydrous slat the crystalline magnesium and aluminum sulfate anhydride to amorphous alumina magnesium sulfate anhydride decomposed to amorphous magnesia and these amorphous oxides reacted completely each other to form a spinel at $1000^{\circ}C$ The apparent activation energy of forming reaction of spinel was 36.5 kcal/mole($900^{\circ}C$~$1000^{\circ}C$) The crystallite size of spinel obtained at $1000^{\circ}C$ after 1 h was 380$\AA$.
박홍채,이윤복,이철규,오기동 ( Hong Chae Park,Yoon Bok Lee,Cheol Gyu Lee,Ki Dong Oh ) 한국공업화학회 1994 공업화학 Vol.5 No.6
Ar 또는 Ar/H₂, 가스유통(100∼500㎖/min)하에서 ZrSiO₄/C계 및 ZrSiO₄/Al/C계로부터 ZrC/SiC 복합분체의 합성을 1600℃ 온도범위 내에서 시도하고, 이의 생성기구, 생성속도 및 분체특성을 검토하였다. ZrSiO₄/C계에서는 1400℃ 이상에서 ZrO₂(s)와 SiO(g)가 각각 탄소와 경쟁반응하여 ZrC 및 SiC를 생성하였다. ZrC생성을 위한 겉보기활성화에너지는 약 18.5㎉/㏖(1400-1600℃)이었다. 한편 ZrSiO₄/Al/C계에서는 1200℃ 이상에서 ZrO(g)가 Al(l, g) 및 탄소와 반응하여 ZrC를 생성하였으며, 1300℃ 이상에서는 SiO(g)가 Al(l,g) 및 탄소와 환원-탄화반응하여 SiC를 생성하였다. 1600℃, 5시간 반응으로 얻은 생성물은 평균입경 21.8㎛을 갖는 분말로서 ZrC의 격자정수는 4.679Å, 결정자크기는 640Å이었으며 SiC의 격자정수는 4.135Å, 결정자크기는 540Å 정도이었다. The preparation of ZrC/SiC mixed powders from ZrSiO₄/C and ZrSiO₄/Al/C systems was attempted in the temperature range below 1600℃ under Ar or Ar/H₂ gas flow(100-500㎖/min). The formation mechanism and kinetics of ZrC/SiC were suggested and the resultant powders were characterized. In ZrSiO₄/C system, ZrC and SiC were formed by competitive reaction of ZrO₂(s) and SiO(g) with carbon at temperature higher than 1400℃. The apparent activation energy for the formation of ZrC was approximately 18.5㎉/㏖(1400-1600℃). In ZrSiO₄/Al/C system, ZrC was formed by reaction of ZrO(g) with Al(l, g) and carbon at temperature higher than 1200℃, and SiC was formed by reduction-carbonization of SiO(g) with Al(l, g) and carbon at temperature higher than 1300℃. The products obtained at 1600℃ for 5h consisted of ZrC with lattice constant of 4.679Å and crystallite size of 640Å, and SiC with lattice constant of 4.135Å and crystallite size of 500Å. And also, the mean particle size was about 21.8㎛.
박홍채,오기동 한국세라믹학회 1987 한국세라믹학회지 Vol.24 No.5
Kinetic studies were made on the thermal decomposition of hydrated magnesium aluminum double sulfate by a nonisothermal TG method. Thermal analyses of the dehydration of tricosahydrate showed that the reaction proceeded via decahydrate to the anhydrous MgAl2(SO4)4 in the range 50$^{\circ}$to 400$^{\circ}C$. Decomposition of MgAl2(SO4)4 occurred as the two-step between 650$^{\circ}$ and 970$^{\circ}C$. Dehydration of MgAl2(SO4)4$.$23H2O and a 2D diffusion controlled with an activation energy of 16.6kcal/mole, respectively. MgAl2(SO4)4 fitted the contracting volume model with an activation energy of 10.5kcal/mole, and MgSO4 fitted a contracting area model with an activation of 4.5kcal/mole.
지르코니아 분말의 치밀화와 소결거동 : II. 소결거동
박홍채,김겸,김영우,이윤복,오기동,Park, H.C.,Kim, K.,Kim, Y.W.,Lee, Y.B.,Oh, K.D.,Riley, Frank L. 한국세라믹학회 1993 한국세라믹학회지 Vol.30 No.6
Sintering behaviour of zirconia powders prepared by different processing treatment was discussed. About >99% densities of theoretical were obtaiend on sintering at 140$0^{\circ}C$ for 2h in case of 300MPa uniaxially cold-pressed compact. But the lower densities were obtained on sintering above this temperature due to abnormal grain growth enabling the tetragonal to monoclinic phase transformation during cooling resulted in microcracks. All kinds of different dried powders exhibited nearly the same shrinkage behaviour with end-point shrinkage between 19 and 20%, and had maximum shrinkage rate (0.99~1.27%/min) around 120$0^{\circ}C$. During whole sintering process densification was mainly governed by grain growth and rearrangement of agglomerates. Heterogeneous abnormal grain growth and abrupt decrease in shrinkage were observed when continuous interagglomerate pore collapsed into isolated pores.
균일침전법에 의한 수화 염기성 알루미늄염의 합성 및 열분해
박홍채,김주석,이승호,오기동 한국세라믹학회 1989 한국세라믹학회지 Vol.26 No.1
High purity(99.99%) spherical particles of hydrated Basic Aluminum Salts(BAS) were prepared by a homogeneous precipitation process utilizing the urea decomposition reaction and characterized by XRD, SEM, TG-DTA, IR and PSA methods. Amorphous hydrated BAS was precipitated in the range of pH 4~6. The molar ratio [Al3+]/[SO42-] for the precipitate particles was about 3.7. With increasing the concentration of aluminum sulfate the precipitation of the hydrated BAS occurred slowly and the precipitate particles with a narrow size distribution were fine(1-2${\mu}{\textrm}{m}$ in diameter). At temperatures in the range 400$^{\circ}$to 95$0^{\circ}C$, desulfurization and dehydroxylization resulted in weight loss with 22%. When the precipitate particles were thermally treated, the crystlline ${\gamma}$-Al2O3 was identifited by XRD at 50$0^{\circ}C$ and ${\gamma}$-Al2O3 particles were transformed into $\alpha$-Al2O3 at 100$0^{\circ}C$. A vermicular network was produced by calcining at 125$0^{\circ}C$ for 30min.