Process development for porous Si-based ceramics by a decarburization method

박이현,Tatsuya Hinoki,Akira Kohyama 한양대학교 세라믹연구소 2009 Journal of Ceramic Processing Research Vol.10 No.3

Recently, there has been an increasing interest in the applications of porous SiC ceramics as functional materials. A number of manufacturing approaches have been applied to fabricate porous SiC including polymer pyrolysis, oxidation bonding, and reaction bonding. However, these processes are complicated and conventional porous SiC shows insufficient physical and chemical stability under a high temperature environment. Therefore, from the view point of safety and stability, it is necessary to develop an uncomplicated manufacturing method for high performance porous SiC ceramics. In this study, SiC nano-powder and carbon particles have been used as starting material and pore former, respectively. Mixed powders were hot-pressed under a pressure of 20 MPa at 1900℃ for 1 h. Carbon powder which was added to the sintered body was burned out by a decarburization process in air at 700℃. The porosity was measured by the Archimedes method with an immersion medium of water and an image analysis method. The microstructure was examined by scanning electron microscopy. Mechanical properties were investigated using three-point bend test. It was established that the critical additive amount of carbon particles for porous SiC ceramics was about 20 vol.%, through the microstructure and thermogravimetric analysis during the decarburization process. The porosity of the porous SiC ceramics could be controlled with a high degree of accuracy, from the relationship between the added amount of carbon particles and porosity. The flexural strength of the porous SiC ceramics with 50% pores, where spherical pores were introduced, was about 170MPa. These porous SiC ceramics exhibited a substantially high strength in comparison with other conventionally processed porous SiC ceramics, due to their robust microstructures consisting of spherical pores.

The effect of ceramic fiber on the rheological and mechanical properties of porous Al2O3 ceramics

Kamrun Nahar Fatema,Hyung Mi Lim,Joung Sook Hong,Kee Sung Lee,Ik Jin Kim 한양대학교 청정에너지연구소 2023 Journal of Ceramic Processing Research Vol.24 No.1

Porous ceramics having oriented pores find widespread use in filtration, insulation, biomaterials, and catalysis. Because of theshape of the interconnected pores, porous alumina (Al2O3) ceramics synthesized via direct foaming have poor mechanicalstrength. The physical and mechanical characteristics of porous Al2O3 ceramics were systematically explored in this work bymodulating the microstructure and rheological properties by the inclusion of ceramic fibers. Because of the incorporation ofceramic fibers, the fiber-containing wall structure is generated in porous ceramics. The physical properties and mechanicalstrength of porous ceramics increase as the fiber content increases. To stabilize the wet foam and enhance the mechanicalproperties of the porous ceramics, ceramic fibers are added to the Al2O3 colloidal suspension. With 2.0 wt.% ceramic fibers,wet foam stability of 84% was obtained. Adequate addition of 2.0 wt.% ceramic fibers in the slurry may improve compressivestrength, however excess fibers reduce compressive strength. The load-bearing capacity and elastic modulus of sinteredsamples were determined using the Hertzian indentation method. The load-bearing capacity and elastic modulus increasedfrom 65.35 to 235.45 N and 28.52 to 270.75 MPa, respectively, as the ceramic fiber content increased from 0.5 to 3.0 wt.%.

카본블랙을 첨가하여 제조한 다공성 BaTiO₃계 세라믹스의 미세구조 및 PTCR 특성 변화

이기주,당동욱,조원승,Lee, Ki-Ju,Tang, Dongxu,Cho, Won-Seung 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.1

As a pore precursor, carbon black with different content of 0 to 60 vol% were added to (Ba,Sr)$TiO_3$ powder. Porous (Ba,Sr)$TiO_3$ ceramics were prepared by pressureless sintering at $1350^{\circ}C$ for 1h under air. Effects of carbon black content on the microstructure and PTCR characteristics of porous (Ba,Sr)$TiO_3$ ceramics were investigated. The porosity of porous (Ba,Sr)$TiO_3$ ceramics increased from 6.97% to 18.22% and the grain size slightly decreased from $7.51\;{\mu}m$ to $5.96\;{\mu}m$ with increasing carbon black contents. PTCR jump of the (Ba,Sr)$TiO_3$ ceramics prepared by adding carbon black was more than $10^5$, and slightly increased with increasing carbon black. The PTCR jump in the (Ba,Sr)$TiO_3$ ceramics prepared by adding 40 vol% carbon black showed an excellent value of $9.68{\times}10^5$, which was above two times higher than that in (Ba,Sr)$TiO_3$ ceramics. These results correspond with Heywang model for the explanation of PTCR effect in (Ba,Sr)$TiO_3$ ceramics. It was considered that carbon black is an effective additive for preparing porous $BaTiO_3$ based ceramics. It is believed that newly prepared (Ba,Sr)$TiO_3$ cermics can be used for PTC thermistor.

컬럼반응조 내 충진된 다공성 zeolite-slag 세라믹에 의한 산성광산배수의 처리특성

임수빈 ( Soo-bin Yim ) 한국수처리학회(구 한국수처리기술연구회) 2018 한국수처리학회지 Vol.26 No.5

The objective of this research is to investigate the removal characteristics of heavy metals and sulfate ion from acid mine drainage (AMD) in a column reactor system by spherical-type porous zeolite-slag ceramics (ZS ceramics). The hydraulic retention time (HRT) condition of 24 hours in the column reactor system was found to more efficiently treat the AMD than that of 12 hours. The increment of mixing amount of converter slag in porous ZS ceramics from 1:1(Z:S) to 1:3(Z:S) was observed to enhance the removal efficiency of Cu, Cd, Mn, and Zn by 13.4%, 32.6%, 22.0%, and 48.2%, respectively. In addition, the 1:3(Z:S) porous ZS ceramics increased the alkali-supply capacity and average cycling period of back-washing relative to 1:1(Z:S) porous ZS ceramics. The average removal efficiencies of heavy metals and sulfate ion from AMD by the 1:3(Z:S) porous ZS ceramics in the column reactor under the HRT condition of 24 hours were Al 97.2%, As 98.3%, Cd 89.9%, Cu 95.5%, Fe 99.5%, Mn 76.0%, Pb 97.5%, Zn 73.2%, and SO4 2- 75.9% during 71 days of operation time. The experimental results exhibited that the porous ZS ceramics in the column reactor system could function as an efficient media for the long-term treatment of heavy metals and sulfate ion from AMD.

Wet Foam Stability from Colloidal Suspension to Porous Ceramics: A Review

Kim, Ik Jin,Park, Jung Gyu,Han, Young Han,Kim, Suk Young,Shackelford, James F. The Korean Ceramic Society 2019 한국세라믹학회지 Vol.56 No.3

Porous ceramics are promising materials for a number of functional and structural applications that include thermal insulation, filters, bio-scaffolds for tissue engineering, and preforms for composite fabrication. These applications take advantage of the special characteristics of porous ceramics, such as low thermal mass, low thermal conductivity, high surface area, controlled permeability, and low density. In this review, we emphasize the direct foaming method, a simple and versatile approach that allows the fabrication of porous ceramics with tailored microstructure, along with distinctive properties. The wet foam stability is achieved under the controlled addition of amphiphiles to the colloidal suspension, which induce in situ hydrophobization, allowing the wet foam to resist coarsening and Ostwald ripening upon drying and sintering. Different components, like contact angle, adsorption free energy, air content, bubble size, and Laplace pressure, play vital roles in the stabilization of the particle stabilized wet foam to the porous ceramics. The mechanical behavior of the load-displacements curves of sintered samples was investigated using Herzian indentations testes. From the collected results, we found that microporous structures with pore sizes from 30 ㎛ to 570 ㎛ and the porosity within the range from 70% to 85%.

Mechanical properties of carbon fiber-reinforced Al2O3 porous ceramics

Byun Young Min,Lee Gye Won,Lee Kee Sung,Park Jung Gyu,김익진 한국세라믹학회 2021 한국세라믹학회지 Vol.58 No.3

This study reports the improvement of the mechanical properties of Al 2 O 3 porous ceramics from particle-stabilized colloidal suspension with the addition of carbon fiber through direct foaming. The initial colloidal suspension of Al 2 O 3 was partially hydrophobized by a surfactant, propyl gallate (2 wt%), to stabilize the wet foam used with the addition of carbon fiber from 2 to 8 wt% as reinforcement. The influence of carbon fiber on the air content, bubble size, pore size, and pore distribution were discussed in terms of the wet foam stability and the physical properties of the porous ceramics. The mechanical properties of the sintered porous samples were investigated by the Hertzian indentation test. The results show that the wet foam stability of more than 90% corresponds to the compressive load bearing capacity of 110 N using tungsten carbide ball with a radius of r = 7.93 mm and the elastic modulus of 114.3 MPa in the sintered sample with 2 wt% of carbon content. This study reports the improvement of the mechanical properties of Al 2 O 3 porous ceramics from particle-stabilized colloidal suspension with the addition of carbon fiber through direct foaming. The initial colloidal suspension of Al 2 O 3 was partially hydrophobized by a surfactant, propyl gallate (2 wt%), to stabilize the wet foam used with the addition of carbon fi ber from 2 to 8 wt% as reinforcement. The influence of carbon fiber on the air content, bubble size, pore size, and pore distribution were discussed in terms of the wet foam stability and the physical properties of the porous ceramics. The mechanical properties of the sintered porous samples were investigated by the Hertzian indentation test. The results show that the wet foam stability of more than 90% corresponds to the compressive load bearing capacity of 110 N using tungsten carbide ball with a radius of r = 7.93 mm and the elastic modulus of 114.3 MPa in the sintered sample with 2 wt% of carbon content.

Enhancement of Porosity and Strength of Porous Al₂O₃ Ceramics by Al(H₂PO₄)₃ Addition

Bai, Jiahai,Piao, Jiasi,Gao, Jie,He, Jing,Du, Qingyang,Li, Chengfeng The Korean Ceramic Society 2019 한국세라믹학회지 Vol.56 No.4

Porous alumina ceramics with addition of 0, 5, 10, 15, and 20 wt% Al(H₂PO₄)₃ were sintered at 1300, 1350, and 1400℃. The effects of the Al(H₂PO₄)₃ addition on crystal phases, water absorption, open porosity, pore size distribution, microstructures, and flexural strength were studied extensively. The experimental results revealed that only characteristic peaks of corundum were indexed in the XRD patterns of the as-prepared porous ceramics. The water absorption and open porosity of the porous Al₂O₃ ceramics increased remarkably with an increase in Al(H₂PO₄)₃ addition. The flexural strength first increased to a maximum value when 5 wt% Al(H₂PO₄)₃ was added and then decreased as additional Al(H₂PO₄)₃ was further added. SEM images showed that the average Al₂O₃ grain size in the porous ceramics changed in an opposite way as the flexural strength. The porous Al₂O₃ ceramics with 10 wt% Al(H₂PO₄)₃ addition exhibited comparable flexural strength to the ceramics without Al(H₂PO₄)₃ addition, although the latter had much higher porosity.

직접 발포법을 이용해 제조된 실리카 흄-SiO₂계 다공성 세라믹의 열적 특성

하태완,강승구,김강덕,Ha, Taewan,Kang, Seunggu,Kim, Kangduk 한국결정성장학회 2021 한국결정성장학회지 Vol.31 No.4

무기질 단열재 개발을 위해 포말법을 이용하여 다공성 세라믹스를 제조하였다. 실리카 흄과 SiO₂를 주 원료로 사용하였으며, 다공성 세라믹의 균일한 기공 형성을 위한 첨가제로 벤토나이트를 사용하였다. 다공성 세라믹은 1200℃에서 소결하였으며, 기공율, 밀도, 압축강도, 미세구조 그리고 열전도도 분석을 수행하였다. 다공성 세라믹은 SiO₂에 대한 실리카흄의 함량이 70~90 % 증가할수록 비중이 0.63에서 0.69로 증가하였으며, 압축강도는 9.41 Mpa에서 12.86 Mpa로 증가하였다. 그러나, 기공율은 비중과 반대로 72.07 %에서 70.82 %로 감소하는 경향을 나타내었다. 열전도도 측정 결과, 실리카 흄의 함량이 70 %인 F7S3 다공성 세라믹의 경우 25~800℃ 온도조건에서 0.75~0.72 W/m·K의 열전도도를 나타내었으며, 실리카 흄의 함량이 90 %인 F9S1 다공성 세라믹의 경우 0.66~0.86 W/m·K를 나타내어 실리카 흄 함량이 적을수록 낮은 열전도도를 나타내었다. 이는 기공율 결과와 일치한 것을 확인하였다. SEM(Scanning Electron Microscope)을 이용한 미세구조 분석 결과, 다공성 세라믹 내/외부에 전체적으로 수십~수백 ㎛ 범위 기공이 관찰되었으며 기공 분포가 비교적 균일한 것을 확인할 수 있었다. Porous ceramics were manufactured using the foaming method for the development of inorganic insulating materials. Silica fume and SiO₂ were used as main raw materials, and bentonite was used as a rapid setting agent for uniform structure formation of porous ceramics. The porous ceramics were sintered at 1200℃, and porosity, density, compressive strength, microstructure and thermal conductivity were analyzed. As the content of silica fume to SiO₂ of the porous ceramics increased 70 to 90 %, the specific gravity increased from 0.63 to 0.69, and the compressive strength increased from 9.41 Mpa to 12.86 Mpa. But, the porosity showed a tendency to decrease from 72.07 % to 70.82 %, contrary to the specific gravity. As a result of measuring the thermal conductivity, the porous ceramic with a silica fume content of 70 % showed a thermal conductivity of 0.75 to 0.72 W/m·K at 25 to 800℃, respectively, and, another that a silica fume content of 90 % showed a 0.66~0.86 W/m·K. So the lower the silica f ume content, the lower the thermal conductivity, which was conf irmed to be consistent with porosity result. As a result of microstructure analysis using SEM (Scanning Electron Microscope), pores in the range of tens to hundreds ㎛ were observed inside and outside the porous ceramic, and it was confirmed that the pore distribution was relatively uniform.

중공형 미세구를 이용한 마이크로셀룰라 지르코니아의 기공 특성 고찰

이은정,송인혁,김해두,김영욱,배지수 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.1

In this study, a novel-processing route for producing microcellular zirconia ceramics has been developed. The proposed strategy for making the microcellular zirconia ceramics involves hollow microsphere as a pore former which has extremely low density of 0.025 g/㎤. Effects of hollow microsphere content and sintering temperature on microstructure, porosity, pore distribution, and compressive strength were investigated in the processing of microcellular zirconia ceramics. By controlling the content of hollow microsphere, it was possible to make the porous zirconia ceramics with porosities ranging from 45% to 75%. Typical compressive strength value of microcellular zirconia ceramics with ~65% porosity was over 50MPa. By adjusting the mixing ratio of large and small zirconia powders, it was possible to control the pore structure from close to open pores. In this study, a novel-processing route for producing microcellular zirconia ceramics has been developed. The proposed strategy for making the microcellular zirconia ceramics involves hollow microsphere as a pore former which has extremely low density of 0.025 g/㎤. Effects of hollow microsphere content and sintering temperature on microstructure, porosity, pore distribution, and compressive strength were investigated in the processing of microcellular zirconia ceramics. By controlling the content of hollow microsphere, it was possible to make the porous zirconia ceramics with porosities ranging from 45% to 75%. Typical compressive strength value of microcellular zirconia ceramics with ~65% porosity was over 50MPa. By adjusting the mixing ratio of large and small zirconia powders, it was possible to control the pore structure from close to open pores.

컬럼반응조 내 충진된 다공성 zeolite-slag 세라믹에 의한 산성광산배수의 처리기작에 대한 미세분석 연구

임수빈 한국수처리학회 2018 한국수처리학회지 Vol.26 No.6

This research was conducted to elucidate the removal mechanism of heavy metals and sulfate ion from acid mine drainage(AMD) by porous zeolite-slag ceramics (ZS ceramics) packed in a column reactor system. The average removal efficiencies of heavy metals and sulfate ion from AMD by the 1:3(Z:S) porous ZS ceramics in the column reactor under the HRT condition of 24 hours were Al 97.5%, As 98.8%, Cd 86.1%, Cu 96.2%, Fe 99.7%, Mn 64.1%, Pb 97.2%, Zn 66.7%, and SO42- 76.0% during 121 days of operation time. The XRD analysis showed that the ferric iron from AMD could be removed by adsorption and/or ion-exchange on the porous ZS ceramics. In addition it was known that Al, As, Cu, Mn, and Zn could adsorb or coprecipitate on the surface of Fe precipitates such as schwertmannite, ferrihydrite, or goethite. The EDS analysis revealed that Al, Fe, and Mn, which were of relatively high concentration in the AMD, would be adsorbed and/or ion-exchanged on the porous ZS ceramics and also exhibited that Al, Cu, Fe, Mn, and Zn could be precipitated as the form of metal hydroxide or sulfate and adsorbed or coprecipitated on the surface of Fe precipitates. The microscopic results on the porous ZS ceramics and precipitated sludge in a column reactor system suggested that the heavy metals and sulfate ion from AMD would be eliminated by the multiple mechanisms of coprecipitation, adsorption, ion-exchange as well as precipitation.