• 한국입자에어로졸학회지
• /
• 제7권3호
• /
• pp.79-85
• /
• 2011

Porous $TiO_2-SiO_2$ particles were synthesized by co-assembly of nanoparticles of $TiO_2$ and $SiO_2$ in evaporating aerosol droplets. Poly styrene latex (PSL) particles were employed as a template of porous particles. Flowrate of dispersion gas, weight ratio of $TiO_2/SiO_2$ and $SiO_2$ concentration in the precursor, and PSL size were chosen as process variables. The morphology, crystal structure, chemical bonding, and pore size distribution were analyzed by FE-SEM, XRD, FT-IR, BET. The morphology of porous $TiO_2-SiO_2$ particles was spherical and the average particle size range were from 1 to $10{\mu}m$. The particles were composed of meso and macro pores. The average particle diameter and pore volume of the as prepared particles were dependant on process variables. It was found that UV-Vis absorption of the porous particles was comparable with pure $TiO_2$ nanoparticles even though $TiO_2/SiO_2$ ratio is low in the porous particles.

• Composites Research
• /
• 제20권5호
• /
• pp.20-25
• /
• 2007

열주기법은 다공성 소재의 열확산도를 측정하는데 유용한 방법이다. 본 논문의 주 목적은 진공환경에서 다공성 소재의 열확산도 측정 시스템을 개발하고 검증하는데 있다. 이 방법을 검증하기 위하여 알루미나 시편과 폴리스티렌 폼의 열확산도를 측정하였다. 이 시편들의 열확산도는 참고값과 일치하였다. 탄소/에폭시 소재와 다공성 단열소재의 열확산도를 대기상온과 대기진공 환경에서 측정하였다. 탄소/에폭시 소재와 다공성 단열소재의 진공환경에서 열확산도는 대기환경에 비하여 각각 66.4%와 64.9% 감소하였다. 이 차이는 소재내의 기공에 있는 공기의 영향으로 추정된다.

• 한국재료학회지
• /
• 제16권8호
• /
• pp.503-510
• /
• 2006

The measurement of specific gases is based on the reversible conductivity change of sensing materials in semiconductor type gas sensors. For an application as gas sensors of high sensitivity, porous $SnO_2$ films have been fabricated by anodizing of pure Sn foil in oxalic acid and characteristics of anodic tin oxide films have been investigated. Pore diameter and distribution were dependent on process conditions such as electrolyte concentration, applied voltage, anodizing temperature, and time. Characteristics of anodic films were explained with current density-time curves.

• 한국재료학회지
• /
• 제17권9호
• /
• pp.500-506
• /
• 2007

The effects of anisotropic surface energy on the microstructure development of porous materials have been studied through Monte Carlo simulation using a three dimensional lattice. The changes in porosity ($f_v$), mean grain diameter ($D_s$), fraction of connected pores ($f_{v,c}$) and contiguity of the solid phase (C) were examined in cases with three different ${\gamma}_{SV}$ relations and initial grain diameters ($D_{s,o}$). It has been found that larger ${\gamma}_{SV}$ enhances sintering of particles and increases C and does not change $D_s$. And Introducing anisotropic ${\gamma}_{SV}$ brought an increase in $f_v$ and $f_{v,c}$ and an decrease in $D_s$ and C, and this tendency become more marked for fine $D_{s,o}$.

• 한국세라믹학회지
• /
• 제46권3호
• /
• pp.275-281
• /
• 2009

Porous materials were manufactured by hydrothermal treatment of waste bottle glass without foam agent. Factorial design was applied to analyze data by statistical methods and deal with the important factors for a process. The largest effect for porosity was for temperature of hydrothermal treatment. Amount of water and temperature-water interaction appeared to have little effect. The particle size of raw material was also identified as a major factor by one-way ANOVA and the porosity decreased as the size increased. The sintering temperature was not statistically significant for the porosity but was significant for the pore size. The porous material had compressive strength and thermal conductivity comparing with those of ALC (autoclaved lightweight concrete), although it has higher porosity than for ALC.

• 한국재료학회지
• /
• 제26권6호
• /
• pp.320-324
• /
• 2016

Porous SiC beads were prepared by freeze-drying a polycarbosilane (PCS) emulsion. The water-in-oil (w/o) emulsion, which was composed of water, PCS dissolved p-xylene, and sodium xylenesulfonate (SXS) as an emulsifier, was frozen by dropping it onto a liquid $N_2$ bath; this process resulted in 1~2 mm sized beads. Beads were cured at $200^{\circ}C$ for 1 h in air and heat-treated at $800^{\circ}C$ and $1400^{\circ}C$ for 1 h in an Ar gas flow. Two types of pores, lamella-shaped and spherical pores, were observed. Lamellar-shaped pores were found to develop during the freezing of the xylene solvent. Water droplets in the w/o emulsion were changed into spherical pores under freeze-drying. At $1400^{\circ}C$ of heat-treatment, porous SiC was synthesized with a low level of impurities.

• 한국정밀공학회지
• /
• 제16권7호
• /
• pp.158-167
• /
• 1999

Heat and moisture transfer associated with porous materials are investigated. The heat and moisture transfer in porous materials caused by the interaction of moisture gradient, temperature gradient, conduction, and evaporation are considered. The variations of temperature and moisture not only change the volume but also induce the hygro-thermal stress. The finite element formulation for solving the temperature and moisture transfer as well as the associated hygro-thermal stresses is developed. In order to verify the finite element formulation, the heat and moisture moving boundary problem in a half space and the hygro-thermo-mechanical problem in an infinite plate with a circular hole are analyzed. Temperature profile, moisture profile, and hygro-thermal stresses are compared with those of analytic solution and other investigator. Good agreements are examined

• 한국주조공학회지
• /
• 제25권2호
• /
• pp.80-87
• /
• 2005

The microstructure and mechanical property of the Ni and Ni-Cr porous metal reinforced AC4C matrix composites fabricated by squeeze casting were investigated. In this study Ni, Ni-Cr porous metals which are estimated to be easy to fabricate by squeeze casting are used as strengtheners for composite materials. As a matrix material, Al-7wt.%Si-0.3wt.%Mg(AC4C) has been used. In case of Ni/AC4C and Ni-Cr/AC4C composite, $750^{\circ}C$ melt temperature and minimum 25MPa squeezing pressure are needed to produce sound composite materials. The observation of interfacial reaction zone at various heat treatment condition shows that atsolutionizing temperature of above $520^{\circ}C$, the interfacial reaction zone increases proportionally with heat treatment time and the reaction products formed by interfacial reactions are mainly composed by $Al_{3}Ni$ and $Al_{3}Ni_{2}$ phases.

• Carbon letters
• /
• 제8권1호
• /
• pp.17-24
• /
• 2007

Microporous carbons with narrow pore size distribution have been successfully synthesized by using hydrolyzed and calcined silica as templates and phenol formaldehyde (pf) resin as carbon precursor. Phenol formaldehyde-silica micro composites were prepared by solution route. Subsesequently, silica templates were removed by HF leaching. Resulting carbons were steam activated. The porous carbons were characterized by nitrogen adsorption-desorption isotherm, SEM, FTIR analysis, iodine adsorption, thermogravimetry analysis, etc. Adsorption isotherms show that the porous carbon prepared from calcined silica as templates are microporous with 88% pores of size <2 nm porosity and are of type I isotherm, while porous carbon prepared by using hydrolyzed silica are microporous with 89% microporosity, shows hysteresis loop at high relative pressure indicating the presence of some mesoporosity in samples. The microporosity in porous carbon materials has a bearing on the nature of silica templates used for pore formation.

• 한국분말야금학회:학술대회논문집
• /
• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
• /
• pp.475-476
• /
• 2006

Using microwave synthesized HAp nano powder and polymethyl methacrylate (PMMA) as a pore-forming agent, the porous biphasic calcium phosphate (BCP) ceramics were fabricated depending on the sintering temperature. The synthesized HAp powders was about 70-90 nm in diameter. In the porous sintered bodies, the pores having $150-180\;{\mu}m$ were homogeneously dispersed in the BCP matrix. Some amounts of pores interconnected due the necking of PMMA powders which will increase the osteoconductivity and ingrowth of bone-tissues while using as a bone substrate. As the sintering temperature increased, the relative density increased and showed the maximum value of 79.6%. From the SBF experiment, the maximum resorption of $Ca^{2+}$ ion was observed in the sample sintered at $1000^{\circ}C$.