• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.25 no.11
• /
• pp.886-894
• /
• 2012

In order to develop electrical insulation materials, epoxy-nanosilica-microsilica mixture composites (ENMC) was synthesized, and mechanical properties such as their tensile and flexural strength, and AC insulation breakdown strength were investigated. Properties of mechanical strength and AC insulation breakdown strength are analyzed as scale and shape parameter with respect to weibull plot. Their tensile and flexural strength, AC insulation breakdown strength were compared original epoxy or EMC to ENMC. The 4 phr nano-silica addition and the 65 wt% micron-silica mixture composite (ENMC) was found to have the highest tensile and flexural strength. In the tensile strength was improved 29%, and flexural strength was improved 60.9% higher than those of the original epoxy. In the insulation breakdown strength, ENMC_4 phr was improved 17% and ENMC_5 phr was improved 15.8% higher than those of the EMC.

• Geomechanics and Engineering
• /
• v.12 no.1
• /
• pp.127-138
• /
• 2017

A series of high-pressure isotropic compression tests were performed on four types of poorly graded silica sand that were artificially prepared based on representative grading curves and similar mineralogy composition of seabed sediment containing different fines contents existing in the Nankai Trough. The addition of fines steepens the initial compression path and increases the decrement of the void ratio after loading. The transitional behaviour of the poorly graded sand with a larger amount of fines content was identified. The slope of the normal compression line shows a slight decreasing tendency with the level of fines content. The bulk modulus of silica sand with fines was lower when compared with the published results of silica sand without fines. A small amount of particle crushing of the four types of poorly graded sand with variable fines content levels was noticed, and the results indicated that the degree of particle crushing tended to decrease as the fines content increased.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.1
• /
• pp.48-54
• /
• 2000

Influence of seed addition on the mullite synthesis was investigated from mixture powders of kaolin and aluminium trihydroxide which contain various $Al_2O_3$/SiO_2$ ratio (silica rich, stoichiometric, alumina rich). The flexural strength increases with the increase of the mullite-seed content in case of silica rich and stoichiometric mullite, but flexural strength decreases with the increase of the mullite-seed content in case of alumina rich mullite. Microstructural investigation revealed that aspect ratio of mullite grains increased with higher alumina content, along with lower sintered density. Mullite contents of specimens are increased with seed content regardless of $Al_2O_3$/SiO_2$ ratio of the mixture composition.

• Elastomers and Composites
• /
• v.37 no.1
• /
• pp.14-20
• /
• 2002

Silica-filled rubber compound needs longer mixing time compared to carbon black-filled one since it has poor dispersion or the filler. Influence of the mixing procedure on the properties of natural rubber compound filled with both silica and carbon black was studied. The discharge temperature of the master batch (MB) mixing was $150^{\circ}C$. The mixing time was longer when silica and carbon black were loaded separately than when loaded simultaneously. The mixing time was longer when silica was loaded first than when carbon black is loaded first. The compounds prepared by one MB step (conventional mixing) were compared with the compounds prepared by two MB steps (two-step mixing). Scorch times of the two-step mixing compounds were longer than those by the conventional mixing ones. Bound rubber contents of the formers were lower than those of the tatters. The two-step mixing vulcanizates had longer elongation at break, higher tensile strength, and better fatigue life.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.7
• /
• pp.2369-2377
• /
• 2012

The gas-phase dehydration of glycerol to acrolein was carried out over silicotungstic acid ($H_4SiW_{12}O_{40}{\cdot}xH_2O$, HSiW) catalysts supported on $SiO_2$, ${\eta}-Al_2O_3$, and silica-aluminas with different Al contents. The HSiW catalysts supported on silica-aluminas showed higher glycerol conversions and acrolein yields during the initial 2 h at $315^{\circ}C$ than did $SiO_2$- and ${\eta}-Al_2O_3$-supported HSiW catalysts. Among the tested catalysts, HSiW/$Si_{0.9}Al_{0.1}O_x$ exhibited the highest space-time yield during the initial 2 h. The loaded HSiW species can change the acid types and suppress the formation of carbonaceous species on Al-rich silica-aluminas. The deactivated HSiW supported on silica-aluminas can be fully regenerated after calcination in air at $500^{\circ}C$. As long as the molar ratio between water and glycerol was in the range of 2-11, the acrolein selectivity increased significantly with increasing water content in the feed, while the surface carbon content decreased owing to the suppression of heavy compounds.

• Elastomers and Composites
• /
• v.41 no.3
• /
• pp.164-171
• /
• 2006

Stress softening behaviors of SBR vulcanizates reinforced with silica or carbon black were studied. Two types of SBR with different 1,2-unit contents of 18 and 60 wt% were used and three filler systems of carbon black and silica with/without silane coupling agent were employed. Stress softening behaviors of the SBR vulcanizates were varied with the SBR types as well as the filler systems. The silica-filled rubber specimens had higher residual strains than the carbon black-filled ones. The residual strains of silica-filled vulcanizates were remarkably reduced by adding a silane coupling agent. The maximum loads at 50% maximum stretch of the carbon black-filled vulcanizates were lower than those of the silica-filled ones. On the contrary, the maximum loads at 200% maximum stretch of the carbon black-filled vulcanizates were higher than those of the silica-filled ones. The maximum loads of the specimens with the 1,2-unit content of 60 wt% are higher than those with the 1,2-unit content of 18 wt% irrespective of the filler systems.

• New Physics: Sae Mulli
• /
• v.68 no.11
• /
• pp.1203-1207
• /
• 2018

In this study, silica nanowires were formed using silicon oxide films with different oxygen contents, and their microstructure and physical properties were compared with those of silica nanowires formed using Si wafers. The silicon oxide films were fabricated by using a plasma-enhanced chemical vapor deposition method. Silica nanowires were formed by thermally annealing silicon oxide films coated with nickel films as a catalyst. In the case of silicon oxide films having an oxygen content of approximately 50 at.% or less, the formation mechanism, microstructure, and physical properties of the nanowires were not substantially different from those of the silicon wafer. In particular, the uniformity of the thickness showed better behavior in the silicon oxide films. These results imply that silicon oxide films can be used as an alternative for fabricating high-quality silica nanowires at low cost.

• Composites Research
• /
• v.29 no.5
• /
• pp.306-314
• /
• 2016

In this study, to improve the thermal stabilities of the epoxy composite specimens in addition to the enhanced mechanical properties, those were reinforced with carbon nanotubes and micrometer-sized silica particles. To disperse the filler in matrix relatively simple physical process, specimens were fabricated using shear mixing and sonication. Tensile strength, coefficients of thermal expansion and thermal conductivity of the specimens were measured with varied contents of the two fillers. The mechanical and thermal properties were also discussed, and the experimental results of thermal expansion related to the thermal stability of the specimens were compared with those from several micromechanics models. The hybrid composites specimens incorporating 0.6 wt％ of carbon nanotubes and 50 wt％ of silica particles showed better mechanical properties than the others with increase in tensile strength up to 11％, with respect to those of the baseline specimens. As the silica contents were increased the thermal expansion was reduced down to 36%, and the thermal stability was improved with the decreased thermal deformation. Thermal conductivity of the epoxy composite specimens incorporating 50 wt％ of silica particles was enhanced, which demonstrate improvement of 72%. The mechanical and thermal properties of the hybrid composites specimens incorporating the two fillers were improved simultaneously.

• Journal of the Microelectronics and Packaging Society
• /
• v.18 no.4
• /
• pp.39-42
• /
• 2011

The composite electroplating is accomplished by adding inert materials during the electroplating. Permalloy is the term for Ni-Fe alloy and it is used for industrial applications due to its high magnetic permeability, surface wear resistance, corrosion protection. Microhardness for microdevices is enhanced after composite coating and it increases the life cycle. However, the hydroxyl group on the silica makes their surface susceptible to moisture and it causes the silica nanoparticles to be agglomerated in the aqueous solution. The agglomeration problem causes poor dispersion which eventually interrupts uniform deposition of silica nanoparticles. In this study, the dispersion of silica nanoparticles in the permalloy electroplated layer is reported with variation of additives and current densities. The optimum current density was 20 $mA/cm^2$ and the silica content was 9 at% at $50^{\circ}C$. The amount of silica nanopowder codeposition and surface morphologies were influenced with variation of additives. In the bath, smooth surface morphology and relatively high contents of silica nanopowder codeposition were obtained with addition of sodium lauryl sulfate.

• Journal of the Korea Concrete Institute
• /
• v.20 no.3
• /
• pp.307-315
• /
• 2008

In this study, it is investigated the properties of high strength concrete using mineral admixture, on the purpose of use of meta kaolin for the substitutive materials to silica fume which is so expensive. The plain mixtures are 3 degrees which are ordinary portland cement, blast furnace slag cement and OPC included fly ash 20%, and silica fume and meta kaolin are substituted for the each plain mixtures in the range of 20%. The results of experiment showed as follows. In case of silica fume was only used, the viscosity and slump flow of fresh concrete were much decreased, on the contrary air content increased. But as usage of meta kaolin increased, to being increase the viscosity of fresh concrete, slump flow increased and air content and usage of super-plasticizer were decreased. Accordingly the workabilities of concrete were against tendency between silica fume and meta kaolin. The compressive strength, velocity of ultrasonic pulse and unit weight were increased according to usage of meta kaolin, the properties of hardened concrete were judged that they are affected with air content of fresh concrete, so it is very important to control air content of high strength concrete. Therefore, the use of meta kaolin is prospected to the substitutive material of silica fume, in case of using silica fume and meta kaolin, it is judged that the optimum usage of silica fume and meta kaolin is about 10% respectively, considering workability and strength of concrete.