• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.2
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• pp.51-55
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• 2015

The present research is focused on the effect of porous graphite what is influenced on the 4H-SiC crystal growth by PVT method. We expect that it produces more C-rich and a change of temperature gradient for polytype stability of 4H-SiC crystal as adding the porous graphite in the growth cell. The SiC seeds and high purity SiC source materials were placed on opposite side in a sealed graphite crucible which was surrounded by graphite insulator. The growth temperature was around $2100{\sim}2300^{\circ}C$ and the growth pressure was 10~30 Torr of an argon pressure with 5~15 % nitrogen. 2 inch $4^{\circ}$ off-axis 4H-SiC with C-face (000-1) was used as a seed material. The porous graphite plate was inserted on SiC powder source to produce a more C-rich for polytype stability of 4H-SiC crystal and uniform radial temperature gradient. While in case of the conventional crucible, various polytypes such as 6H-, 15R-SiC were observed on SiC wafers, only 4H-SiC polytype was observed on SiC wafers prepared in porous graphite inserted crucible. The defect level such as MP and EP density of SiC crystal grown in the conventional crucible was observed to be higher than that of porous graphite inserted crucible. The better crystal quality of SiC grown using porous graphite plate was also confirmed by rocking curve measurement and Raman spectra analysis.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.363-370
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• 2016

Lightweight geopolymers are more readily produced and give higher fire resistant performance than foam cement concrete. Lowering the density of solid geopolymers can be achieved by inducing chemical reactions that entrain gases to foam the geopolymer structure. This paper reports on the effects of adding different concentrations of aluminum powder on the properties of cellular structured geopolymers. The apparent density of lightweight geopolymers has a range from 0.7 to $1.2g/m^3$ with 0.025, 0.05 and 0.10 wt% of a foaming agent concentration, which corresponds to about 37~60 % of the apparent density, $1.96g/cm^3$, of solid geopolymers. The compressive strength of cellular structured geopolymers decreased to 6~18 % of the compressive strength, 45 MPa of solid geopolymers. The microstructure of geopolymers gel was equivalent for both solid and cellular structured geopolymers. The workability of geopolymers with polyprophylene fibers needs to be improved as in fiber-reinforced cement concrete. The lightweight geopolymers could be used as indoor wall tile or board due to fire resistance and incombustibility of geopolymers.

• Journal of the Korean Institute of Gas
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• v.23 no.5
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• pp.24-34
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• 2019

In this study, the experimental studies were conducted to analyzing characteristics of combustion and flame stabilizing according to with and without water tube in boiler. The burner has consisted of SiC foam where has the location of submerged flame between a ceramic board acting as flash-back arrestor. Porous burner is also insulated to minimize heat loss in the radial direction. In the condition of fixed equivalence ratio, the flame mode was divided into three stability zones by the flow rate. The main factor for blow-off and flash-back depends on mixture flow rate. Consequently, the case of burner with water-tube has higher NOx emissions than without case. This result explains that the presence of water-tube makes the heat loss resistant to ambient temperature with increasing of NOx. This tendency was proved by predicting the relationship between O₂ emission and NO production rate, and by analysing temperature profiles.

• Resources Recycling
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• v.17 no.4
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• pp.30-36
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• 2008

The preparation of porous lightweight materials as well as the measurement of physical properties has been performed by using SSA(sewage sludge ash) as the raw material. For this aim, two types of lightweight filler, that is, perlite and silica sphere were employed respectively and bentonite was also used as an inorganic binder. The properties of lightweight specimen calcined at 1,000 were measured in terms of density, compressive strength, thermal conductivity and sound absorption to examine the effect of material composition as well as the preparation condition on the properties of lightweight material. As a result, the density of specimen prepared with perlite was ranged from 1.23 to $1.37g/cm^3$ and the compressive strength was ranged from 242.3 to $370.5kg/cm^2$. In case of specimen prepared with silica sphere, it was found that the compressive strength was less than $100kg/cm^2$ even though density was lower than that of specimen with perlite. As far as the thermal conductivity of specimen was concerned, it was ranged from 0.3 to $0.5W/m^{\circ}K$ depending on material composition so that the insulation effect was superior to conventional concrete.

• Korean Journal of Environment and Ecology
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• v.29 no.6
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• pp.936-946
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• 2015

This study is aimed to analyze the reduction performance of building energy consumption according to planting base types of panel-type green walls which can be applied to existing buildings. The performance was compared to the general performance of green walls that have demonstrated effects of improving the thermal environment and reducing building energy consumption in urban areas. The number of planting base types was 4 in total, and simulations were conducted to analyze the thermal conductivity, thermal transmittance, and overall building energy consumption rate of each planting base type. The highest thermal conductivity by the planting base type was Case C (0.053W/mK), followed by Case B (0.1W/mK) and Case D (0.17W/mK). According to the results of energy simulation, the most significant reduction of cooling peak load per unit area was Case C (1.19%), followed by Case B (1.14%) and Case D (1.01%) when compared to Case A to which green wall was not applied; and the most significant reduction of heating peak load per unit area was estimated to be Case C (2.38%), followed by Case B (1.82%) and case D (1.50%) when compared to Case A. The amount of yearly cooling and heating energy use per unit area showed 3.04~3.22% of reduction rate. The amount of the 1st energy use showed 5,844 kWh/yr of decrease on average for other types when compared to Case A. The amount of yearly $CO_2$ emission showed 996kg of decrease on average when compared to Case A to which the green wall was not applied. According to the results of energy performance evaluation by planting location, the most efficient energy performance was eastward followed by westward, southward and northward. According to the results of energy performance evaluation by planting location by green wall ratio, it was found that as the ratio of green wall increased, the energy performance displayed better results, showing approx. double reduction rate in energy consumption at 100% of green wall ratio than the reduction rate at 20% to 80% of green wall ratio.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.4
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• pp.345-352
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• 2017

In this study, the effect of cryogenic liquefied natural gas leakage and loading on liquefied natural gas cargo hold is investigated to observe the performance of the polymer foam material that comprises the cryogenic insulation of the cargo hold. The primary barriers of liquefied natural gas carrier that are in contact with the liquefied natural gas will leak if damage is accumulated, owing to fluid impact loads or liquefied natural gas loading / unloading over a long period. The leakage of the cryogenic fluid affects the interior of the polymer foam, which is a porous closed cell structure, and causes a change in behavior with respect to the working load. In this study, mechanical properties of polyisocyanurate foam specimen, which is a polymer material used as insulation, are evaluated. The performance of the specimens, owing to the cold brittleness and the impregnation effects of the cryogenic fluids, are quantitatively compared and analyzed.

• Clean Technology
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• v.28 no.4
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• pp.301-308
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• 2022

Since nanoporous silica aerogel was first synthesized in 1931, its potential as an ultra-lightweight superinsulation material has been steadily attracting attention. Silica aerogel is the best thermal insulation material to date. However, the potential applications of this lightweight material have so far been hindered by its inherent fragibility and brittleness arising from its ultra-porous nature. Although the monolithic form of silica aerogel has the best ultra-lightweight superinsulation properties, it cannot be used in this form. Instead it is used in the form of powders, particles, and blankets. However, these forms still have shortcomings. Silica aerogel is most widely applied in the form of a fiber-reinforced aerogel blanket, but this form is likely to generate dust when handled. Although silica aerogel particles have been proven to be non-toxic to humans, dust formation remains a major barrier to the widespread application of silica aerogel blankets. This paper will investigate the unique properties of silica aerogel and determine what fields it can be used in or potentially be used in due to its unique properties. In addition, we will review the important advances in silica aerogel synthesis technology and its commercialization so far, and then consider the problems that exist for its widespread commercialization in the future and how to overcome them.