• Applied Biological Chemistry
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• v.40 no.6
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• pp.531-535
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• 1997

An efficient process for recovery of calcium from the eggshell was developed and some organic acids were used in an attempt to enhance the degree of calcium ionization. Eggshell membrane was readily separated from crushed eggshell based on the differences in specific gravities. The conditions which allowed most efficient membrane removal were found to be 30 rpm of speed, 30 min of residence time and 0.08 of volume fraction. It took 3 hours for the eggshell powder prepared at $1000^{\circ}C$ to reach L value of 90 with the Hausner ratio being 1.43. The calcium ion concentrations were 990, 3500, 3900 and 4200 ppm in pure water, acetic acid, citric acid and lactic acid$(0.05{\sim}3%)$ aqueous solution, respectively. The degrees of ionization of calcium-citrate-malate complex(CCM), calcium-citric acid complex(CC) and calcium malic acid complex(CM) increased by 4 to 5 times compared to eggshell calcium powder.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.560-566
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• 2007

AlN plates were fabricated by hot pressing at $1700-1900^{\circ}C$ using yttria and alumina (3 and $10\;{\mu}m$ particle size) powders as additives and characterized: density, thermal conductivity, transverse rupture strength, and grain size measurement by SEM and EDS. Density values of $3.31-3.34\;g/cm^3$ are largely attributed to hot pressing of powder mixtures in carbon mold under $N_2$ atmosphere which caused effective degree of oxygen removal from yttrium-aluminate phase expected to form at $1100^{\circ}C$. The grain size of hot pressed AlN was almost homogeneous, with size approximately from 3.2 to $4.0\;{\mu}m$ after hot pressing. $Al_2O_3$ powder of $3\;{\mu}m$ particle size resulted in better transverse rupture strength and finer grain size compared to $10\;{\mu}m$ $Al_2O_3$ powder. The thermal conductivity of AlN ranged between $83-92.7\;W/m{\cdot}K$ and decreased with $Al_2O_3$ addition. Fine grain size is preferred for better mechanical properties and thermal conductivity.

• Journal of Energy Engineering
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• v.11 no.2
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• pp.114-121
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• 2002

Alkali metal compounds existed in original coal or sorbents are exhausted as vapor or small particle at the outlet of combustor when operating PFBC power plant. These compounds can be removed with dust removal equipment, but total generation efficiency will be decreased because of lower operating temperature of dust removal equipment. Alkali metal contained in vapor phase is initially deposited onto turbine blade results in serious corrosion. The concentration of alkali vapor in the PFBC flue gas is 20∼40 ppm which is dependent on mineral characteristics and composition as well as operating condition of PFBC. However, the allowance limit of alkali metal vapor is assigned as less than 50 ppb for gas turbine when coal or oil is used as fuel. Therefore, alkali metal vapor in PFBC or IGCC process should be removed by solid sorbents to prevent corrosion of turbine blade and improve plant efficiency. In the present investigation, powder of Bauxite, Kaolinite and Limestone is used in the preparation of cylinder-type pellet which is inserted into the pressurized alkali removal reactor for the alkali absorption experiment. Experimental results showed that the alkali removal efficiency in the order of Bauxite, Kaolinite and Limestone. Alkali vapor removal efficiency is related with reaction temperature, porosity of pellet and alkali vapor concentration of flue gas.

• Korean Chemical Engineering Research
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• v.43 no.6
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• pp.751-755
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• 2005

Carbon dioxide, included in the flue gas from the combustion of fossil fuel, was known as a representative green house gas and various removal and utilization technologies of it has been studied for the prevention of global warming. This study was performed as an effort to find out a method to reuse carbon dioxide separated from flue gas by magnetite powder. Magnetite powder was synthesized using various oxidizers and alkalinity controlled aqueous solutions of $FeSO_4{\cdot}7H_2O$ and NaOH at 50, 80, 90, $100^{\circ}C$ and analyzed by XRD and SEM. The analysis results showed that magnetite powder synthesized at higher alkalinity and temperature had crystalline spinel and cubic structure. The reduction by hydrogen and the oxidation by carbon dioxide of synthesized powder were studied by TGA. The results showed that magnetite powder synthesized at low alkalinity and temperature was non-cubical amorphous but crystalline and cubical at high alkalinity and temperature. Comparing magnetite powders synthesized using oxidants(air and oxygen) and nitrogen, magnetite powder using more oxygen containing oxidant synthesized more crystalline magnetite powder. The experimental results of redox reaction of the synthesized magnetite powder showed that the reduction by hydrogen and the oxidation by carbon dioxide were seldom observed below $400^{\circ}C$ and observed well at $500^{\circ}C$. Magnetite powder synthesized at $100^{\circ}C$ and alkalinity(molal concentration ratio of $FeSO_4{\cdot}7H_2O$ to NaOH) of 2.0 using $O_2$ showed the highest reduction of 27.15 wt％ and oxidation of 26.73 wt％, especially at reaction temperature of $500^{\circ}C$.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.36 no.4 s.107
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• pp.60-66
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• 2004

In this paper, oyster shell, diatomaceous earth, and active carbon were used as filter media for treating wastewater produced in paper mills. After filtering, the changes of COD and turbidity were investigated. As the results of estimating the efficiency of wasterwater treatment, porous oyster shell having higher specific surface area in powder was more effective than the others in removal of contaminants in waterwater, especially turbidity.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.1
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• pp.61-70
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• 2004

Generally, ceramics are very difficult-to-cut materials because of its high strength and hardness. The machining process of ceramics can be characterized by cracking and brittle fracture. In the machining of ceramics, edge chipping and crack propagation are the principal reasons to cause surface integrity deterioration. Such phenomenon can cause not only poor dimensional and geometric accuracy, but also possible failure of the ceramic parts. Ceramics can be machined with traditional method such as grinding and polishing. However, such processes are generally cost-expensive and have low material removal rate. Thus, in this paper, to overcome these problems. BN powder, which gives good cutting property, is added for the fabrication of machinable ceramics by volume of 5,10,15,20,25 and 30%. And, mechanical properties, R-curve behavior and machining tests are carried out to evaluate the machining properties of the manufactured machinable ceramics.

• Carbon letters
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• v.12 no.2
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• pp.85-89
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• 2011

Coloured wastewater is released as a direct result of the production of dyes as well as from various other chemical industries. Many dyes and their breakdown products may be toxic for living organisms. Activated carbon is one of the best materials for removal of dyes from aqueous solutions. The present study describes the adsorption behaviour of methylene blue dye on three microporous activated carbons, where two samples (AC-1 and AC-2) were prepared by a polymer blend technique and the other is a microporous activated carbon (ARY-3) sample from viscose rayon yarn prepared by chemical-physical activation. The effects of contact time and activated carbon dosage on decolourisation capacity have been studied. The results show that activated carbon having mixed microporosity and mesoporosity show tremendous decolourisation capacity for methylene blue. In addition, the activated carbon in the powder form prepared by the polymer blend technique shows better decolourisation capacity for methylene blue than the activated rayon yarn sample.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.379-382
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• 2004

Abrasive jet machining (AJM) has a large number of parameters such as powder flow rate, air pressure, diameter of abrasive, stand off distance, material hardness and fracture toughness, etc. It is not easy matter to control those parameter. To achieve high accurate machining, in this study, Taguchi method was used to select process parameters. The objective of the optimization was to get higher material removal rate (MRR). From the experiments and analysis, some process parameters were found to make efficient machining.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.588-591
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• 2004

Generally, $TiO_2$ powders absorb ultraviolet rays and make oxidation/reduction reactions on its surface. Hydroxide radical(OH), a product of photocatalyst reactions, has so strong oxidation/reduction electric potential that it can oxidize noxious gas like VOCs(Volatile Organic Compounds) and NOx. In this study, $TiO_2$ was substituted for exposed concrete to investigate the purifying degree of VOCs(Benzene, Toluene) and NOx. Anatase types of $TiO_2$ were used as photocatalyst. The sun rays and the ultraviolet were used as a light source. Anatase type $TiO_2$ was better than rutile type in purifying performance. The sunray showed the best purifying performance among the light sources. $3\%$ substitution of $TiO_2$ with the sunray was enough to purify VOCs(Benzene, Toluene) and NOx efficiently.

• Journal of the Korean Ceramic Society
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• v.28 no.4
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• pp.269-278
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• 1991

Fine AlN powder was synthesized by carbothermal reduction and nitridation of alumimun hydroxide prepared from Al-isopropoxide. AlN ceramics with Y2O3 and CaO were prepared by hot-pressing under the pressure of 30 MPa at 180$0^{\circ}C$ for 1 h in N2 atmosphere. Grain boundary behavior and purification mechanism of AlN lattice were examined by heat treatment of AlN ceramics at 185$0^{\circ}C$ for 1-6 h in N2 atmosphere. AlN ceramics without sintering additives showed poor sinterability. However, Y2O3-doped and CaO-doped AlN ceramics were fully densified nearly to theoretical density. As the heat treatment time increased, c-axis lattice parameter increased. This is attributed to the removal of Al2O3 in AlN lattice. This purification effect of AlN attice depended upon the quantity of secondary oxide phase in the inintial stage of heat treatment and the heat treatment time.