• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.279-286
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• 2017

This review paper evaluates different kinds of synthesis methods for calcite precipitated calcium carbonates by using different materials. The various processing routes of calcite with different compositions are reported and the possible optimum conditions required to synthesize a desired particle sizes of calcite are predicted. This paper mainly focuses on that the calcite morphology and size of the particles by carbonation process using loop reactors. In this regard, we have investigated various parameters such as $CO_2$ flow rate, Ca $(OH)_2$ concentration, temperature, pH effect, reaction time and loop reactor mechanism with orifice diameter. The research results illustrate the formation of well-defined and pure calcite crystals with controlled crystal growth and particle size, without additives or organic solvents. The crystal growth and particle size can be controlled, and smaller sizes are obtained by decreasing the Ca $(OH)_2$ concentration and increasing the $CO_2$ flow rate at lower temperatures with suitable pH. The crystal structure of obtained calcite was characterized by using X-ray diffraction method and the morphology by scanning electron microscope (SEM). The result of x-ray diffraction recognized that the calcite phase of calcium carbonate was the dominating crystalline structure.

• Bulletin of the Korean Chemical Society
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• v.25 no.4
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• pp.525-528
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• 2004

The photoluminescence (PL) emission of Si nanocrystals synthesized by 400 keV Si ion implanted in $SiO_2$ is studied as a function of ion dose and annealing time. The formation of nanocrystals at around 600 nm from the surface was confirmed by RBS and HRTEM, and the Si nanocrystals showed a wide and very intense PL emission at 700-900 nm. The intensity of this emission showed a typical behaviour with a fast transitory increase to reach a saturation with the annealing time, however, the red shift increased continuously because of the Ostwald ripening. The oversaturation of dose derived a decrease of PL intensity because of the diminishment of quantum confinement. A strong enhancement of PL intensity by H passivation was confirmed also, and the possible mechanism is discussed.

• Resources Recycling
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• v.17 no.4
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• pp.57-65
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• 2008

The behavior of Na-A type zeolite formed in hydrothermal synthesis of melting slag from municipal incineration ash has been investigated with varying synthesis time and $SiO_2/Al_2O_3$ ratio. Sodium silicate and sodium aluminate feed was found to initially form nuclei of Na-A type zeolite in the behavioral study of the reaction products with different synthesis times. As the synthesis time increased, the nuclei have grown to Na-A type zeolite crystals by reacting with $SiO_2$ and $Al_2O_3$ dissolved from the melting slag. The hydrothermal synthesis was completed in 10 hr in the $SiO_2/Al_2O_3$ ratio of 1.38 and after that time, the Na-A type zeolite formed was dissolved and transformed into hydroxysodalite. Only Na-A type zeolite was formed in the $SiO_2/Al_2O_3$ ratio ranging 0.80 to 1.96, whereas Na-P type zeolite as well as Na-A type was formed in the $SiO_2/Al2O_3$ ratio of 2.54.

• Journal of the Mineralogical Society of Korea
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• v.19 no.4 s.50
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• pp.301-310
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• 2006

Smectites were synthesized from Na-P type and Na-A type zeolites by the hydrothermal synthetic method, and their physicochemical properties were studied. The optimal synthetic conditions for producing smectite were $290^{\circ}C$, 72 hr and $75{\sim}100kgf/cm^2$ in autogenous pressure. pHs of initial reaction solutions for the synthesis of smectites from Na-P type and Na-A type zeolite s were pH 6 and pH 10, respectively. The synthetic smectite was confirmed as $12{\AA}$-beidellite by a series of analysis such as X-ray diffraction analysis with random and oriented mounts, ethylene glycol treatment, and Greene-Kelly test, and their several physicochemical properties were studied.

• Resources Recycling
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• v.18 no.3
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• pp.49-54
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• 2009

The effect of MgO in synthesis of alinite clinker was investigated. Clinker of alinite composition ratio and alintite clinker substituted for MgO of 3.77% were sintered at $760^{\circ}C$ and between $800^{\circ}C$ and $1,400^{\circ}C$ at the interval of $100^{\circ}C$. Synthesized phases and hydration heat of alinite clinker with MgO and without MgO were then investigated. As a result, alinite, CCA, ${\beta}-C_2S$ and f-CaO phases are synthesized in alinite clinker without MgO sintered at $1,300^{\circ}C$, while only alinite phase is synthesized in alinite clinker with MgO sintered at $1,300^{\circ}C$ with the highest synthesis rate. Heat evolution of alinite clinker with MgO has no induction period.

• Transactions of the Korean hydrogen and new energy society
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• v.15 no.2
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• pp.119-128
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• 2004

DME(Dimethyl Ether) was directly produced from the synthesis gas using the slurry phase reactor. The catalyst for DME production prepared two types (A type; Cu:Zn:Al=57:33:10, B type; Cu:Zn:Al=40:45:15, molar ratio). It was evaluated for the effect of the reaction medium oil using the small size slurry phase reactor. DME production yield and the methanol selectivity decreased in the order: n-hexadecane oil> mineral oil> therminol oil. The long-term test of DME production was carried out using A and B type catalyst, and n-hexadecane oil and mineral oil, respectively. It was confirmed that the use of A type for the catalyst and n-hexadecane for the reaction medium oil was very useful for the viewpoint of the DME production form the synthesis gas.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.624-628
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• 2003

Lanthanum oxyfluoride can be synthesized by mechanochemical (MC) reaction between lanthanum oxide ($La_2O_3$) and polytetrafluoroethylene (PTFE, ($({CF_2CF_2}_n)$) in air using a planetary mill. MC reaction between the two materials induced from intensive grinding operation. The MC reaction is almost finished by 240min, and the products ground for 240min or more are composed of LaOF, amorphous $La(CO_3)F$ and amorphous carbon (C). Heating this MC reaction products at $600^{\circ}C$ enables us to eliminate amorphous C and decompose $La(CO_3)F$ into LaOF, so that pure LaOF material can be obtained as the final product. The average particle size of the final product (purified LaOF) is around few ten nanometers.

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2004.05a
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• pp.159-163
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• 2004

• Proceedings of the Korean Institute of Resources Recycling Conference
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• 2006.05a
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• pp.124-128
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• 2006

• Journal of Powder Materials
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• v.15 no.3
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• pp.221-226
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• 2008

Silver coated copper composite powders were prepared by electroless plating method by controlling the activation and deposition process variables such as feeding rate of silver ions solution, concentration of reductant and molar ratio of activation solution $(NH_4OH/(NH_4)_2SO_4)$ at room temperature. The characteristics of the product were verified by using a scanning electron microscopy (SEM), X-ray diffraction (XRD) and atomic absorption (A.A.). It is noted that completely cleansing the copper oxide layers and protecting the copper particles surface from hydrolysis were important to obtain high quality Ag-Cu composite powders. The optimum conditions of Ag-Cu composite powder synthesis were $NH_4OH/(NH_4)_2SO_4$ molar ratio 4, concentration of reductant 15g/l and feeding rate of silver ions solution 2 ml/min.