• The Journal of Engineering Research
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• v.5 no.1
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• pp.73-87
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• 2004

The synthesis and crystallization of amorphous calcium carbonate($CaCO_3$.$nH_2 O$) obtained from gas-liquid reaction between aqueous solution of calcium hydroxide and carbon dioxide at 15~$50^{\circ}C$ are investigated by electrical conductometry, XRD and TEM. The results are as follows: The initial reaction products prior to the formation of precipitated calcium carbonate is amorphous calcium carbonate. The electrical conductivity values in the slurry are decreased during the formation of amorphous calcium carbonate which covers particle surface of calcium hydroxide and retard the dissolution of calcium hydroxide into the solution. that amorphous calcium carbonate is unstable in the aqueous solution and crystallizes finally to calcite by the through-solution reaction. While amorphous calcium carbonate crystallizes into chain-like calcite, the conductivity values are recovered rapidly and the apparent viscosity of slurry containing higher concentration of calcium hydroxide increase. At below pH 9.5, chain-like calcite separates into individual particles to form precipitated calcium carbonate. The formation and synthetic temperature range of amorphous calcium carbonate is most suitable a primary decreasing step(a-step) at $15^{\circ}C$ in the electrical conductometry.

• Composites Research
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• v.36 no.2
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• pp.126-131
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• 2023

Growing environmental concerns regarding pollution caused by conventional plastics have increased interest in biodegradable polymers as alternative materials. The purpose of this study is to develop a 100% biodegradable nanocomposite material by introducing organic nucleating agents into the biodegradable and thermoplastic resin, poly(lactic acid), to improve its properties. Accordingly, cellulose nanofibers, an eco-friendly material, were adopted as a substitute for inorganic nucleating agents. To achieve a uniform dispersion of cellulose nanofibers (CNFs) within PLA, the aqueous solution of nanofibers was lyophilized to maintain their fibrous shape. Then, they were subjected to primary mixing using a twin-screw extruder. Test specimens with double mixing were then produced by injection molding. Differential scanning calorimetry was employed to confirm the reinforced physical properties, and it was found that the addition of 1 wt% CNFs acted as a reinforcing material and nucleating agent, reducing the cold crystallization temperature by approximately 14℃ and increasing the degree of crystallization. This study provides an environmentally friendly alternative for developing plastic materials with enhanced properties, which can contribute to a sustainable future without consuming inorganic nucleating agents. It serves as a basis for developing 100% biodegradable green nanocomposites.

• Economic and Environmental Geology
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• v.48 no.6
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• pp.431-449
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• 2015

The study area is located in the western part of the Precambrian stock type of Sancheong anorthosite complex, the Jirisan province of the Yeongnam massif, in the southern part of the Korean Peninsula. We perform a detailed field geological investigation on the Sancheong anorthosite complex, and report the characteristics of lithofacies, occurrences, foliations, and research formation process and its mechanism of the Sancheong anorthosite complex. The Sancheong anorthosite complex is classified into massive and foliation types of Sancheong anorthosite (SA), Fe-Ti ore body (FTO), and mafic granulite (MG). Foliations are developed in the Sancheong anorthosite complex except the massif type of SA. The foliation type of SA, FTO, MG foliations are magmatic foliations which were formed in a not fully congealed state of SA from a result of the flow of FTO and MG melts and the kinematic interaction of SA blocks, and were continuously produced in the comagmatic differentiation. The Sancheong anorthosite complex is formed as the following sequence: the massive type of SA (a primary fractional crystallization of parental magmas under high pressure)${\rightarrow}$ the foliation type of SA [a secondary fractional crystallization of the plagioclase-rich crystal mushes (anorthositic magmas) primarily differentiated from parental magmas under low pressure]${\rightarrow}$the FTO (an injection by filter pressing of the residual mafic magmas in the last differentiation stage of anorthositic magmas into the not fully congealed SA)${\rightarrow}$the MG (a solidification of the finally residual mafic magmas). It indicates that the massive and foliation types of SA, the FTO, and the MG were not formed from the intrusion and differentiation of magmas which were different from each other in genesis and age but from the multiple fractionation and polybaric crystallization of the coeval and cogenetic magma.

• Polymer(Korea)
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• v.36 no.3
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• pp.332-337
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• 2012

The primary objective of this work is to find the properties of sustained release dissolution pattern depending on solubility of drugs, so venlafaxine HCl and carbamazepine tablets were made by using polymer wich various particle size. Hydroxy propyl methyl cellulose (HPMC) has been utilized in this study as an excipient that is one of the most widely used polymers for an oral sustained release formulation, and drug release pattern was strongly influenced by swelling rate depending on particle size of HPMC. Scanning electron microscope (SEM) was employed to investigate the surface of tablets with various HPMC particle size, and differential scanning calorimeter (DSC) was employed to investigate the crystallization of drugs in tablets. The release model equation was applied to analyze the main mechanism of drug release pattern. The results demonstrate that drug release pattern is controlled by the drug solubility and HPMC particle size.

• Economic and Environmental Geology
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• v.29 no.4
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• pp.483-493
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• 1996

The tectonic environment and source characteristics of the Daebo granitic batholith in the central Ogcheon Belt were investigated based upon major and trace element geochemistry. The batholith is comprised of three granite types; a biotite granite (DBBG), K-feldspar megacryst-bearing biotite granite (DBKG), and a more mafic granodiorite (DBGD). The variations of Na and K in the granites can not be explained by simple fractional crystallization from the same primary magma. The irregular behavior of these alkali elements indicates a variety of source materials or incomplete mixing of different source materials. The large ion lithophile (LIL) element enrichment and low Ta/Hf ratios of the granites are typical characteristics of normal, calc-alkaline continental arc granitoids. Based upon REE patterns of the granites, it seems to be unreasonable to regard the felsic DBBG as a late stage differentiate formed by residual melts after the fractionation of major constituent minerals of the more mafic DBGD. Inconsistent variations in ${\varepsilon}_{Nd}(t)$ and LIL element concentrations of the granites preclude a mixing model between primitive melt and LIL element-enriched upper crustal materials. The irregular geochemical variation of the granites is taken to be largely inherited from an already heterogeneous source region.

• The Journal of the Petrological Society of Korea
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• v.26 no.3
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• pp.183-200
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• 2017

Alkali rhyolites in the Cheonmunbong of the Mt. Baekdu stratovolcano show porphyritic texture in the glassy or aphanic groundmass. Major phenocryst is alkali-feldspar, pyroxene, and amphibole, and small amount of microphenocryst is olivine, quartz, opaque mineral (ilmenite). The content of $Fe^{2+}/(Fe^{2+}+Mg^{2+})$ and alkali elements in the mafic minerals is high. Alkali feldspar is classified as sanidine or anorthclase, olivine as fayalite, and pyroxene as ferro-hedenbergite of ferro-augite area. Amphibole belongs to alkali amphibole group, but FeO and $Fe_2O_3$ were not separated, so it is required future studies. Nb(-) anomaly suggesting that slab-derived materials might have played a primary role in the genesis of the rhyolite magma, is not observed. It is noted that they originated in the within plate environment which is not related to subduction zone of the convergent plate boundary. The Mt. Baekdu alkaline rocks are classified into the comendite series. The alkali rhyolites of the summit at Mt. Baekdu shows the disequilibrium mineral assemblages, suggesting that it evolved from thrachytic magma with experience of magma mixing as well as fractional crystallization.

• Korean Journal of Materials Research
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• v.7 no.12
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• pp.1063-1069
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• 1997

For me1t-spun Fe-Nd-C alloys, variation of phase development and magnetic properties with the variety of alloy compositions and production conditions were investigated. To find out whether hard magnetic $Fe_{14}Nd_2C$ is crystallized direct1y from the melt by rapid quenching, the phase development of the as-spun ribbons spun at various speed was a1so studied. For the ribbons spun at 10m/s, ${\alpha}-Fe$ was the primary crystallization phase followed by the secondary $Fe_{17}Nd_2C$. At 20m/s ${\alpha}-Fe$ was suppressed so that the primary $Fe_{17}Nd_2C$ coexisted with the secondary ${\alpha}-Fe$ and the amorphous phase. Above 30m/s the ribbons were a1most amorphous, and the amorphization was complete at 40m/s. $Fe_{14}Nd_2C$ therefore was not found in as-spun state but obtained after heat treating the ribbons. The effective temperature range ($700{\sim}900^{\circ}C$) in which $Fe_{14}Nd_2C$ can be obtained was wider than that of a cast alloy. An alloy made with the wheel speed of 20 or 30m/s yielded higher coercivities after heat treatment. In iron-rich Fe-Nd-C, the composition range in which a high coercivity (more than 10kOe) is expected is narrow, i.e., 77~78 Fe and 7~8 C(at.%).

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.210-225
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• 1997

From their general natures of peraluminous, S-type and ilmenite-series granites, two-mica granites in the Cheongsan, Inje-Hongcheon, Yeongju and Namwon areas were originated from crust-derived granitic magma and solidified under reducing condition. Each two-mica granite in Inje-Hongcheon and Namwon districts was differentiated from the the residual magma of porphyric biotite granite and high Ti/Mg biotite granite, respectively. The genetic relationships between two-mica granite and porphyritic biotite granite in Chenongsan district and between two-mica granite and biotite granodiorite in Yeongju district are ambiguous. In Namwon district granitic magmas were water-saturated and possible water solubilities in magmas were more than 5.8wt.%. In Yeongju district two-mica granitic magma was nearly water-saturated and showed possible water solubilities between 2.4~5.8wt.%. Two-mica granitic magmas in Cheongsan and Inje-Hongcheon districts were water-undersaturated. Pressure-dependent minimum melt compositions (0.5~2kb) and petrographic textures of two-mica granites in Inje-Hongcheon and Yeongju districts represent that the granites intruded and solidified at shallow level, whereas those in Cheongsan and Namwon districts exhibit relatively deeper level of granitic intrusion (2-3kb). The intersection of granite-solidus/muscovite stability indicates that magmatic primary muscovite can be crystallized from the water-saturated magma above 1.6kb (ca. 6km), but below the pressure muscovite can be formed by the subsolidus reaction. On the other hand, more pressure would be necessary for the crystallization of primary muscovite from the water-undersaturated magma. This pressure condition can explain the occurrence of primary and secondary muscovites from the two-mica granites in the areas considered. The experimental muscovite stability must be cautious of the application to examine the origin of muscovite. The muscovite stability can move toward high temperature field with adding of Ti, Fe and Mg components to the octahedral site of pure muscovite end member.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.35-51
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• 1996

The granitic rocks in the vicinity of the Mt. Sorak, the northeastern part of the NE-SW elongated Mesozoic granitic batholith in the Kyeonggi massif, consist of granodiorite, biotite granite, two-mica granite and alkali feldspar granite. Variations In major and most trace elemental abundances show a typical differentiation trend in a granitic magma. Granitic rocks all display a calc-alkaline trend in the AFM diagram. Also, In the ACF diagram discriminating between I- and S-type granitic rocks, granodiorite and most biotite granite in the southeastern area represent I-type and magnetite-series characteristics, while most biotire granite and two-mica granite in the northwestern area exhibit S-type and ilmenite-series ones.According to recent studies of the granitle rocks In the Inje-Hongcheon district. all ihe granitic rocks distributed in the northeastern part of the Kyeonggi massif have been classified as late Triassic to early Jurassic Daebo granite. With reference of the formerly published ages, an age oi $125.6{\pm}4.4$ Ma calculated by the slope in the plot of $^{87}Rb/^{86}Sr-^{87}Sr/^{86}Sr$ for the biotite granite samples from the southeastern area is inferred as an emplacement age for the granitic rocks in the vicinity of the Mt. Sorak. On the basis of elemental variations and Sr isotope compositions, an possible evolutional process for the granitic magmas in this area is suggested. The primary magma of I-type and magnetite-series generated about 125 Ma by partial melting of igneous originated crustal materials, might be emplaced and evolved through fractional crystallization, convection and assimilation of the surrounding Precambrian metasediments to become S-type and ilmenlte-serles in the outer area, and then solidified to granodiorite, biotite granite and two-mica granite.At the latest stage, the evolved hydrothermal solution altered the formerly solidified biotite granite to alkali feldspar granite and probably later local igneous activities affected the alkali feldspar granite again.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.185-209
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• 1997

Granitic rocks in the Cheongsan area cosist of three plutons-Baegrog granodiorite, Cheongsan porphyritic granite, and two mica granite. Amphilboles from the Baegrog granodiorite belong to the calcic amphilbole group and show compositional variations from magnesio-hornblende in the core to actinolitic hornblende in the rim. Biotites from the three granites represent intermediate compositions between phlogopite and annite. Muscovites from the two mica granite are considered to be primary muscovite in terms of the occurrence and mineral chemistry. Each granitic rock reveals systematic variation of major oxide contents with $SiO_2$. Major oxide variation trends of the Baegrog granodiorite are fairly different from those of Cheongsan porphyritic granite and two mica granite. The latter two granitic rocks are also different with each other in variation trends for some oxides. Thus three granitic rocks in the Cheongsan area were solidifield from the independent magmas of chemically different, heterogeneous origin. The granitic rocks in the area show calc-alkaline nature. The whole rock geochemistry shows that the Baegrog granodiorite and Cheongsan porphyritic granite belong to metaluminous, I-type granite, whereas the two mica granite to peraluminous, I/S-type granite. The opaque mineral contents and magnetic susceptibility represent that the granitic rocks in the area are ilmenite-series granite, indicating that each magma was solidified under relatively reducing environment. The tectonic environment of the granitic activity in the area seems to have been active continental margin. Alkali feldspar megacryst in the Cheongsan porphyritic granite is considered to be magmatic, judging from the crystal size, shape, arrangement, and distribution pattern of inclusions. The petro-graphical characteristics of the Cheongsan porphyritic granite can be explained by two stage crystallization. Under the smaller degree of undercooling the alkali feldspar megacrysts rapidly grew owing to slow rate of nucleation and fast growth rate. At the larger degree of undercooling the nucleation rate and density drastically increased and the small crystals of the matrix were formed.