• Korean Journal of Materials Research
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• v.22 no.8
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• pp.397-402
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• 2012

Morphological control on hydroxyapatite crystals has attractive prospects in research to clarify the effects of crystal planes on biological performance. Hydrothermal processing is known as a typical type of processing for fabricating well-grown crystals with unique morphology. The purpose of the present study is to examine the feasibility of well-crystallized crystals with oriented structures through hydrothermal treatment of calcite. A single crystal of calcite was applied to hydrothermal treatment in a phosphate solution at $160^{\circ}C$. Rod-shaped hydroxyapatite crystals with micrometer-size were formed on the {100} face of calcite after treatment, while nanometer-sized hydroxyapatite crystals were formed on the (111). The hydroxyapatite crystals formed on each plane were not morphologically changed with increasing treatment periods. An oriented structure of rod-shaped hydroxyapatite was constructed after hydrothermal treatment of {100} planes on the calcite single, while such orientation was not observed on the (111) plane after the treatment. The layer of hydroxyapatite formed on the {100} plane was thicker than that of the (111) plane. The {100} plane of calcite shows a higher reactivity than that of the (111) plane, which results in rapid crystal growth of hydroxyapatite. The difference in the morphology of the formed hydroxyapatite was governed by the reactivity of each crystal plane exposed to the surrounding solution.

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.30-35
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• 1996

Calcite(CaCO3) single crystals were grown hydrothermally and transmittance of as grown crystals was measured. Instead of platinium, teflon was lined onto the wall of autoclave to prevent the corrosion of autoclave wall by acidic NH4Cl solution. Spontaneous nucleation and growth of calcite crystal on teflon was reduced considerably by addition of NaCl and /or CH3COOH and applying low temperature gradient. When the temperature gradient exceeded to a few degrees from the critical temperature gradient(6-7℃), spontaneous nucleation and growth was rapidly increased in any hydrothermal solutions. Precise temperature control is thought to be the most important factor for the growth of calcite single crystal by hydrothermal technique. As grown calcite single crytal showed high transmittance compared to natural one by UV-visible analysis.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.3
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• pp.93-98
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• 2005

The crystal growth of calcite at a low temperature range was carried out by the hydrothermal method using amorphous calcium carbonate which has excellent solubility in water. Amorphous calcium carbonate was prepared by the wet chemical reaction of a stoichiometric mixture of $CaCl_2\;and\;Na_2CO_3$. An important factor was the reaction temperature and time taken in preparation of the amorphous calcium carbonate. From the solubility results calculated by the weight loss method, $NH_4NO_3$ solutions were found to be the most promising solvents to grow calcite single crystals. The hydrothermal conditions for high growth rates of calcite single crystals were as follows: starting material: amorphous calcium carbonate, solvent: 0.01 m $NH_4NO_3$, temperature: $180^{\circ}C$, duration: 30 days. And properties of calcite single crystals were follows: dislocation density: $10^6{\sim}10cm^{-2}$, UV-visible transmittance: about 80% from 190 to 400 nm and birefringence: $0.17{\sim}0.18$. Also, it can be known from the FT-IR results that the absorption peak by injection of $HCO_3^-\;and\;OH^-$ ions was not shown.

• Korean Chemical Engineering Research
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• v.50 no.2
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• pp.300-303
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• 2012

Phase change of calcium carbontae crystals in crystallization of precipitated calcium carbonate was researched by adding additives such as ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), citric acid (CIT) and pyromellitic amid (PMA). At low temperature $20^{\circ}C$, calcite crystal was made. At high temperature $80^{\circ}C$, aragonite crystal was made without additives. At middle temperature $40^{\circ}C$ and $60^{\circ}C$, Aragonite crystal also made by adding EDTA, DTPA. The crystal growth of Aragonite was retarded by the presence of CIT, PMA and the single phase of calcite was made. It was found that additives were important factors to make the single phase of calcium carbonate.

• Korean Journal of Materials Research
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• v.31 no.1
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• pp.1-7
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• 2021

The characteristics and morphology of precipitated calcium carbonate (PCC) particles produced by carbonation process with various experimental conditions are investigated in this study. The crystal structures of PCC formed by carbonation process are calcite and aragonite. The crystal structure of PCC particles synthesized without adipic acid additive is calcite only, regardless of the reaction temperature. Needle-like shape aragonite phase started to form at reactor temperature of 80℃ with the adipic acid additive. Particle size of the single phase calcite PCC synthesized without adipic acid additive is about 1 ~ 3 ㎛, with homogenous distribution. The aragonite PCC also shows uniform size distribution. The reaction temperature and concentration of adipic acid additive do not show any significant effects on the particle size distribution. Aragonite phase grown to a large aspect ratio of needle-like shape showed relatively improved whiteness. The measured whiteness value of single calcite phase is about 95.95, while that of the mixture of calcite and aragonite is about 99.11.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.10
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• pp.4069-4074
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• 2010

Phase change of calcium carbontae crystals in crystallization of precipitated calcium carbonate was researched by adding additives such as ethylenediaminetetraacetic acid(EDTA), diethylenetriaminepentaacetic acid(DTPA), citric acid(CIT) and pyromellitic amid(PMA). At low temperature $20^{\circ}C$, calcite crystal was made. At high temperature $80^{\circ}C$, aragonite crystal was made without additives. At middle temperature $40^{\circ}C$ and $60^{\circ}C$, Aragonite crystal also made by adding EDTA, DTPA. The crystal growth of Aragonite was retarded by the presence of CIT, PMA and the single phase of calcite was made. It was found that additives were important factors to make the single phase of calcium carbonate.

• Korean Chemical Engineering Research
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• v.60 no.4
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• pp.564-573
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• 2022

Calcium carbonate (CaCO₃) exhibits three polymorphs: calcite with arhombohedral, vaterite with a spherical, and aragonite with a needle-like structure. Qualitative and quantitative analyses of the morphology of CaCO₃ are very important to investigate the synthesis of single-crystal vaterite and aragonite. In this work, the polymorphs of calcium carbonate were quantitatively analyzed using XRD. Pure vaterite and pure aragonite were synthesized and the peak distribution of a single phase was analyzed. The vaterite fraction of a mixture of calcite and vaterite was calculated based on the intensity of a specific diffraction peak, and compared to the results based on the peak area. The mean value of f_sV (the correction factor for the peak area of vaterite) was 0.654. The phase analysis of calcite-aragonite mixtures was performed, and the mean value of f_sA (the correction factor for the peak area of aragonite) was obtained as 0.6713. Using these factors, Eq. (24)~Eq. (32) for the quantitative analysis based on the total peak area of XRD were derived to calculate the phase contents of ternary phase CaCO₃. And three-component XRD section was defined considering overlapping sections.

• Journal of the Mineralogical Society of Korea
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• v.28 no.1
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• pp.9-16
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• 2015

A mineralogical analysis on the factors affecting the luster of pearls was carried out using gravity measurement, optical microscope observation, X-ray diffraction analysis, and scanning electron microscopy. We divided the seawater cultured pearls from Tongyeong into the following four types based on luster and shape; good luster and round (LR), lackluster and round (LLR), lackluster and baroque (LLB), and lackluster and two nucleus (LTN) pearls. Pearls with high-quality luster had slightly lower specific gravity as compared to pearls with low-quality luster, but both these types of pearls are within the specific gravity range of commercial pearls. Regarding the cross-sectional thickness of the mother-of-pearl layer, LR pearls showed a uniform thickness of about 0.3 mm in average. On the other hand, LLR pearls were characterized by relatively thinner, but uniform thickness. LTN and LLB pearls showed a tendency of significantly large variation in thickness even within a single pearl. For the surface of pearls, pearls with high-quality luster showed narrower and clearer growth lines of aragonite crystals as compared to pearls with low-quality luster. Pearls with high-quality luster were characterized by fewer aragonite crystal lattice defects as compared to pearls with low-quality luster, and the former showed parallel arrangement, thinner thickness, and less difference in thickness on the surface and inside. If a pearl has a prismatic layer, it is composed of aragonite with calcite in the prismatic and nacreous layer, and calcite content is very high in the lackluster pearl. Pearls without a prismatic layer were devoid of calcite irrespective of their quality of luster, and were composed of aragonite.

• Journal of the Mineralogical Society of Korea
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• v.28 no.4
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• pp.333-341
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• 2015

As results of X-ray diffraction analysis, samples of asbestos and soil were composed maily of dolomite ($CaMg(Co_3)_2$, tremolite ($Ca_2Mg_5Si_{18}O_{22}(OH)_2$), actinolite ($Ca(Mg,\;Fe)_6Si_8O_{22}(OH)_2$), talc ($Mg_3Si_4O_{10}(OH)_2$), calcite ($CaCO_3$) and small amounts of quartz ($SiO_2$) and clay minerals. The average size of asbestos fibers was about $100{\mu}m$ and maximum of some asbestos was $250.0{\mu}m$ in length. The aspect ratio of asbestos fiber were over 3 : 1 and inclined extinction in the range of $8.0-19.5^{\circ}$. Single isolated fragments of asbestos are probably fiber and acicula form in crystal edge along the cleavage plane. Tremolite that composed main asbestos mineral in rock and soil around Dong-a mine is higher content of Fe than actinolite asbestos.

• Economic and Environmental Geology
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• v.8 no.3
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• pp.117-124
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• 1975

Wet chemical analysis (for $MnO_2$, MnO, and $H_2O$(+)) and electron microprobe analysis (for $Fe_2O_3$ and PbO) give $MnO_2$ 74.91, MnO 11.33, $Fe_2O_3$ (total Fe) 4.19, PbO 0.03, $H_2O$ (+) 9.46, sum 99.92%. 'Available oxygen determined by oxalate titration method is allotted to $MnO_2$ from total Mn, and the remaining Mn is calculated as MnO. Traces of Ba, Ca, Mg, K, Cu, Zn, and Al were found. Li and Na were not found. The existence of (OH) is verified from the infrared absorption spectra. The analysis corresponds to the formula $Mn^{4+}{_{4.85}}(Mn^{2+}{_{0.90}}Fe^{3+}{_{0.30}})_{1.20}O_{8.09}(OH)_{5.91}$, on the basis of O=14, 'or ideally $Mn^{4+}{_{5-x}}(Mn^{2+},Fe^{3+})_{1+x}O_{8}(OH)_{6}$ ($x{\approx}0.2$). X-ray single crystal study could not be made because of the distortion of single crystals. But the x-ray powder pattern is satisfactorily indexed by an orthorhombic cell with a 9.324, b 14.05, c $7.956{\AA}$., Z=4. The indexed powder diffraction lines are 9.34(s) (100), 7.09(s) (020), 4.62(m) (200, 121), 4.17(m) (130), 3.547(s) (112), 3.212(vw) (041), 3.101(s) (300), 2.597(w) (013), 2.469(m) (331), 2.214(vw)(420), 2.098(vw) (260), 2.014 (vw) (402), 1.863(w) (500), 1.664(w) (314), 1.554(vw) (600), 1.525(m) (601), 1.405(m) (0.10.0). DTA curve shows the endothermic peaks at $250-370^{\circ}C$ and $955^{\circ}C$. The former is due to the dehydration: and oxidation forming$(Mn,\;Fe)_2O_3$(cubic, a $9.417{\AA}$), and the latter is interpreted as the formation of a hausmannite-type oxide (tetragonal, a 5.76, c $9.51{\AA}$) from $(Mn,\;Fe)_2O_3$. Infrared absorption spectral curve shows Mn-O stretching vibrations at $515cm^{-1}$ and $545cm^{-1}$, O-H bending vibration at $1025cm^{-1}$ and O-H stretching vibration at $3225cm^{-1}$. Opaque. Reflectance 13-15%. Bireflectance distinct in air and strong in oil. Reflection pleochroism changes from whitish to light grey. Between crossed nicols, color changes from yellowish brown with bluish tint to grey in air and yellowish brown to grey through bluish brown in oil. No internal reflections. Etching reactions: HCl(conc.) and $H_2SO_4+H_2O_2$-grey tarnish; $SnCl_2$(sat.)-dark color; $HNO_3$(conc.)-grey color; $H_2O_2$-tarnish with effervescence. It is black in color. Luster dull. Cleavage one direction perfect. Streak brownish black to dark brown. H. (Mohs) 2-3, very fragile. Specific gravity 3.59(obs.), 3.57(calc.). It occurs as radiating groups of flakes, flower-like aggregates, colloform bands, dendritic or arborescent masses composed of fine grains in the cementation zone of the supergene manganese oxide deposits of the Janggun mine, Bonghwa-gun, southeastern Korea. Associated minerals are calcite, nsutite, todorokite, and some undetermined manganese dioxide minerals. The name is for the mine, the first locality. The mineral and name were approved before publication by the Commission on New Minerals and Mineral Names, I.M.A.