• Journal of the Mineralogical Society of Korea
• /
• v.13 no.2
• /
• pp.84-95
• /
• 2000

Tremolite crystals from the Dongyang talc deposit were studied using high-resolution transmission electron microscopy (HRTEM) to characterize the tremolite-to-talc reaction. [001] HRTEM images of tremolite show intergrowths of wide-chain pyriboles and talc; talc is the primary alteration product of tremolite, and triple-chain structures occur sparsely. The boundaries between tremolite and talc are commonly well defined by (010) and (100) interfaces. (001) talc layers are parallel to (100) of tremolite, and the interfaces between tremolite and talc appear to be coherent in HRTEM images, indicating that most talc laters formed directly from tremolite by a gydration reaction. However, some talc formed along (110) of tremolite, and talc layers are not extended from (010) of tremolite, suggesting that part of talc in the deposit was produced through a dissolution-precipitation mechanism. Carbonate minerals are also associated with tremolite and talc. Common replacement of dolomite by calcite indicates that the tremolite-to-talc reaction results in remnant Ca, which was eventually consumed to replace dolomite to form clacite. Some Mg Produced by dolomite during reaction to calcite was apparently utilized to form talc, because talc formation from tremolite requires extra Mg. Although talc could be formend directly from dolomite, extensive alteration of tremolite to talc suggests that part of talc of the deposit was produced from tremolite that was formed by dolomite reaction during an early stage metamorphism.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.10 no.2
• /
• pp.166-170
• /
• 2000

Amorphous calcium carbonate was prepared by wet chemical method and performed the control of their shape using crystalline calcium carbonate that prepared from oyster shell by the $CO_2$ gas blowing method. As a result, amorphous calcium carbonate was obtained by the dissolution process of crystalline calcium carbonate in the dil-HC1 solution, mixing of sodium carbonate solution, precipitation and filtering with high speed. And using the amorphous calcium carbonate of mud type, crystalline calcium carbonates with cubic, needle, spindle, spherical and plate shape were obtained in the temperature rang of 2~$85^{\circ}C$ and reaction time range of 5~60 minute.

• Analytical Science and Technology
• /
• v.13 no.3
• /
• pp.282-290
• /
• 2000

In this study, polymer additives were extracted and separated by Soxhlet extraction method and the dissolution-precipitation method from a polycarbonate (optical grade) which completely absorbed UV light below 390 nm. Analytical techniques such as UV-Vis spectroscopy, FT-IR, and HPLC were applied to analyze additives in polycarbonate. Separated materials from the polycarbonate may be a complex mixture containing additives such as UV stabilizer, antioxidants (primary and secondary), monomers, and oligomers. Several compounds such as bisphenol A, Irganox 1010, and Cyasorb UV-5411 were identified by chromatograms and UV spectra obtained from RP HPLC analysis using Bondapak $C_{18}$ column, methanol mobile phase, and a photodiode array (PDA) detector. Also, the content of UV-5411 in the polycarbonate was about 0.12 wt% by a quantitative analysis through UV spectroscopy.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.09b
• /
• pp.1179-1180
• /
• 2005

To immobilize the pollutants from wastewater in situ, two phosphatic clays collected from different areas in Egypt (eastern and western Sebaia, Aswan-Isna, Upper Egypt) used to remove contaminant ions from industrial wastewater. Obtained results confirmed the strong relationship between phosphatic clay and Pb elimination from wastewater. The sensitivity classification of phosphatic clay toward ions retained as described in three categories: highly sensitive to retain Pb , Al and Cr ; moderately sensitive for Mn; and weakly sensitive for Band Zn. Data suggested that large fraction of Pb removed by phosphatic clays stayed intact under a wide variation in extracting solution pH (3-11). In situ immobilization is considered a promising technique that has the potential to remove contaminant ions from wastewater. Two important factors need to be considered when applying this technique: The first, is the clay must be effective and selective under different composition of wastewater. The second, is the immobilized ions should be stable and non-leacheable under varying water conditions. Phosphatic clays with $Pb^{2+}$ were suitable to achieve these two factors. Possible mechanism for removal $Pb^{2+}$ by phosphatic clays is the formation of fluoropyromorphite through the dissolution of fluoro and hydroxyl apatite by its precipitation from solution, beside, Pb complexation at phosphatic clay surface at P-OH sites.

• Proceedings of the KSME Conference
• /
• 2003.04a
• /
• pp.403-408
• /
• 2003

The erosion behavior of :artificially aged HK40 steel was investigated. Erosion tests were conducted at room temperature, $200^{\circ}C$ and $400^{\circ}C$ using $Al_2O_3$ particles. Erosion rates increased with increment of temperature. The maximum erosion rate increased with the impingement angle of 30 degree. The erosion rate increased, reached the maximum at 1000 hours, and after that, decreased with heat treatment time. The mechanism of erosion seems to be the cutting wear which is very much associated with the strength of material. As results, the erosion rates were rather affected by the tensile strength and the strain hardening coefficient than the hardness and the yield strength. Such changes of material properties would be caused by the change of micro-structure due to the precipitation of carbide and the dissolution of solid element within matrix during the heat treatment.

• Applied Chemistry for Engineering
• /
• v.10 no.4
• /
• pp.509-514
• /
• 1999

In Preparing $BaTiO_3$ powder under hydrothermal conditions, effects of reaction period feedstock concentration and mixing rate on crystallinity, mean size and size distribution of particles were studied. Experimental results showed that the particle size became smaller with its narrow distribution as the reaction period and mixing rate increased, but feedstock concentration decreased in contrast with the results based on the classical nucleation-growth model. From these results, $BaTiO_3$ particles seem to be prepared hydrothermally through a multiple reaction procedure that includes dissolution, precipitation, hydrolysis-condensation, aggregation, diffusion and transformation.

• Journal of Korea Foundry Society
• /
• v.37 no.2
• /
• pp.31-37
• /
• 2017

A new form of austenitic heat-resistant ductile iron was developed and its microstructures and elevated temperature properties were compared to those of Ductile Ni-Resist D5S. According to JMatPro calculations, it was predicted that Mo-rich carbides would be crystallized before the eutectic reaction starts in the developed alloy. At the austenite cell boundaries of the developed alloy, both Mo-rich carbides and Cr-rich carbides were found. In addition, Ni-silicides were found adjacent to Cr-rich carbides in D5S specimen and were identified as $Ni_2Si$. The developed alloy also had greater yield strength and lower tensile strength levels with less elongation due to the dissolution of Mo atoms into the austenite matrix and the precipitation of Mo-rich carbides. From the results of elevated temperature tensile tests and stress-rupture tests, it was found that the developed alloy had elevated temperature properties superior to those of D5S. This was due to the pinning effect of the dissolved Mo atoms in the austenite matrix.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.2
• /
• pp.84-87
• /
• 2014

Separation/recovery of valuable metals such as zinc, nickel or tin from copper alloy dross has recently attracted from the viewpoints of environmental protection and resource recycling. In this study, preliminary investigation on separation of tin (Sn) from copper alloy dross using selective dissolution method was performed. The tin in the copper alloy dross did not dissolve in an aqueous nitric acid solution which could allow the concentration/separation of tin from the copper alloy dross. Precipitation of tin as $H_2SnO_3$ (meta stannic acid)occurred in the solution and transformed to tin dioxide ($SnO_2$) after drying process. The dried sample was heat-treated at low temperature and its crystal structure, surface morphology and chemical composition were investigated.

• Ceramist
• /
• v.23 no.2
• /
• pp.114-131
• /
• 2020

Fracture in the titanium carbonitride-metal composites occurs by crack propagation through the carbonitride grains or in the interfaces. Thus, intrinsic properties of the carbonitride need to be enhanced and the interfaces should be also modified to coherent structure to strengthen the composites. Especially, interfacial structure can be the main factor to determine the mechanical properties of titanium carbonitride-metal composites because the interfaces between carbonitride grains and metallic phase are weak parts due to heterogeneous nature of carbonitride and metallic phase. In this paper, methodologies for improving the interfacial structure of titanium carbonitride-metal composites are suggested. Total area of the interfaces can be reduced using solid solution type carbonitrides as raw materials instead of a mixture of various carbonitrides in the composites. Also, synthesis of titanium carbonitride-metal composite powders and the low-temperature sintering of the composite powders for short time can be the way for formation of coherent interfaces. The sintering of the composite powders for short time at low temperature can reduce the potential of formation of interfaces by dissolution and precipitation of carbonitride in the liquid metal. As a result of formation of coherent boundaries due to low-temperature and short-time sintering, interfaces between titanium carbonitride grains and metallic phase have the favorable structure for the enhanced fracture toughness. It is believed that the low-temperature sintering of solid solution type composite powders for short time can be the way to improve the low toughness of the titanium carbonitride-metal composites.

• Korean Journal of Metals and Materials
• /
• v.46 no.5
• /
• pp.276-282
• /
• 2008

Material degradation of Cr steels in boiler tubes was accompanied by the microstructural changes including carbide behavior and crack formation. The microstructural change and the mechanical behavior of hardness and creep properties in accelerated heat-treatments were studied in order to identify the material degradation of the X20 Cr steel. The degradation behavior was occurred in the hardness increasing followed by decreasing due to carbide dissolution and precipitation.