• Journal of the Korean Ceramic Society
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• v.31 no.11
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• pp.1249-1258
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• 1994

Titanium carbide was synthesized by reacting the prepared titanium powder and carbon black using SHS method sustains the reaction spontaneously, utilizing heat generated by the exothermic reaction itself. In this process, the effect of the particle size of titanium powder on combustion temperature and combustion wave velocity was investigated. By controlling combustion temperature and combustion wave velocity via mixing Ti and C powder with TiC, the reaction kinetics of TiC formation by SHS method was considered. Without reference to the change of combustion temperature and combustion wave velocity, TiC was easily synthesized by combustion reaction. As the particle size of titanium powder was bigger, or, as the amount of added diluent(TiC) increased, combustion temperature and combustion wave velocity were found to be decreased. The formation of TiC by combustion reaction in the Ti-C system seems to occur via two different mechanisms. At the beginning of the reaction, when the combustion temperatures were higher than 2551 K, the reaction was considered to be controlled by the rate of dissolution of carbon into a titanium melt with an apparent activation energy of 148 kJ/mol. For combustion temperatures less than 2551 K, it was considered to be controlled by the atomic diffusion rate of carbon through a TiC layer with an apparent activation energy of 355 kJ/mol. The average particle size of the synthesized titanium carbide was smaller than that of the starting material(Ti).

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.99-105
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• 2011

Lead titanate ($PbTiO_3$) powder was prepared from lead nitrate ($Pb(NO_3)_2$) and titania ($TiO_2$) by hydrothermal route. Phase formation process was investigated by observing the phases formed in various experimental conditions like different KOH concentration, reaction temperature and time. $PbTiO_3$ powder was fabricated when the KOH concentration was 0.8M or higher. An intermediate compound, $PbTi_{0.8}O_{2.6}$, was formed at first by a reaction between PbO and $TiO_2$ and changed into $PbTiO_3$ powder with a perovskite crystal structure. A $PbTiO_3$ phase was formed in a shorter time when a KOH concentration was increased from 0.8M to 8M because a driving force for a $PbTiO_3$ formation was increased due to an increase in a degree of supersaturation. And $TiO_2$ (rutile) and $3PbO{\cdot}H_2O$ were observed at room temperature in a 0.8M KOH solution and $TiO_2$(rutile) and PbO (litharge) in a 8M KOH. A $PbTiO_3$phase was also formed in a shorter time at a higher reaction temperature as a reaction temperature influenced the rates for a dissolution and a precipitation.

• Journal of the Mineralogical Society of Korea
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• v.26 no.1
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• pp.45-54
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• 2013

In order to dissolve Au, Ag, and other valuable metals from gold ore concentrate, raw gold concentrate was pre-treated by roasting and salt-roasting at $750^{\circ}C$. The roasted concentrate was treated with aqua regia digestion to dissolve the valuable metals and higher amount of Au, Ag, and valuable metals were extracted from the roasted concentrates than from the raw concentrate. Higher amount of these metals were also extracted from the salt-roasted concentrate than from the roasted concentrate. The results of the gold dissolution experiments showed that the gold dissolution was most efficient when particle size, roasting temperature, and the percentage of added salt in salt roasting were about $181{\sim}127{\mu}m$, $750^{\circ}C$, and was 20.0%, respectively. The XRD analysis suggests that quartz and pyrite were not destroyed even through roasting at $750^{\circ}C$ and decomposition with aqua regia. However, through salt roasting, pyrite was completely decomposed, whereas quartz could not be destroyed through salt-roasting at $750^{\circ}C$ and aqua regia digestion. Accordingly, it was expected that the gold contained in quartz can not be dissolved through salt-roasting and treatment with aqua regia.

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.150-155
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• 1999

The Electrochemical stabilities of the Brewer-Engel type intermetallic compounds of Co-Mo $(35 wt\%)$ and Ni-Mo$(35 wt\%)$ manufactured by the arc-melting method for the hydrogen electrode of $H_2-O_2$ alkaline fuel cell were investigated. Effects of temperature and concentration on the electrochemical behavior of the electrodes in the $80^{\circ}C$ 6 N KOH solution deaerated with $N_2$ gas were studied by electrochemical methods. The effect of overpotential on the electrochemical stabilities of Co-Mo and Ni-Mo intermetallic compounds was also discussed under the normal operation condition of AFC. It was shown that Co-Mo electrode had lower electrochemical stability as compared to Ni-Mo. In the case of Co-Mo electrode, a simultaneous dissolution of cobalt and molybdenum has occurred at low anodic overpotential form equilibrium hydrogen electrode potential, but the dissolution of cobalt was serious, and Co(OH)l layer on the electrode surface formed at the high anodic overpotential. In contrast the Ni-Mo electrode had high electrochemical stability because formation of the dense and thin protective $Ni(OH)_2$ layer prevented the dissolution of molybdenum.

• Resources Recycling
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• v.13 no.1
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• pp.14-21
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• 2004

Spent catalysts containing platinum were generated in petroleum refinery and other chemical industries. The reclamation of platinum metals from such wastes has long been attempted in view of their rare, expensive and indispensable nature. In this study, the recovery of platinum from petroleum catalysts was attempted by a method consisting mainly of dissolving alumina carrier with sulfuric acid thereby concentrating insoluble platinum. Also, platinum dissolved partially in sulfuric acid was recovered by a cementation method using aluminum metal as a reductive agent. The effect of temperature, time, concentration of sulfuric acid, and pulp density on the dissolution of carrier was investigated. When the carrier of platinum catalyst was $\Upsilon-Al_2$O$_3$ about 95% alumina was dissolved in 6.0 M sulfuric acid at $100^{\circ}C$ for 2 hours. When the carrier was the mixture of $\Upsilon-Al_2$$O_3$ and $\alpha$-$Al_2$$O_3$ about 92% was dissolved after 4 hours. As a result, more than 99% of platinum could be recovered by this method and aluminum sulfate was also obtained as byproduct.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1999.04a
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• pp.5-5
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• 1999

The Principal deficiency of the existing notion about the sintering-mixtures consists in the fact that almost no attention is focused on the Phenomenon of alloy formation during sintering, its connection with dimensional changes of powder bodies, and no correct ideas on the driving force for the sintering process in the stage of establishing chemical equilibrium in a system are available as well. Another disadvantage of the classical sintering theory is an erroneous conception on the dissolution mechanism of solid in liquid. The two-particle model widely used in the literature to describe the sintering phenomenon in solid state disregards the nature of the neighbouring surrounding particles, the presence of pores between them, and the rise of so called arch effect. In this presentation, new basic scientific principles of the driving forces for the sintering process of a two-component powder body, of a diffusion mechanism of the interaction between solid and liquid phases, of stresses and deformation arising in the diffusion zone have been developed. The major driving force for sintering the mixture from components capable of forming solid solutions and intermetallic compounds is attributed to the alloy formation rather than the reduction of the free surface area until the chemical equilibrium is achieved in a system. The lecture considers a multiparticle model of the mixed powder-body and the nature of its volume changes during solid-state and liquid-phase sintering. It explains the discovered S-and V-type concentration dependencies of the change in the compact volume during solid-state sintering. It is supposed in the literature that the dissolution of solid in liquid is realised due to the removal of atoms from the surface of the solid phase into the melt and then their diffusicn transfer from the solid-liquid interface into the bulk of liquid. It has been shown in our experimental studies that the mechanism of the interaction between two components, one of them being liquid, consist in diffusion of the solvent atoms from the liquid into the solid phase until the concentration of solid solutions or an intermetallic compound in the surface layer enables them to pass into the liquid by means of melting. The lecture discusses peculimities of liquid phase formation in systems with intermediate compounds and the role of the liquid phase in bringing about the exothermic effect. At the frist stage of liquid phase sintering the diffusion of atoms from the melt into the solid causes the powder body to grow. At the second stage the diminution of particles in size as a result of their dissolution in the liquid draws their centres closer to each other and makes the compact to shrink Analytical equations were derived to describe quantitatively the porosity and volume changes of compacts as a result of alloy formation during liquid phase sinteIing. Selection criteria for an additive, its concentration and the temperature regime of sintering to control the density the structure of sintered alloys are given.

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.110-117
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• 2005

In this work, solid-state inclusion complex powders of itraconazole and $2-hydroxypropyl-{\beta}-cyclodextrin(HP-{\beta}-CD)$ were produced by a supercritical anti-solvent (SAS) process. In order to evaluate the degree of complexation, the thermal behavior of the microparticulate complexes was investigated using differential scanning calorimetry. The experimental results obtained for the solubility and dissolution rate of the microparticulate inclusion complexes in a buffer solution of pH 1.2 showed that the complexation of itraconazole with $HP-{\beta}-CD$ results in a significant increase in the solubility and dissolution rate of itraconazole. The particle size of the SAS-produced inclusion complexes was dramatically reduced ($<0.1-0.5{\mu}m$) compared with untreated itraconazole ($30-50{\mu}m$) and $HP-{\beta}-CD$ ($50-100{\mu}m$). The solubility of itraconazole was increased with the increase of pressure at a constant temperature to ca. $758.6{\mu}g/mL$ in an aqueous medium of pH 1.2. The dissolution rate of itraconazole was observed to be significantly improved and about 90% of itraconazole was found to be dissolved within 5-10 min.

• Resources Recycling
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• v.29 no.1
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• pp.25-34
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• 2020

Electrochemical Quartz Crystal microbalance is a tool that is capable of measuring nanogram-scale mass change on electrode surface. When applying alternating voltage to the quartz crystal with metal electrode formed on both sides, a resonant frequency by inverse piezoelectric effect depends on its thickness. The resonant frequency changes sensitively by mass change on its electrode surface; frequency increase with metal dissolution and decrease with metal deposition on the electrode surface. The relationship between resonant frequency and mass change is shown by Sauerbrey equation so that the mass change during metal dissolution can be measured in real time. Especially, it is effective in the case of reaction mechanism and rate studies accompanied by precipitation, volatilization, compound formation, etc. resulting in difficulties on ex-situ AA or ICP analysis. However, it should be carefully considered during EQCM experiments that temperature, viscosity, and hydraulic pressure of solution, and stress and surface roughness can affect on the resonant frequency. Application of EQCM was shown as a case study on leaching of platinum using aqueous chlorine for obtaining activation energy. A platinum electrode of quartz crystal oscillator with 1000 Å thickness exposed to solution was used as leaching sample. Electrogenerated chlorine as oxidant was purged and its concentration was controlled in hydrochloric acid solution. From the experimental results, platinum dissolution by chlorine is chemical reaction control with activation energy of 83.5 kJ/mol.

• Journal of the Mineralogical Society of Korea
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• v.32 no.2
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• pp.79-86
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• 2019

The white aluminum phases in acid mine drainage usually precipitates when mixed with stream waters with relatively high pH. The minerals in white precipitates play important roles in controlling the behavior of heavy metals by adsorbing and coprecipitation. By the phase transition of these minerals in white precipitates, dissolution and readsorption of heavy metals may occur. This study was conducted to obtain preliminary information on the phase transition of the mineral phases in white precipitates. In this study, the mineral phase changes in the white precipitates collected from the stream around Dogye Mining Site over time were investigated with different pH values and temperatures. White precipitates consist mainly of basaluminite, amorphous $Al(OH)_3$ and a small amount of $Al_{13}$-tridecamer. During aging, the incongruent dissolution of the basaluminite occurs first, increasing the content of the amorphous $Al(OH)_3$. After that, pseudoboehmite is finally precipitated following the precursor phase of pseudoboehmite. At $80^{\circ}C$, this series of processes was clearly observed, but at relatively low temperatures, no noticeable changes were observed from the initial condition with coexisting basaluminite and amorphous $Al(OH)_3$. At high pH, the desorption of $SO{_4}^{2-}$ group in basaluminite was initiated to promote phase transition to the pseudoboehmite precursor. Over time, the solution pH decreases due to the dissolution and phase transition of the minerals, and even after the precipitation of pseudoboehmite, only the particle size slightly increased but no clear cystal form was observed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.138-141
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• 2008

The effects of annealing temperature and time on mechanical properties and microstructures were investigated in cold drawn pearlitic steel wires. During annealing, the increment of the tensile strength at low temperatures found to be due to age hardening, while the decrease in the tensile strength at high temperatures was attributed to age softening, involving the spheroidization of lamellar cementite and recovery of lamellar ferrite. Since tensile strength and the occurrence of the delamination would be closely related to the dissolution of cementite, the lower annealing temperature and the increase of drawing strain caused the higher tensile strength and the easier occurrence of the delamination in cold drawn pearlitic steel wires.