• Journal of Pharmaceutical Investigation
• /
• v.34 no.3
• /
• pp.169-176
• /
• 2004

Acyclovir(ACV) is an important antiviral drug used extensively against infections caused by herpes viruses, especially herpes simplex and varicella zoster. Because of high crystallinity and large particle size, solubility of intact ACV is very low in water(1.3 mg/ml). The goal of this work is to enhance the solubility of ACV. To make solid dispersion, Polyethyleneglycol, Hydroxyprophylmethylcelluose and Polyvinylpyrrolidone were used as polymer carriers in this work. Polymer carriers and drug were dissolved in acetic acid. And then spray drying method and freeze drying method were used as solvent extraction. Morphology, crystallization and functional group were characterized using SEM, XRD and FT-IR. The result of in vitro test showed the sample using PVP as polymer carrier had higher dissolution rate(up to 466%) than intact ACV.

• Journal of the Microelectronics and Packaging Society
• /
• v.6 no.2
• /
• pp.69-74
• /
• 1999

Graphite and carbonaceous materials intercalate and deintercalate Li-ion reversibly into their layered structures. These materials show an excellent capacity for using a negative electrode in Li-ion batteries, because the electrochemical potential of Li-ion intercalated carbon is almost identical with that of lithium metal. Carbon used in this study was obtained by the pyrolysis of petroleum pitch, and heat-treated at the several temperatures between $700^{\circ}C$ and $1300^{\circ}C$. XRD analysis revealed that crystallization of carbon increased with increasing the heat treatment temperature. Charge/discharge properties were studied by a constant-current step at the rate of 0.1C, and the interfacial reaction between the electrolyte and the surface of carbon electrode was studied by cyclic voltammetry. Cell capacities were investigated in terms of the heat treatment temperature and the cycle number. Reversible capacity increased with the heat treatment temperature up to $1000^{\circ}C$, thereafter decreased continuously. Also, charge capacity decreased with the cycle number, while the reversibility improved with it.

• Journal of Pharmaceutical Investigation
• /
• v.34 no.6
• /
• pp.443-452
• /
• 2004

Habit is the description of the outer appearance of a crystal. If the environment of a growing crystal affects its external shape without changing its internal structure, a different habit results. Crystal habit and the internal structure of a drug can affect bulk and physicochemical properties, which range from flowability to chemical stability. A polymorph is a solid crystalline phase of a given compound resulting from the possibility of at least two different arrangements of the molecules of that compound in the solid state. Chemical stability and solubility changes due to polymorphism can have an impact on a drug's bioavailability and its development program. During crystallization from a solution, crystals separating may consist of a pure component or be a molecular compound. Solvates are molecular complexes that have incorporated the crystallizing solvent molecule in their lattice. When the solvent incorporated in the solvate is water, it is called a hydrate. To distinguish solvates from polymorphs, which are not molecular compounds, the term pseudopolymorph is used. Identification of possible hydrate compounds is important since their aqueous solubilities can be significantly less than their anhydrous forms. Conversion of an anhydrous compound to a hydrate within the dosage form may reduce the dissolution rate and extent of drug absorption. An amorphous solid may be treated as a supercooled liquid in which the arrangement of molecules is random. Amorphous solids lack the three-dimensional long-range order found in crystalline solids. Since amorphous forms are usually of higher thermodynamic energy than corresponding crystalline forms, solubilities as well as dissolution rates are generally greater. A study on crystal form includes characterization of (l)crystal habit, (2)polymorphism, (3)pseudopolymorphism, (4)amorphous solid.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.29 no.5
• /
• pp.222-228
• /
• 2019

In this study, we carried out the experiment to prepare lithium carbonate powder through gas-liquid reactions with a lithium-containing solution and $CO_2$ gas using lithium hydroxide, lithium chloride, and lithium sulfate. Thermodynamically, the carbonation reaction of a lithium-containing solution showed that aqueous reaction of lithium hydroxide occurs spontaneously, but aqueous reactions of lithium chloride and lithium sulfate does not occur spontaneously. In the case of lithium hydroxide solution, the recovery rate of lithium carbonate was 69.8 % at room temperature ($25^{\circ}C$), and increased to 89.4 % at $60^{\circ}C$. In the case of lithium chloride and lithium sulfate solution, lithium carbonate could be prepared using sodium hydroxide as an additive, but the recovery rates were 19.2 % and 16.7 %, respectively.

• Korean Chemical Engineering Research
• /
• v.60 no.4
• /
• pp.499-505
• /
• 2022

This study presents a conceptual design of vanillin production from Kraft lignin. Most of the existing Kraft lignin is used as low-quality boiler fuel or discarded as wastewater, and only 2% or less of lignin has been refined into high-quality products. We propose the process developed in this study to utilize discarded Kraft lignin. The existing vanillin production concept process consisted of alkali oxidation using NaOH, filtration, chromatography, and crystallization. Chromatography, which is difficult to commercialize, was changed to a solvent extraction process. The recovery rate of vanillin of the proposed solvent extraction process is 92.9%, and the purity is 99.5%, which is similar to the existing chromatography process. The reason why the solvent extraction process showing similar results to chromatography can replace the existing chromatography process was analyzed.

• Transactions of Materials Processing
• /
• v.32 no.5
• /
• pp.239-246
• /
• 2023

To reduce the forming load due to the temperature drop, during the hot forging process, a reheating hot forging process design is required that to repeat heating and forging. However, if the critical strain required for recrystallization is not induced during forging and grain growth becomes dominant due to the reduction in dislocation density due to repeated heating, the mechanical properties may deteriorate. Therefore, in this study, Inconel 706 alloy was applied, and the grain refinement behavior was comparatively analyzed according to the number of reheating times and effective strain during reheating hot forging process. Reheating was carried out with a total compression rate of 40% up to 4 times. The Inconel 706 compression test specimens heated once showed finer grains as the effective strain increased due to the dynamic recrystallization phenomenon. However, as the number of heating increases, grain refinement was observed even in a low effective strain distribution of 0.43 due to static recrystallization during reheating. Moreover, grain growth occurs at a relatively low effective strain of 0.43 when the number of reheating is four or more. Therefore, it was effective to apply an effective strain of 0.43 or more during hot forging to Inconel 706 in order to induce crystallization through grain refinement and improve the properties of forged products. In addition, we could notice that up to three reheating times condition was appropriate to prevent grain growth and maintain fine grain size.

• Journal of the Korean Magnetics Society
• /
• v.7 no.4
• /
• pp.173-179
• /
• 1997

Change in phases, microstructures, and magnetic properties by the variation of quench rate and heat treatment were investigated for melt-spun $Fe_{77}Pr_{15}C_8$ ribbons. The amorphization of as-spun ribbons increased as the quench rate increased. As a result, the ribbon quenched at 40 m/s was almost entirely amorphous. Similarly to cast alloys, the primary phase in crystalline ribbons quenched at 10 m/s was $\alpha$-Fe followed by the secondary $Fe_{17}Pr_2C_x$. Crystalline phases were still dominant in the ribbon spun at 20 m/s, but in this case crystallization of $Fe_{17}Pr_2C_x$ was remarkable with a little suppression of $\alpha$-Fe. At 30 m/s an amorphous phase obviously dominated in the as-spun ribbons with small fraction of crystals. Therefore, substantial amount of hard magnetic $Fe_{14}Pr_2C$ was not obtained from the as-spun state but, as in cast alloys, produced only by a solid-state transformation. Within a few minutes fine grains of $Fe_{14}Pr_2C$ were easily obtained at relatively low temperature when the degree of amorphization of as-spun ribbons was higher. The grain size of $Fe_{14}Pr_2C$ was well less than 1${\mu}{\textrm}{m}$. The ribbons quenched at 20 or 30 m/s yielded higher coercivities after heat treatment.

• Korean Journal of Food Science and Technology
• /
• v.36 no.2
• /
• pp.288-293
• /
• 2004

Differential scanning calorimetry (DSC) was used to study effects of sucrose and gluten on wheat starch glass transition, gelatinization, and retrogradation. Glass transition temperature ($T_{g}$) of wheat starch decreased as the ratio of sucrose or gluten to starch increased. Both peak temperature ($T_{G}$) and enthalpy values of gelatinization endotherm increased or decreased with increasing ratio of sucrose or gluten, respectively. Wheat starch gel with no sucrose and gluten recrystallized up to 4 weeks of storage at $4^{\circ}C$, whereas those with sucrose and gluten completed recrystallization within 1 week. Both wheat starch gels with no sucrose and gluten, and those with sucrose and gluten at storage temperature of $32^{\circ}C$ recrystallized up to 4 weeks, with wheat starch-sucrose-gluten (1 : 0.5 : 0.12) system, which had highest ratios of gluten and sucrose to starch, showing lowest recrystallization. Nucleation and propagation rates of starch gel recrystallization based on polymer crystallization principles can be converted into peak width (${\delta}T$) and peak temperature ($T_{R}$) of retrogradative endotherm by DSC, because higher nucleation rate at storage temperature of $4^{\circ}C$ close to $T_{g}$ showed higher ${\delta}T$, whereas higher propagation rate at $32^{\circ}C$ (close to $T_{G}$) had higher $T_{R}$.

• Proceedings of the IEEK Conference
• /
• 2000.06b
• /
• pp.80-83
• /
• 2000

In this work we deposited Pentacene thin film by OMBD at the various substrate temperatures, deposition rate and the various annealing temperatures for the fabrication of organic TFT and investigated the electrical and film surface characteristics such as sheet resistance, contact resistance and conductance Film thickness were measured by $\alpha$-step and the sheet resistance, contact resistance and conductance were extracted from the relation between the distance of the contacts and the resistance. During the film deposition the substrate temperature was held at 3$0^{\circ}C$, 4$0^{\circ}C$, 5$0^{\circ}C$, 6$0^{\circ}C$, 8$0^{\circ}C$ and 10$0^{\circ}C$, respectively. After the film deposition, Au contact was deposited by thermal evaporation. For the effect of annealing, the thin film was annealed in the nitrogen environment at 10$0^{\circ}C$ and 14$0^{\circ}C$ for 10 seconds, respectively. Film surface characteristics at the vatious substrate temperatures were measured by AFM. The crystallization of thin film was improved as the substrate temperatures were increased and the maximum gram size was 4${\mu}{\textrm}{m}$. The conductivity of thin film was found to be 7.40 $\times$10$^{-7}$ ~ 7.78$\times$10$^{-6}$ S/cm and the minimum contact resistance was 2.5324 ㏁.

• Applied Chemistry for Engineering
• /
• v.4 no.4
• /
• pp.721-730
• /
• 1993

Various catalysts of $Cu_xH_3-{_{2x}}PMo_{12}O_{40}{\cdot}_nH_2O$ with different x-values have been prepared and characterized by thermal analysis, X-ray powder diffraction, infrared spectroscopy, BET surface-area measurement, electron microscopy, and temperature programmed desorption of ammonia. The properties of these catalysts in acrolein oxidation have been investigated in a continuous-flow fixed-bed reactor. The catalysts lost their water of crystallization at about $200^{\circ}C$ and their constitutional water between 300 and $400^{\circ}C$. The Keggin structure of the catalysts was identified by infrared spectroscopy. The decomposition of Keggin anion, $(PMo_{12}O_{40})^{3-}$, was increased with the increase of substituted copper content and identifiable $MoO_3$ and $P_2O_5$ as decomposition products were observed. The conversion of acrolein decreased with the increase of x probably due to the decrease of specific surface area and of total amount of acid sites. But specific reaction rate and selectivity to acrylic acid were maximized at x=1.0, and it showed specific acid site distributions.