• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.119-124
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• 2016

Plasma electrolytic oxidation (PEO) is a promising coating process to produce ceramic oxide on valve metals such as Al, Mg and Ti. The PEO coating is carried out with a dilute alkaline electrolyte solution using a similar technique to conventional anodizing. The coating process involves multiple process parameters which can influence the surface properties of the resultant coating, including power mode, electrolyte solution, substrate, and process time. In this study, ceramic oxide coatings were prepared on commercial Al alloy in electrolytes with different KOH concentrations (0.5 ~ 4 g/L) by plasma electrolytic oxidation. Microstructural and electrochemical characterization were conducted to investigate the effects of electrolyte concentration on the microstructure and electrochemical characteristics of PEO coating. It was revealed that KOH concentration exert a great influence not only on voltage-time responses during PEO process but also on surface morphology of the coating. In the voltage-time response, the dielectric breakdown voltage tended to decrease with increasing KOH concentration, possibly due to difference in solution conductivity. The surface morphology was pancake-like with lower KOH concentration, while a mixed form of reticulate and pancake structures was observed for higher KOH concentration. The KOH concentration was found to have little effect on the electrochemical characteristics of coating, although PEO treatment improved the corrosion resistance of the substrate material significantly.

• Journal of the Korean Vacuum Society
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• v.11 no.4
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• pp.249-255
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• 2002

For a formation of membrane structures, single crystal silicon wafers have been anisotropically etched with solutions of KOH and KOH-IPA. The etching rate was observed to be strongly dependent upon the etchant temperature and concentration. Mask patterns for the etching experiment was aligned to incline $45^{\circ}$on the primary flat of the silicon wafer. The different etching characteristics were observed according to pattern directions and etchant concentration. When the KOH concentration was fixed to 20 wt%, the U-groove etching shape was observed for the etching temperature of above $80^{\circ}C$, and V-groove shapes observed at below $80^{\circ}C$. Hillocks, which were generated at the etched silicon surfaces, has been decreased as the increasing of the etchant temperature and concentration.

• Journal of Environmental Science International
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• v.12 no.12
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• pp.1321-1327
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• 2003

Two different kinds of cases, with and without addition of noncrystalline silica to the Hadong kaolin were studied to obtain useful information on the synthesis of zeolite. The research was carried out to investigate the formation area and the crystalized degree of zeolite according to a synthetic time, the water content of raw material mixture, KOH concentration, and stirring intensity. In the case of without addition of noncrystalline silica to the Hadong kaolin and the low concentration range of KOH, the structure of the kaolin was not changed. However, when the mole ratio of K2O/SiO$_2$ in natural kaolin was increased, Linde-L zeolite and unknown structure of kaolins, U-1 and U-2 were produced. While in the high concentration range of KOH, the unknown structure of kaolins, U-6 and U-2, were produced and the production rate of U-6 was increased with the increased of K2O/SiO$_2$ mole ratio. In the case of with addition of noncrystalline silica to the Hadong kaolin and treatment with KOH hydrothermal processing, ZSM-5, ZSM-35, and Linde-L zeolites and the mixture of unknown structure of zeolites, U-1, U-2, U-3, and U-4, were obtained. Both cases demonstrated that the synthesis of zeolite from the Hadong kaolin was highly influenced by KOH concentration of raw material mixture.

• Elastomers and Composites
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• v.14 no.4
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• pp.231-252
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• 1979

Polymerization of 2-pyrrolidone was carried out through anionic mechanism using $SO_2/KOH$ as catalyst. The effects of KOH concentration, $SO_2/KOH$ mole ratio and temperature on polymerization were investigated. The conversion and viscosity of polymers were measured at various polymerization conditions. It was observed that as the concentration of KOH was increased, equilibrium conversion was also increased. It was, however, found that after the concentration of KOH was reached above 8 mole percent, the equilibrium conversion was decreased. The highest rate of polymerization and maximum conversion were obtained when $SO_2/KOH$ mole ratio was around 0.5. It was also found that the rate of polymerization and the equilibrium conversion were higher at $50^{\circ}C$. than at $30^{\circ}C$. but the viscosity of polymer solution at $50^{\circ}C$. was not so high as expected. The rate constant, $K_p$ of polymerization, was determined by least square method: the value of $K_p$ was observed as 16 liter/mole hour at $50^{\circ}C$. and 2.6 liter/mole hour at $30^{\circ}C$., respectively. The mechanism of polymerization was also discussed.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.38 no.1
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• pp.31-37
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• 1993

To analyze and classify the varietal variation of alkali digestibility in detail, which is closely connected with the gelatinization temperature and physical characteristics of cooked rice, the patterns of alkali decomposition changed along the alkali concentration were investigated for thirty three Korean leading rice cultivars and new breeding lines(japonica : 25, Tongil-type:8) including five glutinous rice. Principal component analysis was used to condense the information and to classify rice materials according to decomposed reaction pattern at several levels of potassium hydroxide(KOH) concentration. Thirty three rice varieties were classified largely into four groups by the distribution on the plane of upper two principal component scores which contained above 92% of total informations. Group I was consisted of one variety, Dobongbyeo, which owned almost same strong resistance to alkali digestion at the range of 0.8% to 1.6% KOH solutions. Group II included three japonica and Tongil-type glutinous rice varieties, which revealed medium alkali digestion value(ADV) at 1.4% KOH solution and intermediate change in ADV from 0.8% to 1.6% KOH solutions. Most of Tongil-type and early-maturity japonica rice, which exhibited medium-high ADV at 1.4% of KOH concentration and large ADV difference between low and high alkali solutions, were contained in Group III. Group N included most of medium or medium-late-maturity japonica, which showed high ADV at 1.4% KOH and medium or intermediate-high ADV change between low and high alkali solutions. The 1st principal component indicated the average index of ADV through 0.8-1.6% KOH solutions and the 2nd principal component pointed out the factor related with ADV difference between low and high alkali solutions or regression coefficients of ADV change along with the KOH concentrations.

• Polymer(Korea)
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• v.37 no.5
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• pp.592-599
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• 2013

In this study, polyacrylonitrile (PAN)-based porous carbon nanofibers were prepared from PAN polymer solution by electrospinning and KOH activation with various concentrations, and the characterization of pore structures and carbon dioxide adsorption was investigated. Manufactured PAN-based activated carbon nanofibers tend to decrease diameter and increase surface oxygen functional groups depending on the increasing concentration of KOH solution. In addition, according to the results of nitrogen adsorption for pore properties analysis, it indicated increase of the specific surface area in conformity with increasing concentration of KOH solution. Micropore volume of treated activated carbon nanofibers (ANCF) by 4 M KOH was the largest compared with other samples and mesopore volume of treated ANCF by 8 M KOH was the largest volume, respectively. The concentration of KOH effects textural and surface properties, as represented by BET and XPS, which enhance carbon dioxide adsorption capacity at 0 and $25^{\circ}C$.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.798-803
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• 2019

The self-discharge behavior of zinc-air batteries is a critical issue induced by corrosion and hydrogen evolution reaction (HER) of zinc anode. The corrosion reaction and HER can be controlled by a gelling agent and concentration of potassium hydroxide (KOH) solution. Various concentrations of KOH solution and polyacrylic acid have been used for gel electrolyte. The electrolyte solution is prepared with different concentrations of KOH (6 M, 7 M, 8 M, 9 M). Among studied materials, the cell assembled with 6 M KOH gel electrolyte exhibits the highest specific discharge capacity and poor capacity retention. Whereas, 9 M KOH gel electrolyte shows high capacity retention. However, a large amount of hydrogen gas is evolved with 9 M KOH solution. In general, the increase in concentration is related to ionic conductivity. At concentrations above 7 M, the viscosity increases and the conductivity decreases. As a result, compared to other studied materials, 7 M KOH gel electrolyte is suitable for Zn-air batteries because of its higher capacity retention (92.00 %) and specific discharge capacity (351.80 mAh/g) after 6 hr storage.

• Fashion & Textile Research Journal
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• v.7 no.1
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• pp.91-95
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• 2005

The purpose of this study is to investigate the improvement of fiber surface, physical properties and research the physical properties and dyeability of cotton fabrics treated with KOH solution at low and high temperature. The treatment conditions for mercerization with KOH were changed various temperatures(25, $90^{\circ}C$), concentrations(15, 20, 25, 30%. w/v) and times(30, 60, 180, 300sec). The effects of mercerization after KOH treatment estimated with tensile strength, tearing strength, shrinkage, drape stiffness, moisture regain, fiber surface, and dyeability. The optimal conditions were concentration of KOH 20%, time 180sec in low temperature and concentration of KOH 20%, time 60sec in high temperature. The results are as follows; Tensile strength, tearing strength and moisture regain were much improved than those of untreated cotton fabric. Shrinkage and drape stiffness of KOH treated cotton were more increased at $25^{\circ}C$ than $90^{\circ}C$. Fiber surface showed more rounded shape at $25^{\circ}C$ than $90^{\circ}C$. Dyeability of cotton fabrics improved by KOH treatment.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.393-396
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• 1997

Electro Discharge Machining (EDM) is a so-call non-conventional machining technique. This paper presents the experimental results of an EDM technique for the fabircation of microholes on #7440 pyrex glans. With various applied voltages and at various concentration of KOH solution, the glass substrate have been microdrilled using the copper electrodes of which diameters are 250$\mu\textrm{m}$ to 450$\mu\textrm{m}$, respectively. The machined throughholes have been observed the top diameter, the bottom diameter, hollow width and hole diameter of the hole, and machining time hale been measured. The experimental results show that the machining time decreases as the concentration of KOH solution increases or the applied voltage increase. Also, The top diameter increases as the concentration of KOH solution decreases or the allied voltage increases. The bottom and hollow width decreases as the of KOH solution increases or the applied voltage decreases.

• Journal of the Korean Electrochemical Society
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• v.4 no.4
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• pp.166-171
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• 2001

In an aluminum-air unit cell used alkaline solution, Hydrogen evolution rates were investigated far the observation of the effects of alloy element, inhibitor and its concentration in electrolyte, KOH concentration, solution temperature, and current density loaded to cell. Hydrogen evolution rates were reduced up to $50\%$ by saturating the solution with ZnO, while ZnAc(Zinc Acetate) did not work as inhibitor. The inhibition effect of ZnO increased with increasing the KOH concentration and solution temperature. They were linearly increased with the KOH concentration and current density in first order and exponentially increased with the solution temperature.