• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.192-202
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• 1996

In Li0.4Ca0.05AlP0.5Si0.75O4.5 composition glass, glass-ceramic having a near 100% crystallinity after nucleation heat treatment of 74$0^{\circ}C$/2 h and crystallization heat treatment of 90$0^{\circ}C$/2 h and in-situ TiO2 whisker reinforced glass-ceramic after heat treatment of 105$0^{\circ}C$ for 20 h were fabricated with the addition of 4% TiO2 as a nucleating agent. With these materials a ball-on-disc type wear test was conducted in order to examine the effect of TiO2 whisker prepcipitation on ambient and high temperature wear properties of the glass-ceramic. Wear test results indicated that all specimens exhibited micro-fracture wear mechanism in ambient temperature. As temperature increased the wear rates of the materials were increased. However the in-situ TiO2 whisker reinforced glass-ceramic exhibited the lowest wear rate over the test temperature range. This resulted from the improvement of harness and fracture toughness of the material as the glass converted into the glass-ceramic followed by precipitation of TiO2 whiskers throughout the glass-ceramic matrix.

• Journal of Applied Biological Chemistry
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• v.49 no.4
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• pp.157-161
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• 2006

The performance of abiotic degradation of oxadiazon was investigated by applying zerovalent iron(ZVI), potassium permanganate($KMnO_4$) and titanium dioxide($TiO_2$) in the contaminated water. Experimental conditions allowed the disappearance of oxadiazon in the abiotic system. The degradation of this herbicide was monitored in buffer solutions having pH 3, 5 and 7 in the presence of iron powder in which the maximum degradation rate was achieved at acidic condition(pH 3) by 2% of ZVI treatment. The oxidative degradation of oxadiazon was observed in aqueous solution by $KMnO_4$ at pH 3, 7 and 10 in which the highest disappearance rate was found at neutral pH when treated with 2% of $KMnO_4$. The catalytic degradation of oxadiazon in $TiO_2$ suspension was obtained under dark and UV irradiation conditions. UV irradiation enhanced the degradation of oxadiazon in aquatic system in the presence of $TiO_2$. Conclusively, the remediation strategy using these abiotic reagents could be applied to remove oxadiazon from the contaminated water.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.394-400
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• 2018

The current work investigates the effects of nucleation heat treatments, on the microstructure and mechanical properties of a novel silicate glass in $Li_2O-BaO-SiO_2$ system with 1 mol% $P_2O_5$ as nucleating agent. As-cast glass was exposed to nucleation heat treatments at $490-550^{\circ}C$ for 1-3 h. The microstructural examination was performed by SEM/EDS. The highest Vickers microhardness was determined to be 650 Hv for the sample heat treated at $550^{\circ}C$ for 1 h. The increase in the nucleation time also affected Vickers microhardness and the highest one was determined to be 600 Hv after nucleation for 3 h. The fracture toughness, $K_{IC}$ reached $2.51MPa.m^{1/2}$ after nucleation at $550^{\circ}C$ for 1 h. The nucleation temperatures had a more pronounced effect on the fracture toughnesses in comparison to nucleation times. The indentation toughness data was used to determine Weibull parameters from Ln ln [1/(1-P)]-$lnK_{IC}$ plots. Weibull modulus, m of the samples nucleated at 500, 510, 530, $550^{\circ}C$ for 1h. and $540^{\circ}C$ for 2 h. were determined similarly to be 3.8, 3.5, 4.7 and 3.9, respectively. The rest of the samples indicated higher Weibull moduli, which may be attributed to the formations of microcracks due to the mismatch in between newly formed crystals and remaining glassy matrix.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.799-807
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• 1990

In this study, effects of oxide additives on mechanical properties and microstructure of A1N and A1N polytype ceramics were investigated. Fine A1N powder was synthesized by nitriding alumiuim hydroxide prepared from Al-isopropoxide, at 1350$^{\circ}C$ for 10h in N2 atmosphere. By adding 3w/o Y2O3, 0.56w/o CaO, and 10w/o SiO2 to AlN powder, AlN and AlN polytype ceramics were prepared by hot-pressing under the pressure of 30 MPa at 1800$^{\circ}C$ for 1h. AlN ceramics with no additives formed considerable amount of AlON phase, while AlN ceramics doped with Y2O3 or CaO decreased AlON phase and formed Y-Al or Ca-Al oxide compound. AlN＋10w/o SiO2(＋3w/o Y2O3) composition produced AlON and AlN polytype compound having 21R as a major phase. Room temperature flexural strength of AlN ceramics with no additive was 246MPa, and room temperature flexural strength and critical temperature difference by thermal shock(ΔTc) of AlN ceramics dooped with Y2O3 or CaO were 532MPa/340$^{\circ}C$ and 423MPa/300$^{\circ}C$, respectively. Y2O3 and CaO used as sintering agent played roles of densification and oxygen removal of AlN ceramics, and affected grain growth/grain morphologies of AlN ceramics.

• Journal of the Korean Chemical Society
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• v.24 no.1
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• pp.8-14
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• 1980

Solvolysis rate constants for methylchloroformate, $CH_3O$(CO)Cl, methylthiono-chloroformate, $CH_3O$(CS)Cl, and methylthiolchloroformate, $CH_3S$(CO)Cl, have been determined conductometrically in acetone-water and acetonitrile-water mixtures, and activation parameters, ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$, have been derived. Results show that in water-rich regions the order of rate increases as $$CH_3O(CO)Cl while in dipolar aprotic solvent-rich region this order reverses. The plots of log k vs. solvent parameters, Y, $\frac{D-1}{2D+1}$ and log($H_2$) show that the order of rate increase in water-rich region is the results of increase in $S_N1$ character. It is concluded that $CH_3S$(CO)Cl solvolyzes via $S_N1$ mechanism whereas $CH_3O$(CO)Cl reacts via $S_N2$ and $CH_3O$(CS)Cl via intermediate mechanism in water-rich region.

• The Korean Journal of Ceramics
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• v.1 no.3
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• pp.131-136
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• 1995

It has been reported that the biocement obtained by mixing $CaO-SiO_2-P_2O_5$ glass powders with ammonium phosphate solution has biocompatibility as will as high strength. The hardening mechanism and hydroxyapatite forming mechanism were discussed when $53.6%CaO_1,\; 38.1%SiO_2,\; 7.7P_2O_6,\; 0.6%CaF_2$(mole %) glass powder was reacted with ammonium phosphate solution and reacted in tris-buffer solution, respectively. High strength hardened biocement was obtained for the specimen with $CaNH_4PO_4\;H_2O$ crystal when the glass powder was mixed with ammonium phosphate solution, and hydroxyapatite crystal was rapidly formed only in the sample with $CaNH_4PO_4\;H_2O$ crystal when it was reacted in tris-buffer solution.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.35.2-35.2
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• 2015

We present the results of simultaneous observations of the H2O and SiO masers emitted from the circumstellar envelopes (CSEs) of the late-type stars. These observations have been carried out at the four frequency bands (K, Q, W and D bands) using KVN to apply the source frequency phase referencing (SFPR) analysis to the maser lines. We obtain the relative positions between the H2O and the SiO maser spots by using the SFPR method, which are very important to study the physical links between the inner and the outer parts of the CSEs of the late-type stars. The relative positions between the SiO maser spots of the different transitions are also obtained very accurately, which are very crucial to investigate the pumping mechanism of the SiO maser lines. From our results, the capability of the simultaneous multi-band observation of KVN is proved to be powerful to study the complicated physical environments of the CSEs and the stellar evolution of the late-type stars.

• Korean Chemical Engineering Research
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• v.46 no.5
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• pp.868-874
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• 2008

The Ni based adsorbent was prepared by co-precipitation method and its performance for removing carbon monoxide was investigated. Here, silica, aluminium silicate and ${\gamma}$-alumina were used for carriers of catalyst. $Ni(NO_3)_2{\cdot}6H_2O$ and $Ni(CH_3COO)_2{\cdot}4H_2O$ were utilized for Ni precursors. Precipitants were urea and citric acid. After precipitation of Ni salt on the carrier and following reduction using $H_2$ gas, adsorbent was prepared and its performance was analyzed based on EDS, TPR and XRD experiments. In accordance with change of precipitation agents, Ni salts on carrier, carriers and reduction condition. Adsorbent performance for removing carbon monoxide was investigated. The adsorbent with 54.8 wt% Ni prepared using urea precipitant under reduction condition at $500^{\circ}C$ for 3 h exhibited the best CO removal performance.

• Korean Chemical Engineering Research
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• v.59 no.2
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• pp.281-295
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• 2021

In this study, the direct amination of ethanol was performed over impregnated Ni on SiO2-Al2O3 mixed oxide catalysts prepared by varying Si/(Si + Al) molar ratio to 30 mol%. To characterize the physico-chemical properties of the catalysts used, X-ray diffraction (XRD), N2-physisorption, temperature-programmed desorption of iso-propyl alcohol (IPA-TPD), temperature-programmed desorption of ethanol (EtOH-TPD), temperature-programmed reduction with H2 (H2-TPR), H2-chemisorption and transmission electron microscopy (TEM) were used. The acidic property was continuously increased until Si/(Si + Al) = 30 mol% in SiO2-Al2O3 mixed oxides used. The dispersion of Ni metal and surface area, acid characteristics of the supported Ni catalyst have a complex effect on the catalytic reaction activity. The low reduction temperature of nickel oxide and acidic properties were beneficial to the formation of acetonitrile. In terms of conversion of ethanol, Ni/SiO2-Al2O3 catalyst with a molar ratio of 10 mol% Si/(Si+Al) showed the highest activity and a volcanic curve based on it. The tendency of results were consistent in the metal dispersion and catalytic activity.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 1999.11a
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• pp.111-115
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• 1999

The $Li_2O-MgO-MgF_2-SiO_2$glasses with addition of $B_2O_3$ were investigated in order to make glass-ceramics for low temperature firing substrate. Glasses were made by melting at $1450^{\circ}C$ in the electronic furnace and crystallized at $750^{\circ}C$. After the crystallization, crystal phases and microstructure were observed. The crystal phases were polycrystalline of lithium boron fluorphlogopite and lithium fluorhectorite. The crystal shape was changed to grande type from needle type with the increase in $B_2O_3$ contents. Average particle size of the glass-ceramics aftar water swelling was $3.77{\mu}{\textrm}{m}$. The optimum sintering temperature and sintering shrinkage of the substrate were $900^{\circ}C$ and 13.4vol%, respectively.