• 한국세라믹학회지
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• 제25권5호
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• pp.561-569
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• 1988

Mixtures of very small amounts of additive, carbon and silica(about 0.46${\mu}{\textrm}{m}$) which synthesized by the hydrolysis of ethyl silicate, the molar ratio of SiO2/C was fixed to 1/10, was nitrided at 145$0^{\circ}C$. It was considered that the optimum amount of additive to promote the nitridation reaction was below 2.0wt%. By the addition of additive, the nitridation reaction was promoted and formation of $\beta$-Si3N4 was promoted at 145$0^{\circ}C$ for 1hour, but, the nitridation reaction was decreased and the ratio of $\alpha$/$\beta$ of Si3N4, was increased at 145$0^{\circ}C$ for 5 hours. The crystal phase was $\alpha$ phase and the nitridation reaction was promoted and the particle size of silicon nitride was become smaller by the addition of $\alpha$-Si3N4, but silicon nitride of whisker-like form was produced by the addition of transition elements. There was a difference in the lattice constants of $\alpha$-Si3N4, but no difference in its of $\beta$-Si3N4 according to kinds of added substance and reaction time.

• 펄프종이기술
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• 제41권5호
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• pp.26-32
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• 2009

As a part of utilizing the nanocellulose (NC) from lignocellulosic components of wood biomass, this paper reports preliminary results on the products of sulfuric acid hydrolysis. The purpose of this study was to investigate the morphology of both NC and micro-sized cellulose fiber (MCF) isolated by acid hydrolysis from commercial microcrystalline cellulose (MCC). Field emission.scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were employed to observe the acid hydrolysis suspension, NC, and MCF. The electron microscopy observations showed that the acid hydrolysis suspension, before separation into NC and MCF by centrifugation, was composed of nano-sized NCs and micro-sized MCFs. The morphology of isolated NCs was a whisker form of rod-like NCs. Measurements of individual NCs using TEM indicated dimensions of 6.96$\pm$0.87 nm wide by 178$\pm$55 nm long. Observations of the MCFs showed that most of the MCC particles had de-fibered into relatively long fibers with a diameter of 3-9 ${\mu}m$, depending on the degree of acid hydrolysis. These results suggest that proper technologies are required to effectively realize the potentials of both NCs and MCFs.

• 한국세라믹학회지
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• 제45권2호
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• pp.99-104
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• 2008

Zeta potential, sedimentation bulk density and rheology in the dispersion system have been studied in terms of solid loading (40-55 vol%), and types of additives. Ammonium polymethacrylate, glycerol, ethoxylated acetylenic diol, and polyvinyl alcohol have been used as the dispersant, cryo-protectant, surfactant, and binder, respectively. Sedimentation density greatly increased upon adding dispersant; the effect was more pronounced with ionic alumina suspension compared with covalent silicon carbide. With further addition of cryo-protectant and surfactant to dispersant, the sedimentation density increased somewhat. The suspension viscosity generally behaviored in an opposite manner to the sedimentation density, i.e., high sedimentation gave low high-shear viscosity, indicative of low order structure formation in the suspended particles. Shear rate rheology in shear rate of $2-300\;sec^{-1}$ showed a shear thinning and its onset began at similar shear rate (${\sim}100\;sce^{-1}$), regardless of solid loading.

• 한국세라믹학회지
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• 제40권8호
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• pp.720-724
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• 2003

Aluminum nitride (AlN) powders were synthesized by using a mixture of an aluminum nitrate or sulfate salt and carbon (mole ratio of $Al^{3+}$ to carbon=L : 30). The AlN was obtained by calcining the mixture under a flow of nitrogen in the temperature range 1100-1$600^{\circ}C$ and then burning out the residual carbon. The process of conversion of the salt to AlN was monitored by XRD and $^{27}$ Al magic-angle spinning (MAS) NMR spectroscopy. The salt decomposed to ${\gamma}$-alumina and then converted to AlN without phase transition from ${\gamma}$-to-$\alpha$-alumina. $^{27}$ Al MAS NMR spectroscopy shows that the formation of AlN commenced at 110$0^{\circ}C$. AlN powders obtained from the sulfate salt were superior to those from the nitrate salt in terms of homogeneity and crystallinity. A very small amount of AlN whiskers was obtained by calcining a mixture of an aluminum sulfate salt and carbon at 115$0^{\circ}C$ for 40 h, and the growth of the whiskers is well explained by the particle-to-particle self-assembly mechanism.

• 한국세라믹학회지
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• 제40권6호
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• pp.608-614
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• 2003

pH 9.1, 9$0^{\circ}C$, 6시간의 조건에서 $\alpha$-tricalcium phosphate ($\alpha$-Ca$_3$(PO$_4$)$_2$)의 가수분해반응에 의해서 잘 발달된 수산화아파타이트 휘스커상 (길이 5$mu extrm{m}$,지름 0.5$\mu\textrm{m}$)이 합성되었다 수산화아파타이트로 $\alpha$-Ca$_3$(PO$_4$)$_2$의 전환에 미치는 반응조건(온도, 시간, pH)의 영향이 조사되었다. 아울러 XRD, SEM, ICP, TGA와 같은 분석기기를 사용하여 수산화아파트의 미세구조, 조성, 열적 안정성을 검토하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집A
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• pp.198-203
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• 2001

This study is about controlled impurities, which make metal alloys, especially AC4CH alloy that is made by restraining 0.2% Fe and Aluminum to make a matrix material. A metal matrix composite is produced using the squeeze casting method. The first step in the squeeze casting method is to add some organic binder including aluminum borate whisker into the matrix. After the fabrication of a metal matrix composite, each is individually appended to an inanimate binder such as $SiO_2,\;Al_2O_3$, and $TiO_2$. Through experiments the mechanical property changes were investigated between the metal matrix composite and AC4CH alloy. This study proves the superiority of the mechanical property of a metal matrix composites over AC4CH according to the previous tests and results that were mentioned above. One excellent property of matrix material composites is the infiltrated $TiO_2$ reinforcement. This material is a good substitute for the existing materials that are used in the development of industries today.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.61-66
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• 2003

In this paper, the effect of binder additive on the fracture toughness was metal matrix composite produced by squeeze casting method. In this study using the matrix is AC4CH and reinforcement used Aluminum borate whisker. Each MMC was produced by add inanimate binder ($SiO_2,\;Al2O_3,\;TiO_2$) to whiskers for increase the binding together of whiskers. Fracture toughness test were carry out in accordance with the ASTM E-399 standard test method, W=25mm, b=12.5mm CT(half size) specimen. However Base metal AC4CH was not meet the qualification of $P_m/P_Q<1.1$, so that test were performed $J_{IC}$ test. $K_{J_{IC}}$ value was measuring by $J_{IC}$ value change into $K_{IC}$. $J_{IC}$ test was carry out in accordance with the ASTM 1820.

• 한국연초학회지
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• 제20권1호
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• pp.108-114
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• 1998

This study was conducted to evaluate the techniques or analyzing tobacco smoke by statistical treatment method for the analytical data through Asia Collaborative Study V. In addition to five smoke components analysis, consisting of TPM, water, nicotine, NFDPM, and puff count of four cigarettes samples, statistical parameters such as mean, standard deviation, box-and-whisker plots, h plots, k plots, regression coefficients, reproducibility (R), and repeatability (r) were also calculated. Analysis of water content of cigarette smoke was the most difficult task, whereas puff count analysis was the easiest as well recognized by all laboratories. Analysis of nicotine and puff count accounted for both the lowest and the highest variation among four parameters. The water coefficients indicated more randomness or variation in the slops. The NFDPM data exhibited both types of deviations from linearity. Water content of sample D indicated the highest difference between two single results and between two interlaboratory test results. As a whole, KGTRI ranked higher in the analytical techniques for statistical evaluation of results when compared with the practices of 28 other laboratories.

• 대한기계학회논문집
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• 제17권7호
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• pp.1772-1782
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• 1993

The characteristics of metal matrix composite under dynamic tension at high strain rates up to the order of $10^3/sec$ is studied by using newly developed apparatus. The composite material processed in this research is aluminum-alumina metal matrix composites, arid fabricated by compocasting with the fiber volume fraction from 5 to 20%. The whisker and matrix material used in this paper were ${\delta}-Al_2O_3$ and Al-6061, respectively. The mechanical tests performed in this research are low and high strain rate tensile test. At low strain-rate tensile test, the modulus of elasticity and the ultimate tensile strength of the composites were improved about 77 pct. and 55 pct., respectively comparing with the unreinforced materials. At strain-rate from $10^{-3}\;to\;10^3/s$, the effect of strain-rate on the modulus, ultimate strength, flow stress is determined. Also the effect of strain rate on the modulus, ultimate tensile strength, flow stress and elongation to failures were investigated.

• 한국분말재료학회지
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• 제5권3호
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• pp.199-209
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• 1998

A new low melting inorganic binder, monoclinic $HBO_2$, has been developed for Selective Laser Sintering (SLS) of alumina powder by dehydration process of boron oxide powder in a vacuum oven at $120^{\circ}C$. It led to better green SLS parts and higher bend strength far green and fired parts compared to other inorganic binders such as aluminum and ammmonium phosphate. This appeared to be due to its low viscosity and better wettability of the alumina particle surface. A low density single phase ceramic, aluminum borate ($Al_{18}B_4O_{33}$), and multiphase ceramic composites, $A_{12}O_3-A_{14}B_2O_9$, were successfully developed by laser processing of alumina-monoclinic $HBO_2$ powder blends followed by post-thermal processing; both $Al_{18}B_4O_{33}$ and $A_{14}B_2O_9$ have whisker-like grains. The physical and mechanical properties of these SLS-processed ceramic parts were correlated to the materials and processing parameters. Further densification of the $A_{12}O_3-A_{14}B_2O_9$ ceramic composites was carried out by infiltration of colloidal silica, and chromic acid into these porous SLS parts followed by heat-treatment at high temperature ($1600^{\circ}C$). The densities obtained after infiltration and subsequent firing were between 75 and 80% of the theoretical densities. The bend strengths are between 15 and 33 MPa.