• 한국세라믹학회지
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• 제44권10호
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• pp.562-567
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• 2007

To precipitate the complex gels of the pH 6, 7, 8, 9 included in a flux and an aluminum hydroxides gel, an aqueous solution of a mixture of $Na_2CO_3\;and\;Na_2PO_4{\cdot}12H_2O$ was added with stirring in an aqueous solution of a mixture of $Al_2(SO_4){_3}{\cdot}18H_2O,\;Na_2SO_4\;and\;K_2SO_4$, and then the complex gels were aged in 20 h at $90^{\circ}C$. As the hydrolysis pH changed, it had an effect on the physical properties such as the crystal structure, crystal morphology and a phase transition temperature of the AlO(OH) gel, and also on the crystal structure, crystal morphology, particle size and particle size distribution of the ${\alpha}-Al_2O_3$ platelets prepared by molten-salt precipitation. Also, in this study, the complex gels were crystallized at $1,200^{\circ}C$ and thereafter dried at $110^{\circ}C$, and then it was investigated to effect of the hydrolysis pH on the crystal structure, morphology and particle size distribution of the ${\alpha}-Al_2O_3$ platelets crystals using XRD, DTA, SEM and particle size analyzer.

• 자연과학논문집
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• 제8권1호
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• pp.47-51
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• 1995

알루미나와 Hydroxyapatite(HAp)의 결합을 연구하기 위하여 9 가지의 중간 유리상을 연구하였다. 그 중간상의 화학 조성은 $CaO-Al_2O_3$에서 정하였으며 CaO/$Al_2O_3$의 몰 비율은 0.5에서 3 까지 변화 시켰다. 가장 낮은 용융은 CaO/$Al_2O_3$의 몰 비율이 2이고 $1355^{\circ}C$때 나타났다. $Al_2O_3$의 양을 증가시킴에 따라 용융점은 점점 높아 졌고 많은 기공들이 발견 되었다. 단면 조직 조사에 따르면 높은 CaO양 시편에서 양호한 흡수접착을 발견할 수 있었고, 이것은 CaO/$Al_2O_3$ 비가 2보다 큰것에서 더좋은 흡수접착을 얻을 수 있음을 의미한다. 열처리후 상변태는 발견되었으나, HAp의 중요한 피크는 그대로 남아 있음을 알 수 있다.

• 대한화학회지
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• 제35권4호
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• pp.422-426
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• 1991

천연 규산 알루미늄 광인 할로이사이트 광물로부터 고순도 ${\alpha}-Al_2O_3$을 합성하기 위해 ${\alpha}-Al_2O_3$의 전구물질인 수산화 알루미늄과 암모니움 명반을 합성하였다. 이들에 대한 열분해 반응기구는 열분석, XRD 및 IR 측정으로부터 규명되었고, 열분해로부터 얻어진 ${\alpha}-Al_2O_3$의 미세구조 및 비표면적은 SEM 및 BET 측정에 의해 수행되었다. 이때 ${\alpha}-Al_2O_3$ 입자의 크기는 모두 ${\phi}$ = 0.1∼0.5 ${\mu}$m이었으나, 비표면적의 크기는 암모니움 명반으로부터 얻어진 경우(89.0 m$^2$/g)가 수산화 알루미늄으로부터 얻어진 경우(7.3 m$^2$/g)보다 매우 높은 결과를 얻었다.

• 한국재료학회지
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• 제21권11호
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• pp.604-610
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• 2011

The effect of $BaF_2$ flux in $Y_3Al_5O_{12}:Ce^{3+}$(YAG:Ce) formation was investigated. Phase transformation of $Y_3Al_5O_{12}$(YAG) was characterized by using XRD, SEM, and TEM-EDS, and it was revealed that the sequential formation of the $Y_4Al_2O_9$(YAM), $YAlO_3$(YAP) and $Y_3Al_5O_{12}$(YAG) in the temperature range of 1000-1500$^{\circ}C$. Single phase of YAG was revealed from 1300$^{\circ}C$. In order to find out the effect of $BaF_2$ flux, three modeling experiments between starting materials (1.5$Al_2O_3$-2.5$Y_2O_3$, $Y_2O_3$-$BaF_2$, and $Al_2O_3$-$BaF_2$) were done. These modeling experiments showed that the nucleation process occurs via the dissolution-precipitation mechanism, whereas the grain growth process is controlled via the liquid-phase diffusion route. YAG:Ce phosphor particles prepared using a proposed technique exhibit a spherical shape, high crystallinity, and an emission intensity. According to the experimental results conducted in this investigation, 5% of $BaF_2$ was the best concentration for physical, chemical and optical properties of $Y_3Al_5O_{12}:Ce^{3+}$(YAG:Ce) that is approximately 10-15% greater than that of commercial phosphor powder.

• 대한전기학회논문지
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• 제35권10호
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• pp.465-472
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• 1986

The present study was carried out to investigate the mechanism which control the voltage instability and the breakdown of CVD Al2O3 on Si substrates. Our sample were metal-Al2O3-Oi Capacitors with both Al and Au field plates. Electron injection and trapping, with resultant positive flatband voltage shift, occur at fields as low as 1-2[MV/cm.] We developed an approximate method for computing the location of the centroid of the trapped electrons. Our results indicate that the electrons are trapped near the injecting interface, at least for fields less than about 5[MV/cm ] Because of continued charging, a true steady state is probably never reached, and the only unique I-V curve is the one obtained initially, when the traps are empty. We measured this I-V curve for both polarities of applied voltage, using a fresh sample for each point. The observed current densities are much larger than those obtained in thermally grawn SiO2.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.144-148
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• 1999

The relationship between oxidation and sliding wear behavior of Fe-28 at%. Al alloys with B2 ordered structure has been investigated. Sliding wear tests of the alloys have been carried out under various environmental conditions using a pin-on-disk wear tester. The wear rate of the ordered alloys in an oxygen atmoshpere was found to be much lower than in an oxygen atmosphere showed that Fe2O oxides formed on the wearing surface. The oxide layer prevented direct contact of the two mating materials and therefore improved wear resistance of the Fe-Al intermetallic alloy. It was found that the surface Al2O3 oxide layer which provides good oxidation resistance and improved mechanical properties broke down easily and didnot function properly as an oxidation barrier.

• 한국세라믹학회지
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• 제39권2호
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• pp.153-158
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• 2002

습식법에 의하여 제조된 $Al_2O_3$-1∼11 wt% $TiO_2$계 복합체를 1350$^{\circ}C$, 1450$^{\circ}C$ 에서 2시간 열처리 한 후 이에 대한 기계적 물성변화 및 미세구조를 조사하였다. 그 결과, $TiO_2$ 첨가량이 3 wt%였을 때의 복합체가 bulk density도 높고 기공율도 낮은 치밀한 미세구조를 이루었으며 이 때 young's modulus는 35.5 GPa, 곡강도값은 68.7 MPa로서 다른 $TiO_2$ 첨가량에 비하여 우수한 물성을 나타내었다. $TiO_2$ 첨가량이 증가할 수록 많은 양의 aluminium titanate의 합성으로 인해 열팽창 계수는 낮은 값을 나타내었다.

• 한국세라믹학회지
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• 제28권9호
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• pp.705-711
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• 1991

Alumina precursor sol was obtained by the reaction of Al(OC4H9)3 and acetylacetone in the solvent followed by the partial hydrolysis. This sol was measured by viscosity and the effect of pH. The powders obtained from this sol were calcined at the various temperatures. The transition of crystals and crystal state were investigated at the various temperatures. The powders dried at 90$^{\circ}C$ showed amorphous and ${\gamma}$-Al2O3 at 900$^{\circ}C$, ${\alpha}$-Al2O3 mono-phase at 1050$^{\circ}C$ respectively. As a result of Al27-MASNMR analysis, amorphous and ${\alpha}$-Al2O3 powders showed 6-coordinated Al, ${\gamma}$-Al2O3 4-coordinated Al respectively.

• 열처리공학회지
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• 제26권1호
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• pp.1-6
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• 2013

The B2-ordered NiAl has attracted much attention as one of the candidates as a next generation high temperature material, because it has a high melting temperature, a low specific gravity and an excellent high temperature oxidation resistance. However, the application of NiAl to structural materials needs the improvement of its brittleness at room temperature. The study was carried out on the relation between several properties of NiAl and some variation of Ni content within NiAl phase, which means deviations from the stoichiometric composition. The main results were as follows; (i) Good ductility was obtained at the testing temperature more than 1073 K irrespective of Ni content. (ii) Increasing Ni content offered preferable tensile properties. (iii) Every NiAl with varying Ni contents showed the superior oxidation resistance.

• Journal of the Optical Society of Korea
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• 제15권2호
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• pp.124-127
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• 2011

Quantum dots were designed within a GRIN-SCH(Graded index - Separate confinement Heterostructure) heterostructure to create a high power InAlAs/AlGaAs laser diode. 808 nm light emission was with a quantum dot composition of In0.665Al0.335As and wetting layer composition of Al0.2Ga0.8As by LASTIP simulation software. Typical characteristics of GRIN structures such as high confinement ratios and Gaussian beam profiles were shown to still apply when quantum dots are used as the active media. With a dot density of 1.0x1011 dots/cm2, two quantum dot layers were found to be good enough for low threshold, high-power laser applications.