• Journal of Korea Foundry Society
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• v.13 no.4
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• pp.350-358
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• 1993

Aluminum base composites reinforced with various amount of SiC particles and Mg contents have been investigated by different fabrication method for twenty-years. In this paper, how the decomposition and dissolution behaviors of $SiCp(20{\mu}m)$ in the melt of Al composites arised was studied. As the results, the decomposition and dissolution of SiCp into the melt of Al composites increased with increase of the temperature above $720^{\circ}C$, and holding time at a given melting temperature. Because SiC is thermodynamically unstable in this Al-SiCp composite at temperature above the liquidus, SiCp dissolves and reacts with Al in matrix to form $Al_4C_3$ according to following chemical equation $4Al+3SiC{\rightarrow}Al_4C_3+3Si$, Si decomposed and dissolved from SiCp increases Si content of matrix, while liquidus temperature of matrix decrease with increase of SiC content in matrix. The hardness of SiCp decreased with increase of the melting temperature, the hardness of the matrix /particle interface increased with increase of the melting temperature due to increase of the $Mg_2Si$ and $Al_4C_3$ intermetallic compounds, etc.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.413-419
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• 2002

Particulate composites of $Al_2O_3$/TiC/SiC, $Al_2O_3$/TiC and $Al_2O_3$/SiC have been fabricated by hot pressing and their R-curve behaviors and mechanical properties were investigated. $Al_2O_3$ containing 30 vol% TiC particles showed higher toughness by 8% than that for monolithic alumina and its fracture strength was increased significantly by approximately 30%. On the other hand, the addition of 30 vol% SiC of $3{\mu}m$ in $Al_2O_3$ decreased the fracture strength slightly but induced a rising R-curve behavior owing to the strong crack bridging of SiC particles. In case of $Al_2O_3$/TiC/SiC, arising R-curve behavior was also observed and the fracture toughness reached 6.6 MPa${\cdot}\sqrt{m}$ at the crack length of $1000{\mu}m$, which was lower than that of $Al_2O_3$/SiC, however, while the fracture strength was higher by about 20%. The fracture toughness seemed to be decreased as smaller TiC particles roughened the SiC interface and pullout of the SiC particles for crack bridging became less active.

• Journal of Sensor Science and Technology
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• v.7 no.3
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• pp.218-224
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• 1998

2nO and $Al_{2}O_{3}$ powder were weighed in 1 : 1 mole ratio and ball-milled in ethanol for 3 h. Dried mixture were pressed and then sintered at $900^{\circ}C{\sim}1200^{\circ}C$ for 3 h in vacuum($3{\times}10^{-5}$ Torr). According to XRD, remnant ZnO and $Al_{2}O_{3}$ not converted to $ZnAl_{2}O_{4}$ were observed up to $1100^{\circ}C$, which were completely changed to$ZnAl_{2}O_{4}$ ternary compound at $1200^{\circ}C$. Optical bandgap is calculated at 4.75 eV. With increasing sintering temperature, PL spectrums shifted to shorter wavelengths and are appeared 430nm at $1200^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.406-412
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• 1997

Al2O3/SiC hybrid-composite has been fabricated by the conventional powder process. The addition of $\alpha$-Al2O3 as seed particles in the transformation of ${\gamma}$-Al2O3 to $\alpha$-Al2O3 provided a homogeneity of the microstructure. The grain growth of Al2O3 are significantly surpressed by the addition of nano-size SiC particles. Dislocation were produced due to the difference of thermal expansion coefficient between Al2O3 and SiC and piled up on SiC particles in Al2O3 matrix, resulting in transgranular fracture. The high fracture strength of the composite was contributed to the grain refinement and the transgranular fracture mode. The addition of SiC platelets to Al2O3/SiC nano-composite decreased the fracture strength, but increased the fracture toughness. Coated SiC platelets with nitrides such as BN and Si3N4 enhanced fracture toughness much more than non-coated SiC platelets by enhancing crack deflection.

• Journal of the Korean Ceramic Society
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• v.51 no.5
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• pp.392-398
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• 2014

$Al_2O_3$-SiC composites reinforced with SiC whisker ($SiC_w$) were fabricated using three different methods. In the first, $Al_2O_3-SiC_w$ starting materials were used. In the second, $Al_2O_3-SiC_w$-SiC particles ($SiC_p$) were used, which was intended to enhance the mechanical properties by $SiC_p$ reinforcement. In the third method, reaction-sintering was used with mullite-Al-C-$SiC_w$ starting materials. After hot-pressing at $1750^{\circ}C$ and 30 MPa for 1 h, the composites fabricated using $Al_2O_3-SiC_w$ and $Al_2O_3-SiC_w-SiC_p$ showed strong mechanical properties, by which the effects of reinforcement by $SiC_w$ and $SiC_p$ were confirmed. On the other hand, the mechanical properties of the composite fabricated by reaction-sintering were found to be inferior to those of the other $Al_2O_3$-SiC composites owing to its relatively lower density and the presence of ${\gamma}-Al_2O_3$ and ${\gamma}-Al_{2.67}O_4$. The greatest hardness and $K_{1C}$ were 20.37 GPa for the composite fabricated using $Al_2O_3-SiC_w$, and $4.9MPa{\cdot}m^{1/2}$ using $Al_2O_3-SiC_w-SiC_p$, respectively, which were much improved over those from the monolithic $Al_2O_3$.

• Journal of the Korean Society for Heat Treatment
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• v.11 no.3
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• pp.168-176
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• 1998

The mechanical properties of mechanically alloyed Al-4wt%Mg alloys dispersed with $MgAl_2O_4$ dispersoilds at room and elevated temperatures were investigated. The powders in steady state during mechanical alloying consisted of Mg-supersatu rated Al solid solution and $Al_4C_3$ which resulted from the reaction of Al with C in process control agent (methanol). The hot-extruded materials consisted of uniformly dispersed fine $MgAl_2O_4$, ${\gamma}-Al_2O_3$, $Al_2O_3$ and matrix with extremly fine substructure. Tensile specimens prepared from the extruded bars were tested at room temperature to $400^{\circ}C$ under different strain rates. The tensile strength of alloys at room temperature ranged from 500 to 594MPa. At elevated temperatures, the tensile strengths and elongations decreased with increasing temperature. Adding 3% $MgAl_2O_4$ to Al-4wt%Mg increased the tensile strength of 50MPa at rowan temperature and 20MPa at $400^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.2
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• pp.185-190
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• 1999

An $Al_2O_3/Fe$ composite was synthesized through the double stage processes by a reaction sintering which requires simple process and equipments but provides near-net-shape, a reduction/oxidation process for 5 hrs at $650^{\circ}C$ was followed by sintering at $1200^{\circ}C$ to form an $Al_2O_3/Fe$ composite. The composite processed through the double stage sintering are mainly consists of $\alpha$-Fe and ${\alpha}Al_2O_3$ with minor amount of $FeAl_2O_4$, a spinnel structure which is known to prevent Fe from filling up the pores and good contact with $Al_2O_3/Fe$ particles.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.12
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• pp.668-673
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• 2015

Alumina-based catalysts with different Ce loadings were studied in the decomposition of $CF_4$ using microwave heating system. Heating material of microwave system used Silicon Carbide. The crystallographic phases of catalysts were investigated by XRD and decomposition rates of $CF_4$ were examined by GC-TCD. The catalysts of 10 wt% Ce modified $Al_2O_3$ showed higher $CF_4$ decomposition rate than un-modified $Al_2O_3$ for $500^{\circ}C$ reaction temperature. The k value of catalysts shows the order of $Ce(20)/Al_2O_3=Ce(0)/Al_2O_3<Ce(5)/Al_2O_3<Ce(10)/Al_2O_3$. XRD patterns of $Ce(0)/Al_2O_3$ were no difference before and after the reaction and showed $Al_2O_3$ phases. With the increase in Ce loadings, $CeO_2$, $AlF_3$ of XRD peaks was observed. The results was indicated that Ce modifed $Al_2O_3$ than un-modifed $Al_2O_3$ was decreased reaction temperature to $200^{\circ}C$ with same decomposition rate. Also the appropriated cerium sulfate loadings on $Al_2O_3$ were 5~10 wt%.

• Advances in materials Research
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• v.5 no.4
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• pp.263-277
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• 2016

Mechanical properties of $Al/Al_2O_3$ and $Al/B_4C$ composites prepared through powder metallurgy are estimated up to 50% $Al_2O_3$ and 35% $B_4C$ weight fractions using micromechanics models and experiments. The experimental Young's modulus up to 0.40 weight fraction of ceramic is found to lie closely between Ravichandran's/Hashin-Shtrikman lower/upper bounds, and close to self consistent method/Miller and Lannutti method/modified rule of mixture/fuzzy logic method single value predictions. Measured Poisson's ratio lies between rule of mixture/Ravichandran lower and upper bound/modified Ravichandran upper bounds. Experimental Charpy energy lies between Hopkin-chamis method/equivalent charpy energy/Ravichandran lower limit up to 20%, and close to the reciprocal rule of mixture for higher $Al_2O_3$ content. Rockwell hardness (RB) and Micro-hardness of $Al/Al_2O_3$ are closer to modified rule of mixture predictions.

• Cement
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• s.51
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• pp.20-30
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• 1973

1) electron-microprobe를 응용하여 $CaO-SiO_2-Al_2O_3$ 계에서 생성한 $C_2S$, $C_3S$ 에 존재하는 sulfate의 solid, solution을 정량적으로 구할 수 있었으며 이 결과로 $C_2S$ 에 $Al_2O_3$, $SO_3$ 등이 solid soln 등으로 침적되고 이들이 $C_3S$의 생성을 억제한다는 mechanism이 확인되었다. 2) phase equilibrium(상평형)에 의하면 $Na_2SO_4$, $K_2SO_4$는 mineralizer로서 작용하며 $C_3S$ 의 생성을 돕는다. 그러나 $K_2SO_4$ 와 $Al_2SO_3$ 가 결합상태로 존재할 경우는 1,400 $^{\circ}C$에서 광범위한 liquid를 생성하며 quenching하면 glass질과 $\beta-C_2S$ 만이 얻어지고 $C_3S$ 는 생성되지 않는다. 또 이를 1,250 $^{\circ}C$ 까지 서냉하면 $C_2S$ 와 Ca, K, Al, S, 등을 함유한 새로운 물질이 생성된다. 3) $CaO-SiO_2-Al_2O_3-Fe_2O_3$ 계에서 $C_3S$ 의 생성에 미치는 $Na_2SO_4$, $K_2SO_4$ 의 영향을 실험실적으로 검토한 결과 complex interaction이 확인되었으며 $Na_2SO_4$ 는 어떤 경우에는 mineralizing effect를 상실한다는 재미 있는 사실이 발견되었다.