• Korean Journal of Materials Research
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• 제23권2호
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• pp.89-97
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• 2013

The study of grinding behavior characteristics on aluminum powders and carbon nano tubes (CNTs) has recently gained scientific interest due to their useful effect in enhancing advanced nano materials and components, which significantly improves the property of new mechatronics integrated materials and components. We performed a series of dry grinding experiments using a planetary ball mill to systematically investigate the grinding behavior during Al/CNTs nano composite fabrication. This study focused on a comparative study of the various experimental conditions at several variations of rotation speeds, grinding time and with and without CNTs. The results were monitored for the particle size distribution, median diameter, crystal structure from XRD pattern and particle morphology at a given grinding time. It was observed that pure aluminum powders agglomerated with low rotation speed and completely enhanced powder agglomeration. However, Al/CNTs composites were achieved at maximum experiment conditions (350 rpm, 60 min.) of this study by a mechanical alloy process for Al/CNTs mixed powders because the grinding behavior of Al/CNTs composite powder was affected by addition of CNTs. Indeed, the powder morphology and crystal size of the composite powders changed more by an increase of grinding time and rotation speed.

• Transactions of the Korean Society of Mechanical Engineers A
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• 제26권9호
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• pp.1831-1841
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• 2002

The effect of a rubber mould on densification and deformation of aluminum alloy powder was investigated during warm isostatic pressing. The hyperelastic constitutive equations based on various strain energy potentials were employed to analyze deformation of rubber. The parameters in the strain energy potentials were obtained from experimental data for uniaxial and volumetric compression of Viton rubber at two warm temperatures. For elastoplastic response, the yield function of Shima and Oyane was implemented into a finite element program (ABAQUS) to predict compaction responses of metal powder during warm isostatic pressing. Finite element results were compared with experimental data for densification and deformation of aluminum alloy powder with/without a rubber mould under warm die pressing.

• Journal of Powder Materials
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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.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 한국분말야금학회 2004년도 International Symposium on Powder Materials and Processing
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• pp.80-81
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• 2004

The results obtained are summarized as follows; (1) Boehmite produced in the high temperature and acid region showed a nano fibrous shape with several nm in diameter and several hundreds nm in length having high specific surface areas with a maximum value of $409m^2/g$. (2) In order to obtain nano fibrous boehmite with high surface areas from nano metal powder, the hydrolysis reaction should be done at a high temperature over $50^{\circ}C$, high acidity under pH 6, and terminated before a transition to the bayerite phase.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.708-709
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• 2006

New Al-based alloys with very high ultimate tensile strength were developed in high Al concentration range of 91-95 at.% for Al-Fe-Cr-Ti-M (M: Co and Mo) systems and Al-Fe-Cr-Mo-Ti-Co system by the dispersion of nanoscale quasicrystalline particles in Al phase. The effect of adding elements, M was discussed in the viewpoint of stability of super-cooled liquid state and formation ability of quasicrystalline phase. The P/M Al-Fe-Cr-Ti-M alloys with dispersed nanoscale quasicrystalline particles exhibited ultimate tensile strength of 350MPa at 573K and 200MPa at 673K.

• Nuclear Engineering and Technology
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• 제45권7호
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• pp.979-986
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• 2013

Uranium metal particle dispersion plates have been proposed as targets for Molybdenum-99 (Mo-99) production to improve the radioisotope production efficiency of conventional low enriched uranium targets. In this study, uranium powder was produced by centrifugal atomization, and miniature target plates containing uranium particles in an aluminum matrix with uranium densities up to 9 $g-U/cm^3$ were fabricated. Additional heat treatment was applied to convert the uranium particles into UAlx compounds by a chemical reaction of the uranium particles and aluminum matrix. Thus, these target plates can be treated with the same alkaline dissolution process that is used for conventional $UAl_x$ dispersion targets, while increasing the uranium density in the target plates.

• Journal of the Korean Chemical Society
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• 제37권1호
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• pp.165-167
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• 1993

• The Korean Journal of Ceramics
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• 제3권4호
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• pp.269-273
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• 1997

Chemical composition of cement powder influences the setting time and early compressive strength development. The setting time increases as the amounts of zinc oxide and magnesium oxide are increased. For one day compressive strength development, a cement powder with a composition 90% ZnO, 8% MgO and 2% silica resulted in the highest strength (greater than 1, 090 kg/$\textrm{cm}^2$). Cement-forming liquids also need to be buffered, with both aluminum and zinc ions, for a good consistency and a higher strength of the zinc phosphate cement. These liquids control the setting reactions.

• Journal of Powder Materials
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• 제13권4호
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• pp.243-249
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• 2006

Yttrium aluminum garnet (YAG) powders were synthesized via mechanochemical solid reaction using $Y_2O_3$ with three types of aluminum compounds. $Y_2O_3$ reacted mechanochemically with all A1 compounds and formed YAM (yttrium aluminum monoclinic), YAG and YAP (yttrium aluminum perovskite) phases depending on the starting materials. The ground samples containing ${\gamma}-A1_2O_3$ showed the best reactivity, whereas the ground sample containing A100H, which had the largest surface area, exhibited pure YAG after calcination at $1200^{\circ}C$. The sample containing Al had the least reactivity, producing YAP along with YAG at $1200^{\circ}C$. The types and grinding characteristics of the starting materials and grinding time are believed to be important factors in the mechanochemical synthesis of YAG.

• Journal of Powder Materials
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• 제15권6호
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• pp.496-502
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• 2008

Aluminum nitride (AlN) powders were prepared by the chemical vapor synthesis (CVS) process in the $AlCl_{3}-NH_{3}-N_{2}$ system. Aluminum chloride ($AlCl_3$) as the starting material was gasified in the heating chamber of $300^{\circ}C$. Aluminum chloride gas transported to the furnace in $NH_{3}-N_{2}$ atmosphere at the gas flow rate of 200-400ml/min. For samples synthesized between 700 and $1200^{\circ}C$, the XRD peaks corresponding to AlN were comparatively sharp and also showed an improvement of crystallinity with increasing the reaction temperature. In additions, the average particle size of the AlN powders decreased from 250 to 40 nm, as the reaction temperature increased.