• Journal of the Korean Ceramic Society
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• v.43 no.1 s.284
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• pp.48-54
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• 2006

Hydroxyapatite $(HAp,\;Ca_{10}(PO_4)_6(OH)_2)$/alumina composites were fabricated with the addition of fluorides, such as $MgF_2$ and $CaF_2$. In this study, the effect of fluorides on the inhibition of phase decomposition and the mechanical properties of HAp was investigated. Due to the higher solubility of F ion in HAp structure, $MgF_2$ additive was more effective compared to $CaF_2$ additive in the lowering decomposition temperature of HAp. Therefore, the dissociation tendency of HAp was fully inhibited below $1400^{\circ}C$. The mechanical properties of HAp composites with $MgF_2$ additive showed higher value (flexural strength: $\~170MPa$, Vickers hardness: $\~7\;GPa$, fracture toughness: $\~1.5\;MPam^{1/2}$) compared to $MgF_2-free$ composites. The linear thermal expansion coefficient of HAp composites with $MgF_2$ showed the value of $16.4\times10^{-6}/^{\circ}C\;at\;20\~400^{\circ}C $.

• Journal of Technologic Dentistry
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• v.30 no.2
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• pp.39-45
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• 2008

Titanium and its alloys are widely used as dental implants materials because of their excellent mechanical properties. However, the alumina and zirconia ceramics are preferred to use as the substitute of Ti implants because there is a problems in esthetics and biocompatibility in Ti implant. The the glass infiltrated alumina ceramics are studied to increase the toughness and biocompatibility. The 45S5 and soda-lime glass powder was mixed with ethanol at ratio of 1:1 and brushed on the surface of alumina. Then it was heat treated in the electric furnace at $1400^{\circ}C$ from 30 min. to 5 hours. The glass powder was controlled from 200 to $350{\mu}m$ using ball milling. After heat treatment, the glass infiltrated specimen was tested in universal testing machine to measure the bending strength. The surface microstructure of each specimen was observed with SEM. The biocompatibility of 45S5 and soda-lime glass coated alumina was investigated using PBS at $36.5^{\circ}C$ incubator. The specimen was immersed in PBS for 3, 5, 7, 10 days. After that, the surface morphology was investigated with SEM. As the results of experiment, the 45S5 bioglass infiltrated alumina show the increase of bending strength according to the increasing of heat treatment time from 30 min. to 5 hours at $1400^{\circ}C$ Finally the 1370N bending strength of alumina increased to 1958N at 5 hours heat treatment, which shows 1.4 times higher. In contrast to this, the soda lime glass infiltrated alumina ceramics shows the convex curve according to heat treatment time. Thus it shows maximum bending strength of 1820N at 1 hour heat treatment of $1400^{\circ}C$ It gives 1.3 times higher. However, the bending strength of soda lime glass infiltrated alumina is decreasing with increasing heat treatment time after 1 hour. The precipitation on the surface of 45S5 glass infiltrated alumina was revealed as a sodium phosphate ($Na_{6}P_{6}O_{24}6H_{2}O$) and the amount of precipitation is increasing with increasing of immersion time in PBS. In contrast to this, there is no precipitation are observed on the surface of soda lime glass infiltrated alumina. This implies that 45S5 glass infiltrated alumina brings more biocompatible when it is implanted in human body.

• The Korean Journal of Ceramics
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• v.5 no.1
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• pp.25-29
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• 1999

Complex viscosities of dense alumina slurries over 45% volume density measured with the oscillating method were correlated well with Casson model. Among several monosaccharides and disaccharides studied here, fructose and sucrose showed good rheological properties in making dense alumina slurry plastic compared to other monosaccharides and disaccharides like glucose, galactose, arabinose, xylose and maltose. Sucrose content or additional water content in dense alumina slurry with sucrose contributed to the plasticity of the slurries.

• Journal of the Korean Ceramic Society
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• v.16 no.1
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• pp.21-25
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• 1979

This study is proposed to find an appropriate body for high expansion glass ceramics of ${Na}_2O-{Al}_2O_3-{SiO}_2$ system. The compositions of basic glasses are selected to be melted easily and to be crystallized into nepheline with various contents of alumina. The crystallization temperatures of basic glasses are determined by DTA. The crystals in the basic glasses developed by heat treatment are investigated by X-ray diffraction analysis, and thermal properties such as expansion coefficients, fusion points are measured. We find, therefore,that crystallization temperatures, crystal phases and thermal properties are affected by content of alumina.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.1
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• pp.36-39
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• 2002

Molybdena powder was heated at both 660$^{\circ}C$ and 700$^{\circ}C$ for half-hour in an evaporation-deposition device. The molybdena thin films deposited on the surfaces of alumina ceramics displayed two kinds of fractal aggregates, i.e., the stackings of ribbon-like crystals and ramified palm-like structures. It is revealed from the experimental results that the microstructures of these fractal aggregates depended strongly on their growth conditions. The dynamics of fractal growth of molybdena thin film is discussed.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1253-1259
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• 1996

In the fabrication of alumina-based multilayer ceramics sintering shrinkages with lamination conditions such as lamination pressure temperature and laminating with and without press die were compared. The sintering shrinkage was affected substantially by lamination pressure and temperature and in the case of laminatino without press die the lower laminated density and a large difference in shrinkage with direction were observed. These results can be explained by introducing a new factor which is the ratio of the changes of areas before and after lamination.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.2
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• pp.103-116
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• 1993

Recently, engineering ceramics called as the 3 material have been concerned significantly with some excellent mechanical properties and many functions as new materials for high precision mechanical components and engineering parts for at large. Then, for designing engineering parts using engineering ceramics, bending strength value data with high reliability is more essential than any other mechanical properties. But, because of brittleness and structural characteristic, it is very hard to grind with conventional tools, and the generation of cracks and various defects of engineering ceramics parts during grinding machining process are serious problems. Thus, in present study, surface grinding experiments with various machining conditions using resin bond diamond wheels are carried out to obtain the most excellent guality of testpiece surface and optimum step of grinding process for the high efficient stock removal rate to save running time. As the results from grinding experiments and 3-points bending strength test of ground Al2O3 ceramics parts on Korean Standard, manufactured in our country and Japan, basic technology and know-how to develop the optimum grinding machining conditions and also high bending strength values with high reliability are obtained.

• Journal of Welding and Joining
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• v.21 no.2
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• pp.35-41
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• 2003

Sintered alumina ceramics were joined by 2 kinds of SiO$_2$-CaO-A1$_2$O$_3$ glass solders having a similar expansivity as alumina. Wetting of glass/alumina was examined by sessile drop method. The observation of interface and bending strength related to alumina/glass/alumina systems were investigated by means of SEM/EDX and 4-point bending test. the result are summarized as follow: (1) Wetting of glass solders on alumina was good at temperatures higher than 145$0^{\circ}C$. (2) When the joining temperature wan high, diffusion and/or reactions between solder md alumina took place at the interface. These diffusions and reactions occurring at the interface greatly affected the bending strength of joining body. (3) Highest strength corresponding to 80% that of alumina was obtained by the solder of 35SiO$_2$-35CaO-30A1$_2$O$_3$(wt%) glass.

• The Korean Journal of Ceramics
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• v.5 no.1
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• pp.12-18
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• 1999

Alumina matrix composites reinforced with up to 20vol% of aligned SiC whiskers were fabricated by tape casting and hot pressing. Alumina composited with randomly distribution SiC whiskers were also fabricated in order to investigate the effect of whisker alignment on properties of the composites. XRD and optical microscopy were used to examine the whisker orientation. The fracture toughness increased with increasing whisker content, and it was higher in the direction normal to the tape casting direction.

• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.706-714
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• 1998

The MgO-{{{{ { {Al }_{2 }O }_{3 } }}-{{{{ { {SiO }_{2 } }_{ } }}system containing alumina powder was fabricated sintered at various temperature and analyzed in order to study the sintering mechanism and crystallization characteristics. The specimen composed of glass powder with average particle size of 8.27 $\mu\textrm{m}$ and 0-40 vol% alumina powder were sint-ered for 3 hrs at the temperature between 850$^{\circ}C$ and 1350$^{\circ}C$ The sintering mechanism consists of the redis-tribution of particles occuring at 750$^{\circ}C$ and the viscous flow at 850∼950$^{\circ}C$. The degree of crystallization and sintering temperatue were dependent upon the ratio of glass/alumina. The second phase from the reaction between glass and alumina was not observed which was confirmed by XRD and properties analysis. The density dielectric constant and specific resistivity of specimen were 2.30∼3.26g/cm2 5.8∼7.38 at 1 GHz density dielectric constant and specific resistivity of specimen were 2.30∼3.26g/cm3 5.8∼7.38 at 1GHz and 1.23∼4.70${\times}$107 $\Omega$$.$m respectively.