• Journal of Welding and Joining
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• 제21권2호
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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.

• 한국세라믹학회지
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• 제41권12호
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• pp.939-945
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• 2004

[ $SiO_2-B_{2}O_3-Al_{2}O_3-CaO-La_{2}O_3$ ]계 유리에서 $La_{2}O_3$를 변화시키며 다양한 조성의 유리를 만든 후 이를 다공성 알루미나에 침투시켜 알루미나-유리 복합체를 얻었다. 여기서 유리의 조성 변화에 따른 침투특성 및 기계적 강도의 변화를 관찰하였다. 유리중의 $La_{2}O_3$는 유리의 고온 점도를 감소시켜 유리의 젖음성과 유동성을 향상시키고 유리의 침투를 용이하게 한다. 유리가 다공성 알루미나에 침투하여 기공을 메우면서 일부 알루미나를 용해시킨다. 이 유리 용융물 중 $Al_{2}O_3$ 성분은 결정질 알루미나에 다시 석출하여 입자성장이 일어나는데 이때 특정 방향으로 알루미나 입자가 성장한다. $La_{2}O_3$가 20 몰 $\%$ 첨가된 유리를 침투시켰을 때 유리가 결정화하여 복합체의 강도를 증진시켰다.

• 대한치과보철학회지
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• 제31권3호
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• pp.317-349
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• 1993

This study investigated the effect of filler particle size and weight% on mechanical properties of dental core porcelain. In alumina, variation in particle size and weight% and in zirconia, variation in weight%, all specimens were tested three-point bending strength, transmittance, thermal expansion coefficient, porosity and shrinkage and observed with SEM and analysed with X-ray diffractometer. In order to develop shrink-free porcelain, after firing alumina only, glass wasinfiltrated. And aluminum was added to alumina with the expanding character of aluminum oxidize into alumina, and was followed by second firing of glass infiltration procedure. Then mechanical properties were observed. The results of this study were obtained as follows. 1. The bending strength of zirconia was higher than that of alumina, and $5{\mu}m$ alumina had highest strength in variation of particle size of alumina. Except for $5{\mu}m$ alumina, increased with weight%, bending strength increased up to 80% and decreased at 90%. In case of glass infiltration, bending strength was slight higher than 80% and 90% of $5{\mu}m$ alumina. 2. Transmittance increased with increase of shrinkage, decrease of porosity, and with increase of filler size and had no direct correlation with weight%. 3. Thermal expansion coefficient of alumina group was $7.42\sim8.64\times10^{-6}/^{\circ}C$ and that of zirconia group was $9.83\sim12.11\times10^{-6}/^{\circ}C$ and the latter was higher than the former. 4. In x-ray diffraction analysis, alumina group and zirconia group increased $Al_2O_3$ peak and $t-ZrO_2$ peak with increase of weight%. The second phase(cristobalite peak) was observed in zirconia 40% group. 5. Porosity of zirconia was lower than that of alumina and $5{\mu}m$ alumina group had many pores with SEM. In case of low filler content, fracture occurred in glass and high filler content, in glass and filler. In case of aluminum addition to alumina, small oxidised aluminum was observed. 6. Zirconia group had high shrinkage than alumina group, and mixed group of alumina group had high shrinkage. In case of glass infiltration, shrinkage decreased and aluminum addition to alumina group was almost shrink-free.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 추계학술대회 논문집 전기설비전문위원
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• pp.261-262
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• 2008

Damaged glass insulator that is utilized the high-speed railroad in domestic try to find the cause. This paper is investigated on the characteristics of alumina cement as the binder of class insulator. The components of glass insulator ore stub(tin), rod(tin), shed(tempered glass), and alumina cement. If composition of alumina cement is not unified, crack of alumina cement generated. As these results, cracked marks of cement is appeared and composition of alumina cement is not unified. Therefore, it is estimated that main element of long-term degradation is a alumina cement.

• The Korean Journal of Ceramics
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• 제4권4호
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• pp.363-367
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• 1998

Alumina/mica and spinel/mica composites were fabricated by sintering of compacts containing 20 mass% fluoromica ($KMg_3AlSi_3O-{10}F_2$) glass and alumina or spinel. In both composites, mica precipitated as plate-like crystals at temperatures lower than $1300^{\circ}C$ and melted at $1300^{\circ}C$ to $1400^{\circ}C$. In alumina/mica composites, alumina and glass reacted to produce spinel, and the densification progressed by the solution-precipitation of alumina. Consequently, the glass composition changed and the mica did not precipitate at temperatures higher than $1400^{\circ}C$. However, mica precipitated after a reheating process. In spinel/mica composites, the glass composition did not change. After the mica phase melted, it recrystallized during slow cooling. The relative density reached the maximum at $1500^{\circ}C$ for alumina/mica and at $1300^{\circ}C$ spinel/mica composites, and decreased at further high temperatures.

• 한국세라믹학회지
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• 제36권10호
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• pp.1123-1131
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• 1999

Alumina-glass composites which are considered as the material of the choice for all dental crown was prepared by aqeous-based tape casting and sintering for 2h at 1120$^{\circ}C$ followed by glass infiltration for 2h at 1100$^{\circ}C$ Biaxial strength and fracture toughness of the composites were evaluated to determine the optimum composition of the tape as a function of the amount of constituent such as alumina binder and plasticizer. The strength and the fracture toughness of the alumina tape increased with increasing the contents of alumina and binder. These observations are consistent with in fluence of the constituents on mean alumuna particle distance in tapes suggesting that high strength of the glass infiltrated alumina composites is related to toughening by crack bowing. The biaxial strength and the fracture toughness of the composite containing the optimum constituent composition were 523 MPa and 3.3 MPa$.$1/2 respectively.

• 한국세라믹학회지
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• 제37권6호
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• pp.545-551
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• 2000

Sintering behaviors of the glass-alumina composites for low firing temperature were investigated as a function of the particle size of glass frit. The system of glass frit was Pb-B-Si-Al-O. The median particle sizes of the glass frits were 2.72$\mu\textrm{m}$, 2.67$\mu\textrm{m}$ and 1.33$\mu\textrm{m}$, which were prepared with changing ball-milling times as 24 h, 48 h and 96 h. The glass-alumina composites showed maximum density at certain temperature, and further heating led to dedensification behaviors, so called over-firing. The sintering temperature, which showed maximum density, raised from 425$^{\circ}C$ to 475$^{\circ}C$ with increase of particle size of glass frit from 1.33$\mu\textrm{m}$ to 2.72$\mu\textrm{m}$. Especially, the over firing behaviors, which were occurred at high sintering temperatures, were greatly increased with decrease of particle size of glass frit.

• 대한치과보철학회지
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• 제38권5호
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• pp.595-605
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• 2000

Dental ceramics have good aesthetics, biocompatibility, low thermal conductivity, abrasion resistance, and color stability. However poor resistance to fracture and shrinkage during firing process have been limiting factors in their use, particularly in multiunit ceramic restorations. A new method for making all-ceramic crowns that have high strength and low processing shrinkage has been developed and is referred to as the Vita In-Ceram method. This study was performed to investigate the effect of $CeO_2$ addition in borosilicate glasses on the strength of alumina-glass composites. Porous alumina compacts were prepared by slip casting and sintered at $1,100^{\circ}C$ for 2 hours. Dense composites were made by infiltration of molten glass into partially sintered alumina at $1,140^{\circ}C$ for 4 hours. Specimens were polished sequentially from #800 to #2000 diamond disk. and the final surface finishing on the tensile side was received an additional polishing sequence through $1{\mu}m$ diamond paste. Biaxial flexure test was conducted by using ball-on-three-ball method at a crosshead speed of 0.5mm/min. To examine the microstructural aspect of crack propagation in the alumina-glass composites, Vickers-produced indentation crack was made on the tensile surface at a load of 98.0 N and dwell time of 15 sec, and the radial crack patterns were examined by an optical microscope and a scanning electron microscope. The results obtained were summarized as follows; 1. The porosity rates of partially sintered alumina decreased with the rising of firing temperature. 2. The maximum biaxial flexure strength of 423.5MPa in alumina-glass composites was obtained with an addition of 3 mol% $CeO_2$ in glass composition and strength values showed the aspect of decrease with the increase of $CeO_2$ content. 3 The biaxial flexure strength values of alumina-glass composites were decreased with rising the firing temperature. 4. Observation of the fracture surfaces of alumina-glass composites indicated that the enhancement of strength in alumina-glass composites was due to the frictional or geometrical inter-locking of rough fracture surfaces and ligamentary bridging by intact islands of materials left behind the fracture front.

• 한국세라믹학회지
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• 제15권2호
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• pp.89-97
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• 1978

The basic mechanism of adherence in sintered high purity alumina ceramic-to-metal bonding was studied. Emphasis was placed on flux composition, porosity of the fired ceramics, and metallizing mixtures. The study was conducted on 95 and 99.5% alumina, using molydbenum-manganese, molybdenum-manganese-silicon dioxide metallizing compositions. Metallizing was performed in wet hydrogen (dew point, ＋17$^{\circ}C$) at 145$0^{\circ}C$ for 45min. This experiment indicated that adhernece mechanism of ultra high purity alumina ceramic was attributed to formation of $MnAl_2O_$4, and in the case of 95% alumina containing glass, the migration of glass from the interface into the void of the metal coating was the main role to the adhrence. It showed also that greater the bond-strength was resulted as porosity was increased.

• 한국세라믹학회지
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• 제16권1호
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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.