• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.353-359
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• 2004

In this study. porcelain insulator samples which have a different alumina composition were manufactured in order to test electrical and mechanical properties and make an analysis of the propagation phenomena of micro cracks on porcelain body. From XRD quantitative analysis the crystalline phases were different with alumina composition, sample C and D which have about l7wt％ Corundum phase without the Cristobalite phase shows better electrical and mechanical properties than sample A and B which have the Cristobalite phase. In dielectrics test on porcelain samples with below l7wt％ alumina composition, it was found that the amount of glass phase(SiO$_2$) have an main effect to decrease the dielectric loss(tan$\delta$), and the dielectric breakdown voltage of aluminous porcelain insulators was largely affected by its relative density. As a micro tracks analysis, HRB were measured, then the intensity of HRB increased with the amount of alumina composition. On the other hand, the propagation behaviors of cracks was fairly influenced by the distribution of pores.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.85-88
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• 2003

In this study, porcelain insulator samples which have a different alumina composition were manufactured in order to test electrical and mechanical properties and make an analysis of the propagation phenomena of micro cracks on porcelain body. From XRD quantitative analysis the crystalline phases were different with alumina composition, sample C and D which have about 17wt% Corundum phase without the Cristobalite phase shows better electrical and mechanical properties than sample A and 8 which have the Cristobalite phase. In dielectrics test on porcelain samples with below 17wt% alumina composition, it was found that the amount of glass phase$(SiO_2)$have an main effect to decrease the dielectric loss$(tan{\delta})$, and the dielectric breakdown voltage of aluminous porcelain insulators was largely affected by its relative density. As a micro cracks analysis, HRS were measured, then the intensity of HRS increased with the amount of alumina composition. On the other hand, the propagation behaviors of cracks was fairly influenced by the distribution of pores.

• The Journal of Korean Academy of Prosthodontics
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• v.37 no.6
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• pp.756-766
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• 1999

This study was performed to evaluate effect on color and opacity of 3 different copy-milled In-Ceram cores by glass infiltration and porcelain veneering. Color was evaluated by the $CIEL^*a^*b^*$ readings were recorded with a Colorimeter, Color difference value(${\Delta}E^*_{ab}$) was calculated and opacity was represented by the contrast ratio. The variance of each color parameter ($L^*,\;a^*,\;b^*$), color difference value, and opacity change after glass-infiltrated and after veneered with porcelain was compared. Three experimental groups were fabricated as follows. Group 1 (Alumina core) 15 Alumina blanks was infiltrated with originally marketed glass (A1) and veneered with porcelain(A1) Group 2 (modified Alumina core) : 15 Alumina blanks was infiltrated with its associated glass(S11) and veneered with porcelain(A1) Group 3 (Spinell core) : 15 Spinell blanks was infiltrated with originally developed glass(S11) and veneered with porcelain(A1). The results were as follows: 1. After glass infiltration, $L^*$ value showed decrease, $a^*$ value showed decrease only group 1(p<0.001) and $b^*$ value showed increase on group 1, increase on group 2, 3(p<0.001). 2. After porcelain veneering, $L^*$ value showed decrease(p<0.001), $a^*$ value showed increase on group 1, decrease on group 2(p<0.05) and $b^*$ value showed decrease on group 1, increase on group 2, 3 (p<0.001). 3. ${\Delta}E^*_{ab}$ between before and after glass infiltration was more than 13.77, and between after glass infiltration and after porcelain veneering more than 19.63. 4. After glass infiltration and porcelain veneering, Alumina showed the lowest $L^*,\;a^*$ value and highest $b^*$ value among 3 different groups (p<0.05). ${\Delta}E^*_{ab}$ between group 1-2, 1-3 was higher than that of group 2-3. 5. After glass infiltration, opacity showed decrease, Group 1 had the highest opacity(p<0.05), but no significant differences between group 2 and 3. Above results suggest that glass infiltration and porcelain veneering effects on color and opacity of In-Ceram core, and that modified In-Ceram Alumina uses single crowns or bridges like In-Ceram Spinell.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.61-68
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• 1999

To analyze several defects and residual stress in sintering of layer structure materials, multiayer materials with TZP/SUS and ZT/SUS, and bilayer materials with porcelain/alumina and porcelain/Y-TZP were fabricated by sintering method. Multilayer materials prepared by pressureless sintering show the sintering defect such as warping, splitting, cracking originated from the difference of sintering shrinkage between each layer, which could be controlled by the adjustment of number and thickness in interlayer. In tape casting, a certain pressure given during sintering relaxed the sintering defects, specially warping. The residual stress in bilayer was examined with Vickers indentation method. A small tensile stress in porcelain/alumina and a large compressive stress in porcelain/Y-TZP were generated on the porcelain interface due to the thermal expansion mismatch, which affected the strength of bilayer materials. As a consequence, the sintering defects of multilayer materials and the residual stresses of bilayer materials were dominantly influenced on material design and starting material constants.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.168-172
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• 2011

Alumina powder was added in a general porcelain (Backja) with clay, feldspar and quartz contents to promote the mullite ($3Al_2O_3{\cdot}2SiO_2$) generation in the porcelain. Low melting materials ($B_2O_3(450^{\circ}C)$, $MnO_3(940^{\circ}C)$, CuO($1080^{\circ}C$)) were doped at ~3 wt% to modify the sinterability of porcelain with a high alumina contents and promote the mullite generation. Green body was made by slip casting method with blended slurry and then, they were fired at $1280^{\circ}C$ for 1hr by a $2^{\circ}C/min$. Densifications of samples with high alumina contents (20~30 wt%) were impeded. As the doping contents of low melting materilas increased, the sinterability of samples was improved. The shrinkage rate and bulk density of samples were improved by doping with low melting materials. Mullite phase increased with increasing the low melting contents in the phase analyses. This means lots of alumina and quartz were transformed into mullite phase by low melting contents doping. In the results, high bending strength of samples with high alumina contents was accomplished by improving the densification and mullite generation in the porcelain.

• Transactions on Electrical and Electronic Materials
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• v.18 no.4
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• pp.207-210
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• 2017

The suspension arrangement of insulators provides flexibility and assists in power transmission in transmission lines. The performance of the insulator string is strongly influenced by the environmental conditions to which it is exposed, its shape and the inherent material properties of suspension-type insulators. The suspension-type insulators are mostly made from glass, porcelain and ceramic material due to their high resistivity. Irregularity in charge distribution throughout the porcelain insulator may lead to accelerated aging and electrical breakdown. A very high and steep lightning impulse voltage may also cause breakdown of suspension-type insulators. We investigated various material characteristics such as alumina addition, surface morphology, x-ray diffraction pattern and relative density of suspension porcelain insulators manufactured in 1989 (36,000 lbs.), 1995 (36,000 lbs.) and 2001 (36,000 lbs.) by the KRI Company for use in 154 kV high power transmission lines. We compared the material characteristics of these porcelain insulators with that of the top-of-the-line porcelain insulators (36,000 lbs.) manufactured by the NGK Company in 2000. These suspension-type porcelain insulators were exposed to arc and flashover tests to examine their electrical and mechanical strength. It was noted that alumina addition (17 wt.%) for K-2001 was one of the major contributors to the enhancement of the performance of the porcelain insulators and to their ability to withstand very high current generation during the arc test. The porcelain insulators manufactured during 2001 also showed the highest relative density of 95.8% as compared to the other insulators manufactured in 1989 and 1995 respectively 94.2% and 91.5%. We also discuss reports of various failure modes of suspension-type porcelain insulators.

• The Journal of Korean Academy of Prosthodontics
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• v.31 no.3
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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.

• KIEE International Transactions on Electrophysics and Applications
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• v.5C no.1
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• pp.8-13
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• 2005

In order to analyze the properties of domestically produced 36,000lb porcelain insulators by change of the alumina addition to raw materials, 36000lb ball socket type suspension insulators that were manufactured in 1989, 1995 and 2001 were removed from transmission lines and an experiment was performed. The results indicated that 8 [wt.%] alumina, which influences the mechanical properties and arc resistance properties in the case of insulators that were manufactured in 1989 was contained, and the relative density and the fracture toughness of insulators appeared by 94.2% and 1.4 [MpaㆍM/sup 1/2/], respectively. However, 12 [wt.%] alumina was contained in the case of insulators that were manufactured in 1995, and the relative density and the fracture toughness of insulators appeared preferably lower by 92% and 1.3 [MpaㆍM/sup 1/2/], respectively. The greatest amount of alumina was contained by 17 [wt.%] in the case of insulators that were manufactured in 2001. It was confirmed that the electrical and mechanical characteristics such as the relative density and the fracture toughness appeared remarkably by 96% and 1.7 [Mpaㆍm/sup 1/2/], respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.33 no.1
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• pp.50-55
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• 2020

Porcelain insulators have been used for a long time in 154 kV power transmission lines. They are likely to be exposed to sudden failure because of product deterioration. This study was conducted to evaluate the quality of porcelain insulators. After stresses were applied, the damaged regions of aged insulators were investigated in terms of chemical composition, material structure, and other properties. For porcelain insulators that were in service for a long time, the mechanical failure load was 126 kN, whereas the average mechanical failure load was 167.3 kN for new products. It was also determined that corrosion occurred at the metal pin part due to the penetration of moisture into the gap between the pin and the ceramic. Statistical analyses of failure were performed to identify the portion of the insulators that were broken. Cristobalite porcelain insulators fabricated without alumina additives had a high failure rate of 54% for the porcelain component. In the case of the addition of Alumina (Al₂O₃) to the porcelain insulators to improve the strength of the ceramic component, a more frequent damage rate of the cap and pin of 73.3% and 27%, respectively, was observed. This study reports on the material component of SiO₂ and the percentage of alumina added, with respect to the mechanical properties of porcelain insulators.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.317-318
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• 2005

This paper presents the analysis on the properties of porcelain insulators with the manufactured year. The domestic porcelain insulators manufactured in 1995, 1997, and 2002 and the imported one are prepared. The content of alumina was increased with the manufactured year, and the hardness of ceramic parts showed the same trend. Moreover, the distribution and the size of pore were more decreased and reduced on the junction parts between the glaze and the ceramic. Therefore, we concluded that the domestic porcelain insulators have been improved with the lapse of time.