• Korean Journal of Materials Research
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• v.10 no.9
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• pp.619-623
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• 2000

Alumina membrane was prepared by sol-gel coating method using boehmite powder(${\Upsilon}-AlOOH$). The supported and the unsupported alumina membrane were fabricated to investigate the phase transformation and change of microstructure. It is important to control the homogeneous pore size and distribution in application of filtering process. The ${\theta}-to\;{\alpha}-AL_2O_3$ phase transformation (XRD) and the change of microstructure was investigated using scanning electron microscopy(SEM). XRD patterns showed that the supported membrane had $100^{\circ}C$ higher ${\theta}-to\;{\alpha}-AL_2O_3$ transformation temperature compared to the unsupported membrane. The similar effect was also observed for microstructural change of the membrane.

• The Journal of Advanced Prosthodontics
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• v.7 no.3
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• pp.214-223
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• 2015

PURPOSE. To measure the surface loss of dental restorative zirconia and the short-term bond strength between an indirect composite resin (ICR) and zirconia ceramic after various sandblasting processes. MATERIALS AND METHODS. Three hundred zirconia bars were randomly divided into 25 groups according to the type of sandblasting performed with pressures of 0.1, 0.2, 0.4 and 0.6 MPa, sandblasting times of 7, 14 and 21 seconds, and alumina powder sizes of 50 and $110{\mu}m$. The control group did not receive sandblasting. The volume loss and height loss on zirconia surface after sandblasting and the shear bond strength (SBS) between the sandblasted zirconia and ICR after 24-h immersion were measured for each group using multivariate analysis of variance (ANOVA) and Least Significance Difference (LSD) test (${\alpha}$=.05). After sandblasting, the failure modes of the ICR/zirconia surfaces were observed using scanning electron microscopy. RESULTS. The volume loss and height loss were increased with higher sandblasting pressure and longer sandblasting treatment, but they decreased with larger powder size. SBS was significantly increased by increasing the sandblasting time from 7 seconds to 14 seconds and from 14 seconds to 21 seconds, as well as increasing the size of alumina powder from $50{\mu}m$ to $110{\mu}m$. SBS was significantly increased from 0.1 MPa to 0.2 MPa according to the size of alumina powder. However, the SBSs were not significantly different with the sandblasting pressure of 0.2, 0.4 and 0.6 MPa. The possibilities of the combination of both adhesive failure and cohesive failure within the ICR were higher with the increases in bonding strength. CONCLUSION. Based on the findings of this study, sandblasting with alumina particles at 0.2 MPa, 21 seconds and the powder size of $110{\mu}m$ is recommended for dental applications to improve the bonding between zirconia core and ICR.

• Journal of Life Science
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• v.13 no.3
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• pp.365-373
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• 2003

Instead of deodorization appararus of fish oil, an adsorbent such as activated charcoal, activated alumina, silicagel, bamboo charcoal was packed in column alone or mixed with preparative ratio, and then test the effective deodorization with bleaching. In the progress of degumming, the effective method was 18 ml of 2.5% oxalic acid per 100m1 of crude large anchovy oil. The optical condition to deacidified was treating for 30 min at $40^{\circ}C$ with 2.5% sodium hydroride solution. The effective deodorization was added with 3% silicagel under the alone treating adsorbent, and mixed treating was 30% activated alumina and 10% silicagel but added to green tea powder was not effective. The major fatty acid of total lipid were 16:0, 20:5n-3, 18:1n-9, 16:1n-7 and 22:6n-3 after treatment of degumming, deacidfication and deodorizing in the large anchovy oil. The oxidative stability of refined anchovy oil added to $\alpha$-tocopherol was validated 20 days under the control, and 30 days in the case of $\alpha$-tocopherol. The 0.01% $\alpha$-tocopherol was more effective than 0.02% $\alpha$-tocopherol.

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.100-108
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• 1989

Aluminum hydroxides were prepared by the alkoxide hydrolysis method using Al-isopropoxide as a starting material and NH4OH as a catalytic agent. When Al-isopropoxide was hydrolyzed in a H2O-NH3 system, only Al(OH)3 was obtained over all pH values. However, AlOOH was formed besides Al(OH)3 when Al-isopropoxide was hydrolyzed in a H2O-NH3-isopropyl alcohol system. The AlOOH/Al(OH)3 ratio was increased as the isopropyl alcohol content was increased. The hydroxides, Al(OH)3 and AlOOH, obtained in this study and the commerical products, $\alpha$-Al2O3 and AlOOH were subjected to the carbothermal reduction and nitridation reaction to product AlN powder, using carbon black as a reducing agent under N2 atmosphere at various temperatures. AlN was synthesized from the obtained Al(OH)3 and the commercial AlOOH at 145$0^{\circ}C$, however, synthesized from the obtained AlOOH and the commercial alpha-alumina at 135$0^{\circ}C$. The temperature difference is assumed to be attributed to the reactivity of those powders. AlN powder prepared from the Al-isopropoxide was observed to have the narrower particle size distribution than that prepared from the commercial $\alpha$-Al2O3 or AlOOH.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.1007-1010
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• 2002

Alpha alumina platelet particles were synthesized from the powder mixture of ${\gamma}-Al_2O_3and\;Na_2SO_4$ with the use of microwave heating. The characteristics of the particles such as particle size and particle size distribution were compared with those of particles obtained from the same mixture without the use of microwave. Sample with the use of microwave showed small particle size and narrow particle size distribution compared to that without the use of microwave.

• Korean Chemical Engineering Research
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• v.43 no.4
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• pp.503-510
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• 2005

In this research, composite alumina was prepared to add the various promoters by sol-gel method and examined its thermal stability. After sintering at $1,200^{\circ}C$, the thermal stability resulted in following order, $Si{\fallingdotseq}La$ > Ti > $Ba{\fallingdotseq}Ce$ > Y > $Zr{\fallingdotseq}Mg$, in accordance with adding the promoters. Especially in case of silica-added alumina, a phase transformation temperature to ${\alpha}$-alumina increased about $150^{\circ}C$ and after sintering at $1,200^{\circ}C$, it showed to maintain in ${\gamma}$-form and ${\delta}$-form alumina phase. Also it showed an increase of surface area from $3m^2/g$ to $71m^2/g$ compared with pure ${\alpha}$-alumina. In the case of silicaadded alumina, the characterization change of this alumina particle resulted in a delay of phase transformation because Si-O-Al bond was increased when sintered at high temperature. In case of lanthanum-added alumina, there was a sintering delay phenomenon in inter-particles as $LaAlO_3$ structure existed. The existence of lanthanum structure was confirmed by XRD and XPS analysis. It appeared on the alumina surface as $La_2O_3$ structure when it was sintered under $1,000^{\circ}C$, as the perovskite structure of $LaAlO_3$ at above $1,000^{\circ}C$ and as the magneto-plumbite structure of $LaAl_{11}O_{18}$ at above $1,300^{\circ}C$.

• The Korean Journal of Ceramics
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• v.1 no.3
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• pp.137-142
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• 1995

Monodispersed $Al_2O_3-TiO_2$ Powder was prepared by metal-alkoxide hydrolsis. A homogeneous nucleation/growth occurred in the solutions containing ethanol, butanol and acetonitrile, and resulted in spherical, submicrometer-sized powder. The titania and the alumina crystals were formed at $800^{\circ}C$ and $1000^{\circ}C$, respectively. These crystala were subsequently reacted each other beyond $1320^{\circ}C$ and formed $Al_2TiO_5$. The relative densities of sintered bodies prepared with as-received powder were examined at the temperature range of 1300-$1500^{\circ}C$ and they were about 79% at $1300^{\circ}C$. The formation of aluminum titanata decreased the relative density at the temperature range of 1300-$1450^{\circ}C$, and at above $1450^{\circ}C$, the relative density started to increase again. It was observed that $\alpha-Al_2O_3$-doped aluminum titanate was more stable than pure aluminum titante at $1200^{\circ}C$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.645-650
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• 1998

Alumina- and yttria-coated SiC powder was prepared by the surface-induced precipitation method, and sintered properties of silicon carbide prepared from this powder were investigated. After a well dispersion of SiC powders in the aqueous solution of $Al_2(SO_4)_3$ and $Y_2(SO_4)_3$, the mixed precursors of aluminum hydroxide, aluminum carbonate, yttrium hydroxide, and yttrium carbonate were precipitated on the surfaces of SiC particles through the hydrolysis reaction of urea. SiC specimens with alumina and yttria exhibit, 97.8% of theoretical density after the sintering at $1900^{\circ}C$ for 2 hrs. During annealing at $2000^{\circ}C$, $\beta$longrightarrow$\alpha$ phase transformation of SiC had taken place and resulted with a rodlike microstructure. Toughness of sintered SiC was enhanced by crack deflection around the rodlike grains. In case of annealing less than that of 3 hr, the fracture toughness of SiC was slightly improved with increasing the amount of sintering aid. However, annealed specimens for a long time showed constant fracture toughness even though the amount of sintering aid increased. It is resulted that the main factor for toughening in annealed SiC for a long time is the pullout effect of rodlike grains during the propagation of cracks, and the amount of sintering aids is less effective on the fracture toughness of SiC.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.513-519
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• 1994

Alumina composite was fabricated by introducing tetragonal ZrO2 in alumina composite of $\alpha$-alumina reinforced with in-situ formed La-$\beta$-aluminate (LaAl11O18). The powder mixture of composition (100-x)[88 Al2O3+(La2O3+11 Al2O3)]+x vol% ZrO2 was prepared with x from 0 to 40. Dense composites fabricated by hot-pressing exhibited bending strength up to 1200 MPa. The gain growth inhibiting effect of ZrO2 grains and La-$\beta$-aluminate platelets, and possibly the stress-induced phase transformation of ZrO2 have resulted in the high bending strength. The fracture toughness of the composite also increased up to 8.5 MPa.m1/2. The enhancement in toughness can be explained by transformation and microcrack toughening of ZrO2 and by crack deflection and bridging of La-$\beta$-aluminate platelets and ZrO2.

• Journal of the Microelectronics and Packaging Society
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• v.23 no.4
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• pp.57-61
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• 2016

Thick film sealing glass paste is required for cell packaging of NaS based battery for energy storage system, to join the beta-alumina electrolyte tube and the alpha-alumina battery cell cap components. This paper presents the effect of the particle sizes of seal glass powder and the sealing temperatures on the microstructure of the glass sealants was investigated. It was found that the larger in the particle size of seal glass powder, the smaller the pore volume and the number of pores in a unit area. Also, the number of pores decreased with increasing the sealing temperatures while the pore size was increased. This result enables the control of porosity, pore distribution and number of pores in a microstructure of glass sealing component by proper selection of glass powders particle size and sealing temperature.