• Journal of the Korean Ceramic Society
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• v.33 no.2
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• pp.163-168
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• 1996

Measurements of proton adsorption density have been conducted in preparing alumina suspensions with aqueous solutions of HCL, HNO3, H2SO4 and H3PO4 And effects of anion acid concentration proton adsorption density and solid loading on the viscosity of the alumina suspensions have been investigated. Aqueous solutions of HCl. or HNO3 were suitable for the preparation of highly concentrated suspensions as the generation of surface charge on alumina particles was depressed by the specific adsorption of {{{{ {SO }`_{4 } ^{2- } }} and {{{{ { PO}`_{4 } ^{3- } }} Optimum conditions for maximizing solid loading were dependent upon proton adsorption density and acid concentration.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1401-1407
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• 1995

Zirconia powder coated with alumina was prepared by hydrolysis of alumina butoxide. The coated powder was obtained by a hydrolysis reaction between the adsorbed water on the surface of zirconia particles and aluminum sec-butoxide. Amorphous aluminum hydroxide was uniformly coated on the surface of zirconia particles with the thickness of about 30 nm. The shape and distribution of aluminum hydroxide was varied with an existence of surfactant. The coated layer of aluminum hydroxide consists of the fine particle size, and the zirconia powder coated by alumina hydroxide have the large specific surface area of 120 $m^2$/g, compared with that of starting zirconia powder.

• Journal of the Korean Ceramic Society
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• v.15 no.4
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• pp.199-204
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• 1978

In the present investigation, refined alumina obtained from alunite locally available was used as a aluminous source to synthesize monocalcium aluminate $(CA)_3$ the major mineral constituent of alumina cement. The influence of $SiO_2$ and $Fe_2O_3$ contents on the formation of monocalcium aluminate was studied by X-ray diffraction analysis mainly. About 0.8-1.0 of $Al_2O_3/C_3O$ mol ratio and less than 4 percent of $SiO_2$ were desirable for the effective formation of CA. The small amount of alkali and sulphur contents contained in refined alumina from alunite as the impurities were affected to form $C_4A_3S$ and $C_3S_2$, disadvantageous compounds for the alumina cement, therefore the impurities should be restricted in minimum content as possible.

• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.60-66
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• 1991

The polymeric alumina sol was prepared by partial hydrolysis of aluminum sec-butoxide reacted with acetylacetone and its characteristics was investigated. The effects of alcohol solvent, acetylacetone, and acid concentration to the sol were investigated. FT-IR and Al27-MASNMR were used to study hydrolysis and polymerization reaction of aluminum complex. Synthesized sol showed the characteristics of polymeric alumina sol. To make a clear polymeric alumina sol, the optimum contents of acetylacetone, H2O and alcohol solvent were 0.4-0.6 mole, 0.25-1.25 mole, 3-5 mole per one mole alkoxide respectively. As a result of the Al27-MASNMR analysis, it was noted that hexa-penta-coordinated Al were main structure.

• Journal of the Korean Ceramic Society
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• v.30 no.11
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• pp.933-940
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• 1993

SO42-/Al2O3 powder was prepared by the coprecipitation method from the Al(NO3)3.9H2O and NH4OH and followed by being treated with various concentrations of sulfuric acid. The characterization of these powders was performed with XRD, BET and FT-IR. The surface charge density at alumina/KCl(aq) interface was measured by potentiometric titration method. From the experimental data it was shown that acid strength, specfic surface area, and structure of surface treated alumina were independent on the amount of exchanged SO42-. However, the acid amounts of alumina were increased with the amounts of SO42- formed on alumina surface. The relation between the acid amount of SO42- ion exchanged alumina surface and the surface charge density for SO42-/Al2O3/KCl(aq) interface was investigated.

• Journal of the Korean Ceramic Society
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• v.31 no.4
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• pp.347-358
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• 1994

Creep densification and grain growth of alumina powder compacts during high temperature processing were investigated. The creep densification and grain growth of alumina powder compacts during various sintering processes were analyzed by employing the consitutive model by Kwon and Kim. Theoretical results from the constitutive model were compared with various experimental data of alumina powder compacts in the literature including pressureless sintering, sinter forging and hot pressing. The proposed constitutive equations were implemented into finite element analysis program (ABAQUS) to simulate densification for more complicated geometry and loading conditions. The effects of friction between die and powder compact or punch and powder compact during sinter forging and hot pressing are investigated by using the finite element method. Also, high temperature forming processing of alumina compact with complicated shape was simulated.

• The Journal of Korean Academy of Prosthodontics
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• v.42 no.2
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• pp.125-132
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• 2004

Statements of problem: All ceramic fixed partial denture cores can be made by the slip casting method and the advanced alumina tape method. The fracture resistance of these core connector areas is relatively low. Purpose: The purpose of this study is to standardize the appropriate volumetric figure and location of the connectors in the alumina core fabricated in alumina tape to be used in fixed partial dentures by way of topology optimization. Material and method: A maxillary anterior three-unit bridge alumina core with teeth form and surrounding periodontal apparatus model was used to ultimately design the most structurally rigid form of the connector. Loadings from a $0^{\circ}$, $45^{\circ}$ and $60^{\circ}$ to the axis of each tooth were applied and analyzed with the 3-D finite element analysis method. Using the results from these experiments, the topology optimization was applied and the optimal reinforcement layout of connector was obtained and the detail shape in the fixed partial denture core was designed. Results: The modified prosthesis with the form of a bulk in the lower lingual surface of the connector in the event, reduced the stress concentration up to 20% in the 3-D FEA. Conclusion: The formation of a bulk in the lower lingual connector area of an alumina core for a fixed partial denture decreases the stress to a clinically favorable measure but does not harm the esthetic point of view. This result illustrates the possibility of clinical application of the modified form designed by the topology optimization method.

• Journal of the Korean Ceramic Society
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• v.41 no.7
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• pp.508-512
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• 2004

For abutment of dental implants, (Y, Nb)-TZP/Alumina composites were prepared by addition of 10-90 vol% alumina at an interval of 10 vol％ into tetragonal zirconia solid solution which consists of 90.24 mol% Zr $O_2$, 5.31 mol% Y$_2$ $O_3$, and 4.45 mol% Nb$_2$O$\_$5/. Biaxial flexure strength and fracture toughness of composite were optimized by adding 10 vol% alumina, which resulted in 900 MPa and 8.9 MPam$\^$1/2/, respectively. The composite did not undergo low temperature degradation even after autoclave treatment at 200$^{\circ}C$ for 10 h. 65 of (Y, Nb)-TZP/Alumina composite abutments were employed into 40 patients and any adverse reaction, screw loosing, or fracture of abutments was not observed for the span of 2 years, indicating that the ceramic abutments can be safely used for restorations.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.1 s.178
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• pp.80-88
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• 2006

In this study, unsintered and presintered low purity alumina ceramics were machined with various tools to clarify the machinability and the optimum cutting conditions. The main conclusions obtained were as fellows. Machined with ceramic tool, the ceramics presintered at the temperature range of $1000\~1100^{\circ}C$ showed the best machinability due to the adhesion formed in weared surface within a certain cutting speed range. In the above combination and conditions, the ceramic tool showed the highest productivity through all experiments. The life of CBN tool was longer in machining of the ceramics presintered at $1000^{\circ}C$ than in the case of that presintered at $600^{\circ}C$, but the diamond tool showed adverse tendency. In machining of the ceramics presintered at $1000^{\circ}C$, the ceramic tool exhibits the longest tool life in high speed, the tool lives became extremely worse in the order of CBN tool and diamond tool. However, in the case of the ceramics presintered at $600^{\circ}C$, the diamond tool shows the longest tool life, the tool lives was much worse in the order of CBN tool and ceramic tool.

• Journal of Powder Materials
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• v.22 no.6
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• pp.438-442
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• 2015

Porous thick film of alumina which is fabricated by freeze tape casting using a camphene-camphor-acrylate vehicle. Alumina slurry is mixed above the melting point of the camphene-camphor solvent. Upon cooling, the camphene-camphor crystallizes from the solution as particle-free dendrites, with the $Al_2O_3$ powder and acrylate liquid in the interdendritic spaces. Subsequently, the acrylate liquid is solidified by photopolymerization to offer mechanical properties for handling. The microstructure of the porous alumina film is characterized for systems with different cooling rate around the melting temperature of camphor-camphene. The structure of the dendritic porosity is compared as a function of ratio of camphene-camphor solvent and acrylate content, and $Al_2O_3$ powder volume fraction in acrylate in terms of the dendrite arm width.