• Journal of the Korean Applied Science and Technology
• /
• v.33 no.2
• /
• pp.247-254
• /
• 2016

Since microzirconia has excellent thermal and mechanical properties with high chemical and electrical resistance, it can be used in various fields. When the surface of zirconia becomes hydrophilic, its dispersibility in water will be improved as well as the resistance to most hydrophobic contaminants will be increased. In this study, we investigated the introduction of a hydrophilic groups on the microzircornia surface through hydrolysis and condensation reactions with two different silanes containing hydrophilic functional groups, such as ${\gamma}$-aminopropyltrimethoxysilane (APS) and ${\gamma}$-ureidopropyltrimethoxysilane (UPS) at different pH and concentration conditions. A covalent bond formation between the surface hydroxyl groups of zirconia and that of hydrolyzed silanes was confirmed by ninhydrin test and FT-IR spectroscopy. However, the presence of Si on the surfaces of both silane modified microzirconias was unable to detect by SEM/EDS technique. In addition, particle size analysis results provide that the size of microzirconia was changed to smaller or bigger than that of original zirconia due to crushing and aggregation during the modification process. The water dispersibility was improved for only APS modifed zirconia (AS-2 and AS-3) under neutral pH condition, but the water dispersibility and stability for all cases of 0.5~2% UPS modifed zirconia (US series) were much improved.

• Resources Recycling
• /
• v.25 no.3
• /
• pp.49-54
• /
• 2016

In this study, zircon sand is separated into zirconia and silica by using the Ar-$H_2$ arc plasma refining. And then silica is removed from it by the microwave leaching method to produce a high pure zirconia. Plasma melting consist of two sequential processes; reduction process with Ar gas only followed by refining process with Ar-$H_2$ gas. After cooling in chamber. The solid phase obtained at $240^{\circ}C$ were found to be composed of 20% sulfuric acid solution. The solution was used as a leaching solution with microwave irradiation to obtain a high purity zirconia.

• Journal of Dental Rehabilitation and Applied Science
• /
• v.25 no.2
• /
• pp.95-107
• /
• 2009

The purpose of this research was to examine the fitness of zirconia cores that were made by different sintering methods; generic electricity furnace and microwave furnace. Firstly, 12 cores for each group were made by using each different sintering process and attached them to a metal die with silicon. The internal and marginal gap of sintered zirconia was measured by using Skyscan 1076 micro-CT, then it was reorganized by CT-An software. To each samples, we extracted B-L image, M-D image of cutting side, and cross-sectional side of tooth long axis and calculated the mean value of marginal, axial, and occlusal gap each side. Results: 1. The mean marginal gap of sintered zirconia was $36.20{\mu}m$ for EVE, $47.67{\mu}m$ for LAV, $52.47{\mu}m$ for DEN, and $54.63{\mu}m$ for CER. 2. For the axial wall, the research showed the largest value of $63.49{\mu}m$ for EVE, but there were no statistical significance. 3. In related to the occlusal internal measurement, DEN showed the smallest value ($77.06{\mu}m$), EVE and CER showed significantly high value. From this study, it is suggested that CAD/CAM zirconia core which was made in the process of microwave sintering has clinically acceptable values in marginal and internal gap.

• Journal of the Microelectronics and Packaging Society
• /
• v.21 no.4
• /
• pp.133-137
• /
• 2014

As a preceding process for preparing several micrometer sized Ag-coated Cu flakes, ball milling of submicrometer-sized Cu particles synthesized through a wet chemical method was performed in order to convert the particles into flakes. To suppress oxidation and aggregation of the particles during ball milling, ethylene glycol and ethyl acetate were used as a medium and a surface modifying agent, respectively. Results obtained with different rotation speeds of a jar indicated that the rotation speed changes a rotating mode, and strikingly alters the final shapes and shape uniformity of Cu particles after milling. The diameter of zirconia ball was also confirmed. Although there was aggregates in the initial submicrometer-sized Cu particles, therefore, well-dispersed Cu flakes with a size of several micrometers were successfully prepared by ball milling through optimization of rotation speed, amount of ethyl acetate, and diameter of zirconia ball.

• Journal of the Microelectronics and Packaging Society
• /
• v.6 no.1
• /
• pp.23-29
• /
• 1999

An yttria-stabilized zirconia(YSZ) thin film on a porous NiO-YSZ substrate for an anode support type solid oxide fuel cell(SOFC) was prepared by an electrophoretic deposition(EPD). Deposition condition and film properties in order to obtain the homogeneous YSZ thin film from the EPD solution with different polarity were studied. In different case of alcohol solution, hydrogen gas was produced in aqueous solution from the electrolyte reaction under constant current above 0.138 mA /$\textrm{cm}^2$.Its reaction generated the bubble-formed defect in the deposited film and decreased weight of the film. The homogeneous YSZ thin film was formed in alcohol solution at a constant current, 0.035 mA /$\textrm{cm}^2$ for 10 s.

• Journal of the Microelectronics and Packaging Society
• /
• v.6 no.1
• /
• pp.51-58
• /
• 1999

The effects of glass composition on the wettability and reactivity with $ZrO_2$substrate was evaluated and fabrication variables and glass compositions was investigated. Various glass compositions was investigated. Alkaline earth silicate glass show good wettability and lower viscosity and crystallization of glass could be prevented by $B_2O_3$.The sealant glass begin to wet on $ZrO_2$substrate below $900^{\circ}C$ and porosity occurred in various glass compositions, the crystallization and porosity in the glass could be prevented by the addition of flux into glass composition. But flowability and reactivity of glass with $ZrO_2$substrate was enhanced. Processing variables should be optimized to reduce the porosity by enhancing the sintering of glass powder. Many silicate glasses were investigated for the applications of high temperature sealants. Wetting and bonding of glass was good enough to seal together between $ZrO_2$and other ceramic components of SOFC. But porosity and reaction layer were occurred in the sealant glass. It will be possible to produce glass sealant without porosity and reaction layer at the interface by optimization of processing variable and modify the glass compositions. In present study, wettability of glass-filler composite was investigated. The porosity, shape of filler and interfacial reactions of sealant glass with fillers were examined.

• Journal of the Korean Ceramic Society
• /
• v.46 no.1
• /
• pp.108-115
• /
• 2009

In this study, a novel-processing route for producing microcellular zirconia ceramics has been developed. The proposed strategy for making the microcellular zirconia ceramics involves hollow microsphere as a pore former which has extremely low density of $0.025\;g/cm^3$. Effects of hollow microsphere content and sintering temperature on microstructure, porosity, pore distribution, and compressive strength were investigated in the processing of microcellular zirconia ceramics. By controlling the content of hollow microsphere, it was possible to make the porous zirconia ceramics with porosities ranging from 45% to 75%. Typical compressive strength value of microcellular zirconia ceramics with ${\sim}65%$ porosity was over 50 MPa. By adjusting the mixing ratio of large and small zirconia powders, it was possible to control the pore structure from close to open pores.

• Journal of Technologic Dentistry
• /
• v.34 no.1
• /
• pp.11-21
• /
• 2012

Purpose: Densification and mechanical properties of dental zirconia ceramics were evaluated by different sintering methods. Materials and Methods: Y-TZP zirconia block(Kavo $Everest^{(R)}$ ZS blank, Kavo dental GmbH, Bismarckring, Germany) was used in this study. Sintering were performed in heat sintering furnace and microwave sintering furnace, and then experimented and analyzed on a change in densification according to the sintering time, a change in densification according to thickness, flexural strength and micro-structure in zirconia specimens. Results: Microwave sintering was very effective in considerable mechanical properties such as flexural strength and bulk density was drastically increased than conventional electric heating method. It is also shown that microwave sintering time was faster and more economical than common method to be present in qualities which equal or exceed. Conclusion: It will be important to seek the accurate sintering condition of dental zirconia by microwave sintering method and the continuous research is necessary for the study of relationship between sintering methods and mechanical properties.