• Journal of Biomedical Engineering Research
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• v.19 no.5
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• pp.433-441
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• 1998

This study was performed to evaluate the effects of surface flaw on the fracture of all-ceramic materials. A feldspathic porce lain of VMK68, a cashable ceramic of IPS-Empress, and an alumina-glass composite of In-Ceram were used. Specimens were prepared as 12$\times$3$\times$1mm in dimensions, and a Vickers-produced indentation crack was made at the center of the tensile surface. Test specimens were immersed in dlstilled water and In oil, which were broken under a crosshead speed of 0.05 mm/min by 3-point bend test at 37$^{\circ}C$. The characteristic patterns of Vickers indentation and fracture surfaces were examined by an optical microscope and a scanning electron microscope. The fracture surfaces of the VMK68 and the IPS-Empress showed a median crack pattern at the fracture origin and indicated a tendency to cleavage hackle. The fracture surface of the alumina-glass composite, In-Ceram, showed a Palmqvist crack pattern at the fracture origin and indicated a tendency of toughening by the frictional Interlocking between the microstructurally rough fracture surfaces.

• Proceedings of the Korean Ceranic Society Conference
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• 2002.10a
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• pp.181.1-181
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• 2002

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.279-279
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• 2007

Synthesis and dielectric properties of glass-ceramic composites with zinc borosilicate glass(here after ZBS glass) were investigated as functions of $ZnAl_2O_4$ phase synthesis method, glass addition (50~60 vol%) and sintering temperature ($600{\sim}950^{\circ}C$ for 2 hrs). The 50 vol% ZBS glass-$Al_2O_3$ and 60 vol% ZBS glass-$ZnAl_2O_4$ ensured successful sintering below $900^{\circ}C$. But the composition of 100-x-y vol% ZBS glass-x vol% $Al_2O_3-y$ vol% ZnO exhibited poor sinterability below $900^{\circ}C$ and the swelling phenomenon occurred in this composite with the large amount of ZBS glass. The sintering behavior of Glass-ceramic composites was affected by the crystallization of $ZnAl_2O_4$ which was formed by the reaction between ZBS glass and $Al_2O_3$. Dielectric constant (${\varepsilon}_r$), $Q{\times}f$ value and temperature coefficient of resonant frequency (${\tau}_f$) of the composite with 50 and 60 vol% ZBS glass contents demonstrated $ZBS-Al_2O_3({\varepsilon}_r=5.7)$, $ZBS-ZnAl_2O_4({\varepsilon}_r=5.8)$ which is applicable to substrate requiring an low dielectric properties.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.1
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• pp.44-50
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• 2013

E-glass fiber is the most widely used glass fiber for reinforced composite materials of aircrafts, automobiles and leisure equipments. But recently researches are being progressed to reduce boric oxide from 8 % to 0 (zero), as is called 'Boron free E-glass', because of increasing material cost, environmental problem, and improving chemical resistance and mechanical properties of E-glass fiber. In this study, we fabricated the bulk glass and fiber glass of 'Boron free E-glass (BF) compositions', and characterized thermal properties and optical properties. 'Boron free E-glass (BF)' was obtained by the melting of mixed batch materials at $1550^{\circ}C$ for 2 hrs with different $Al_2O_3$ compositions 5~10 %. We obtained transparent clear glass with high visible light transmittance value of 81~86 %, and low thermal expansion coefficient of $4.2{\sim}4.9{\times}10^{-6}/^{\circ}C$ and softening point of $907{\sim}928^{\circ}C$. For the chemical resistance test of 'BF' fiber samples, we identified that the higher alumina contents gives the better corrosion resistance of glass fiber.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.12
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• pp.1106-1111
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• 2006

To improve warpage, delamination and the chemical reaction between 2 different co-fired materials, the bonding behavior with common glass was studied. As shown in the previous paper, the phenomenon of the infiltration is different with the composition of the glass. In particular, in the case of low temperature melting glass, infiltration is experimented in this study. GA-1 glass is infiltrated among $BaTiO_3$ particles below $800^{\circ}C$ and is made by glass/ceramic composite. Until the laminate is fired under $850^{\circ}C$, provskite phase is observed. Although in the case of GA-12 glass, the temperature of the glass infiltration is lower than it of GA-l glass, the perovskite phase already disappears at $800^{\circ}C$. As a result, GA-1 and GA-12 glasses are infiltrated among particles at low temperature, however, the chemical reactivity of the glass/ceramic and sintering temperature should be considered.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.6
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• pp.429-433
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• 2013

PTFE composites for use of microwave substrate were fabricated by impregnation and heat treatment fabrication with glass fabric. This study shows dielectric properties such as dielectric constant and loss can be controlled by thickness of PTFE composite with change of pressure condition in heating press process. The dielectric constant of the PTFE composites has decreasing tendency as given higher pressure condition. The dielectric loss has similar result too. Especially, the case of the dielectric loss was affected by the condition of pressure at heating press and had the best performance under 3 MPa. In order to see the reason why thickness conditions make different, their microstructures were also observed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.10
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• pp.1514-1519
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• 2001

This paper is concerned with design, manufacturing and performance test of LIPCA ( Lightweight Piezo- composite Curved Actuator) using a top carbon fiber composite layer with near -zero CTE(coefficient of thermal expansion), a middle PZT ceramic wafer and a bottom glass/epoxy layer with high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by thigh tweight fiber reinforced plastic layers without losing capabilities to generate high force and large displacement. It is possible to save weight up to about 30% if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature (177 $^{circ}C$ after following an autoclave bagging process. It was found that the manufactured composite laminate device had a sufficient curvature after detached from a flat mold. The analysis method of the cure curvature of LIPCA using the classical lamination theory is presented. The predicted curvatures are fairly in agreement with the experimental ones. In order to investigate the merits of LIPCA, a performance test of both LIPCA and THUNDE$^{TM}$ were conducted under the same boundary conditions. From the experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDERT$^{TM}$.

• Journal of the Korean Ceramic Society
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• v.32 no.4
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• pp.405-412
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• 1995

In order to estimate the wettability of the borosilicate glasses with different composition on the noble metals of gold and silver, the measurements of the contact angle between the solid and the liquid were made at various temperatures and holding times using the sessil-drop method. The wetting behavior and the adhesion of the phases were strongly influenced by the thermal or the physical characteristics of the materials. The dependence of wetting angle ($\theta$) on the holding time (t) could be represented by the relation of $\theta$=a.tb, whereby the wettability of the systems was quantitatively compared. Also with increasing content of borosilicate glass in the glass-gold matrix composite, the tensile strength was decreased whereas the elastic modulus was increased.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.542-548
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• 2012

The viscosity of a ceramic slurry depends on the slurry concentration, particle shape and size, hydrodynamic interactions, temperature, shear rate, pre-treatment condition and the method of measurement with the selected equipment. Representative ceramic slurries with low to high viscosity levels are selected from colloidal silica, barium titanate slurry and glass frit paste. Rotational rheometers and vibrational viscometers are used to compare the measured viscosity for various ceramic slurries. The rotational rheometer measured the viscosity according to the change of the shear rate or the rotational speed. On the other hand, the vibrational viscometer measured one point of the viscosity in a fixed vibrational mode. The rotational rheometer allows the measurement of the viscosity of a ceramic paste with a viscosity higher than 100,000 cP, while the vibrational viscometer provides an easy and quick method to measure the viscosity without deformation of the ceramic slurry due to the measurement method. It is necessary to select suitable equipment with which to measure the viscosity depending on the purpose of the measurement.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.4
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• pp.180-188
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• 2013

The glass of E-glass fiber composition was fabricated by using refused coal ore which is obtained as by-product from Dogye coal mine in Samcheok. We used silica-alumina refused coal ore which has low carbon content relatively, and the amount of refused coal ore has been changed from 0 to 35 % in batch composition. E-glass was fabricated by the melting of mixed batch materials at $1550^{\circ}C$ for 2 hrs with different refused coal ore composition of 0~35 %. We obtained a transparent and clear glass with high visible light transmittance value of 81~84%, thermal expansion coefficient of $5.39{\sim}5.61{\times}10^{-6}/^{\circ}C$ and softening point of $851{\sim}860^{\circ}C$. The glass fiber samples were also obtained through fiberizing equipment at $1150^{\circ}C$, and tested chemical resistance and tensile strength to evaluate the mechanical property as a reinforced glass fiber of composite material. As the result, we identified the properties of E-glass fiber by using refused coal ore are plenty good enough compare to that of normal E-glass without refused coal ore, and confirmed the possibility of refused coal ore as for the raw material of E-glass fiber.