• The Journal of the Acoustical Society of Korea
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• 제17권2E호
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• pp.47-52
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• 1998

An analysis of dynamic responses is carried out on monoclinic anisotropic system due to a buried harmonic line source. The load is in the form of a normal stress acting along an arbitrary axis on the plane of symmetry within the orthotropic materials: In case that the line load is acting along the symmetry axis normal to the plane of symmetry, plane wave equation is coupled with verital shear wave and longitudinal wave. However, if the line load is acting along an arbitrary axis normal to the plane of symmetry, plane wave equation is coupled with vertical shear wave, longitudinal wave and horizontal shear wave. We first considered the equation of motion in a reference coordinate system, where the line load is coincident with a symmetry axis of the orthotropic material. Then the equation of motion is transformed into one with respect to general coordinate system with azimuthal angle by using transformation tensor. Plane wave solutions of monoclinic systems are derived for infinite media. Finally complete solutions for the plane harmonic wave are obtained by calculating the inverse of the integral transforms, in which bulk wave poles are avoided by deforming the contour of the integration to the complex plane. Numerical results for examples of orthotropic material belonging to monoclinic symmetry are demonstrated.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1998년도 추계학술대회 논문집
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• pp.311-314
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• 1998

The effects of the additions of transition metal oxides on ZrO$_2$ - Y$_2$O$_3$ (Y$_2$O$_3$ - containing tetragonal zirconia polycrystals : Y-TZP) system has been studied by investigating fracture toughness and phase stability of the sintered specimens. In the specimens sintered at 1450$^{\circ}C$ for 2hrs in air the phase transformation from tetragonal to monoclinic was observed. The ratios of monoclinic phase to tetragonal phase were changed with the additions of CoO, Fe$_2$O$_3$ and MnO$_2$, respectively, from 0.00 to 8.00wt%. The fracture toughness was increased with increasing the monoclinic to tetragonal phase ratio and was maximum at the ratio of about 18%. However, the hardness was decreased with increasing the ratio. The additions of CoO, Fe$_2$O$_3$ and MnO$_2$ together into Y-TZP resulted in more complex behaviors of fracture toughness and hardness. The specimen with the additions of 1.5wt% Fe$_2$O$_3$, 3.0wt% Al$_2$O$_3$ and 1.5wt% CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$\^$$\frac{1}{2}$/ and Vickers hardness of 1201kgf/mm$^2$.

• 대한치과기공학회지
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• 제33권4호
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• pp.323-329
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• 2011

Purpose: This study was conducted to examine the phase transition according to the zirconia surface treatment. Methods: The specimens were divided to four groups. The first group was sintered at $1,500^{\circ}C$ and ground; the second group was sintered at $700^{\circ}C$, ground, and sintered at $1,500^{\circ}C$; the third group was sintered at $1,500^{\circ}C$, ground, and $110{\mu}m$-sandblasted; and the fourth group was sintered at $1,500^{\circ}C$, ground, $110{\mu}m$-sandblasted, treated with 9.5% hydrofluoric acid, and ultrasonic cleaner-washed for two minutes. The monoclinic fractions were measured, and the surface was observed via SEM. Results: The monoclinic fraction was $0.13{\pm}0.19%$ in the control group Zr1, $1.91{\pm}0.15%$ in the experimental group Zr2, $7.71{\pm}0.34%$ in Zr3, and $8.39{\pm}0.25%$ in Zr4. On the surface, the phase transition hardly occurred in the control group Zr1, but it increasingly occurred in the experimental groups Zr3 and Zr4. Conclusion: The monoclinic fraction was high in the experimental groups Zr3 and Zr4. The phase transition did not occur in the control group, but increasingly occurred in the experimental groups.

• Journal of Magnetics
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• 제21권2호
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• pp.168-172
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• 2016

$BiMnO_3$ has been a promising candidate as a magnetoelectric multiferroic while there have been many controversial reports on its ferroelectricity. The detailed analysis of its film growth, especially the growth of thin film having monoclinic symmetry has not been reported. We studied the effect of miscut angle, the substrate surface, and film thickness on the symmetry of $BiMnO_3$ thin film. A flat $SrTiO_3$ (110) substrate resulted in a thin film with three domains of $BiMnO_3$ and 1 degree miscut in the $SrTiO_3$ (110) substrate resulted in dominant domain preference in the $BiMnO_3$ thin film. The larger miscut resulted in a nearly perfect detwinned $BiMnO_3$ film with a monoclinic phase. This strong power of domain selection due to the step edge of the substrate was efficient even for the thicker film which showed a rather relaxed growth behavior along the $SrTiO_3$ [1-10] direction.

• The Journal of Advanced Prosthodontics
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• 제16권1호
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• pp.25-37
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• 2024

PURPOSE. To investigate the effect of sintering programs and surface treatments on surface properties, phase transformation and flexural strength of monolithic zirconia. MATERIALS AND METHODS. Zirconia specimens were sintered using three distinct sintering programs [classic (C), speed (S), and superspeed (SS)] (n = 56, each). One sample from each group underwent scanning electron microscopy (SEM) and grain size analysis following sintering. Remaining samples were divided into five subgroups (n = 11) based on the surface treatments: control (CL), polish (P), glaze (G), grind + polish (GP), and grind + glaze (GG). One sample from each subgroup underwent SEM analysis. Remaining samples were thermally aged. Monoclinic phase volume, surface roughness, and three-point flexural strength were measured. Monoclinic phase volume and surface roughness were analyzed by Kruskal-Wallis and Dunn tests. Flexural strength was analyzed by two-way ANOVA and Weibull analysis. The relationships among the groups were analyzed using Spearman's correlation analysis. RESULTS. Sintering program, surface treatment, and sintering × surface treatment (P ≤ .010) affected the monoclinic phase volume, whereas the type of surface treatment and sintering × surface treatment affected the surface roughness (P < .001). Type of sintering program or surface treatment did not affect the flexural strength. Weibull analysis revealed no significant differences between the m and σ_o values. Monoclinic phase volume was positively correlated with surface roughness in the SGG and SSP groups. CONCLUSION. After sintering monolithic zirconia in each of the three sintering programs, each of the surface treatments can be used. However, for surface quality and aging resistance, G or GG can be recommended as a surface finishing method.

• 한국표면공학회지
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• 제34권5호
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• pp.486-493
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• 2001

Partially stabilized zirconia (PSZ) is an attractive material for thermal barrier coating. Zirconia exists in three crystallographic phases: cubic, tetragonal and monoclinic. Especially, the phase transformation of tetragonal phase to monoclinic phase accompanies significant volume expansion, so this transition generally results in cracking and contributes to the failure of the TBC system. Both the plasma sprayed ZrO$_2$-8Y$_2$O$_3$ (YSZ) coat and the ZrO$_2$,-25CeO$_2$,-2.5Y$_2$O$_3$ (CYSZ) coat are isothermally heat -treated at 130$0^{\circ}C$ and 150$0^{\circ}C$ for 100hr and cooled at different cooling rates. The monoclinic phase is not discovered in all the CYSZ annealed at 130$0^{\circ}C$ and 150$0^{\circ}C$. In the 150$0^{\circ}C$ heat-treated specimens, the YSZ contains some monoclinic phase while none exists in the 130$0^{\circ}C$ heat-treated YSZ coat. For the YSZ, the different phase transformation behaviors at the two temperatures are due to the stabilizer concentration of high temperature phases and grain growth. For the YSZ with 150$0^{\circ}C$-100hr annealing, the amount of monoclinic phase increased with the slower cooling rate. The extra oxygen vacancy, thermal stress, and c to t'phase transformation might suppress the t to m martensitic phase transformation.

• 한국세라믹학회지
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• 제21권3호
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• pp.239-244
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• 1984

The effect of tetragonal $ZrO_2$ phase on the mechanical behavior in 7 mole% calcia partially stabilized zirconia has been studied. The $ZrO_2$ powder containg 7 mole% CaO prepared by Hot Petroleum Drying Method calcined at 80$0^{\circ}C$ for 1 hour was nearly 100% tetragonal but as the calcining temperature increased certain amount of monoclinic phase appeared. The sintered specimen at 1$700^{\circ}C$ for 5 hours was aged at 130$0^{\circ}C$ for 0, 24, 48, 72 hours. X-ray diffraction data showed that in the aged specimen monoclinic tetragonal and cubic phase coexisted. The Kc value of aged specimen for 48 hr was about 4.5MN/m3/2 much greater than unaged sample. But aged for 72 hr the KiC value was decreased. The increasing of toughness in PSZ is based on the Stress-Induced Phase Transformation that is metastable tetra-gonal $ZrO_2$ changes t stable monoclinic phase within the stress field of crack and the mechanical fracture energy absorption is occured But in this case due to certain amount of tetragonal phase transformed to monoclinic phase during cooling the microcrack effect by transformation also considered. Trerefore both Stress-Induced Phase Transformation and inclusion induced microcracking effect contrbute to the increase of fracture toughness of 7 mole% CaO-$ZrO_2$ containing monoclinic and tetragnola phase simulataneously.

• 한국결정성장학회지
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• 제32권5호
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• pp.205-211
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• 2022

GSV (Granule Spray in Vacuum)는 상온의 진공하에서 나노 크기의 치밀한 세라믹 코팅층을 형성하는 방법이다. 일반적으로, 단사정의 지르코니아는 1150℃에서 정방정으로 변태하며, 이때 6.5 %의 체적변화를 일으켜 치밀한 단사정의 지르코니아를 만들기 어렵다. 본 연구에서는 코팅 효율에 대한 두 가지 처리 변수의 효과를 조사하는 데 중점을 두었다. 아울러, 특별한 가열과정 없이 형성된 필름의 미세구조에 관찰하였다. 샘플 기판에 증착된 지르코니아 필름에 대한 X-ray diffractometer (XRD) 분석은 단사정 지르코니아 필름이 성공적으로 증착되었음을 보여주었다.

• The Journal of the Acoustical Society of Korea
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• 제17권2E호
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• pp.53-58
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• 1998

In this paper, we study the response of several anisotropic systems to buried transient line loads. The problem is mathematically formulated based on the equations of motion in the constitutive relations. The load is in form of a normal stress acting with arbitrary axis on the plane of monoclinic symmetry. Plane wave equation is coupled with vertical shear wave, longitudinal wave and horizontal shear wave. We first considered the equation of motion in reference coordinate system, where the line load is coincident with symmetry axis of the orthotrioic material. Then the equation of motion is transformed with respect to general coordiante system with azimuthal angle by using transformation tensor. The load is first described as a body force in the equations of the motion for the infinite media and then it is mathematically characterized. Subsequently the results for semi-infinite spaces is also obtained by using superposition of the infinite medium solution together with a scattered solution from the free surface. Consequently explicit solutions for the displacements are obtained by using Cargniard-DeHoop contour. Numerical results which are drawn from concrete examples of orthotropic material belonging to monoclinic symmetry are demonstrated.

• 한국지구과학회지
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• 제24권1호
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• pp.36-45
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• 2003

This study is made for examining the characteristics of the lead-zinc deposition from the mineralogy of pyrrhotite at the Yeonhwa 1 Mine, Korea. The pyrrhotite of the Yeonhwa 1 mine is divided two species; the pynhotites I and II. The pyrrhotite I that represents the product in Stage II mineralization is characterized by hexagonal pyrrhotite occurring as the mechanical mixtures of hexagonal and monoclinic phases with various proportion. These mixtures might be formed from 'primary' hexagonal pyrrhotite by the subsequent retrograde reaction and/or by the influence of later mineralization in Stage III. Whereas the pyrrhotite II crystallized out in later Mineralization Stage III (hydrothermal stage) is always monoclinic variant with ferromagnetic properties; no two phase mixtures have been recognized.