• 한국재료학회지
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• 제9권4호
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• pp.434-438
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• 1999

Vickers microhardness for polished Cu specimen has been measured by conventional and new methods. The conventional microhardness was measured by observing the diagonal of indentation after the load was removed. Whereas, the new method for microhardness was obtained by measuring the penetration depth of indenter into the specimen under the load. As the applied load was increased, the microhardness obtained by new method was increased. When the applied load was in the range of 5mN to 80mN, the rate of elastic to total depth of indenter was about 6% and the calculated depth of rounded indenter was 0.07$\mu\textrm{m}$. The difference in microhardness measured by two different methods such as conventional and new methods can be explained in terms of the elastic deformation of specimen, the shape of practical indenter and pile up of material.

• 한국자기학회지
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• 제8권5호
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• pp.249-254
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• 1998

자기측정법에 의한 조사손상 평가 가능성을 조사하기 위하여 SA508 CI.3강 모재금속의 중성자 조사 및 열처리 온도에 따른 자기특성(자기이력곡선, Barkhausen Noise(BN) 진폭, BN 에너지)과 경도 변화를 측정 비교하였다. 중성자 조사에 따라 자화율, BN 진폭, BN 에너지는 감소하였고 보자력과 경도는 증가하였으며, 포화자화 값은 변화하지 않았다. 열처리된 조사시편의 경우, 열처리 온도 증가에 따라 BN 에너지는 증가하였으며, 경도는 감소하였다. 결함과 전위혹은 자벽 이동과의 상호작용에 의한 경도 및 자기특성의 일관성 있는 변화는 원자로 압력용기 재료의 조사손상 평가와 관련 자기적 측정법 응용 가능성을 보여주었다.

• 한국재료학회지
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• 제10권5호
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• pp.335-342
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• 2000

리늄판의 미세경도를 압흔 하중 및 온도의 함수로 구하였다. 미세경도의 온도의존성은 상온에서 100$0^{\circ}C$까지의 범위에서 Vickers 압흔기가 내장된 고온 미세압흔기를 이용하여 연구되었다. 미세경도의 하중의존성은 Vickers와 Knoop 압흔기를 이용하여 검토되었다. 압흔 크기 영향은 표준화된 Meyers법칙에 위해 충분히 설명 되었다. 압흔도중 압흔기 아래에서의 가공경화 때문에 어닐링된 리늄판 경도값은 높은 압흔 하중에서 압련되 리늄판의 경도값에 접근하였다. 경도의 하중의존성으로부터 외삽하여 얻어진 하중 영에서의 경도값은 경도값이 다른 열활성을 나타내는 두 개의 다른 기구에 의해 제어됨을 제시하였다. 낮은 온도에서 활성화에너지는 0.02eV 였으며, 한편 높은 온도에서 활성화에너지는 0.15eV 였다. 이때 전이온도는 대략 $250^{\circ}C$ 이었다.

• Journal of Korean Dental Science
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• 제17권1호
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• pp.36-44
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• 2024

Purpose: This study investigated the effect of dentin bonding agent acidity on surface microhardness of MTA. Materials and Methods: Forty cylindrical molds (3 mm×5 mm) were prepared, and three dentin bonding agents with different acidities: Adper Single Bond 2 (ASB), Single Bond Universal (SBU), and Clearfil SE bond 2 (CSE) were applied to the inner surface of the molds (n=10). No bonding agent was applied in the control group. MTA was mixed and inserted into the molds and sealed with a wet cotton pellet for 4 days. After setting, the Vickers microhardness (HV) test was done at 200, 400, 600 ㎛ from the inner surface of the mold. One-way ANOVA was conducted for all samples. A P-value of less than .05 was considered significant. Tukey HSD test was performed for post-hoc analysis. Results: The mean HV values and standard deviations were 67.02±11.38 (Con), 48.76±11.33 (ASB), 43.78±11.19 (CSE), 37.84±9.36 (SBU), respectively. The difference between the control group and the experimental groups was statistically significant (P<0.001). The difference between ASB and SBU was statistically significant (P<0.001), while the difference between SBU and CSE was not. There were no statistically significant differences between the various points from the inner surface of the mold within each group (P>0.05). Conclusion: Results of the current study indicate that use of dentin bonding agents with MTA can reduce the surface microhardness of MTA. Moreover, there is a direct relationship between the acidity of dentin bonding agents and the surface microhardness of MTA.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1992년도 춘계학술대회 논문집
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• pp.84-88
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• 1992

Laser beam hardenling of 12%-Cr steel has been evaluated by using a continuous wave 3 kW CO$\_$2/ laser with a hardening mirror set. Experiment was performed on the optimum hardening condition with a laser power of 2.85kW and travel speed of 10 and 5 m/min. Multi passes have been alsotried to find the hardening characteristics of partly overlapped zone. The black paint to use at high temperature was adopted to increases the absorptivity of laser beam energy with the wavelength of 10.6 .mu. m at the surface of bese metal. The microstructure of the hardened layers was observed by using a light microscopy. SEM and TEM. A fine lamellar martensite formed in the hardened zones exhibits very high Vickers microhardness of 600 Hv, whereas the tempered martesite distributes in the base metal with Vickers microhardness of 240 Hv. It has been found that laser hardening with multi pass showed no significant drop of the hardness between adjacent passes.

• Journal of Ceramic Processing Research
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• 제19권5호
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• pp.394-400
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• 2018

The current work investigates the effects of nucleation heat treatments, on the microstructure and mechanical properties of a novel silicate glass in $Li_2O-BaO-SiO_2$ system with 1 mol% $P_2O_5$ as nucleating agent. As-cast glass was exposed to nucleation heat treatments at $490-550^{\circ}C$ for 1-3 h. The microstructural examination was performed by SEM/EDS. The highest Vickers microhardness was determined to be 650 Hv for the sample heat treated at $550^{\circ}C$ for 1 h. The increase in the nucleation time also affected Vickers microhardness and the highest one was determined to be 600 Hv after nucleation for 3 h. The fracture toughness, $K_{IC}$ reached $2.51MPa.m^{1/2}$ after nucleation at $550^{\circ}C$ for 1 h. The nucleation temperatures had a more pronounced effect on the fracture toughnesses in comparison to nucleation times. The indentation toughness data was used to determine Weibull parameters from Ln ln [1/(1-P)]-$lnK_{IC}$ plots. Weibull modulus, m of the samples nucleated at 500, 510, 530, $550^{\circ}C$ for 1h. and $540^{\circ}C$ for 2 h. were determined similarly to be 3.8, 3.5, 4.7 and 3.9, respectively. The rest of the samples indicated higher Weibull moduli, which may be attributed to the formations of microcracks due to the mismatch in between newly formed crystals and remaining glassy matrix.

• Restorative Dentistry and Endodontics
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• 제41권1호
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• pp.12-21
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• 2016

Objectives: To evaluate the effects of three acids on the microhardness of set mineral trioxide aggregate (MTA) and root dentin, and cytotoxicity on murine macrophage. Materials and Methods: OrthoMTA (BioMTA) was mixed and packed into the human root dentin blocks of 1.5 mm diameter and 5 mm height. Four groups, each of ten roots, were exposed to 10% citric acid (CA), 5% glycolic acid (GA), 17% ethylenediaminetetraacetic acid (EDTA), and saline for five minutes after setting of the OrthoMTA. Vickers surface microhardness of set MTA and dentin was measured before and after exposure to solutions, and compared between groups using one-way ANOVA with Tukey test. The microhardness value of each group was analyzed using student t test. Acid-treated OrthoMTA and dentin was examined by scanning electron microscope (SEM). Cell viability of tested solutions was assessed using WST-8 assay and murine macrophage. Results: Three test solutions reduced microhardness of dentin. 17% EDTA demonstrated severe dentinal erosion, significantly reduced the dentinal microhardness compared to 10% CA (p = 0.034) or 5% GA (p = 0.006). 10% CA or 5% GA significantly reduced the surface microhardness of set MTA compared to 17% EDTA and saline (p < 0.001). Acid-treated OrthoMTA demonstrated microporous structure with destruction of globular crystal. EDTA exhibited significantly more cellular toxicity than the other acidic solutions at diluted concentrations (0.2, 0.5, 1.0%). Conclusions: Tested acidic solutions reduced microhardness of root dentin. Five minute's application of 10% CA and 5% GA significantly reduced the microhardness of set OrthoMTA with lower cellular cytotoxicity compared to 17% EDTA.

• Restorative Dentistry and Endodontics
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• 제29권1호
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• pp.58-67
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• 2004

The objectives of this study was to evaluate current visible light curing units regarding microhardness and microleakage. Fourty samples of composite resin(Z-250, 3M) were cured by different light curing units (Flipo, LOKKI; Credi II, 3M; XL 3000, 3M: Optilux 500, Demetron) in acrylic blocks. Microhardness was measured using a calibrated Vickers indenter on both top and bottom surfaces after 24 hours of storage in air at room temperature. Class V cavities were prepared on buccal and lingual surfaces of fourty extracted human molars. Each margin was on enamel and dentin/cementum. Composite resin(Z-250, 3M) was filled in cavities and cured by four different light curing units (Flipo, LOKKl; Credi II, 3M; XL 3000, 3M: Optilux 500, Demetron). The results of this syudy were as follows: Microhardness 1. Flipo showed low microhardness compared to Optilux 500, Credi II significantly in upper surface. Flipo didn't show a significant difference compared to XL 3000. 2. The microhardness resulting from curing with Flipo was lower than that of others on lower surfaces. Microleakage 1. Dentin margin showed significantly high dye penetration rate than enamel margin in all groups(p<0.05). 2. No significant differences were found on both enamel and dentin margin regarding curing units.

• 대한소아치과학회지
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• 제47권3호
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• pp.320-326
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• 2020

이 연구의 목적은 최근 소개된 alkasite 수복재료의 압축강도와 미세경도를 글라스아이오노머 시멘트와 유동성 복합레진과 비교하여 alkasite 수복재의 물성을 예측하는 것이었다. 압축강도와 비커스 미세경도 측정을 위해 각 재료당 20개의 시편을 제작하였다. 만능시험기를 사용하여 초 당 1 mm 횡단 속도 하에서 압축강도를 측정하였으며, 미세경도는 비커스 미세경도 측정기를 사용하여 보압 시간(dwelling time) 10초 조건 하에서 500 g의 힘을 가해 시편 제작 1시간, 1일, 7일, 14일, 21일, 35일 후에 측정하였다. 연구결과 압축강도는 복합레진이 가장 높았으며 alkasite, 글라스아이오노머 시멘트 순이었다. 미세경도 측정 결과 복합레진은 연구기간동안 미세경도의 변화가 없었으며 시편제작 1시간 후, 1일차, 7일차 측정까지 가장 높은 미세경도를 보였다. 글라스아이오노머 시멘트의 경우 7일차까지 미세경도가 증가하여 복합레진과 차이가 없어진 반면, alkasite는 14일차까지 서서히 미세경도가 증가하다가 이후 다시 감소하는 양상이 관찰되었다.

• Restorative Dentistry and Endodontics
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• 제40권3호
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• pp.188-194
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• 2015

Objectives: This study evaluated the effect of lactic acid and acetic acid on the microhardness of a silorane-based composite compared to two methacrylate-based composite resins. Materials and Methods: Thirty disc-shaped specimens each were fabricated of Filtek P90, Filtek Z250 and Filtek Z350XT. After measuring of Vickers microhardness, they were randomly divided into 3 subgroups (n = 10) and immersed in lactic acid, acetic acid or distilled water. Microhardness was measured after 48 hr and 7 day of immersion. Data were analyzed using repeated measures ANOVA (p < 0.05). The surfaces of two additional specimens were evaluated using a scanning electron microscope (SEM) before and after immersion. Results: All groups showed a reduction in microhardness after 7 day of immersion (p < 0.001). At baseline and 7 day, the microhardness of Z250 was the greatest, followed by Z350 and P90 (p < 0.001). At 48 hr, the microhardness values of Z250 and Z350 were greater than P90 (p < 0.001 for both), but those of Z250 and Z350 were not significantly different (p = 0.095). Also, the effect of storage media on microhardness was not significant at baseline, but significant at 48 hr and after 7 day (p = 0.001 and p < 0.001, respectively). Lactic acid had the greatest effect. Conclusions: The microhardness of composites decreased after 7 day of immersion. The microhardness of P90 was lower than that of other composites. Lactic acid caused a greater reduction in microhardness compared to other solutions.