• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.187-192
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• 2000

We prepared $SiO_2-Na_2O-R_mO_n$ thin films based on economics of water glass and investigated optical, mechanical properties of product thin films. Coating sol stabilized with 1 N HCl and 1 N $NH_4OH$, was fabricated by using water glass and calcium nitrate, and aluminum nitrate as starting materials. As-coated films on stainless steel, Si wafer and soda-lime-silica glass by spinning were finally annealed at 500, 750 and $900^{\circ}C$. Micro hardness and nitrogen content in film surface of annealed films were measured by Knoop hardness tester and EDX, respectively. Field Emission Scanning Electron Microscope (FE-SEM) and UV-VIS spectroscopy were adopted to analyze surface morphology and thickness and reflectance of our films.

• Restorative Dentistry and Endodontics
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• v.31 no.5
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• pp.352-358
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• 2006

The purpose of this study was to investigate the influence of thickness on the degree of cure of dual-cured composite core. 2, 4, 6, 8 mm thickness Luxacore Dual and Luxacore Self (DMG Inc, Hamburg, Germany) core composites were cured by bulk or incremental filling with halogen curing unit or self-cure mode The specimens were stored at $37^{\circ}C$ for 24 hours and the Knoop's hardness of top and bottom surfaces were measured. The statistical analysis was performed using ANOVA and Tukey's test at p = 0.05 significance level. In self cure mode, polymerization is not affected by the thickness. In Luxacore dual, polymerization of the bottom surface was effective in 2, 4 and 6 (incremental) mm specimens. However the 6 (bulk) and 8 (bulk, incremental) mm filling groups showed lower bottom/top hardness ratio (p < 0.05). Within the limitation of this experiment, incremental filling is better than bulk filling in case of over 4 mm depth, and bulk filling should be avoided.

• Korean Journal of Materials Research
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• v.32 no.12
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• pp.560-564
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• 2022

In this study, lanthanum boron silicate glasses were prepared with a composition of x Li₂O-(60-x)B₂O₃-5CaO-5BaO-7ZnO-10SiO₂-10La₂O₃-3Y₂O₃ where x = 1,3,5,7, and 9 mol%. Each composition was melted in a platinum crucible under atmospheric conditions at 1,400 ℃ for 2 h. Clear glasses with a transmittance exceeding 85 % were fabricated. Their optical, thermal, and physical properties, such as refractive index, Abbe number, density, glass transition (T_g) and Knoop hardness were studied. The results demonstrated that refractive index was between 1.6859 and 1.6953 at 589.3 nm. The Abbe number was calculated using an equation for 589.3 nm (nd), 656.3 nm (nf) and 486.1 nm (nc) and was observed to be in the range from 57.5 to 62.6. As the Li₂O content increased, the glass transition temperature of the optical glass decreased from 608 ℃ to 564 ℃. If glass mold pressing is performed using a material with a low transition temperature and high mechanical strength, then the optical glasses developed in this study can be completely commercialized.

• Restorative Dentistry and Endodontics
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• v.4 no.1
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• pp.35-38
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• 1978

The purpose of this study was to measure micro-knoop hardness and coefficient of thermal expansion on composite resins (Epolite, Adaptic, Hipol and Compo T.) Four different type of composite resins were measured at the varying depth of 30, 60, 90, 150, 200, 400, 700 and 1000 micron from the surface to deep portion. The specimens were stored both in the air room temperature for 2 days, 30 days and in water at $37^{\circ}C$ for 30 days. Thermal expansions of specimens(4mm in diameter and 50mm in height) were measured in quartz tube dilatometer from $20^{\circ}$ to $70^{\circ}C$ The following results were obtained. 1. The hardness of superficial portion were lower than inner portion of resin. 2. The value of hardness obtained from the specimen stored in room temperature in the water at $37^{\circ}C$ for 30 days were lower than above described Cases. 3. The coefficient of thermal expansion of Adaptic had $29.75{\times}10^{-6}/^{\circ}C$, Hipol had $30{\times}10^{-6}/^{\circ}C$, Epolite had $39.85{\times}10^{-6}/^{\circ}C$ and Compo T had $36.95{\times}10^{-6}/^{\circ}C$.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.7 no.4
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• pp.3-9
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• 2008

The ion implantation technology is generally used in order to improve surface mechanical properties, especially tribological properties, of engineering metals. In this study, experimental works were carried out to investigate the surface properties, such as hardness, wear quantity, wear rate and friction force, of a nitrogen ion implanted tool steel STD11 under dry condition. Specimens for the wear test were made to investigate the influences of the initial ion implantation temperature and the total ion radiation. Wear properties, such as the wear quantity and the wear rate, of the nitrogen ion implanted tool steel were considerably improved, especially under the low sliding speed and the low applied load.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.285-285
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• 2007

Friction material in a piezoelectric system is a important part to affect to moving performance. In this paper, alumina ceramics $(AlO_2)$, silicon carbide (SiC), high speed steel and super-hard alloy (WC, Tungsten Carbide) having a hardness knoop of 1000 to 2000 $kg/mm^2$ were tested as a friction material of AF module. Even though $AlO_2$, SiC and high speed steel were a high-hardness material, $AlO_2$ and SiC were worn by a rough surface, and SiC is rusted in humidity condition. AF module using super-hard alloy has showed a stable moving performance in life time test.

• Restorative Dentistry and Endodontics
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• v.24 no.3
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• pp.511-518
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• 1999

This study was performed to evaluate the mechanical properties of light-cured restorative composites by compression and indentation tests. Five commercially available light-activated composites (Heliomolar : HM, Aelitefil : AF, Amelogen : AG, Clearfil AP-X : CF, Z100 ZH) were used Disc specimens of 12mm in diameter and 1 mm in thickness and Cylindrical specimens of 3mm in diameter and 6mm in length were prepared for the indentation and compressive test, respectively. All specimens were immersed in distilled water at $37^{\circ}C$ for 30 days. An indentation test of 68-degree trigonal diamond pyramid was made under 10 g load for 15 seconds and an Knoop indentation test was made under 50 g load for 15 seconds. Hardness numbers, characteristic indentation depths and permanent deformation were measured during indentation of the 68-degree trigonal diamond pyramid compressive test was carried out at a crosshead speed of 0.5mm/min. The results obtained were summarized as follows, 1. The highest hardness value was obtained in the CF group and the lowest value was obtained in the HM group. Hardness values showed no significant, difference between AG group and HM group but other groups showed the significant differences in each group(p<0.05). 2. Hardness number by Knoop pyramid were higher than those of 68-degree trigonal diamond pyramid. 3. Plastic deformation during the indentation of 68-degree trigonal diamond pyramid was the lowest in the CF group and the largest in the HM group. Results of Tukey test showed the significant difference between CF group and others; also between ZH and AF groups and AG and HM groups(p<0.05) 4. The highest compressive strength was obtained in the CF group and the lowest compressive strength was obtained in the ZH group. Compressive strength values showed no significant difference between CF group and ZH group but other groups showed the significant differences in each group(p<0.05).

• Journal of Surface Science and Engineering
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• v.39 no.5
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• pp.235-239
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• 2006

The aluminum nitride(AlN) layer on Al7075 substrate has been formed through nitrogen ion implantation process. The implantation process was performed under the conditions : 100 keV energy, total ion dose up to $2{\times}10^{18}\;ions/cm^2$. XRD analysis showed that aluminum nitride layers were formed by nitrogen implantation. The formation of Aluminum nitride enhanced surface hardness up to 265HK(0.02 N) from 150HK(0.02 N) for the unimplanted specimen. Micro-Knoop hardness test showed that wear resistance was improved about 2 times for nitrogen implanted specimens above $5\;{\times}\;10^{17}\;ions/cm^2$. The friction coefficient was measured by Ball-on-disc type wear tester and was decreased to 1/3 with increasing total nitrogen ion dose up to $1\;{\times}\;10^{18}ions/cm^2$. The enhancement of mechanical properties was observed to be closely associated with AlN formation. AES analysis showed that the maximum concentration of nitrogen increased as ion dose increased until $5\;{\times}\;10^{17}\;ions/cm^2$.

• Restorative Dentistry and Endodontics
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• v.20 no.1
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• pp.303-315
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• 1995

An adequate and homogeneous cure of light-activated restroative material is very important for improvement of marginal adaptation and prevention of marginal leakage, secondary caries and pulpal irritation as well as expressing natural physical property of that material. The purpose of this study was to evaluate the change of surface hardness and cure uniformity of light-activated glass ionomer cements. Restorative(Fuji II LC, Vitremer) and lining(Baseline VLC, Vitrebond) light-activated glass ionomer cements were investigated for this study. The surface hardness of the top and bottom surfaces and cure uniformity of each 1mm, 1.5mm, 2mm, 2.5mm & 3mm in the thickness of specimen were measured immediately, at 1 hour, 24 hours and 1 week after light activation. The surface hardness change and cure uniformity of all the specimens were measured by Knoop hardness tester. The results were as follows. 1. The surface hardness of top and bottom surfaces in all groups increased with time(p<0.01). 2. Both top and bottom surfaces hardness of Vitrebond group measured immediately after light-activation were significantly lower than those of the other groups(p<0.01). 3. The surface hardness of top and bottom surfaces of restorative light -activated glass ionomer cements was higher than those of lining materials at 1 week(p<0.10). 4. Surface hardness of Vitremer group decreased as the specimen thickness increased, except top and bottom surfaces hardness of the specimen at 1 week(p<0.01). There was no significant difference in the surface hardness of Fuji II LC with changes in the thickness except bottom surface hardness of specimen at 24 hours and 1 week (p>0.05). 5. Surface hardness of Vitrebond group significantly decreased as the specimen thickness increased(p<0.01). There was no significant difference in the surface hardness of Baseline VLC group with changes in the thickness except bottom surface hardness of specimen measured immediately after light -activation(p>0.05). 6. The hardness ratio of top against bottom surface in all groups decreased with time(p<0.05). 7. There was no significant difference in the hardness ratio of top against bottom surface with changes of the thickness except Vitrebond group, 24 hours and 1 week of Vitremer group and 1 week of Baseline VLC group (p>0.05). These results suggest that surface hardness of restorative ligh-activated glass ionomer cements were highter than those of lining light-activated materials. In all groups, the surface hardness and cure uniformity continuously increased with time.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.4
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• pp.546-554
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• 2007

Statement of problem: Die materials require abrasion resistance, dimensional stability with time, and high surface wettability for adequate material properties. Wear of gypsum materials is a significant problem in the fabrication of accurately fitting cast prosthetic devices. So It has been recommended that the use of die hardener before carving or burnishing of the wax pattern. Purpose: The purpose of this study was to compare the abrasion resistance and surface microhardness(Knoop) with 3 commonly used gypsum die materials(MG Crystal Rock, Super plumstone, GC $FUJIROCK^{(R)}$ EP) with and without the application of 2 die hardeners. Material and methods: Three die materials were evaluated for abrasion resistance and surface microhardness after application of 2 die hardeners(Die hardener and Stone die & plaster hardener). Thirty specimens of each gypsum material were fabricated using an impression of resin die(Pattern resin; GC Corporation, Japan) with 1-mm high ridges, sloped 90 degrees. Gypsum materials were mixed according to manufacturer's recommendations and allowed to set 24 hours before coating. Specimens were arbitrary assigned to 1 of 3 treatment subgroups (n=10/subgroup): no treatment(control), coated with Die hardener, and coated with Stone die & plaster hardener. Abrasion resistance(measured by weight loss) was evaluated using device in 50g mass perpendicular to the ridges. Knoop hardness was determined by loading each specimen face 5 times for 15 seconds with a force of 50g. A scanning electron microscope was used to evaluate the surface of specimens in each treatment subgroup. Conclusions: The obtained results were as follows: 1. 3 types of die stone evaluated in this study did not show significant differences in surface hardness and abrasive resistance(P<.05). 2. In the abrasive resistance test, there were no significant differences between GC $FUJIROCK^{(R)}$ EP and MG Crystal Rock with or without 2 die hardener(P<.05). 3. Super plumstone treated with Stone die & plaster hardener showed increased wear loss(P<.05) 4. Die hardener coatings used in this study decreased the surface hardness of the gypsum material(P<.05).