• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.31 no.2
• /
• pp.15-24
• /
• 1999

A new technique for recycling of white water was developed in order to reduce the calcium hardness in a closed OCC recycling system. Calcium ions present in the white water were precipitated as calcium carbonate by reacting with sodium carbonate, and the precipitated $CaCO_3$ was removed from the system using a flotation fractionation method, which has been commonly used in deinking process. In the flotation stage, a mixed gas of $CO_2$-air was purged into the flotation cell because the pH of $Na_2CO_3$-treated white water was reduced to neutral by $CO_2$ gas. Since $CaCO_3$ precipitate tends to stick onto fine fiber surface and then selectively removed from the white water, a proper amount of suspended solid in white water acts as an important factor for deciding the removal efficiency. By the application of $Na_2CO_3$ addition-$CO_2$ flotation to the short circulated white water, the calcium hardness was significantly reduced by 87% and more. Removal of calcium ions with fine fibers led to a drainage improvement, reduction of fresh water consumption, and enhanced efficiency of wet-end chemicals.

• Journal of Technologic Dentistry
• /
• v.27 no.1
• /
• pp.57-63
• /
• 2005

Experimental Ti-13%Zr and Ti-13%Zr-5%Cu alloys were made in an argon-arc melting furnace. The grade 2 CP Ti was used to control. To investigate the surface reaction layers produced by the reaction with mold materials and the influence of the reaction layers on the hardness of castings, A phosphate bonded $SiO_2$ base investment was used as mold material, and microstructure observation and hardness test were performed. The surface reaction layers of Ti-13%Zr and Ti-13%Zr-5%Cu alloys were thinner than that of CP Ti had a clearly multiple structure. A difference of the hardness between surface and inner of the Ti-13%Zr and Ti-13%Zr-5%Cu alloys became less than that of CP Ti. From the results, it was found that the Ti-Zr-(Cu) based alloys were possible to cast with $SiO_2$ base investment without the great changes of mechanical properties of the castings.

• Journal of the Korean Society for Precision Engineering
• /
• v.23 no.7 s.184
• /
• pp.101-107
• /
• 2006

Cold gas dynamic spray or cold spray is a novel manufacturing method for coatings. Cold spray is a high rate and direct material deposition process that utilizes the kinetic energy of particles sprayed at high velocity (300-1,200m/s). In this research, a technique to repair the damaged mold by cold spray deposition and mechanical machining was proposed. An aluminum 6061 mold with three-dimensional surface was fabricated, intentionally damaged and material-added by cold spray, and its original geometry was re-obtained successfully by Computer Numerical Control (CNC) machining. To investigate deformation of material caused by cold spray, deposition was conducted on thin aluminum plates ($100mm{\times}100mm{\times}3mm$). The average deformation of the plates was $205{\sim}290{\mu}m$ by Coordinate Measurement Machine (CMM). In addition, the cross section of deposited layer was analyzed by scanning electron microscopy (SEM). To compare variation of hardness, Vickers hardness was measured by micro-hardness tester.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
• /
• 1999.11b
• /
• pp.164-171
• /
• 1999

A new technique for recycling process water was developed in order to reduce the calcium hardness of the closed OCC recycling system. Calcium ions present in the white water were precipitated as calcium carbonate by a reaction with sodium carbonate and the CaCO$_3$precipitates were easily removed from the system by a dissolved air flotation(DAF) method. After the DAF stage, CO$_2$-gas was purged into the water because the pH of Na$_2$CO$_3$-treated white water was reduced to neutral by CO$_2$gas. Since CaCO$_3$precipitate tends to stick onto the fine fiber surface and then is selectively removed from the water, a proper amount of suspended solid in the process water acts as an important factor in deciding the removal efficiency. By the application of Na$_2$CO$_3$addition - DAF - CO$_2$purging to the short circulated white water the calcium hardness was significantly reduced by 92% and more. The removal of calcium ions with fine fibers led to drainage improvement, reduction of fresh water consumption, and enhanced efficiency of wet-end chemicals.

• Journal of the East Asian Society of Dietary Life
• /
• v.24 no.6
• /
• pp.785-792
• /
• 2014

This study investigated the optimal mix ratio of frozen-dried loquat fruit powder and the optimun conditions for making Seolgidduk by analyzing chemical properties, rating moisture contents, color, mechanical quality characteristics and sensory characteristics Seolgidduk was made with 0, 2, 4, 6 and 8% frozen-dried loquat fruit powder, which contains functional components. Chemical analysis showed that loquat fruit powder contained of 12.87% water, 2.23% crude protein, 0.55% crude fat, 3.57% crude ash and 3.89% crude fiber. Water content of Seolgidduk containing loquat fruit ranged from 36.58~39.18%. With more loquat fruit powder L value decreased, while the 'a' value and 'b' values increased. According to scanning electronic microscopy, Seolgidduk containing frozen-dried loquat fruit powder showed weak coherence. Hardness decreased with more frozen-dried loquat fruit powder. In the sensory test, Seolgidduk with 4% loquat fruit powder was the most preferred with less sourness, proper softness, moisture and chewiness. Based on the results of this experiment, Seolgidduk with 4% loquat fruit powder showed less hardness than the control group. These results show that quality and preference increased when 4% loquat fruit powder was added to Seolgidduk. Therefore, Seolgidduk with 4% of loquat fruit powder is expected to increase quality and preference of Seolgidduk.

• Journal of the East Asian Society of Dietary Life
• /
• v.24 no.5
• /
• pp.621-630
• /
• 2014

This study presents the quality characteristics of blueberry bread. Blueberry fruit powder was added to bread dough at various concentrations ranging from 3~9%, after which physicochemical properties of dough and bread containing blueberry fruit powder were determined. The pH, loaf volume, specific loaf volume, dough volume and baking loss decreased with increasing amount of blueberry fruit powder in bread, whereas loaf weight and hardness were reduced. In particular, hardness appeared to be 1.98 times higher in the control without blueberry powder compared to the bread containing 9% blueberry powder. For color, increasing the amount of blueberry fruit powder reduced L and b values, whereas a value was increased. In the sensory evaluation, the highest overall preference score was observed in bread containing 6% blueberry powder, whereas the lowest score was observed in bread with 9% blueberry powder. From these results, blueberry bread with good acceptability has an optimum blueberry powder concentration of 6%.

• Journal of the Korean Society of Industry Convergence
• /
• v.26 no.5
• /
• pp.743-750
• /
• 2023

Aluminum alloy is a material widely used in the aircraft industry. However, since it has relatively low hardness, strength and tribological properties, it is necessary to improve these properties. In this paper, a TiN thin film was coated on the surface of AL7075-T7351 using DC magnetron sputtering. The coating was performed by setting different deposition pressure, deposition time, and applied power. Then, the tribological properties of the thin film were investigated. As a result of the experiment, the hardness of the thin film was higher than that of the base material, and the specimen with the highest hardness had excellent friction coefficient, wear amount, and adhesive strength characteristics. Through this study, it was confirmed that the tribological characteristics of aluminum alloy can be improved by depositing thin films using DC magnetron sputtering.

• Restorative Dentistry and Endodontics
• /
• v.36 no.6
• /
• pp.483-489
• /
• 2011

Objectives: The purpose of this study was to examine the effect of glycerin topical application on the surface hardness of composite after curing. Materials and Methods: A composite (Z-250, 3M ESPE) was packed into a disc-shaped brass mold and light cured according to one of the following protocols. Group 1 (control) was exposed to air and light cured for 40 sec, group 2 was covered with a Mylar strip and light cured for 40 sec, group 3 was surface coated with glycerin and light cured for 40 sec, and group 4 was exposed to air and light cured for 20 sec and then surface coated with glycerin and cured for additional 20 sec. Twenty specimens were prepared for each group. The surface hardnesses of specimens were measured with or without polishing. Five days later, the surface hardness of each specimen was measured again. Data were analyzed by three-way ANOVA and Tukey's post hoc tests. Results: The surface hardnesses of the unpolished specimens immediately after curing decreased in the following order: group 2 > 3 > 4 > 1. For the polished specimens, there was no significant difference among the groups. Within the same group, the hardness measured after five days was increased compared to that immediately after curing, and the polished specimens showed greater hardness than did the unpolished specimens. Conclusions: The most effective way to increase the surface hardness of composite is polishing after curing. The uses of a Mylar strip or glycerin topical application before curing is recommended.

• Journal of Oral Medicine and Pain
• /
• v.21 no.2
• /
• pp.207-224
• /
• 1996

This study was designed to determine the most effective concentration of fluoride and energy density of laser irradiation for the anticarious effect. For this study surface hardness in enamel was measured before and after irradiation with pulsed Nd;YAG laser and the topical application of fluoride. Of the permanent mandibular anterior hovine teeth, healthy, carious free ones were used. Three hundred specimens were made. Specimens within 25~45 Vickers hardness numbers were assigned to 20 control and experimental stoops ; each containing 15 specimens. After forming artificial carious lesions, 10 J/$\textrm{cm}^2$, 20 J/$\textrm{cm}^2$, and 30 J/$\textrm{cm}^2$ energies were irradiated on the enamel surface of each experimental group. Also NaF, NH4F, Elmex gel(amine fluoride) and APF gel fluoride compounds were applied topically. Next, all the specimens were placed into the pH circulatory procedures for eight days. Vickers hardness numbers were measured using a microhardness tester. Surface changes of the enamel were observed using an scanning electron microscope. The comparative ana1ysis yielded the following results : 1. The reduction of surface hardness of the enamel surface was less in all groups with fluoride application than in the group without fluoride application. 2. The APF gel croup with 10 J/$\textrm{cm}^2$ irradiation showed the lowest reduction of surface hardness. 3. The reduction of surface hardness of the enamel surface in the group of laser irradiation without fluoride application not showed any significant difference according to the energy density of the laser. 4. Under the scanning electron microscope, in enamel irradiated with 10J/$\textrm{cm}^2$ showed appearance similar to acid etching surface. In enamel irradiated with 20 J/$\textrm{cm}^2$, line enamel crack was detected. In enamel irradiated with 30j/$\textrm{cm}^2$, severe enamel crack and fusion of enamel were detected. These results suggest that one could obtain the best anticariogenic effects without damage to teeth in the group of application of APF gel after laser irradiation with 10 J/$\textrm{cm}^2$.

• Journal of the korean academy of Pediatric Dentistry
• /
• v.25 no.4
• /
• pp.825-836
• /
• 1998

The intention of this study was to investigate the preventive effect of chlorhexidine varnish on enamel demineralization. The sample consisted of 57 first premolars scheduled to be extracted for orthodontic purposes. The control group (N=10) was left untreated and the experimental groups were worn with specially designed stainless steel orthodontic bands on premolar for plaque accumulation. The group 1 (N=9) was worn band only, the group 2 (N=19) was applied with chlorhexidine varnish for one time, and the group 3 (N=19) was applied with chlorhexidine varnish for 3 times once a week. After 4 weeks of experimental periods, every specimen were examined by SEM and Vickers hardness test to evaluate and compare the degree of enamel decalcification. The results were as follows: 1. Although SEM revealed various degree of enamel demineralization in every experimental groups, the group 1 showed more severe demineralizations than the group 2 and 3. 2. The mean Vickers Hardness Numbers measured in this study seemed to reveal that there was a statistically significant difference between the control goup and the group 1 (P<0.05), and also a significant difference between the group 1 and the group 2, 3 (P<0.05). And there was no significant difference between the group 2 and the group 3 (p>0.05). 3. The results of VHN did not deemed to show a statistically significant difference between maxillary premolar and mandibular premolar in both group 2 and group 3 (P>0.05).