• Applied Chemistry
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• v.9 no.2
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• pp.25-28
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• 2005

To evaluate the dental restorative application of polymer composites filled with hydroxyapatite (HAP) which is an inorganic component of human bone material, dental properties of the polymer composites were investigated. A visible light system was utilized to activate the acrylate resin matrix of the composites. Maximum loading percentage of HAP in composite was 65 wt% and the depth of cure was 6.0 mm which can be applicable for dental restoration. With increasing the HAP content, degree of conversion of polymer composites was slightly decreased, however, polymerization shrinkage value was not varied. Diametral tensile strength value was enhanced with an increase of HAP content, however, there was no strict trend between flexural strength and HAP concentration. Anyhow, polymer composites prepared herein have superior mechanical properties sufficient specifications applicable to dental materials.

• Journal of Ceramic Processing Research
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• v.21 no.1
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• pp.113-118
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• 2020

The fabrication of continuous carbon fiber-reinforced carbon-silicon carbide matrix (Cf/C-SiC) cross-ply composites is highly attractive from a practical viewpoint due to their homogeneous microstructures and isotropic mechanical properties. However, the properties of Cf/C-SiC composites depend significantly on their processing conditions and temperatures, especially the pyrolysis conditions and temperatures. In this study, cross-ply Cf/C-SiC composites were fabricated using different pyrolysis protocols with phenolic resin via a liquid silicon infiltration. The effects of the pyrolysis conditions on the microstructures of the composites and their mechanical properties as well as on crack formations were evaluated at room temperature. Pyrolysis was performed at 600 ℃ for 1 h in a nitrogen atmosphere at different heating rates. The flexural strength varied from a minimum of 47 ± 3 MPa to a maximum of 62 ± 6 MPa (~ 35% increase) depending on the pyrolysis conditions.

• Journal of the korean academy of Pediatric Dentistry
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• v.34 no.1
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• pp.73-80
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• 2007

Compomer that release fluoride could be used on proximal caries of child effectively. But oral cavity is always wet, so saliva inhibits bonding of tooth and compomer. When the saliva exist on bonding, it can be occured microleakages. The purpose of this study was to evaluate the influence of salivary contamination on compomer restoration and degree of microleakage according to restoration methods. Dyract $AP^{(R)}$ and prime and $bond^{(R)}$ NT was applied by the manufacture s instructions. Elipar Trilight was applied for light curing. Saliva pool was made for reconstruction of oral cavity. Two premolar was embedded in acrylic resin. After class II cavity preperation, Dyract $AP^{(R)}$ was restored under several condition, the specimen was thermocycled 500 times with 30 second dwell time. 0.5% methylene blue was used for microleakage test. Micoleakage was measured by the ratio of the infiltration length to occlusal and gingival side interface. Data were analyzed statistically using Kruskal Wallis Test, Mann-Whitney Test. The Result were as follows ; 1. In occlusal side, there were no statistical differences. 2. In gingival side, there were no statistical differences in Group III ($ContactMatrix^{TM}$, Rubber dam, $Oraseal^{(R)}$), Group IV (No saliva contamination). 3. In gingival side, there were no statistical differences in Group I$(ContactMatrix^{TM})$, II($ContactMatrix^{TM}$, Rubber dam). 4. In gingival side, there were statistical differences in Group I$(ContactMatrix^{TM})$, II($ContactMatrix^{TM}$, Rubber dam).

• The Journal of Korean Academy of Prosthodontics
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• v.53 no.4
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• pp.325-329
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• 2015

Purpose: The aim of this study was to compare the film thicknesses of several resin cements as a function of time after mixing and to examine the effect of working time on the film thicknesses. Materials and methods: The film thickness (${\mu}m$) of 4 resin cements (n=10), 1 composite resin (Panavia F 2.0), 3 self-adhesive resin (Clearfil SA luting, Zirconite, RelyX U200) cements was measured at 20-second intervals after mixing of the cements up to 200 seconds under a load of 50 N. Linear regression was fitted to verify the effect of working time on the film thickness of each cement. Data were compared to the working time recommended by manufacturers using Wilcoxon test ($\alpha$=.05). Results: All of the materials showed a positive linear correlation between the film thickness and working time. There was no statistically significant difference between the working time based on our results and the values recommended by the manufacturers even though there was a discrepancy between those two values. Conclusion: The film thickness of resin cements could increase with the increase of working time. Working time to meet the ISO standard of $50-{\mu}m$ maximum film thickness could be different from the manufacturer's recommended value.

• Bulletin of the Korean Chemical Society
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• v.27 no.9
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• pp.1293-1296
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• 2006

In this study, a solid phase extraction method has been developed for the preconcentration and separation of the elements Cr(III), Fe(III), Co(II) and Pb(II) at trace levels by using a column packed with Amberlite XAD-1180 resin loaded with 4-(2-pyridylazo)-resorcinol (PAR) reagent. After preconcentrating, the metals retained on the column were eluted with 20 mL of 3 mol/L $HNO_3$ and then determined by flame atomic absorption spectrometry (FAAS). The factors affecting the recovery of the elements, such as pH, type and concentration of eluent, volume of sample and elution solution, and matrix components, were also ascertained. The recoveries of Cr(III), Fe(III), Co(II) and Pb(II) were found to be $99\;{\pm}\;4,\;97\;{\pm}\;3,\;95\;{\pm}\;3$ and $98\;{\pm}\;4$%, respectively, under the optimum conditions at 95% confidence level and the relative standard deviations found by analyzing of nine replicates were $\leq4.4$%. The preconcentration factors for Cr(III), Fe(III), Co(II) and Pb(II) were found as 75, 125, 50 and 75 respectively. The detection limits (DL, 3s/b) were 3.0 $\mu g/L$ for Cr(III), 1.25 $\mu g/L$ for Fe(III), 3.3 $\mu g/L$ for Co(II), and 7.2 $\mu g/L$ for Pb(II). The recoveries achieved by adding of metals at known concentrations to samples and the analysis results of Buffalo river sediment (RM 8704) show that the described method has a good accuracy. The proposed method was applied to tap water, stream water, salt and street dust samples.

• Applied Chemistry for Engineering
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• v.24 no.2
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• pp.121-125
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• 2013

In this work, we prepared the carbon paper from chopped carbon fibers using a gas diffusion matrix in polymer electrolyte membrane fuel cells by wet processing. The process of making carbon paper using wet processing is consisted of the three steps involving the dispersion of chopped carbon fibers, the preparation of the carbon fiber web, the impregnating of phenol resin. This work was focused on finding the optimal surfactant to make the carbon paper with 2D orientation of carbon fibers by investigating the dispersion state of carbon fibers in different dispersion solutions. Furthermore, the effect of phenol resin and carbon black contents on properties of electric conductivity was analyzed. As a result, it is confirmed that the carbon fiber was well dispersed when using sodium dodecyl sulfate as a surfactant, and the carbon paper with 8 wt% of phenol and 5 wt% of carbon black contents showed the most excellent electrical property.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.3
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• pp.254-263
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• 1997

As the communication and electronic industry develops, it is important to study the electromagnetic shielding effectiveness (SE) of carbon fiber (CF) reinforced thermal plastics (CFRTP) against the electromagnetic (EM) radiation. In this paper the shielding effectiveness of CFRTP was measured experimentally in an electromagnetic shielding room. The resin ma- terials used were PC, PP, PEI, PMMA and PA. Experiments were carried out by using a copper box and a monopole antenna with a spectrum analyzer. From the experimental results it was found that CF was a good candidate as an electromagnetic shielding material. The sheilding effectiveness was found to be increased in the composite as the number of laminated layers of CF was increased. As the minor damage increased, the SE increased due to increasing of the plane density, transmitting thickness and reflected angle of the CF. Other characteristics of the SE depended on the material used for the resin matrix, distance of the antennas and the noise frequency band.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.172-176
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• 1998

Epoxy adduct carboxyl terminated butadiene acrylonitrile(CTBN) was prepared by blending of CTBN and epoxy resin. CTBN/PU/epoxy was prepared from polyurethane(PU), epoxy resin, and CTBN. The CTBN/PU/epoxy using 5 wt% of CTBN content showed shifting damping peak as PU content increased. It suggested that CTBN/PU/epoxy had good compatibility for all composition at 5 wt% of CTBN content. But miscibility of CTBN/PU/epoxy decreased with the increase of the CTBN content. PU content for maximum flexural properties of CTBN/PU/epoxy was 10 wt%, but decreased with the increase of the PU content. The fracture toughness of CTBN/epoxy was improved by addition of the PU. Fracture surfaces of CTBN/PU/epoxy showed the shear deformation and generation of stress whitening which is associated with the cavitation. Cavitation in the CTBN and shear defomation in the PU modified epoxy matrix are the toughening mechanisms for CTBN/PU/epoxy.

• Journal of Dental Rehabilitation and Applied Science
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• v.21 no.1
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• pp.15-23
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• 2005

The purpose of this study was to evaluate effect of aging and thermocycling on the tensile strength of restorative composite resins. Eight commercially available light-cured restorative composites (Heliomolar: HM, Palfique Estelite: PE, Spectrum: ST, UniFil-F: UF, Z100: ZH, Clearfil AP-X: CA, P60: PS, and Palfique Toughwell: PT) were selected as experimental materials. Rectangular-shaped tensile test specimens were fabricated in a teflon mold giving 5 mm in gauge length and 2 mm in thickness. All samples were stored in distilled water at $37^{\circ}C$ for 100 days. Every 10 days, specimens were thermocycled for 1,000 cycles with 15 seconds of dwelling time in each $5^{\circ}C$ and $55^{\circ}C$ water baths. Tensile testing was carried out at a crosshead speed of 0.5 mm/min and fracture surfaces were observed with a scanning electron microscope. The results obtained were summarized as follows; 1. The strength degradation of thermocycled group was severer than that of the aged group (P<0.01). 2. The tensile strength of the CA and ST groups were significantly higher than that of other groups after thermocycling treatment (P<0.05). 3. Fracture surfaces showed that the composite resin failure developed along the matrix and the filler/resin interface region.

• Journal of Powder Materials
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• v.22 no.4
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• pp.234-239
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• 2015

Electronic products are a major part of evolving industry and human life style; however most of them are known to emit electromagnetic waves that have severe health hazards. Therefore, different materials and fabrication techniques are understudy to control or limit transfer of such waves to human body. In this study, nanocomposite powder is dispersed into epoxy resin and shielding effects such as absorption, reflection, penetration and multiple reflections are investigated. In addition, nano size powder (Ni, $Fe_2O_3$, Fe-85Ni, C-Ni) is fabricated by pulsed wire evaporation method and dispersed manually into epoxy. Characterization techniques such as X-ray diffraction, Scanning electron microscopy and Transmission electron microscopy are used to investigate the phase analysis, size and shape as well as dispersion trend of a nano powder on epoxy matrix. Shielding effect is measured by standard test method to investigate the electromagnetic shielding effectiveness of planar materials, ASTM D4935. At lower frequency, sample consisting nano-powder of Fe-85%Wt Ni shows better electromagnetic shielding effect compared to only epoxy, only Ni, $Fe_2O_3$ and C-Ni samples.