• Korean Journal of Materials Research
• /
• 제28권4호
• /
• pp.221-226
• /
• 2018

The property changes of 18, 14, and 8K green gold alloys for jewelry are observed by adding 0.0, 3.0, and 5.0 wt% of indium (In), respectively. To check the composition of the alloys, an energy dispersive spectroscopy (EDS) analysis is conducted. Color and microstructure analysis is executed through bare-eye, macro camera, UV-VIS-NIR-colormeter, and optical microscope. The melting point, wetting angle, and hardness are measured using TGA-DTA, a wetting angle tester, and a Vickers hardness tester. The EDS analysis result demonstrates that each of the green gold alloys was manufactured with purposed contents. The color analysis result shows that the color of the alloys is similar to the color of the conventional 4 wt%-Cd 18K green gold, and the green color improves as the In content increases. The micro structure analysis result demonstrates that grain refinement improves as the amount of In increases. Enhancements in the melting point, wettability, and Vickers hardness changes appear as the In content increases and Au content decreases. The hardness is up to 260, which implies good durability. Therefore, the results suggest that the proposed 18, 14, and 8K In-added green gold alloys enhance the properties of jewelry products with regard to the green color, castability, and durability.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 한국재료학회 2011년도 춘계학술발표대회
• /
• pp.57.1-57.1
• /
• 2011

The effects of relative humidity on the properties of the porous $ZrO_2$ ceramics were investigated in terms of the curing behavior of phenolic resin as a binder. The $ZrO_2$ powders containing 5wt% of phenolic resin were conditioned in a consistent chamber condition at a temperature of $50^{\circ}C$ and different humidity levels (25, 50, 75, and 95%) for 1 h. The exposure of humid atmosphere caused changes of density and microstructure in the green bodies. The higher level the powders were exposed to the humid atmosphere, the lower green density was obtained and the more irregular microstructure was observed due to aggregation by the curing of phenolic resin. After firing, the porosity of specimens has risen from 35.7% to 38.1% and Young's modulus has declined in response to the variation of green density. These results could be explained by the degree of resin cure which was associated with the area under the exothermic peak enclosed by a baseline of DSC thermogram curve. Also, the curing behavior of phenolic resin according to relative humidity has been confirmed by decrease of ether groups which have interacted with the phenolic-OH group and the hexamine as a curing agent. Consequently, it could be demonstrated that increase the relative humidity during fabrication of porous $ZrO_2$ diminished the compaction and properties of specimens after firing owing to curing of phenolic resin.

• Proceedings of the Korean Ceranic Society Conference
• /
• 한국세라믹학회 2002년도 추계총회 및 연구발표회 초록집
• /
• pp.67.1-67
• /
• 2002

• Proceedings of the Korean Ceranic Society Conference
• /
• 한국세라믹학회 2002년도 추계총회 및 연구발표회 초록집
• /
• pp.68.1-68
• /
• 2002

• Journal of the Korean Ceramic Society
• /
• 제46권3호
• /
• pp.306-312
• /
• 2009

The size of various alumina ceramics used in semiconductor and display industry is also required to increase with increase in wafer and panel size. In this research, large alumina ceramics was fabricated by filter pressing of alumina slurry using commercial powder and thereafter sintering at $1600^{\circ}C$ in gas furnace. The characteristics of large alumina ceramics thereby were compared to those of small alumina ceramics prepared by pressure forming such as uniaxial pressing and CIP. Careful control of properties of alumina slurry and filter pressing made the fabrication of large alumina ceramics possible, and its characteristics were equivalent to those of small alumina ceramics. The large alumina ceramics, prepared by sintering the green body of 63% relative density at $1600^{\circ}C$, exhibited both dense microstructure corresponding to 98.5% of relative density and 99.8% of high purity as in starting powder.

• Journal of the Korean Ceramic Society
• /
• 제51권2호
• /
• pp.103-106
• /
• 2014

Nacre is an organic-inorganic composite material; it is composed of $CaCO_3$ platelet and protein. The microstructure of nacre is a matrix that is similar to bricks and mortar. Technology inspired by nature is called biomimetic technology. In this study, to make high thermal conducting ceramic composite materials using biomimetic technology, a porous green body was prepared with BN platelets. PMMA was infiltrated into the porous green body to make a composite. The microstructure of the composite was observed with FESEM, and the thermal properties were measured. The thermal conductivity of the prepared organic-inorganic composite was 4.19 $W/m{\cdot}K$.

• Advances in concrete construction
• /
• 제14권5호
• /
• pp.341-354
• /
• 2022

Treatment of solid waste building materials is a crucial method of disposal and an area of ongoing research. New standards for the treatment of solid waste building materials are necessary due to multisource features, huge quantities, and complicated compositions of solid waste. In this research, sustainable nanomaterial mixtures containing nano-paper waste (NPW) and nano-metakaolin (NMK) were used as a substitute for Portland cement. Portland cement was replaced with different ratios of NPW and NMK (0%, 4%, 8%, and 12% by weight of cement) while the cement-to-water ratio remained constant at 0.4 in all mortar mixtures. The fresh properties had a positive effect on them, and with the increase in the percentage of replacement, the fresh properties decreased. The results of compressive strength at 7 and 28 days and flexural strength at 28 days show that the nanomaterials improved the strength, but the results of NMK were better than those of NPW. The best replacement rate was 8%, followed by 4%, and finally 12% for both materials. The combination of NMK and NPW as a replacement (12% NMK + 12% NPW) showed less shrinkage than the others because of the high pozzolanic reactivity of the nanomaterials. The combination of NMK and NPW improved the microstructure by increasing the hydration volume and lowering the water in the cement matrix, as clearly observed in the C-S-H decomposition.

• Journal of the Korean Ceramic Society
• /
• 제32권2호
• /
• pp.217-226
• /
• 1995

Alumina powders were dispersed using crosslinkable organic molecules by electrosteric stabilization and then consolidated by crosslinking of organic molecules. The effect of processing variables such as the physicochemical properties of both solvent media and organic molecules, the proportions of mixed organic media, etc. were studied. FT-IR was used todeduce the mechanism of organic molecules adsorption on the alumina particle surfaces. The adsorption characteristics and the electrokinetic behavior of alumina suspensions were correlated with the stability of particle in alumina suspension using rheological measurements. The green body of alumina consolidated by the chemical crosslinking of the adsorbed organic molecules after the alumina suspension had been stabilized was tough enough for green machining and the sintered alumina fabricated by this proposed process also showed a high bending strength and a homogeneous microstructure.

• Journal of the Korean Ceramic Society
• /
• 제28권10호
• /
• pp.767-776
• /
• 1991

Effects of the additions of SiB4 as burnable poison to UO2 on the green density, densification, interdependence between density-grain growth and microstructure of sintered UO2 were studied. UO2 pellets were sintered in flowing hydrogen, at temperature 1200, 1350, 1500, and 168$0^{\circ}C$ for 3 hours and at 168$0^{\circ}C$ for 0, 1, 3, and 10 hours, respectively. Green densities were in the range of about 4.5~5.4 g/㎤, and decreased as the amount of SiB4 increased when green pellets were made by with use of a double action press at 1000 kg/$\textrm{cm}^2$. The density of sintered UO2 pellets was around 92~94% of the theoretical density and did not change significantly as the amount of SiB2 addition increased. However, the density of sintered pellets decreased with the increase in SiB4. The grain growth could be characterized in terms of two stages: Grain growth occurred with the increasing density in the first stage, whereas the second stage was characterized by the grain growth without increasing of density. A liquid phase was observed at grain boundaries and grain edges in the microstructure of sintered UO2 pellets with 5000 ppm and 10,000 ppm SiB4. This liquid, possible formed at about 168$0^{\circ}C$, did not enhance the shrinkage, but appeared to accelarate the grain growth. It seems that the second stage grain growth was due to the presence of pressurized insoluble trapped gas in isolated pores.

• Journal of the Korean Ceramic Society
• /
• 제55권6호
• /
• pp.581-589
• /
• 2018

This work concentrated on the effect of different laser beams on the microstructure and dielectric properties of $BaTiO_3$ nanoparticles at different calcinations times during the gelling preparation step. The nanoparticles were prepared by the sol-gel method. A green (1000 mW, 532 nm) and red laser beam (500 mW, 808 nm), were applied vertically at the center of stirring raw materials. The samples were sintered at $1000^{\circ}C$ for 2, 4, and 6 h. X-ray diffraction (XRD) analysis showed that samples prepared under the green laser have the highest purity. The FT-IR spectra showed that the stretching and bending vibrations of TiO bond without any other bonds, which are compatible to the X-ray diffraction (XRD) results. Samples were characterized by transmission electron microscopy (TEM), Scan electron microscopy (SEM), and UV-Visible spectrophotometer. Characterization showed the samples prepared under the green laser to have the highest particle size (~ 50 nm) and transparency for all sintering durations. Laser beam effects on electrical characterization were studied. BT nanoparticles prepared under the green laser show the higher dielectric constant, which was found to increase with sintering temperature.