Materials Science Forum Vols. 544-545

Abstract: The object of this study is to prepare adsorbents to remove heavy metals from abandoned mine residues. There are many factors that affect the adsorptivity of prepared adsorbents. The adsorptivity of prepared adsorbents is evaluated by cation exchange capatity(CEC). The maxium CEC value is obtained by Dongwon mine residues treated with NaOH. The optimum condition at that time is 75/25 wt% of mixing ratio of Dongwon mine residues and NaOH under N2 atmosphere at the activation temperature of 500°C. The CEC value was 95meq/100g at this condition. 99.5% of Pb was removed under the condition of 50 mg/L, pH 5 and reaction time of 1hr.

Abstract: Waste sediment (WS) from three different aluminum factories and rice husk ash (RHA) from power plants are used as precursors. Each WS is calcined to remove structural water then mixed and wet milled with RHA by 70 wt% until a homogeneous slip is obtained. The samples are formed by means of slip casting in plaster molds and fired at 1400 °C for 2 hours. The fired samples normally contain ~94 wt% mullite, 6 wt% residual silica and small amount of oxides of alkali and alkaline earth elements. It is found that their density and flexural strength are affected by alkali and alkaline earth contents and generally range from 1.53 to 2.38 g/cm3 and 18.11 to 76.37 MPa, respectively. While thermal expansion coefficient varies from 5.78 x 10-6 to 8.16 x 10-6 /°C and thermal shock resistance (T) from =200 to 300 °C.

Abstract: This study was conducted to investigate on crystallization condition and its effect on quality of melted slag that was made from incineration ash of domestic waste. By increasing operating temperature, good crystallization was developed and 900~1,000°C was proved optimal. Longer detention time made better crystallization development, and critical detention time was 3 hour. But too a long detention time caused residual stress by mutual interference of long crystals. Cooling rate might affect the quality of crystallization, but below 5°C/min had no difference. For quality and economics, minimum operating conditions could be comparatively low temperature of 800°C and detention time of 1~3 hour from which high Vickers hardness of about 660~720 kgf/mm2 was achieved. It was compared well with crystallized commercial glass which is about 630 kgf/mm2. Thus, optimum crystallization conditions was suggested to be : temperature 900~1000°C, detention time 3 hours, and cooling rate 5°C /min. Also, observation of microstructure of crystallized slag by SEM identified reinforcement of matrix by particles and crack deflection that could render the crystallized slag an improved mechanical strength.

Abstract: A process for the recovery of nanoporous silica and sodium fluoride from hexafluorosilicic acid and sodium silicate under the different molar ratios was studied. In order to prepare the appropriate solutions of initial compounds 25% of hexafluorosilicic acid and the 18% of sodium silicate were used. Obtained nanoporous silica and sodium fluoride have been characterized by XRD, BET, TGA, EDX and SEM.

Abstract: In this study, we investigate to use waste rock as a filler for filling the cavity of abandoned mines. We discuss that waste rock can be used as a filler in the side of environmental and structural stability. Waste rocks from four mines, such as Samgi, second Yeonwha, Dongwon and Dogye, are used. Leaching tests are conducted to check the environmental stability by four methods of Soil Leaching Test, MALT, TCLP and KSLT. According to the results, Cu, Cd, Cr and As were not detected and other metals leached below 0.5 ppm. Compressive strength of waste rock and crushed waste rock are measured to evaluate the structural stability. Mixtures of crushed waste rock are used to evaluate the possibility of enhancing compressive strength. Mixture 1 is composed of 11.1% of above 13.2mm, 22.2% of 9.5-13.2mm, 33.3% of 6.7-9.5mm, 22.2% of 3.5-6.7mm and 11.1% of 2.0-3.5mm. And mixture 2 is composed of 50% of above 13.2mm and 50% of 9.5-13.2mm. Compressive of the latter was more than that of the former. Waste rock can be probably used as a filler, considering the compressive strength of commercialized filler, or 40 Kg/cm2.

Abstract: Thermo-mechanical reliability of the solder bumped flip chip packages having underfill encapsulant was evaluated with thermal shock testing. In the initial reaction, the reaction product between the solder and Cu mini bump of chip side was Cu6Sn5 IMC layer, while the two phases which were (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4 were formed between the solder and electroless Ni-P layer of the package side. A crack was formed at the upper edge region of solder bump, and propagated through the solder region. The primary failure mechanism of the solder joints in this type of package was confirmed to be thermally activated solder fatigue failure. After thermal shocks of 2000 cycles, one more crack which was not observed in the case of non-underfill encapsulated flip chip was observed at the left side of interface between solder bump and substrate. The addition of this crack formation should be due to the underfill encapsulation between the Si chip and substrate.

Abstract: We developed the remodeling techniques of water storage tanks and the residual chlorine remaining devices. Eco-TIR((Total Internal Remodeling) is remodeling technique that cover the inside wall of concrete tank with SMC(Sheet Mold Compound) Block. Eco-SL(Stainless steel Lining) and Eco-GS(Glass sheet) is similar to Eco-TIR(Total Internal Remodeling) but stainless steel or glass tile is substituted for SMC block as a cover material. We tested the residual chlorine remaining devices and the results are as follows. First, it was estimated that mixing efficiency is increased if inflow energy to the water tank is used in the results of variation of residual chlorine concentration. Secondly, result showed that the removal percent of residual chlorine concentration was up to 90% by using ACF filter and feed water of high residual chlorine concentration can be controlled to 0.2mg/L〜0.4mg/L by using ACF and by-pass of inflow to the water tank. Also, in the water tank inlet pipe of 3-ways out using inflow energy is more effective in mixing than conventional inlet pipe. It is expected to enhance the safety of service water and management efficiency by applying mentioned techniques properly.

Abstract: In this study, natural fiber drains made with coconut coir, rice straw and jute filter were tested to evaluate their practical applicability if used in fields properly. Firstly, the tensile strength, and discharge capacity of the natural fiber drains were tested and verified prior to usage. Based on the test results, natural fiber drains excelled in tensile strength, but their initial discharge capacity obtained from composite discharge capacity tests was less than that of plastic drain board. Although their initial discharge capacity was relatively low compared to that of plastic drain board, the surface settlement from installation of the natural fiber drains, which is one of the most important factors to control the construction progress, was identical to that of plastic drain board. Therefore, it was concluded that the natural fiber drain boards satisfy the required minimum discharge capacity as a vertical drain and have great potential as a substitute for conventional plastic drain board. Secondly, long term changes in tensile strength of natural fiber drains embedded in sea water and clayey soil were examined. The tensile strength of fiber drain board in clayey soils decreased with time. These results indicated active decomposition of natural fibers embedded in sea water and clayey soils.

Abstract: Ferroelectric Pb(Zr0.6Ti0.4)O3 (PZT(60/40)) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The Pt bottom electrodes were screen-printed on the alumina substrate. The PZT(60/40) thick films were annealed at 1050°C for 10min in PbO atmosphere. Pb(Zr0.4Ti0.6)O3 (PZT(40/60)) precursor solution, which prepared by sol-gel method, was spin-coated on the PZT thick films to obtain a densification. These PZT multilayered thick films were annealed at 650°C for 2 h in PbO atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at 590°C for 10min. Its structural and electrical properties of the PZT thick films with the treatment of PZT(40/60) precursor solution coating were investigated. The coating and drying procedure was repeated 4 times. And then the PZT(40/60) precursor solution was spin-coated on the multilayered thick films. A concentration of a coating solution was 1.5 mol/L and the number of coating was repeated from 0~15. The porosity of the thick films was decreased with increasing the number of coatings. All PZT multilayered thick films showed the XRD patterns of typical peroveskite polycrystalline structure. The relative dielectric constant of the PZT-15 (15: number of solution coatings) thick film were 370. And the PZT-15 thick film shows the remanent polarization of 23.5 μC/cm2 and coercive field of 18.0 kV/cm, respectively.