• Geomechanics and Engineering
• /
• v.21 no.4
• /
• pp.337-348
• /
• 2020

Tropical organic soils having more than 65% of organic matters are named "peat". This soil type is extremely soft, unconsolidated, and possesses low shear strength and stiffness. Different conventional and industrial binders (e.g., lime or Portland cement) are used widely for stabilisation of organic soils. However, due to many factors affecting the behaviour of these soils (e.g., high moisture content, fewer mineral particles, and acidic media), the efficiency of the conventional binders is low and/or cost-intensive. This research investigates the impact of different constituents of cement-sodium silicate grout system on the compressibility behaviour of organic soil, including settlement and void ratio. A microstructure analysis is also carried out on treated organic soil using Scanning Electron Micrographs (SEM), Energy Dispersive X-ray spectrometer (EDX), and X-ray Diffraction (XRD). The results indicate that the settlement and void ratio of treated organic soils decrease gradually with the increase of cement and kaolinite contents, as well as sodium silicate until an optimum value of 2.5% of the wet soil weight. The microstructure analysis also demonstrates that with the increase of cement, kaolinite and sodium silicate, the void ratio and porosity of treated soil particles decrease, leading to an increase in the soil density by the hydration, pozzolanic, and polymerisation processes. This research contributes an extra useful knowledge to the stabilisation of organic soils and upgrading such problematic soils closer to the non-problematic soils for geotechnical applications such as deep mixing.

• Computers and Concrete
• /
• v.24 no.1
• /
• pp.1-6
• /
• 2019

Within the scope of this study, the foam solution was prepared by properly mixing sulfonate based foam agent with water. Furthermore, this solution was mixed with the mixture of fine sand, cement, and water to produce foamed concrete. The mixture ratios which are the percentage of foam solution used in foam concrete were chosen as 0, 20, 40 and 60% by vol. After these groups reached 28 days of strength, they were heated to 20, 100, 400 and $700^{\circ}C$ respectively. Afterward, high-temperature effects on the foamed concrete were obtained by employing physical and mechanical properties tests. Additionally, SEM (scanning electron microscope) and EDX (energy-dispersive X-ray spectroscopy) tests were employed to analyze the microstructure, and ${\mu}-CT$ (micro computed tomography) images were used to reconstruct 3-D models of the heat-treated specimens. Then, these models are analyzed to examine the void structures and the changes in these structures due to the high temperatures. The study has shown that the void structures reduce the high-temperature effects and the foam solution could be mixed with concrete up to 40 % by vol. where the high strength of foamed concrete is non-mandatory.

• Applied Chemistry for Engineering
• /
• v.28 no.2
• /
• pp.214-220
• /
• 2017

The spherical Al/RDX/AP composites with an average size of $550{\mu}m$ were successfully prepared by drowning-out/agglomeration (D/A) process. The surface morphology and dispersion of Al particles of those composites were investigated using SEM and EDS (energy dispersive spectrometry). As a result of thermal analysis, the onset temperature of thermal decomposition of the Al/RDX/AP composites by the D/A process was found to decrease about $50^{\circ}C$ and their thermal stability was shown to be relatively enhanced due to the increase of activation energy compared to those of using the physical mixing method. In the first decomposition region of AP, Prout-Tompkins model was shown to describe well the thermal decomposition of both composites by the physical mixing and D/A process. On the other hand, in the second decomposition region of AP, the decomposition mechanisms of composites by the physical mixing and D/A process were explained by the zero-order and contracting volume model, respectively.

• Journal of Powder Materials
• /
• v.24 no.6
• /
• pp.437-443
• /
• 2017

SiC-based composite materials with light weight, high durability, and high-temperature stability have been actively studied for use in aerospace and defense applications. Moreover, environmental barrier coating (EBC) technologies using oxide-based ceramic materials have been studied to prevent chemical deterioration at a high temperature of $1300^{\circ}C$ or higher. In this study, an ytterbium silicate material, which has recently been actively studied as an environmental barrier coating because of its high-temperature chemical stability, is fabricated on a sintered SiC substrate. $Yb_2O_3$ and $SiO_2$ are used as the raw starting materials to form ytterbium disilicate ($Yb_2Si_2O_7$). Suspension plasma spraying is applied as the coating method. The effect of the mixing method on the particle size and distribution, which affect the coating formation behavior, is investigated using a scanning electron microscope (SEM), an energy dispersive spectrometer (EDS), and X-ray diffraction (XRD) analysis. It is found that the originally designed compounds are not effectively formed because of the refinement and vaporization of the raw material particles, i.e., $SiO_2$, and the formation of a porous coating structure. By changing the coating parameters such as the deposition distance, it is found that a denser coating structure can be formed at a closer deposition distance.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.1
• /
• pp.54-71
• /
• 1990

The fabrication of ceramic machine components by injection molding(CIM : Ceramic Injection Molding) is critically dependent on the shaping and binder extraction techniques. Injection molding is of keen interest to ceramic industries because CIM is suitable for making an intricate shape and manufacturing cost is lower than other process when production scale is large. The success of the molding process is dependent on the correct formulation of the organic vehicle and the achievement of optimum filler loading. Fine alumina powders and polyethylene binder systems were employed to prepare moldable blend then produce a simple specimen by compression molding. Flow characteristics of the mixture was evaluated by viscosity measurement. Optimum binder system and ceramic volume loading for injection molding were determind. A good debinding technique was utilized to improve the quality of debinded parts and save the debinding time. The simple ceramic part was successfully sintered after debinding and its microstructure examined with SEM revealed good consolidation.

• Transactions of the Korean hydrogen and new energy society
• /
• v.22 no.4
• /
• pp.488-494
• /
• 2011

Gasket plays an important role on sealing of the polymer electrolyte membrane fuel cell (PEMFC) stack. Stack requires gaskets in each cell to keep the hydrogen and air/oxygen within their respective regions. The failure of the gasket creates the problems of fuel leakage, mixing, damage on parts and can be a direct reason for the degrading the efficiency of fuel cell. The purpose of this paper researches on how mechanical properties of EPDM gasket in PEMFC are changed after long-term operations. The EPDM (ethylenepropylene-diene monomer) gaskets are obtained from the stack after long-term operations. DMA (dynamic mechanical analysis) is conducted to access the change of mechanical properties of the EPDM gasket. SEM/EDS (scanning electron microscope/energy dispersive spectroscopy) was used to show the surface topography and chemical characterization on the sample surface.

• Economic and Environmental Geology
• /
• v.24 no.1
• /
• pp.1-8
• /
• 1991

North ore deposits of the Dunjeon gold mine is disseminated-stockworks deposits emplaced in Ordovician Dongjeom quartzite. Six types of fluid inclusions are recongnized in the stage I quartz. Among them polyphase inclusions(type-IV-A, B) are predominent in the lower part of stage I quartz crystals whereas liquid and gas inclusions(type I, II) are abundant in the upper part of the same quartz crystals. Liquid $CO_2$-bearing inclusions(type III-A, B)occur as pseudosecondary inclusions. Solid phases in polyphase inclusions are identified by using scanning electron microscopy combined with energy dispersive x-ray spectroscopy. The solid phases are as follows; halite, sylvite, hydrophyllite, quartz, muscovite, calcite, ankerite, K-Mg-Fe-Al-Si mineral, Ca-Fe-Si mineral, Mg-Al-Si mineral, two kinds of Fe-mineral and Cu-Fe mineral. Results of freezing and heating experiments of fluid inclusions and identification of daughter minerals in polyphase inclusions in the stage I quartz reveal that ore fluids were high saline system NaCl-KCl-$CaCl_2$-$H_2O$ in the earier stage and then evolved to rather simple system NaCl-$H_2O$ in the later stage, and temporally fluid mixing occured with system $CO_2$-$H_2O$. Homogenization temperatures and salinity of fluid inclusions in the stage I range from 290 to $454^{\circ}C$ and from 0.2 to 54.2 wt. % equivalent to NaCl.

• Computers and Concrete
• /
• v.22 no.2
• /
• pp.153-159
• /
• 2018

Accelerators are used to speed up the construction by accelerating the setting time which helps in early removal of formwork thus leading to faster construction rate. Admixtures are used in mortar and concrete during or after mixing to improve certain properties of material which cannot be achieved in conventional cement mortar and concrete. The various industrial by products make nuisance and are hazardous to ecosystem as well. These wastes can be used in the construction industries to reduce the consumption of cement/aggregates, cost; and save the energy and environment by utilising waste and eliminate their disposal problem as well. The effect of calcium nitrate and triethanolamine (TEA) as accelerators and marble powder (MP) as waste material on the various properties of cement paste and mortar has been studied in the present work. The replacement ratio of MP was 0-10% @ 2.5% by weight of cement. The addition of calcium nitrate was 0% and 1%; and variation of addition of TEA was 0-0.1@ 0.025% and 0.1-1.0@ 0.1% by weight of cement. On the basis of setting time, some mix proportions were selected and further investigated. Setting time and soundness of cement paste; compressive strength and microstructure of mortar mix of selected mix proportions were studied experimentally at 3, 7 and 28 days aging. Results showed that use of MP, calcium nitrate, TEA and their combination reduced setting time of cement paste for all the mixes. Addition of calcium nitrate increased the compressive strength at all curing ages while MP and TEA decreased the compressive strength. The mechanism of additives was discussed through scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis of the specimens.

• Korean Journal of Materials Research
• /
• v.24 no.1
• /
• pp.53-59
• /
• 2014

The corrosion resistance of submerged entry nozzle (SEN) materials were investigated for high-class steel manufacturing. Composite samples were fabricated by mixing $ZrO_2$, $Al_2O_3$, MgO, mullite, spinel, and carbon. The raw materials were mixed with attrition milling, compacted in a uniaxial pressure of 200MPa and calcined at $1000^{\circ}C$ for 3 h in $N_2$ atmosphere. The bulk density and apparent porosity of the calcined samples were measured by the liquid displacement method in water using Archimedes's principle. The corrosion resistance of the samples were measured by cup test with mold powder at $1550^{\circ}C$ for 2 h. The microstructure and elemental analysis of samples were observed by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and X-ray diffraction pattern (XRD). The XRD result shows that the starting raw materials were crystalline phase. The microstructure of fabricated specimen was investigated before and after corrosion tests at $1000^{\circ}C$ and $1550^{\circ}C$ for 2h. $ZrO_2$-C composite showed good resistance in the slag corrosion test. Among the composite oxide materials, $ZrO_2-Al_2O_3$-C and $ZrO_2$-MgO-C showed better resistance than $ZrO_2$-C in the slag corrosion test. The diameter variation index of $ZrO_2$-C refractory was 16.1 at $1000^{\circ}C$ for 2 h. The diameter variation index of the $ZrO_2-Al_2O_3$-C refractory was larger than that of the $ZrO_2$-C refractory at $1550^{\circ}C$ for 2 h.

• Journal of Powder Materials
• /
• v.26 no.1
• /
• pp.49-57
• /
• 2019

Layered $LiNi_{0.83}Co_{0.11}Mn_{0.06}O_2$ cathode materials single- and dual-doped by the rare-earth elements Ce and Nd are successfully fabricated by using a coprecipitation-assisted solid-phase method. For comparison purposes, non-doping pristine $LiNi_{0.83}Co_{0.11}Mn_{0.06}O_2$ cathode material is also prepared using the same method. The crystal structure, morphology, and electrochemical performances are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) mapping, and electrochemical techniques. The XRD data demonstrates that all prepared samples maintain a typical ${\alpha}-NaFeO_2$-layered structure with the R-3m space group, and that the doped samples with Ce and/or Nd have lower cation mixing than that of pristine samples without doping. The results of SEM and EDS show that doped elements are uniformly distributed in all samples. The electrochemical performances of all doped samples are better than those of pristine samples without doping. In addition, the Ce/Nd dual-doped cathode material shows the best cycling performance and the least capacity loss. At a 10 C-rate, the electrodes of Ce/Nd dual-doped cathode material exhibit good capacity retention of 72.7, 58.5, and 45.2% after 100, 200, and 300 cycles, respectively, compared to those of pristine samples without doping (24.4, 11.1, and 8.0%).