• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
• /
• 2003.10a
• /
• pp.24-29
• /
• 2003

Deep sea water has cold temperature, abundant nutrients and minerals, and good water quality that is pathogen-free and stable. Compared with surface water, deep sea water contains more nutrition salt, such as nitrogen and phosphor. Moreover, if has the good balance of minerals. Because of the ability of the spray drying process to produce a free-flowing power considering of spherical particles with a well-defined size distribution and the rapid drying times for heat-sensitive material, spray drying is attractive for a wide range of applications spray drying is a unique unit operation in which powders are produced from a liquid feed in a single processing step. Key component of the process are atomizer, spray chamber. Design of spray chamber should be based on the atomizer type, the production rate, and the particle size required. Because of the complex processes taking place during spray drying, traditional design method are based on pilot-plant tests and empirical scale-up rules. Modern technique such as CFD have a role to play in design and troubleshooting.

• Carbon letters
• /
• v.19
• /
• pp.23-31
• /
• 2016

Carbon rich fly ash was recently reported to have compositions that are ideal for use as a precursor and catalyst for carbon nanotube growth. This fly ash powder is mostly composed of pure carbon, predominantly present as sp². In this work, the effect of sonication time on the morphology and structural properties of carbon rich fly ash particles is reported. The obtained results show that ultrasound treatment is an effective tool for producing ultrafine particles/fragments with higher porosity, which might be suitable for the adsorption of gasses. Moreover, carbon nanoparticles (CNPs) of this fly ash were produced in parallel using the ball milling technique, and were evaluated as reinforcements for epoxy based composites. These CNPs have almost spherical shapes with particle sizes of around 30 nm. They were found to have strong C=O carbonyl group bonds, which might be generated during the ball milling process. The tensile testing results of a fly ash CNP reinforced epoxy composite showed significant improvements in the mechanical properties, mainly in the stiffness of the polymer. The stiffness value was increased by around 23% of that of neat epoxy. These CNPs with chemically active groups might also be useful for other applications.

• Journal of the Korean Ceramic Society
• /
• v.32 no.4
• /
• pp.482-488
• /
• 1995

The phase transformation temperature from $\theta$- to $\alpha$-alumina was lowered from 1214$^{\circ}C$ to 114$0^{\circ}C$ in DSC by treating ${\gamma}$-alumina obtained by calcination of boehmite at $700^{\circ}C$ for 2hrswith $\alpha$-Al2O3 seeds (d50=0.36${\mu}{\textrm}{m}$) and 3wt% of the alumina sol. $\alpha$-Al2O3 seeds seemed to lower to the transformation temperature and the alumina sol suppressed the high temperature agglormeration. The effect was increased as the amount of the sol was increased, which was supported by TEM and particle size distribution. For an example, spherical ${\gamma}$-alumina powder with d50=0.54${\mu}{\textrm}{m}$ was prepared by treating the ${\gamma}$-alumina with 9 wt% of the alumina sol and 3wt% of the $\alpha$-Al2O3. It sintered to 99% of the theoretical density at 150$0^{\circ}C$ for 2hrs. and it had relatively homogeneous microstructure with 2~3${\mu}{\textrm}{m}$ sized grains.

• Journal of Electrochemical Science and Technology
• /
• v.3 no.3
• /
• pp.135-142
• /
• 2012

Over the past few years, $LiFePO_4$ has been actively studied as a cathode material for lithium-ion batteries because of its advantageous properties such as high theoretical capacity, good cycle life, and high thermal stability. However, it does not have a very good power capability owing to the low lithium-ion diffusivity and poor electronic conductivity. Reduction in particle size of $LiFePO_4$ to the scale of nanometers has been found to dramatically enhance the above properties, according to many earlier reports. However, because of the intrinsically low tap density of nanomaterials, it is difficult to commercialize this method. Many studies are being carried out to improve the volumetric energy density of this material and many methods have been reported so far. This paper provides a brief summary of the synthesis methods and electrochemical performances of micro-spherical $LiFePO_4$ having high volumetric energy density.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.7 no.4
• /
• pp.599-609
• /
• 1997

The phase behavior and dynamics of colloid suspensions and the resulting structures and properties of powder compacts were examined by a computer experimental method for cooperative packing processes. A wide range of properties and process conditions such as arbitrary particle size, medium densities, field strength, and temperature could be examined using the Peclet number (Pe). We demonstrated that an optimum range of Peclet number for the ordering of sediments was present and that the phenomena related to the ordering such as the onset of crystallization, the phase behavior, etc. strongly depend on process conditions. The present work appears to be useful to design the processing method of ceramic spherical submicron powders for the preparation of high-density green compacts.

• Transactions of the Korean hydrogen and new energy society
• /
• v.28 no.1
• /
• pp.70-76
• /
• 2017

To synthesize copper nanoparticle a thermal decomposition was adopted. And to solve the problem of surface oxidation of the synthesized copper powder an electroless Ag plating method was used. The size and shape of synthesized Cu nanoparticle were affected by the size of copper oxalate used as a precursor, reaction solvent, reaction temperature and amount of reducing agent. Especially reaction solvent is dominant factor to control shape of Cu nano-particle which can have the shapes of sphere, polygon and rod. In case of glycerol, it produced spherical shape of about 500 nm in size. Poly ethylene produced uniform polygonal shape in about 700 nm and ethylene glycol produced both of polygon and rod having size range between 500 and 1500 nm. The silver coated copper powder showed a high electrical conductivity.

• Transactions of the Korean hydrogen and new energy society
• /
• v.28 no.1
• /
• pp.77-84
• /
• 2017

In this study, Poly-urethane acrylate (PUA) was synthesized by the reaction between Polycaprolactonetriol (PCLT) and Isophorone dissocyanate (IPDI) and hybridized with inorganic materials. Tetraethylortho silicate (TEOS) and nano clay (Closite 20A) were used as inorganic particles. For the hybridization of TEOS with PUA, sol-gel method is used, in which TEOS is made into spherical particle in the firsthand. In the case of Nano clay, hybridization is carried out through the dispersion as Nano clay has a layered structure. The solution of PUA hybrid was made into a film after UV curing and its thermo and electrical properties were measured. The experimental analysis and result demonstrate that the PUA hybrid shows an improved thermal properties and lower dielectric constant than that of the non-hybrid PUA. The trend of improved properties was different depending on structure of inorganic materials.

• Korean Journal of Materials Research
• /
• v.15 no.5
• /
• pp.285-292
• /
• 2005

Anti-reflection film was coated by using spherical silica nano colloids. Silica colloid sol was reserved between two inclined slide glasses by capillary force, and particles were convectively stacked to form a film onto the substrate as the water evaporates. As the sliding speed increased, the thickness of the film decreased and the wavelength at the maximum transmittance decreased. The microstructure observed by SEM showed that silica particles were nearly close packed, which enabled the calculation of the effective refractive index of the film. The film thickness was measured by proffer and calculated from the wavelength of maximum transmittance and the effective refractive index. The effective refractive index of the film could be controlled by a subtle controlling of the coating speed and by mixing two different sized silica particles. When the 100 nm and 50 m particles were mixed at 4:1-5:1 volume ratio, the maximum transmittance of $95.2\%$ for one-sided coating was obtained. This is the one that has increased by $3.8\%$ compared to bare glass substrate, and shows that $99.0\%$ of transmittance or $1.0\%$ of reflectance can be achieved by the simple process if both sides of the substrate are coated.

• Korean Journal of Materials Research
• /
• v.14 no.7
• /
• pp.511-515
• /
• 2004

Fe nano powders were synthesized by plasma arc discharge (PAD) process and studied by means of X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). Pure Fe rod($99.9\%$) was used as a source of metallic vapor under argon and hydrogen mixed atmosphere. The synthesized Fe nano powders had nearly spherical shapes and core-shell type structures. The influence of process parameters on the structure and size was investigated. The powder size increased with increasing of the chamber pressure and input current. High hydrogen gas ratio in chamber atmosphere affected the particle size and amount of Fe nanopowder.

• Korean Journal of Materials Research
• /
• v.20 no.11
• /
• pp.592-599
• /
• 2010

A porous nickel-tin nano-dendritic electrode, for use as the anode in a rechargeable lithium battery, has been prepared by using an electrochemical deposition process. The adjustment of the complexing agent content in the deposition bath enabled the nickel-tin alloys to have specific stoichiometries while the amount of acid, as a dynamic template for micro-porous structure, was limited to a certain amount to prevent its undesirable side reaction with the complexing agent. The ratios of nickel to tin in the electro-deposits were nearly identical to the ratios of nickel ion to tin ion in the deposition bath; the particle changed from spherical to dendritic shape according to the tin content in the deposits. The nickel to tin ratio and the dendritic structure were quite uniform throughout the thickness of the deposits. The resulting nickel-tin alloy was reversibly lithiated and delithiated as an anode in rechargeable lithium battery. Furthermore, the resulting anode showed much more stable cycling performance up to 50 cycles, as compared to that resulting from dense electro-deposit with the same atomic composition and from tin electrodeposit with a similar porous structure. From the results, it is expected that highly-porous nickel-tin alloys presented in this work could provide a promising option for the high performance anode materials for rechargeable lithium batteries.