• Proceedings of the KWS Conference
• /
• 2004.05a
• /
• pp.311-313
• /
• 2004

WC-12-17%Co powders with nano- and micro-structures were deposited by cold spray process using nitrogen and helium gases. The results show that there is no detrimental phase transformation and/or decarburization of WC by cold spray deposition as expected. It is also observed that nano-sized WC in the feedstock powder is maintained in the cold spray deposition. It is demonstrated that it is possible to fabricate the nano-structured WC-Co coating with low porosity and very high hardness (-2050 HV) by cold spray deposition with reasonable powder preheating.

• Transactions of the Korean hydrogen and new energy society
• /
• v.18 no.3
• /
• pp.238-243
• /
• 2007

The composite powder of Cu and YSZ was synthesized for a high temperature electrolysis cathode by mechanical milling. The average Cu particle size was reduced to 5 micro-meter from 48 micro-meter after the mechanical ball milling. The composite powder showed that Cu particles were uniformly covered with finer YSZ particles. Sub-micron sized pores were uniformly dispersed in the Cu/YSZ composit. Homogeneously-dispersed fine YSZ in the composite is expected to the increase in triple phase boundaries, thereby leading the enhanced performance of cathode.

• Journal of the Korean Ceramic Society
• /
• v.54 no.1
• /
• pp.43-48
• /
• 2017

In this study, we investigate the effect of additive size on the densification and thermal conductivity of AlN ceramics with $MgO-CaO-Al_2O_3-SiO_2$ (MCAS) additives. Micro-sized MCAS powder prepared via melting and nano-sized MCAS powder synthesized via the polymeric complex method are used as sintering additives. We analyze the densification behavior of AlN added with 5 wt.% of MCAS by dilatometry as well as by isothermal sintering in the temperature range of $1300{\sim}1700^{\circ}C$. AlN exhibits higher sinterability with nano-MCAS than with micro-MCAS, and both specimens approach their maximum densities when sintered at $1600^{\circ}C$ for 4 h. The thermal conductivities of AlN with 5 wt% of nano- and micro-MCAS additives sintered at $1600^{\circ}C$ are 82.6 and 32.0 W/mK, respectively. We find that nano-MCAS is more effective in sintering of AlN ceramics at lower temperatures, and thus for enhancing their thermal conductivities.

• Korean Chemical Engineering Research
• /
• v.50 no.4
• /
• pp.690-695
• /
• 2012

Gas hydrate is an inclusion compound consisting of water and low molecular weight gases, which are incorporated into the lattice structure of water. Owing to its promising aspect to application technologies, gas hydrate has been widely studied recently, especially $CO_2$ hydrate for the CCS (Carbon Capture and Storage) issue. The key point of $CO_2$ hydrate technology for the CCS is how to produce gas hydrate in an efficient and economic way. In this study, we have tried to study the characteristic of gas hydrate formation using micro-sized ice through an ultrasonic nozzle which generate 2.4 MHz frequency wave. $CO_2$ as a carrier gas brings micro-sized mist into low-temperature reactor, where the mist and carrier gas forms $CO_2$ hydrate under $-55^{\circ}C$ and atmospheric pressure condition and some part of the mist also remains unreacted micro-sized ice. Formed gas hydrate was average 10.7 of diameter at average. The starting ice particle was set to constant pressure to form $CO_2$ hydrate and the consumed amount of $CO_2$ gas was simultaneously measured to calculate the conversion of ice into gas hydrate. Results showed that the gas hydrate formation was highly suitable because of its extremely high gas-solid contact area, and the formation rate was also very high. Self-preservation effect of $CO_2$ hydrate was confirmed by the measurement of $CO_2$ hydrate powder at normal and at pressed state, which resulted that this kind of gas storage and transport could be feasible using $CO_2$ hydrate formation.

• Korean Journal of Materials Research
• /
• v.12 no.12
• /
• pp.941-946
• /
• 2002

Both Cu and Cu-oxide nanopowders have great potential as conductive paste, solid lubricant, effective catalysts and super conducting materials because of their unique properties compared with those of commercial micro-sized ones. In this study, Cu and Cu-oxide nanopowders were prepared by Pulsed Wire Evaporation (PWE) method which has been very useful for producing nanometer-sized metal, alloy and ceramic powders. In this process, the metal wire is explosively converted into ultrafine particles under high electric pulse current (between $10^4$ and $10^{ 6}$ $A/mm^2$) within a micro second time. To prevent full oxidations of Cu powder, the surface of powder has been slightly passivated with thin CuO layer. X-ray diffraction analysis has shown that pure Cu nanopowders were obtained at $N_2$ atmosphere. As the oxygen partial pressure increased in $N_2$ atmosphere, the gradual phase transformation occurred from Cu to $Cu_2$O and finally CuO nanopowders. The spherical Cu nanopowders had a uniform size distribution of about 100nm in diameter. The Cu-oxide nanopowders were less than 70nm with sphere-like shape and their mean particle size was 54nm. Smaller size of Cu-oxide nanopowders compared with that of the Cu nanopowders results from the secondary explosion of Cu nanopowders at oxygen atmosphere. Thin passivated oxygen layer on the Cu surface has been proved by XPS and HRPD.

• International Journal of Precision Engineering and Manufacturing
• /
• v.9 no.1
• /
• pp.51-53
• /
• 2008

A new nano-particle deposition system (NPDS) was developed for a ceramic and metal coating process. Nano- and micro-sized powders were sprayed through a supersonic nozzle at room temperature and low vacuum conditions to create ceramic and metal thin films on metal and polymer substrates without thermal damage. Ceramic titanium dioxide ($TiO_2$) powder was deposited on polyethylene terephthalate substrates and metal tin (Sn) powder was deposited on SUS substrates. Deposition images were obtained and the resulting chemical composition was measured using X-ray photoelectron spectroscopy. The test results demonstrated that the new NPDS provides a noble coating method for ceramic and metal materials.

• Proceedings of the SAREK Conference
• /
• 2009.06a
• /
• pp.1367-1372
• /
• 2009

A proprietary device is adopted to break out the membrane of cell in the rigid polyurethane foam. As it is known, the membrane of cell is hardly tearing-off thoroughly in a mechanical way due to both its elastic characteristic and micro sized pores. In this study, a novel experimental approach is introduced to burst out all gases inside the cells of the rigid polyurethane foam by abrasively grinding micro-cells completely into fine powder. The biggest advantage of this approach is to be capable of releasing all gases out from the cell even in the micro pores. As clearly reflected from the repeatability, the accuracy of the result is highly improved and high confidence in the data sets as well. For the measurements of not only gas composition but partial pressure for each gas simultaneously as well, a precision gas mass spectrometer is used in-line directly to the abrasive grinding device. To control the starting point of the polyurethane foam, all samples were prepared on site in the laboratory. Manufactured time is one of the most critical factors in characterization of cell gas composition because it is known that one of gas composition, especially, carbon dioxide, is diffused out dramatically in a short period of time as soon as it is foamed.

• Journal of Powder Materials
• /
• v.21 no.1
• /
• pp.39-43
• /
• 2014

Bulk nanostructured copper was fabricated by a shock compaction method using the planar shock wave generated by a single gas gun system. Nano sized powders, average diameter of 100 nm, were compacted into the capsule and target die, which were designed to eliminate the effect of undesired shock wave, and then impacted with an aluminum alloy target at 400 m/s. Microstructure and mechanical properties of the shock compact specimen were analyzed using an optical microscope (OM), scanning electron microscope (SEM), and micro indentation. Hardness results showed low values (approximately 45~80 Hv) similar or slightly higher than those of conventional coarse grained commercial purity copper. This result indicates the poor quality of bonding between particles. Images from OM and SEM also confirmed that no strong bonding was achieved between them due to the insufficient energy and surface oxygen layer of the powders.

• Advances in materials Research
• /
• v.12 no.3
• /
• pp.227-242
• /
• 2023

Polyester composites play a vital role in civil engineering applications, especially in bridge and car park structures. Therefore, the addition of waste silica-based fillers will both improve the mechanical and durability performance of composites and produce an environmentally friendly material. In this study, the mechanical performance of polyester composites was investigated experimentally and numerically by adding micro and nano-sized silica-based fillers, marble powder, silica fume and nano-silica. 24 cubes for the compression test and 18 prisms for the flexural test were produced in six different groups containing 30% marble powder, 5% silica fume and 1% nano-silica by weight. SEM/EDS testing was used to investigate the distribution of filler particles in the matrix. Experimentally collected results were used to validate tests in the Abaqus software. Additionally, the Extended Finite Element Method (XFEM) was used to estimate the fracture process for the flexural test. The results show that the added silica fume, marble powder and nano silica improves the compressive strength of polyester composites by 32-38% and the flexural tensile strength by 10-60% compared to pure polyester composite. The numerically obtained results matched well with the experimental data, demonstrating the accuracy and feasibility of the calibrated finite element model.

• Journal of Sensor Science and Technology
• /
• v.19 no.4
• /
• pp.291-296
• /
• 2010

Recently, recycling method of waste wafer has been an area of solar cell to cut costs. Micro_blasting is one of the promising candidates for recycling of waste wafer due to their extremely simple and cost-effective process. In this paper, we attempt to explore the effect of micro_blasting and DRE(damage removal etching) process for solar cell. The optimal process conditions of micro_blasting are as follows: $10{\mu}m$ sized $Al_2O_3$ powder, jetting pressure of 400 kPa, and scan_speed of 30 cm/s. And the particles formed on micro_blasted wafer were removed by DRE precess which was performed by using HNA(HF/$HNO_3$/$CH_3COOH$) and TMAH(tetramethyl ammonium hydroxide). Structural analysis was done using a-step and the XRD patterns.