• Corrosion Science and Technology
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• v.6 no.4
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• pp.159-163
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• 2007

Micron size Co-alloy 800 (T800) powder is coated on the high temperature, oxidation and corrosion resistant super alloy Inconel 718 substrate by the optimal high velocity oxy-fuel (HVOF) thermal spray coating process developed by this laboratory. For the study of durability improvement of high speed spindle operating without lubricants, friction and sliding wear behaviors of the coatings are investigated both at room and at an elevated temperature of $1000^{\circ}F(538^{\circ}C)$. Friction coefficients, wear traces and wear debris of coatings are drastically reduced compared to those of non-coated surface of Inconel 718 substrate both at room temperature and at $538^{\circ}C$. Friction coefficients and wear traces of both coated and non-coated surfaces are drastically reduced at higher temperature of $538^{\circ}C$ compared with those at room temperature. At high temperature, the brittle oxides such as CoO, $Co_{3}O_{4}$, $MoO_2$ and $MoO_3$ are formed rapidly on the sliding surfaces, and the brittle oxide phases are easily attrited by reciprocating slides at high temperature through oxidation and abrasive wear mechanisms. The brittle solid oxide particles, softens, melts and partial-melts play roles as solid and liquid lubricants reducing friction coefficient and wear. These show that the coating is highly recommendable for the durability improvement coating on the machine component surfaces vulnerable to frictional heat and wear.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.9
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• pp.429-433
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• 2006

PZT(80/0) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The coating and drying procedure was repeated 4 times. And then the PZT(20/80) precusor solution was spin-coated on the PZT thick films. A concentration of a coating solution was 0.5mol/L and the number of coating was varied from 0 to 6. The porosity decreased and the grain size increased with increasing the number of coatings. The thickness of the PZT-6(6: number of coatings) films was about $60{\mu}m$. The relative dielectric constant increased and the dielectric loss decreased with increasing the number of PZT(20/80) sol coatings. The relative dielectric constant and dielectric loss of the PZT-6 thick film were 275 and 3.5%, respectively. The remanent polarization, coercive field and breakdown strength of the PZT-6 film were $19.8{\mu}C/cm^2$, 13.7kV/cm and 130kV/cm, respectively.

• Progress in Superconductivity and Cryogenics
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• v.16 no.1
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• pp.14-18
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• 2014

The mechanical, electrical and thermal characteristics of insulating materials may significantly affect the performance and reliability of electrical devices using superconductors. General method to provide insulating layer between coated conductors is wrapping coated conductor with Kapton tape. But uniform and compact wrapping without failure or delamination in whole coverage for long length conductor is not a simple task and need careful control. Coating of insulating layer directly on coated conductor is desirable for providing compact insulating layer rather than wrapping insulating layers around conductor. Ceramic added polymer has been widely used as an insulating material for electric machine because of its good electrical insulating properties as well as excellent heat resistance and fairy good mechanical properties. The insulating layer of coated conductor should have high breakdown voltage and possesses suitable mechanical strength and maintain adhesiveness at the cryogenic temperature where it is used and withstand stress from thermal cycling. The insulating and mechanical properties of polymer can be improved by adding functional filler. In this study, insulating layer has been made by adding ceramic particles such as $SiO_2$ to a polymer resin. The size, amount and morphology of added ceramic powder was controlled and their effect on dielectric property of the final composite was measured and discussed for optimum composite fabrication.

• Journal of the Korean institute of surface engineering
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• v.54 no.3
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• pp.144-151
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• 2021

In the present work, planar-type ZnO powder of [0001] plane with a high aspect ratio range of 20:1 to 50:1 was synthesized. Ag or CuO could be coated on the planar-type ZnO powder by wet methods such as centrifugation or ball milling. During the coating, the average size of the powder was slightly increased while maintaining the shape and XRD pattern of ZnO. When Ag or CuO was coated, the absolute value of the zeta potential, as well as the concentration of oxygen vacancy, was increased. Ag or CuO coated planar-type ZnO power exhibited excellent antibacterial performance, which seems to be related to their high electrostatic attraction force. They could be made into a masterbatch by mixing with ABS resin, and their applicability to antibacterial substances was confirmed by manufacturing the caps of a keyboard.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1035-1040
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• 2011

This research was performed on a microfilter made of a hybrid material (ceramic + metal) that was coated with ceramics on the metal-filter surface by using the thermal spray method. The ceramic powders used were $Al_2O_3+40TiO_2$ powder with a particle size of $20{\mu}m$ and $Al_2O_3$ (98%+)powder with a particle size of $45{\mu}m$. The metal filters were filter-grade $20{\mu}m$, $30{\mu}m$, and $50{\mu}m$ sintered metal powder filters (SIKA-R 20 IS, 30 IS, 50 IS; Sinter Metals Filters) and filter-grade $75{\mu}m$ sintered mesh filter with five layers. Ceramic-coated filters that were coated using the thermal spray method had a great influence on powder material, particle size, and coating thickness. However, these filters showed a fine performance when used as micro-filters.

• Archives of Plastic Surgery
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• v.36 no.3
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• pp.247-253
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• 2009

Purpose: Hydroxyapatite(HA) has been widely used due to its chemical similarity to bone and good biocompatibility. HA is composed of macropores and micropores. Too much irregularities of the micropores are ineffective against the adhesion and proliferation of osteoblast. Many efforts have been tried to overcome these drawbacks. HA crystal coating on the irregular surface of HA scaffold, crystallized HA, is one of the method to improve cell adhesion. Meanwhile, the collagen has been incorporated with HA to create composite scaffold that chemically resembles the natural extracellular matrix components of bone. The authors proposed to examine the effect of collagen - coated crystallized HA on the adhesion and proliferation of osteoblast. Method: HA powder containing $10{\mu}m$ pore size was manufactured as 1 cm pellet size. For the making crystallized HA, 0.1 M EDTA solution was used to dissolve HA powder and heated $100^{\circ}C$ for 48 hours. Next, the crystallized HA pellets were coated with collagen (0.1, 0.5, and 1%). The osteoblasts were seeded into HA pellets and incubated for the various times (1, 5, and 9 days). After the indicating days, methylthiazol tetrazolium (MTT) assay was performed for cell proliferation and alkaline phosphatase (ALP) activty was measured for bone formation. Result: In SEM study, the surface of crystallized HA pellet was more regular than HA pellet. MTT assay showed that the proliferation of osteoblasts increased in a collagen dose - dependent and time - dependent manner and had a maximum effect at 1% collagen concentration. ALP activity also increased in a collagen dose - dependent manner and had a highest effect at 1% collagen concentration. Conclusion: These data showed that crystallization and collagen coating of HA was effective for osteoblast proliferation and ALP activity. Therefore, our results suggest that crystallized - HA scaffold with collagen coating is may be a good strategy for tissue engineering application for bone formation.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.3
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• pp.83-88
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• 2015

Coating materials used in the electron beam (EB) deposition method, which is being studied as one of the fabrication methods of thermal barrier coating, are exposed to high power electron beam at focused area during the EB deposition. Therefore the coating source for EB process is needed to form as ingot with appropriate density and microstructure to sustain their shape and stable melts status during EB deposition. In this study, we tried to find the optimum powder condition for fabrication of ingot of 8 wt% yttria stabilized zirconia which can be used for EB irradiation. It seems that the ingot, which is fabricated through bi-modal type initial powder mixture which consists of tens of micro and nano size particles, was shown better performance than the ingot which is fabricated using monolithic nanoscale powder when exposed to high power EB.

• Korean Journal of Materials Research
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• v.24 no.2
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• pp.98-104
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• 2014

Vacuum kinetic spray(VKS) is a relatively advanced process for fabricating thin/thick and dense ceramic coatings via submicron-sized particle impact at room temperature. However, unfortunately, the particle velocity, which is an important value for investigating the deposition mechanism, has not been clarified yet. Thus, in this research, VKS average particle velocities were derived by numerical analysis method(CFD: computational fluid dynamics) connected with an experimental approach(SCM: slit cell method). When the process gas or powder particles are accelerated by a compressive force generated by gas pressure in kinetic spraying, a tensile force generated by the vacuum in the VKS system accelerates the process gas. As a result, the gas is able to reach supersonic speed even though only 0.6MPa gas pressure is used in VKS. In addition, small size powders can be accelerated up to supersonic velocity by means of the drag-force of the low pressure process gas flow. Furthermore, in this process, the increase of gas flow makes the drag-force stronger and gas distribution more homogenized in the pipe, by which the total particle average velocity becomes higher and the difference between max. and min. particle velocity decreases. Consequently, the control of particle size and gas flow rate are important factors in making the velocity of particles high enough for successful deposition in the VKS system.

• Korean Journal of Materials Research
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• v.27 no.5
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• pp.289-293
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• 2017

$Y_2Ti_2O_7$ nanoparticles (0.3 mol%) have been successfully synthesized by the co-precipitation process. The samples, adjusted to pH7 with ammonia solution as catalyst and calcined at $700{\sim}900^{\circ}C$, exhibit very fine particles with close to spherical shape and average size of 10-30 nm. It was possible to control the size of the synthesized $Y_2Ti_2O_7$ particles by manipulating the conditions. The $Y_2Ti_2O_7$ nanoparticles were coated on a glass substrate by a dipping coating process with inorganic binder. The $Y_2Ti_2O_7$ solution coated on the glass substrate had excellent adhesion of 5B; pencil hardness test results indicated an excellent hardness of 6H. The thickness of the thick film was about $30{\mu}m$. Decomposition of MB on the $Y_2Ti_2O_7$ thin film shows that the photocatalytic properties were excellent.

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