• Journal of the Korean institute of surface engineering
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• v.49 no.2
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• pp.172-177
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• 2016

In this paper, various electrochemical experiments were conducted in seawater solution to evaluate corrosion damage behavior of arc thermal sprayed Inconel 625 coating on SS400 steel in marine environment. As a result, corrosion damages of thermal sprayed Inconel 625 coating preferentially occurred at the defect area, and they were observed as a form of pitting corrosion in the galvanostatic experiments. In Tafel analysis, corrosion current density of Inconel 625 coating was relatively high due to influence of interconnected pores and Cr oxides in the thermal spray coating layer. On the other hand, the result of the potential measurement, thermal sprayed Inconel 625 coating should need the post-treatment which can compensate the defects like pores and cracks because Inconel 625 coating presented a higher potential of about 290 mV than that of the SS400 steel.

• Fire Science and Engineering
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• v.17 no.4
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• pp.36-41
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• 2003

This experimental study shows the combustion characteristics for each coating thickness of water and oil paint which are used as fire retardant paints that prevent fire propagation through cables in underground culverts and trays. To evaluate combustion characteristics, smoke density(ASTM E 662) and Limited Oxygen Index(ASTM D 2863) experiment method was used. As the results of this study, the combustion characteristics of fire retardant paints produced the following : (a) The molt suitable coating thickness of fire retardant paint was 1.5∼2.0 mm in water paint and 0.2 mm in oil paint. (b) Flaming method in experiments of smoke density were found to be higher than Non-flaming method. (c) Water paint has the fire retardant effect and characteristics better than oil paint in measurement results of smoke density and oxygen index. (d) The oxygen index of water and oil fire retardant was able to know that it was satisfied a standard (30 or above).

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.105-105
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• 2016

Recently, high power impulse magnetron sputtering (HIPIMS) has attracted considerable attentions due to its high potential for industrial applications. By pulsing the sputtering target with high power density and short duration pulses, a high plasma density and high ionization of the sputtered species can be obtained. HIPIMS has exhibited several merits such as increased coating density, good adhesion, microparticle-free and smooth surface, which make the HIPIMS technique desirable for synthesizing hard coatings. However, hard coatings present intrinsic defects (columnar structures, pinholes, pores, discontinuities) which can affect the corrosion behavior, especially when substrates are active alloys like steel or in a wear-corrosion process. Atomic layer deposition (ALD), a CVD derived method with a broad spectrum of applications, has shown great potential for corrosion protection of high-precision metallic parts or systems. In ALD deposition, the growth proceeds through cyclic repetition of self-limiting surface reactions, which leads to the thin films possess high quality, low defect density, uniformity, low-temperature processing and exquisite thickness control. These merits make ALD an ideal candidate for the fabrication of excellent oxide barrier layer which can block the pinhole and other defects left in the coating structure to improve the corrosion protection of hard coatings. In this work, CrN/Al2O3/CrN multilayered coatings were synthesized by a hybrid process of HIPIMS and ALD techniques, aiming to improve the CrN hard coating properties. The influence of the Al2O3 interlayer addition, the thickness and intercalation position of the Al2O3 layer in the coatings on the microstructure, surface roughness, mechanical properties and corrosion behaviors were investigated. The results indicated that the dense Al2O3 interlayer addition by ALD lead to a significant decrease of the average grain size and surface roughness and greatly improved the mechanical properties and corrosion resistance of the CrN coatings. The thickness increase of the Al2O3 layer and intercalation position change to near the coating surface resulted in improved mechanical properties and corrosion resistance. The mechanism can be explained by that the dense Al2O3 interlayer acted as an excellent barrier for dislocation motion and diffusion of the corrosive substance.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.6
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• pp.573-580
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• 2012

Corrosion resistance and basic physical properties of solid tantalum are not comparable to most of the structural metallic materials. The relative high cost and melting temperature of tantalum are obstacles to be widely applied to general engineering processes. Electrodeposition in molten salt enables compact and uniform tantalum coating. In this study, Ta was coated onto base metal (SUS316L) with different current densities (0.5, 5, $20mA/cm^2$) by using MSE (Molten Salt Electrodeposition). In this study, it showed that deposition efficiency and microstructure of Ta coating layer were strongly depended on current density. In the case of the current density of $5mA/cm^2$, densest microstructure was obtained. The current density above $5mA/cm^2$ caused non-uniform microstructure due to rapid deposition rate. Dense microstructure and intact coating layer contributed to significant corrosion resistance enhancement.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
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• 2003.04a
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• pp.70-79
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• 2003

Paper coating can give smoothness surface and good printability to uncoated paper. Macro roughness of base paper would be decreasing its groove and grit in view of side. Nevertheless its improving effect for paper, some kind of problem is showing in the fine coated paper. Especially, back trap mottle is one of serious problems in printing with fine coated paper. Printers can not adjust conditions to overcome the problem. Also large amounts of paper can be rejected. There are many factors that influence back trap mottle. However it is not clear what the important parameters are in back trap mottle. Back trap mottle has some relationship with ink setting but good guidelines are not clear. Back trap mottle has been linked to non-uniform ink setting. We do not know how much variation in setting we can tolerate. Other mottle issues such as micro-picking and ink refusal are still common. This paper was prepared to identify correlation with ink setting and delta ink density obtained from experiment and then tried to find out some relationships with ink setting and back trap mottle. Basically fine calcium carbonate and ciay was used for main components and coarse calcium carbonate was mixed in two fine pigments to change its porosity and ink acceptance. Micro ink tack force at KRK printing tester was adapted to measure ink setting rate. KRK units were used for back trap mottle simulation and two printed samples were prepared to check delta ink density. Clay base coating has more fast ink setting time than calcium carbonate's though smoothness of clay was better than calcium carbonate. It could be explained by that clay has finer pore in its coating than calcium carbonate. DID(delta ink density) has shown a good correlation with ink setting time from micro ink tack. The total pore volume of coating layer did not match with ink setting and DID. From the results we might conclude coating that has fine pore size around 0.05 ${\mu}m$ can be exposed to high possibility of back trap mottle.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.30 no.3
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• pp.74-83
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• 1998

The phenomenon of decrease in sizing efficiency when the stock temperature is increased is well recognized as summer sizing, and this is believed to be caused by uneven distribution of sizing agents on paper surface most often incurred by coagulation of sizing agents. When unevenly sized paper is used as coating base stock, nonuniform consolidation of the coating layer may result, which, in turn, causes uneven distribution of binder on coating surface. This causes nonuniform ink absorption to produce print mottle. In this study the effects of simple or polymeric electrolytes, storage temperature and time on the coagulation of cationic dispersed rosin size were investigated using a turbidity measurement method which was verified to correlate well with the particle size of rosin emulsion or its coagulates. Handsheets sized with rosin dispersions coagulated under various conditions were prepared and their sizing degree and coated paper properties including gloss and ink density were examined. The relationship between the sizing nonuniformity of coated papers and its ink absorption property was evaluated. Turbidity of rosin emulsion increased as the storage temperature and time were increased. Addition of simple or polymeric electrolytes caused reduction in $zeta$ -potential of the rosin dispersion and accelerated the coagulation tendency substantially. Reversion of the $zeta$ -potential of rosin dispersion, however, did not occur when coagulation was induced with simple electrolytes. On the other hand, addition of an anionic polyelectrolyte reversed the $zeta$ -potential of the flocculated rosin dispersion. This indicated that electrical double layer compaction and bridging flocculation were coagulation mechanisms for simple and polymeric electrolytes, respectively. Sizing degree decreased as coagulation of rosin was increased. Paper gloss, ink gloss and ink density were increased when sizing degree of base stock was increased most probably due to prevention of base paper swelling and increased binder migration to coating surface. This suggested that uneven printing ink density occurred when uneven sizing development was induced by coagulation of rosin particles.

• Journal of Powder Materials
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• v.6 no.3
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• pp.224-230
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• 1999

Oxide powders of $Cr_2O_3 \;and\;Cr_2O_3+3{\%}TiO_2$ were prepared by spray drying, plasma densification and fused+crushed processes. The oxide coating layers were made by plasma spray and characterized by microstructure, hardness, adhesion strength and relative density. The optimum spray distance for the high quality coatings by spraying dried powders was found to be 9cm. A small amount addition of $TiO_2\;in\;Cr_2O_3$ powder significantly improved coating characteristics by lowering the melting point of powders. The hardness and relative density of coating layers of the plasma densified powders were comparable to fused and crushed powders, however, the adhesion strength was much higher in the former case.

• Journal of the Korean institute of surface engineering
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• v.31 no.4
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• pp.181-190
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• 1998

Al ion plating was carried to improve corrosion resistance of Nd-based permanent magnet made by prwder molding method. The effects of applied votage, pressyre and temperature were investigated to find the reation between coating parameters and their properties. Density of coating layer increased with voltage and thus corrosion resistance improved. However when voltage was applied more than 1000V, corrosion resistance whet down because of resputtering effect. Good corrosion resistance was acquired when gas pressure was $5.0\times10^-2$>torr, which is satisfied momentum energy of Ar, Al ions as well as quantity of plasma. The layer coated in low temperature range have better surface density and corrosion resistance than in high temperature. This result is seemed due to the characteristics of substrate itself. All coating layers were showed stong adhesion with substrate.

• Journal of Power System Engineering
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• v.18 no.4
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• pp.72-77
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• 2014

The aim of this study to investigate polarization characteristics of WC-based alloy coatings fabricated by high velocity oxygen fuel(HVOF) process. The coatings were fabricated by HVOF process with WC-CrC-Ni, WC-Co-Cr, WC-Co composite powders. Corrosion tests were carried out using potentiostat/galvanostat at solution with pH 2 and pH 6. Corrosion potential(Ecorr) and corrosion current density(Icorr) could be analyzed from polarization curve. WC-Co-Cr coating showed more incorrodible characteristics than other coatings at solution pH 2. WC-CrC-Ni coating was more favorable anti-corrosion characteristics than other coatings at solution with pH 6.

• Journal of Powder Materials
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• v.5 no.1
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• pp.28-34
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• 1998

Plasma sprayed ceramic coatings are widely used in various industrial fields to improve their properties or to reduce the production cost. The ceramic powders for plasma spray coating have been mainly manufactured by spray drying or fused+crushed process. In this study, chromium oxide which has better mechanical properties than those of the other ceramic was selected and agglomerated chromium oxide powders for plasma spray coating were produced by spray drying process with a various processing condition. The large hollow powders and the harsh surfaced powders are formed at high slurry feed rate more than 163 g/min. and low binder concentration less than 2wt%, respectively. These powders cause the considerable decrease of flowability and apparent density. The powders produced by spray drying process have the spherical shape with the mean size of 45 ${\mu}m$, but these are shown lower apparent density and flowability than the powders produced by fused+crushed powders. The plasma spray coated layers by spray dried powders are shown a different microstructure with that by fused+crushed powders in porosity shape, but their properties such as density, hardness and bond strength are similar.