• Korean Journal of Materials Research
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• v.3 no.6
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• pp.606-613
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• 1993

This was studied about aging characteristic of AC4A/$SiC_{w}$ 10-30v/o reinforced composite. Aging hardenability was decreased $SiC_{w}$ 30% > 10% > 20%. Aging hardening of T6 treatmented composite was higher absolute value than AC4A I/M material. And this results indicated initial hardening phenomenon according to increase $SiC_{w}$ volume fraction. Reinforced effect by pressure was the same effect as before aging treatment and the best condition pressure at 75MPa. Similar to reinforced effect according to $SiC_{w}$ volume fraction was 30 % > 10 % > 20 %. In case of pressure is low, whisker is not break the same time press with base metal after wetting. After it is wetting with base metal, a part transformed or wetting part break and whisker maintain original shape or a part transformed on the otherhand, in case of pressure is high, whisker is break in same time it was not against pressure and whisker's shape is near a polygon or spherical shape.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.150-150
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• 2016

Mankind is enjoying a great convenience of their life by the rapid growth of secondary industry since the Industrial Revolution and it is possible due to the invention of huge power such as engine. The automobile which plays the important role of industrial development and human movement is powered by the Engine Module, and especially Diesel engine is widely used because of mechanical durability and energy efficiency. The main work mechanism of the Diesel engine is composed of inhalation of the organic material (coal, oil, etc.), combustion, explosion and exhaust Cycle process then the carbon compound emissions during the last exhaust process are essential which is known as the major causes of air pollution issues in recent years. In particular, COx, called carbon oxide compound which is composed of a very small size of the particles from several ten to hundred nano meter and they exist as a suspension in the atmosphere. These Diesel particles can be accumulated at the respiratory organs and cause many serious diseases. In order to compensate for the weak point of such a Diesel Engine, the DPF(Diesel Particulate Filter) post-cleaning equipment has been used and it mainly consists of ceramic materials(SiC, Cordierite etc) because of the necessity for the engine system durability on the exposure of high temperature, high pressure and chemical harsh environmental. Ceramic Material filter, but it remains a lot of problems yet, such as limitations of collecting very small particles below micro size, high cost due to difficulties of manufacturing process and low fuel consumption efficiency due to back pressure increase by the small pore structure. This study is to test the possibility of new structure by direct infiltration of SiC Whisker on Carbon felt as the next generation filter and this new filter is expected to improve the above various problems of the Ceramic DPF currently in use and reduction of the cost simultaneously. In this experiment, non-catalytic VS CVD (Vapor-Solid Chemical Vaporized Deposition) system was adopted to keep high mechanical properties of SiC and MTS (Methyl-Trichloro-Silane) gas used as source and H2 gas used as dilute gas. From this, the suitable whisker growth for high performance filter was observed depending on each deposition conditions change (input gas ratio, temperature, mass flow rate etc.).

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.9
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• pp.2374-2385
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• 1994

SiCw/Al composite material is especially attractive because of their superior specific strength, specific stiffness, corrosion fatigue resistance, creep resistance, and wear resistance compared with the corresponding wrought Al alloy. In this study, Fatigue crack growth behavior and fatigue crack path morphology(FCPM) of SiC whisker reinforced Al 6061 alloy with 25% SiC volume fraction and Al 6061 allay were performed. Result of the fatigue crack growth test sgiwed that fatigue crack growth rate of SiCw/Al 6061 composite was slower than that of Al 6061 matrix therefore it was confirmed that Sic whisker have a excellent fatigue resistance. And Al 6061 matrix had only FCPM perpendicular to loading direction. On the other hand SiCw/Al 6061 composite had three types in fatigue crack path morphology. First type is that both sides FCPM of artificial notch are perpendicular to loading direction. Second type is that a FCPM in artifical notch has slant angle to loading direction and the other side FCPM is perpendicular to loading direction. Third type is that both sides FCPM of notch have slant angle to loading direction. It was considered that this kinds of phenomena were due to non-uniform distribution of SiC whisker and confirmed by SEM observation for fracture mechanism study.

• Advanced Composite Materials
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• v.18 no.2
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• pp.187-195
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• 2009

Much attention has been paid to the processing of inorganic whisker, especially calcium carbonate whisker, which can be used as reinforcement materials of polymer composite due to its low price. Unfortunately, the present synthesis technique of calcium carbonate whisker starts from calcinations of limestone, which involves high energy consumption and furthermore is a highly environment polluting reaction. In this report, needle-like aragonite was synthesized with a reversible solution reaction from limestone without calcination. Optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to characterize the morphology and crystal structure of intermediates as well as that of the product, aragonite. GCC (grinding calcium carbonate) powder was dissolved in an aqueous solution of magnesium sulfate with reflux and air flush. EDTA titration was used to evaluate reaction rate of the dissolution. A kinetics equation of the dissolution reaction was constructed, which displayed second-order kinetics with respect to the concentration of magnesium sulfate. A rate constant of $0.0015\;l^{-3}{\cdot}mol^{-1}{\cdot}h^{-1}$ was obtained. The dissolution reaction gave fiber-like magnesium hydroxide sulfate and gypsum crystal. Then needle-like aragonite with a length of $9.13\;{\pm}\;1.02\;{\mu}m$ and an aspect ratio of $5.64\;{\pm}\;1.37$ was synthesized from the dissolution product with $CO_2$ bubbling at $70^{\circ}C$.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.410-415
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• 1997

Fibrious potassium hexatitanate whisker was produced from the calcination process using a mixture of the natural rutile ore and industrial $K_2CO_3$. Fibrous Potassium titanate was prepared by the following procedures the starting material consisting of $K_2O{\cdot}4.4TiO_2$ was calcined at $1050^{\circ}C$ for 3 hrs. The calcined products obtained under the above condition consisted mainly of potassium hexatitanate with a small admixture of potassium dititanate and potassium tetratitanate. Therefore the single phase of potassium hexatitanate was obtained by heat treatment of $850^{\circ}C$, 3 hrs.

• Computers and Concrete
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• v.22 no.5
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• pp.481-492
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• 2018

In this paper, a new hybrid fiber system (NHFS) is investigated for the application of slab. The steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate ($CaCO_3$) whisker is added to form NHFS. The four-point bending test is carried out on the flexural properties of slab with plain, steel fiber, traditional hybrid fiber system (THFS) and NHFS reinforced cementitious composites. The flexural behavior is evaluated by ASTM C1018-97, JCI-SF4 and post-crack strength (PCS) technique. The evaluation parameters of flexural toughness such as toughness index (TI), equivalent flexural strength (EFS) and PCS are determined. The size of slab specimens is $15mm(thickness){\times}50mm(width){\times}200mm(length)$. The results show that adding $CaCO_3$ whisker to THFS can significantly improve the flexural strength, TI, EFS, PCS of the slab. The empirical relation between reinforcing index ($RI_v$) and flexural parameters show that flexural parameters of slabs increase first and then decrease; which indicates that optimum $RI_v$ values can be helpful in the considering the mix design of steel-PVA fibers-$CaCO_3$ whisker composites for achieving the desired flexural-related properties. The scanning electron microscopy is performed to observe the micro-morphological characteristics of the fracture surface, which proved the positive hybrid effect among the different fibers in cementitious composites. The NHFS can arrest the generation and propagation of the crack from micro to macro level.

• Applied Chemistry for Engineering
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• v.9 no.4
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• pp.585-590
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• 1998

Fibrous $Na_xTi_nO_{2n+1}$ whisker was prepared by $H^+/Na^+$ ion-exchange on layered hydrous titanium dioxide ($H_2Ti_4O_9{\cdot}nH_2O$). The ion-exchange reaction was proceeded at 0.5~2.0 M NaOH solution. In the ion-exchange at 2.0 M NaOH solution, 73% of sodium was exchanged and the prepared $Na_xTi_nO_{2n+1}$ whisker was a fibrous crystal of about $10{\sim}20{\mu}m$ of length and about $0.7{\mu}m$ of diameter. The phase transition of the ion-exchange phases identified by the thermal analysis. The result showed that the $Na_xTi_nO_{2n+1}$ whisker was decomposed into $Na_2Ti_6O_{13}$ and $TiO_2$ in the temperature of $200{\sim}600^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.37 no.1
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• pp.21-25
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• 2000

Gas pressure sintered silicon nitride based composites with 5 wt% $\beta$-Si3N4 whiskers were prepared, and the variations depending on sintering additives and sintering temperature were studied. Sintering additives were 6 wt% Y2O3-1 wt% MgO(6Y1M), 6 wt%Y2O3-1 wt% Al2O3(6Y1A), 6 wt% Y2O3-1 wt% SiO2(6Y1S), and whiskers were unidirectionally oriented by a modified tape casting technique. Samples were fully densified by gas pressure sintering at 2148 K and 2273 K. As the sintering temperature increased, the size of large elongated grains was increased. Three point flexural strength of 6Y1M and 6Y1M samples was higher than that of 6Y1S sample, and the strength decreased as the sintering temperature increased. The indentation crack length became shorter for the sample sintered at higher temperature, and the difference between the cracks length parallel to and normal to the direction of whisker alignment was decreased. In case of cracks 45$^{\circ}$off the whisker alignment direction, the crack length anisotropy disappeared.

• Korean Journal of Materials Research
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• v.31 no.6
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• pp.313-319
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• 2021

Understanding of effects of changes in the particle size of the matrix material on the mullite whisker growth during the production of porous mullite is crucial for better design of new porous ceramics materials in different applications. Commercially, raw materials such as Al₂O₃/SiO₂ and Al(OH)₃/SiO₂ are used as starting materials, while AlF₃ is added to fabricate porous mullite through reaction sintering process. When Al₂O₃ is used as a starting material, a porous microstructure can be identified, but a more developed needle shaped microstructure is identified in the specimen using Al(OH)₃, which has excellent reactivity. The specimen using Al₂O₃/SiO₂ composite powder does not undergo mulliteization even at 1,400 ℃, but the specimen using the Al(OH)₃/SiO₂ composite powder had already formed complete mullite whiskers from the particle size specimen milled for 3 h at 1,100 ℃. As a result, the change in sintering temperature does not significantly affect formation of microstructures. As the particle size of the matrix materials, Al₂O₃ and Al(OH)₃, decreases, the porosity tends to decrease. In the case of the Al(OH)₃/SiO₂ composite powder, the highest porosity obtained is 75 % when the particle size passes through a milling time of 3 h. The smaller the particle size of Al(OH)₃ is and the more the long/short ratio of the mullite whisker phase decreases, the higher the density becomes.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.127-131
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• 2010

Biomimetic whisker-like apatite was formed on thermally and NaOH-treated titanium powder in a simulated body fluid (SBF). In the early process of the SBF immersion, the surface structure of the titanium powder was loosened, possibly due to the dissolution of $Na^+$ ions on the surface of the titanium powder into SBF. When immersed for 7 days in SBF, fine precipitates appeared on the titanium surfaces; the coating layer (<200 nm in thickness) consisted of nanostructured, amorphous whisker-like and particulate phase, observed by TEM. With the extension of the immersion time to 16 days, the chrysanthemum flower type morphology of carbonated hydroxyapatite with a nanocrystallinity was developed on the surface of the titanium powder.