In the present work, we use multiwall carbon nanotubes (MWCNT) as the starting material for the fabrication of sintered carbon steel. A comparison is made with conventionally sintered carbon steel, where graphite is used as the starting material. Milling is performed using a horizontal mill sintered in a vacuum furnace. We analyze the grain size, number of pores, X-ray diffraction patterns, and microstructure. Changes in the physical properties are determined by using the Archimedes method and Vickers hardness measurements. The result shows that the use of MWCNTs instead of graphite significantly reduces the size and volume of the pores as well as the grain size after sintering. The addition of Y₂O₃.to the Fe-MWCNT samples further inhibits the growth of grains.

In the present work, we apply a technique that has been used for the expansion of graphite to multiwall carbon nanotubes (MWCNT). The nanotubes are rapidly heated for a short duration, followed by immersion in acid solution, so that they undergo expansion. The diameter of the expanded CNTs is 5-10 times larger than that of the asreceived nanotubes. This results in considerable swelling of the CNTs and opening of the tube tips, which may facilitate the accessibility of lithium ions into the inner holes and the interstices between the nanotube walls. The Li-ion storage capacity of the expanded nanotubes is measured by using the material as an anode in Li-ion cells. The result show that the discharge capacity of the expanded nanotubes in the first cycle is as high as 2,160 mAh/g, which is about 28% higher than that of the un-treated MWCNT anode. However, the charge/discharge capacity quickly drops in subsequent cycles and finally reaches equilibrium values of ~370 mAh/g. This is possibly due to the destruction of the lattice structures by repeated intercalation of Li ions.

In this study, bulk nickel-carbon nanotube (CNT) nanocomposites are synthesized by a novel method which includes a combination of ultrasonication, electrical explosion of wire in liquid and spark plasma sintering. The mechanical characteristics of the bulk Ni-CNT composites synthesized with CNT contents of 0.7, 1, 3 and 5 wt.% are investigated. X-ray diffraction, optical microscopy and field emission scanning electron microscopy techniques are used to observe the different phases, morphologies and structures of the composite powders as well as the sintered samples. The obtained results reveal that the as-synthesized composite exhibits substantial enhancement in the microhardness and values more than 140 HV are observed. However an empirical reinforcement limit of 3 wt.% is determined for the CNT content, beyond which, there is no significant improvement in the mechanical properties.

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• Fabrication of nanocomposites by electric explosion of stainless steel capillaries filled with carbon nanotubes
  Tao Jiang, Zhongyu Hou
  Applied Surface Science.2020; 513: 145824.     CrossRef
• Effect of a nano-sized TiC particle addition on the flow-assisted corrosion resistance of SA 106B carbon steel
  Jin-Ju Park, Eun-Kwang Park, Gyoung-Ja Lee, Chang-Kyu Rhee, Min-Ku Lee
  Applied Surface Science.2017; 415: 143.     CrossRef

We demonstrate the electrochromic properties of TiO₂ nanotubes prepared by an anodization process and investigate the effects of heat treatment and viologen incorporation on them. The morphology and crystal structure of anodized TiO₂ nanotubes are investigated by scanning electron microscopy and X-ray diffraction. As-formed TiO₂ nanotubes have straight tubular layers with an amorphous structure. As the annealing temperature increases, the anodized TiO₂ nanotubes are converted to the anatase and rutile phases with some cracks on the tube surface and irregular morphology. Electrochemical results reveal that amorphous TiO₂ nanotubes annealed at 150°C have the largest oxidation/ reduction current, which leads to the best electrochromic performance during the coloring/bleaching process. Viologenanchored TiO₂ nanotubes show superior electrochromic properties compared to pristine TiO₂ nanotubes, which indicates that the incorporation of a viologen can be an effective way to enhance the electrochromic properties of TiO₂ nanotubes.

In this study, we demonstrate the photoelectrochromic devices composed of TiO₂ and WO₃ nanostructures prepared by anodization method. The morphology and the crystal structure of anodized TiO₂ nanotubes and WO₃ nanoporous layers are investigated by SEM and XRD. To fabricate a transparent photoelectrode on FTO substrate, a TiO₂ nanotube membrane, which has been detached from Ti substrate, is transferred to FTO substrate and annealed at 450°C for 1 hr. The photoelectrode of TiO₂ nanotube and the counter electrode of WO₃ nanoporous layer are assembled and the inner space is filled with a liquid electrolyte containing 0.5 M LiI and 5 mM I₂ as a redox mediator. The properties of the photoelectrochromic devices is investigated and Pt-WO₃ electrode system shows better electrochromic performance compared toWO₃ electrode.

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• Synthesis and characterization of nitrogen-doped TiO 2 coatings on reduced graphene oxide for enhancing the visible light photocatalytic activity
  Yifan Zhang, Hye Mee Yang, Soo-Jin Park
  Current Applied Physics.2018; 18(2): 163.     CrossRef
• Photocatalytic and Adsorption Properties of WO3 Nanorods Prepared by Hydrothermal Synthesis
  Su-Yeol Yu, Chunghee Nam
  Journal of Korean Powder Metallurgy Institute.2017; 24(6): 483.     CrossRef
• Synthesis and Photo Catalytic Activity of 10 wt%, 20 wt%Li-TiO2 Composite Powders
  Hyeong-Chul Kim, Jae-Kil Han
  Journal of Korean Powder Metallurgy Institute.2016; 23(1): 33.     CrossRef

SKD11 (ASTM D2) tool steel is a versatile high-carbon, high-chromium, air-hardening tool steel that is characterized by a relatively high attainable hardness and numerous, large, chromium rich alloy carbide in the microstructure. SKD11 tool steel provides an effective combination of wear resistance and toughness, tool performance, price, and a wide variety of product forms. Adding of CNTs increased the performance of mechanical properties more. 1, 3 vol% CNTs was dispersed in SKD11 matrix by mechanical alloying. SKD11 carbon nanocomposite powder was sintered by spark plasma sintering process. FE-SEM, HR-TEM and Raman analysis were carried out for the SKD11 carbon nanocomposites.

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• Study on Effects of Mold Temperature on the Injection Molded Article
  J.-H. Han, Y.-C. Kim
  Archives of Metallurgy and Materials.2017; 62(2): 1271.     CrossRef

A powder-in-sheath rolling (PSR) process utilizing a copper alloy tube was applied to a fabrication of a multi-walled carbon nanotube (CNT) reinforced aluminum matrix composite. A copper tube with an outer diameter of 30 mm and a wall thickness of 2 mm was used as a sheath material. A mixture of pure aluminum powders and CNTs with the volume contents of 1, 3, 5 vol% was filled in the tube by tap filling and then processed to 93.3% height reduction by a rolling mill. The relative density of the CNT/Al composite fabricated by the PSR decreased slightly with increasing of CNTs content, but showed high value more than 98%. The average hardness of the 5%CNT/Al composite increased more than 3 times, compared to that of unreinforced pure Al powder compaction. The hardness of the CNT/Al composites was some higher than that of the composites fabricated by PSR using SUS304 tube. Therefore, it is concluded that the type of tube affects largely on the mechanical properties of the CNT/Al composites in the PSR process.

A powder-in-sheath rolling method was applied to a fabrication of a carbon nano tube (CNT) reinforced aluminum composite. A STS304 tube with an outer diameter of 34 mm and a wall thickness of 2 mm was used as a sheath material. A mixture of pure aluminum powders and CNTs with the volume contents of 1, 3, 5 vol was filled in the tube by tap filling and then processed to 73.5% height reduction by a rolling mill. The relative density of the CNT/ Al composite fabricated by the powder-in-sheath rolling decreased slightly with increasing of CNTs content, but exhibited high value more than 98. The grain size of the aluminum matrix was largely decreased with addition of CNTs; it decreased from 24 μm to 0.9 μm by the addition of only 1 volCNT. The average hardness of the composites increased by approximately 3 times with the addition of CNTs, comparing to that of unreinforced pure aluminum. It is concluded that the powder-in-sheath rolling method is an effective process for fabrication of CNT reinforced Al matrix composites.

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• Torsion Property of the Structure Bonded Aluminum Foam Due to Impact
  G.W. Hwang, J.U. Cho
  Archives of Metallurgy and Materials.2017; 62(2): 1353.     CrossRef
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  J.H. Lee, J.U. Cho
  Archives of Metallurgy and Materials.2017; 62(2): 1359.     CrossRef
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  Y.C. Kim, H.K. Choi, J.U. Cho
  Archives of Metallurgy and Materials.2015; 60(2): 1151.     CrossRef
• Experimental Study On Fracture Property Of Tapered Double Cantilever Beam Specimen With Aluminum Foam
  Y.C. Kim, S.S. Kim, J.U. Cho
  Archives of Metallurgy and Materials.2015; 60(2): 1459.     CrossRef
• Microstructure and Mechanical Properties of CNT/Al Composite Fabricated by a Powder-in-Sheath Rolling Method utilizing Copper Tube as a Sheath
  Seong-Hee Lee
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