Sung Hun Cho

Electrodeposition and characterization of Ni-TiB2 composite coatings

Nickel-titanium diboride (Ni-TiB2) composite coatings were successfully fabricated by pulse electrodeposition techniques from nickel sulfamate bath containing dispersed submicron TiB2 particles. The effect of TiB2 codeposition on the morphological, microstructural, microhardness and anti-corrosive properties of the composite coatings have been investigated by using scanning electron microscopy coupled with energy dispersive spectroscopy system, X-ray diffraction (XRD), vickers microhardness, and electrochemical impedance spectroscopy (EIS) techniques. Incorporation of TiB2 particles into the nickel matrix has modified the regular crystal growth of nickel. The XRD patterns revealed that the preferred (100) crystallite orientation of pure nickel has been modified into mixed orientations by the enhancement of (111) and attenuation of (200) diffraction intensities by the incorporation of TiB2 particles into the nickel matrix. Vickers microhardness of the Ni-TiB2 composite coating is found to be increased which is nearly 3 times higher than pure nickel coating. The results obtained by polarization curves and EIS analysis in 3.5 wt% NaCl solution have shown the improved corrosion resistance properties of Ni-TiB2 composite coating over pure nickel electrodeposit.

Effects of Different Solid Lubricants on Mechanical and Tribological Properties of Al2O3/ZrO2 Nanocomposites

Solid lubricants were suited for the applications of high temperature parts. Recently, researches for self-lubricating ceramic matrix composites using solid lubricants, such as MoS2, WS2, h-BN, and graphite etc., became active. This work is to use the spark plasma sintering (SPS) technique in order to make self-lubricating Al2O3/15wt% ZrO2 nanocomposites with higher mechanical properties. To optimize the self-lubricating Al2O3/15wt% ZrO2 nanocomposite systems were added with different solid lubricants (CaF2, BaF2, MoS2, WS2, h-BN, and graphite). The coefficient of friction of CaF2, h-BN and graphite added composites in steady-state at room temperature are below 0.3.

Pulsed Electric Current Sintering of the Al2O3 - 15wt% ZrO2 Nanocomposites with 3wt% of Different Solid Lubricants

High temperature low friction materials are sought for use in engines in order to reduce energy consumption of the machines. Due to the high service temperatures solid lubricating materials are necessary. This study is designed to find the optimal processing conditions for preparing these materials by pulsed electric current sintering. In this study, the Al2O3 - 15wt% ZrO2 (AZ) nanocomposite was modified with 3 wt% of self-lubricating component (CaF2, BaF2, MoS2, WS2, h-BN, or graphite). After the preparation of the alumina-zirconia powder mixture solid lubricant powder was added. Powders were then mixed in ethanol for 24 h, dried in a rotary evaporator, and in oven at 80°C for 24 h. The particle size distribution of the powders was established with the laser method. Powders were compacted by using pulsed electric current sintering technique at 1300 °C with 50 MPa for 5 min in vacuum. The structure of the materials was studied with XRD and SEM. Density of the compacts was measured with the Archimedes method and their hardness was evaluated by applying HV1 hardness with the instrumented indentation techniques. Their mechanical behavior was further studied with the instrumented scratch testing.

Electrodeposition of Ni-SiC Nano Composite in Presence of Ultrasound

Ni-SiC nano composite coatings were fabricated using electrodeposition technique with the aid of ultrasound. The properties of the nano composite were investigated using SEM and Vicker’s microhardness tester. The results demonstrated that the microhardness of composite coatings under ultrasonic vibrations was improved significantly as compared to conventional electrodeposition techniques without ultrasound. The nano particles were found to be distributed homogeneously with reduced agglomeration due to the ultrasonic vibration.

Red Tide Inactivation by Silver Doped TiO2 Produced in Sono-Chemistry Method

Nano-technology is a super microscopic technology to deal with the structures of 100 nm or smaller. This technology also involves the developing of TiO2 materials or TiO2 devices within that size. The aim of the present paper is to synthesize the silver doped nano-TiO2 by Sonochemistry method and to evaluate the effect of different percentages (0.2-1.5%) of silver load on TiO2 in the algae inactivation, The sample were characterized by using different techniques as XPS, TEM, SEM. Photo-catalytic activity of Silver doped TiO2 were evaluated through the inactivation of red tide (Cochlodinium) using UV-irradiation (315-400nm). The best result was found with silver doped TiO2.

Photocatalytic Activities of Transition Metal-Doped TiO2 Nano-Powders by Sonochemical Method and their Physicochemical Properties

With respect to metal doping into TiO2, the doping limits for V, Cr, Zr, Nb, Mo, and W are predicted to be higher than other transition metals according to the binding energy calculations in a unit cell model of anatase TiO2, which suggests that Cr and W can be doped into anatase structure more easily than Ag or Pt, for example. Our investigation has twofold research objectives. One is to prepare metal-doped TiO2 nano-powders from these transition metals, and the other is to test photocatalytic activity of each resulting powder. For the former, sonochemical process has been used to produce Cr-doped, W-doped, Ag-doped, and Pt-doped TiO2 nanoparticles. For the latter, we have performed photocatalytic oxidation of methylene blue. The combined results of the morphology and photocatalytic activites have enabled characterization of the physicochemical properties of these transition metal-doped nanoparticles.

Comparison of Sonochemistry Method and Sol-Gel Method for the Fabrication of TiO2 Powder

Sol-gel with sonochemical process and sol-gel method were used for the fabrication of photocatalytic TiO2 powder and the properties of the TiO2 powder thus prepared were examined and compared. For the synthesis of TiO2 powder, the starting material was Ti-butoxide and H2O and the reaction was carried out at 80 °C in a sol-gel method. On the other hand, Ti-butoxide was reacted with H2O in an ultrasonic frequency of 23 kHz with ultrasonic powers of 800 W for two hours. After evaporation, 24 hours aging time was kept at 400 °C in both cases, the final product appeared was the anatase phase. Ultrasonic chemical method was found to be excellent for flocculation and crushing effects where as in sol-gel method, the product obtained was of high purity and high homogeneity. Sol-gel with sonochemical process has found to be excellent for flocculation and crushing effects. From Sol-gel method, the size of TiO2 particles produced were found to be about 20 nm, spherical, homogeneous while severe agglomeration. In contrast, by sonochemistry method, the size of TiO2 particles produced were about 10 ~ 22 nm size and it has shown more photocatalytic activity than sol-gel sample which is about 28.7 % greater efficiency

Mechanical Properties of Dysprosia (Dy2O3) Added Al2O3 ZrO2 HA Composite

Alumina (Al2O3)-zirconia (ZrO2)-hydroxyapatite (HA) composite is used as biomaterials. Biomaterials must be bio-compatible to the body and should have excellent mechanical and tribological properties. 1 wt.% of rare earth oxide (Dy2O3) was added to the basic composition of composite Al2O3 -ZrO2 (15wt.%)-HA(1wt.%). The powder mixture was hot-pressed at 1300°C in Ar gas environment under 30 MPa pressure for densification sintering. The microstructural analysis, phase transformation, surface morphology and mechanical properties like hardness, fracture toughness, mechanical strength of the composite were observed and evaluated by SEM , XRD, Vickers hardness, etc. The results demonstrated that the addition of 1 wt.% dysprosia has increased the mechanical properties of composite.

Removing Algae with Pt-Doped TiO2 Coatings on Foamed Glass

The commercial nano-sized TiO2 powder (P25) coated with PtO2 powder by a sonochemistry method was immobilized on the foamed waste-glass substrates by using plasma spray coating technology. The immobilized TiO2-Pt coatings were applied to treat both green tide and red tide under illumination of an UV light. Their photocatalytic characterizations were evaluated as functions of the number of residual algae, transmission as well as pH value with illumination time. It’s found that the plasma sprayed Pt-doped TiO2 nanostructured coatings on foamed waste-glass showed higher photocatalytic activity, which was effective to treat the green tide and red tide.

Effect of Simultaneous Sonication with Horn and Plate Types on the Preparation of Few Layer Graphite.

The effect of different ultrasonication types on the production of few layer graphite (FLG) from graphite powder (270 μm) in ethanol was systematically investigated. Ultrasonic irradiation was done by using plate type (23.3 kHz, 500 W), horn type (20 kHz, 500 W), and combination of both types for 3 hr at room temperature. The obtained graphitic products were characterized by Scanning Electron Microscope (SEM), Fourier Transform Infrared (FT-IR) Spectroscopy, X-ray Diffraction (XRD) and Raman Spectroscopy. It has been observed that depending upon the applied ultrasonic types; variations in the properties of obtained FLG were noticed. The obtained FLG were also found to be oxidized into graphene oxide and other intermediate products containing hydroxide and carbonyl groups depending upon the ultrasonic sources applied.