• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2014.11a
• /
• pp.304-304
• /
• 2014

Quaternary Ti-Al-Si-N films were deposited on WC-Co substrates by a hybrid deposition system of arc ion plating (AIP) method for Ti-Al source and DC magnetron sputtering technique for Si incorporation. The synthesized Ti-Al-Si-N films were revealed to be composites of solid-solution (Ti,Al)N crystallites and amorphous $Si_3N_4$ by instrumental analyses. The Si addition in Ti-Al-N films affected the refinement and uniform distribution of crystallites by percolation phenomenon of amorphous silicon nitride, similarly to Si effect in TiN film. As the Si content increased up to about 9 at.%, the hardness of Ti-Al-N film steeply increased from 30 GPa to about 50 GPa. The highest microhardness value (~50 GPa) was obtained from the Ti-Al-Si-N film having the Si content of 9 at.%, the microstructure of which was characterized by a nanocomposite of $nc-(Ti,Al)N/a-Si_3N_4$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.7
• /
• pp.594-598
• /
• 2011

We have investigated the sensing properties of ethanol gas sensor with pure ZnO and Ga-doped ZnO nanowires on Au coated (0001) sapphire substrates grown by hot walled pulsed laser deposition. Randomly aligned ZnO nanowires arrays were grown on a Au-electrode patterned under ambient conditions. ZnO nanowires have various sizes and shapes with a different substrate position inside a furnace. The average of length and diameter of the ZnO nanowires were $8\;{\mu}m$ and 100 nm respectively, and confirmed by field emission scanning electron microscopy. Sensitivity chanege characterization of the gas sensor was found that measured sensitivities of the ethanol gas sensors were 83.3% and 68.3% at $300^{\circ}C$ respectively.

• Journal of the Korean Ceramic Society
• /
• v.42 no.12 s.283
• /
• pp.821-826
• /
• 2005

Gadolinia-doped ceria nanopowder was prepared by glycine-nitrate combustion method with different glycine/nitrate mixing ratio. The characteristics of the synthesized powder were investigated by X-ray diffraction method, transmission electron microscopy, thermal gravity, differential thermal analysis and thermo-mechanical analysis. The smallest powder was obtained with glycine/nitrate ratio 1.00 and the lowest organic and water vapor contained powder was made with glycine/nitrate ratio 1.75. According to dilatometry, fast densification was occurred around $1000^{\circ}C$ and shows full density over $1300^{\circ}C$. Finally near-fully dense ceria electrolyte was fabricated with conventional sintering technique. Glycine-nitrate process yields fine nanopowders which enable low temperature sintering and fabrication of fully dense and nanostructured oxide electrolyte.

• Korean Journal of Materials Research
• /
• v.23 no.11
• /
• pp.620-624
• /
• 2013

Nanocrystalline materials have recently received significant attention in the area of advanced materials engineering due to their improved physical and mechanical properties. A solid-solution nanocrystalline powder, (Ti,Mo)C, was prepared via high-energy milling of Ti-Mo alloys with graphite. Using XRD data, the synthesis process was investigated in terms of the phase evolution. Rapid sintering of nanostuctured (Ti,Mo)C hard materials was performed using a pulsed current activated sintering process (PCAS). This process allows quick densification to near theoretical density and inhibits grain growth. A dense, nanostructured (Ti,Mo)C hard material with a relative density of up to 96 % was produced by simultaneous application of 80 MPa and a pulsed current for 2 min. The average grain size of the (Ti,Mo)C was lower than 150 nm. The hardness and fracture toughness of the dense (Ti,Mo)C produced by PCAS were also evaluated. The fracture toughness of the (Ti,Mo)C was higher than that of TiC.

• Korean Journal of Materials Research
• /
• v.30 no.2
• /
• pp.81-86
• /
• 2020

MoO₃ metal oxide nanostructure was formed by hydrothermal synthesis, and a perovskite solar cell with an MoO₃ hole transfer layer was fabricated and evaluated. The characteristics of the MoO₃ thin film were analyzed according to the change of hydrothermal synthesis temperature in the range of 100 ℃ to 200 ℃ and mass ratio of AMT : nitric acid of 1 : 3 ~ 15 wt%. The influence on the photoelectric conversion efficiency of the solar cell was evaluated. Nanorod-shaped MoO₃ thin films were formed in the temperature range of 150 ℃ to 200 ℃, and the chemical bonding and crystal structure of the thin films were analyzed. As the amount of nitric acid added increased, the thickness of the thin film decreased. As the thickness of the hole transfer layer decreased, the photoelectric conversion efficiency of the perovskite solar cell improved. The maximum photoelectric conversion efficiency of the perovskite solar cell having an MoO₃ thin film was 4.69 % when the conditions of hydrothermal synthesis were 150 ℃ and mass ratio of AMT : nitric acid of 1 : 12 wt%.

• Korean Journal of Materials Research
• /
• v.30 no.2
• /
• pp.93-98
• /
• 2020

Effective control of the heat generated from electronics and semiconductor devices requires a high thermal conductivity and a low thermal expansion coefficient appropriate for devices or modules. A method of reducing the thermal expansion coefficient of Cu has been suggested wherein a ceramic filler having a low thermal expansion coefficient is applied to Cu, which has high thermal conductivity. In this study, using pressureless sintering rather than costly pressure sintering, a polymer solution synthesis method was used to make nano-sized Cu powder for application to Cu matrix with an AlN filler. Due to the low sinterability, the sintered Cu prepared from commercial Cu powder included large pores inside the sintered bodies. A sintered Cu body with Zn, as a liquid phase sintering agent, was prepared by the polymer solution synthesis method for exclusion of pores, which affect thermal conductivity and thermal expansion. The pressureless sintered Cu bodies including Zn showed higher thermal conductivity (180 W/m·K) and lower thermal expansion coefficient (15.8×10^-6/℃) than did the monolithic synthesized Cu sintered body.

• Korean Journal of Materials Research
• /
• v.11 no.9
• /
• pp.797-801
• /
• 2001

In this study, the solution combustion method was employed to synthesize stoichiometric mullite, and hence the attrition process was employed to prepare ultrafine mullite particles with nano size. The thermal decomposition behavior and partial pressure of equilibrium species of both oxidizer and fuel were considered during solution combustion process. The synthesized product was mullite phase with 40 nm crystalline size, and the alumina contents of the product by TEM/EDS quantity analysis was 3.12$\pm$04 mole. The result showed that the synthesized mullite was almost close to the it's stoichiometric composition. For attrition process, the dispersion behavior of the mullite suspension was controlled and was comminuted with the condition of 800 rpm for 4 hours using 0.3 mm zirconia ball media. As a result of comminution, the mean particle size was 80 nm.

• Korean Journal of Materials Research
• /
• v.12 no.3
• /
• pp.169-175
• /
• 2002

Semiconductive nano $(Ba_{1-x}Sb_x)TiO_3$ powders were synthesized by the hydrothermal process and Sb was simultaneously doped in the hydrothermal condition. $(Ba_{1-x}Sb_x)TiO_3$ powders obtained from optimum condition(at 20$0^{\circ}C$ for 3hr) exhibited spherical shape, high purity and nano size. The PTCR characteristics was observed when 0.1 and 0.2 mole% Sb were added and sintered at over 130$0^{\circ}C$ for 1 hour, respectively. And The ceramics exhibit the PTCR characteristics with a resistively jump $ratio($\rho$_{max}/$\rho$_{min})$ of about $10^4$. Also we found that PTCR characteristics were dependent on the microstructure.

• Korean Journal of Materials Research
• /
• v.24 no.2
• /
• pp.67-72
• /
• 2014

Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties, including high strength, high hardness, excellent ductility and toughness. In this study, nanopowders of $Al_2O_3$, MgO and $TiO_2$ were prepared as starting materials by high energy ball milling for the simultaneous synthesis and sintering of the nanostructured compound $Mg_4Al_2Ti_9O_{25}$ by high-frequency induction heating process. The highly dense nanostructured $Mg_4Al_2Ti_9O_{25}$ compound was produced within one minute by the simultaneous application of 80MPa pressure and induced current. The sintering behavior, grain size and mechanical properties of the $Mg_4Al_2Ti_9O_{25}$ compound were evaluated.

• Korean Journal of Materials Research
• /
• v.19 no.3
• /
• pp.169-173
• /
• 2009

In chemistry, the study of sonochemistry is concerned with understanding the effect of sonic waves and wave properties on chemical systems. In the area of chemical kinetics, it has been observed that ultrasound can greatly enhance chemical reactivity in a number of systems by as much as a million-fold. Nano-technology is a super microscopic technology in which structures of 100 nanometers or smaller can be investigated. This technology has been used to develop $TiO_2$ materials and $TiO_2$ devices of that size. Thus far, electrochemistry methods and photochemistry methods have generally been used to create $TiO_2$ nano-size particles. However, these methods are complicated and create pollutants as a by-product. In the present study, nano-scale silver particles (5 nm) were prepared in a sonochemistry method. Sonochemistry deals with mechanical energy that is provided by the collapse of cavitation bubbles that form in solutions during exposure to ultrasound. $TiO_2$ powders 25 nm in size doped with Ag were formed using an ultrasonic sound technique. The experimental results showed the high possibility of removing pollution through the action of a photocatalyst. This powder synthesis technique can be considered as an environmentally friendly powder-forming processing owing to its energy saving characteristics.