Abstract: Maghemite and hematite nanospheres were synthesized by using the Sol-gel technique.
The structural properties of these nanosphere powders were characterized by X-ray diffraction
(XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy
(FESEM),and pore size distribution.Hematite phase shows crystalline structures.The mean particle
size that resulted from BET and XRD analyses were 4.9 nm and 2 nm. The field emission scanning
electron microscopy shows iron-oxide powder is composed of nanosized particles, but in nanosized
aggregates (agglomeration of particles). It can be seen from transmission electron microscopy
that the size of the particles are very small which is in good agreement with the FESEM and the Xray
diffraction. TEM and FESEM confirmed that the iron-oxide powder is composed of sizes from
8 nm to 10 nm. The BET and pore size method were employed for specific surface area
Abstract: N-type Bi2Te3-Sb2Te3 solid solutions doped with CdCl2 was prepared by melt spinning,
crushing and vacuum sintering processes. Microstructure, bending strength and thermoelectric
property were investigated as a function of the doping quantity from 0.03wt.% to 0.10wt.% and
sintering temperature from 400oC to 500oC, and finally compared with those of conventionally
fabricated alloys. The alloy showed a good structural homogeneity as well as bending strength of
3.88Kgf/mm2. The highest thermoelectric figure of merit was obtained by doping 0.03wt.% and
sintering at 500oC.
Abstract: Vacuum carburization of nanometer tungsten powder was investigated in a simple
designed apparatus. An X-Y recorder was used to plot differential thermal analysis (DTA) curves to
determine the starting temperature of carburization of four samples with different specific surface
area. The product was characterized by X-ray Diffraction (XRD) and small angle X-ray scattering
(SAXS). The results show that finer tungsten powder has lower starting temperature of
carburization. Tungsten powder, the BET surface area of which is 32.97m2/g, was completely
carburized to tungsten carbide at 1050°C, even though the starting temperature was 890°C. The
particle was found to grow sharply before carburization.
Abstract: Usual process for production of W-Cu nanocomposite is ball–milling and sintering of W and
Cu mixed powder. Recently, mechanochemical process (MCP) using WO3 and CuO powders have
been developed. In the present work, the influence of the ball-milling time from 1 to 30 hour, milling
atmosphere such as Argon and Hexane as Process Control Agent (PCA) and weight ratio of ball to
powder on characteristics of WO3-CuO was studied. The microstructure of WO3–CuO powder
prepared by milling was investigated by x-ray diffraction (XRD) and scanning electron microscopy
(SEM). Results show that, the grain sizes of the WO3 and CuO in the ball-milled powder mixture were
significantly decreased with increasing the milling time. Those of each oxide ball–milled in Argon and
Hexane atmosphere for 30 and 20 hour were about 98 and 84 nm, respectively. After milling of 20 hour
in Hexane as PCA, the powder had a homogeneously mixed structure and the average size of WO3–
CuO powders was determined to about 230nm.
Abstract: The thermoelectric properties of Ag2Se and excess Ag alloys synthesized by mechanical
alloying process were studied. The absolute S value slightly decreased with the Ag content.
Contrary to that, the electrical conductivity (σ) increased with the Ag content. This was due to the
increased carrier concentration supplied by the excess Ag clusters. Below 280K, the σ value of the
excess Ag alloys is almost constant regardless of temperature, which means that the Ag excess
alloys is highly degenerated. At higher temperatures above 290 K, the intrinsic conduction behavior
for all materials is observed and the band gap energy for Ag2Se calculated from the slope of curve
in this higher temperature range is about 220 meV. The figure of merit value (Z) was increased by
the excess Ag, from 0.28/K (Ag2Se) to 0.91/K (Ag2.05Se0.95).
Abstract: Fe doped skutterudite CoSb3 with a nominal composition of FexCo1-xSb12 (0≤x≤2.5) have
been synthesized by mechanical alloying (MA) of elemental powders, followed by vacuum hot
pressing. Phase transformations during mechanical alloying and vacuum hot pressing were
systematically investigated using XRD. Single phase skutterudite was successfully produced by
vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase
in the form of marcasite structure FeSb2 was found to exist in case of x≥2, suggesting the solubility
limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe
contents were evaluated for the hot pressed specimens. Fe doping up to x=1.5 with Co in FexCo4-xSb12
appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at
525K in this study.
Abstract: Various reactions and the in-situ formation of new phases can occur during the
mechanical alloying process. In the present study, Al powders were strengthened by AlN, using the
in-situ processing technique during mechanical alloying. Differential thermal analysis and X-ray
diffraction studies were carried out in order to examine the formation behavior of AlN. It was found
that the precursors of AlN were formed in the Al powders and transformed to AlN at temperatures
above 600oC. The hot extrusion process was utilized to consolidate the composite powders. The
composite powders were canned in an Al can and then extruded at elevated temperatures. The
microstructure of the extrusions was examined by SEM and TEM. In order to investigate the
mechanical properties of the extrusions, compression tests and hardness measurements were carried
out. It was found that the mechanical properties and the thermal stability of the Al/AlN composites
were significantly greater than those of conventional Al matrix composites.
Abstract: In present work, manufacturing technologies of titanium hydride powder were studied for
recycling of titanium tuning chip and for this, attrition ball milling was carried out under H2
pressure of 0.5 MPa. Ti chips were completely transformed into TiH2 within several hundred
seconds that is very short time comparing to that in the previous report. Dehydrogenation process
TiH2 powders is consist of two reactions: one is reaction of TiH2 to TiHx and the other
decomposition of TiHx to Ti and H2. The former reaction shows relatively low activation energy
ranged from about 100 KJ/mol to 250 KJ/mol and it is suggested that the reaction is caused by
introduction of defects due to milling. In case of TiH2 powders that hardly contains defects,
decomposition of TiH2 to Ti and H2 occurs directly without the reaction of TiH2 to TiHx and
activation energy is very large as much as 929 KJ/mol.
Abstract: Fabrication of Fe3AlC matrix in-situ composite, reinforced by a FeAl phase, was
studied by using the powder metallurgical processing route. Especially, in order to disperse the
second phase more finely, we chose the mechanical alloying process. We investigated the
microstructural and mechanical properties of the consolidated material. After consolidation by
vacuum hot pressing, the compact showed almost full density and consisted of a Fe3AlC matrix and
FeAl second phase (average particle size was less than 1μm). The compact showed HV746, which
was higher than that of the arc melted Fe3AlC monolithic material, HV650.
Abstract: This study examines the ball-milling of CVD-processed multi-wall carbon nanotubes
for cutting and opening their tips. Results show that dry milling causes nanotubes to rapidly
collapse, hence transforming into graphite structure, while wet milling with some organic
compounds effectively shortened and opened the nanotubes. Carbon-based milling agents are
known to alter surface structure of carbon nanotubes, minimizing an excess algglomeration and
consequently improving dispersion of nanotubes. The open tip structure was unstable and quite
susceptible to re-close during milling and thermal treatments to minimize their surface energy.