The effects of silica addition on the thermal stability of flame-synthesized gamma -Al sub(2)O sub(3) nanoparticles are investigated in this study. Based on the electron microscope images of pure ...alumina, nanoparticles with diameters ranging from 20 nm to 30 nm were synthesized. No significant changes were observed after heat treatment at 900 degree C, 1100 degree C, and 1180 degree C. After heat treatment at 1260 degree C, sintered particles larger than 100 nm were observed. All images of the nanoparticles doped with silica, including those taken after heat treatment at 1260 degree C, showed similar particle sizes regardless of treatment temperature. Based on the X-ray diffraction patterns and specific surface areas, the onset temperature of the phase transition to alpha -Al sub(2)O sub(3) for the flame-synthesized pure alumina was near 1180 degree C. The addition of silica greatly increased the thermal stability of the synthesized gamma -Al sub(2)O sub(3) nanoparticles.
Gadolinium oxyorthsilicate doped with cerium, Gd
2
SiO
5
:Ce (GSO:Ce), is a scintillator crystal discovered in 1983, which has excellent properties, high light yield, fast decay time, and good ...radiation hardness. The Gd
2
SiO
5
(GSO) and GSO:Ce (0.5 mole%) single crystals were grown by Czochralski method under argon atmosphere. After the growth, thermal treatment of the GSO crystals was carried out at 1780K for 3 hours under argon atmosphere. The maximum wavelength of the emission spectrum of the GSO:Ce scintillator was 430 nm. The energy resolution of the GSO:Ce scintillator was 9.1 % with PMT, when it was exposed to
137
Cs γ-ray. The luminescence decay time of the GSO:Ce scintillator has two exponential components with 68.7 ns and 754 ns time constant.
Recently, some studies have utilized silicon (Si) as an anode material of lithium ion battery by recycling Si from the slurry of wafer slicing dust. The filtration of Si particles condensed from Si ...vapors that were exhausted from the ingot growing furnace could propose another method of Si recycling. In this study, we investigated the possibility of using such collected silicon oxides (SiO
) particles as an anode material. After collecting SiO
particles, FE-SEM, TEM, EDS, XRD, XPS analysis, and charge/discharge test were carried out to investigate characteristics and usability of these particles. FE-SEM and FE-TEM images showed that these particles mainly consisted of spherical primary particles with a diameter of 10 nm or less. Agglomerates of these primary particles were larger than 300 nm in diameter. In TEM image and EDS analysis, crystalline particles were observed along with amorphous particles. As a result of XRD analysis, amorphous silica (SiO
) and crystalline Si were observed. Charge/discharge tests were carried out to determine the feasibility of using these particles as an anode material for lithium ion batteries. A cycle efficiency of 40.6% was obtained in the test in which the total number of charge/discharge cycle was 100 under the condition of C-rate 0.2 for the first three times and C-rate 1.0 for the remaining 97 times. Results showed that these collected particles could be used as an anode material for lithium ion batteries.
A composite polycrystalline stilbene scintillator of ¿ 200 mm × 20 mm was specially developed for fast neutron detection. These composite stilbene scintillators have advantages that can be used ...without special housing, and do not have any toxic. The neutron-gamma ray separation tests have been performed by neutron radiation source and compared with the single crystal stilbene. The neutron source used for this study is 252 Cf and mono-energy fast neutrons by using the accelerator in Korea Institute of Geoscience and Mineral Resources (KIGAM). The measured results are compared to the response of a small size (¿25 mm × 20 mm) single crystal stilbene.
Discontinuous carbon fiber (CF) composite materials have potential as heating elements, but the practical realization of heat-generating characteristics has been restricted by the high resistance of ...conventional CF composites. In this study, the electrical, mechanical, and thermal properties of heating sheets with discontinuous CFs were investigated. The properties were found to vary depending on CF length and the dispersant content. Sheets containing CFs 6 mm in length and 16.9–45.8 wt% dispersant showed optimum electrical and mechanical properties for heating elements. The CF heating sheets showed a low volume resistivity and a high glass transition temperature. The far-infrared emissivity of the CF heating sheets corresponded to 90% of that of a black body and was higher than that of a nichrome wire. Internal energy saturation of the CF heating sheets occurred within 5 s owing to low heat capacity. These features indicate that the CF heating sheets are suitable for application as a portable heating element.
This study involves the investigation of mechanical damping and thermal stability of hybrid epoxy composites with two types of fillers, graphitized carbon nanofiber (CNF) and micron size silicon ...dioxide (SiO
2) particles. While viscoelastic properties of the composites were characterized for the study of mechanical damping, the linear coefficient of thermal expansion (CTE) was evaluated for investigation of thermal stability of the hybrid composites. The effect of filler loading was investigated with respect to both mechanical and thermal stability of the hybrid composite materials. It has been found that the addition of 3% weight fraction of SiO
2 particles along with 3% weight fraction of CNF can improve damping loss factors by up to 15.6% at room temperature while at the same time improving thermal stability with up to 15% reductions in CTE. This study also presents semi-empirical models which can account for both the fillers in prediction of viscoelastic properties and CTE of the hybrid composites. It is observed that there is reasonable agreement in both mechanical damping and CTE for the hybrid composites between the experimental data and the predicted data.
In this article, TiO sub(2) nanoparticles were synthesized by using O sub(2)-enriched coflow, hydrogen, diffusion flames. We investigated the thermal stability of the flame-synthesized TiO sub(2) ...nanoparticles by examining the crystalline structures of the nanoparticles and by analyzing the photocatalytic degradations of methylene blue solutions. Also, the results were compared with those of commercial P-25 nanoparticles. The maximum centerline temperature of the flame was measured to be 1,743 C. Under this synthesis condition, TiO sub(2) nanoparticles, which were spherical with diameters approximately ranging from 30 to 60 nm, were synthesized. From the XRD analyses, about 96 wt.% of the synthesized nanoparticles were anatase-phase. After the heat-treatment at 800 C for 30 min, the synthesized TiO sub(2) nanoparticles showed no significant changes of their shapes and crystalline phases. On the other hand, most of the commercial particles sintered with each other and changed to the rutile-phase. Whereas the photocatalytic ability of heat-treated commercial particles deteriorated, that of the flame-synthesized particles improved. On the basis of the improved result of photocatalytic degradation of methylene blue by using the heat-treated flame-synthesized nanoparticles, it is believed that the flame-synthesized TiO sub(2) nanoparticles have higher thermal stability at 800 C than the commercial particles.
The effect of ultrasonic processing on the phase transformation of flame-synthesized anatase TiO
2 nanoparticles heated to the rutile phase was investigated. TiO
2 nanoparticles of various sizes were ...prepared using a coflow hydrogen diffusion flame and an ultrasonic processor. Smaller nanoparticles having a similar portion of anatase phase using the ultrasonic processor were produced. On the basis of scanning electron microscopy images and specific surface areas, we observed that smaller nanoparticles tended to be sintered more easily than larger nanoparticles. From X-ray diffraction analysis, we demonstrated that when heated, TiO
2 nanoparticles synthesized using the ultrasonic processor at 60% of its maximum amplitude were transformed from the anatase phase to the rutile phase more easily than those formed without or with the ultrasonic processor operated at 20% of its maximum amplitude.
PDF
