The crystallization behaviour of amorphous melt spun Fe82−x−yCr18ZrxBy (x=0–8, y=10–20) ribbons have been investigated using differential scanning calorimetry. The crystallization temperature and
crystallization behaviour change with varzing Zr and B content.
The microstructural development during annealing of amorphous Fe64Cr18Zr8B10 has been investigated by a combination of transmission electron microscopy and energy dispersive X-ray microanalysis. Isothermal
annealing for 2 h at temperatures in the range 600–1000°C produces a variety of different microstructures depending on the
annealing temperature. At 600°C, the amorphous alloy partially crystallizes to a form a microstructure consisting of 9 nm
sized bee ferrite grains embedded in an amorphous matrix. At temperatures in the range 700–900°C, the alloy microstructure
transforms into a mixture of bee ferrite, faulted fcc MB12 boride particles and tetragonal M3B boride particles. At 1000°C, the faulted fcc MB12 boride particles are replaced by orthorhombic M4B boride particles.
Thermal ionization mass spectrometry (TIMS) is an effective method for isotopic and ultra-sensitivity determination of plutonium.
This project aims at improving the National Institute of Standards and Technology (NIST) TIMS system sensitivity for the analysis
of plutonium from environmental samples. The TIMS detection limits for direct, electrodeposition, and resin bead source loading
techniques were determined by systematically varying the amount of plutonium loaded on the rhenium filament. It has been shown
in our preliminary work that the resin bead could produce a stable TIMS ion beam for as long as 6 h period with »108 Pu atoms loaded onto a single resin bead.
Authors:T. C. K. Yang, W. H. Chang, and D. S. Viswanath
Thermal degradation of poly(vinyl butyral) (PVB) and its mixtures with alumina, mullite and silica was investigated by non-isothermal thermogravimetry in the temperature range of 323 to 1273 K. The analysis of the data was carried out using a three-dimensional diffusion model. Results showed that the kinetic parameters (activation energy and pre-exponential factor) of the PVB degradation are different for polymer alone, and ceramic/polymer composites. The overall weighted mean apparent activation energy showed an increasing reactivity in the order of PVB<alumina+PVB<mullite+PVB<silica+PVB. This shows that the acidic and basic surface characteristics of the ceramics promote the thermal degradation of PVB and, the more acidic silica affects the degradation more than mullite and alumina. The effect of pellet compression pressure in the range of 4000 to 8000 psig is also investigated.
research investigated the influence of binary solutions of benzene and methanol
for their vapor flammability characteristics. The different mixing ratios
(100/0, 75/25, 50/50, 25/75 and 0/100 vol%) samples were injected into a 20-liter
spherical explosion vessel under various initial temperatures (100, 150 and
200C) to study their flammability behaviors. According to the experimental
results, the flammability diagram of mixtures can be completely illustrated
and combined with specific safety-related properties such as lower explosion
limit (LEL), upper explosion limit (UEL), minimum oxygen concentration (MOC),
maximum explosion overpressure (Pmax),
and gas or vapor deflagration index (Kg).
The experimental results showed that the UEL, Pmax
and Kg all increased
with the temperature, pressure and oxygen concentration, whereas there was
no significant variation on the part of LEL. The results can provide specific
information on fire and explosion hazards for related industries.
Authors:C. Kim, C. Kim, B. Chang, S. Choi, C. Chung, G. Hong, K. Hirose, and H. Pettersson
239+240Pu concentrations and 240Pu/239Pu atom ratios in bottom sediments of the Yellow Sea, Korea Strait, East Sea (Sea of Japan), Sea of Okhotsk, and Northwest Pacific Ocean were determined. In coastal sediments near the Korean Peninsula, 239+240Pu concentrations varied from 0.02 to 1.72 Bq.kg-1, and their 240Pu/239Pu atom ratios from 0.15 to 0.24, with an average of 0.20±0.03. 240Pu/239Pu atom ratios of bottom sediments in the deep NW Pacific Ocean and its marginal seas (East, Okhotsk seas) were in the range of 0.15-0.23. A little elevated 240Pu/239Pu atom ratios in the bottom layer sediment may be due to Pu released into the environment during the pre-moratorium period, having high 240Pu/239Pu atom ratios and low 238Pu/239+240Pu activity ratios.
Authors:G. Kim, W. Hong, H. Woo, J. Kim, C. Eum, J. Chang, and K. Park
A nanosecond proton bunching system has been constructed at Korea Institute of Geoscience and Mineral Resources (KIGAM). This
pulsed ion beam will be converted into corresponding duration of neutron pulse, which can reduce the scattered neutron background
during neutron spectroscopy. The pulsed beam is obtained by deflection and double bunching by RF field. RF fields are applied
to deflection and bunching electrodes as 2 kV p-p, 4 MHz and 2 kV p-p, 8 MHz, respectively. A push-pull RF amplifier has been
designed and constructed with a maximum output power of 300 W continuous wave (CW) between 2 and 30 MHz. The main parameters
of bunching beam were as follows: 8 MHz repetition rate, 2 ns FWHM, approximately 20% of duty factor and the maximum energy
spread of 2 keV within a pulse.
Authors:G. Kim, H. Woo, H. Choi, N. Kim, T. Yang, J. Chang, and K. Park
Neutron capture cross sections on 63Cu and 186W were measured by fast neutron activation method at neutron energies from 1 to 2 MeV. Monoenergetic fast neutrons were produced
by 3H(p,n)3He reaction. Neutron energy spread by target thickness, which was assumed to be the main factor of neutron energy spread,
was estimated to be 1.5% at neutron energy of 2.077 MeV. Neutron capture cross sections on 63Cu and 186W were calculated by reference comparison method on those of 197Au(n,γ). Not only statistical errors of gamma-counts from samples but also systematic errors in the counting efficiency for
HP Ge detector and the uncertainty of areal density of samples were considered in calculating neutron capture cross section.
Estimated neutron capture cross sections on 63Cu and 186W were also compared with ENDF-6 data.
Authors:R.-L. Yun, Y.-M. Chang, C.-H. Lin, K.-H. Hu, and C.-M. Shu
In industrial processes, information
on the safety property of chemicals is essentially crucial for safe handling
during unit operations. Ensuring the safe use of combustible or flammable
substances in processes is unlikely without detailed investigations of their
flammability characteristics and related hazards. We studied 3-methyl pyridine
(3-picoline), e.g., flammability limits (LFL/UFL), maximum explosion pressure
explosion pressure rise (dP/dt)max, minimum oxygen concentration
(MOC), vapor deflagration index (Kg),
and characterized the influence of inert steam (H2O)
on critical parameters for 3-picoline/water mixtures at 270C, 1 atm,
various oxygen concentrations, and vapor mixing ratios (100/0, 30/70, 10/90
and 5/95 vol.%) with a 20-L-Apparatus in simulated conditions, respectively.
The results showed that the flammability characteristics
of 3-picoline(aq) all increased with the oxygen concentration.
However, as the composition of inert steam increased, the flammability parameters
and the degree of fire and explosion hazards were significantly reduced, instead.
This study elucidated the flammability properties of 3-picoline mixed with
inert steam. The conclusions could be applied to proactively prevent the relevant
processes from incurring fire and explosion accidents.
Authors:Chang-Kyu Kim, A. Takaku, M. Yamamoto, H. Kawamura, K. Shiraishi, Y. Igarashi, S. Igarashi, H. Takayama, and N. Ikeda
A new analytical technique using ICP-MS was applied to the determination of237Np in some environmental samples. The accuracy and precision of the new method were assessed by comparison with those of conventional NAA and -spectrometric method as well as by analysis of the intercomparison sample of Ravenglass NRPB silt. The results obtained by ICP-MS were in good agreement with those by NAA or -spectrometry at a relative deviation of 2–9%. The detection limit is 0.02 mBq/ml (26 mBq=1 ng).