General purpose poly(styrene) is a large
volume commodity polymer widely used in a range of applications. For many
of these the presence of an additive to impart some flammability resistance
is required. Most commonly, brominated aromatics are used for this purpose.
As the polymer undergoes combustion these compounds decompose to generate
bromine atoms and/or hydrogen bromide which escape to the gas phase and trap
flame propagating radicals. While these species are effective in inhibiting
flame propagation they present the opportunity for loss of halogen to the
atmosphere. For this reason, the use of these compounds is being limited in
some parts of the world. Phosphorus compounds, on the other had, impart a
flame retarding influence by promoting char formation at the surface of the
burning polymer. This prevents heat feedback to the polymer and consequent
pyrolysis to generate fuel fragments. The combination of both bromine and
phosphorus present in a single compound might generate a superior flame-retarding
additive in that both modes of retardancy might be promoted simultaneously.
Should this be the case smaller amounts of additive might be necessary to
achieve a satisfactory level of flame retardancy. A series of such additives,
brominated aryl phosphates, has been synthesized and fully characterized spectroscopically.
Blends of these additives, at various levels, with poly(styrene) have been
examined by DSC, TG and in the UL-94 flame test. The flammability of the polymer
is dramatically diminished by the presence of the additive.
Certain five-membered dioxaheterocyclic compounds (hetero atoms may be P, Si, S, etc.) contain a strained carbon–carbon bond
which may undergo homolytic thermolysis at modest temperatures to generate a diradical capable of initiating vinyl polymerization.
If substituents contain flame-retarding moieties this represents a convenient method for imparting flame retrdancy to a polymeric
material. Of particular interest has been 2,4,4,5,5-pentaphenyl-1,3,2-dioxaphospholane. The thermal degradation of this compound
has been studied using 13C NMR spectroscopy. This may conveniently be done by monitoring the intensity of the signal for the benzylic carbon atom as
a function of time and temperature. A simple transformation is the conversion of the cyclic compound to the linear polymer.
Fully substituted 1,3-dioxa-2-siloles contain a strained carbon–carbon bond that will undergo thermolysis at modest temperatures to generate a diradical capable of initiating vinyl polymerization. If the substituents contain flame-retarding moieties, e.g., halogen or phophorus-containing groups, the use of such compounds as initiators serves to incorporate a flame-retarding unit into the polymer mainchain. Both 2,2-dialkyl- and 2,2-diaryl-4,4,5,5-tetra(3,5-dibromophenyl)-1,3-dioxa-2-siloles may be prepared from the appropriate tetra(bromoaryl)-1,2-ethanediol and are obtained as white solids. Thermal decomosition (thermogravimetry) of these materials occurs in two stages. Initial decomposition is observed at about 250 °C and corresponds to the loss of nearly half of the initial sample mass.
The scavenging of UO22+ using 4-sulfonic calixarene in the presence of a strong adsorbent was studied as a function of pH. The adsorbent selected
was goethite because of its strong affinity for UO22+ and its abundance in natural soils. In order to understand the underlying chemistry of the scavenging process, the adsorption
of UO22+ and 4-sulfonic calixarene onto goethite, respectively, and the extraction of adsorbed UO22+ from goethite surface were modeled using the triple-layer model. The model well explained the pH dependence of the adsorption
and extraction processes. This work showed that maximum extraction was obtained around pH 10.5 in the presence of 12g/l goethite
in the case of a 1:3TU(VI):Tcalixareneratio.
Authors:J. Jung, S. Hyun, J. Lee, Y. Cho, and P. Hahn
The prediction of the adsorption behavior of natural composite materials was studied by a single mineral approach. The adsorption
of U(VI) on single minerals such as goethite, hematite, kaolinite and quartz was fully modeled using the diffuse-layer model
in various experimental conditions. A quasi-thermodynamic database of surface complexation constants for single minerals was
established in a consistent manner. In a preliminary work, the adsorption of a synthetic mixture of goethite and kaolinite
was simulated using the model established for a single mineral system. The competitive adsorption of U(VI) between goethite
and kaolinite can be well explained by the model. The adsorption behavior of natural composite materials taken from the Koongarra
uranium deposit (Australia) was predicted in a similar manner. In comparison with the synthetic mixture, the prediction was
less successful in the acidic pH range. However, the model predicted well the adsorption behavior in the neutral to alkaline
pH range. Furthermore, the model reasonably explained the role of iron oxide minerals in the adsorption of U(VI) on natural
The thermal degradation of a series of 1,1,2,2-tetraaryl-1,2-ethanediols has been examined using thermogravimetry (TG) and gas chromatography/mass spectrometry (GC/MS). These compounds are smoothly converted to the corresponding diaryl ketone and diaryl carbinol, i.e., the compounds undergo disproportionation arising from homolytic cleavage of the central carbon–carbon bond. Presumably, cleavage of the carbon–carbon bond generates a radical pair which disproportionates to provide the observed products.
The determination of the hydrogen concentrations in coal and metal samples were investigated by using the PGAA system at the
HANARO Research Reactor, KAERI. The calibration curve of the hydrogen concentration was obtained from a standard sample and
the effects of the interference peaks near the gamma-energy region of hydrogen were investigated. The background in the hydrogen
peak of a prompt gamma-ray spectrum was measured for the sample chamber and shielding materials of an atmospheric state. The
combined uncertainties estimated for the analysis procedure were in the range of 4–5%. Two kinds of certified reference materials,
NIST SRM 1632c (Coal), NIST SRM 173c (Titaniumbase Alloy) and NIST SRM 2453 (Titanium Alloy) were used to verify the accuracy
and precision of the measurement. The relative error was in the range of 3–6% and the relative standard deviation were less
Authors:S. Y. Cho, J. Y. Lee, H. J. Khu, J. H. Kang, M. Y. Yoon, and J. C. Kim
Accelerator mass spectrometry (AMS) is the most sensitive, safe and precise analytical method for quantifying long-lived isotope in biomedical research with animals as well as human beings. In Korea, AMS Laboratory has been operating successfully for years measuring especially archeological samples for 14C dating. In this year, a biological sample pretreatment facility was setup and we have also started to work on biomedical applications. As a preliminary study, we have measured the natural background levels of 14C in tissues and blood of humans and rats. The results were agreed with the other reported levels and gave stable and reproducible results within 1-2%.
Authors:J. Lee, J. Kim, K. Cho, J. Woo, M. Han, and Y. Chung
Trace impurity elements in high purity copper metal (4 mine class) put on the market were analyzed by Instrumental Neutron
Activation Analysis (INAA) and the results compared with those from Graphite Furnace Atomic Absorption Spectrophotometry (GFAAS)
and Inductively Coupled Plasma Atomic Emission Spectrophotometry (ICP-AES). The sample irradiation was done at the irradiation
facilities (thermal neutron flux, 5·1012 n·cm−2·s−1) of the TRIGA Mark-III research reactor in the Korea Atomic Energy Research Institute. Four unalloyed copper standards (NIST
SRM # 393, 394, 395 and 398) were used to identify the accuracy and precision of the analytical procedure. The homogeneity
of samples was assessed by means of the elements such as Ag, As, Co, Sb, Se and Zn. The analytical results of INAA, GFAAS
and ICP-AES were in good agreement within expected uncertainties each other and showed the possibility of using them for the
analytical quality control.
Authors:K. Lee, M. Yang, Y. Yoon, S. Shim, S. Cho, B. Seo, Y. Chung, and J. Lee
Most elemental concentrations in crops should be related to those in soil and other circumferential environments. In the present study, more than thirty minor and trace elements in soils and crops were determined by the use of ICP, XRF and NAA. Soil and crop samples were collected at eleven abandoned mine regions in Chungnam province located in the middle part of Korea. The elemental concentrations in soils were compared to the crustal mean concentrations in both Chungnam area and worldwide. The concentration ratios of the elements in soils and crop compartments were calculated and the distribution characteristics of each element were investigated between soil and crop compartments.