• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.833-838
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• 2012

The thermal degradation products of polytrimethylene terephthalate (PTT) obtained by heating the sample in the temperature range of $250-360^{\circ}C$ under non-oxidative conditions was characterized using MALDI-TOF (matrix assisted laser desorption/ionization) mass spectrometry. The structures of the degradation products were determined and the relative compositions were estimated. The MALDI-TOF mass spectra of the thermally degraded PTT sample showed three main series of oligomer products with different end groups, which were carboxyl/carboxyl, carboxyl/allyl, and allyl/allyl. In contrast to the thermal degradation of polyethylene terephthalate (PET), the oligomers containing terephthalic anhydrides were not detected, whereas the formation of oligomers containing the unsaturated allyl ester group was confirmed by mass assignment. From these results, it was concluded that the thermal degradation of PTT proceeds exclusively through the ${\beta}$-CH hydrogen transfer mechanism, which is in accordance with the proposed reaction mechanism for the thermal degradation of polybutylene terephthalate (PBT).

• Bulletin of the Korean Chemical Society
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• v.27 no.10
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• pp.1557-1561
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• 2006

The use of chemically modified silica-salen$(NEt_2)_2$ was studied for the separation and concentration of the metal ions from an aqueous solution by a solid phase extraction. After the salen(NEt2)2 was synthesized, it was chemically bonded to silica gel by a diazonium coupling reaction. The adsorption capacities and binding constants were obtained with respect to Cu(II), Mn(II), Pb(II) and Zn(II) by a graphical method. Some experimental conditions were optimized for the determination of the trace elements. After the silica-salen(NEt2)2 was pulverized in a sample solution of which the pH was adjusted, the solution was stirred to pre-concentrate the metal ions. The metal ions adsorbed were desorbed with nitric acid solution. And the concentrated analytes were determined by a flame AAS. The method proposed here was so rarely influenced by a sample matrix that the procedure was applied to 3 types of water samples. The reproducible results of less than 10% RSD were obtained at the concentration level of ca. 100 ng/mL and the recoveries of 95-109% were obtained in the spiked samples in which given amounts of analytes were added.

• KSBB Journal
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• v.25 no.4
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• pp.371-378
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• 2010

For the biodiesel fuel production from microalgae, the lipid from wet and dry samples of green algae Scenedesmus sp. was extracted by using various solvents and pre-treatment methods. Extraction yield of the lyophilized sample was better than that of dry sample. Chloroform/methanol (2:1, v/v) and ultrasonication or homogenization method were also selected as the most effective solvent and pre-treatment methods for lipid extraction, respectively. Under these constraint conditions, optimization experiment of lipid extraction was investigated by Taguchi approach using orthogonal matrix $L_9$ ($3^4$) method. The optimum extraction conditions of lipid extraction was obtained at pre-treatment of homogenization, extraction time of 5 hour, temperature of $35^{\circ}C$, and solvent ratio of 1:20 (w/v). Yield of extraction at optimized condition was 20.55% and it was 96% of total lipid content (21.38%) of Scenedesmus sp.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.4
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• pp.525-531
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• 2012

This study aims at the structural analysis of vibration and fatigue according to the configuration of engine mount. Maximum equivalent stress or deformation is shown at bracket or case respectively. As harmonic vibration analysis, the maximum displacement amplitude is happened at 4,000Hz. Among the cases of nonuniform fatigue loads, 'SAE bracket history' with the severest change of load becomes most unstable but 'Sample history' or 'Saw tooth' becomes most stable. In case of 'Sample history' or 'Saw tooth' with the average stress of 4,200MPa or 0MPa and the amplitude stress of -3,000MPa or 7MPa, the possibility of maximum damage becomes 70%. This stress state can be shown with 7 times more than the damage possibility of 'SAE bracket history' or 'SAE transmission'. The structural result of this study can be effectively utilized with the design on engine mount by investigating prevention and durability against its damage.

• The Korean Journal of Applied Statistics
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• v.28 no.6
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• pp.1113-1120
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• 2015

We propose a multi-proportions randomized response model by stratified simple random sampling for surveys of sensitive issues of a polychotomous population composed of several stratum. We also systemize a theoretical validity to apply multi-proportions randomized response model (Abul-Ela et al.' model, Eriksson's model) to stratified simple random sampling and derive the estimate and its dispersion matrix of the proportion of sensitive characteristic of population using the suggested model. Two types of sample allocations (proportional allocation and optimum allocation) are considered under the fixed cost. In efficiency, the Eriksson's model by stratified sampling are compared to the Abul-Ela et al.' model.

• Steel and Composite Structures
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• v.19 no.4
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• pp.939-952
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• 2015

In this paper, brake pad performance of two organic matrix composites namely, Sample 1 (contains no brass filler) and Sample 2 (contains 1.5% brass filler), is studied based on tribological and squeal noise behavior. In the first stage, a pin-on-disc tribometer is used to evaluate the frictional behavior of the two pads. On the following stage, these pads are tested on squeal noise occurrence using a drag-type brake dynamometer. From the two type of tests, the results show that; (i) brass fillers play a dual role; firstly as reinforcing element of the brake pad providing primary contact sites, and secondly as solid lubricant by contributing to the formation of a layer of granular material providing velocity accommodation between the pad and the disc; (ii) brass fillers contribute to friction force stabilization and smooth sliding behavior; (iii) the presence of small weight quantity of brass filler strongly contributes to squeal occurrences; (iv) there is close correlation between pin-on-disc tribometer and brake dynamometer tests in terms of tribological aspect.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1993.11a
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• pp.75-79
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• 1993

The Thermally Stimulated Current(TSC) method has been allied to study the influence of the structural change and interface on the electrical properties of epoxy composites. Three DGBA- MeTHPA matrix model samples mixed different ratios arts silica(SiO$_2$) filled sample and silaln treating-filled sample have been studied. Above room temperature, the relaxation mode ${\alpha}$ peak associated with T$\_$g/ has been located at 110$^{\circ}C$. Below glass transition temperature(T$\_$g/), three relaxation modes are observed in all samples : a ${\beta}$ mode situated at 10$^{\circ}C$, a ${\gamma}$ mode located at -40$^{\circ}C$ and a $\delta$mode appeared in -120$^{\circ}C$, which may be due to segmental motion, side chains, substitution and terminal groups. The analysis of its fine structure indicates that constitution of elementary processes is characterized by the activation energy and relaxation time. Also the change of the molecular structure and their thermal motion are compared with the relaxation mode and conduction mechanism in TSC spectra through the dielectric properties and FTIR measurements.

• Korean Journal of Materials Research
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• v.30 no.2
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• pp.74-80
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• 2020

Synthesis of composite powders for the Fe₂O₃-Zn system by mechanical alloying (MA) has been investigated at room temperature. Optimal milling and heat treatment conditions to obtain soft magnetic composite with fine microstructure were investigated by X-ray diffraction, differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM) measurement. It is found that α-Fe/ZnO composite powders in which ZnO is dispersed in α-Fe matrix can be obtained by MA of Fe₂O₃ with Zn for 4 hours. The change in magnetization and coercivity also reflects the details of the solid-state reduction process of hematite by pure metal of Zn during MA. Densification of the MA powders was performed in a spark plasma sintering (SPS) machine at 900 ~ 1,000 ℃ under 60 MPa. Shrinkage change after SPS of sample MA'ed for 5 hrs was significant above 300 ℃ and gradually increased with increasing temperature up to 800 ℃. X-ray diffraction results show that the average grain size of α-Fe in the α-Fe/ZnO composite sintered at 900 ℃ is in the range of 110 nm.

• Bulletin of the Korean Chemical Society
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• v.29 no.5
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• pp.969-973
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• 2008

Solvent extraction using a Schiff-base, salen$(NEt_2)_2$, as a chelating agent has been conducted on several water samples to study the determination of trace Cu(II), Mn(II) and Zn(II). Experimental conditions for the formation and extraction of metal complexes were optimized with an aqueous solution similar in composition to the samples. The matrix difference between the sample and standard solutions was approximately matched, and the pH of each sample solution was adjusted to 9.5 with $NaHCO_3/NaOH$ buffer. The concentration of salen$(NEt_2)_2$ was $7.3\;{\times}\;10^{-3}$ mol/L, and the complexes were extracted into MIBK solvent followed by the measurement of AAS absorbance. The potential interference of concomitant ions was investigated, but no interference from alkaline and alkali earth ions was shown in this procedure. The given procedure is precise, as judged from the relative standard deviation of less than 5% for five measured data. The recovery of 93-103% shows that this method is quantitative for such trace metal analysis.

• International Journal of Reliability and Applications
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• v.13 no.1
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• pp.19-35
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• 2012

This paper presents an optimum design of step-stress partially accelerated life test (PALT) plan which allows the test condition to be changed from use to accelerated condition on the occurrence of fixed number of failures. Various life distribution models such as exponential, Weibull, log-logistic, Burr type-Xii, etc have been used in the literature to analyze the PALT data. The need of different life distribution models is necessitated as in the presence of a limited source of data as typically occurs with modern devices having high reliability, the use of correct life distribution model helps in preventing the choice of unnecessary and expensive planned replacements. Truncated distributions arise when sample selection is not possible in some sub-region of sample space. In this paper it is assumed that the lifetimes of the items follow Truncated Logistic distribution truncated at point zero since time to failure of an item cannot be negative. Optimum step-stress PALT plan that finds the optimal proportion of units failed at normal use condition is determined by using the D-optimality criterion. The method developed has been explained using a numerical example. Sensitivity analysis and comparative study have also been carried out.