• Korean Journal of Materials Research
• /
• v.9 no.7
• /
• pp.701-706
• /
• 1999

The crystal structure and magnetic properties of magnetic oxide system (F $e_2$ $O_3$)$_{5}$(A $l_2$ $O_3$)$_{4-x}$(G $a_2$ $O_3$)$_{x}$)SiO has been studied using X-ray diffraction and Mossbauer spectroscopy The changes of magnetic structure by the Ga ion substitution and the temperature variation have been investigated using Mossbauer spectroscopy, and the results are compared with those of the SQUIB measurements. Results of X-ray diffraction indicated that the crystal structures of the system change from a cubic spinel type to an orthorhombic via the intermediate region. This magnetic oxide system seems to be new kind of spinel type ferrites containing high concentration of cation vacancies. Various and complicated Mossbauer spectra were observed in the samples (x>0.2) at temperatures lower than room temperature. This result could be explained by freezing of the superparamagnetic dusters. On cooling and substitution, magnetic states of the system show various and multicritical properties. Unexpected dip in magnetization curves below 50K was observed in SQUID measurements. It was interpreted as an effect of spin canting including spin freezing or collective spin behavior.ior.r.

• Journal of Conservation Science
• /
• v.29 no.3
• /
• pp.261-277
• /
• 2013

This study aims to research the relationship between whitewares and their rare materials from the site of Yanggu and Bunwon through the componential characteristic of the excavated whitewares from the 1st and the 2nd kilns of Chiljeon-ri in Bangsan-myeon, Yanggu-gun. As a result, the sherds were devided according to the chemical compositions of the body and the glaze via their respective production era. However, it considered that the whitewares from Chiljeon-ri had been manufactured with geochemically similar materials and the production process, such as refining and combining materials, had been different. It assumed that the firing temperatures of the whitewares from Chiljeon-ri were around $1,100-1,200^{\circ}C$ and substantially lower than for general whitewares. In the componential analysis, there were disparate properties in the cobalt pigment, which contained trace elements and rare earth elements. A review of the literature revealed a correlation between the whitewares from the late Chosun kiln site in Bunwon-ri and the raw materials from Yanggu-gun, but this was there were various techniques for refining and combining materials in Bunwon-ri.

• Explosives and Blasting
• /
• v.22 no.3
• /
• pp.79-84
• /
• 2004

It is well accepted that modem emulsion explosives are intrinsically much less sensitive than traditional products such as dynamites or black powder. However, they have still been involved in a significant number of accidental explosions. In October 1975, Canadian Research, Limited's, Energetic Research Laboratory in Quebec exploded. Although explanations for the incident varied, one logical explanation was that the pump used in transporting the emulsion dead headed, thereby turning mechanical work in to frictional heating under a zero flow rate. There is a minimum pressure required for combustion(MBP) to propagate in emulsion explosives. A stable deflagration may lead to a deflagration-to-detonation transition(DDT) in emulsion explosives. Tests were also performed on sensitized sampled consisting of 6 to 21% waters as well as 1 to 11% aluminium powder. It was founded the emulsion explosives consisting of 6% waters had the lowest minimum homing pressure(MBP) of 3 bar, and the 21% waters were unable to achieve sustained homing at pressures as high as 100 bar. The aluminium contained explosives tested here displayed a MBP higher than that of without emulsion. It appears that this test may offer a firm ground for the classification of emulsion explosives in view of the regulating the hazards associated with the various process used for their manufacturing and transport.

• Korean Journal of Materials Research
• /
• v.10 no.6
• /
• pp.437-444
• /
• 2000

We investigated the effect of substrate temperature, chemical composition and post-deposition heat-treatment on the crystal structure and electrical transport of $La_{1-x}Sr_xMnO_{3-{\delta}}$(0.19${\leq}x{\leq}$0.31) thin films. As-prepared $La_{1-x}Sr_xMnO_{3-{\delta}}$ films grown at $500^{\circ}C$ by sputter techniques were found to have the pseudo-tetragonal system(a/c=0.97) and a highly preferential <001> orientation. The films were changed to be of the cubic system by post-deposition annealing at around $900^{\circ}C$. A main target of $La_{0.67}Sr_{0.33}MnO_3$ as well as auxliary targets of $La_{0.3}Sr_{0.7}MnO_3$ ceramics were co-sputtered to control the chemical composition of the film. The Sr content(x) of the film ranged from 0.19 to 0.31, depending on the number of the auxiliary target. When x increased from 0.19 to 0.31, the electrical resistivity of the film decreased and the transition temperature between metal and semiconductor shifted to higher temperature. With a magnetic field of 0.18 T, the magneto-resistance ratio (MR(%) = (${\rho}_o-{\rho}_H/{\rho}_H$) of the $La_{0.69}Sr_{0.31}MnO_3$ thin film was about 390%.

• Applied Chemistry for Engineering
• /
• v.1 no.1
• /
• pp.83-90
• /
• 1990

The semiconducting $(Pb_1\;_xSn_x)_1$ $_yTe_y$, one of the low - temperature thermoelectric materials, has been prepared and its chemical composition and nonstoichiometry has been analyzed. The content of Pb in the specimens was determined by the complexometric back - titration method with EDTA and Pb(II) standard solutions. Te - content was analyzed with the redox titration method. The electrical conductivity and the thermoelectric power have also been measured by the DC 4 - probe and the heat-pulse technique, respectively. All of the specimens showed a nonstoichiometric behavior in their chemical compositions (Te excess), thus gave rise to a p - type semiconducting property, and the nonstoichoimetry became bigger as the Sn - content increased. The thermoelectric power vs. temperature results have been analyzed upon the basis of the Fermi level vs. temperature profiles in the saturation regime. The specimen of x=0.1 evolved a transition from p - to n - type property at about 670K, which has been explained by the fact that the mobility of electrons is bigger than that of holes in the temperature range of the intrinsic regime.

• Applied Chemistry for Engineering
• /
• v.24 no.6
• /
• pp.593-598
• /
• 2013

In this study, we have evaluated the water absorption phenomenon of photoresist dry film, which is commonly used to build circuits on PCB (Printed Circuit Board) by photolithography, by using ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared). We have firstly observed significant change in fracture mode of dry film with respect to temperature and humidity, which we assumed the material transition from ductile to brittle. Secondly, we have established the process of absorption test for determining the diffusion coefficients of water into the dry film both with gravimeter and ATR-FTIR. We have successfully calculated the diffusion coefficients for each environmental conditions from the results which we achieved by gravimeter and ATR-FTIR. Compared to the gravimeter which is a conventional method for absorption test, the ATR-FTIR method in this study has been found to be very easy to use and have the same accuracy as gravimeter. Moreover, we are expecting to use the ATR-FTIR as an appropriate method to study the absorption phenomena related to any kinds of solvent and polymer system.

• Applied Chemistry for Engineering
• /
• v.28 no.1
• /
• pp.42-49
• /
• 2017

To replace phthalate plasticizer for PVC, acetylated monoglyceride (AMG) plasticizers were prepared from plant oil and their plasticization effects were also investigated. Transesterification of coconut oil by glycerol followed by acetylation with acetic anhydride gave AMG-CoCo (Coco : Coconut Oil). In addition, AMG-GMO (GMO : Glycerol monooleate) and AMG-GMO-Epoxy were synthesized by acetylation and epoxidation with glycerol monooleate. It was found that the thermal stability of AMG plasticizers increased in the following order: AMG-GMO-Epoxy > AMG-GMO > AMG-CoCo and all three plasticizers were thermally more stable than those of common petroleum-based plasticizer DOP (Dioctyl phthalate). The tensile strain values of the PVC containing AMG compounds were ca. 770~810%, while tensile strength values were ca. 19~22 MPa, which were higher than those of PVC containing DOP. DMA (Dynamic Mechanical Analysis) results showed that the miscibility of AMG-GMO-Epoxy in PVC was excellent and the $T_g$ of PVC containing AMG-GMO-Epoxy at 50 phr decreased down to $24^{\circ}C$. Finally, the leaching experiment result showed that the weight loss values of PVC containing AMG-GMO and AMG-GMO-Epoxy at 50 phr were as low as 2 and 1%, respectively, indicating that they have high water migration resistance. The above findings suggested that AMG-GMO-Epoxy could be one of plant oil-based PVC plasticizers to replace DOP.

• Korean Journal of Food Science and Technology
• /
• v.26 no.2
• /
• pp.117-122
• /
• 1994

The characteristics of amylose-lipid complex(AL-complex) and cyclodextirn-lipid complex(CL-complex) were investigated by using Differential Scanning Calorimetry(DSC). The enzymatic hydrolysis of amylose which was liberated from AL-complex by the addtion of ${\beta}-cyclodextrin({\beta}-CD)$was also studied. The melting temperatures of AL-complex in corn, wheat, and rice starch were above $100^{\circ}C$ and there were no differences among them. In the presence of lysolecithin, the melting enthalpy and temperature of AL-complex were increased and lysolecithin was very effective in the formation of AL-complex. When ${\beta}-CD$ was added to AL-complex, the endothermic peak of AL-complex at $100^{\circ}C$ decreased and that of CL-complex at $70^{\circ}C$ appeared. These results indicated that the amylose was released from AL-complex by substituting ${\beta}-CD$ for amylose, then by forming CL-complex. As the added amount of ${\beta}-CD$ increased, the peak of AL-complex decreased whereas that of CL-complex increased. Enzymatic hydrolysis rate of AL-complex increased in the presence of ${\beta}-CD$, suggesting that amylose was dissociated from AL-complex and hydrolyzed by amylase.

• Journal of the Korean Magnetics Society
• /
• v.17 no.1
• /
• pp.43-46
• /
• 2007

The samples were synthesized by using a solid state reaction. The X-ray diffraction pattern for $Ti_{0.96}Co_{0.02}Fe_{0.02}O_2$ showed a pure rutile phase with tetragonal structures. Mixtures of the proper proportions of the elements sealed in evacuated quartz ampoule were heated at $870{\sim}930^{\circ}C$ for one day and then slowly cooled down to room temperature at a rate of $10^{\circ}C/h$. In order to obtain single phase material, it was necessary to grind the sample after the first firing and to press the powders into pellets before annealing them for a second time in evacuated and sealed quartz ampoule. Magnetic properties have been investigated using the vibrating sample magnetometer(VSM). Room temperature magnetic hysteresis(M-H) curve showed an obvious ferromagnetic behavior and the magnetic moment per Fe atom under the applied of 0.8T was estimated to be about $1.3{\mu}_B/CoFe$. But the magnetic moment per Fe atom under the applied of 0.8T was estimated to be about $0.02{\mu}_B/CoFe$ without Ti-getter.

• Journal of the Korean Chemical Society
• /
• v.17 no.5
• /
• pp.337-345
• /
• 1973

The nonstoichiometry of the iron oxide system has been studied by analyzing the weight loss of a sample, measured by using a quartz microbalance, in a temperature range from $0^{\circ}C$ to $1200^{\circ}C$ under oxygen pressures from $10^{2}mmHg$ to $10^{-4}mmHg$. The Y values of the formula, $FeO_{1+\gamma}$, that have been obtained by this means for various conditions of temperature and pressure in this range are considered to be more accurate than values obtained by methods requiring thste quenching of the sample before measurements are made. The plots of log Y vs $log PO_2$ (or $log Y =_n log PO_2$) show linearity and n calculated from the slope of the plot is about 1/10 at $1000^{\circ}C$, indicating a difference between the nonstoichiometric and oxidation mechanisms. The condition for the formation of stoichiometric FeO was determined to be $1200^{\circ}C$ under $10^{-3}mmHg$ of $O_2$ and the composition of the oxide under standard conditions was $FeO_{1.11185}$. As in general more oxygen dissolves into the oxide system at lower temperatures and higher oxygen pressures, the deviation from stoichiometric FeO is greater under those conditions. A comparison of the change in conductivity of the sample indicates that full phase transition does not take place with conductivity transition.