• Bulletin of the Korean Chemical Society
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• v.35 no.4
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• pp.1067-1072
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• 2014

In this study, we report a new approach for $Mn_3O_4$-graphene nanocomposite by ex situ method. This nanocomposite shows two-dimensional aggregation of nanoparticle, and doping effect by decorated manganese oxide ($Mn_3O_4$), as well. The graphene film was made through micromechanical cleavage of graphite on the $SiO_2/Si$ wafer. Manganese oxide ($Mn_3O_4$) nanoparticle with uniform cubic shape and size (about $5.47{\pm}0.61$ nm sized) was synthesized through the thermal decomposition of manganese(II) acetate, in the presence of oleic acid and oleylamine. The nanocomposite was obtained by self-assembly of nanoparticles on graphene film, using hydrophobic interaction. After heat treatment, the decorated nanoparticles have island structure, with one-layer thickness by two-dimensional aggregations of particles, to minimize the surface potential of each particle. The doping effect of $Mn_3O_4$ nanoparticle was investigated with Raman spectra. Given the upshift in positions of G and 2D in raman peaks, we suggest that $Mn_3O_4$ nanoparticles induce p-doping of graphene film.

• Journal of the Korean Ceramic Society
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• v.35 no.8
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• pp.783-790
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• 1998

The characterization of the complexation reaction of PVA and Al(III) ion at different pH and the sint-ering behaviour of UO2 containing the PVA-Al(III) complexes were investigated. Compared with pure PVA powder the complexed PVA-Al(III) powder had compacter shape and lower decomposition temperature The major phase of PVA-Al(III) complex decomposed at 90$0^{\circ}C$ was $\alpha$-Al2O3 The PVA-Al(III) complex formed at pH 9 had the lowest relative viscosity the highest Al content of 36% and the smallest particle size of 19${\mu}{\textrm}{m}$ While the pure UO2 pellet appeared with bimodal one. The grain size of the pure UO2 pellet was 7${\mu}{\textrm}{m}$ but that of the PVA-Al(III) complex added UO2 pellet was increased up to 36${\mu}{\textrm}{m}$ The largest grain size was ob-tained when the PVA-Al(III) complex formed at pH9 was added and the PVA-Al(III) complex formed at pH 11 had the greatest effect on increasing pore size.

• Proceedings of the KAIS Fall Conference
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• 2000.10a
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• pp.39-41
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• 2000

Newly modified spray Pyrolysis system was developed to Produce ultra Pure and fine Powder by spray Pyrolysis Process. In this system, raw material solution was effectively atomized and sprayed into the reaction furnace. Also, thermal decomposition process fully completed in the three zone reaction furnace, and produced powder was effectively collected. A technology to reduce impurities in complex acid solution below 20ppm was also developed. The characteristics of produced powder were studied by changing the reaction conditions such as reaction temperature, the injection velocity of the solution and air, nozzle tip size and concentration of solution. The morphology of powder had spherical shape under the most experimental conditions, and the composition and the particle size distribution were almost uniform. Under the most experimental conditions average particle size of most produced powder was below 100nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.91-92
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• 2006

The important merit of Bi-2212/Ag wire is to apply cable as round wire state. Bi-2212 high Tc superconducting wires were fabricated in order to apply Rutherford cable near the future. Various Ag ratio from 0.22 to 0.42 of Ag tubes for PID (powder-In-Tube) process were used to investigate the workability and to prevent breakage of filaments during drawing. In order to find proper heat treatment condition, we investigated micro-structure of Bi-2212/Ag wires by using differential thermal analysis, XRD and SEM. The effect of atmosphere on the peritectic decomposition temperature of precursor was investigated. The shape of grain was observed by SEM to investigate Bi-2212 phase formation in filaments. The higher of Ag ratio of mono filament had the higher critical current density, Jc. The wire with 0.42 of Ag ratio showed 7,886 A/cm2 of Jc at 77K.

• Elastomers and Composites
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• v.54 no.2
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• pp.142-148
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• 2019

In this study, the effects of filler particle size and shape on the physical properties of silicone rubber composites were investigated using inorganic fillers (Minusil 5, Celite 219, and Nyad 400) except silica, which was already present as a reinforcing filler of silicone rubber. Fillers with small particle sizes are known to facilitate the formation of the bound rubber by increasing the contact area with the polymer. However, in this experiment, the bound rubber content of Celite 219-added silicone composite was higher than that of Minusil 5-added silicone composite. This was attributed to the porous structure of Celite 219, which led to an increase in the internal surface area of the filler. When the inorganic fillers were added, both thermal decomposition temperature and thermal stability were improved. The bound rubber formed between the silicone rubber and inorganic filler affected the degree of crosslinking of the silicone composite. It is well-known that as the size of the reinforcing filler decreases, the reinforcing effect increases. However, in this experiment, the hardness of the composite material filled with Celite 219 was the highest compared to the other three composites. Furthermore, the highest value of 2.19 MPa was observed for 100% modulus, and the fracture elongation was the lowest at 469%. This was a result of excellent interaction between Celite 219 filler and silicone rubber.

• Journal of Powder Materials
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• v.28 no.4
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• pp.342-351
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• 2021

Because of its unique properties, tungsten is a strategic and rare metal used in various industrial applications. However, the world's annual production of tungsten is only 84000 t. Ammonium paratungstate (APT), which is used as the main intermediate in industrial tungsten production, is usually obtained from tungsten concentrates of wolframite and scheelite by hydrometallurgical treatment. Intermediates such as tungsten trioxide, tungsten blue oxide, tungstic acid, and ammonium metatungstate can be derived from APT by thermal decomposition or chemical attack. Tungsten metal powder is produced through the hydrogen reduction of high-purity tungsten oxides, and tungsten carbide powder is produced by the reaction of tungsten powder and carbon black powder at 1300-1700℃ in a hydrogen atmosphere. Tungsten scrap can be divided into hard and soft scrap based on shape (bulk or powder). It can also be divided into new scrap generated during the production of tungsten-bearing goods and old scrap collected at the end of life. Recycling technologies for tungsten can be divided into four main groups: direct, chemical, and semi-direct recycling, and melting metallurgy. In this review, the current status of tungsten smelting and recycling technologies is discussed.

• Advances in concrete construction
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• v.11 no.5
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• pp.397-407
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• 2021

This paper investigates the optimal sensor placements and capabilities of this procedure for dynamic characteristics identification of arch dams. For this purpose, a prototype arch dam is constructed in laboratory conditions. Berke arch dam located on the Ceyhan River in city of Osmaniye is one of the highest arch dam constructed in Turkey is selected for field verification. The ambient vibration tests are conducted using initial candidate sensor locations at the beginning of the study. Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods are used to extract experimental dynamic characteristics. Then, measurements are repeated according to optimal sensor locations of the dams. These locations are specified using the Effective Independence Method. To determine the optimal sensor locations, the target mode shape matrices which are obtained from ambient vibration tests of the selected dam with a large number of accelerometers are used. The dynamic characteristics obtained from each ambient vibrations tests are compared with each other. It is concluded that the dynamic characteristics obtained from initial measurements and those obtained from a limited number of sensors are compatible with each other. This situation indicates that optimal sensor placements determined by the Effective Independence Method are useful for dynamic characteristics identification of arch dams.

• Economic and Environmental Geology
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• v.49 no.2
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• pp.77-88
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• 2016

Chrysotile is a 1:1 sheet silicate mineral belonging to serpentine group. It has been highlighted studies because of uses, shapes and structural characteristics of the fibrous chrysotile. However, it was designated as Class 1 carcinogen, so high attentions were being placed on detoxification studies of chrysotile. The objectives of this study were to investigate changes of mineralogical characteristics of chrysotile and to suggest detoxification mechanism of chrysotile by thermal decomposition. Samples for this study were obtained from LAB Chrysotile mine in Canada. The samples were heated in air in the range of 600 to $1,300^{\circ}C$. Changes of mineralogical characteristics such as crystal structure, shape, and chemical composition of the chrysotile fibers were examined by TG-DTA, XRD, FT-IR, TEM-EDS and SEM-EDS analyses. As a result of thermal decomposition, the fibrous chrysotile having hollow tube structure was dehydroxylated at $600-650^{\circ}C$ and transformed to disordered chrysotile by removal of OH at the octahedral sheet (MgOH) (Dehydroxylation 1). Upon increasing temperature, it was transformed to forsterite ($Mg_2SiO_4$) at $820^{\circ}C$ by rearrangement of Mg, Si and O (Dehydroxylation 2). In addition, crystal structure of forsterite had begun to transform at $800^{\circ}C$, and gradually grown 3-dimensionally to enstatite ($MgSiO_3$) by recrystallization after the heating above $1,100^{\circ}C$. And then finally transformed to spherical minerals. This study showed chrysotile structure was collapsed about $600-700^{\circ}C$ by dehydroxylation. And then the fibrous chrysotile was transformed to forsterite and enstatite, as non-hazardous minerals. Therefore, this study indicates heat treatment can be used to detoxification of chrysotile.

• Journal of the Korea Organic Resources Recycling Association
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• v.25 no.1
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• pp.23-33
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• 2017

In this study, water and organic treatment efficiency and operating characteristics (temperature, salinity effect) were evaluated when food waste with high water content was treated by Bio-dying method. In addition, the optimum conditions for producing pellets for evaluating the decomposition products as SRF(Solid Refuse Fuel) after Bio-drying and evaluating the use value of SRF as a solid fuel were analyzed. As a result, the temperature, $CO_2$ concentration, organic matter removal rate and weight reduction rate according to the daily dose were about 86% and 68% at the input of 2.4 kg/day. The optimal food waste input was estimated to be 2.4 kg/day. As a result of the pellet molding and produce, Pellets can be produced within 10~25% of raw material water content. It was judged that the water content of 25%, which showed the best quality results in terms of external shape maintenance and strength. The high calorific value of SRF of decomposition products after Bio-drying was more than 3,500 kcal/kg.

• Applied Chemistry for Engineering
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• v.19 no.5
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• pp.568-573
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• 2008

Kinetic tests on pyrolysis of waste fishing net [WFN; nylon-6], waste ship lubricating oil [WSLO] and their mixture were carried out by thermogravimetric analysis (TGA) with heating rate of 0.5, 1.0, and $2.0^{\circ}C/min$. Pyrolysis of waste fishing net started at $300^{\circ}C$, and the main region of decomposition temperature was between 360 and $440^{\circ}C$ at each heating rate. Decomposition temperature of the mixture of WFN and WSLO was lower than that of WFN and WSLO, and the shape of thermogravimetic graph of mixture was different as well. The corresponding kinetic parameters including activation energy and pre-exponential factor were determined by differential method over the degree of conversions. The values of activation energies for the mixture of WFN and WSLO were between 98 and 427 kJ/mol as the conversion increased from 5% to 95%. Tubing reactor was used to analysis of pyrolyzed oil at $440^{\circ}C$ for 80 min. The selectivity of specific hydrocarbons was not detected and the carbon number distribution of the pyrolyzed oil was below $C_{22}$.