• 한국재료학회지
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• 제13권9호
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• pp.581-586
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• 2003

3%C-18%Cr-1%Mo-2%Ni-1%Mn high chromium cast iron was casted and destabilized at temperatures of 900, 1000 and $1100^{\circ}C$ for 1, 2, 4 and 8hr under $N_2$atmosphere to observe the effect of destabilization temperature and time on the carbide and matrix structures. In as-cast condition, the microstructure consisted of $M_{ 7}$$C_3$ carbides and matrix structures which were composed of 91.50% austenite and 8.50% martensite. Numerous fine secondary carbides were observed in the specimens destabilized at $900^{\circ}C$ for 1, 2, 4 and 8hr. But, the number of secondary carbides were much reduced with the increased destabilization temperature. More austenite was formed in the matrix with the higher destabilization temperature. The amounts of austenite in the matrix were 4.23% at $900^{\circ}C$, 29.68% at $1000^{\circ}C$ and 66.51% at$ 1100^{\circ}C$, respectively. However, the effect of destabilization time on the secondary carbide and matrix was very weak compared with that of destabilization temperature. The ranges of the amount of austenite in the matrix from 1hr to 8hr destabilization heat treatment were: 3.95%-4.35% at $900^{\circ}C$, 28.89%-30.15% at $1000^{\circ}C$ and 65.13%-67.12% at $1100^{\circ}C$, respectively. The variation ranges were very narrow. The equilibrium concentration of C and Cr in austenite was already reached within 1hr during destabilization heat treatment. After an attainment of the equilibrium concentration of C and Cr in austenite, no more secondary carbide was precipitated from the matrix.

• 한국주조공학회지
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• 제13권5호
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• pp.432-440
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• 1993

Ductile cast iron has a good ductility and toughness than those of gray cast iron, because the shape of graphite is spheroidal. Also, it has been reported that, additional strengthening and toughening of the ductile cast iron can be obtainded from the proper combination of matrix structures by the heat treatment and addition of alloying elements. In this study the effect of special heat treatment and addition of alloying elements(Ni, Mo) on the multi-phase(ferrite-bainite-martensite) structures, strength and toughness of ductile cast iron were studied systematically. In water quenching from $770^{\circ}C$, the martensite volume(%) increased, but the ferrite volume(%) decreased with increment of Ni content. In as cast, pearlite volume(%) and hardness increased with increment of Mo and Ni contents. And with the increment of the destabilization austempering holding time, the bainite volume(%) increased but the martensite volume(%) decreased. As destabilization austempering holding time is same, bainite volume(%) decreased, martensite increased with the increment of Ni and Mo contents. The hardness and tensile strength decreased, but impact energy increased with the decrease of Ni and Mo contents, and increment of holding time of destabilization austempering treatment.

• 한국재료학회지
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• 제6권4호
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• pp.372-378
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• 1996

고크롬주철에 있어서 기지 및 탄화물의 조직제어는 내마모성의 향상을 위해 필수적이다. 특히 기지조직내의 잔류오스테나이트함량은 최적 내마모성을 얻기위해 반드시 조절되어야 한다. 본 연구에서는 3% C-18%(or 25%)Cr-Mo-Ni-Mn 고크롬주철을 80$0^{\circ}C$, 90$0^{\circ}C$, 100$0^{\circ}C$ 및 110$0^{\circ}C$의 질소분위기 하에서 각각 20분 불안정화열처리를 행한 후 공냉시켰다. 잔류오스테나이트의 함량은 Xtjs 회절시험을 통해 측정하였으며 회절 peak는 $\alpha$200, $\alpha$220, ${\gamma}$220그리고 ${\gamma}$311을 이용하였다. 화학조성, 불안정화열처리의 온도 및 시간, 그리고 잔류오스테니이트함량강의 관계식을 도출하였다.

• Membrane and Water Treatment
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• 제9권3호
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• pp.147-153
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• 2018

This study investigates the role of microbial extracellular polymeric substances (EPSs) as bioflocculants to harvest microalgae (water-microalgae separation). The EPS extracted from waste activated sludge (WAS) by heat extraction were fractionated into soluble EPS (S-EPS), loosely-bound EPS (LB-EPS) and tightly-bound EPS (TB-EPS) forms. All the EPSs facilitated the flocculation of microalgal cells from stable growth medium. Of those EPSs, the TB-EPS showed the highest flocculating activity (FA) resulting in the substantial decrease in the amount of EPS added in terms of total organic carbon (TOC) during flocculation. The FA of microalgae was improved with the increase in TB-EPS dose, however, excessive dose of TB-EPS adversely affected it due to destabilization. Both LB- and TB-EPS could be utilized for flocculating microalgae as a sustainable option to the existing chemical-based flocculants. In addition to the conventional assessments, the effectiveness of the two bioflocculants for floc forming was also confirmed using a novel assessment of lens-free shadow imaging technique (LSIT), which was firstly applied for the rapid and quantitative assessment of microalgal flocculation.

• 대한치과기공학회지
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• 제29권1호
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• pp.121-131
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• 2007

A preparation process's conditions of aqueous sol which contains anatase-type nano titania particles with photocatalyic properties was established by using Yoldas process, so called, DCS(Destabilization of Colloidal Solution) process in this study. And crystal size change and phase transformation of titania particles in aqueous titania sol depending on reaction conditions was investigated by a light scattering method and XRD analysis of frozen dried powders, respectively. This sol with photo catalytic nano titania particles was used to the following hydrophilic hybrid coating film's fabrication and its properties was evaluated. Subsequently, for coating film using the above mentioned aqueous titania sol, non-aqueous titania sol was prepared without any chemical additives and its time stability according to aging time was investigate. By using the above mentioned aqueous titania sol and non-aqueous sol, a complex oxide coating sol for metal and ceramic substrate and a organic-inorganic hybrid coating sol for polymer substrate was prepared and it's hydrophilicity depending on UV irradiation conditions was evaluated. As a conclusions, the following results were obtained. (1)Aqueous titania sol The average particle size of titania in formed aqueous titania sol was distributed between 20$\sim$90nm range depending on reaction conditions. And the crystal phase of titania powders obtained by frozen drying method was changed from amorphous state to anatase and subsequently transformed to rutile crystal phase and it is attributed to concentration gradient in aqueous sol. (2)Non-aqueous titania sol Non-aqueous titania sol was prepared using methanol as a solvent and a little distilled water for hydrolysis and nitric acid as a catalyst were used. The obtained non-aqueous titania sol was stable at room temperature for 20 days. Additionally, non-aqueous titania sol with addition of chealating reagent such as acethylaceton and ethylene glycol prolonged the stability of sol by six months. (3)Complex sol and hybrid sol with super hydrophilicity The above mentioned aqueous titania sol as a main photocataylic component and non-aqueous titania sol as a binder for coating process was used to prepare a complex sol used for metal, ceramic and wood material substrate and also to prepare the organic-inorganic hybrid sol for polymer substrate such as polycarbonate and polyethylene, in which process APMS(3-Aminopropyltrimethoxysilane), GPTS(3-Glycidoxypropyl-trimethoxysilane) as a hydrophilic silane compound and HEMA(2-Hydroxyethyl methacrylate) as a forming network in hybrid coating film were used. The hybrid coating film such as prepared through this process showed a superhydrophilicity below 1$10^{\circ}$ depending on processing conditions and a pencil's hardness over 6 H.