• The Korean Journal of Ceramics
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• v.4 no.4
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• pp.279-285
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• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• Transactions of the Korean hydrogen and new energy society
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• v.20 no.5
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• pp.432-438
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• 2009

In this paper, we synthesized LSG powder by Modified-GNP method. Lanthanum, strontium and gallium (LSG) were selected in the preparation of an oxygen-electrode (anode) for High Temperature Steam Electrolysis system (HTSE). The used amount and concentration of nitric acid were varied to find out an appropriate composition for oxygen-electrode (anode). In order to optimize the molar ratio of La and Sr, ratio of La to Sr was varied that 2:8, 5:5 and 8:2. The combined LSGs were calcined for 2 hours at $700^{\circ}C$ and were sintered in a furnace for 4 hours at $1200^{\circ}C$. The phase and crystallinity of LSG powder were determined by XRD. The surface morphology was observed through SEM photograph, and the specific surface area was investigated with BET. The thermochemical property was determined by TG/DTA. The synthesized preparation was obtained of $La_{0.8}Sr_{0.2}GaO_{3}$ formula for 3M nitric acid, which was the best perovskite phase.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.15 no.2
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• pp.68-74
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• 2005

The electrical arc furnace (EAF) classified as a special waste contains many flux components producing melts during a sintering process, so it decreases the sintering temperature and improves the mechanical properties of specimens. Increasing dust content in a clay-dust system brick, however, may cause the fraction defective higher due to the excessive liquid produced. To control the liquid behavior produced during sintering process for the clay-dust system specimens, the $Al_2O_3$ was added and the physical properties were analyzed. The microstructure for the clay-dust system body sintered with $Al_2O_3$ became homogeneous and the overall size of pores decreased. Adding $Al_2O_3$ to clay-dust system body increased the mechanical properties and the temperature of maximum strength increased as much as $50^{\circ}C$, and the apparent density increased and the absorption decreased. The mullite ($3Al_2O_3{\cdot}2SiO_2$) was produced during sintering process by reaction of $Al_2O_3$ and $SiO_2$ which could participate to liquid-producing-process and the viscosity of melts increased which was proved by measuring a critical viscosity temperature (Tcv) therefore, the refractoriness of specimens were improved to lower the fraction defective.