• Nuclear Engineering and Technology
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• v.31 no.5
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• pp.455-464
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• 1999

The effect of TiO$_2$ on the sintering behavior of mixed UO$_2$-U$_3$O$_{8}$ Powder compacts has been investigated using the U$_{3}$O$_{8}$ powder made tv oxidation of defective UO$_{2}$ pellets. Without TiO$_2$, UO$_2$ pellet density is inversely proportional to U$_3$O$_{8}$ content and is below 94 %TD in the U$_3$O$_{8}$ range above 15 wt%. Using more than 0.1 wt % TiO$_2$, however, the density decreases slightly with U$_3$O$_{8}$ content and thus is higher than about 94% TD in the whole range of U$_3$O$_{8}$ content. The grain sizes of UO$_2$ pellets with more than 0.1 wt % TiO$_2$are larger than about 30${\mu}{\textrm}{m}$. Therefore, the U$_3$O$_{8}$ Powder can be reused without any restriction on its amount in UO$_2$ pellet fabrication by sintering the mixed UO$_2$-U$_3$O$_{8}$ compact with the aid of TiO$_2$. Mechanisms for densification and grain growth are proposed and discussed, based on a dilatometry study and an examination of microstructure. microstructure.

• Journal of Powder Materials
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• v.7 no.4
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• pp.237-243
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• 2000

The property and performance of the $Al_2O_3/Ni$ nanocomposites have been known to strongly depend on the structural feature of Ni nanodispersoids which affects considerably the structure of matrix. Such nanodispersoids undergo structural evolution in the process of consolidation. Thus, it is very important to understand the microstructural development of Ni nanodispersoids depending on the structure change of the matrix by consolidation. The present investigation has focused on the growth mechanism of Ni nanodispersoids in the initial stage of sintering. $Al_2O_3/Ni$ powder mixtures were prepared by wet ball milling and hydrogen reduction of $Al_2O_3$ and Ni oxide powders. Microstructural development and the growth mechanism of Ni dispersion during isothermal sintering were investigated depending on the porosity and structure of powder compacts. The growth mechanism of Ni was discussed based upon the reported kinetic mechanisms. It is found that the growth mechanism is closely related to the structural change of the compacts that affect material transport for coarsening. The result revealed that with decreasing porosity by consolidation the growth mechanism of Ni nanoparticles is changed from the migration-coalescence process to the interparticle transport mechanism.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1133-1137
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• 1998

By the mechanical alloying method Ni-W(WC) composite materials were prepared to improve the resistance for creep and sintering of Ni-anode at the operating temperature of$ 650^{\circ}C$. Amorphization was observed from the XRD analysis of mechanically alloyed powder caused by the destruction of ordered crystals. Sintering was performed at $1280^{\circ}C$ for 10 hours in $H_2$ atmosphere. From the result of dot-mapping and TEM analysis the second phase was not observed at Ni-W interface while W particles of less 0.lam were distributed finely and uniformly in Ni matrix. This finely and uniformly distributed W in Ni matrix is expected to enhance the mechanical properties of Ni-anode through the dispersion and solid solution hardening mechanisms.

• Journal of Powder Materials
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• v.15 no.6
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• pp.450-457
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• 2008

The objectives of this study were the development of a synthesis technique for highly active nanosized ITO powder and the understanding of the reaction mechanisms of the ITO precursors. The precipitation and agglomeration phenomena in ITO and $In_{2}O_{3}$ precursors are very sensitive to reaction temperature, pH, and coexisting ion species. Excessive $Cl^-$ ion and $Sn^{+4}$ ions had a negative effect an synthesizing highly active powders. However, with a relevant stabilizing treatment the shape and size of ITO and $In_{2}O_{3}$ precursors could be controlled and high density sintered products of ITO were obtained. By applying the reprecipitation process (or stabilization technique), highly active ITO and $In_{2}O_{3}$ powders were synthesized. Sintering these powders at $1500^{\circ}C$ for 5 hours produced 97% dense ITO bodies.

• Advances in nano research
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• v.13 no.4
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• pp.313-323
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• 2022

The microstructure and mechanical properties of Cr-Ni steel and Cr-Ni steel-matrix nanocomposites reinforced with nano-ZrO₂ particles were investigated in this study. Cr-Ni steel and Cr-Ni/ZrO₂ nanocomposites were produced using a combination of high-energy ball milling, pressing, and sintering processes. The microstructures of the specimens were analyzed using EDX and XRD. Compression and hardness tests were performed to determine the mechanical properties of the specimens. Nano-ZrO₂ particles were effective in preventing chrome carbide precipitate at the grain boundaries. While t-ZrO₂ was detected in Cr-Ni/ZrO₂ nanocomposites, m-ZrO₂ could not be found. Few α'-martensite and deformation bands were formed in the microstructures of Cr-Ni/ZrO₂ nanocomposites. Although nano-ZrO₂ particles had a negligible impact on the strength improvement provided by deformation-induced plasticity mechanisms in Cr-Ni/ZrO₂ nanocomposites, the mechanical properties of Cr-Ni steel were significantly improved by using nano-ZrO₂ particles. The hardness and compressive strength of Cr-Ni/ZrO₂ nanocomposite were higher than those of Cr-Ni steel and enhanced as the weight fraction of nano-ZrO₂ particles increased. Cr-Ni/ZrO₂ nanocomposite with 5wt.% nano-ZrO₂ particles had almost twofold the hardness and compressive strength of Cr-Ni steel. The nano-ZrO₂ particles were considerably more effective on particle-strengthening mechanisms than deformation-induced strengthening mechanisms in Cr-Ni/ZrO₂ nanocomposites.

• Journal of Powder Materials
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• v.31 no.1
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• pp.30-36
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• 2024

The aerospace and power generation industries have an increasing demand for high-temperature, high-strength materials. However, conventional materials typically lack sufficient fracture toughness and oxidation resistance at high temperatures. This study aims to enhance the high-temperature properties of Nb-Si-Ti alloys through ball milling. To analyze the effects of milling time, the progression of alloying is evaluated on the basis of XRD patterns and the microstructure of alloy powders. Spark plasma sintering (SPS) is employed to produce compacts, with thermodynamic modeling assisting in predicting phase fractions and sintering temperature ranges. The changes in the microstructure and variation in the mechanical properties due to the adjustment of the sintering temperature provide insights into the influence of Nb solid solution, Nb5Si3, and crystallite size within the compacts. By investigating the changes in the mechanical properties through strengthening mechanisms, such as precipitation strengthening, solid solution strengthening, and crystallite refinement, this study aims to verify the applicability of Nb-Si-Ti alloys in advanced material systems.

• Carbon letters
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• v.14 no.2
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• pp.99-104
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• 2013

We investigated the effects of parametric synthesis conditions of catalysts such as sintering temperature, sorts of supports and compositions of catalysts on alignment and length-control of carbon nanotubes (CNTs) using catalyst powders. To obtain aligned CNTs, several parameters were changed such as amount of citric acid, calcination temperature of catalysts, and the sorts of supports using the combustion method as well as to prepare catalyst. CNTs with different lengths were synthesized as portions of molybdenum and iron using a chemical vapor deposition reactor. In this work, the mechanisms of alignment of CNTs and of the length-control of CNTs are discussed.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.79-82
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• 2012

The gas-solid reactor, such as rotary kiln, sintering bed, incinerator and CFB boiler, is the one of most widely used industrial reactors for contacting gases and solids. the gas-solid reactor are mainly used for drying, calcining and reducing solid materials. In the gas-solid reactor, heat is supplied to the outside of the wall or inside of the reactor. The heat transfer in gas-solid reactor encompasses all the modes of transport mechanisms, that is, conduction, convection and radiation. The chemical reactions occurring in the bed are driven by energy supplied by the heat transfer. This paper deal with the effect of heat transfer and chemical reaction in the gas-solid reactor.

• Journal of the Korean Ceramic Society
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• v.28 no.7
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• pp.549-555
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• 1991

Mullite-zirconia (0∼4 mol% yttria) composites were obtained by In-situ sintering of zircon and alumina mixture, and their mechanical properties were studied in conjuction with microstructure observation. Martensitic transformation temperature (Ms) of zirconia dispersed in the mullite matrix decreased with Y2O3 contents and was about 600$^{\circ}C$ for ZrO2 containing 4 mol% Y2O3. On cooling of this composites, tetragonal to monoclinic phase transformation induced microcracks at the grain boundary of mullite matrix. The microcracks seemed to absorb the fracture energy in stress field during mechanical tests. Therefore, toughening mechanisms of this composite were considered to nucleation and extension of microcrack, and crack deflection mechanism due to the difference of thermal expansion coefficient between matrix and dispersed phase.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.891-892
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• 2006

To test the correlation between grain shape and growth behavior we prepared WC-TiC-Co samples with rounded (Ti, W)C grains and faceted WC grains. The growth of rounded (Ti, W)C grains was normal. In contrast, the growth of faceted WC grains was abnormal or suppressed depending on the initial size of WC particles. These observations were explained using growth theories of crystals in a liquid and were also confirmed by a simulation using their growth equations. The present results thus demonstrate that the growth behavior of carbide grains in a liquid is governed only by their shape, irrespective of the presence of another phase.