• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1994.04c
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• pp.7-7
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• 1994

For more than a decade components of low alloy iron powder with nickel and/or molybdenum for general engineering applications have been manufactured from powder metal. In the time to come such PM steel components will gain increasing significance. Because of various manufacturing difficulties they are mostly produced in two separate steps - sintering and hardening - which means high energy and labour requirements. The paper describes how such PM components are produced in just one run through a conveyor belt furnace with automatic atmosphere control and gas quenching zone. Energy and labour costs are low and reproducible quality is exceilent. The mechanical properties obtained with some powder alloys are presented as well.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.68-69
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• 2006

When an alloy such as Ni-W is liquid phase sintered, heavy solid W particles sedimentate to the bottom of the container, provided that their volume fraction is less than a critical value. The sintering process evolves typically in two stages, diffusiondriven macrosegregation sedimentation followed by true sedimentation. During macrosegregation sedimentation, the overall solid volume fraction decreases concurrently with elimination of liquid concentration gradient. However, in the second stage of true sedimentation, the average solid volume fraction in the mushy zone increases with time. It is proposed that the true sedimentation results from particle rearrangement for higher packing efficiency.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.292-295
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• 2001

The NdBaCuO superconducting samples were prepared by the Zone melting under low oxygen partial pressure. After the zone-melting the oxygenation process of the NdBaCuO samples in a oxygen flow furnace was studied. In order to compare the oxygenation condition the sintering NdBaCuO samples were studied also. In the study it is found that the optimum temperature for the oxygenation is $350^{\circ}C$, and the oxygen flow speed, the sample volume and the surface area of the sample would influence the oxygenation and the oxygen content.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.292-295
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• 2001

The NdBaCuO superconducting samples were prepared by the Zone melting under low oxygen partial pressure. After the zone-melting the oxygenation process of the NdBaCuO samples in a oxygen flow furnace was studied. In order to compare the oxygenation condition the sintering NdBaCuO samples were studied also. In the study it is found that the optimum temperature for the oxygenation is $350{\circ}C$, and the oxygen flow speed, the sample volume and the surface area of the sample would if1uence the oxygenation and the oxygen content.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.528-535
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• 1997

$LiTaO_3$ single crystals of congruently melting composition were grown by the halogen lamp type floating zone system. Calcination and sintering parameters for the growth were established. Optimum crystal growth conditions were investigated by a controlling of growth rates, rotation speeds and atmospheres. Based on the melting aspect and the shape of molten zone, stable conditions could not be found in air or Na atmosphere. However the growth stability in Ar atmosphere was more regular than that in air or $N_2$. The grown crystals were characterized using Laue back reflection, Curie temperature, refractive index and transmittance. Curie temperature fluctuation in the section of the grown crystal part of top, body and tail was $1^{\circ}C$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 1999.04a
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• pp.5-5
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• 1999

The Principal deficiency of the existing notion about the sintering-mixtures consists in the fact that almost no attention is focused on the Phenomenon of alloy formation during sintering, its connection with dimensional changes of powder bodies, and no correct ideas on the driving force for the sintering process in the stage of establishing chemical equilibrium in a system are available as well. Another disadvantage of the classical sintering theory is an erroneous conception on the dissolution mechanism of solid in liquid. The two-particle model widely used in the literature to describe the sintering phenomenon in solid state disregards the nature of the neighbouring surrounding particles, the presence of pores between them, and the rise of so called arch effect. In this presentation, new basic scientific principles of the driving forces for the sintering process of a two-component powder body, of a diffusion mechanism of the interaction between solid and liquid phases, of stresses and deformation arising in the diffusion zone have been developed. The major driving force for sintering the mixture from components capable of forming solid solutions and intermetallic compounds is attributed to the alloy formation rather than the reduction of the free surface area until the chemical equilibrium is achieved in a system. The lecture considers a multiparticle model of the mixed powder-body and the nature of its volume changes during solid-state and liquid-phase sintering. It explains the discovered S-and V-type concentration dependencies of the change in the compact volume during solid-state sintering. It is supposed in the literature that the dissolution of solid in liquid is realised due to the removal of atoms from the surface of the solid phase into the melt and then their diffusicn transfer from the solid-liquid interface into the bulk of liquid. It has been shown in our experimental studies that the mechanism of the interaction between two components, one of them being liquid, consist in diffusion of the solvent atoms from the liquid into the solid phase until the concentration of solid solutions or an intermetallic compound in the surface layer enables them to pass into the liquid by means of melting. The lecture discusses peculimities of liquid phase formation in systems with intermediate compounds and the role of the liquid phase in bringing about the exothermic effect. At the frist stage of liquid phase sintering the diffusion of atoms from the melt into the solid causes the powder body to grow. At the second stage the diminution of particles in size as a result of their dissolution in the liquid draws their centres closer to each other and makes the compact to shrink Analytical equations were derived to describe quantitatively the porosity and volume changes of compacts as a result of alloy formation during liquid phase sinteIing. Selection criteria for an additive, its concentration and the temperature regime of sintering to control the density the structure of sintered alloys are given.

• Journal of the Korean Ceramic Society
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• v.44 no.7
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• pp.343-348
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• 2007

Alumina/silver nanocomposites were fabricated using a soaking method through a sol-gel route to construct an intra-type nanostructure. The pulse electric-current sintering (PECS) technique was used to sinter the nanocomposites. Several specimens were annealed after sintering. The microstructure, mechanical properties, critical frontal process zone (FPZ) size, and thermo-mechanical properties of the nanocomposites were estimated. The relative densities of the specimens sintered at 1350 and $1450^{\circ}C$ were 95% and 99%, respectively. The maximum value of the three-point bending strength was found to be 780 MPa for the $2{\times}2{\times}10 mm$ specimen sintered at $1350^{\circ}C$. The fracture toughness of the specimen sintered at $1350^{\circ}C$ was measured to be $3.60 MPa{\cdot}m^{1/2}$ using the single-edge V-notched beam (SEVNB) technique. The fracture mode of the nanocomposites was transgranular, in contrast to the intergranular mode of monolithic alumina. The fracture morphology suggested that dislocations were generated around the silver nanoparticles dispersed within the alumina matrix. The specimens sintered at $1350^{\circ}C$ were annealed at $800^{\circ}C$ for 5 min, following which the maximum fracture strength became 810 MPa and the fracture toughness improved to $4.21 MPam^{1/2}$. The critical FPZ size was the largest for the specimen annealed at $800^{\circ}C$ for 5 min. Thermal conductivity of the alumina/silver nanocomposites sintered at $1350^{\circ}C$ was 38 W/mK at room temperature, which was higher than the value obtained with the law of mixture.

• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.171-182
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• 1995

Five eucryptite and ten spodumene compositional powders were syntehsized from three sillimanite group, two kaolin group, and five pyrophyllite group silicate minerals. Those powders were isotatically pressed and fired at 1200~135$0^{\circ}C$ for 2 hrs, and then the sintered bodies were characterized. Silicate minerals with molar ratio of Al2O3 to SiO2 correspond to those of eucryptite and spodumene are kaolin and pyrophyllite group silicate minerals, respectively. Sintering characteristics of eucryptite from kaolin group and spodumene from pyrophyllite group mineral were superior to those from other silicate minerals. Eucryptite sintered bodies with 95~97% relative densities and densified microstructures can be obtained using Hadong pink kaolin as starting materials by sintering over broad temperature zone(1250~135$0^{\circ}C$). The eucryptite sintered bodies which were fired at 130$0^{\circ}C$ for 2hrs, from Hadong pink kaolin had within 3.0wt% microstructural compositional variations compaired with stoichiometric compound, and had good negative thermal expansiion property with -3.55$\times$10-6/$^{\circ}C$ thermal expansion coefficient. Spodumene sintered bodies which were prepared from pyrophyllite group silicate minerals, had dense microstructures and high densities by densification through liquid phase sintering with enlarged temperature range. The specimens which were fired at 130$0^{\circ}C$ for 2 hrs from Gusipyrophillite, had dense microstructure with crystallines mainly, and low thermal expansion property with 0.62$\times$10-6/$^{\circ}C$ thermal expansion coefficient. The porous texture and residual glass phase in LAS system ceramics which were prepared from silicate minerals, tend to increase the thermal expansion properties of sintered bodies to positive direction.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.4
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• pp.521-527
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• 1997

Ruby single crystals of 6-7 mm in dialneter and 20-25 mm in length were grown by the xenon-arc type floating zone method using a self-designed FZHY1, Calcination and sintering conditions were investigated and optimum growth conditions were established for controlling the factors such as growth rates, rotation speeds and cooling rates. Also the available energy levels of $Cr^{3+}$ were calculated from transmission data. The growth direction of the crystals was [1010] direction identified by Laue back reflection pattern. The distribution of refractive indices on the wafer of the grown crystals was homogeneous except for the edges of the wafer. The crystals could be used as a laser material with a wavelength of 693 nm and a metastate level.

• Computers and Concrete
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• v.8 no.6
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• pp.617-629
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• 2011

In this investigation, reservoir sediment and municipal sewage sludge were sintered to form the artificial lightweight aggregates. The sintered aggregates were compared with the commercialized lightweight aggregates to in terms of potential alkali-silica reactivity and chemical stability based on analyses of their physical and chemical properties, leaching of heavy metal, alkali-silica reactivity, crystal phase species and microstructure. Experimental results demonstrated that the degree of sintering of an aggregate affected the chemical resistance more strongly than did its chemical composition. According to ASTM C289-94, all potential alkali-silica reactivity of artificial lightweight aggregates were in the harmless zone, while the potential reactivity of artificial lightweight aggregates made from reservoir sediment and municipal sewage sludge were much lower than those of traditional lightweight aggregates.