• Advances in concrete construction
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• v.6 no.1
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• pp.69-85
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• 2018

In order to provide sufficient stability and resistance against bleeding and segregation during transportation and placing, mineral admixtures are often used in self-compacting concrete mixes (SCC). These fine materials also contribute to reducing the construction cost and the consumption of natural resources. Many studies have confirmed the benefits of these mineral admixtures on properties of SCC in standard curing conditions. However, there are few published reports regarding their effects at elevated curing temperatures. The main objective of this study is to investigate the effect of three different mineral admixtures namely limestone powder (LP), granulated blast furnace slag (GS) and natural pozzolana (PZ) on mechanical properties and porosity of SCC when exposed to different curing temperatures (20, 40, 60 and $80^{\circ}C$). The level of substitution of cement by mineral admixture was fixed at 15%. The results showed that increasing curing temperature causes an improvement in performance at an early age without penalizing its long-term properties. However the temperature of $40^{\circ}C$ is considered the optimal curing temperature to make economical and high performance SCC. On the other hand, GS is the most suitable mineral admixture for SCC under elevated curing temperature.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.577-582
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• 2015

The present study is concerned with the influence of niobium(Nb) addition and austenitizing temperature on the hardenability of low-carbon boron steels. The steel specimens were austenitized at different temperatures and cooled with different cooling rates using dilatometry; their microstructures and hardness were analyzed to estimate the hardenability. The addition of Nb hardly affected the transformation start and finish temperatures at lower austenitizing temperatures, whereas it significantly decreased the transformation finish temperature at higher austenitizing temperatures. This could be explained by the non-equilibrium segregation mechanism of boron atoms. When the Nb-added boron steel specimens were austenitized at higher temperatures, it is possible that Nb and carbon atoms present in the austenite phase retarded the diffusion of carbon towards the austenite grain boundaries during cooling due to the formation of NbC precipitate and Nb-C clusters, thus preventing the precipitation of $M_{23}(C,B)_6$ along the austenite grain boundaries and thereby improving the hardenability of the boron steels. As a result, because it considerably decreases the transformation finish temperature and prohibits the nucleation of proeutectoid ferrite even at the slow cooling rate of $3^{\circ}C/s$, irrespective of the austenitizing temperature, the addition of 0.05 wt.% Nb had nearly the same hardenability-enhancing effect as did the addition of 0.2 wt.% Mo.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.4
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• pp.306-317
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• 1995

Abstract Gallium arsenide crystal is usually grown from the melt by the horizontal Bridgman method. We constructed pseudo - steady - state model for crystal growth of GaAs which inclue melt, crystal and the free interface. Mathematical equations of the model were solved for flow, temperature, and concentration field in the melt and temperature field in the crystal. The location and shape of the interface were also solved simultaneously. In 2 - dimensional model, the shape of the interface is flat with adiabatic thermal boundary condition, but it becomes curved with completely conducting thermal boundary condition. In 3 - dimensional model, the interface is less curved than 2 - dimensional case and the flow intensity is similar to that of 2 - dimensional case. With the increase of flow intensity vertical segregation shows maximum value in both 2 - and 3 - D model. However, the maximum value occurs in lower flow intensity in 2 - D model because the interface is more curved for the same flow intensity.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.25 no.2
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• pp.15-22
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• 1980

Alkali digestion value of rice kernels was increased with delayed planting date and decreased with temperature during ripening. Varietal difference in average digestion value between low and high groups of rice varieties was the greatest under the conditions of 1.4 percent solution of potassium hydroxide, early planting and day/night temperature of 30/22$^{\circ}C$ Segregation ratio of alkali digestion value in $F_2$ generation was varied with crosses showing 3:1 for nine crosses, 1:3 for one cross, 9:7 and 13:3 for two crosses respectively and non-segregation for one cross of 15 crosses between low and high varieties in the digestion value.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.42 no.6
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• pp.766-777
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• 1997

The purpose of this study was to investigate inheritance modes of low temperature germinability(LTG) on rice. Two experiments were carried out: In experiment I, the seeds of 10 rice varieties yielded at the different cultivation conditions which were transplanted in a paddy field from May 20 to July 5 with 15-day interval, were tested at fixed temperature (13$^{\circ}C$) in-door and at field with natural conditions to find out the change of LTG according to different cultivating condition among the each variety, In experiment II, F$_1$ seeds of full diallal cross from six parents, were analyzed for combining ability and reciprocal differences of low temperature germinability. The results are summarized as follows. The seeds of 10 varieties showed significant differences of LTG at the different cultivation conditions, varieties and their interaction. And the relationship between LTG coefficient at 13$^{\circ}C$ and low temperature emergence(LTE) coefficient at field was highly significantly positive(r=0.511). From the analysis of the diallel cross, high significance was found at reciprocal difference and alpha inheritance. The mean squares of general combining ability(GCA) and specific combining ability of LTG were highly significant with higher mean squares of GCA. Seventeen out of 30 cross combinations showed transgressive segregation.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.2
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• pp.16-20
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• 2009

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.124-128
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• 2001

Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum ahoy has been studied Two-phase fluid flow model to investigate the velocity field and temperature distribution is proposed. The unposed mathematical model is applied to the die shape of the two type. To calculate the velocities and temperature fields during rheology forming process, the each governing equation correspondent to the liquid and solid region are adapted. Theoretical model on the basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on the liquid and solid viscosity.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.139-142
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• 2004

Nickel base superalloys are widely used for high temperature applications due to heat resisting capability and corrosion resistance at high temperatures. Superalloys with many strengthening alloying elements are frequently used in powder form to alleviate harmful effects of alloy segregation. HIP (hot isostatic pressing) and DB (diffusion bonding) as a form of solid-state bonding process is used to make turbine components, such as integrated turbine rotors. HIP/DB process requires many technical overcomes related to dimensional changes as well as microstructural control. In this research, HIP/DB process for nickel base superalloys, Udimet 720 and MM 247, were investigated with a view to control the dimensional change during the consolidation process. Simple disc-shaped cans were used to select the conceptual die design for the control of the dimensional change especially in radial direction. The change in the shape of consolidated shape was investigated using commercial FE code with constitutive equations fur low temperature plasticity deformation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.902-905
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• 2000

As the manufacturing processes of automotive engine piston, gravity die-casting, squeeze casting, hot forging and powder forging process are generally used for the various specifications. As the semi-solid forming(SSF) is compared with conventional casting such as gravity die-casting and squeeze casting for the characteristics of its process, the product without inner defects such as gas porosity and segregation can be obtained and its microstructure is globular grain. In SSF process, the materials are heated up to the temperature between the solvus and liquidus line at which the materials exists in the form of liquid-solid mixture. In this time, Discussion is given about reheating process of row material and results are presented regarding accurate temperature and process variables controlling for right solid fractions.

• Journal of the Korean Institute of Telematics and Electronics
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• v.25 no.9
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• pp.1060-1067
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• 1988

In this paper, we have investigated the effects of rapid thermal process on the electrical and structural properties of silicon films. It was shown that required times and temperature for the successful activation of dopants (Boron, Phosphorus:5E15atoms/cm\ulcorner were above 1000\ulcorner, 10sec, respectively. The typical resistivities of films deposited below 600\ulcorner were in the range of 1.0 E-3ohm-cm which was 20-30% lower than that of initially polycrystalline silicon depositd above 600\ulcorner. After rapid thermal process at high temperature above 1000\ulcorner, the films did not reveal any change in resistivity due to the dopant segregation, and better electrical conductivity could be obtained by increasing the process time. The grain growth by RTA treatment was more salient in the case of the doped amorphous than that of initially polycrystalline. The surface of the films also preserved the higher structural perfection and surface smoothness.