• Journal of the Korean Ceramic Society
• /
• v.31 no.12
• /
• pp.1570-1576
• /
• 1994

Effect of Na2O/SiO2 molar ratio, calcining temperature and addition of NaCl were investigated on the hydrothermal formation of X-type zeolite from the natural mordenite, which is a kind of rock deposited abundantly in kuryong po. Pulverized mordenite was first mixed with NaOH or NaOH-NaCl solution, and crystallized under hydrothermal condition at 90~10$0^{\circ}C$ for 10 hrs. Optimum condition for synthesis of the X-type zeolite were \circled1 the ratio Na2O/SiO2, NaCl/Al2O3 and H2O/Na2O:0.68, 11.4 and 40, respectively, \circled2 calcining temperature of starting materials: 90$0^{\circ}C$, \circled3 aging time: 48 hrs. and \circled4 crystallization temperature: 10$0^{\circ}C$. The yield of X-type zeolite under the optimum condition was about 55~60%, and the major crystallized X-type zeolite was faujasite phase. Zeolite of then type X was crystallized when NaCl was added to treating solution with in the limit 14.25 of NaCl/Al2O3 molar ratio. As the calcination temperature (from 50$0^{\circ}C$ to 95$0^{\circ}C$) of starting materials increases, yield of zeolite x increase.

• Advances in concrete construction
• /
• v.11 no.1
• /
• pp.81-88
• /
• 2021

Rice Husk Ash (RHA) geopolymer paste activated by sodium aluminate were characterized by X-ray diffractogram (XRD), scanning electron microscope (SEM), energy dispersion X-Ray analysis (EDAX)and fourier transform infrared spectroscopy (FTIR). Five series of RHA geopolymer specimens were prepared by varying the Si/Al ratio as 1.5, 2.0, 2.5, 3.0 and 3.5. The paper focuses on the correlation of microstructure with hardened state parameters like bulk density, apparent porosity, sorptivity, water absorption and compressive strength. XRD analysis peaks indicates quartz, cristobalite and gibbsite for raw RHA and new peaks corresponding to Zeolite A in geopolymer specimens. In general, SEM micrographs show interconnected pores and loosely packed geopolymer matrix except for specimens made with Si/Al of 2.0 which exhibited comparatively better matrix. Incorporation of Al from sodium aluminate were confirmed with the stretching and bending vibration of Si-O-Si and O-Si-O observations from the FTIR analysis of geopolymer specimen. The dense microstructure of SA2.0 correlate into better performance in terms of 28 days maximum compressive strength of 16.96 MPa and minimum for porosity, absorption and sorptivity among the specimens. However, due to the higher water demand to make the paste workable, the value of porosity, absorption and sorptivity were reportedly higher as compared with other geopolymer systems. Correlation regression equations were proposed to validate the interrelation between physical parameters and mechanical strength. RHA geopolymer shows comparatively lower compressive strength as compared to Fly ash geopolymer.

• Economic and Environmental Geology
• /
• v.29 no.2
• /
• pp.129-138
• /
• 1996

The ores of the Bobae mine are mainly composed of sericite and quartz, and with appreciable amount of some other minerals such as andalusite. pyrophyllite, and albite, etc.. Sericite occurs in various a1teration zones having different crystal size and habit. Sericites can be c1assified into two types based on the crystal size; fine-grained and coarse-grained sericite. Fine-grained sericite occurs as an aggregate. Mineralogical characterizations of both types of sericites have been studied with various methods. Lattice parameters of two types of sericites occurred in various alteration zones are almost identical. but b parameter of coarse-grained sericite appears to be slight1y bigger than that of fine-grained aggregates. Average structural formula of fine- and coarse-grained sericite is $K_{1.44}Al_{3.86}(Si_{6.35}Al_{1.65})O_{20}(OH)_4$ and $K_{1.71}Al_{3.82}(Si_{6.20}Al_{1.80})O_{20}(OH)_4$, respectively. Structural formulae of coarse-grained sericites are close to that of muscovite. Infrared spectra show that there is slight distinction between sericites occurred in andalusite-pyrophyllite zone and other subzones. IR spectra of sericites due to Si-O vibration ($540{\sim}530cm^{-1}$) tend to shift to smaller wavenumber side from center to outer alteration zone. All samples have litt1e or no interstratified minerals. and this is demonstrated by Ir and DTA-TG results. It indicates that the Bobae mine is formed at relatively high temperature. That the ratio of quartz to sericite in ores varies greatly indicates that several discontinuous hydrothermal alteration processes have been involved.

• Korean Chemical Engineering Research
• /
• v.47 no.4
• /
• pp.424-429
• /
• 2009

The effects of $Na_2O$, $SiO_2$ and $H_2O$ contents of the synthetic mixtures prepared from water glass on the crystallinity and crystallite size of sodalite were studied. The composition of the synthetic mixtures described by $x\;Na_2O{\cdot}y\;SiO_2{\cdot}Al_2O_3{\cdot}z\;H_2O$ was varied within x=2.5~7.5, y=1.4~3.0, z=140~400. The hydrothermal reaction was carried out at $140^{\circ}C$ for 2 days. High content of $Na_2O$ resulted in the high crystallinity and small crystallite of sodalite. The $SiO_2/Al_2O_3$ molar ratios of around 2 were suitable for the synthesis of sodalite, and produced zeolite species were varied by the $H_2O$ content. Sodalite was mainly obtained with a high crystallinity from the synthetic mixtures with $SiO_2/Al_2O_3$ molar ratio of around 2 and high content of $Na_2O$. The high content of sodium ions caused a decrease in the particle sizes because of their role of structure directing agent.

• Journal of the Korean Magnetics Society
• /
• v.11 no.5
• /
• pp.196-201
• /
• 2001

The dependence of CoFe interfacial layer thickness and plasma oxidation condition on tunneling magnetoresistance (TMR) in Ta/NiFe/FeMn/NiFe/Al$_2$O$_3$/NiFe/Ta tunnel junctions was investigated. As the CoFe layer thickness increases, TMR ratio rapidly increases to 13.7 % and decreases with further increase of the CoFe layer thickness. The increase of TMR with the CoFe thickness up to 25 was thought to be due mails to the high spin-polarization of CoFe. The maximum MR of 15.3% was obtained in the Si(100)/Ta(50 )/NiFe(60 )/FeMn(250 )/NiFe(70 )/Al$_2$O$_3$/NiFe(150 )/Ta(50 ) magnetic tunnel junction with a 16 Al oxidized for 40 sec using a Ar/O$_2$ (1:4) mixture gas.

• Journal of the Korean Ceramic Society
• /
• v.49 no.6
• /
• pp.498-504
• /
• 2012

Oxide layers were prepared by an environmentally friendly plasma electrolytic oxidation (PEO) process on an Al-1050 substrate. The electrolyte for PEO was an alkali-based solution with $Na_2SiO_3$ (8 g/L) and NaOH (3 g/L). The influence of the electrical parameters on the phase composition, microstructure and properties of the oxide layers formed by PEO were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The voltage-time responses were recorded during various PEO processes. The oxides are composed of two layers and are mainly made of ${\alpha}$-alumina, ${\gamma}$-alumina and mullite phases. The proportion of each phase depends on various electrical parameters. It was found that the surface of the oxides produced at a higher current density and Ia/Ic ratio shows a more homogeneous morphology than those produced with the electrical parameters of a lower current density and lower Ia/Ic ratio. Also, the oxide layers formed at a higher current density and higher Ia/Ic ratio show high micro-hardness levels.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1991.10a
• /
• pp.37-39
• /
• 1991

This paper is studies the effects of additives on the magnetic properties of Sr-ferrite. The specimens have been composed of SrO and Fe$_2$O$_3$with ratio of 1:5.9. As 1st additives, it is mixed to 0.2wt%, 0.7wt% and 1wt% of CaCo$_3$with 0.3wt% SiO$_2$. As 2nd addition, it is mixed to 0.5wt%, 1wt% of Na$_2$SiO$_3$, 0.5wt%, 1wt% of Cr$_2$O$_3$and 0.5wt%, 1wt% of Al$_2$O$_3$and sintering conditions was carried out at 1210$^{\circ}C$, 1230$^{\circ}C$ and 1250$^{\circ}C$. From experiments on the magnetic properties of specimen, the results were shown follows; (1) In case of additive SiO$_2$and CaO, it is stable magnetoplumbite structure for liquid phase grown, enhances mignetic propertics. (2) In case of basic compositions + 0.5wt% Al$_2$O$_3$, it is confirmed better properties by increasing of the coercivity than 0.5wt% Cr$_2$O$_3$additives. (3) In case of mixed additives of Cr$_2$O$_3$and Al$_2$O$_3$, magnetic propeties decrease with sintering density.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 1999.05a
• /
• pp.24-37
• /
• 1999

A comprehensive methodology to consolidate the hypereutectic Al-27Si-X alloy via spray forming was investigated in an attempt to judge the feasiblilty of this alloy in applying wear resistant components. Billets having desired shape and microstructures were fabricated using forming parameters obtained from numerical calculations. Prior to tube extrusion of the spray formed billets, effects of various extrusion conditions, such as extrusion ratio, die temperature, and die configuration, on microstructures of the billet were studied. Based on results obtained from the preliminary extrusion tests, the formed billets were then hot extruded into a tubular shape. Various material properties of the extruded billet were measured and compared with the other candidate materials for anti-wear applications.

• Journal of the Mineralogical Society of Korea
• /
• v.9 no.1
• /
• pp.7-16
• /
• 1996

Partially sericitized tourmaline from a pegmatite, Black Hills, South Dakota, U.S.A., was investigated using high-resolution transmission electron microscopy (HRTEM). Muscovite occurs as the only alteration product of tourmaline, and it is developed extensively as narrow veinlets along the {110} and {100} cleavage directions of tourmaline, indicating that a cleavage-controlled alteration mechanism was dominant. Muscovite was characterized mainly as two-layer polytypes with minor stacking disorder, but tourmaline is almost free of structural defects. HRTEM images of tourmaline-muscovite interfaces revealed that the interfaces between two minerals are composed of well-defined {110} and {100} boundaries of tourmaline. The (001) of muscovite is in general parallel to the c-axis of tourmaline, but tourmaline and replacing muscovite do not show specific crystallographic orientation relationship; muscovite consists of numerous 100-1000$\AA$ thick subparallel packets, and the angles between the (001) of muscovite and (110) of tourmaline is highly variable. Al/Si ratios of both minerals suggest that tourmaline to muscovite alteration by late magnetic fluids has been facilitated by their similar Al/Si ratio in the incipient alteration stage, in that the hydration reaction with preservation of Al and Si would require only addition of K+ and H2O. Aluminous minerals other than muscovite were not characterized as the alteration products of tourmaline, indicating that tourmaline reacted directly to muscovite; the tourmaline alteration apparently occurred by the presence of residual fluids in which K+ is available and silica was not undersaturated.

• Journal of Korea Foundry Society
• /
• v.14 no.5
• /
• pp.438-446
• /
• 1994

The effect of various thermomechanical treatments on the structure and rheological behaviour of Al-6.2wt%Si alloy in its solidification range were investigated using a Searle type high temperature viscometer. During continuous cooling, the viscosity increases gradually with increasing fraction of solidified alloy, until a critical fraction of solidified alloy is reached above which the viscosity sharply increases. The viscosity of the slurry, at a given volume fraction wolid, decreased with increasing shear rate. The size and morphology of primary solid particles during stirring is influenced strongly by shear rates, cooling rates, volume fraction and stirring time of solid. Morphological changes during stirring as a function of solid volume fractions, shear rate and processing time were also reported. In this study, the size of primary solid particles in these alloys consistently increases and the it`s aspect ratio decrease with the increase in fraction solid and decrease in shear rate. Crystal morphology changes from rosette type to spheroid type with the increase in shear rate and solid fraction.