Yang-Su Han

New organo-montmorillonite complexes with hydrophobic and hydrophilic functions

Quaternary alkylammonium cations (R4N+) with different molecular structures were intercalated into layered aluminosilicate, Na+-montmorillonite (M), by ion exchange reaction. Four kinds of R4N+ molecular ions, [(CH3(CH2)17)xN(CH3)4 − x]+ with x = 1 (ODTM) and x = 2 (DMDS) and [(CH3(CH2)15COO(CH2)2)xN(CH3)(CH2CH2OH)3 − x]+ with x = 1 (DHMC) and x = 2 (DCEM), were used as intercalants. The relative dispersibility of intercalated R4N+M samples in polar and nonpolar solvents were evaluated on the basis of viscosity. Even in an aqueous solution, the DHMC-M and DCEM-M complexes, exhibited good dispersibility due to the hydrophilic functional groups in the organic cations. On the other hand, the DMDS-M and ODTM-M complexes containing only aliphatic long chain showed enhanced dispersibility in nonpolar solvents like n-hexane.

Layered double hydroxide as gene reservoir

Abstract Novel bio-/organic-inorganic hybrid compounds of deoxyribonucleic acid (DNA) and methotrexate (MTX)-layered double hydroxide are prepared by ion-exchange type intercalation reaction. The layered inorganic support. Mg2Al(NO3)-LDH, is at first obtained by coprecipitation in an aqueous solution, and then the interlayer NO3 − anions are replaced by guest molecules such as methotrexate (an anticancer drug) and deoxyribonucleic acid (about 500 ∼ 1000 base pairs), leading to form new bio-/organic-nanohybrids. Upon intercalating guest molecules into hydroxide layers, the basal spacing of LDH increases from 8.5 Å (NO3 −) to 20.8 Å (MTX) and 23.9 Å (DNA), respectively. According to the X-ray diffraction and infrared spectroscopic analyses, it is found that the target molecules are safely preserved by hydroxide layers maintaining their chemical and structural properties.

Citrate route to the piezoelectric Pb(Zr,Ti)O3oxide

A homogeneous and stoichiometric Pb(Zr 1-x Ti x )O 3 (x=0.52; PZT) powder with a particle size of 20–40 nm has been prepared by the citrate route. Solubility isotherms have been calculated for metal–citric acid–water systems at 25 °C to predict the optimum pH condition, which was found to be pH=6.5 for preparing pure and stable citrate complexes. Monodispersive nanometer-sized particles could be obtained by thermal decomposition of the optimally prepared citrate precursor at a temperature as low as 800 °C. The crystallization process and particle characteristics of the citrate-derived PZT powder are described in detail along with the preliminary results on the sinterability and piezoelectricity.

Hydroxide coprecipitation route to the piezoelectric oxide Pb(Zr,Ti)O3(PZT)

A homogeneous and stoichiometric fine powder of the piezoelectric oxide Pb(Zr0.52Ti0.48)O3(PZT) has been prepared by the hydroxide coprecipitation route. By considering the thermodynamic equilibrium constants, the solubility and ionic equilibria relationships for individual metal hydroxides in aqueous media could be theoretically evaluated as a function of solution pH and metal ion concentration. An optimal pH of 9 for the coprecipitation of the ternary Pb-Zr-Ti system as hydroxides was predicted from the solubility diagrams, and the quantitative coprecipitation of metal hydroxides was confirmed experimentally. Pb(Zr0.52Ti0.48)O3 as a single phase was obtained by thermal decomposition of the coprecipitated hydroxide precursor above 500 °C. The calcined powders at various temperatures were characterized by inductively coupled plasma (ICP) studies, thermogravimetry-differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements.

Citrate route to ultra-fine barium polytitanates with microwave dielectric properties

Highly reactive and ultra-fine barium polytitanates (BaO-nTiO2, n= 4, 4.5, 5) with a particle size of 30–50 nm have been prepared by the citrate route. Solubility isotherms were calculated for the BaCO3-citric acid-H2O and TiO(OH)2-citric acid-H2O2-H2O systems at 25 °C to predict the optimum pH condition for preparing pure and stable citrate complexes. Pure and well crystallized powders with monodispersive, nanometer-sized particles could be obtained by thermal decomposition of the optimally prepared citrate precursors at relatively low temperatures. Details of the crystallization process and particle characteristics of citrate-derived barium polytitanates are described. The sinterability and microwave dielectric properties of BaTi4O9 and Ba2Ti9O20 were also measured and are discussed briefly.

A combinative flux evaporation–slow cooling route to potassium titanate fibres

Abstract Two-dimensional potassium tetratitanate (K2Ti4O9) and three-dimensional potassium hexatitanate (K2Ti6O13) fibers have been prepared by slow-cooling calcination, flux melting, flux evaporation and the combinative route of flux evaporation and slow cooling process. In the slow-cooling calcination process, the control of cooling rate was crucial to growth of K2Ti4O9 long fibers. It was also found that the fiber growth reaction is strongly dependent on the mole ratio of flux (F) to raw material (R), which is 7:3 as for the optimum growth conditions in the flux melting process. A columnar shaped potassium titanate fiber has been prepared by the new combinative route of flux evaporation and slow-cooling. Relatively long potassium tetratitanate (K2Ti4O9) fibers (average length is 4 to 5 mm) with prismatic shape could be grown by the combinative growth technique. When this new route is applied for the growth of potassium hexatitanate (K2Ti6O13), monofilament-type fibers (≈1.5 mm) with columnar shape could be obtained.

Citrate route to the preparation of nanometer size (Pb, La) (Zr, Ti)O3 oxide

Abstract Homogeneous and stoichiometric lanthanum-modified lead zirconium titanate (Pb 0.92 La 0.08 )(Zr 0.65 Ti 0.35 )O 3 (PLZT) particles with a nanometer size of 20–40 nm have been prepared by the citrate route. The solubility isotherms for individual metal-citric acid-H 2 O systems at 25 °C were calculated to predict the optimum pH condition, which was found to be 6.5 for preparing pure and stable citrate complexes. A monophasic PLZT powder consisting of monodispersive and nanometer-sized particles could be obtained by thermal decomposition of the optimally prepared citrate precursor at a considerably low temperature of 800 °C. Details of crystallization process and particle characteristics of the citrate-derived PLZT powder have been described along with the preliminary results on the sinterability.

Oxalate coprecipitation route to the piezoelectric Pb(Zr,Ti)O3 oxide

A homogeneous and stoichiometric Pb(Zr,Ti)O 3 (PZT) fine powder was prepared by thermal decomposition of the metal oxalate precursor formed by the precipitation reaction of the metallic components in aqueous solution with oxalic acid. Theoretical solubility isotherms of metal oxalates were established as a function of the solution pH and the metal ion concentration using thermodynamic equilibrium constants for the corresponding metal salts in aqueous solution. Through the theoretical solubility isotherms, the optimum pH domain for preparing the homogeneous and stoichiometric PZT–oxalate precursor was found to be 3–4. Crystalline PZT with tetragonal symmetry began to form after heating the precursor at 600 °C and a monophasic PZT powder consisting of submicrometer (0.3–0.5 µm) particles with spherical shape could be obtained after calcination at 800 °C for 2 h. The oxalate-derived PZT powder showed a good sinterability even below 1150 °C where the piezoelectric properties were optimized.

Physico-Chemical Characterization of Na3Zr2Si2PO12 Fine Powders Prepared by Sol-Gel Method Using Citrates

Sodium superionic conductor (NASICON) powders have been prepared by sol-gel technique using citrates. The optimum pH condition (\cong6) for sol-gel process was predicted by theoretical consideration of thermodynamic equilibrium constants for corresponding metal salts in aqueous solution. The pure NASICON phase with rhombohedral unit cell could be obtained by thermal decomposition of citrate precursors at a relatively low temperature (850°C). When the calcining temperature was raised to 1100°C, however, slight monoclinic distortion with formation of a trace of monoclinic ZrO2 was observed. Thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) technique, scanning electron microscopy (SEM) and 31P static and magic angle spinning (MAS) NMR have been used to characterize the calcined powders.

Modification of the interlayer pore structure of silica iron oxide sol pillared clay using organic templates

A novel route for modifying the interlayer pore structure of silica iron oxide sol particle pillared montmorillonite was proposed based on the post-intercalation of organic templates. The pristine mixed oxide sol pillared montmorillonite (SFM) was prepared by the reaction of Na-montmorillonite with silica iron sol particles obtained by depositing iron hydroxy cations on hydrolyzed silica sol surfaces. Three kinds of surfactant molecules with different molecular geometries and sizes were subsequently introduced between the interlayer spaces of the oxide sol exchanged montmorillonite. Upon intercalating the organic templates, a part of the interlayer sol particles was replaced and rearranged by the templates. Removing the templates by calcination at 550 °C resulted in the mesoporous sol pillared clays with controlled pore structures. The porous characteristics of the modified pillared clays were analyzed in detail using nitrogen and some selected solvent adsorption–desorption isotherms, which exhibited extremely large BET surface areas up to 750 m2 g–1 and enlarged pore sizes of >20 A.