Geopolymer is an alumina silicate-based ceramic material that has good heat-resistance and fire-resistance; it can be cured at room temperature, and thus its manufacturing process is simple. Geopolymer can be used as a reinforcement or floor finish for high-speed curing applications. In this manuscript, we investigate a high-speed curing geopolymer achieved by adding calcium to augment the curing rate. Metakaolin is used as the main raw material, and aqueous solutions of KOH and K2SiO3 are used as the activators. As a result of optimizing the high bending strength as a target factor for geopolymers with SiO2 / Al2O3 ratio of 4.1 ~ 4.8, the optimum ranges of the active agent are found to be 0.1 ≤ K2O / SiO2 ≤ 0.4 and 10 ≤ H2O / K2O ≤ 32.5, and the optimum range of the curing accelerator is found to be 0.82 Ca (OH)2 / Al2O3 2.87. The maximum flexural strength is found to be 1.35 MPa at Ca (OH)2 / Al2O3 = 2.82, K2O / SiO2 = 0.3, and H2O / K2O = 11.3. The physical and thermal properties are analyzed to validate the applicability of these materials as industrial insulating parts or repairing·finishing materials in construction.

Al2O3 nanosol dispersed under ethanol or N-Methyl-2-pyrrolidone(NMP) was studied and optimized with various dispersion factors and by utilizing the silane modification method. The two kinds of Al2O3 powders used were prepared by thermal decomposition method from aluminum ammonium sulfate(AlNH4(SO4)2) while controlling the calcination temperature. Al2O3 sol was prepared under ethanol solvent by using a batch-type bead mill. The dispersion properties of the Al2O3 sol have a close relationship to the dispersion factors such as the pH, the amount of acid additive(nitric acid, acetic acid), the milling time, and the size and combination of zirconia beads. Especially, Al2O3 sol added 4 wt% acetic acid was found to maintain the dispersion stability while its solid concentration increased to 15 wt%, this stability maintenance was the result of the electrostatic and steric repulsion of acetic acid molecules adsorbed on the surface of the Al2O3 particles. In order to observe the dispersion property of Al2O3 sol under NMP solvent, Al2O3 sol dispersed under ethanol solvent was modified and solventexchanged with N-Phenyl-(3-aminopropyl)trimethoxy silane(APTMS) through a binary solvent system. Characterization of the Al2O3 powder and the nanosol was observed by XRD, SEM, ICP, FT-IR, TGA, Particles size analysis, etc.

To study the dispersion factors of silica sol prepared from fumed silica powder, we prepared silica sol under an aqueous system using a batch type bead mill. The dispersion properties of silica sol have a close relationship to dispersion factors such as pH, milling time and speed, the size and amount of zirconia beads, the solid content of fumed silica, and the shape and diameter of the milling impellers. Especially, the silica particles in silica sol were found to show dispersion stability on a pH value above 7, due to the electrostatic repulsion between the particles having a high zeta potential value. The shape and diameter of the impellers installed in the bead mill for the dispersion of fumed silica was very important in reducing the particle size of the aggregated silica. The median particle size (D50) of silica sol obtained after milling was also optimized according to the variation of the size and amount of the zirconia beads that were used as the grinding medium, and according to the solid content of fumed silica. The dispersion properties of silica sol were investigated using zeta potential, turbiscan, particle size analyzer, and transmission electron microscopy.

Fe2O3 coated plate mica(Fe2O3/mica) for infrared reflectance red pigment was prepared under hydrothermal treatment. Fe2O3 was perfectly coated on mica via the difference of surface charge between Fe2O3 and mica particles at pH 3. Fe2O3/mica was then calcined at 800 oC to stabilize the coated layer on mica. The infrare (IR) reflectance pigments were characterized by X-ray diffraction, FE-SEM, zeta potential, and a UV-Vis-NIR spectrophotometer. In particular, the CIE color coordinate and IR reflectance properties of Fe2O3/mica pigments were investigated in relation to the thickness variation of the Fe2O3 layer coated on mica of various lateral sizes. The isolation-heat red paints containing the pigments were prepared and optimized with a thinner, settling agent, and dispersant. Then, the films were made. The thermal property of isolation-heat on these films was observed through the relationship of the IR reflectance value, which was based on the variation of the Fe2O3 layer’s thickness coated on mica and mica’s lateral size as IR reflectance pigment. With an increase in IR reflectance on these films, the thermal property of isolation-heat was effectively enhanced.

Fe4[Fe(CN)6]3 coated on a mica or TiO2/mica surface as infrared reflective blue pigment was prepared by a hydrothermal method. Fe4[Fe(CN)6]3, used as coloring agent, was uniformly coated on mica or TiO2/mica under the optimized condition of a 1.2 : 1 weight ratio between iron(III) chloride hexahydrate and potassium ferrocyanidetrihydrate at the initial pH level of 4.5 at 70˚C. The infrared (IR)-reflective pigments were characterized by SEM, Zeta-potenial, FT-IR, and UV-VIS NIR spectrophotometry. Especially the CIE color coordinate and total solar reflectance(TSR) properties of the pigments were investigated in relation to variation of the coating and coated substrate thicknesses. Isolation-heat paint was prepared with 20 wt% blue pigments fully dispersed in acryl-urethane resin and several additives to coat the film uniformly. The films were also measured with CIE color coordinate, TSR, and the surface temperature was recorded by an isolation-heat measuring system. The pigments and films of Fe4[Fe(CN)6]3 coated on mica and TiO2/mica showed high TSR values compared with the TSR value of Fe4[Fe(CN)6]3 itself. According to the increase of TSR value, the property of isolation-heat is effective. To realize the optimal blue color, we applied the the pigment to TiO2 coated mica(TM(b)) which has blueish interference color. The pigment of Fe4[Fe(CN)6]3 coated on TM(b) shows a strong blue color compared with that of Fe4[Fe(CN)6]3 coated on TiO2/Mmca(TM(w)), which has a whitish interference color.

Graphene oxide powders prepared by two different drying processes, freeze drying and spray drying, were studied to compare the effect of the drying method on the physical properties of graphene oxide powder. The graphene oxide dispersion was prepared from graphite by chemical delamination with the aid of sulfuric acid and permanganic acid, and the dispersion was further washed and re-dispersed in a mixed solvent of water and isopropyl alcohol. A freeze drying method can feasibly minimize damage to the sample, but it requires a long process time. In contrast, spray drying is able to remove a solvent in a relatively short time, though this process requires exposure to a high temperature for a rapid evaporation of the solvent. The powders prepared by freeze drying and spray drying were characterized and compared by Raman spectroscopy, X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and by an elemental analysis. The graphene oxide powders showed similar chemical compositions; however, the morphologies of the powders differed in that the graphene oxide prepared by spray drying had a winkled morphology and a higher apparent density compared to the powder prepared by freeze drying. The graphene oxide powders were reduced at 900˚C in an atmosphere of N2. The effect of the drying process on the properties of the reduced graphene oxide was examined by SEM, TEM and Raman spectroscopy.

Coatings composited with alumina and Perfluoro alkoxyalkane (PFA) resin were deposited on stainless steel plate (SUS304) to further improve corrosion resistance. Plate (ca. 10μm) and/or nanosize (27~43 nm) alumina used as inorganic additives were mixed in PFA resin to make alumina-fluoro composite coatings. These coatings were deposited on SUS304 plate with wet spray coating and then the film was cured thermally. According to the amount and ratio of the two kinds of alumina having plate morphology and nano size, corrosion resistance of the film was evaluated under strong acids (HF, HCl) and a strong base (NaOH). The film prepared with the addition of 5~10 wt% alumina powders in PFA resin showed corrosion resistance superior to that of pure PFA resin film. However, for the film prepared with alumina content above 10 wt%, the corrosion resistance did not improve with the physical properties, such as surface hardness and adhesion. The film prepared with plate/nanosize (weight ratio = 1/2) alumina especially enhanced the surface hardness and corrosion resistance. This can be explained as showing that the plate and the nanosize alumina dispersed in PFA resin effectively suppressed the penetration of cations and anions due to the long penetration length and fewer defects that accompany the improved surface hardness under a serious environment of 10% HF solution for over 120 hrs.

Hollow silica spheres were prepared by spray drying of precursor solution of colloidal silica. The precursor solution is composed of 10-20 nm colloidal silica dispersed in a water or ethanol-water mixture solvent with additives of tris hydroxymethyl aminomethane. The effect of pH and concentrations of the precursor and additives on the formation of hollow sphere particles was studied. The spray drying process parameters of the precursor feeding rate, inlet temperature, and gas flow rate are controlled to produce the hollow spherical silica. The mixed solvent of ethanol and water was preferred because it improved the hollowness of the spheres better than plain water did. It was possible to obtain hollow silica from high concentration of 14.3 wt% silica precursor with pH 3. The thermal conductivity and total solar reflectivity of the hollow silica sample was measured and compared with those values of other commercial insulating fillers of glass beads and TiO2 for applications of insulating paint, in which the glass beads are representative of the low thermal conductive fillers and the TiO2 is representative of infrared reflective fillers. The thermal conductivity of hollow silica was comparable to that of the glass beads and the total solar reflectivity was higher than that of TiO2.

The particle size of MgO was examined as a function of the Na content in Mg(OH)2 powders and the calcination temperature. Mg(OH)2 suspension was obtained by dropwise precipitation of Mg(NO3)2·6H2O and NaOH solutions. The suspension was diluted by varying the dilution volume ratio of distilled water to Mg(OH)2 suspension to change the Na salt concentration in the suspension. Mg(OH)2 slurry was filtered and dried at 60˚C under vacuum, and then its Mg(OH)2 powder was calcined to produce MgO with different amount of Na content at 500~900˚C under air. Investigation of the physical and chemical properties of the various MgO powders with dilution ratio and calcination temperature variation was done by X-ray diffraction, transmission electron microscopy, BET specific surface area and thermal gravimetric analysis. It was observed that MgO particle size could depend on the condition of calcination temperature and dilution ratio of the Mg(OH)2 suspension. The particle size of the MgO depends on the Na content remaining in the Mg(OH)2 powder, which powder was prepared by changing the dilution ratio of the Mg(OH)2 suspension. This change increased as the calcination temperature increased and decreased as the dilution ratio increased. The growth of MgO particle size according to the increase of temperature was more effective when there was a relatively high content of Na. The increase of Na content lowered the temperature at which decomposition of Mg(OH)2 to MgO took place, thereby promoting the crystal growth of MgO.

Magnesium hydroxide-melamine core-shell particles were prepared through the coating of melamine monomer on the surface of magnesium hydroxide in the presence of phosphoric acid. The melamine monomer was dissolved in hot water but recrystallized on the surface of magnesium hydroxide by quenching to room temperature in the presence of phosphoric acid. The core-shell particle was applied to low-density polyethylene/ ethylene vinyl acetate (LDPE/EVA) resin by melt-compounding at 180˚C as flame retardant. The effect of magnesium hydroxide and melamine content has been studied on the flame retardancy of the core-shell particles in LDPE/EVA resin according to the preparation process and purity of magnesium hydroxide. Magnesium hydroxide prepared with sodium hydroxide rather than with ammonia solution revealed higher flame retardancy in core-shell particles with LDPE/EVA resin. At 50 wt% loading of flame retardant, core-shell particles revealed higher flame retardancy compared to that of the exclusive magnesium hydroxide in LDPE/EVA composite, and it was possible to satisfy the V0 grade in the UL-94 vertical test. The synergistic flame retardant effect of magnesium hydroxide and melamine core-shell particles was explained as being due to the endothermic decomposition of magnesium hydroxide and melamine, which was followed by the evolution of water from the magnesium hydroxide and porous char formation due to reactive nitrogen compounds, and carbon dioxide generated from melamine.

Inorganic oxide colloids dispersed in alcohol were applied to a stainless steel substrate to produce oxide coatings for the purpose of minimizing emissive thermal transfer. The microstructure, roughness, infrared emissive energy, and surface heat loss of the coated substrate were observed with a variation of the nano oxide sol and coating method. It was found that the indium tin oxide, antimony tin oxide, magnesium oxide, silica, titania sol coatings may reduce surface heat loss of the stainless steel at 300˚C. It was possible to suppress thermal oxidation of the substrate with the oxide sol coatings during an accelerated thermal durability test at 600˚C. The silica sol coating was most effective to suppress thermal oxidation at 600˚C, so that it is useful to prevent the increase of radiative surface heat loss as a heating element. Therefore, the inorganic oxide sol coatings may be applied to improve energy efficiency of the substrate as the heating element.