TiO2 powders were synthesized by a sol–gel method from tetrabutyl orthotitanate solution in the presence of water and hydrochloric acid. In order to study the effect of water content and hydrolysis catalyst (HCl) on crystal structure of the TiO2, a composition of H2O:EtOH:HCl was varied to 1:3:1, 1.5:1.5:2, 2:2:1 and 3:1:1. An increase of water and hydrochloric acid content in the precursor led to faster sol formation and greater yield of the TiO2 particle. Both water and hydrochloric acid were also found to promote the formation of rutile phase. Very fine spherical anatase and rutile crystals were obtained from the precursor containing small amount of water, while much larger needle‐shaped pure rutile was obtained when the precursor contained high amount of water. It was shown that phase composition can be monitored by easy manipulation of basic synthesis parameters such as the amount of water and acid catalyst. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Phase evolution and microstructure development of metakaolin-rice husk ash geopolymer have been investigated. The initial molar ratios of SiO 2 /Al 2 O 3 were designed in the range of 2.0-7.0 with Na 2 O/Al 2 O 3 ratios of 0.6-1.6, Na 2 O/SiO 2 of 0.20-0.72 and H 2 O/Na 2 O of 10.0-20.0. The specimens were cured at 30 o C for 1-90 days prior to characterization of phase and microstructure as well as mechanical properties. The designed molar ratios were found to correlate with phase and microstructure of reaction products related to their compressive properties. Various zeolite types (sodalite, zeolite A, zeolite Y, zeolite X and faujasite) were prominently observed in samples containing low initial molar ratios of SiO 2 /Al 2 O 3 (2.0-2.5) with Na 2 O/Al 2 O 3 ≥ 1.0 and H 2 O/Na 2 O in the range of 10.0-20.0. These low SiO 2 /Al 2 O 3 ratios provided low strength geopolymer. Formation of geopolymeric structures was established in samples containing higher initial molar ratio of SiO 2 /Al 2 O 3 (3.0-4.0) with Na 2 O/Al 2 O 3 ratio of 1.0 and H 2 O/Na 2 O ratios in the range of 10.0-15.0. The highest strength was achieved when initial molar ratios of SiO 2 /Al 2 O 3 , Na 2 O/Al 2 O 3 and H 2 O/Na 2 O were 4.0, 1.0 and 10.0, respectively. When the initial molar ratios of SiO 2 /Al 2 O 3 increased to 6.0-7.0 with Na 2 O/ Al 2 O 3 ratios of 1.0-1.6 and H 2 O/Na 2 O ratios of 10.0-15.0, sodium bicarbonate compounds and unreacted raw materials were observed within the geopolymeric structures. Correlation of phase structures of reaction products with different starting chemical compositions were evaluated and revealed in a ternary composition diagram.

Titanium dioxide nanofibers were fabricated by electrospinning technique. The titania solutions were obtained from adding various types of Ti precursor (Ti(OBu)4, Ti(OiPr)4, and Ti(OPr)4) to an ethanol solution containing polyvinyl pyrrolidone (PVP). Acetic acid was used to stabilize the solution and to control the hydrolysis reaction. The porous and well-defined crystalline structure was obtained after calcined at 450oC for 1 h. The thermal behavior, phase composition including crystallite size, as well as the morphology of as-synthesized nanofibers was obtained from thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The average diameter of these nanofibers was in the range from 100 to 400 nm depending on titania precursor. The photocatalytic activity of TiO2 fibers were evaluated for NOx degradation in a gaseous phase. The results demonstrated that at the same catalyst loading, the photocatalytic activity of TiO2 nanofiber was higher than the commercial Degussa P-25.

Metakaolin based geopolymer binder was synthesized using variable factors such as Na2O/SiO2, Na2O/Al2O3 and H2O/Na2O molar ratios as well as curing time. Metakaolin was used as an alumino-silicate source incorporating with strong alkali activators; sodium hydroxide solution to undergo polycondenation and hence a formation of hardened geopolymeric binder. This work was aimed to investigate the effect of Na2O/SiO2, Na2O/Al2O3 and H2O/Na2O ratios, as well as curing time on phase transformation. The chemical composition, phase development and microstructure of reaction products were examined by X-ray fluorescence, X-ray diffraction analysis and scanning electron microscopy with respect to their final compressive strength. Increasing the molar ratios of Na2O/Al2O3 and H2O/Na2O tended to favour the transformation of amorphous gel to various types of crystalline zeolite. Sodalite (pseudo-phase zeolite) and zeolite belonging to the Faujasite group, as well as zeolite X and A were identified in these mixtures. Based on this study, systems that favoured the formation of zeolitic products tended to possess lower strengths.Keywords: Geopolymer binder, Microstructure, Zeolite, Amorphous gel, Aluminosilicates IntroductionGeopolymer or alkali polysialate is an entirely known material that could be used in a wide range of potential applications includes: fire resistant materials, thermal insulation, ceramic tiles, thermal shock refractories, cements and concretes, high-tech composites aircraft interior and automobile, radioactive and toxic waste containment, arts and decoration. These can be formed by mixing aluminate and-silicate materials such as silica fume, fly ash, rice husk ash, slag, waste glass, industrial wastes, kaolinite and metakaolin with strong alkali activators or solution [1][2][3]. The basic of geopolymerization process involve dissolution of solid alumino-silicate oxides in alkali hydroxide or alkali silicate solution, diffusion or transportation of the dissolved Si and Al complexes from the initial raw material, formation of a gel phase and finally hardening of the gel phase. The hydration products forming in the thee-dimensional rigid network geopolymer are composed of variety structures, such as amorphous phase, semi-crystalline phase, as well as fully crystalline zeolite phase. A high content of amorphous geopolymeric gel resulted to the high compressive strength, while a formation of zeolite phase in geopolymer matrix produced lower strength [4][5][6][7].

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