| Research Abstract |
Fabrication of ceramic materials has been undertaken by using polyhydroxoaluminum (PHA) solutions, which lead gels on drying and consist of bulky and planar Al species, obtained by Al metal dissolving method.
Transparent gels were obtained from PHA solutions having different [OH/Al] ratios of 2.00-2.53. These gels were transformed into activated alumina and α-alumina by heating at 500-900℃ and 1000℃, respectively. Activated alumina thus obtained exhibited two kinds of pores, i.e., smaller pores of 3-4 nm and larger pores of 4-30 nm in diameter. To obtain activated alumina having uniform pores, tetramethylammonium chloride (TM) were added to the PHA solutions followed by drying to form PHA-TM composite gels. The γ-alumina obtained from the composite gels having【greater than or equal】30% TM content showed a sharp and precisely controlled monomodal pore size distribution in the range of 3 to 4 nm, depending on the heating temperature. The γ-alumina gave the highest pore volume of 0.25 cm^3
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g^<-1> at 400℃.
Alumina-pillared fluorine micas were obtained from PHA solutions and expandable synthetic fluorine micas. Sintered bodies of the alumina-pillared micas having machinability were obtained by firing the powder compacts of the alumina-pillared micas at 500-700℃ with retaining their pillared structure. Thermal durability of the pillared structure depends on the particle size of alumina-pillared fluorine micas, especially on the c^*-dimension of the host mica crystals ; thermal durability of the sintered bodies obtained from coarse particles is higher than that from fine particles.
In order to obtain microporous solids having high thermal durability, synthesis of alumina pillared fluorine micas has been undertaken under the presence of poly (vinyl alcohol)(PVA). The products thus obtained gave the large basal spacing of 2.7 nm at 500℃ and the maximum surface area of 403 m^2g^<-1> at 600℃. The surface area of the product was above 300 m^2g^<-1> even after heating at 800℃, showing high thermal durability.
Sintered bodies of alumina-pillared fluorine mica/γ-alumina composites were obtained from the alumina-pillared micas and the gels or calcined gels containing PHA.The sintered composite bodies prepared by using the calcined gels retained microporous properties. The precursors of alumina-pillared micas, i.e., PHA intercalated fluorine micas, can be used as binders for sintering composites at low temperatures. Less
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