NANOSTRUCTURED CERAMICS AND COMPOSITES FOR REFRACTORY APPLICATIONS IN COAL GASIFICATION

Brown, Paul

Penn State University (United States)

关键词: Coal Gasification;    Copper Additions;    Surface Area;    Carbon Black;    01 Coal, Lignite, And Peat;   

DOI  :  10.2172/840414
RP-ID  :  NONE
RP-ID  :  FG26-01NT41278
RP-ID  :  840414

美国|英语

来源: UNT Digital Library

【 摘 要 】

A class of ceramics, capable of exhibiting low coefficients of thermal expansion and catalytic properties was investigated. Investigations were directed towards nanoengineering of NZP ceramics and NZP-based composites by chemical means by controlling their compositions and processing variables. NaZr{sub 2}(PO{sub 4}){sub 3} (NZP) was synthesized by combining water-soluble precursors leading to the precipitation of a gel that was dried, calcined, pressed into pellets, then fired at 850 C. Without chemical additives, the resulting ceramic comprised pores ranging in size from approximately 25 to 50 nm and a surface area of about 30m{sup 2}/g. Hydroxyapatite, which has a needle-like morphology, was mechanically mixed with the calcined gel to template NZP crystallization. What resulted was a coarsening of the pore structure and a decrease in surface area. When copper nitrate was added to the solution during synthesis, the resulting ceramic underwent shrinkage upon firing as well as an increase in strength. HAp and copper additions combined resulted in 40% volume shrinkage and a doubling of the tensile strength to 16MPa. A very different type of porosity was achieved when silica was partly substituted for phosphorous in the NZP structure. Na{sub 3}Zr{sub 2}(Si{sub 2}P)O{sub 12} (NASCION) was synthesized in the same manner as NZP, but the fired ceramic possessed a reticulated pore structure comprising large cavities ranging in size from 5 to 50 {micro}m. The NASCION ceramic either shrank or expanded upon firing depending on when the silica was added during synthesis. When the silica precursor (amorphous, precipitated silica) was added before the calcining step, the pressed pellets expanded during firing, whereas they shrank when the silica was added after the gel was calcined. The observed dilation increased with increasing calcining temperature and particle size, up to 26%. The contraction of the ceramic when fired increased with increasing calcining temperature and a greater surface area of the gel. Direct addition of Silica fiber was only modestly beneficial. Fiber addition combined with controlled densification resulted in the greatest improvement in strength. Ion exchange properties of NASICON were established for Cs, Pb, and Cd. It was found that the extent of ion exchange depended on ion size and that Cd could be fully exchanged into NASICON. Catalytic activity of Cu and Ag substituted compositions were determined and it was found that Ag substitution reduced the temperature at which carbon black could be oxidized. However, Ag substitution results in the formation of zircon. Ion conductivity of NASCION was determined and it was found to compare well with other ionic conductors.