Millimeter (mm) long vertically aligned carbon nanotubes (CNTs) were grown by the catalyst assisted thermal chemical vapor deposition (CVD) technique. The continuous growth of CNTs as long as 7 mm was observed after 12 h of deposition by adjusting the growth parameters for making the catalyst active for a long time. The direct dependence of the number of walls of mm-long CNTs on the Fe catalyst thickness was observed. The successful syntheses of single-walled nanotubes (SWNTs), double-walled nanotubes (DWNTs), and multiwalled nanotubes (MWNTs) with high percentages (∼80%) were achieved by varying the catalyst layer thickness. The effect of Al 2 O 3 buffer layer was found to be critical for this controlled synthesis, which has been discussed in detail. The possible growth mechanism is also discussed to better understand this phenomenon.

In the system Zr0,-Al,O,, a new method for preparing ZrO, solid solutions from ZrCl, and AICl, using hydrazine monohydrate is investigated. c-ZrO, solid solutions containing up to -40 mot% AI,O, crystallize at low temperatures from amorphous materials. The formation mechanism is discussed from IR spectral data. The values of the lattice parameter a increase linearly from 0.5072 to 0.5105 nm with increasing AI,O, content. At higher temperatures, transformation of the solid solutions proceeds as follows: c(ss) + t ( s s ) + t ( s s ) + (Y-AI,O, + m + a-Al,O,. rn-Zr0,-a-Al,O, composite ceramics are fabricated by hot isostatic pressing for 2 h at 1250°C and 196 MPa. Microstructures and mechanical properties are examined, in connection with increasing AI,O, content.

Sodium potassium niobate, (Na(0.5)K(0.5))NbO(3), fine powder has been successfully synthesized at the low temperature of 550 degrees C through a modified solid-state reaction method, in which urea [CO(NH(2))(2)] plays an important role. High-density (Na(0.5)K(0.5))NbO(3) ceramics could be obtained by conventional sintering of the synthesized (Na(0.5)K(0.5))NbO(3) fine powder with the addition of 0.03 mol% Co(3)O(4) as a sintering additive. The crystal structure, microstructure, and dielectric and piezoelectric properties were characterized. The (Na(0.5)K(0.5))NbO(3) ceramic showed a comparatively saturated P-E hysteresis loop. The (Na(0.5)K(0.5))NbO(3) ceramic also displayed piezoelectricity with a piezoelectric constant d(33) of 126 pC/N and a planar electromechanical coupling factor k(p) of 33%.

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doped ZrO, composite powders with 50 mol% AI,O, are prepared by the hydrazine method. As-prepared powders are mixtures of AIO(0H) gel and amorphous ZrO, solid solutions containing Y,O, and AI,O,. The formation process leading to a-Al,O,-t-ZrO, composite powders is examined. Hot isostatic pressing is performed for 2 h at 1400°C under 196 MPa using BAl,O,-t-ZrO, composite powders. The resulting dense, sintered a-AI,O,-I-ZrO, composites show excellent mechanical strength.

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The corrosion rate (Cr) of commercially available ball bearings made of silicon nitride (Si3N4) of high degree (HD) and standard quality (S) was measured at hydrothermal conditions in different aqueous concentrations of sulphuric acid (H2SO4) and sodium hydroxide (NaOH). The Cr magnitude for the materials diminished when increasing the acid concentration. At higher concentrations of H2SO4 (98%) the formation of SiO2 on the surface of the balls inhibited the progress of corrosion. The corrosion rate of the materials was increased when the sodium hydroxide solution concentration was increased. The surface of the materials was analyzed by means of scanning electron microscopy (SEM), while the corrosion rate was determined based on weight losses.

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