Chanel Ishizaki

Surface hydration states of commercial high purity α-Al2O3 powders evaluated by temperature programmed desorption mass spectrometry and diffuse reflectance infrared Fourier transform spectroscopy

Abstract The surface of three different grades of commercial high-purity α-Al2O3 powders produced by hydrolysis of aluminum alkoxide, which differ each other in SSA are evaluated by temperature programmed desorption mass spectrometry (TPDMS) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. For the DRIFT evaluation the powders were heated in situ under vacuum from 25 to 700 8C. The TPDMS spectra of desorbed H2O were obtained by heating the samples under ultra high vacuum at a rate of 20 K minK1 up to 1200 8C. The presence of hydrogen bonded water molecules, amorphous Al(OH)3 and AlOOH structures, as well as associated and isolated hydroxyl groups on the surface of all the a-Al2O3 powders investigated is demonstrated. On the surface of one of the powders the presence of crystalline Al(OH)3 structures, as evidenced by an additional sharp peak in the H2O TPDMS spectrum, is confirmed.

Silicon nitride and oxide powder surface characterization by TPD

Abstract Surfaces of silicon nitride powders produced by three different production processes were analyzed by temperature programmed desorption (TPD) technique. The main desorbed species detected in the temperature range 40–1300 °C are H 2 , H 2 O, NH 3 and N 2 from Si 3 N 4 and Si 2 N 2 O powders, and H 2 and H 2 O with small amounts of N 2 from SiO, SiO 2 (am and c). Powders SiO and SiO 2 (am) show much larger desorption quantities than the other powders investigated. The distributions of desorbed species fractions reflect the production process and nitridation media. Powders produced using N 2 are strongly affected by the final treatment. Heating in air produces a powder with large amount of OH groups (B1), meanwhile acid and water washings reduce the -OH groups and increase -NH 2 and -NH groups (C5, C6). For a powder using NH 3 (g) + CH 4 as nitridation media, the heat treatment in air does not seem to increase -OH (B2), however shows similar desorption distribution to the powder using NH 3 (g) as nitridation media, but produced by a different method (A2). The use of NH 3 (l) appears to enhance the formation of surface groups which evolve as NH 3 and N 2 , with respect to the use of NH 3 (g) (A1).

Fluidity-increasing behaviour of silicon nitride powder by aqueous washing

On etudie les relations entre les modifications quantitatives des especes desorbees provoques par le lavage et la fluidite des poudres de Si 3 N 4 destinees a la fabrication de ceramiques thermomecaniques

An analytical electron microscopy study of a commercial activated carbon

Abstract The inorganic constituents of a commercially available active carbon produced from coal by high temperature steam activation (F200, Calgon Corporation) has been investigated by means of two different analytical electron microscopy techniques: electron probe microanalysis (EPM) and scanning transmission electron microscopy (STEM) both coupled with energy dispersion X-ray spectroscopy (EDX). Submicron mineral inclusions with a variety of sizes, shapes and compositions were identified. Clays, primarily kaolinite followed by illite were the main mineral phases. The results show that pyrite which may have been present in the original coal raw material has been disproportionated during the activation process, possibly rendering an organic sulfur content in the activated carbon larger than the one in the original coal. A heat-treated (1000°C in a nitrogen atmosphere for 17 h) product of the original active carbon was also investigated. This carbon shows a decrease in the total sulfur content and nucleation of iron rendering iron-rich precipitates to be present.

Commercial Silicon Nitride Powders Surface Groups Measured by Diffuse Reflectance Infrared Fourier Transform Spectroscopy

The DRIFT spectra of seven commercial Si3N4 powders produced by three different processes (diimide precipitation, carbothermal reduction and nitridation of silicon) and four nitriding media (NH3 gas, NH3 liquid, N2 gas and mixture of N2 + H2 gas) with different final treatments were investigated in the NHx/OH (4000 – 2800 cm -1 ) and SiHx (2300 – 2000 cm -1 ) stretching absorbance regions. For six powders the largest intensity bands correspond to Si-NHx groups and H-SiSiSiO configuration, and only the powder produced by the carbothermal reduction method using N2 as nitridation media shows the highest intensity bands for Si-OH groups and H-SiOOO configuration. Introduction NHx, OH and SiHx groups have been observed in the IR spectra of different Si related materials and films. A review of the literature indicates a very wide range of wavenumbers for these groups [1,2]. In the present work, the DRIFT spectra of seven commercial Si3N4 powders produced by three different production processes including four different nitriding media and different final treatments were investigated in the NHx/OH (4000 – 2800 cm -1 ) and SiHx (2300 – 2000 cm -1 ) stretching absorbance regions. The effect of nitriding media and further treatments on the surface layer composition is discussed. Experimental Diffused reflectance infrared Fourier transform (DRIFT) spectra of seven commercial Si3N4 powders: two powders produced by diimide precipitation method using NH3(l) (A1) and NH3(g) (A2) as nitriding media; two powders produced by carbothermal reduction method using N2 (B1) and NH3(g) (B2) as nitriding media and three powders produced by direct nitridation of silicon using N2 (C4) and mixture of N2+H2 (C5, C6) as nitriding media. The C4 and C6 powders were Key Engineering Materials Online: 2004-05-15 ISSN: 1662-9795, Vols. 264-268, pp 1119-1122 doi:10.4028/www.scientific.net/KEM.264-268.1119