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SnO 2 nanotubular materials were prepared by using a natural cellulosic substance (filter paper) as template, and their morphologies were determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cellulose fibers were first coated with SnO 2 gel layers by the surface sol-gel process using Sn(O i Pr) 4 as precursor, followed by calcination in air to give SnO 2 nanotubular materials as hollow replicas of natural cellulose fibers. The nanotubes obtained by calcination at 450 °C were amorphous-like and composed of fine particles with sizes smaller than ca. 5 nm. The outer diameters are tens to two hundred nanometers, and wall thicknesses are 10-15 nm. Calcination at 1100 °C yielded tubelike polycrystalline SnO 2 nanocages (outer diameter 100-200 nm), which were composed of rutile-phase SnO 2 nanocrystallites with sizes of 10-20 nm. The thermal behavior and the crystalline property of the powder obtained from calcination of the as-prepared SnO 2 sheet were examined in the temperature range of 300-900 °C. The sizes of the nanoparticle obtained by calcination at 300 and 900 °C were 2.0 and 9.2 nm, respectively, in fair agreement with TEM observation. Calcination temperatures above 500 °C are needed to obtain pure SnO 2 . A sensor setup was fabricated from the SnO 2 nanotube sheet, and the sensor performance was measured for H 2 , CO, and ethylene oxide. The sensor signal, S, was 16.5 at 450 °C to 100 ppm H 2 , and was comparable to that of the conventional SnO 2 sensor. Finally, the sensor characteristics were discussed in relation to the morphology of the nanotube sheet.

In view of the importance of air in science and technology and the abundance of experimental data, we present in this report a consistent set of critically evaluated data and an up-to-date correlation of the viscosity and the thermal conductivity of air in the gaseous phase over a wide range of temperature and pressure. This is especially important for the viscosity, since the recent data show systematic differences compared with the old standard value used for many years. The present paper was written in order to document the critical evaluation of the latest data sets and to present a new set of correlations of the viscosity and the thermal conductivity of air. The range covered is from 85 to 2000 K for temperature and up to 100 MPa for pressure.