Preparation experiments under optimal conditions

In order to verify the feasibility of operation and to provide certain amounts of sample product for further application testing, experiments were carried out repeatedly under the optimized conditions listed in Table 14.2. 

The following are observed in the experiments the reaction solution is initially colored green and turns to brown after 3 min, and then to brown-black after 20 min the reaction is stopped at 40 min when the solution is colored black. During the reaction a little gaseous ammonia escapes from the solution. The results detected by TEM for a typical product show the precipitate being black clumped particles of good dispersity and an average size of 5.1 nm with a very narrow size distribution. The TEM photo of the product is shown in Fig. 14.7. 

Twenty experimental runs in total were carried out under the same conditions for testing the sample product the average size of the mixed sample is measured by TEM to be about 10 nm, suggesting the experimental operations for the preparation of the sample product have very good stability. Furthermore, part of the sample product was used by Xu et al. [195] to formulate the nano lubricating grease, which has exhibited very good performances. 

4 Comparison of the results of preparations with various technologies and devices 

Comparison is always of interest. Table 14.3 gives a comparison between the mean sizes of nano copper powders prepared with various technologies, different reaction agents and in various reactors. It appears that the SCISR has significant superiority for the preparation of nano materials by liquid reaction- precipitation. 

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The modified supported powder electrodes used in the experiments hitherto described on the anodic activity of CoTAA are out of the question for practical application in fuel cells, as they do not have sufficient mechanical stability and their ohmic resistance is very high (about 1—2 ohm). For these reasons, compact electrodes with CoTAA were prepared by pressing or rolling a mixture of CoTAA, activated carbon, polyethylene, and PTFE powders in a metal gauze. The electrodes prepared in this way show different activities depending on the composition and the sintering conditions. Electrodes prepared under optimal conditions can be loaded up to about 40 mA/cm2 at a potential of 350 mV at 70 °C in 3 M HCOOH, with relatively good catalyst utilization (about 5 A/g) and adequate stability. 

In spite of the constant density of the gel, the friction of the poly(N-isopropylacrylamide) gel reversibly decreases by three orders of magnitude and appears to diminish as the gel approaches a certain temperature. This phenomenon should be universal and may be observed in any gel under optimal experimental conditions of the solvent composition and the temperature because the unique parameter describing the friction is the correlation length which tends to diverge in the vicinity of the volume phase transition point of gels. The exponent v for the correlation length obtained from the frictional experiment is far from the theoretical value. It will, therefore, be important to study a poly(N-isopropylacrylamide) gel prepared at the critical isochore where the frictional property of gel may be governed by the critical density fluctuations of the gel. 

In order to examine the operational conditions determined and to make the results more feasible for industrial application, and also to provide sample product for further application testing, experiments for mass-preparation are carried out under the optimal conditions determined above, following the procedure described in Section 15.2 and with commercial TiCl4 as the raw material, the composition of which is indicated in Table 15.5. 

Electrochemical methods for the reduction of aromatic substrates utilizing ammonia and amines as solvents with lithium salts as electrolytes have been successful. Toluene was reduced to the 2,5-dihydro derivative in 95% yield in methylamine-lithium chloride if an undivided cell was used, while a 53 47 mixture of 3- and 4-methylcyclohexenes was formed in a divided cell.. Of greater interest, however, are attempts to achieve these reductions in aqueous media. In one experiment utilizing a two-phase mixture of substrate in aqueous tetra-n-butylammonium hydroxide and a mercury cathode, anisole was reduced on a preparative scale (15 g) to its 2,5-dihydro derivative in 80% yield. The optimal temperature for most reductions appeared to be 60 °C and under these conditions, even suspensions of high molecular weight substrates could be successfully reduced, e.g. steroid (226) afforded a >90% chemical yield of (227). Much higher coulombic yields were obtained when a small amount of THE was added to the mixture, however. 

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