Ormosils of High Hardness
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power was kept constant at 210 W throughout the experiment. The temperature of the solution initially increased drastically and then became stable at the boiling points of the alcohol [9,101 and thus isopropanol and ethanol were evaporating during ultrasonic irradiation. The solutions gelled after about 50 min's ultrasonic irradiation. The solutions were cast into plastic molds just before gelation (- 10 poises, 45 min's ultrasonic irradiation) and the obtained gels were dried in air at up to 200 2C. The preparation procedure for TiO2-containing hard ormosils also consisted of first preparing two mixtures. One was TEOS and DMDES with 40% isopropanol (A') and the other was water (2 mol per mol of TEOS + I mol per mol of DMDES) and HCl with the balance isopropanol (B'). The total volume of isopropanol was 25 cm 3 and the molar ratios of HCII(TEOS+TIOT+DMDES) and isopropanol/(TEOS+TIOT+DMDES) were kept constant at 0.01 and 2, respectively. After pouring B' into A', the resulting solution was intimately mixed using a magnetic stirrer. After 10 min's stirring, TIOT was added into the solution and the solution ws intimately mixed for another 10 min. The mole fraction of TIOT (TIOT/(TEOS+TIOT+DMDES)) was 0.3. Then, 2 mol water per mol of TIOT was further added drop by drop to complete hydrolysis while stirring the solution intimately. Immediately after adding the water, the solution was submitted to ultrasonic irradiation and the following procedure was the same as the above-described. Liquid state 29 Si NMR spectra were recorded on an AM 360 Bruker spectrometer with a pulse width of 10 uis and a relaxation delay of 6 s. Liquid sample solutions at various stages of the reaction were diluted to 50 vol% with isopropanol and quenched into liquid nitrogen to arrest the reaction until they were subjected to NMR spectroscopy. 4 cm 3 of each diluted solution was 3 thawed out just prior to the measurement, put into a 10 mm silica tube and mixed with 0.1 cm of 3 TMS and 0.9 cm of a mixture of CDC13 and Cr(acac). CDC13 was used for internal field/ frequency control (lock). Since 2 9 Si typically has a very long spin-lattice relaxation time and there exists the possibility of negative nuclear Overhauser enhancement (NOE), the non-polar 29 paramagnetic relaxation agent, Cr(acac), was used at low concentration (- 0.01 M) to relax Si through the unpaired electron spin density of the metal ion, and hence shorten the time for data acquisition and eliminate NOE [111. Bulk densities were measured by the Archimedes method using isopropanol. For all the samples, pore sizes were small enough to neglect the effect of liquid penetration. Vickers hardnesses were measured using a Micromet II microhardness tester. The loads used for the hardness measurement were 100-300 g. In these measurement, the average values among 5 samples were chosen. EQUATION FOR THE CALCULTAION OF VICKERS HARDNESS Yamane and Mackenzie derived an equation for the calculation of Vickers hardness [131. Their method is based on a consideration of deformation during indentati
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