OCR Text |
Show 4 controlled by nitrogen of cylinder2 in keeping at the concentration (1mol%). The refined gas is supplied to the tube with variations of residence time (0.05 to 1.00 sec). The experimental conditions are shown in Table 1. Soot produced by the benzene pyrolysis are collected by a glass filter at the end of the tube. Electron micrographs of the soot are obtained by transmission electron microscope (TEM). The magnification of 150,000 is applied to the measurement of the particle diameter and the magnification of 85,000 to the measurement of the aggregate structure. Diameters of 1000 particles are measured to obtain the average particle diameter of one sample. The example of such photograph is shown in Fig. 3. Table 1 Experimental conditions Residence [sec] 0.05 0.1 0.2 0.5 1 time Concentration [mol%] 1 1 1 1 1 Temperature [K] 1573 1573 1573 1573 1573 N2 flow rate [ml/min] 407.2 203.6 101.8 40.7 20.4 Shape parameters which are maximum Feret's diameter (_.), width (W), area (A) and perimeter (P) of soot aggregate, are obtained using 100 aggregates for one sample. From the analysis of these data, 100 aggregates are divided into four kinds, i. e. sphere, ellipsoidal, linear and brunched shapes. In addition, the peripheral fractal dimension (Dper) proposed by Gerspacher and O'Farrell [12] is applied to evaluate complexity of the shape of aggregates. Dperi is expressed by Eq. (1); p~__4_Wi/*. (j) The logarithmic expression of Eq. (1) is 2 log P = Dp€„-log A 4-C. (2) <: • _ » 1:00 nm Fig. 3 TEM photograph of soot produced by benzene pyrolysis (Average diameter: 34.9nm at 1573K and residence time: 0.1 sec) D hr which is a kind of an index of complexity, is obtained as a slope when P and A are plotted in the logarithmic form as shown in Eq. (2). A perfect circle would give a value of 1. D • becomes larger as the shape of an aggregate is more complex. |