(a) |
(b) |
(c) |
(d) |
(e) |
(f) |
(g) |
(h) |
(i) |
(j) |
Figure 6: Response surface three-dimensional plots of the interaction of every two variables: (a) percentage of HCl (X_{1}) and temperature (X_{2}); (b) percentage of HCl (X_{1}) and stirring speed (X_{3}); (c) percentage of HCl (X_{1}) and S/L ratio (X_{4}); (d) percentage of HCl (X_{1}) and time (X_{5}); (e) temperature (X_{2}) and stirring speed (X_{3}); (f) temperature (X_{2}) and S/L ratio (X_{4}); (g) temperature (X_{2}) and time (X_{5}); (h) stirring speed (X_{3}) and S/L ratio (X_{4}); (i) stirring speed (X_{3}) and time (X_{5}); (j) S/L ratio (X_{4}) and time (X_{5}). |