Fig. 9

SEM picture of the filter cake (left), corresponding mapping (right, top), and EDX spectrum (right, bottom) on the \(0.1\,\upmu \hbox {m}\) filters, here at \({T}_{\mathrm{Inj}} = 110\,^{\circ }\hbox {C}\) during production stage. Iron is the dominant element. Modeling and a Pourbaix diagram indicate iron hydroxides