Improving an alumina fiber filter membrane for hot gas filtration using an acid phosphate binder

Alumina fiber based filter membranes were prepared using acid phosphate (phosphoric acid plus aluminum hydroxide), colloidal alumina, monoaluminum phosphate and three types of colloidal silica binders at various binders contents. The filter membranes containing between 5% and 10% by weight of acid phosphate binder exhibited the highest flexural strength, compressive strength, work of fracture and elastic modulus in comparison to those containing the other binders at equivalent binder contents, and exhibited the lowest pressure drop in comparison to membranes with other binders and having equivalent flexural and compressive strengths. Microscopy showed that the acid phosphate caused the fibers to bond at their junctions only, whereas colloidal alumina or colloidal silica binders caused free binder particles within the fiber network.