Effect of cellulose nanofibrils on mechanical and electrical properties of metal ceramic heater

The effect of cellulose nanofibrils (CNFs) on the mechanical properties of substrate of metal ceramic heater and electrical properties of electrically conductive layer were studied experimentally in a tube furnace at 1600 °C under reduced atmosphere. The alumina ceramics with 96 wt % of alumina and 4 wt % of sintering additives, namely SiO2 and MgO were applied as the substrate. There was a noticeable rise in fracture toughness of alumina ceramics. The addition of 3 wt % of CNFs in ceramic had a significant effect on the improvement of fracture toughness. A KIC of 6.52 MPa·m1/2 was achieved through the addition of 3 wt % CNFs. A considerable decrease in KIC was observed with addition beyond 3 wt % of CNFs. On the other hand, the relative density and bending strength had been steadily dropping with addition of CNFs. The bending strength was 296 MPa with no addition of CNFs. The bending strength of only 158 MPa was achieved with the addition of 5 wt % of CNFs. The sample with 1 wt % CNFs was selected as the substrate. The SiO2 in the ceramic was reduced by pyrolysis of CNFs and formed W–Si solid solution. The temperature coefficient of resistance was decreased by the solution of Si into W.