[NZP]: A new family of ceramics with low thermal expansion and tunable properties

Ceramic materials belonging in the sodium zirconioum phosphate (NZP), family were prepared and characterized, with the view to identify a ceramic material, that may be used as honeycomb material in three way catalysts (TWC), Two different families were studied. The first one belongs to the system Ca1-xBaxZr4P6O24 (x=0-1). This system was chosen because CaZr4P6O24 contracts while BaZr4P6O24 expands on heating. The material for x = 0.25 has a thermal expansion coefficient value close to zero and its flexural strength varies between 36 and 50 MPa for porosity of 17-28%. However, this system is quite unstable in acidic environments. Another NZP system, namely Ba1+xZr4P6-2xSi2xO24 (x=0-0.4) was investigated. The effect of the addition of Si substituting P was studied. As x increases, the thermal expansion coefficient decreases. For x = 0.22, the material is chemically stable and has a TEC value close to zero. Its porosity was quite high (36-47%) combined with flexural strength in the range of 20-40 MPa. Additionally, it was proved that materials with adequate physical and mechanical properties can be produced at relatively fast firing schedules. Optimum calcination time is 4 h and optimum sintering time is 8 h. (c) 2006 Elsevier Ltd. All rights reserved.