Silicon Carbide has several advantageous material properties as a particulate filter material:
However, the most important key to successful use of SiC is closely linked to a thorough understanding of the thermal stresses induced in SiC.
Notox Ceramic Filters has gained extensive experience in how to tailor material properties to a Wall Flow Filter (WFF) design, to secure the durability and at the same time deliver a satisfactory pressure drop.
Extruder Heads - available in different shapes and sizes:
Silicon Carbide has many advantageous material properties making it a prime choice for a WFF for the Notox diesel particulate filter applications:
The most important key to the successful use of SiC as a WFF material is closely linked to a thorough understanding of the thermal stresses induced in SiC, due to the high thermal expansion of SiC (~4 x10-6 mm/°K). The Notox ceramic technology comprises a thorough understanding of the chemical and physical reactions involved in creating a highly porous structure of recrystallized Silicon Carbide (SiC). Notox filed the very first patent application of its kind on how to extrude and fire coarse grained Silicon Carbide (SiC).
Our key to success is the deployment of a very coarse fraction, creating the porous structure and a very fine fraction adding the reactivity to the blend required to make it sinter together. A simple and very innovative solution, protected by patent rights that enabled us to produce porous structures with pore sizes from a few microns up to more than 100 microns.
Such a porous structure, constituted of particles, bonded together in the contact points, has a 100 % open porosity, and no dead-end pores. The permeability of the Notox material is therefore much higher than most competing filter materials, enabling us to provide more robust filters, with the same pressure drop as competing technologies.
The raw materials used for the manufacture of Notox Silicon Carbide Diesel Particulate Filters (DPF) are commercial grades of Silicon Carbide together with organic binders and additives. The forming steps of Notox type Silicon Carbide involve traditional ceramic processes. First step is the mixing of the raw materials to form a plastic compound. The compound is then formed by extrusion into segments of different cross section, using extrusion dies developed by Notox.
The extruded pieces are then dried and cut to desired length. The extruded pieces are at this production step very similar to substrates for catalytic converters.
To create a honeycomb filter, every second channel is closed in both ends, in a way that each channel has a closed and an open end.
Finally the filter segments are fired in a high temperature furnace, capable of reaching 2800 degrees celcius in argon protective atmosphere.
When the high temperature firing is completed, the filters are heated again in normal air to remove any excess carbon from the structure. Finally the filter segments are assembled into filter units using traditional ceramic cement.