The Trouble With Silicon Carbide
Enable the sealless transition with ceramic-matrix composites.
Sealless pumps, such as magnetic-driven and canned-motor pumps, are becoming more common in the petrochemical and power industries for their enhanced reliability and reduced leakage. Traditionally, pump manufacturers used SiC (silicon carbide) for bushings and bearings in these pumps because of its high hardness and ability to withstand abrasive wear in solid media.silicon carbide manufacturers
Since the early 1980s, OEM pump manufacturers have been using sintered SiC bearings for the stationary and rotating components of tubular casing pumps. While SiC has been the preferred bearing material over other alternatives such as carbon, its vulnerability to thermal and mechanical shock can cause fractures. Due to the material’s high hardness, the splintered pieces of fractured bearing can lead to a catastrophic pump failure—resulting in significant process disruption and downtime.
New technologies and processing techniques have been developed to bring a new ceramic-matrix composite (CMC) material to the market—enabling the transition to sealless pumps with bushings and bearings that virtually eliminate catastrophic failure in magnetic-driven and canned-motor pumps with superior fracture resistance over traditional silicon carbide components. It is the material properties of these composites that deliver improved mean time between failures (MTBF), reduced maintenance costs and increased safety.
CMCs consist of a ceramic matrix reinforced by either continuous fibers, short fibers, whiskers and/or particles. These reinforcements are designed to improve the fracture toughness of conventional ceramics, which are inherently brittle materials. A number of fabrication techniques—such as chemical vapor or liquid phase infiltration and the standard hot pressing and sintering techniques—are available. One available CMC material is produced by a chemical vapor infiltration process in which crystalline silicon carbide is deposited on and between SiC fibers by process gasses. The major disadvantage of this CMC material is the long process times due to the slow growth of the SiC that translates into a high-cost material.black silicon carbide powder
A new CMC material is processed using a multi-step infiltration and pyrolysis process. The resulting microstructure of this CMC after this process is shown in a cross-sectional view in Figure 1 with the dark regions (A) showing the carbon fibers included to prevent crack propagation for improved impact and thermal shock resistance, while the lightest grey regions (B) are SiC particles included to enhance the stability of the composite and improve its wear resistance. These particles also reduce the shrinkage of the overall matrix during densification, which improves the process-ability. The remaining medium-grey area (C) is the SiC matrix that binds the overall composite together.