Abstract
Pressure measurement in high temperature environments is important in many applications to provide valuable information for performance studies. Information on pressure patterns is highly desirable for improving performance, condition monitoring and accurate prediction of the remaining life of systems that operate in extremely high temperature environments, such as gas turbine engines. A number of technologies have been recently investigated, however these technologies target specific applications and they are limited by the maximum operating temperature. Thick and thin films of SiCN can withstand high temperatures. SiCN is a polymer-derived ceramic with liquid phase polymer as its starting material. This provides the advantage that it can be molded to any shape. CERASET™ also yields itself for photolithography, with the addition of photo initiator 2, 2-Dimethoxy-2-phenyl-acetophenone (DMPA), thereby enabling photolithographical patterning of the pre-ceramic polymer using UV lithography. SiCN fabrication includes thermosetting, crosslinking and pyrolysis. The technology is still under investigation for stability and improved performance. This work presents the preparation of SiCN films to be used as the body of a sensor for pressure measurements in high temperature environments. The sensor employs the phenomenon of drag effect. The pressure sensor consists of a slender sensitive element and a thick blocking element. The dimensions and thickness of the films depend on the intended application of the sensors. Fabrication methods of SiCN ceramics both as thin (about 40–60 μm) and thick (about 2–3 mm) films for high temperature applications are discussed. In addition, the influence of thermosetting and annealing processes on mechanical properties is investigated.
Highlights
Gas turbine engines in the aerospace industry operate at very challenging levels of performance requiring stable operation of the compressor at all times
As polymer should be removed from the mold before crosslinking and pyrolysis, the usage of gelatine, which can be dissolved in hot water, is very effective for formation of very thin Silicon carbon-nitride (SiCN) layers
Use of SiCN ceramics for building pressure sensors for high temperature applications is discussed along with the fabrication of shaped thin and thick SiCN films for use in the pressure sensor.Gelatin technique is used for thin film molding and PDMS polymer for thick film molding
Summary
Gas turbine engines in the aerospace industry operate at very challenging levels of performance requiring stable operation of the compressor at all times. During take off and landing, transient pressure fluctuations normally arise, resulting in blade stall that is propagated to adjacent blades and back through the various stages of the compressor This could lead to engine surge for high speed turbines in fraction of seconds and subsequently damage the engine [1]. The widely used semiconductor pressure sensors capable of operating at high temperature by Kulite semiconductors Inc and Vibro-meter have several limitations including reduced long-term stability and reliability. Quest for a sensor to operate in a temperature range of more than 500 °C and to address the fabrication issues resulted in the exploitation of a new class of polymer-derived ceramics, which essentially consist of amorphous alloys of silicon, carbon and nitrogen, and is known as Silicon. The influence of parameters such as thermosetting and annealing temperatures on the properties of SiCN ceramics including hardness and reduced Young’s modulus, which are important for the construction of pressure sensors, are discussed
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