Advanced Ceramics for Thermo Sensors and Thermal Sensor Housing
Examples of advanced-ceramic applications provided by Morgan Technical Ceramics-Alberox business (MTC-Alberox) are temperature-monitoring sensors, thermocoupling housings and fire-detection feedthroughs constructed from a variety of metal components and high-purity alumina ceramic. Used primarily in aerospace applications, they are also suitable for use in temperature-sensing units for manufacturing processes or in pressure sensors monitoring industrial processes.
Ceramic-to-Metal Brazing Ensures Electrical IsolationCeramic-to-metal connector assemblies are used when electrical isolation is required. They consist of a metal component, usually a cap or tube, brazed to an insulator made of ceramic, in a variety of purity levels, which is then brazed to another metal component (again, usually a cap or tube). The ceramic provides the electrical isolation between the two metal components. These ceramic-to-metal components are sealed to metals by high-performance brazing alloys that provide an extremely reliable seal.
Junction boxes for thermocouples consist of matched pairs of thermocouple material in insulator assemblies, which are brazed into a metal housing. The material is typically type-K material in terminal stud form. Type K (chromel–alumel) is the most common general-purpose thermocouple. A connection to the leads of the terminal studs is made and attached to the thermocouple assembly.
Examples of Ceramics Used for Thermal ApplicationsAluminum Oxide (Alumina)
A variety of ceramic materials are used in thermal applications. For example, aluminum oxide (Al2O3) is a major engineering material that offers a combination of good mechanical properties and electrical properties leading to a wide range of applications. Alumina can be produced in a range of purities with additives designed to enhance properties. A wide variety of ceramic processing methods can be applied, including machining or net-shape forming, to produce a wide variety of sizes and shapes of components. In addition, it can be readily joined to metals or other ceramics using metallizing and brazing techniques.
One important application example is fire-detection feedthroughs for aerospace applications. Fire-detection feedthroughs, constructed from a variety of corrosion-resistant metal components and high-purity Al2O3 ceramic, yield stable hermiticity in severe environments. Component durability is tested by subjecting all ceramic-to-metal assemblies to thermal cycling from –55°F to 900°F, as well as extended periods at elevated temperatures up to 900°F. Manufactured using high-temperature braze materials, the thermocouples are leak-tested with helium, ensuring their reliability and sealing.
Typical alumina characteristics include good strength and stiffness, good hardness and wear resistance, good corrosion resistance and good thermal stability. This makes alumina an excellent choice for thermocouple tubes and seal rings, as well as applications such as electrical insulators and laser tubes.
Magnesium Oxide (Magnesia)
Dense magnesia is not normally used as an engineering ceramic. However, lower-density magnesia (with 30% porosity, for example) is used in a variety of applications due to its electrical and refractory properties. MTC makes a range of lower-density magnesia called Luminex. Typical magnesium-oxide characteristics include high-temperature capability, low electrical conductivity, high thermal conductivity and good corrosion resistance. The material is ideal for use in heating elements, thermocouple tubes, high-temperature crucibles and kiln furniture.
Silicon nitride has good high-temperature strength, creep resistance and oxidation resistance. In addition, its low thermal-expansion coefficient gives good thermal shock resistance compared with most ceramic materials. Typical silicon-nitride applications include thermocouple sheaths, bearing balls and rollers, cutting tools, molten-metal handling, welding jigs and fixtures, and welding nozzles. IH
For more information: Visit www.morgan technicalceramics.com or contact one of our sales offices. In Europe, Morgan Technical Ceramics, Bewdley Road, Stourport, Worcestershire, DY13 8QR; tel: +44 1299 872210; fax: +44 1299 872218; e-mail: mtcuksales@ morganplc.com. In North America, Morgan Technical Ceramics, 26 Madison Road, Fairfield, NJ 07004; tel: 800-433-0638; fax: 973-227-7135
Additional related information may be found by searching for these (and other) key words/terms via BNP Media SEARCH at www.industrialheating.com: brazing, alumina, net-shape forming, transducers.