Laboratory space, portability, power efficiency and performance continue to be the market drivers of new instrumentation designs. Instrument designers are continually looking to OEM suppliers for components that are smaller, lighter, thinner and paradoxically more powerful. This explains the development of new heating technologies such as advanced ceramic heaters.
What is “Advanced Ceramic”?
Ceramic is a generic term associated with a particular type of chemical composition. In common terms, if a material is not a plastic or a metal, it is a ceramic. The clay in soil is a naturally occurring ceramic raw material that, when baked at a high temperature, becomes very hard. As such, it has been used for centuries as baking pots, figurines and floor tiles.
Advanced ceramics, materials such as aluminum oxide, silicon carbide, boron nitride and aluminum nitride (AlN), do not occur naturally. They are man-made and begin in a powder form. Construction of advanced ceramic heaters involves molding the powder in a high-pressure press followed by heating or sintering, at elevated temperatures. Sintering allows the ceramic powder to chemically bond; a process that virtually eliminates porosity making the ceramic part nearly 100 percent dense. This construction creates a monolithic, geometrically stable structure offering:
- high dielectric strength,
- low leakage current,
- uniform temperatures,
- high durability at low mass,
- a rapid ramp rate and
- a low coefficient of thermal expansion (CTE).
Each ceramic material is unique with respect to temperature limits, heat conduction properties, durability, electrical characteristics, hardness and geometric stability. Depending on the application demands, these properties then become the selection criteria to determine which advanced ceramic material is appropriate for a particular heating requirement. AlN is an excellent material due to:
- High thermal conductivity - the construction enables the heater to be developed with a high watt density, giving it the ability to heat up at a rate of 150°C (270°F) per second.
- Clean, non-contaminating material - the manufacturing process of high heat and pressure results in a heater that is very hard and dense with virtually no porosity or surface roughness.
- Resistance to chemical degradation – AlN in advanced ceramics is resistant to many acids and is impervious to moisture unlike many alternative insulation materials.
- High dielectric strength and high insulation resistance – AlN is a very good electrical insulator that offers low leakage current, a highly sought after characteristic for many applications.
High-performance, AIN ceramic heaters can be operated up to 600°C (1112°F) with a ramp rate of up to 150°C (270°F) per second depending on the application, heater design and process parameters. The heater contains a unique integrated thermocouple configuration that improves the reliability of the sensor/heater interface to ensure fast responsiveness during high ramp rate applications.
When to Apply Advanced Ceramic Heaters in Your Laboratory?
Advanced ceramic heaters make it possible for samples, carrier gases or effluent streams to be heated directly with minimal fear that contamination, memory effects or reactive surface will influence the data. In addition, ceramic heaters have a leakage current of less than 10µA, making it easier to pass electrical certification requirements. A low voltage ac or dc laboratory grade power supply and an expensive isolation transformer are not usually needed when using a heater. With fewer components in the electronics package, the system can be made smaller and lighter to the advantage of the customer. From a thermo-mechanical point of view, the superb thermal conductivity and the low temperature coefficient of thermal expansion (CTE) are two important properties for the system designer to consider.
To tackle the stringent thermal performance required in many analytical applications, Watlow uses simulation techniques, such as finite element analysis (FEA), to optimize circuit layouts and ensure performance. Utilizing FEA also allows for faster, customized prototyping as the heaters can be machined to meet specific design requirements found in the varied, and challenging, instrumentation applications.
Advanced ceramic heaters are an opportunity to improve upon an existing heating solution. Without realizing it, a legacy heating solution may contain hidden costs associated with assembly labor, reliability or simply unrealized performance benefits. Should these potential improvements exist, then the benefits of advanced ceramic heaters may be worth exploring.
